Evaluation of the Low-Energy 

Design and Energy 

Performance of the Zion 

National Park Visitors Center 

February 2005 • NREL/TP-550-34607 

P. Torcellini, N. Long, S. Pless, and R. Judkoff 

National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337

February 2005 • NREL/TP-550-34607 

Evaluation of the Low-Energy 

Design and Energy 

Performance of the Zion 

National Park Visitors Center 

P. Torcellini, N. Long, S. Pless, and R. Judkoff 

Prepared under Task No. BEC3.4005 and BEC2.4002 
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States 

government. Neither the United States government nor any agency thereof, nor any of their employees, 

makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents 

that its use would not infringe privately owned rights. Reference herein to any specific commercial 

product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily 

constitute or imply its endorsement, recommendation, or favoring by the United States government or any 

agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect 

those of the United States government or any agency thereof. 

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy 

Office of Scientific and Technical Information 

P.O. Box 62 

Oak Ridge, TN 37831-0062 

phone: 865.576.8401 

fax: 865.576.5728 

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
iii 

Acknowledgments 

This work was made possible under the U.S. Department of Energy’s (DOE’s) Office of Energy 

Efficiency and Renewable Energy. We appreciate the support and guidance of Dru Crawley, DOE 

Program Manager for High-Performance Buildings as well as the following people who reviewed this 

document prior to publication: John Ryan at DOE; Michael McCabe at Navigant Consulting; Nadav 

Malin at BuildingGreen, Inc.; and Patrick Shea at the National Park Service. In addition, we would like 

to recognize those who helped collect information and provide analysis support for the effort including 

Stefan Craine, Kris Lasnik, and Michael Ketcham (NREL interns); Peter Ellis, Brent Griffith, Sheila 

Hayter, and Lauren Poole (NREL); Tom Wood (Montana State University); Joshua Bruce (former NREL 

employee), and Ed Hancock (Mountain Energy Partnership). 
iv 

Table of Contents 

ACKNOWLEDGMENTS ....................................................................................................................... III

LIST OF FIGURES ................................................................................................................................ VII

LIST OF TABLES ..................................................................................................................................... X

EXECUTIVE SUMMARY ......................................................................................................................XI

NOMENCLATURE...............................................................................................................................XVI

1 INTRODUCTION...............................................................................................................................1

1.1 ENERGY USE IN COMMERCIAL BUILDINGS IN THE UNITED STATES.............................................2

1.2 BUILDING EVALUATION SCOPE ....................................................................................................2

1.3 HIGH-PERFORMANCE BUILDINGS RESEARCH OBJECTIVES ..........................................................2

1.4 REPORT ORGANIZATION ...............................................................................................................2

2 BACKGROUND .................................................................................................................................3

3 DESIGN PROCESS............................................................................................................................5

3.1 RATIONALE FOR DESIGN...............................................................................................................5

3.2 APPLYING THE DESIGN PROCESS ..................................................................................................5

3.2.1 Step 1: Predesign ..................................................................................................... 7

3.2.2 Step 2: Create a base-case building model.............................................................. 8

3.2.3 Step 3: Parametric Analysis.................................................................................... 10

3.2.4 Step 4: Design Solutions to Reduce Energy Consumption .................................... 11

3.2.5 Step 5: Simulate Performance of Design Solutions ................................................ 12

3.2.6 Step 6: Conceptual Design..................................................................................... 13

3.2.7 Step 7: Design Development................................................................................... 15

3.2.8 Step 8: Bid Documents and Specifications ............................................................ 17

3.2.9 Step 9: Construction ............................................................................................... 17

3.2.10 Step 10: Commissioning and Postoccupancy Evaluation....................................... 18

3.3 ENERGY DESIGN PROCESS EVALUATION....................................................................................18

3.3.1 Energy Design Process Questionnaire Methods .................................................... 18

3.3.2 Energy Design Process Questionnaire Results....................................................... 19

4 AS-BUILT BUILDING DESCRIPTION........................................................................................22

4.1 BUILDING ENVELOPE ..................................................................................................................25

4.2 LIGHTING AND DAYLIGHTING.....................................................................................................27

4.3 PV DESCRIPTION.........................................................................................................................31

4.4 MECHANICAL SYSTEMS ..............................................................................................................33

4.4.1 Trombe Wall and Heating Panels........................................................................... 33

4.4.2 Cooling Systems...................................................................................................... 34

4.5 EQUIPMENT .................................................................................................................................36

5 WHOLE-BUILDING ENERGY EVALUATION .........................................................................38

5.1 WHOLE-BUILDING EVALUATION METHODOLOGY......................................................................38

5.2 WHOLE-BUILDING MONITORING ................................................................................................39
v 

5.2.1 Building Monitoring Methods................................................................................. 39

5.2.2 Monitoring System .................................................................................................. 41

5.2.3 Measured Data Analysis......................................................................................... 46

5.3 DEVELOPMENT OF ENERGY MODELS..........................................................................................54

5.3.1 DOE-2 Building Simulation Tool............................................................................ 55

5.3.2 Development of the Base-Case Model .................................................................... 55

5.4 WHOLE-BUILDING ENERGY PERFORMANCE RESULTS ...............................................................57

5.4.1 Energy Cost Analysis .............................................................................................. 57

5.4.2 Site Analysis............................................................................................................ 60

5.4.3 Source Energy Analysis .......................................................................................... 61

6 SUBSYSTEM EVALUATIONS ......................................................................................................63

6.1 HVAC EVALUATION...................................................................................................................63

6.1.1 Heating Evaluation Methods .................................................................................. 64

6.1.2 Heating Evaluation Results..................................................................................... 65

6.1.3 Cooling Systems Evaluation Methods..................................................................... 70

6.1.4 Cooling Systems Evaluation Results....................................................................... 70

6.2 PV SYSTEM EVALUATION...........................................................................................................73

6.2.1 PV System Evaluation Method................................................................................ 73

6.2.2 PV System Evaluation Results ................................................................................ 73

6.3 LIGHTING AND DAYLIGHTING EVALUATION ..............................................................................84

6.3.1 Lighting and Daylighting Evaluation Methods....................................................... 84

6.3.2 Lighting and Daylighting Evaluation Results......................................................... 86

6.4 COMFORT EVALUATION..............................................................................................................94

6.4.1 Comfort Monitoring Methods ................................................................................. 94

6.4.2 Comfort Monitoring Results ................................................................................... 95

6.5 COMFORT STATION ENERGY EVALUATION ..............................................................................100

7 RECOMMENDATIONS................................................................................................................ 102

7.1 LOW-ENERGY DESIGN PROCESS ...............................................................................................102

7.2 VISITOR CENTER COMPLEX SYSTEMS ......................................................................................103

7.2.1 Demand Responsive Controls............................................................................... 103

7.2.2 Trombe Walls........................................................................................................ 104

7.2.3 Electric Heating.................................................................................................... 104

7.2.4 Cooltowers ............................................................................................................ 105

7.2.5 Lighting and Daylighting Systems ........................................................................ 107

7.2.6 PV and UPS System .............................................................................................. 108

7.3 COMMISSIONING .......................................................................................................................109

7.4 POSTOCCUPANCY RESEARCH METHODS ..................................................................................109

8 CONCLUSIONS .............................................................................................................................111

8.1 MEASURED WHOLE-BUILDING PERFORMANCE ........................................................................111

8.2 SIMULATED WHOLE-BUILDING PERFORMANCE .......................................................................112

8.3 PV SYSTEM ............................................................................................................................... 113

8.4 LESSONS LEARNED ...................................................................................................................113

8.5 FUTURE RESEARCH ...................................................................................................................114

9 REFERENCES................................................................................................................................115
vi 

APPENDIX A THE LOW-ENERGY DESIGN PROCESS...............................................................117

APPENDIX B DESIGN PROCESS QUESTIONNAIRE...................................................................120

APPENDIX C ENERGY SUMMARY TABLES................................................................................131

APPENDIX D PV SHADING SIMULATION PROCEDURE..........................................................132

APPENDIX E EXTENDED HVAC AND COMFORT ANALYSIS..................................................135

APPENDIX F EXTENDED LIGHTING ANALYSIS........................................................................136

APPENDIX G LIST OF PEOPLE INVOLVED IN PROJECT........................................................137
vii 

List of Figures 

Figure ES-1 Comparison of base-case model using recorded weather data to measured energy 

consumption .......................................................................................................................xiii

Figure ES-2 1999 Western U.S. site energy intensity by building type, with ZNP Complex average...xiv

Figure 2-1 1999 Energy Use and Costs by Building Type for Western U.S. (EIA 2002) ......................3

Figure 3-1 Summer traffic congestion, traffic back-ups, and parking issues..........................................5

Figure 3-2 Flowchart of building designs ...............................................................................................6

Figure 3-3 Typical monthly average daily weather for ZNP ..................................................................8

Figure 3-4 Simulated 7,600-ft2 (706-m2) base-case model .....................................................................9

Figure 3-5 Parametric analysis results ..................................................................................................11

Figure 3-6 Diagram of energy design solutions for the Visitor Center Complex .................................12

Figure 3-7 Initial proposed design of the Visitor Center.......................................................................14

Figure 3-8 Conceptual design floor plan for Visitor Center and Comfort Station (Step 6) ..................14

Figure 3-9 Simulated energy cost savings of base-case building compared to conceptual design 

(excluding the PV system)...................................................................................................15

Figure 3-10 DOE-2 proposed design model ...........................................................................................16

Figure 4-1 Visitor Center Complex site layout .....................................................................................22

Figure 4-2 As-built Zion layout and energy-efficient features..............................................................23

Figure 4-3 As-built Zion Visitor Center floor plan ...............................................................................24

Figure 4-4 As-built Zion Comfort Station floor plan............................................................................25

Figure 4-5 Typical slab and footing insulation .....................................................................................26

Figure 4-6 Display lighting using 4-ft T-8 Lamps ................................................................................28

Figure 4-7 T-8 space lighting (note the dark ceilings and minimal down lighting)..............................28

Figure 4-8 Lighting in Comfort Station ................................................................................................29

Figure 4-9 Visitor Center lighting plan showing lighting zones ...........................................................29

Figure 4-10 Comfort Station lighting plan..............................................................................................30

Figure 4-11 PV panels installed on the roof at the Visitor Center ..........................................................32

Figure 4-12 PV system configuration .....................................................................................................32

Figure 4-13 Cross-section of Trombe Wall.............................................................................................33

Figure 4-14 Photograph of Trombe wall showing patterned glass over the Trombe wall, row of 

daylighting glass, and overhang to shade wall during the summer .....................................34

Figure 4-15 Illustration of how the cooltowers work at the Visitor Center ............................................35

Figure 4-16 Natural downdraft cooltowers – exterior view ....................................................................36

Figure 4-17 Interior view of a cooltower showing operable shutters that allow cool air to enter the 

building through the bottom louvers ...................................................................................36

Figure 5-1 Timeline of monitoring system and postoccupancy energy evaluation...............................38

Figure 5-2 One-line electrical system plan and data acquisition meter locations .................................40

Figure 5-3 Verification of utility and measured data, November 2001 to February 2003....................44

Figure 5-4 Comparison of average monthly outdoor temperatures for Complex and Cedar City .......45

Figure 5-5 End use daily average monthly consumption, November 2001 through May 2003............46

Figure 5-6 Energy consumption by end use, November 2001 through October 2002..........................47

Figure 5-7 Peak demand day without demand limiting controls, February 2, 2002 .............................48

Figure 5-8 Typical heating profile with demand limiting controls, February 8, 2003..........................50

Figure 5-9 Average daily site energy purchased for heating, cooling, and hot water and PV 

production, Winter 2001–2002 compared to Winter 2002–2003........................................51

Figure 5-10 Visitor Center and Comfort Station peak demand analysis and time of occurrence for each 

month...................................................................................................................................52

Figure 5-11 Whole-building evaluation flowchart: as-built building and base-case model...................55

Figure 5-12 Visitor Center Complex energy costs, Nov. 2001 through May 2003 ................................58
viii 

Figure 5-13 Base-case and energy costs, November 2001 through October 2002 .................................59

Figure 5-14 Base-case energy consumption compared to measured consumption.................................61

Figure 6-1 Histogram of outdoor dry-bulb temperatures during occupied hours .................................63

Figure 6-2 HVAC energy consumption as a function of outdoor temperature .....................................64

Figure 6-3 Cross section of Trombe wall showing location of temperature sensors ............................65

Figure 6-4 Average daily heating energy consumption by month ........................................................66

Figure 6-5 Infrared picture of Trombe wall during heating season 2/9/2000 at 6:00 p.m. ...................67

Figure 6-6 Verification of middle Trombe wall temperature after adjusting thermal conductivity......68

Figure 6-7 Trombe wall and heating system performance, 2001–2002 heating season........................69

Figure 6-8 Trombe wall temperature transients over a 24-hour period.................................................70

Figure 6-9 Water consumption versus daily average outdoor temperature (Summer 2002).................71

Figure 6-10 Plastic blocking device for cooltowers................................................................................72

Figure 6-11 Average hourly AC power profile by month for PV production, November 2001 through 

October 2002 .......................................................................................................................75

Figure 6-12 Modeled array losses ...........................................................................................................76

Figure 6-13 Sandia PV performance model I-V curve tracer model for the Zion PV system ................77

Figure 6-14 PV production for unshaded, horizon shaded, and horizon and tree shaded simulations....78

Figure 6-15 Photo of shaded PV panels (left side of photo) ...................................................................78

Figure 6-16 Model of tree shading of PV array, 3:30 p.m. July 9, 2000.................................................79

Figure 6-17 Simulated power-voltage curve traces for summer weather conditions..............................80

Figure 6-18 Simulated power-voltage curve traces for winter weather conditions.................................81

Figure 6-19 Simulated annual PV production: Best fixed voltage, actual fixed voltage, and maximum 

power-point tracking ........................................................................................................... 81

Figure 6-20 Simulated annual PV production comparisons....................................................................82

Figure 6-21 Voltage and real power of emergency panel versus time for a utility grid power outage ...84

Figure 6-22 Continuous and handheld illuminance measurement locations...........................................86

Figure 6-23 Lighting and daylighting design savings for indoor lighting...............................................88

Figure 6-24 Measured, base case, and actual LPD annual lighting consumption profiles and savings 

(October 2001 to November 2002)......................................................................................89

Figure 6-25 Measured bookstore and outdoor illuminance levels, July 12, September 22, and 

December 16, 2000.............................................................................................................. 90

Figure 6-26 NPS bookstore checkout counter glare from clerestories....................................................91

Figure 6-27 Southeast office afternoon glare..........................................................................................91

Figure 6-28 Illuminance points over the floor plan from electrical lights without daylighting on 

July 10, 2000, 10:00 p.m. ....................................................................................................92

Figure 6-29 Illuminance points across floor plan for a clear sky with lights on; July 11, 2000 at 

12:25 p.m.............................................................................................................................93

Figure 6-30 Illuminance points across floor plan for a partly cloudy sky with lights on as normal; 

December 14, 2000 at 12:15 p.m.........................................................................................93

Figure 6-31 Layout of temperature sensors for Visitor Center ...............................................................95

Figure 6-32 Histogram of winter average temperature in the Visitor Center..........................................96

Figure 6-33 Histogram of hours at average temperature in the Visitor Center during summer..............97

Figure 6-34 Visitor Center Zone 2 comfort histogram during summer ..................................................98

Figure 6-35 Zone 7 exterior door temperatures averaged over October 8, through October 19, 2001 ...99

Figure 6-36 Infrared picture of the interior door in Zone 7, August 18, 2001 12:35 p.m.......................99

Figure 6-37 Comfort Station end use monthly consumption per day, November 2001 through October 

2002...................................................................................................................................100

Figure 6-38 Histogram of hours at average temperature in the Comfort Station during winter ...........101

Figure 6-39 Histogram of hours at average temperatures in the Comfort Station during summer .......101

Figure 8-1 End use daily average monthly consumption, November 2001 through May 2003..........111

Figure 8-2 Annual performance comparison ......................................................................................112
ix 

Figure B-1 Summary of measured and base-case energy use..............................................................131

Figure D-1 Photo of Visitor Center looking south showing southern horizon (canyon walls) accounted 

for in simulations...............................................................................................................132

Figure D-2 Horizontal insolation monthly profile, October 2001 through October 2002 ...................132

Figure D-3 Southern horizon model ....................................................................................................133

Figure D-4 Tree shading of PV array, 3:30 p.m. July 09, 2000...........................................................133

Figure D-5 Model of tree shading of PV array, 3:30 p.m. July 9, 2000...............................................134

Figure E-1 Comfort chart of cash register area during occupied hours...............................................135

Figure F-1 Illuminance for clear sky with lights OFF; July 11, 2000 at 12:05 p.m. ...........................136

Figure F-2 Illuminance for clear sky with lights OFF on December 15, 2000 at 11:15 a.m...............136
x 

List of Tables 

Table ES-1 Cost, Site, and Source Energy Summary, Nov. 2001 to Oct. 2002....................................xiii

Table 2-1 Energy and Cost Intensities by EPA Study ...........................................................................4

Table 3-1 Base-Case Model Characteristics ..........................................................................................9

Table 3-2 Parametric Analysis Description .........................................................................................10

Table 3-3 Energy Use by End-Use ......................................................................................................16

Table 3-4 Energy Cost Savings by End-Use........................................................................................16

Table 4-1 Differences between Proposed Design and As-Built Design ..............................................23

Table 4-2 Building Envelope Construction and Thermal Properties...................................................27

Table 4-3 Lighting Schedule................................................................................................................31

Table 5-1 Energy Monitoring Sensor Descriptions .............................................................................41

Table 5-2 Input Points for BAS and Data Collection ..........................................................................42

Table 5-3 Expected Accuracy of Sensors ............................................................................................43

Table 5-4 Heating and Cooling Degree Days for Cedar City and Zion...............................................44

Table 5-5 Energy Use and Intensity for Each Building, Nov. 2001 to Oct. 2002 ...............................47

Table 5-6 PV Contribution during Peak Demands ..............................................................................52

Table 5-7 Information on Demand Occurrences and Reasonability....................................................53

Table 5-8 As-Built Design and Base-Case Comparisons ....................................................................56

Table 5-9 Visitor Center Complex Energy Costs, Nov. 2001 through May 2003...............................57

Table 5-10 Base-Case and Measured Site Annual Consumption and Savings......................................60

Table 5-11 Electricity Generation Emissions from Coal .......................................................................62

Table 5-12 Emissions Reduction Summary...........................................................................................62

Table 6-1 Heating and Cooling Degree Days for 2001–2002 and 2002–2003 Data ...........................63

Table 6-2 PV Performance: November 1, 2001 through October 31, 2002 ........................................74

Table 6-3 Summary of PV System Losses at 1000 W/m2, 77°F (25°C)..............................................76

Table 6-4 Performance Degradation Results .......................................................................................82

Table 6-5 Base-Case and Actual Lighting Power Density by Space...................................................87

Table 6-6 Visitor Center Area Definitions...........................................................................................95

Table 8-1 Measured Whole-Building Results....................................................................................112

Table 8-2 Cost, Site, and Source Energy Savings, Nov. 2001 to Oct. 2002......................................113
xi 

Executive Summary 

Introduction 

Zion National Park (ZNP) in southwestern Utah has experienced substantial growth in visitors over the 

last two decades. To reduce environmental impact and improve visitor experience, National Park Service 

(NPS) staff undertook the planning and development of a new Visitor Center Complex and an alternative 

transportation system with the gateway community of Springdale. NPS staff wanted their new complex 

to complement the natural beauty of ZNP and had a strong design goal of minimizing energy and 

environmental impact. To help achieve their energy goals, the NPS requested technical support from the 

National Renewable Energy Laboratory’s (NREL’s) Center for Buildings and Thermal Systems. The 

collaboration between the NPS and NREL lasted throughout the duration of the project from predesign 

through postoccupancy. The result was a building with 67% less energy costs than a comparable building 

that just meets the applicable energy code. In addition, construction costs were similar to comparable 

conventional visitor center building in a national park. The facility opened in May 2000 and includes an 

8,800-ft2

 (817-m2) Visitor Center (with interpretative displays, offices, and retail space for the Zion 

Natural History Association and a 2,756-ft2

 (256-m2) Comfort Station (restrooms). This Visitor Center 

Complex is an example of a high-performance building that demonstrates what is possible when an 

aggressive approach is used for achieving extraordinary levels of energy efficiency. Energy features of 

the building include: passive direct evaporative cooling, natural ventilation, external shading devices and 

glazing designed for solar load avoidance in summer and passive solar gain in winter, thermal mass sized 

for the direct gain system, noncirculating Trombe wall, daylighting, photovoltaic uninterruptible power, 

and digital controls to integrate energy operations. 

Research Goals and Approach 

This report is part of a series of six case studies to develop, document, analyze, and evaluate the processes 

by which highly energy-efficient buildings can be reliably produced. In this project, NREL was able to 

test the 10-step low-energy design process that we had previously developed and are continuing to refine 

(Torcellini et. al. 1999). This process covers predesign through postoccupancy, relies heavily on building 

energy simulation, and also includes other important qualitative and quantitative features such as design 

charrettes with all members of the design team, and the establishment of energy goals through the use of 

computer modeling. It would not have been possible for NREL to conduct this research without close 

collaboration with real building design and construction projects. It is not practical to use classical 

controlled repeatable experimental techniques for objects as large and complex as commercial buildings, 

and for design and construction processes that of necessity involve so many different players over an 

extended period. 

Specifically, the objectives of this project were to: 

• evaluate the low-energy design process as applied to the Visitor Center Complex, 

• use careful metering, submetering, and simulation techniques to evaluate the whole-building 

energy performance during normal operation and determine if the original low-energy design 

goals were met, 

• determine lessons learned from designing, constructing, operating, and monitoring the Visitor 

Center Complex for use in future projects, and 

• investigate opportunities for improving the operating performance of the Visitor Center Complex. 
xii 

For its energy performance analysis, NREL collected detailed monitoring data from the Building 

Automation System in each building. In addition to monitoring, researchers had access to the control 

system and developed custom algorithms to operate systems. The overall energy savings of the building 

indicate the design process was successful. The few shortcomings in the project can be traced to 

construction changes that were installed before they could be analyzed or to design changes that occurred 

without the opportunity for proper analysis by the NREL energy specialists. 

Energy Design Concepts 

Part of the success of the project was a commitment to climate-sensitive design starting in the predesign 

stage. The initial predesign activities included a set of on-site charrettes that allowed the design team to 

become familiar with the unique terrain and climate features of the site. It was apparent from the site visit 

that the local microclimate provided many ideas for the design concepts that could be used to provide 

comfort in and around the visitor center. The Virgin River canyon controlled many aspects of the 

microclimate. The narrow canyon walls, splashing water, and vegetation at the riverbanks provided shade 

and evaporatively cooled air in sharp relief to the aridness and extreme heat. In some places, seeps wetted 

the canyon walls, creating a cooling effect. In other places, the seeps nourished blooms of wet moss that 

behave much as the wetted media in a commercial evaporative cooler. The overall geometry of the 

canyon, which was deep and narrow up-river of the site and widened progressively in the down-river 

direction, created a diurnal chimney effect with up canyon winds from about noon to midnight and down 

canyon winds from midnight to noon. The lighting in the narrow parts of the canyon was diffuse with a 

pleasant contrast ratio and without the unpleasant impact of the direct sun. A winter visit was also 

informative with solar heating of exposed canyon mass surfaces often adequate to provide outside 

comfort during the day. 

Thus were born many of the overall energy, lighting and human comfort architectural design concepts for 

the complex. These are summarized as follows: 

• Create a shaded microclimate around the buildings in summer and solar exposure in winter with 

plantings of deciduous trees and overhead arbors. 

• Provide irrigation throughout the space with small irrigation canals similar to the historic ones 

found in the canyon. Although not implemented in this project, it is possible to use porous patio 

materials to create an evaporatively cooled walking surface. 

• Create passive evaporative downdraft cooltowers to cool the building without the need for 

blowers or vapor compression equipment. 

• Use the diurnal winds to help drive a natural ventilation system and to boost the cooltower’s air 

delivery with wind pressure. 

• Control automated clerestory windows and the cooltowers with the building automation system 

to create an integrated, controllable natural cooling system. 

• Specify the thermal and optical properties of glass; size and orient windows and shading devices 

to provide diffuse light with minimal solar load in summer, and light and solar heat in winter. 

• Use massive building materials on the interior to modulate temperature swings and store solar 

heat in winter and cool night air in summer. 

• Construct noncirculating Trombe walls on the south face of the buildings for additional passive 

heating with a time delay into the late afternoon and evening hours. 

• Allow enough south-oriented pitched roof surface to accommodate photovoltaic panels so that 

the building can operate effectively and comfortably despite frequent summer power outages. 
xiii 

Results 

NREL compared monitored energy performance results to base-case building energy models using the 

same weather files. Our criterion for quantifying performance throughout the project was energy cost. 

From November 2001 through October 2002, the annual energy costs for the Visitor Center Complex 

were $5,094/yr or $0.43/ft2

·yr ($4.63/m2·yr), net site energy use was 85,000 kWh/yr or 24.7 kBtu/ft2·yr 

(280.5 MJ/m2

·yr) and source energy intensity was 80 kBtu/ft2·yr (908.5 MJ/m2·yr). Photovoltaic panels 

produced 7,900 kWh/yr or 8.5% of the total site energy use. The base-case energy model, based on 

ASHRAE Standard 90.1, yielded energy costs of $15,250/yr or $1.30/ft2

·yr ($13.99/m2·yr); site energy 

use was 241,800 kWh/yr or 70.3 kBtu/ft2

·yr (798 MJ/m2·yr), translating to a source energy intensity of 

227 kBtu/ft2

·yr (2,580 MJ/m2·yr). This data represents savings (including receptacle loads) of 67% for 

energy cost, 62% for site energy, and 65% for source energy (see Figure ES-1 and Table ES-1). When we 

implemented controls to reduce demand charges, average daily peak demand in winter declined by almost 

50%. 

56% 70%

74% 74%

75%

71%

55% 65%

46%

38% 31%

62%

-30,000

-24,000

-18,000

-12,000

-6,000

0

6,000

12,000

18,000

24,000

30,000

Nov-01Dec-01

Jan-02

Feb-02

Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Monthly Energy Consumption (kWh/month)

0

6,000

12,000

18,000

24,000

30,000

36,000

42,000

48,000

54,000

60,000

Plug Loads Lighting

 Heating Cooling

 Fans DHW

Measured 

2001-2002

Measured 

Weather 

Base-case

Figure ES-1 Comparison of base-case model using recorded weather data to 

measured energy consumption 

Table ES-1 Cost, Site, and Source Energy Summary, Nov. 2001 to Oct. 2002 

Cost Site Energy Source Energy 

$/ft2·yr 

($/m2·yr) 

Percent 

Savings 

kBtu/ft2·yr 

(MJ/m2·yr) 

Percent 

Savings

kBtu/ft2·yr 

(MJ/m2·yr)

Percent 

Savings

Base-case $1.30 

($13.99) 

70.3 

(799) 

227 

(2,580) 

As-built $0.43 

($4.63) 

67% 27.0 

(307) 

62% 80 

(910) 

65% 
xiv 

The Visitor Center Complex is a combination of office, retail, and service areas. Figure ES-2 compares 

measured energy use of the Visitor Center Complex with other types of commercial buildings in the 

western United States (EIA 2002), with the Visitor Center Complex energy use equivalent to a 

warehouse. 

26

27

30

67

75

83

84

86

0 10 20 30 40 50 60 70 80 90 100

Warehouse

Zion National Park

Complex

Religious Worship

Education

Retail and Service

Lodging

Office

Public Assembly

Total Site Energy Intensity (kBtu/ft2

)

Figure ES-2 1999 Western U.S. site energy intensity by building type, with ZNP 

Complex average 

Our experiences with the Visitor Center Complex project, from early conceptual design through three 

years of postoccupancy monitoring, led to the following major conclusions: 

• A multiple-use commercial building that includes retail, office, and public assembly spaces can 

be constructed to use 65% less energy than an equivalent, minimally code-compliant building. 

• The Visitor Center Complex project was successful because: 

• The design team set appropriate energy performance goals early in the process and 

committed to achieve them. 

• The entire design team was involved throughout all phases of the project. 

• We used energy simulation models to predict energy performance of options and 

alternatives throughout the design process. 

• The energy performance of the building was continuously monitored and the information 

was used to evaluate and improve the performance. 

• Building controls can substantially reduce the electrical demand and related charges. 
xv 

• For the climate and scale of the Visitor Center Complex, it is possible to eliminate mechanical air 

systems and use simple localized heating systems to augment passive heating and cooling to 

provide occupant thermal comfort. 

• Cooltowers can effectively combine direct evaporative cooling and passive natural ventilation 

and deliver comfort comparable to mechanical direct evaporative cooling using minimal energy. 

• Daylighting can effectively augment electric lighting in retail spaces as well as reducing cooling 

loads. 

• Solar-electric uninterruptible power systems can add substantial value to buildings in areas with 

poor power reliability. 

• Visitor Center heating is the largest single end use, with plug loads and lighting the next most 

energy intensive loads. 

• The building uses very little energy for heating and cooling when the outdoor temperature is 

between 60°F and 75°F (15.6°C and 23.9°C). 

• Contractors required training on installing energy efficiency and renewable energy technologies 

(especially insulation). 

• Maintenance staff should be involved throughout the design phase. 

• The contractor must be involved as part of the design team, even when a more complex designbid-build process is involved. 

• Changes in rate structures can change the design decisions and operating strategies. 

• Commercial buildings may shift from being cooling dominated to heating dominated because of 

low-energy design. 

For this project, we evaluated the as-built building energy performance as well as the effect of the lowenergy design process on energy performance. Even though the building performs well overall, we found 

it could have performed much better had the low-energy design process been followed more carefully. 
xvi 

Nomenclature 

Commonly used terms in this report are defined below. 

• Building Automation System (BAS) – the central computer used to control HVAC equipment and 

lighting. We also used the BAS to collect most data used in this analysis. 

• Proposed design – the proposed initial design was an “L” shaped building [7,600 ft2

 (710 m2)] 

with a separate building for restrooms [1,560-ft2

 (145 m2)]. Exhibits are located outdoors. 

• Proposed base case – The base-case model corresponding to the proposed design. It is a 7,600-ft2

(710-m2

) solar neutral building with a square footprint. It is used as the benchmark to calculate 

the potential energy performance savings of the proposed design. 

• As-built design – the design as modified to reflect changes made during construction. This model 

represents the building as it was built, including a separate building for restrooms and outdoor 

exhibits to minimize floor area. Schedules are based on actual operation as measured. The 

design consists of a Visitor Center and Comfort Station. 

• Base case – The base-case model corresponding to the as-built design. It is an 11,726-ft2

 (1090- 

m2

) solar neutral building with a square footprint used as the benchmark to calculate energy 

performance savings. Schedules are the same as the as-built design. 

• Visitor Center Complex – The three buildings that make up the Visitor Center Complex defined 

here as Visitor Center, Comfort Station (public restrooms), and Fee Station. Parking lot lights are 

included in the energy use when the Complex is discussed in this report. The Fee Station 

building, although not part of the study, is included in the Visitor Center Complex because the 

utility meters include power from this building. 

• Visitor Center – an 8,800-ft2

 (818-m2) building in the Visitor Center Complex that contains the 

bookstore, offices, and NPS ranger contact counters. 

• Comfort Station – a 2,756-ft2

 (256-m2) building in the Visitor Center Complex that contains the 

restroom facilities 

• Fee Station – a 170-ft2

 (15.8-m2) building in the Visitor Center Complex that is used to collect 

fees for incoming visitors. This building was not part of the research project and was not 

explicitly evaluated. However, the utility meter includes the power from this building. 

• Energy costs – the cost of energy needed to operate the building. The Visitor Center Complex 

only had electricity available at the site. The energy costs include fixed charges, energy use 

charges, and demand charges. 

• Construction costs – the amount of money needed to construct the building. 
1 

1 Introduction 

Zion National Park (ZNP) is located in a canyon in southwestern Utah1. The area is arid, only receiving 

15 inches of precipitation per year (NPS 2003). The location is characterized by sunny days with low 

humidity. During the summer, temperatures can reach 100°F (38°C) or higher. Winters are relatively 

mild with only about 3500 base 65 degree-days. In summer, ZNP hosts as many as 3,000 visitors an 

hour. To reduce visitor impact on resources and to improve visitor experiences, ZNP undertook the 

planning and development of an alternative transportation system with the gateway community of 

Springdale. As a part of the transportation system, several visitor facilities were constructed to make up a 

Visitor Center Complex that consisted of a small building where Park rangers collected visitor fees, a 

retail/interpretive area, and public restrooms. The National Park Service (NPS) decided to pursue an 

innovative building for the Visitor Center Complex—one with an aggressive energy reduction goal. 

Other important issues to the NPS were that the building: 

• blended well with the surrounding canyon walls, 

• mirrored the existing historic architecture of the park, 

• offered continued enjoyment for many generations of people (100 years or longer), 

• reduced environmental impact to the surrounding natural environment, 

• operated during frequent power outages, and 

• presented a model for other NPS facilities. 

Although budgetary limits were important, they were considered within the context of a building that had 

to be constructed in a remote place and be extremely durable to withstand the heavy pedestrian traffic for 

at least 100 years. These requirements are unique to NPS architecture. Nevertheless, some of the energy 

design solutions were able to reduce construction costs as discussed in the design section of this report. 

NPS worked with the National Renewable Energy Laboratory (NREL) to create the plans for the new 

Visitor Center Complex and transportation system. Objectives for NREL’s involvement were established 

early in the process. This report documents the results of this work. NREL’s objectives were to: 

• evaluate the low-energy design process as applied to the Zion Visitor Center Complex, 

• use careful metering, submetering, and simulation techniques to evaluate the whole-building 

energy performance during normal operation and determine if the original low-energy design 

goals were met, 

• determine lessons learned as a result of designing, operating, and monitoring the Visitor Center 

Complex for use in future projects, and 

• investigate opportunities for improving the operating performance of the Visitor Center Complex. 

The postoccupancy evaluation measured and assessed the energy performance of the Visitor Center 

Complex from September 1, 2000 to June 1, 2003. This evaluation was crucial to achieving and verifying 

the low-energy design goals. This report presents results from that multiyear performance monitoring. 

The new transportation system was not studied as part of the building evaluation. 

 

1

 National Park Service Web site for Zion National Park: http://www.nps.gov/zion/home.htm
2 

1.1 Energy Use in Commercial Buildings in the United States 

In 2001, commercial buildings accounted for approximately 18% of total primary energy consumption in 

the United States. The total for all buildings is over one-third of primary energy consumption and 70% of 

primary2

 electricity consumption. Energy use in buildings produces 35% of U.S. and 9% of global carbon 

dioxide (CO2) emissions. Electricity consumption in the commercial building sector has doubled during 

the last 18 years, and if current growth rates continue, it is expected to increase by another 25% by 2030 

(EIA 2002). Reducing site energy consumption in commercial buildings through energy-efficient and 

renewable building technologies would significantly reduce primary energy consumption in the United 

States (DOE 2003). Because utility bills are based on site energy consumption, site energy is also a 

concern for the building owner or those paying the bills. 

1.2 Building Evaluation Scope 

NREL selected the ZNP Visitor Center Complex as a technical case study to further the laboratory’s 

research of high-performance buildings. NREL, in collaboration with the staff at ZNP, monitored, 

evaluated, and documented the energy performance of the Visitor Center Complex and how the design 

process helped to achieve this performance. The evaluation covers the period from September 1, 2000 to 

June 1, 2003. The evaluation presented in this report focuses on the integration and interactions of the 

high-performance building technologies in a whole-building environment, with additional analysis of the 

photovoltaic, cooling, and daylighting systems. 

1.3 High-Performance Buildings Research Objectives 

NREL conducts research for the U.S. Department of Energy’s (DOE) High-Performance Buildings 

initiative (HPBi). HPBi evaluates commercial buildings from a whole-building perspective to understand 

the impact of integrated design issues on energy use and costs in commercial buildings while improving 

other attributes of the building such as occupant satisfaction. Documenting the high performance of 

research-level buildings provides evidence that energy-efficient buildings work, helping transform the 

marketplace. In addition, documenting common threads and analysis methodologies provides direct 

assistance to industry. HPBi’s research objectives are to: 

• develop processes for high-performance building design, construction, and operation, 

• provide the tools needed to replicate the processes, 

• research new technologies for high-performance buildings, 

• develop standardized metrics and procedures for measuring building energy performance, and 

• measure and document building performance in high-profile examples. 

1.4 Report Organization 

Section 2 provides background information on commercial building energy performance. Section 3 

describes the low-energy design process in general terms along with how that process was applied to the 

Visitor Center Complex project. Section 4 describes the building as constructed. Section 5 discusses 

methods for determining overall performance of the Visitor Center Complex as it was built and operated. 

Section 6 provides in-depth analysis of major building systems. Section 7 lists our recommendations 

from lessons learned throughout the project and Section 8 summarizes conclusions from the evaluation of 

the Visitor Center Complex. 

 

2

 Primary electricity is the site electricity plus the distribution and conversion losses at the utility plant. 
3 

2 Background 

NREL selected the Zion National Park Visitor Center Complex as a research effort because the design 

team and building owner were committed to aggressive energy saving goals. The NPS also agreed to 

post-occupancy energy monitoring. Although not used directly for comparison purposes, an analysis of 

commercial buildings in the United States was performed. 

In 2002, the Energy Information Administration (EIA) conducted the Commercial Buildings Energy 

Consumption Survey (CBECS), a national survey that collected information about thousands of 

commercial buildings in the United States including energy consumption during 1999. Data surveyed 

includes building physical and operating characteristics, energy consumption, and energy expenditures for 

all types of commercial buildings across U.S. climatic regions. The EIA defines energy intensity as site 

energy consumption per square foot of total floor space (EIA 2002). The Visitor Center Complex is a 

combination of office, retail, and service and does not directly fit into any specific category of the CBECS 

database. See Figure 2-1 for a comparison of energy use and energy costs for a variety of building types 

in the Western United States. 

26 30

67

75

83 84 86

$0.50 $0.38

$0.89

$1.53

$1.21

$1.42

$0.94

-100

-80

-60

-40

-20

0

20

40

60

80

100

Warehouse Religious

Worship

Education Retail and

Service

Lodging Office Public

Assembly

Energy Use Intensity (kBtu/ft2

)

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

Energy Cost Intensity ($/ft2

)

Energy Use Intensity Energy Cost Intensity

Figure 2-1 1999 Energy Use and Costs by Building Type for Western U.S. (EIA 2002) 

ENERGY STAR® performance ratings for commercial buildings can also be used as a basis for building 

energy use comparison. An EPA study attempted to recognize the most energy-efficient and costeffective commercial buildings in the country (Hicks 2000). The average annual energy use for buildings 

in the study was 56.4 kBtu/ft2

·yr (641 MJ/m2·yr). This average represents buildings of all sizes and 

various sectors. A comparison of CBECS and ENERGY STAR are shown in Table 2-1. These structures 

tend to be larger office buildings with a total area greater than 50,000 ft2

 (4645 m2). 
4 

Table 2-1 Energy and Cost Intensities by EPA Study 

EPA Study 

Site Energy 

Intensity 

kBtu/ft2·yr 

(MJ/m2·yr)

Source Energy 

Intensity 

kBtu/ft2·yr 

(MJ/m2·yr)

Energy Cost 

Intensity 

$/ft2·yr 

($/m2·yr)

ENERGY STAR Average 56.4 (641) 150.9 (1,714) 1.12 (12.06) 

CBECS Adjusted Average 101.1 (1,148) 261.8 (2,973) 1.62 (17.44) 

CBECS Adjusted Top 25% 48.2 (547) 113.9 (1,294) 0.81 (8.72) 

CBECS Adjusted Bottom 25% 217.0 (2,464) 511.0 (5,803) 2.80 (30.14) 

The top CBECS and ENERGY STAR buildings are examples of energy-efficient and cost-effective 

commercial structures. Documenting the performance of other commercial buildings provides a reference 

for comparing these high-performance facilities. A high-performance building is one that is designed, 

built, and operated to use less than one-half the energy of typical buildings. 

Many buildings that are designed to be energy efficient do not actually meet these targets. For example, a 

recently completed educational building designed to be energy efficient did not initially meet the energy 

design expectations (Pless 2004). Postoccupancy evaluation of the building operation identified how this 

low-energy building could operate at high-performance levels. 
5 

3 Design Process 

This section outlines how we used the low-energy design process (located in Appendix A) to integrate 

energy efficiency into the Visitor Center Complex. It describes the steps of the design process starting 

from the beginning, which is setting energy goals, and continues through brainstorming new design 

solutions after initial energy simulation of the base-case building model. 

3.1 Rationale for Design 

The initial motivation for the design of the new Visitor Center Complex was to resolve transportation 

problems within the park. During the summer, more than 3,000 visitors per hour visit ZNP, but only 400 

parking spaces were available in the canyon. As a result, problems such as traffic congestion, noise, and 

visitor safety concerns were increasing. In addition, the automobiles caused substantial damage to the 

canyon’s flora and fauna. Figure 3-1 shows an example of the parking problem. (NPS 1995). 

In addition to the new transportation system, new visitor facilities were needed. The old facility had 

limited space for interpretive displays to describe ZNP features and wildlife. Furthermore, the restrooms 

were unable to handle the increased guest load and the layout of the building was not effective in serving 

large crowds. Another issue that influenced the Visitor Center Complex’s design was the NPS desire to 

have any new buildings complement the surrounding natural environment to preserve the tranquility of 

the area. 

Figure 3-1 Summer traffic congestion, traffic back-ups, and parking issues 

3.2 Applying the Design Process 

The Visitor Center Complex project followed the low-energy design process outlined in Appendix A. 

This section describes how the low-energy design process was applied for this project. Note that several 

building concepts were created during the application of this design process, see Figure 3-2. The original 

conceptual design was an 18,000-ft2

 building with displays and exhibits located indoors. After conceptual 
6 

design, the displays and exhibits were moved outdoors, which enabled us to design a much smaller 

building. In addition, the building was split into two buildings, (1) a Visitor Center [7,600 ft2

 (710 m2)] 

and (2) a Comfort Station [1,560 ft2

 (145 m2)], as shown in Figure 3-2 as the proposed design. The 

proposed base case for the proposed design only modeled the Visitor Center. During design, the location 

of the building on the site changed, requiring a building redesign. The new design (the as-built design) 

consisted of a Visitor Center [8,800 ft2

 (818 m2)], Comfort Station [2,756 ft2 (256 m2)], and a Fee Station 

[170 ft2

 (15.8 m2)]. Details of applying the 10-step low-energy design process are discussed below. 

Base-Case Models Current Design

18,000 ft2

(Not Modeled)

Conceptual Design

Comfort Station

1,560 ft2

 (Not Modeled)

Visitor Outdoor

Center Exhibits

7,600 ft2 (Not Modeled)

Proposed Base Case

Proposed Design

Outdoor

Exhibits

(Not Modeled)

Visitor Comfort

Center Station

8,800 ft2 2,756 ft2

Base Case

As-Built Design

1995 1997 1998

Visitor Center 7,600 ft2 

Comfort Station 1,560 ft2

Visitor Center 8,800 ft2 

Comfort Station 2,756 ft2

Figure 3-2 Flowchart of building designs 
7 

3.2.1 Step 1: Predesign 

Low-energy architecture requires the setting of clear, measurable energy performance goals and tracking 

progress toward that goal. Goals provide an energy saving target to achieve and a value to compare 

energy performance. For this project, an energy-cost saving goal of 70% was set at the beginning of the 

design process and used as an energy saving target throughout the process. 

Another important part of predesign is to evaluate the climate in which the building is located. To help 

the NPS determine the best design for their new building, a series of design charrettes were held at ZNP. 

Participating were ZNP staff, NREL building researchers, and NPS engineers and architects. The 

attendees of the charrette spent several days camping in ZNP to gain a better understanding of the 

environmental conditions of the canyon, which heavily influenced the design process. During the first 

part of the design charrette, NREL and NPS staff observed natural cooling within the canyon that could 

easily be adapted to the built environment. A temporary weather station recorded hourly integrated 

values of shielded air temperature, relative humidity, global horizontal solar radiation, wind speed, and 

wind direction. This data was used to quantify the observations of the design team. These were 

important observations for a region where daily high summer temperatures regularly exceed 100°F 

(38°C), as shown in Figure 3-3. 

It was apparent from the site visit that the local microclimate provided many ideas for the design concepts 

that could be used to provide comfort in and around the visitor center. The Virgin River canyon 

controlled many aspects of the microclimate. The narrow canyon walls, splashing water, and vegetation 

at the riverbanks provided shade and evaporatively cooled air in sharp relief to the aridness and extreme 

heat. In some places, seeps wetted the canyon walls, creating a cooling effect. In other places, the seeps 

nourished blooms of wet moss that behave much as the wetted media in a commercial evaporative cooler. 

The overall geometry of the canyon, which was deep and narrow up-river of the site and widened 

progressively in the down-river direction, created a diurnal chimney effect with up canyon winds from 

about noon to midnight and down canyon winds from midnight to noon. The lighting in the narrow parts 

of the canyon was diffuse with a pleasant contrast ratio and without the unpleasant impact of the direct 

sun. A winter visit was also informative with solar heating of exposed canyon mass surfaces often 

adequate to provide outside comfort during the day. 

Thus were born many of the overall energy, lighting and human comfort architectural design concepts for 

the complex. These are summarized as follows: 

• Create a shaded microclimate around the buildings in summer and solar exposure in winter with 

plantings of deciduous trees and overhead arbors. 

• Provide irrigation throughout the space with small irrigation canals similar to the historic ones 

found in the canyon. Although not implemented in this project, it is possible to use porous patio 

materials to create an evaporatively cooled walking surface. 

• Create passive evaporative downdraft cooltowers to cool the building without the need for 

blowers or vapor compression equipment. 

• Use the diurnal winds to help drive a natural ventilation system and to boost the cooltower’s air 

delivery with wind pressure. 

• Control automated clerestory windows and the cooltowers with the building automation system 

to create an integrated, controllable natural cooling system. 

• Specify the thermal and optical properties of glass; size and orient windows and shading devices 

to provide diffuse light with minimal solar load in summer, and light and solar heat in winter. 

• Use massive building materials on the interior to modulate temperature swings and store solar 

heat in winter and cool night air in summer. 
8 

• Construct noncirculating Trombe walls on the south face of the buildings for additional passive 

heating with a time delay into the late afternoon and evening hours. 

• Allow enough south-oriented pitched roof surface to accommodate photovoltaic panels so that 

the building can operate effectively and comfortably despite frequent summer power outages. 

In addition to borrowing elements from the natural cooling and heating taking place within ZNP, the 

design team also evaluated the original program requirements for building size to discover if further 

energy saving measures could be incorporated into the design. Because 90% of the total annual visitors 

are in ZNP during the hot and dry summer, the design team determined that many of the exhibits could be 

moved to permanent areas outside the building. By providing shading and water for visitors and creating 

outdoor exhibit areas, the building became smaller, less expensive, and thus, it would require less energy 

to operate. Finally, visitors would have access to the displays when the Visitor Center is closed. Overall, 

the building footprint was reduced from 18,000 ft2

 (1,670 m2) to 11,726 ft2 (1090 m2). 

0

20

40

60

80

100

120

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Temperature (°F)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Precipitation (Inches)

Normal Daily High/Low Temperature

Normal Monthly Precipitation

Figure 3-3 Typical monthly average daily weather for ZNP 

3.2.2 Step 2: Create a base-case building model 

At this stage of the project, a base-case model was created for the Visitor Center using DOE-2 simulation 

software (Winkelmann et. al. 1993). The software was used to help design elements of the building 

related to energy efficiency. This model reflected the floor area equal to the proposed smaller footprint 

for the Visitor Center [7,600 ft2 (706 m2

)]. 

The theoretical base-case building was developed to provide a starting point for the analysis as well as a 

metric against which to measure the energy savings success of the project. It also set the groundwork for 

guiding the design process using energy simulation tools. Most of the analysis took place early in the 

design process in parallel with the programming and goal setting exercises. The initial base case was 

modeled as a square, single-floor building, as shown in Figure 3-4. The model was solar neutral (equal 
9 

glazing areas on all orientations) and met the minimum requirements of the Federal Energy Code 10 CFR 

435 (DOE 1995) (based on ANSI/ASHRAE/IESNA Standard 90.1-1989 (ASHRAE 1989) with additional 

lighting requirements). Based on visitor data from the NPS, the maximum number of occupants was 

assumed to be 100, and occupancy schedules were based on typical operation hours of the existing 

facility. Outside ventilation air in the base-case model was set at a constant rate during occupied hours 

equal to 15 cfm per person. Depending on the zone, lighting levels were set to retail, office, and exhibit 

lighting levels with no reduction for daylighting. Table 3-1 summarizes building characteristics used in 

the base-case model. 

Figure 3-4 Simulated 7,600-ft2 (706-m2) base-case model 

Table 3-1 Base-Case Model Characteristics 

Item Proposed Base Case 

Size, ft2 (m2) 7,600 (706) 

Heating System Propane 

Cooling System Packaged Single-Zone 

Air Conditioner 

Hot-Water System Propane 

Wall R-Value, ft2⋅°F⋅hr/Btu (m2·K/W) 13.9 (2.45) 

Window R-Value, ft2⋅°F⋅hr/Btu (m2·K/W) 0.58 (0.10) 

Window-to-Wall Area 30% 

Floor Perimeter Insulation (4 ft of vertical 

foundation insulation) R-Value, 

ft2

⋅°F⋅hr/Btu (m2·K/W)

4 (0.7) 

Roof R-Value, ft2⋅°F⋅hr/Btu (m2·K/W) 22.7 (4.00) 

Infiltration (ACH) 1 

Equipment load, W/ft2 (W/m2) 0.75 (8.1) 

Daylighting No 

Overhangs No 

Demand Limiting Controls No 

Lighting Power Density, W/ft2 (W/m2)

Office Space 1.4 (15) 

Retail and Display Space 2.2 (24) 

Restrooms Not Modeled 

Outdoor and Parking Lot (W) Not Modeled 
10 

The heating and cooling equipment modeled in the initial base-case model represent typical HVAC 

equipment complying with the applicable federal energy code. The heating system was modeled as a 

propane furnace with 80% annual fuel utilization efficiency. The cooling system was modeled as a 

packaged single-zone air conditioner with a coefficient of performance (COP) of 3.0. Many of these 

base-case characteristics were based on typical park practice information provided by NPS staff. Local 

electric utility rates and propane costs were used in the base-case model to calculate energy costs of the 

proposed design and initial base case. Natural gas is not available at the site. 

Conventional retail building construction characteristics vary, so it is difficult to justify base-case model 

characteristics that do not conform to a universally accepted standard set of criteria. ASHRAE Standard 

90.1-1989 is a consensus-based standard that outlines the minimum building energy design requirements. 

The Federal Energy Code (10 CFR 435) adopted this industry standard in its entirety along with stricter 

lighting requirements. Many municipalities do not require or strictly enforce Standard 90.1 or 10 CFR 

435 requirements. Therefore, a building designed to meet 10 CFR 435 is often a better building than 

conventional construction in that year. This also provides a standard metric for comparing percent 

savings among buildings. The base-case building described in this paper is for energy comparison only. 

3.2.3 Step 3: Parametric Analysis 

Using the base-case building simulations, we conducted an elimination parametric analysis to evaluate the 

effects of specific elements of the Visitor Center. See Table 3-2 for a description of the parametric 

simulations. For example, the U-value of the wall, floor, roof, and windows were individually eliminated 

(set to near-zero) to simulate zero heat transfer across these components. As shown in Figure 3-5, the 

building energy requirements resulting from these simulations showed that daylighting, shading, natural 

ventilation, evaporative cooling, and passive solar heating reduced total building energy requirements the 

most. 

Table 3-2 Parametric Analysis Description 

Parametric Alternative Description 

Base Case Code minimum as defined in Step 2 above 

Daylighting On Daylighting enabled in simulation 

No Internal Gains Remove all receptacles, lighting, and occupants 

No Window Conduction No conduction across windows (R-99) 

No Wall Conduction No conduction through walls (R-99) 

No Roof Conduction No conduction through roof (R-99) 

No Floor Conduction No conduction through floor slabs (R-99) 

No Infiltration No uncontrolled outside air 

No Sun (SHGC = 0) No solar heat gain through windows 

5x Internal Mass Five times more thermal capacitance 

25x Internal Mass Twenty five times more thermal capacitance 
11 

0%

20%

40%

60%

80%

100%

120%

Base Case

Daylighting On

No Internal

Gains

No Window

Conduction

No Wall

Conduction

No Roof

Conduction

No Floor

Conduction

No Infiltration

No Sun

(SHGC=0)

5x Internal Mass

25x Internal

Mass

Energy Comparison to Base Case (%)

Fans

Cooling

Heating

Lighting

Plug Loads

Figure 3-5 Parametric analysis results 

3.2.4 Step 4: Design Solutions to Reduce Energy Consumption 

The parametric analysis showed that cooling is a significant part of the building’s total energy loads. 

Eliminating solar gains (“no sun” parametric) produced the greatest reduction in the cooling load. This 

observation helped the design team focus on developing strategies that reduce solar gain. Reducing large 

internal heat gains produced from lighting also reduced the cooling loads. As a result, the design team 

incorporated daylighting strategies and used a daylighting design that avoids excessive solar gains during 

the cooling season. The daylighting design allowed fewer and more efficient lights to be installed, which 

decreased the overall internal loads. 

The building envelope design minimizes summer solar gains with window overhangs and reduces electric 

lighting loads with large south-facing windows that allow more natural light to enter the building (see 

Figure 3-6). However, the building envelope design did not offset the entire cooling load. Next, natural 

ventilation cooling was integrated with the daylighting design—automatic window actuators were added 

to the clerestory windows. For more information on the natural ventilation system, see Section 4.4. The 

remaining cooling loads were met by the evaporative cooltower system discussed below. 
12 

Figure 3-6 Diagram of energy design solutions for the Visitor Center Complex 

The parametric analysis showed that by eliminating solar gains (”no sun” parametric), building heating 

loads would increase. Winter solar gains help reduce heating loads. The resulting design solution 

incorporated direct solar gain through the clerestory windows and a Trombe wall along the entire south 

face of the building; see Section 4.4.1 for more details on the Trombe Wall. A properly sized overhang 

allows the low winter sun to heat the Trombe wall, while shading it in the summer when the sun is higher 

in the sky, thereby decreasing the cooling load. We designed the overhangs for south-facing windows to 

allow direct solar gain in the winter and eliminate summer solar gains. To maximize solar gains through 

south-facing windows, we specified a high SHGC glazing. Because it is difficult to shade west-facing 

windows, we specified all west-facing glass with low SHGCs. Finally, the parametric analysis showed 

that by eliminating window conduction, we could minimize the heating load. This leads to the conclusion 

that we should minimize glass area except for daylighting and passive heating purposes. We determined 

window properties by running simulations with different predefined window constructions. Because 

window SHGC and U-Value are interconnected, we selected windows that matched closest to the 

simulated specifications. 

3.2.5 Step 5: Simulate Performance of Design Solutions 

We used computer simulations to quantitatively evaluate the effectiveness of the various strategies for 

reducing loads and using natural heat flows available in the canyon. We first carefully studied those 

strategies that affected building architecture in preparation for the next design process step. 

Based on our analysis, we had the following recommendations: 

• Minimize east and west glass. West glass should have a low SHGC. North glass should be used 

for daylighting only. 

• Use north, west, and east glass with lowest possible U-values. 

• Use Trombe walls to provide passive solar heat without adding glare to the space. (Trombe 

walls delay heat gain into the buildings to the early evening when it can be best used.) 

• Use extensive daylighting to reduce lighting energy and reduce internal energy loads from the 

lights. 
13 

• Use reasonable levels of insulation, meeting or exceeding the requirements of 10 CFR 435. 

• Use overhangs to block summer sun from south-facing windows. 

• Use natural ventilation together with evaporative cooling to meet the remaining cooling loads. 

3.2.6 Step 6: Conceptual Design 

During this stage of design, energy-efficient strategies were incorporated into the architectural design. 

For example, the original building envelope concept included the use of tall architectural elements to 

unify the building with the surrounding canyon walls. The team evaluated the use of downdraft 

cooltowers for the cooling system as one means of introducing a tall element into the architectural 

scheme. Cooltowers, while similar to direct evaporative coolers, do not use fans. Original plans called 

for five cooltowers located at the building corners. This not only met the architectural needs of the 

building, but also provided benefits for energy performance. 

Further cooling was achieved by strategically placing operable windows to promote natural ventilation 

and passively move cool air through the space. 

Through careful design of shading devices to minimize the solar gains, all cooling loads could be met 

with natural ventilation and the cooltowers. The only mechanical input to the cooling system is a pump 

used to circulate water through the evaporative media. The cooling system meets all summer ventilation 

requirements as well. During the winter, ventilation requirements are lower because of fewer visitors and 

can be met by infiltration through the building envelope as well as people entering and leaving the 

building. 

During the winter, a Trombe wall provides most of the building heating. As with the cooling system 

design, simulations were used to optimize the envelope for winter performance. After the envelope was 

designed, the remaining heating, cooling, and lighting loads were studied and a small heating load 

remained. In the initial proposed design, the building was heated using propane. The initial concept was 

to use a propane fireplace that would serve as an architectural amenity as well as the heating system for 

the building. 

At this point in the process, the design team investigated the potential impact of incorporating a 

photovoltaic (PV) system into the roof for electrical power. The design team provided the option to use 

PV in the future by designing a south-facing roof that was sloped to maximize the production of 

electricity. In addition, conduit to the roof and mounting brackets were added to the base building plan. 

Although not quantified, NPS personnel were concerned about the poor power reliability at the park. A 

UPS (uninterruptible power supply) was included in the original plan for the building electrical system. 

By specifying an inverter for this system that could handle the direct current input from a PV system, the 

UPS requested by the program could be PV powered. The UPS batteries were designed to deliver 2 hours 

of power without any PV. Using 3.6 kW of PV allowed the system to operate as long as there is sun. 

Space for an additional 3.6 kW of PV was allocated on the roof. This system was designed to be directly 

grid-tied. 

Overall, observations from Step 1 of the design process helped clarify understanding of the natural 

environment in which the building would be located and prompted a careful analysis of the programmatic 

needs of the building. Daylighting, natural ventilation, evaporative cooling, minimizing summer solar 

gains with building shape and envelope features, massive building materials to stabilize indoor 

temperatures, passive solar heating, and siting with relation to mature trees and newly constructed outdoor 

shade structures were all part of the integrated building design. A roof-mounted PV array further reduces 

the building’s environmental impact. The resulting proposed design floor plan and southern elevation are 

shown in Figure 3-7 and Figure 3-8. 
14 

Figure 3-7 Initial proposed design of the Visitor Center 

Figure 3-8 Conceptual design floor plan for Visitor Center and Comfort Station 

(Step 6) 

Step 6 resulted in the following design decisions related to energy impacts: 

• The south roof slope should accommodate a future PV system. The electrical system should 

accommodate PV to be used in conjunction with a UPS system. The primary purpose for the PV 

system was to meet minimum building operation requirements. Additionally, electricity would 

serve building electrical needs whenever utility power was available. 

• Cooling loads would be handled by cooltowers. The building interior would be designed to 

accommodate this technology by using operable high windows, natural ventilation, and open 

spaces with good airflow between the spaces. 
15 

• Because the cooltowers use little energy, use them to cool the building as well as some outdoor 

locations as well. Encourage interpretation in these areas with exhibits and staff as “outdoor 

rooms,” because people come to ZNP to spend time outside, not inside a building. 

• Provide heating with a propane-powered fireplace to provide amenity and eliminate the central 

heating system. This eliminates the mechanical room. 

The conceptual design for the Visitor Center is an example of how architectural features can enhance the 

energy performance as well as give the building a unique aesthetic style. In the Visitor Center, the 

building’s window overhangs, clerestories, roofline, massive building materials, and other architectural 

features all contribute to the building’s improved energy performance. Computer simulations allowed 

engineers to create an envelope that serves to function as most of the HVAC system. 

3.2.7 Step 7: Design Development 

The Visitor Center Complex comprised the main center (Visitor Center) and a separate restroom building 

(Comfort Station). The two buildings operated independently in terms of energy. The main interest for 

design development was to determine the savings of just the main Visitor Center. Therefore, we used an 

independently-zoned model to simulate only the main Visitor Center. 

Heating in the proposed design was provided by using direct solar gain through south-facing windows as 

well as a Trombe wall. The design also included using clerestories to increase daylighting. The 

daylighting design was expected to fulfill most of the daytime lighting requirements. 

The remaining electrical demand was small. Therefore, the roof was designed to accommodate a 7.2-kW 

PV system that could offset approximately 30% of the annual electrical load. In addition, the PV system 

is capable of meeting all functional requirements of the building during a daytime power outage—the 

cash registers, security system, BAS, cooltower pumps, and other essential equipment. The daylighting 

design was expected to be sufficient to maintain operational lighting levels during a power outage. 

At the end of design development, energy cost savings were approximately 80% as compared to the 

7,600-ft2

 (706-m2) base case. This was based on proposed design simulation models of the 7,600-ft2

(706-m2

) Visitor Center (not including the Comfort Station). The energy cost savings are shown in 

Figure 3-9, with corresponding cost and site energy savings data shown in Table 3-3 and Table 3-4. 

These savings do not include savings from the PV system. The proposed design model is shown in 

Figure 3-10.

Ventilation 

Fans

17%

Lighting

45%

Plug Loads

6%

Heating

3%

Cooling/Pumps

26%

DHW

3%

Plug Loads

6%

Heating

2%

Lighting

4%

Cooling/Pumps

1%

DHW

2%

Ventilation Fans

5%

Cost Savings

80%

Figure 3-9 Simulated energy cost savings of base-case building compared to 

conceptual design (excluding the PV system) 

7,600-ft2 Base Case 7,600-ft2

 Conceptual Design 
16 

Table 3-3 Energy Use by End-Use 

End Use 

Base 

Case 

(kWh) 

Proposed 

Design 

(kWh) 

Percent 

Savings 

Heating1 12,143 9,569 21.2% 

Cooling 35,492 893 97.5% 

Ventilation Fans 40,800 8,901 78.2% 

Domestic Hot Water1 13,850 9,653 30.3% 

Lighting 79,337 8,489 89.3% 

Plug Loads 14,216 14,216 0.0% 

Total Energy 195,838 51,721 73.6% 

1

27.98 kWh/Gal LPG [95,475 Btu/Gal LPG (7.39 kWh/liter)] 

Table 3-4 Energy Cost Savings by End-Use 

End Use Base 

Case 

Proposed 

Design 

Percent 

Savings 

Heating $312 $246 21.2% 

Cooling $2,743 $97 96.5% 

Ventilation Fans $1,767 $479 72.9% 

Domestic Hot Water $357 $246 31.1% 

Lighting $4,567 $418 90.9% 

Plug Loads $662 $662 0.0% 

Total Cost $10,408 $2,148 79.4% 

Figure 3-10 DOE-2 proposed design model 
17 

The largest end use savings was the lighting. Design savings are based on using daylighting and lighting 

design. With the daylighting system, the lighting needs could be met with 0.75 W/ft2

 (8.1 W/m2). 

Because of contrast ratios from inside to outside, lower light power densities can be used in daylit spaces. 

Typically, at night, less lighting is needed to make a space feel visually comfortable. In addition, most of 

the lights are expected to be off during the day. For a standard space of similar use, the code allows 2.2 

W/ft2

 (24 W/m2). Reducing the lighting also reduced the cooling requirements. 

The Comfort Station was designed in a similar fashion. Two cooltowers were specified in the proposed 

design for cooling the space. A Trombe wall was provided at the south facade for heating, while daylight 

from clerestories provided all the necessary daytime lighting. 

Project Redesign 

Part way through the design development process step, the building site changed. A new plan was 

developed to situate the structure on the east side of the river. The entrance to the building was relocated 

to the north side to facilitate pedestrian flow through the Visitor Center Complex within the new site, 

which allowed the south facade to be unobstructed and increase passive solar gains. For building layout, 

the offices and break room were moved to the south side of the building. The number of cooltowers was 

reduced to three including the one for the Comfort Station because the building engineer concluded that 

there would be sufficient airflow with fewer towers. For architectural reasons, the amount of north and 

west glass increased, although the tree canopy and building shading keep these surfaces shaded most of 

the summer. Finally, the outdoor cooltower was removed, with the two cooltowers being expected to 

condition both inside and outside spaces. A study indicated that the cost of propane in Springdale would 

exceed that of electric resistance heating. This prompted conversion of the building to an all-electric one, 

eliminating the fuel storage from the site. However, this determination is contingent upon restricting use 

of resistance heating during only those nighttime periods when additional demand charges are not 

imposed. To complement heat obtained from the Trombe wall, electric radiant panels were installed in 

the ceiling on twelve zones. The cost of zoning the spaces was minimal and provided for control 

flexibility in controlling building demand. The result was an HVAC system requiring no ductwork or 

mechanical spaces—saving money and allowing for uncluttered ceiling spaces. 

Transfer fans (from the offices to the main space) were installed to pull air from the main space to the 

offices. Transfer grilles were installed between the break room and the main space to cool the break room 

and offices. After the building was operated for a year, fans were added to these transfer grills to 

augment the natural ventilation. 

The building was not resimulated as instructed in the ten-step design process, which will be detailed in the 

design critique section. The design team carefully reviewed all drawings and documents to ensure that 

the altered design intent was clear and minimized any possible errors or misinterpretation of the design 

during construction. The creation of the base cases and redesigns are detailed in Section 5.3.2. 

3.2.8 Step 8: Bid Documents and Specifications 

An “as-designed” computer simulation was not done of the building at this step, but several items in the 

plans were checked. These include thermal bridging, control sequences, lighting layouts (compatibility 

with daylighting system verified), window specifications, and foundation insulation. Window 

specifications were critical because different windows types were to be installed on the various facades. 

3.2.9 Step 9: Construction 

Although the design was entirely done by the NPS, the role of implementing the plans on behalf of the 

NPS was contracted to Post, Buckley, Schuh, and Jernigan, Inc. (PBS&J). A construction manager was 

assigned to the project to ensure that the building was built according to plan. The construction contract 

was awarded to Bud Mahas Construction from Salt Lake City. 
18 

As is typical for construction management, the management can identify problems with areas of their 

expertise. From a construction management point of view, the most important aspect of the building is 

the structural integrity of the building. Expertise in thermal envelopes and energy equipment was 

considered second tier. Shop drawings, color palettes, and equipment selection were approved by NPS, 

Denver Service Center personnel. In addition, NREL staff visited the site several times with the focus of 

ensuring energy aspects were implemented properly. The impacts of these issues will be discussed in later 

sections. 

In general, the buildings were built according to plan. Several issues did surface including: 

• Window glazing specifications were not followed 

• The interface between cooltower shutter doors and the BAS were problematic 

• The interface between the windows and the BAS were problematic 

• The lighting sequencing and zoning did not match the plans 

• The metering in the Comfort Station was not compatible with the electrical configuration. 

In addition, NREL found several areas where insulation was missing. These areas were corrected as the 

building progressed. The most notable was extensive damage to the exterior foundation insulation prior 

to backfilling. 

In general, there was good communication between the design team, the construction manager, and the 

general contractor. 

3.2.10 Step 10: Commissioning and Postoccupancy Evaluation 

There was no formal commissioning of the building’s energy features. Lighting was verified to be 

working as well as basic operation. No formal comparison of the design intent with the as-built building 

was done. 

NREL installed monitoring equipment shortly after occupancy of the building. Through this monitoring, 

several problem areas were identified. NREL worked with Zion staff to correct as many of these issues as 

possible. It is a typical problem that buildings are not formally commissioned and the owner is left to 

correct problems. 

The process of NREL interacting with Zion staff also provided the opportunity to transfer knowledge of 

the design intent to the people operating and maintaining the building. Results of the commissioning and 

postoccupancy will be discussed with further detail in the evaluation section. 

3.3 Energy Design Process Evaluation 

The first segment of the evaluation assessed the design process itself through a design team questionnaire 

and round table session. This assessment was used to capture data related to the type of communication 

and commitment during the design process. 

3.3.1 Energy Design Process Questionnaire Methods 

The goal of the energy design process evaluation was to carry out a systematic assessment of the 

performance of the design team after completion of the project. A questionnaire and round table session 

were used to gather information from the design team. These methods were used to capture data related 

to the 10-step low-energy design process work discussed in Appendix A. This procedure also helped to 

identify possible problem areas within the process between the energy consultant, building owner, 

architect, engineer, and building user. 
19 

The first step of the evaluation involved preparing a questionnaire to survey all the design team members. 

The second step involved developing a structured interview (round table session) to help validate the 

questionnaire. Note that the structured interview was administered after collection of the questionnaire. 

Together, the questionnaire and survey provided the information to: 

• establish if the energy design goals were actually achieved, 

• identify problematic design processes, 

• identify areas of the design process that worked, 

• identify design aspects for long-term research and investigation, 

• institute corrective actions, and 

• determine the level of commitment and understanding amongst team members that is needed for a 

successful low-energy building. 

The end goal of this evaluation was to obtain feedback from the design team to improve the design 

process in the future. 

After the questionnaire and structured interview had both been administered, the submissions were 

analyzed, with the resulting design process analysis discussed in Section 3.4.2. The questionnaire was 

issued after completion of the final design, but before the construction was completed. The questionnaire, 

as shown in Appendix B, was issued to everyone involved in the design process, including the architect, 

landscape architect, mechanical engineer, electrical engineer, and design project manager. 

Results obtained from the questionnaire were also used to establish the presence of either communication 

problems or where specific design team members had difficulty understanding technical issues. 

Specifically, a communication problem exists when design team members have trouble making their ideas 

clear to other team members (either in writing or during discussions). A technical problem exists when a 

technology was not properly implemented by the design team. This data can then be analyzed in 

conjunction with the 10-step process to determine if this breakdown had an overall affect on the success 

of the design implementation. 

The purpose of the round table meeting was to bring together the design team members to discuss issues 

related to the design process. This qualitative information gathering session included individuals who had 

daily impacts on the energy design process. The meeting was used to enhance discussion and to bring up 

points that were either forgotten or too difficult to communicate in the questionnaire. Discussions that 

took place were related to specific issues in the questionnaire that they wanted to resolve further, or areas 

not covered in the questionnaire. 

The evaluation team compiled questionnaire results and presented them to the design team. These results 

were used to create in-depth questions based on the topics that generated concern. This format allowed 

the evaluation team to probe deeper into problems and allowed the interviewees to go into more detail 

than normally capable within the allotted space on the questionnaire. 

3.3.2 Energy Design Process Questionnaire Results 

Results of the questionnaire and meeting are presented below in summary form. Specific comments 

about the questionnaire and round table meeting questions are provided in Appendix B. The primary 

questionnaire objectives are presented below, with specific responses addressing each issue: 

1. Establish whether the energy design goals were actually achieved: 

During the design process, before the building was occupied, the architect felt that it was important to 

verify whether the facility would operate according to the design intent. Building operation was a 
20 

concern because the design team was aware of a previous NPS project that was designed with similar 

intent, but failed in operation. Although the need to verify design goals was emphasized, no 

responders actually provided information about how well these goals were achieved. To fully 

determine if low-energy goals had been achieved, the measured energy performance was obtained. 

This is studied and discussed in further sections.

2. Identify problematic design processes: 

Deviation from traditional expectation and industry norms in materials selection and construction 

techniques were at the forefront of problems revealed by the questionnaire and meeting. Some 

individuals involved in the design process found it difficult to deviate from standard procedure. 

Unconventional building design coupled with the high cost of the cooltowers was initially a cause for 

apprehension because similarly designed facilities built previously had failed to perform adequately. 

Several individuals felt the design process could be greatly optimized by giving project members 

information ahead of time about available technologies, prior to initiation of the project. Because 

some features were implemented late in the design process, their appearance was awkward and 

difficult to integrate into the architecture. Increased communication with designers needs to be 

emphasized in the future in order to promote a more integrated design. Detailed information about 

the local environment should also be made available to reduce the chances of over sizing the 

mechanical design. The excess use of technical details should be avoided in order to prevent the 

possibility of alienating stakeholders and decision makers. For future projects, energy features should 

be brainstormed by the team and then evaluated by the energy consultant before a charrette is used to 

incorporate the features. 

In addition, design team effectiveness could potentially be improved by using better time 

management. A beneficial strategy to improve time management would be to coordinate the progress 

of all disciplines involved. A deeper exploration of sustainable practices and technologies beyond 

those currently applied, and retention of current team members in future endeavors, could also 

enhance team efficacy. 

In general, requests for a closer look at broadening materials selection practices were a recurring 

theme. Concerns about the building control systems were also an issue. Some project members felt 

longevity may become an issue in the next 5-10 years, while others were simply concerned about how 

late the control system was conceived in the design process. The team wanted more information on 

material issues that was not available. 

3. Identify areas of the design process that worked: 

The individual enthusiasm of the team members as well as the motivation of ZNP staff all contributed 

to the development of a viable sustainable design for the Visitor Center Complex. However, it was 

the innovative nature of the project, which many viewed as an opportunity to push the envelope of 

sustainability, which led to a sense of team cohesiveness among the participants. During design and 

construction, many novel approaches were applied in an effort to conserve resources. One such 

approach involved relocating traditionally interior visitor functions to the outdoor environment, 

resulting in reduced facility dimensions with a comparable reduction in energy use. 

All questionnaire responders thought that their ideas were well received. For example, the 

mechanical engineer was pleased with how well the team received his proposal for heating the Visitor 

Center with electric radiant panels. Additionally, all responders unanimously felt that the design team 

interacted and worked well with each other. NREL responded to a majority of team requests with 

accuracy and speed. In addition, NREL played a significant role in facilitating this by serving as a 

single point of contact for team communication related to energy issues. This structure allowed 

reviews, subconsultants and technical information to be distributed very quickly. Occasionally, 
21 

substantial demands for the energy simulations were cause for minor delay, but did not end up posing 

a significant threat toward the progression of ongoing activities. 

NREL’s participation in the project was deemed essential for achieving success in the design. The 

background and vision provided were useful in attaining both a functional as well as visually 

appealing design. This took the form of critical input regarding progress of the design process from 

early stages to project conclusion. Specifically, information about passive solar heating output and 

mass storage calculations were important to drive the design. 

4. Identify design aspects for long-term research and investigation: 

One responder identified increased solar electrical generation as a potential design aspect to be 

researched further. Another issue identified was the complexity of the building control system. The 

mechanical engineer was “skeptical on how the digital controls for daylighting, ventilation, and 

heating will work in 5 or 10 years.” 

5. Identify corrective action: 

Specific suggestions for corrective action were not identified through the questionnaire or meeting, 

although corrective actions have been identified and implemented during the post occupancy 

continuous commissioning process. These corrective actions, as well as the causes of the identified 

problems, are discussed in further sections. One responder did feel that it would be best if the 

original team members were involved in future enhancements of the project. 

Additionally, the project architect had expressed a need “to evaluate the facility during post 

construction operation to determine its success and recommend any modifications that may be needed 

to increase its efficiency." This step is already a current part of the low-energy design process. 

Several recurring comments from the questionnaire reinforced this obligation to review and document 

results with respect to initial design goals. It is noted that this feedback to the design team is often 

omitted. It is important from a design perspective to determine whether application of the low-energy 

design process resulted in measured energy savings during a typical period of operation. 

6. Determine the level of commitment and understanding among team members that is needed for a 

successful low-energy building: 

Overall, communication took place successfully and problems encountered were virtually 

nonexistent. The energy consultant played an effective role in communicating ideas and 

recommendations to the design team, as well as selling the sustainable goals and concepts. This was 

largely responsible for eventual funding of the project, and helped provide added value to the original 

design. 
22 

4 As-Built Building Description 

The as-built Visitor Center Complex includes the Visitor Center, the Comfort Station (public restrooms), 

and a Fee Station for people entering ZNP, Figure 4-1. This section describes the as-built Visitor Center 

Complex and its incorporated energy features. 

The design team insulated the building envelope well to minimize heating and cooling loads. Cooling is 

accomplished with natural ventilation via operable clerestory windows and shutter doors on the bottom of 

the cooltowers. The cooltowers use direct evaporative cooling with buoyancy-driven forces—like a 

reverse chimney. The design team also engineered the window overhangs to minimize summer solar 

loads and allow winter passive solar gains. 

For building heating, the design team sized the windows to provide daylighting to most of the spaces, not 

only to provide natural light, but so that heat from sunlight entering the building could be absorbed by the 

building’s thermal mass material such as Trombe walls and tile floors. Heating is further supplemented 

by electric radiant panels. Providing radiant sources provides comfort at a cooler set-point temperature. 

A roof-mounted PV system offsets building electrical loads and ensures a power supply during the 

frequent utility grid outages caused by thunderstorms. Electrical loads are controlled by a BAS that 

maintains the energy-efficient lighting system as well as the heating and cooling systems. The BAS also 

monitors energy consumption and environmental variables for demand limiting and subsequent analysis. 

Two BASs were installed at the Visitor Center Complex: one in the Visitor Center, and one in the 

Comfort Station. 

Figure 4-1 Visitor Center Complex site layout 

N

Visitor Center 

Comfort 

Station 

Fee 

Station 

Virgin River 

Outdoor 

Exhibits 

Parking 

Lot 
23 

As mentioned in Step 8 of the design process, the NPS changed the proposed building design 

substantially because of a building site change, although the major axis was still south facing. The design 

team had to rearrange the buildings at this point, maintaining as many of the original concepts as possible. 

However, there was some variation between the original design and what was constructed. Major 

changes are detailed in Table 4-1. 

Table 4-1 Differences between Proposed Design and As-Built Design 

Proposed Design As-Built Design 

Size 7,600-ft2 (706-m2

) Visitor Center 

1,560-ft2 (145-m2) Comfort Station 

8,800-ft2 (818-m2

) Visitor Center 

2,756-ft2 (256-m2

) Comfort Station 

170-ft2 (15.8-m2) Fee Station 

Heating Propane Electrical Radiant Panels 

Cooling 5 Internal Towers 

1 External Tower 

3 Internal Towers 

0 External Towers 

The new building site required that the design team alter the layout of the Visitor Center building from the 

original “L” shaped building to the new layout seen in Figure 4-2 and Figure 4-3. The bookstore size was 

increased, along with the restroom facilities. As discussed earlier, studies showed resistive heating to be 

cost competitive as long as demand charges were not incurred. The elimination of propane heat allowed 

designers to avoid allocating space for fuel storage at the facility. Finally, the number of cooltowers was 

reduced based on cost and expected performance of the cooltowers. 

Figure 4-2 As-built Zion layout and energy-efficient features 
24 

Figure 4-3 As-built Zion Visitor Center floor plan 

Adjacent to the Visitor Center is a separate 2,756-ft2 (256.0-m2) building for restrooms called the Comfort 

Station. The Comfort Station includes many features found in the Visitor Center, including a cooltower, a 

separate BAS, and daylighting (Figure 4-4.) Also included in the Visitor Center Complex is a fee station. 

This small 170-ft2

 (15.8-m2) structure is located at the entrance to the park. It is included in the building 

description section because the electric supply for this station is metered along with the rest of the facility. 

It was not part of the design analysis and was not evaluated as part of this study.

Lobby Area 

ZNHA Office 

and Storage 

ZNHA 

Sales 

Area 

NPS Exhibits 

NPS Counter 

Clerestory (above) 

Trombe wall 

NPS Offices 

and Kitchen 

Cooltower 

Cooltower

N 

Trombe walls 
25 

Figure 4-4 As-built Zion Comfort Station floor plan 

The total cost to construct the Visitor Center Complex was less than the original program planned 

building. Integration of energy features into the envelope increased total envelope cost of the buildings; 

however, the reduction of infrastructure and mechanical systems (including elimination of the mechanical 

room) reduced costs. This project demonstrates that it is possible to construct sustainable buildings at 

comparable or less than conventional building techniques. 

4.1 Building Envelope 

The building envelope acts as both the HVAC and lighting systems: window openings in the envelope 

provide daylighting, operable windows provide ventilation, and the Trombe wall provides heat to the 

building. 

The envelope of the Visitor Center includes R-7 vertically insulated footings. In addition, the first 4 ft 

(1.22 m) of slab is insulated to R-7, as shown in Figure 4-5. The walls are 6-in. (15.2 cm) steel-stud with 

expanding blown-in-place foam insulation. The exterior sheathing is 1.5-in. (3.8 cm) extruded foam for a 

total wall R-value of 16.5 hr·ft2

·°F/Btu (2.91 m2·K/W). Siding covers most of this sheathing. The roof is 

made of structural-insulated panels that are arranged to sandwich a layer of rigid foam insulation between 

sheets of oriented strand board (OSB) with an R-value of 30.9 hr·ft2

·°F/Btu (5.45 m2·K/W). This type of 

insulation results in a well-sealed building. 

N 

Cooltower 

Trombe wall 

Family Restroom 

Utility Room 

Area closed 

during winter 

Trombe wall 
26 

The Comfort Station has a similar envelope construction with exception of the walls, which are concrete 

masonry units (CMU) with insulation filled cores and 1.5 in (3.8 cm) of rigid foam on the exterior. 

Figure 4-5 Typical slab and footing insulation 

Both buildings used high thermal mass (concrete floors) to provide additional capacitance. All walls of 

the Comfort Station are composed of CMU. Some of the interior Visitor Center walls are also composed 

of CMU. Both buildings use Trombe walls on the south facade; CMUs are solid filled with concrete. 

The 8-in. (20-cm) CMUs are covered with a selective black surface on the exterior. This selective surface 

has a low emissivity and a high absorptivity. A storefront window system provides a single-glazing unit 

of patterned glass intended to obscure the black Trombe wall. 

The building envelope characteristics are detailed in Table 4-2. The only difference between this table 

and the design was in the south and east windows. These windows were designed to have a SHGC of 

0.55 using a low-e coating on surface 3. The installed windows had the coating on surface 2, which 

reduced the SHGC to 0.44. We discovered this change after the building was completed, but the installer 

was not willing to correct the error. As a design consideration, proper window testing tools should be 

provided to the construction manager to verify the performance of the glass before acceptance. 

Clerestory windows are a passive part of the lighting and HVAC systems. Computer simulations assisted 

design of the windows by providing fenestration sizing data according to daylighting requirements. 

Sunlight is able to enter in the winter and help keep the space heated. Conversely, overhangs shade the 

glass from the high sun and shield the facility from unnecessary solar gains during the summer months. 

The Visitor Center was designed to block west-facing windows from the summer sun. A tree canopy also 

contributes toward this minimization of heat gain on summer afternoons. Glass with a suspended film 

was used to achieve very low SHGCs and low U-values to make this glass less of a cooling burden on 

these facades. 

1-1/2-in. rigid insulation board 

full face of foundation footing 

and perimeter of interior slab 

Stained and sealed 

concrete floor slab 
27 

Table 4-2 Building Envelope Construction and Thermal Properties 

Envelope Component Constructions 

(outside to inside) 

R effective

hr·ft2·°F/Btu 

(m2·K/W) 

Walls 

Trombe Walls 5/32-in. low-iron patterned Trombe wall glazing, 

2.5-in. air gap, 8-in., grout-filled CMU. 

2.3 

(0.41) 

Visitor Center 

Exterior Walls 

Wood siding, 1/2-in. rigid insulation board, 

6-in. metal stud framing with foam-in-place 

insulation, 1/2-in. plywood backing, 5/8-in. Gyp 

board. 

16.5 

(2.91) 

Comfort Station Walls Wood siding, 1-1/2-in. rigid insulation board, 8-in. 

CMU with foam insulation cell inserts 

6.6 

(1.2) 

Windows/Doors 

South/East Glass 

Double-pane, 1-in. insulating glass with low-e 

coating on surface 2. Aluminum frames are 

thermally broken. SHGC = 0.441

2.3 

(0.41) 

North/West Glass Double-pane heat mirror, 1-in. insulating glass with 

thermally broken aluminum frames. SHGC = 0.37. 

2.7 

(0.48) 

Doors Non-store-front doors are insulated steel 11 

 (1.94) 

Roofs 

Typical Roof Wood shingles, 1⁄2-in. sheathing, 2-in. x 4-in. furring, 

8-1/4-in. insulated roof panels, 1 x 6-ft wood ceiling. 

30.9 

(5.45) 

Floors 

All Perimeter 

Footings 

1-1/2-in. rigid insulation, 12-in. concrete footing, 8.3 

(1.46) 

Slab 4-in. concrete floor slab. 0.44 

(0.08) 

Perimeter of Slab 1-1/2-in. rigid insulation, 6-in. slab. Horizontal 

insulation 4 ft from perimeter (See Figure 4-5) 

7.6 

(1.34) 

1 SHGC was supposed to be 0.55, but glass was not as specified. 

4.2 Lighting and Daylighting 

The primary source of light in the Visitor Center is daylight entering through clerestory windows and a 

strip of windows located high on the walls. Electric lighting provides additional light when needed. We 

selected T-8 lights for most of the main open floor areas, as shown in Figure 4-6. Most of the Visitor 

Center fixtures are 88% indirect with 11% direct (see Figure 4-7). Twenty-four zones of lights allow for 

different light levels using stepped controls. Each zone has a minimum threshold for operation as well as 

a time-delay to prevent excessive cycling. In addition, the BAS controls HID spotlights that highlight the 

Trombe wall, wall displays, and the cooltowers. The entryway of the building also uses these fixtures. 

We chose fluorescent fixtures for most of the exterior walls, as shown in the lighting plans in Figure 4-9 

and Figure 4-10. The offices, back hall, break area, storeroom, and restroom in the Visitor Center use 

fluorescent fixtures connected to motion sensor controls. The lighting power density (LPD) in the offices 

is 1.0 W/ft2

 (11 W/m2) and 0.9 W/ft2 (9.7 W/m2) in the bookstore and display areas. 

The Comfort Station uses fluorescent fixtures with T-8 lamps. Compact fluorescent cans are located in 

the entryway and over the sink area, see Figure 4-8. The Comfort Station installed LPD is 1.0 W/ft2

 (11 

W/m2

). The entire Comfort Station is split into seven zones of lights (not pictured in lighting plan), 

controlled with the BAS based on occupancy and available daylighting. Exterior lights are bollard 

fixtures each with a 26-W compact fluorescent lamp. 
28 

The exit signs are 2-W LED fixtures. Egress lighting is provided in the Visitor Center with small battery 

powered incandescent wall packs. Egress lighting in the Comfort Station uses battery back-up ballasts in 

a few of these T-8 fixtures. 

 

Figure 4-6 Display lighting using 4-ft T-8 Lamps 

 

Figure 4-7 T-8 space lighting (note the dark ceilings and minimal down lighting) 
29 

Figure 4-8 Lighting in Comfort Station 

ZN3

ZN13

ZN4 

ZN5 

ZN1 

ZN2 

ZN7 

ZN8

ZN10 

ZN12 

ZN6 

ZN# Lighting Zone

ZN9

ZN8

ZN11

ZN14

ZN15 

ZN17 

ZN16

ZN24

ZN11

Figure 4-9 Visitor Center lighting plan showing lighting zones 
30 

Figure 4-10 Comfort Station lighting plan 
31 

Table 4-3 Lighting Schedule 

Type Description Mounting # Of 

Lamps Lamp Type 

A Vandal Resistant Lensed Fluorescent Wall – Surface 2 FO32 / 35K 

B1 4-ft Fluorescent – Asymmetric Distribution Wall Mounted 1 T-8 - 32 

B2 3-ft Fluorescent – Asymmetric Distribution Wall Mount 1 T-8 - 25 

C 2-ft x 2-ft Parabolic Fluorescent Ceiling – Lay in 2 FB031 / 35K 

D Fluorescent Uplight Pendant 1 F032 / 35K 

E Keyless Porcelain Lamp Holder Ceiling – Surface 1 F13DTT/ D835 

F Compact Fluorescent Track Light Ceiling – Track 2 27W BIAX 

G Undercabinet Fluorescent Cabinet – Surface 1 FO32 / 35K 

H High Abuse Wraparound Fluorescent Ceiling – Surface 2 FO32 / 35K 

I Vandal Resistant Fluorescent Ceiling – Surface 2 FO2 / 35K 

J Compact Fluorescent Track Light Ceiling – Track 1 39W T5 

K Fluorescent Light Deck – Surface 1 FO32 / 35K 

L Lensed Wet Location Fluorescent Wallwasher Ceiling – Recessed 2 F13DTT / D835 

M Fluorescent Flood See M1, M2 & M3 1 

M1 Metal Halide Monopoint Ceiling – Surface 1 35W PAR38 

M2 Suspended Cable Fluorescent Uplight Ceiling – Pendant 1 F32 T-8 

M3 Low Voltage Mini – Floodlight Beam Surface 1 13W TFM 3DTT

X1 Finished Area Exit Light Wall – Surface Incl LED 

X2 Finished Area Emergency Light Wall – Surface 2 DS N080 

X3 Finished Area Exit Light – Pendant Wall – Pendant Incl LED 

AA Exterior Fluorescent Pathlight Ground – Surface 1 22PL120 

AB Exterior Fluorescent Uplight Structure – Surface 1 22PL120 

CC Exterior Metal Halide Downlight Ceiling Recessed 1 70MH120 

DD Exterior Fluorescent Downlight Wall – Surface 1 CF26DT / 835 

FF Exterior Compact Fluorescent Downlight Ceiling Recessed 1 13 DTT 

4.3 PV Description 

Unreliable power at the park’s remote location created a need for a building UPS system. Therefore, 

during the design process, designers anticipated the addition of a future PV system. The roof on which 

the system was to be mounted was pitched at a slope to maximize annual PV performance, as shown in 

Figure 4-11. We also included wiring conduit and roof brackets in the initial design that were installed 

during construction. Although the initial building plans did not have a central UPS system, conduit was 

installed so that it, along with a PV system, could be easily installed when funds became available. 

Just after completing the building construction, funds became available to purchase a 7.2-kW PV array 

along with the inverter system. Proper advance planning resulted in a quick installation of the PV 

modules and integration of the PV array with the building structure and electrical system. 
32 

Figure 4-11 PV panels installed on the roof at the Visitor Center

The roof-mounted, grid-tied PV system is mounted to the south roof of the Visitor Center nearly flush 

with the 4/12-pitched roof (18.4°). The array is composed of 24, 300-W modules divided equally into 

two subarrays. The subarrays are configured identically—an east array and a west array. Each subarray 

is rated for 3,600 W and consists of three parallel strings composed of four modules in series to create a 

nominal 48-V system. Figure 4-12 diagrammatically shows that one subarray charges the building UPS 

system batteries and provides electricity to other building loads. The other subarray is tied directly to the 

building electrical panel and does not function as a back-up circuit. The UPS system contains 200 Ah of 

battery capacity, enough to run the UPS for several hours without solar insolation. With a normal PV 

contribution, the system will run indefinitely during daylit hours. 

Figure 4-12 PV system configuration 

Excess power produced by the PV system is fed into the utility grid. ZNP has a net-metering agreement 

with the local utility so that it receives credit from the utility for excess power produced by the system. 

This agreement was the first net-metering agreement to be placed in the state of Utah. 
33 

4.4 Mechanical Systems 

The HVAC systems for the Visitor Center and Comfort Station have the same design strategies. The 

design simulations indicated that the Trombe walls would meet most of the heating load for both 

buildings. Originally, propane burners were specified to provide the remaining heat. However, the cost 

of propane was similar to the electricity consumption cost. Therefore, electric resistance panels were 

designed to meet the remaining load, creating an all-electric building. Each heating zone has a 

temperature sensor that corresponds to the radiant panels. 

The cooling load is met by natural ventilation and down draft evaporative cooltowers. For cooling 

purposes, the radiant panel sensors are averaged into the north part of the building and the south part of 

the building to correspond with the cooltowers. Ceiling fans are used to help circulate air. Sensors 

located on the ceiling are used to control these fans. 

4.4.1 Trombe Wall and Heating Panels 

The Trombe wall provides a significant portion of space heating. Radiation from the sun is absorbed and 

stored in the masonry wall. The collected heat is then released back into the building when the 

temperature drops later in the day. The exterior sheet of glass and a black selective coating help to reduce 

heat loss from the exterior of the Trombe wall to the environment, see Figure 4-13 and Figure 4-14. The 

temperature of the inside surface of the Trombe wall can reach over 100°F (37.8°C) in the winter. This 

warm surface provides radiant comfort to the visitors. Electrical radiant ceiling panels provide 

supplemental heat during periods of low solar resources when the Trombe wall does not meet the heating 

load. The performance of the Trombe wall can be seen in Section 6.1.2. 

Figure 4-13 Cross-section of Trombe Wall

The location of the Trombe wall footing insulation shown in Figure 4-13 is critical, as Trombe wall 

performance can be diminished due to three-dimensional heat transfer to the ground. By thermally 

8-in.Grout Filled 

CMU Wall 

Selective 

Surface

2-in. Air 

Gap

5/32-in. 

Glazing

Shotcrete 

Wall Finish

(Inside)

Cast-in-Place 

Concrete Wall 

Projections

11⁄2-in Rigid Footing 

Insulation 
34 

decoupling the footings from the ground with insulation, unnecessary heat loss is avoided and more heat 

from the Trombe wall is supplied to the building. 

The performance of Trombe walls is diminished if the wall interior is not open to the interior zones. 

Based on previous experiences with Trombe walls (Balcomb 1998), the heat delivered by a Trombe wall 

in a residence was reduced by over 40% because kitchen cabinets were placed on the interior of the wall. 

The wall design at Zion includes cast-in-place concrete projections attached to the interior of the wall. 

These projections were included to ensure bookshelves were not placed against the Trombe wall. 

The interior surface of the Zion Trombe wall was selected to maximize heat transfer to the space. Some 

interior surfacing materials, such as drywall, can reduce heat delivered by Trombe walls due to 

nonconductive air gaps in between the concrete wall and the interior surface (Balcomb 1998). A 

shotcrete wall finish was specified to provide a more continuous conductivity throughout the wall. 

Figure 4-14 Photograph of Trombe wall showing patterned glass over the Trombe 

wall, row of daylighting glass, and overhang to shade wall during the 

summer 

4.4.2 Cooling Systems 

The cooling system functions in two stages. The first stage occurs when the clerestory windows open and 

natural ventilation cools the space. When natural ventilation is inadequate, the first stage is augmented by 

using the cooltowers to further reduce indoor temperature (second stage). We designed the cooltowers to 

operate on natural convection driven by buoyancy forces and prevailing winds. The cooltowers have 

evaporative cooling pads on all four sides at the top and large operable shutters on all four sides at the 

bottom. Air is cooled by pumping water over the evaporative cooling pads. This cool, dense air “falls” 

through the tower and exits through the large openings at the bottom of the towers, as shown in 

Figure 4-15. The cool air drawn into the building by the cooltowers causes the hot air already inside the 

space to rise and exit the building through the open clerestory windows. 

There are no fans in either of the towers. The only energy required for each tower is a 1/3-hp (249-W) 

pump for water. The building’s energy management computer controls the operable clerestory windows, 

shutter doors, and pumps. The shutter doors on the exterior of the building were intended for cooling the 

patio area, but they are rarely used because the air entering the patio area dissipated quickly and was not 

effective. In addition, using the exterior doors degraded the interior performance. Figure 4-16 and 

Figure 4-17 show the installed towers from the outside and inside the building. Measured airflows from 
35 

each tower are approximately 8,000 ft3

/min (226.5 m3/min) during typical operation. This number is only 

an approximation due to measurement difficulties for very low-pressure systems. To approximate the 

supply air flow from the cooltowers, we used a velocity probe to test air velocity at several different 

locations on the exhaust air grill. 

Figure 4-15 Illustration of how the cooltowers work at the Visitor Center 

Ceiling fans, controlled by the BAS, are located in the main zone of the Visitor Center as well as the 

break room. The fans are controlled based upon zone temperatures, and help to keep air moving. We put 

small fans in the offices to provide additional circulation if needed. These fans exhaust air from the office 

and dump it into the exhibit area. During the wintertime, the cooltower doors are closed. 
36 

Figure 4-16 Natural downdraft cooltowers – exterior view 

Figure 4-17 Interior view of a cooltower showing operable shutters that allow cool air 

to enter the building through the bottom louvers 

4.5 Equipment 

Electrical loads in the building that are not directly related to heating, ventilation, air conditioning, and 

lighting are included in the equipment end use category. Electricity is supplied to the equipment loads at 

the Visitor Center from two sources. The first is a UPS circuit that allows the building to remain 
37 

operational during daylight hours when no power is available. The UPS provides power to the computer 

equipment, cash registers, window actuators, cooltower pumps, telephone switch, and BAS. The UPS 

system is integrated with the photovoltaic system discussed in Section 4.3. During power outages, the 

computer equipment, cash registers, and telephone switch are the minimum equipment required to 

continue business functions, and the window actuators and cooltower pumps ensure continued operation 

of the building cooling system. Note that the daylighting system provides sufficient light during most 

typical business hours. 

The other equipment circuit is a non-UPS plug load, which operates noncritical devices such as the hotwater heaters, exhibits, and noncritical computers. The demand for hot water is low. The only need for 

hot water in the Visitor Center is for cleaning. The need for hot water in the Comfort Station is also 

limited to cleaning; however, sinks are provided with hot water as a convenience. ZNP staff did not want 

to provide unlimited hot water that could be used for hair washing and bathing—a common event in these 

types of facilities. There are three 1.6-kW hot-water heaters in the Visitor Center Complex (one in the 

Visitor Center and two in the Comfort Station). These heaters are controlled by the BAS for limiting 

demand. 
38 

5 Whole-building Energy Evaluation 

5.1 Whole-building Evaluation Methodology 

NREL, in collaboration with NPS staff, evaluated the Visitor Center Complex from a whole-building 

perspective. The whole-building evaluation method looks at how building systems affect the energy 

performance of a building as a whole, rather than looking at how individual systems perform. The 

evaluation measured the performance of the building during typical operation (Step 10 in the low-energy 

design process). It included assessing the Visitor Center and Comfort Station measured energy 

performance from September 1, 2000 to June 1, 2003. The performance study included (1) measuring 

building end-uses, (2) evaluating lighting and daylighting systems, (3) evaluating the PV system, and (4) 

assessing occupant comfort. The building evaluation methodology used a conventional building model 

with measured weather data to calculate energy performance savings from November 2001 through 

October 2002. Performance indicators analyzed included site energy savings, source energy savings, and 

site cost energy savings. This evaluation was a crucial step in achieving and verifying the low-energy 

design goals. 

The building did not have a commissioning phase, either by an independent commissioning agent or by 

the construction management staff. The building, however, was in many ways commissioned as 

instrumentation was installed and verified. In many respects, this is part of the continuous commissioning 

process—examining actual data over a long period to continually refine the operation of the building. 

The staff at ZNP is committed to continually maintaining the building. As shown in the measured data 

evaluation timeline in Figure 5-1, a complete building energy dataset has been collected since November 

2001. Although the system first started collecting data in September of 2000, the dataset was not 

complete until November of 2001 because of problems implementing the energy meter balance. 

Additionally, problems with the data recording and collecting with the BAS resulted in unreliable and 

inconsistent data until November 2001. We addressed this problem by adding energy meters and 

automating the data collection mechanism. In addition, we downloaded the data several times a day, 

resulting in redundant data collection and unnecessary phone usage; however, it was necessary for 

reliable data. The difficult experience of using the BAS to collect energy data shows the importance of 

employing a reliable data acquisition system. The experience gained in this project indicates that a 

dedicated monitoring system should be used independent of the BAS. BAS systems are designed to 

collect information and provide control—not store information for future use. 

May-00

Jul-00

Sep-00

Nov-00

Jan-01

Mar-01

May-01

Jul-01

Sep-01

Nov-01

Jan-02

Mar-02

May-02

Jul-02

Sep-02

Nov-02

Jan-03

Mar-03

May-03

Figure 5-1 Timeline of monitoring system and postoccupancy energy evaluation 

Visitor Center 

opens 

15-min data 

collection starts 

Modeling/Analysis 

year 

Complete 15-min dataset 

with energy balance 

Cooltower

water

meters

installed
39 

5.2 Whole-building Monitoring 

5.2.1 Building Monitoring Methods 

We measured the energy use of the building during typical operation. The energy use metering procedure 

was necessary to complete Step 10 of the energy design process. The team took energy use 

measurements at a variety of end-use locations. Energy use measurements were also taken at building 

energy supply connections from the PV system and the utility company. The building’s BAS measured 

and recorded energy flows every 15 minutes from September 1, 2000 through June 1, 2003. 

The Visitor Center monitoring equipment includes watt-hour transducers that measure electricity flows to 

specific end uses and is recorded with the BAS. The location of each meter is shown in Figure 5-2, with 

meter descriptions summarized in Table 5-1. End uses are grouped into HVAC, lighting, and equipment 

loads, and are categorized by color as shown in Figure 5-2. A calculation of an energy balance around the 

utility meter was made possible by directly measuring the primary end uses in the building. This energy 

balance accounted for electricity flowing into the building and provided an opportunity to verify metering 

reliability. 

In Figure 5-2 and Table 5-1, the meters are color coded to correspond with measurement technique. The 

yellow meters represent directly measured energy using a watt-hour meter. The gray meters represent 

calculated energy, and are typically quantified by recording an on or off signal and multiplying the 

operation time by the load size based on periodic power tests. Finally, the blue meters are inferred 

through an energy balance around an electrical node. For the inferred and calculated meters, Table 5-1 

provides a description of variables necessary for the calculation process. 

We also monitored local environmental conditions. Weather variables monitored included outdoor drybulb temperature, relative humidity, wind speed and direction, and horizontal and vertical irradiance. 
40 

Utility 

Meter 

1 

Lighting 

Panel 

HVAC 

Panel 

Indoor Computer Controlled

Outdoor Computer Controlled 

Switch Controlled 

Heating Panels 

Exhaust Fans 

Ceiling Fans 

5 

4 

3 

21

20

19

18

17

16

UPS 

Panel 

PV Array 

Cooltower Pumps

Emergency Plug 14

13

11

9 10 12

Comfort 

Station 

HVAC 

Panel Cooltower Pumps 

Exhaust Fans 

Computer Controlled Lights

Plug 

Heating Panels 

7 

6 

2 

8 

23

22

15

24 

Fee 

Station 

Fee 

Station Measured Meter 

Calculated Meter 

Inferred Meter 

Energy Flow Measured 

in Direction of Arrow 

HVAC Loads 

Lighting Loads 

Equipment Loads

Plug Panel 

Hot Water 

25 

Hot Water 

26 

Figure 5-2 One-line electrical system plan and data acquisition meter locations 
41 

Table 5-1 Energy Monitoring Sensor Descriptions 

Meter Loads Measured Type of Measurement 

1 Total Loads UPL utility meter (pulse output to BAS) 

2 Total Comfort Station Loads Measured directly 

3 Visitor Center Light Loads Measured directly 

4 Visitor Center HVAC Loads Measured directly 

5 Visitor Center Plug Loads Measured directly 

6 Comfort Station Light Loads Measured directly 

7 Comfort Station HVAC Loads Measured directly 

8 Comfort Station Plug Loads Total CS loads minus light and HVAC loads 

[2 – (6 + 7)] 

9 Energy to Grid Measured directly 

10 Energy from Grid Measured directly 

11 PV Production Total Panel E loads minus net energy from grid 

[12 – (10 – 9)]. Includes inverter/battery losses. 

12 Panel E Total Loads Measured directly 

13 Visitor Center Cooltower Pump Load Power required to run two 1/3-hp. motors 

14 Panel E Plug Loads Total to pump and plug minus pump load (12-13) 

15 Comfort Station Heating Loads Calculated by the BAS based on how long the 

panels are on. 

16 Visitor Center Indoor Computer 

Controlled Lights 

BAS multiplies number of lights that are on by 

the wattage for each light 

17 Visitor Center Outdoor Computer 

Controlled Lights 

BAS multiplies number of lights that are on by 

the wattage for each light 

18 Visitor Center Switched or Motion 

Activated Lights 

Total Visitor Center light load minus indoor and 

outdoor lights [3 – (16 + 17)] 

19 Heating Panels BAS multiplies number of heating panels that are 

on by the wattage for each panel 

20 Exhaust Fans BAS multiplies the wattage of the two exhaust 

fans by the fans’ run time 

21 Ceiling Fans Total Visitor Center HVAC minus heating panel 

load and vent fan load [4 – (19 +20)] 

22 Comfort Station Cooltower Pump Load BAS multiplies the power of a 1/3-hp pump by 

the pump’s run time. 

23 Comfort Station Exhaust Fan Energy required to run the exhaust fan. (7-22). 

24 Fee Station Measured directly 

25 Comfort Station Domestic Hot Water Measured directly 

26 Visitor Center Domestic Hot Water Measured directly 

5.2.2 Monitoring System 

We configured the BAS with the input points listed in Table 5-2. The table indicates the type of input 

point, the name and location of the point in the BAS, and whether the point is used for control. Some 

points were planned for the system and were not used directly for control. In some cases, the points were 

used for monitoring. In other cases, they were not used. Table 5-3 shows the expected accuracy by 

sensor type based on the manufacturer’s literature for the sensors. 
42 

Table 5-2 Input Points for BAS and Data Collection 

Sensor Type 

Location 

BAS Control Point 

Name

BAS Input 

Location Used? 

Temperatures (RTD) 

VC Zone 2 VC_ZN2_TEMP STAT No 

VC Zone 4 VC_ZN4_TEMP 1.IP4 No 

VC Zone 5 VC_ZN5_TEMP 1.IP5 No 

VC Zone 6 VC_ZN6_TEMP 1.IP6 Yes 

VC Zone 7 VC_ZN7_TEMP STAT No 

VC Zone 8 VC_ZN8_TEMP 1.IP7 Yes 

VC Zone 9 VC_ZN9_TEMP 1.IP8 Yes 

VC Zone 10 VC_ZN10_TEMP 1.IP9 Yes 

VC Zone 11 VC_ZN11_TEMP 1.IP10 No 

VC Zone 12 VC_ZN12_TEMP 1.IP11 No 

VC Zone 13 VC_ZN13_TEMP 1.IP12 No 

VC Zone 14 VC_ZN14_TEMP 1.IP13 No 

VC Zone 15 VC_ZN15_TEMP 1.IP14 No 

CS Zone 1 CS_ZN1_TEMP 2.IP4 Yes 

CS Zone 2 CS_ZN2_TEMP 2.IP5 Yes 

CS Zone 3 CS_ZN3_TEMP 2.IP6 Yes 

CS Zone 4 CS_ZN4_TEMP 2.IP7 Yes 

CS Zone 5 CS_ZN5_TEMP 2.IP8 Yes 

CS Zone 6 CS_ZN6_TEMP 2.IP9 Yes 

North Cooltower VC_N_TWR_TEMP 1.IP3 Yes 

South Cooltower VC_S_TWR_TEMP 1.IP36 Yes 

Outdoor Weather Information 

Wind Speed VC_WIND_SPEED 1.IP19 Yes 

Wind Direction VC_WIND_DIR 1.IP20 Yes 

Vertical Solar Insolation VC_SOLAR_VERT 1.IP21 No 

Horizontal Solar Insolation VC_SOLAR_HORIZ 1.IP22 Yes 

Outdoor Temperature VC_TEMP_OUTDOOR 1.IP23 Yes 

Outdoor Relative Humidity VC_RH_OUT 1.IP24 No 

Lighting 

VC NPS Light Level VC_NPS_LT_LVL 1.IP17 Yes 

VC ZNHA Light Level VC_ZNHA_LT_LVL 1.IP18 Yes 

CS Light Level CS_LT_LVL 2.IP10 No 

End Uses 

VC Utah Power and Lights 

Power VC_UPL_POWER 1.PP1 No 

VC Utah Power and Lights 

Energy VCMTR_UPL IC1.6 No 

VC HVAC Energy VCMTR_HVAC IC1.2 No 

VC Heat Energy VCMTR_HEAT 1.GV157 No 
43 

Sensor Type 

Location 

BAS Control Point 

Name

BAS Input 

Location Used? 

VC Hot-Water Energy VCMTR_HOTWAT 1.GV46 No 

VC Light Energy VCMTR_LIGHT IC1.1 No 

VC Computer Controlled 

Light Energy VCMTR_LGTI 1.GV161 No 

VC Outdoor Light Energy VCMTR_LGTO 1.GV164 No 

VC Panel E Energy VCMTR_E IC1.7 No 

VC Plug Energy VCMTR_PLUG 1.GV58 No 

VC Pump Energy VCMTR_PUMP 1.GV136 No 

PV into Building VCMTR_PV IC1.4 No 

PV to Grid VCMTR_PV_B IC1.5 No 

CS Total Energy CSMTR_GEN IC1.3 No 

CS HVAC Energy CSMTR_HVAC 2.IP2 No 

CS Heat Energy CSMTR_HEAT 2.GV170 No 

CS Hot Water #1 CSMTR_DHW1 2.GV30 No 

CS Hot Water #2 CSMTR_DHW2 2.GV31 No 

CS Light Energy CSMTR_LTS 2.IP1 No 

CS Plug Energy CSMTR_PLUG 2.GV100 No 

Fee Station Energy VCMTR_FEE IC1.8 No 

Water 

Water into North Cooltower VC_N_WTR_MTR_1 1.IP1 No 

Water out of North 

Cooltower VC_N_WTR_MTR_2 1.IP2 No 

Water into South 

Cooltower VC_S_WTR_MTR_1 1.IP34 No 

Water out of South 

Cooltower VC_S_WTR_MTR_2 1.IP35 No 

Table 5-3 Expected Accuracy of Sensors 

Data Type Recorded Type of Sensor Used Accuracy 

Temperature (°F) Thermister ± 0.36% 

Relative Humidity (%) Capacitor ± 3% 

Amperage (Amp) Current transformer ± 2% 

Energy (Wh) Watt-hour transducer ± 0.5% 

Water Flow (gal/min) Turbine pulse meter ± 1.5% 

Luminance levels (fc) Blue enhanced photo diode ± 1% 

We configured the monitoring system to allow for redundancy. The energy consumption from the main 

utility meter was compared to the sum of all the other end-use meters. See Figure 5-2 for the meter 

configuration. If the differences of these two values were large, then the meters were unbalanced and the 

data was faulty; however, the energy balance of the installed meters compared very closely to the 

installed utility meter, as shown in Figure 5-3. This figure is an X-Y plot of the Visitor Center Complex 

hourly utility meter versus the hourly sum of the end-use meters from November 2001 to February 2003. 

The comparison of the two meters yielded a 1.4% error, with a linear correlation of nearly one. The 

utility meters at Zion are rated to be accurate to 0.5% of full-scale. Assuming the meters have the same 
44 

scale, then the total error possible of the data is 1.51%. We considered this error reasonable and the data 

was considered reliable. 

y = 1.0143x

R2

 = 0.9992

0

5

10

15

20

25

30

35

0 5 10 15 20 25 30 35

Utility Meter Hourly Average Use (kW)

Sum of End Use Meters Hourly Average Use (kW)

Figure 5-3 Verification of utility and measured data, November 2001 to February 

2003 

We determined three whole-building energy performance metrics: annual energy cost savings, site energy 

savings, and source energy savings. We then compared the simulated base-case energy consumption and 

the measured energy consumption to determine the performance and percentage savings of the building. 

From the design phase, the original weather data used for the simulations was for Cedar City, UT, located 

approximately 60 miles from the Zion site. This weather file represented the closest meteorological site 

compared with Zion. Altitude differences and the canyon effects result in measurable meteorological 

differences between Cedar City and the Zion site. The temperatures at the Visitor Center Complex during 

the first two years of measured data were much warmer than the TMY2 data for Cedar City, as shown in 

Table 5-4 and Figure 5-4. The base case was resimulated using a measured weather file collected at the 

Visitor Center (November 2001 through October 2002). 

Table 5-4 Heating and Cooling Degree Days for Cedar City and Zion 

HDD 

(65°F/18°C) 

CDD 

(75°F/24°C) 

Cedar City 6,055 65 

Zion Measured 3,435 961 
45 

-20

0

20

40

60

80

100

120

NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP OCT

Outdoor Monthly Average, Minimum, 

and Maximum Temperature (°F)

ZION Measured 2001-02 AVG. TEMP

Cedar City TMY2 AVG. TEMP

`

Figure 5-4 Comparison of average monthly outdoor temperatures for ZNP Complex 

and Cedar City 

The initial energy savings due to the low-energy design were based on simulations using the Cedar City 

weather file. Therefore, we designed the heating and cooling systems based on the cooler Cedar City 

weather. Because of the cooler weather file, the designers felt the design used too many cooltowers; 

designers removed one of the three original towers in the as-built building, which contributed to some of 

the cooling problems that will be discussed later. According to step 1 of the low-energy design process, 

the design team needs to develop a thorough understanding of the local weather patterns. Although the 

general patterns of weather were well understood, the magnitude of the climate differences was 

underestimated, resulting in the undersizing of the cooling systems. Reducing the total cooling capacity, 

combined with additional differences in the proposed design and the as-built design, led to some of the 

measured summer comfort problems. 
46 

5.2.3 Measured Data Analysis 

The measured energy consumption and production from November 2001 through May 2003 is shown in 

Figure 5-5. From November 2001 through October 2002, the annual energy use of the Visitor Center 

Complex was 92,876 kWh, at a site energy intensity of 27.0 kBtu/ft2

·yr (306 MJ/m2·yr). The PV system 

produced 7,860 kWh and met 8.5% of the total site load. PV production reduced the net site consumption 

intensity to 24.7 kBtu/ft2

·yr (281 MJ/m2·yr). From June 2002 through May 2003, the site energy intensity 

was 23.8 kBtu/ft2

·yr (270 MJ/m2·yr), with PV production meeting 9% of the total building energy 

requirements. The net energy use from June 2002 through May 2003 was 21.6 kBtu/ft2

·yr (245 

MJ/m2

·yr). The measured site consumption intensity is significantly better than the previously 

documented ENERGY STAR or top CBECS buildings, and it is comparable to other high-performance 

buildings, as previously discussed in Section 2. 

The energy consumption intensity during the evaluation period decreased during the evaluation period 

from 27.0 kBtu/ft2

·yr (306 MJ/m2·yr) to 23.8 kBtu/ft2·yr (270 MJ/m2·yr). A primary reason for the 

reduced site energy use was a reduction in heating energy from the winter of 2001–2002 to 2002–2003. 

As discussed in Section 6.1.2, the occupants reduced the heating set point of the Visitor Center by 2–4°F 

(1.1–2.2°C) during the winter of 2002–2003. This set-point reduction, combined with a warmer 2002–

2003 winter, helped to reduce the overall heating system consumption and improve the whole-building 

site energy performance, as Figure 5-5 shows. 

0

50

100

150

200

250

300

350

400

450

Nov-01Dec-01

Jan-02

Feb-02

Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Nov-02Dec-02

Jan-03

Feb-03

Mar-03

Apr-03

May-03

Daily Average Monthly Consumption and Production 

 (kWh/day)

PV Production Site Plug Loads

Site Lighting Site Heating

Site Cooling Site Fans

Site DHW Fee Station

Figure 5-5 End use daily average monthly consumption, November 2001 through 

May 2003 

Figure 5-6 shows the energy consumption distribution by end use from November 2001 through October 

2002. The monthly and annual end-use distribution data is shown in Appendix C. The minimal energy 

consumption of the Comfort Station results in only 15% of the total site energy consumption, at an energy 

intensity of 17.4 kBtu/ft2

·yr (198 MJ/m2·yr). The Visitor Center heating is the largest single energy end 

use, with Visitor Center plug loads and BAS controlled lighting the next most energy intensive loads. 
47 

Visitor Center Heating

Fee Station

Ceiling and Exhaust Fans

Comfort Station Cooling

Comfort Station Plug Loads

Visitor Center Domestic Hot 

Water Comfort Station Domestic 

Hot Water

Visitor Center Plug Loads

Outdoor 

Comfort Station Visitor Center Switch 

Controlled

Visitor Center Computer 

Controlled

Visitor Center Cooling

Comfort Station Heating

Figure 5-6 Energy consumption by end use, November 2001 through October 2002 

The Fee station used 4,632 kWh of electricity annually, or 5% of the total site use, which included an 

electric heater, lighting, and equipment. The fee station is included in the site analysis because the energy 

to this building is supplied through the Visitor Center utility meter. 

The total annual energy use for the Visitor Center building, not including the Comfort Station, Fee 

Station, or outdoor parking lot lights, is 71,399 kWh, which results in a building energy use intensity of 

27.7 kBtu/ft2

·yr (315 MJ/m2·yr). The energy use and energy intensities for each building in the Visitor 

Center Complex are shown in Table 5-5. A comparison to other buildings is presented in the Executive 

Summary. 

Table 5-5 Energy Use and Intensity for Each Building, Nov. 2001 to Oct. 2002 

Energy Use 

kWh/Year

Energy Intensity 

kBtu/ft2·yr 

(MJ/m2·yr) 

Visitor Center 71,399 27.7 

(315) 

Comfort Station 14,228 17.6 

(200) 

Total Complex (Including Fee 

Station and Outdoor Lighting) 92,876 27.0 

(307) 

5.2.3.1 Demand and Energy Cost Analysis 

The easiest method to reduce energy cost in a commercial building is to reduce the peak demand. As seen 

in Figure 5-13, the demand cost can contribute more than 50% of the total costs. An efficient building 

that uses very little energy could still have large demand charges with poor control. In the attempt to 

minimize the demand costs at ZNP, the evaluation team analyzed all the loads of the building and 

determined typical use trends. Once the end uses that typically contributed to peak demands were 

identified, the researchers determined which loads could potentially be shifted until a peak had passed. 

Equipment/

Other

33%

HVAC

36%

Lighting

31%
48 

The need for demand limiting controls can be seen in Figure 5-7. The cost associated with demand can be 

found by taking the maximum power draw over a 15-minute window multiplied by the $8.10/kW demand 

charge. The peak demand for the winter of 2001–2002 was between 28 and 36 kW, with a typical peak 

demand day shown in Figure 5-7. The reason the winter peak demand occurred was that all end uses 

were on at the same time, including the hot water, lighting, and some heating. Although the key 

contributor to the increase in peak demand was the turning on of lights in the morning, the heat was also 

on, partially because of the recovery from night set back. In Figure 5-7, the hot water, lighting, and 

heating were at a maximum for the day during the demand peak. These types of loads offer the most 

potential for limiting the peak demand because they are not considered essential for short-term operation 

of the building. Hot water and heating systems can be temporarily turned off during potential periods of 

peak demand. These loads are not considered essential for short-term operation because these systems 

use the thermal capacitance of the tank water or the building mass, respectively. The capacitance enables 

these end uses to be turned off near peak demand periods without significant disruption to the operation 

of the building. The building thermal capacitance, in the form of massive concrete, is integral to the 

energy cost savings of the building. During periods of low demand, the hot water and heating systems are 

turned on. The nighttime heating is only used if the building can be brought back up to a comfortable 

temperature without incurring a demand charge. This type of control strategy can also take advantage of 

on-site generation for potential demand reduction by offsetting the utility power draw with on-site 

generation. 

-5

0

5

10

15

20

25

30

35

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

0:00

End Use, Purchased, and PV Production (kW)

Net Used

Total PV

Total HVAC

Total Equipment

Total Lighting

Hot-Water Heaters

Figure 5-7 Peak demand day without demand limiting controls, February 2, 2002 

We implemented the demand limiting controls at ZNP for the winter of 2002–2003 by continuously 

monitoring total power input to the building from the utility. Demand limiting is accomplished by 

continuously adjusting the heating set point of the Visitor Center based on the measured building demand. 

The BAS has the ability to reduce the temperature set point by 0.2°F (0.11°C) every 20 seconds when the 

demand is near the monthly peak demand. The maximum set point reduction is 10°F. For example, if the 

occupants have controlled the heating set point to 72°F (22°C), then the BAS can temporarily adjust the 

actual set point from 62–72°F (17–22°C). To determine how much the set point is reduced, the BAS 
49 

examines the instantaneous peak and the 10-minute average peak. If the instantaneous demand is greater 

than 90% of the previous instantaneous demand, then the heating set point is decreased by 0.1°F (0.06°C). 

If the instantaneous demand is not greater than 90% of the previous day peak demand, then the heating set 

point is not adjusted. Similarly, if the 10-minute demand is greater than 90% of the 10-minute peak 

demand, then the set point is decreased by another 0.1°F (0.06°C). If the 10-minute demand is less than 

90%, then the heating set point is increased by 0.1°F (0.06°C) until it reaches the unadjusted set point. 

The BAS checks the instantaneous demand every 20 seconds and adjusts the heating set point when 

needed. Both the weekly 10-minute peak and the instantaneous peak are reset every Sunday morning to 

70% of the previous week’s maximum. 

The Comfort Station does not use an adjustable set point to control the temperature. During the winter, 

the building is heated to 50°F (10°C), and during the summer, it is cooled to a minimum of 75°F (24°C). 

In the winter of 2003–2004, this was changed to use the same set point reduction as the main building. 

The domestic hot-water (DHW) units in both the Visitor Center and Comfort Station have demand 

limiting controls. The DHW is disabled if the instantaneous building demand exceeds the weekly 10-

minute peak demand. These units will remain off for a minimum of 8 minutes in an attempt to shift the 

load. If the building demand is less than the weekly peak demand, then the DHW units are enabled. The 

DHW is mainly used for cleaning and is usually needed early in the morning. The hot water is not 

considered essential to the normal operation of the building. Before demand limiting, the cleaning crew 

would empty the hot-water heater for cleaning, causing a spike in the usage early in the morning when the 

system tried to recover—just as other loads were also peaking. The strategy shifts the hot-water recover 

to a more advantageous time based on the demand and rate structure. 

Figure 5-8 shows the energy consumption of a typical heating day after demand responsive controls were 

implemented. Similar heating days during the winter of 2001–2002 and 2002–2003 were considered to 

compare the differences between the building without responsive controls (Figure 5-7) and the building 

with responsive controls (Figure 5-8). Figure 5-8 illustrates the demand limiting control strategy. Most 

noteworthy is that when the lights came on in the morning, the heating was reduced to maintain a flat 

profile. Heating consumption was decreased until daylighting reduced the electrical lighting loads and 

the PV system provided sufficient energy to limit demand. The total energy used for heating in 

Figure 5-7 was 233.7 kWh/day. The total heating energy with demand limiting controls (Figure 5-8) was 

similar at 232.7 kWh/day. The values are similar because the morning heating load was shifted to a 

period when the heating system would not incur a peak demand. This shows an effective application of 

demand limiting because the building still used the same energy but over a longer period; the controls 

were effective because the peak was reduced significantly. In addition, the typical 1.5-kW DHW load in 

the morning was also shifted to later in the day. A potential for underheating exists when the demand 

responsive controls reduce the heating set point. Zone temperature fluctuations were reduced during the 

load-shedding period by not setting back the nighttime set point, which allows for increased heat storage 

in the building thermal capacitance during periods of low demand. Again, the equipment and lighting 

loads could not be shifted or limited because they are necessary for building operation. 
50 

-5

0

5

10

15

20

25

30

35

40

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

End Use, Purchased, and PV Production (kW)

Net Used

Total PV

Total HVAC

Total Equipment

Total Lighting

Hot Water Heaters

Figure 5-8 Typical heating profile with demand limiting controls, February 8, 2003 

Figure 5-9 shows the differences of the average monthly winter site purchased electricity use over the 

winter of 2001–2002 (December 2001–March 2002) and the winter of 2002–2003 (December 2002–

March 2003). The graph shows that during the winter of 2001–2002, the building used much more 

energy with a higher average peak, whereas during the winter of 2002–2003, it used much less energy 

with a lower average peak. The average heating profile shows the strategy of demand limiting controls. 

On average, the BAS limits the consumption of the electric heating and the DHW systems in the morning 

(during typical peak lighting consumption) and shifts the heating load to the afternoon (when PV 

production and daylighting are available) and nights (during typical minimum site consumption). The 

average daily heating profile was higher in the winter of 2001–2002 because the occupant controlled set 

point was 2–4°F (1.1–2.2°C) higher than the winter of 2002–2003. The domestic hot-water load without 

controls is lumped in the morning. With the controls, the recovery is spread throughout the day. 
51 

0

5

10

15

20

25

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Time of Day (hr)

Average Consumption and Production (kW)

Winter 2001-2002 Site Purchased

Winter 2002-2003 Site Purchased

Winter 2001-2002 Heating

Winter 2002-2003 Heating

Winter 2001-2002 PV

Winter 2002-2003 PV

Winter 2001-2002 DHW

Winter 2002-2003 DHW

Figure 5-9 Average daily site energy purchased for heating, cooling, and hot water 

and PV production, Winter 2001–2002 compared to Winter 2002–2003 

We computed the energy demand for each month from November 2001 through May 2003, as seen in 

Figure 5-10. Table 5-7 shows the number of hours the building was at certain power consumption ranges 

for each month from November 2001 through May 2003. The table also calculated the load fraction for 

the demand, which is defined as the average power consumption over the month divided by the peak 

demand over the month. We considered the demand controls effective if the load fraction was greater 

than 40%, which occurred most of the time. 

The demands typically occurred during the morning when the building was first occupied. In all the 

cases, the PV production during the time of peak demand was minimal (see Table 5-6); therefore, the PV 

could not help reduce the overall demand and related costs. 
52 

Fri - 01/04/2002 08:30

Thu - 04/24/2003 07:45

Mon - 04/07/2003 08:45

Sat - 03/01/2003 15:15

Sat - 02/08/2003 20:00

Tue - 12/24/2002 09:00

Sun - 12/22/2002 06:15

Sat - 11/16/2002 07:00

Wed - 10/02/2002 15:00

Fri - 09/06/2002 14:45

Mon - 07/15/2002 08:00

Sun - 08/04/2002 08:00

Sun - 06/16/2002 08:00

Thu - 05/02/2002 08:15

Mon - 04/22/2002 06:45

Fri - 02/01/2002 07:30

Sun - 03/17/2002 06:30

Wed - 12/05/2001 08:30

Wed - 11/14/2001 06:45

0

5

10

15

20

25

30

35

40

45

50

Nov-01Dec-01

Jan-02

Feb-02

Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Nov-02Dec-02

Jan-03

Feb-03

Mar-03

Apr-03

May-03

Peak Demand (kW)

DHW

Lighting

Plug Loads

Fans

Cooling

Heating

All peaks occurred during

minimal PV production.

Figure 5-10 Visitor Center and Comfort Station peak demand analysis and time of 

occurrence for each month 

Table 5-6 PV Contribution during Peak Demands 

Month PV 

(W) 

Nov-01 0 

Dec-01 0 

Jan-02 58 

Feb-02 170 

Mar-02 180 

Apr-02 0 

May-02 0 

Jun-02 220 

Jul-02 0 

Aug-02 0 

Sep-02 0 

Oct-02 130 

Nov-02 0 

Dec-02 0 

Jan-03 340 

Feb-03 0 

Mar-03 0 

Apr-03 210 

May-03 320 
53 

Table 5-7 Information on Demand Occurrences and Reasonability 

Number of Hours at kW Demand 

Month 

Peak 

Demand 

(kW)1

Time of Peak 

Demand 

< 10

10 to 

12 

12 to 

14 

14 to 

16 

16 to 

18 

18 to 

20 

20 to 

22 

22 to 

24 

24 to 

26 

26 to 

28 

28 to 

30 

30 to 

32 

Nov-01 14.6 11/14/2001 6:45 532 89 12 3 

Dec-01 28.8 12/5/2001 8:30 324 11 10 22 30 118 77 48 46 34 4 

Jan-02 36.1 1/4/2002 8:30 98 14 14 67 179 230 58 6 5 18 1 

Feb-02 33.4 2/1/2002 7:30 253 9 6 11 132 128 44 13 23 19 9 6 Mar-02 34.4 3/17/2002 6:30 377 7 9 16 110 34 22 24 24 19 4 3 

Apr-02 27.5 4/22/2002 6:45 588 56 13 3 7 14 9 7 10 5 

May-02 26.1 5/2/2002 8:15 587 48 7 1 1 2 1 2 1 1 

Jun-02 12.1 6/16/2002 8:00 609 89 1 

Jul-02 15.0 7/15/2002 8:00 553 117 55 15 

Aug-02 15.1 8/4/2002 8:00 514 113 83 13 

Sep-02 14.1 9/6/2002 14:45 555 133 58 1 

Oct-02 15.3 10/2/2002 15:00 393 267 34 4 

Nov-02 18.6 11/16/2002 7:00 426 243 23 7 8 3 

Dec-02 27.1 12/22/2002 6:15 434 53 18 23 11 19 14 12 4 2 

Jan-03 27.9 12/24/2002 9:00 296 107 41 49 69 53 26 20 12 4 

Feb-03 15.2 2/8/2003 20:00 423 152 46 30 Mar-03 17.4 3/1/2003 15:15 310 120 141 52 21 

Apr-03 29.3 4/7/2003 8:45 629 90 56 16 8 2 1 1 1 1 

May-03 14.6 4/24/2003 7:45 546 89 8 2 

1Peak times represent end of a 15-minute interval
54 

Although the demand responsive controls typically worked, all that is required for a peak demand charge 

is a 15-minute window when the controls fail to limit the demand. During 2003, the demand was slightly 

lower overall, with several months much lower. During the swing season in 2002 (March through May), 

the load fractions were low, which denotes poor controls. During the same period for 2003, the load 

fractions were reasonable. The controls strategies changed by continually monitoring the power 

consumption in the building and preventing new peaks unless necessary. 

For the months of December 2002 and January 2003, the controls worked overall, as is shown by the 

average load profile in Figure 5-9, but failed a few times, resulting in high demand charges. Reasons for 

this failure are partially due to problems with BAS implementing the controls. Demand responsive 

software was difficult to implement due to limited BAS programming flexibility. A BAS system failure 

occurred during the month of April 2003 and variables were reset to defaults. As a result, the demand for 

April 2003 was much higher because all the controls for limiting DHW and heating were unavailable 

during the failure period. 

The peak demand in April 2003 was a result of BAS operation without any demand responsive control. 

The evaluators expect the peak demands for February and March 2003 without demand responsive 

controls would have been similar to, if not greater than, the 29-kW peak demand of April 2003. This 

suggests that the demand responsive controls reduced the peak demands in February and March 2003 by 

at least 38%. 

In general, by identifying short-term, nonessential end uses that contribute to peak demand charges, we 

developed a control strategy to shift these loads to significantly reduce demand charges. Understanding 

the optimal demand controls involves studying precooling/preheating techniques to charge the thermal 

mass of the building during off-peak hours. Using forecasted weather could potentially increase the 

demand savings by optimizing the nighttime setup/setback control strategies. For the ZNP case, a stable 

BAS and control strategy are necessary to realize these potential savings. It is essential that demand 

management systems be robust to prevent unnecessary utility charges. Analysis of peak demands at ZNP 

over the last two winters has shown that a 38% peak demand reduction is possible with successful 

demand responsive controls. If the demand responsive controls had been successful at shifting the 

demand for the entire winter of 2002–2003, the annual demand costs would have been reduced an 

additional $350, or 18% of the total demand charges. Although it is straightforward to estimate potential 

demand savings due to responsive controls, a variable time step, whole-building simulation (including PV 

simulation capabilities) is needed to determine the site consumption costs associated with demand 

responsive control strategies. Table 5.7 shows where there is room for improvement. Months with only a 

few hours at the peak demand indicate that additional peak shedding is possible. 

5.3 Development of Energy Models 

The whole-building evaluation also includes modeling conventional buildings to calculate energy savings 

for typical weather years. A conventional building, or base case, was modeled to provide an energy 

benchmark. The base case was simulated using measured weather, and then compared to measured site 

use, source use, and utility bills. Performance indicators analyzed include site energy savings, source 

energy savings, and site cost energy savings. The flow chart in Figure 5-11 shows how the measured data 

was used in the models and the process used to obtain the simulation results. 
55 

Measured Data Models Measured Results

Simulated Results Percent Savings

Site End Uses

Site Weather Base-case Model with 

Site Weather

Measured Site Use

Measured 

Source Use

Measured Net 

Site Use

Base-case Energy Costs 

Base-case Site Use

Source Use Savings

Site Use Savings

Energy Costs Savings

Extract Equipment 

Loads and Schedules

PV Production Measured PV Production

Utility Bills Monthly Energy Costs

Base-case Source Use

Figure 5-11 Whole-building evaluation flowchart: as-built building and base-case 

model 

5.3.1 DOE-2 Building Simulation Tool 

DOE-2 is a whole-building simulation program that can calculate hourly building heating and cooling 

loads, simulate the operation of primary and secondary HVAC systems, calculate lighting and equipment 

consumption, and perform economic analysis (Winkelmann et al. 1993). The primary inputs required for 

DOE-2 to calculate the design and hourly space loads include building location and weather files; 

constructions for fenestration, walls, roof, and floors; the geometry, size and orientation of the building; 

and internal loads such as occupancy, lighting, and equipment. Characteristics, configurations, and 

controls of the HVAC components for the primary HVAC systems make up the input. The outputs from 

the simulation include a large list of hourly, monthly, and annual verification and summary reports. The 

validity and consistency of DOE-2 has been extensively researched and reported (Pasqualetto 1997). 

5.3.2 Development of the Base-Case Model 

Computer simulations were used to help design the building and provide a base-case benchmark to 

measure energy savings. We modeled the initial base case based on the proposed design as discussed in 

Section 3.2.6. As previously discussed and shown in Table 4-1, the as-built design differed from the 

initial proposed design. To provide a better comparison for evaluating energy savings, the evaluators 

reworked the base-case DOE-2 model derived from as-built characteristics. 

The second base-case model included the initial base-case characteristics as described in Table 3-1 with 

updated as-built characteristics. We modeled the new base-case floor area with an 11,726-ft2

 (1,089-m2) 

square floor plan with solar neutral fenestration. The proposed base-case model only included the Visitor 

Center, while the new base-case model included the Visitor Center and the Comfort Station. The new 

base-case model will be referred to as the base-case model for the remainder of the document. We 

modeled the base-case heating and cooling systems with an electric air-source heat pump and 

supplemental electric resistive heat instead of a propane furnace to be consistent with the fuel that was 

actually approved for availability at the site. We modeled the heating and cooling efficiencies with a 

COP of 2.0 for heating mode and a COP of 3.0 for cooling mode (as specified by 10 CFR 435 and 

ASHRAE 90.1-1989). We modeled heating and cooling set points based on the actual set points. The 

lighting power densities were modeled as 2.2 W/ft2

 (24 W/m2) in the retail and display zones (16.1 kW 

total), 1.4 (15 W/m2

) in the office zones (2.2 kW total), and 1.0 (11 W/m2) for the restroom zones (2.7 kW 
56 

total). For this model, the lights are assumed to be on during occupied hours, as no daylighting or 

occupancy sensors are included in the base case. We modeled occupied hours based on the occupancy 

schedule of 6 a.m. to 7 p.m. in the summer and 6 a.m. to 5 p.m. in the winter. 

To calculate energy costs, the actual utility rate structure was applied to the base-case model. The 

modeled utility rate structure included a consumption charge of $.0277/kWh, a monthly demand charge of 

$8.1/kW, a $15.00 fixed monthly charge, and a small variable rate adjustment charge. 

Table 5-8 As-Built Design and Base-Case Comparisons 

Item Base-Case Model As-Built Building 

Size - ft2 (m2) 11,726 (1089.4) 11,726 (1089.4) 

Heating System Electric Heat Pump Electric Radiant Panels and 

Trombe Wall 

Wall R-Value - ft2⋅°F⋅hr/Btu (m2·K/W) 13.9 (2.45) 2.3 (0.40) (Trombe Wall) 

16.5 (2.91) (Standard Wall) 

Window R-Value - ft2⋅°F⋅hr/Btu (m2·K/W) 1.73 (0.30) 2.3 (0.41) (South and East) 

3.85 (0.678) (North and West) 

Window to Wall Area 28% 28% 

Floor Perimeter Insulation (48 in vertical 

foundation insulation) R-Value - ft2

⋅°F⋅hr/Btu 

(m2·K/W)

4 (0.7) 11.3 (1.99) 

Roof R-Value - ft2⋅°F⋅hr/Btu (m2·K/W) 22.7 (4.00) 30.9 (5.44) 

Infiltration (ACH) 0.3 Unknown (Not Measured) 

Equipment Load - W/ft2 (W/m2) 0.75 (0.13) 0.75 (0.13) 

Daylighting No Yes, clerestories; photo 

sensors controls 

Overhangs No Yes 

Demand Limiting Controls No Yes 

Lighting Levels W/ft2I(W/m2)

Office Space 1.4 (15) 0.96 (10) 

Retail and Display Space 2.2 (24) 0.90 (9.7) 

Restrooms 1.0 (11) 1.0 (11) 

Outdoor and Parking Lot (W) 400 400 

Ideally, the base-case site energy use, source energy use, and energy costs would be compared to an asbuilt model to calculate savings for a typical weather year. In this case, an as-built model of the Zion 

Visitor Center and Comfort Station was beyond the scope of this analysis due to limitations in the wholebuilding simulation tools. These limitations include nonexistent building integrated modeling techniques 

for the energy use and cooling capacity of cooltowers, difficulties modeling the as-built operation of 

subhourly demand limiting controls with integrated PV production, and uncertainties with Trombe wall 

thermal models. We attempted to account for the inherent uncertainty involved in comparing measured 

data to a simulation by calibrating the base-case model with measured weather data, measured equipment 

loads, and operation schedules. We calibrated the base-case model with measured weather data from 

November 2001 through October 2002. This modeling procedure accounted for the actual weather 

conditions in the prediction of base-case performance, allowing for a better comparison of the measured 

energy performance over this simulation period. Actual equipment loads and operation schedules were 

extracted from the measured data and modeled in the calibrated base-case as well. 
57 

5.4 Whole-Building Energy Performance Results 

Whole-building evaluation results included in this section are energy cost savings, site energy savings, 

and source energy savings. Further results presented in Section 6 include Trombe wall performance, 

cooling tower performance, comfort levels, daylighting and lighting results, and PV system performance. 

Evaluation of these issues outline explicit mistakes made during the application of the 10-step low-energy 

design process and the consequential affects that detracted from measured energy performance. 

5.4.1 Energy Cost Analysis 

The Visitor Center Complex was designed to minimize purchased energy costs; therefore, this is the 

primary energy performance metric considered. The monthly energy costs are shown in Table 5-9 and 

Figure 5-12. The total monthly energy costs were obtained from the utility bills and the data shown in 

Table 5-9 were derived from these monthly bills. The monthly utility billing cycle did not start on the 

first of the month and end on the last of the month. Monthly data shown in Table 5-9 and Figure 5-12 are 

represented by the month in which the majority of the data is contained. Included in the monthly energy 

costs are demand charges based on the monthly peak consumption over a 15-minute interval, a 

consumption charge based on the total electricity consumed over the month, and taxes and fixed charges. 

The utility rate structure, based on electrical utility bills from Utah Power, includes an energy charge of 

$0.0277/kWh, a demand charge of $8.1/kW, and a $15.00 fixed charge with a variable rate adjustment 

charge. From June 2002 through May 2003, the annual utility costs were $4,383 or $0.37/ft2

 ($3.98/m2) 

based on 11,726 ft2

 (1089.4 m2) of gross floor area. The energy cost intensity from November 2001 

through October 2002 was $0.43/ft2

 ($4.63/m2). Compared to the energy cost performance of other highperformance commercial buildings, ENERGY STARbuildings, and the top CBECS buildings 

documented in Section 2, the energy cost intensity of the Visitor Center Complex is significantly better. 

Table 5-9 Visitor Center Complex Energy Costs, Nov. 2001 through May 2003 

Demand 

Cost 

Consumption 

Cost 

Taxes/Fixed

Costs 

Total 

Costs 

Nov-01 $122 $129 $27 $277 

Dec-01 $243 $290 $34 $566 

Jan-02 $308 $357 $37 $702 

Feb-02 $300 $292 $35 $627 

Mar-02 $300 $187 $33 $520 

Apr-02 $235 $150 $30 $415 

May-02 $204 $112 $29 $345 

Jun-02 $105 $148 $29 $282 

Jul-02 $146 $179 $32 $356 

Aug-02 $138 $171 $31 $340 

Sep-02 $122 $165 $31 $317 

Running 

Annual 

Total 

Cost 

Intensity 

$/ft2 

($/m2)

Oct-02 $138 $177 $32 $347 $5,094 0.43 (4.6) 

Nov-02 $162 $185 $33 $380 $5,197 0.43 (4.6) 

Dec-02 $284 $187 $37 $508 $5,139 0.44 (4.7) 

Jan-03 $243 $246 $38 $527 $4,964 0.42 (4.5) 

Feb-03 $130 $160 $31 $320 $4,658 0.40 (4.3) 

Mar-03 $154 $190 $35 $378 $4,516 0.39 (4.2) 

Apr-03 $219 $124 $26 $368 $4,470 0.38 (4.1) 

May-03 $113 $121 $25 $259 $4,383 0.37 (4.0) 
58 

$0

$100

$200

$300

$400

$500

$600

$700

$800

Nov-01Dec-01

Jan-02

Feb-02

Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Nov-02Dec-02

Jan-03

Feb-03

Mar-03

Apr-03

May-03

Monthly Utility Costs ($/month)

Taxes and Fixed Charges

Consumption Charges

Demand Charges

Figure 5-12 Visitor Center Complex energy costs, Nov. 2001 through May 2003 

The initial prediction of cost savings was 80% compared to a 7,600-ft2 (706-m2) base case. Using a basecase model simulated with measured weather data from November 2001 through October 2002, the 

energy cost savings were 67%. From November 2001 through October 2002, the measured energy cost 

intensity was $0.43/ft2

 ($4.63/m2) or an annual cost of $5,094, while the simulated base-case model was 

$1.30/ft2

 ($13.99/m2) or an annual cost of $15,250. A monthly energy cost comparison to the base-case 

including demand charges, consumption charges, and taxes is shown in Figure 5-13. 

The reason the energy cost savings are less than the expected 80% savings is because of the differences 

between the as-built building and proposed design used to determine the expected savings levels. A 

significant difference between the as-built and proposed design was the daylighting system. In the 

proposed design, the design team expected daylighting to provide almost all of the necessary daytime 

lighting to the Visitor Center and Comfort Station. This is not the case in the as-built design. The size of 

the specified clerestory visible glazing is not what was installed due to differences in the window 

specifications and actual design. The frames, mullions, screens, and automation mechanisms all reduced 

the amount of visible glazing in the clerestory windows, but also reduced the expected daylighting 

provided by the clerestories from the original design. Additionally, the dark structural beams throughout 

the buildings were not considered when the daylighting features were designed. These dark beams absorb 

and block significant portions of the clerestory daylighting. Finally, the ceiling installed was a lowreflective whitewashed board, rather than a high-reflective white as suggested. The color problems were 

identified during construction based on the proposed colors of the wood and the ceiling. During design, 

we recommended high-reflective white ceiling surfaces. 

When combined, these daylighting design issues reduced the expected daylighting contribution and 

resulted in increased lighting consumption and energy costs, as daylighting was not able to meet the entire 

daytime lighting load. Lighting was responsible for 31% of the annual site energy consumption, as 

shown previously in Figure 5-6 and discussed further in Section 6.3.2. 
59 

Another difference between the proposed and as-built design was the heating systems. The as-built 

heating system includes electric radiant heating panels, while the proposed design included a propane 

furnace. During the redesign/design development step of the low-energy design process, the designers 

decided to use electric radiant heating panels instead of propane. The consumptive cost of electricity was 

similar to the cost of propane. A cost comparison between an electric and a propane heating system 

estimated that the electric system would be more cost effective if it did not create an additional demand 

charge on the building. As shown in Figure 5-10, this is not the case. The heating system was often 

responsible for significant demand charges, which prevented lower measured energy cost savings. This 

problem is still being studied as an area of possible improvement. 

The base case was an all-electric building that used air-source heat pumps, as specified in ASHRAE 90.1. 

Comparing energy consumption of an electric resistive heating system to a more efficient heat pump 

system resulted in a lower energy cost saving as well. Although the energy cost saving was less than 

expected at 67%, the realized cost saving is still significant. Again, if the redesign had been resimulated 

during the design process, the expected energy cost saving would have been recalculated. These energy 

cost savings would have been closer to the realized savings. 

$0

$200

$400

$600

$800

$1,000

$1,200

$1,400

$1,600

$1,800

Nov-01

Dec-01

Jan-02

Feb-02Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Monthly Energy Cost

Base-case Taxes and Fixed Charges

Base-case Consumption Cost

Base-case Demand Cost

Actual Taxes and Fixed Costs

Actual Consumption Cost

Actual Demand Cost

Figure 5-13 Base-case and energy costs, November 2001 through October 2002 

As shown in Figure 5-13, the largest monthly cost savings occur during the summer months. The basecase, heat-pump cooling system uses significantly more energy with higher demand costs than the as-built 

cooltowers. The significant demand cost during the winter of 2001–2002 point to the importance of 

understanding what causes peak demands and if the peak demand is controllable. This offers the most 

potential in optimizing energy costs. 
60 

5.4.2 Site Analysis 

The simulated energy use of the base-case model, as developed in Section 5.3.2 using a measured weather 

file, is 241,706 kWh/yr, at a site energy use intensity of 70.3 kBtu/ft2

·yr (798 MJ/m2·yr). The monthly 

energy use comparison between the base-case model and the Visitor Center Complex is shown in 

Figure 5-14 with corresponding data in Table 5-10. The annual site energy savings from November 2001 

through October 2002 are 62%, not including PV. The peak energy consumption has been shifted from 

the summer to the winter in an area where electrical peaks occur in the summer. Although not 

quantifiable, this reduces the impact on the development to the utility grid. 

The cooling savings are 59,514 kWh. The cooltower pumps consume 93% less energy than the base-case 

air-source heat pumps3

. The downdraft cooltower air delivery mechanism and radiant heating panels also 

reduce fan consumption. Further analysis of the cooling system is included in Section 6.4.2. Significant 

savings are realized due to daylighting and lighting systems. The expected annual lighting savings are 

78,824 kWh. Further analysis of daylighting and lighting savings are included in Section 6.4.4. The 

heating system used more electricity than the base case because the efficiency of the electrical radiant 

system is 100%, while the base-case heat pumps were modeled with a COP of 3.0. Additional heating 

was required to make up for the lighting systems, as these more efficient lights provide less heat to the 

building than do the lights used in the base case. The increased heating energy use in the as-built Visitor 

Center Complex, due to the electric heating systems and efficient lighting systems, counteracts any 

energy savings due to Trombe wall gains and the high-performance envelope. 

No equipment or DHW savings are expected because these loads are dependent on occupancy and 

installed capacity. The base-case loads represent as-built equipment power densities and operational 

schedules. 

Table 5-10 Base-Case and Measured Site Annual Consumption and Savings 

Base-Case Site 

Annual 

Consumption (kWh)

Measured Site 

Annual 

Consumption (kWh)

Site Annual 

Savings 

(kWh)

Site Annual 

Savings 

(%)

Heating 20,608 24,571 –3,963 –19% 

Cooling 63,915 4,401 59,514 93% 

Fans 19,190 4,743 14,447 75% 

Lighting 107,781 28,957 78,824 73% 

Equipment/Other 26,769 26,769 0 0% 

Domestic Hot 

Water 3,443 3,435 8 0% 

Total Complex 

Consumption 241,706 92,876 148,830 62% 

 

3

 The embodied energy in evaporating the water was not considered important because the water supply is gravity 

fed from the river and treated in the park. 
61 

56% 70%

74% 74%

75%

71%

55% 65%

46%

38% 31%

62%

-30,000

-24,000

-18,000

-12,000

-6,000

0

6,000

12,000

18,000

24,000

30,000

Nov-01

Dec-01

Jan-02

Feb-02Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Monthly Energy Consumption (kWh/month)

0

6,000

12,000

18,000

24,000

30,000

36,000

42,000

48,000

54,000

60,000

Plug Loads Lighting

 Heating Cooling

 Fans DHW

Measured 

2001-2002

Measured 

Weather 

Base-case

Figure 5-14 Base-case energy consumption compared to measured consumption 

5.4.3 Source Energy Analysis 

Source energy is the sum of the energy directly consumed at the site and the energy consumed by 

producing and delivering energy products. It represents the total energy required to deliver energy to a 

building. Documenting source energy consumption is useful when emissions from energy sources are a 

concern. We calculated the base-case source energy and measured source energy consumption based on 

31% electricity conversion and delivery efficiency from source to site. The electrical source-to-site 

efficiency was based on the conversion and distribution efficiency averaged over all sources of electricity 

generation in the nation, as specified by EIA’s Annual Energy Review (EIA 2000). With measured 

weather data, the all-electric base-case building (described in Section 5.1.3) was predicted to consume 

779,697 kWh of source electricity. At 11,726 ft2

 (1,089.4 m2), the annual base-case source energy 

consumption intensity was 227 kBtu/ft2

·yr (2,580 MJ/m2·yr). Recall that the base-case building has a 

heat-pump as the HVAC system. 

A primary consideration in the source energy consumption calculation was the electricity that the PV 

system produced on site. This on-site electricity generation offsets the consumption of site electricity and 

the corresponding conversion and transmission losses. Therefore, the net energy consumption (total 

consumption minus PV production) was used to calculate the total source energy required to meet Zion’s 

site electricity load. 

From November 2001 through October 2002, the measured net site energy consumption was 85,016 kWh, 

or 24.7 kBtu/ft2

·yr (281 MJ/m2·yr). At 31% source-to-site electricity conversion efficiency, the source 

energy consumption intensity was calculated to be 80 kBtu/ft2

·yr (909 MJ/m2·yr), which is a source 

energy consumption savings of 65% as compared to the all-electric base-case source energy consumption. 

Compared to the top CBECS buildings, the Visitor Center Complex source energy intensity was 30% 

less. 
62 

NREL also calculated emissions reductions based on source energy consumption for the measured 

consumption and the base case. We calculated electricity emissions based on the data given in 

Table 5-11, which summarizes emissions for electricity generated by coal at a local power plant (EPA, 

2003). 

Table 5-11 Electricity Generation Emissions from Coal 

Emissions 

Emissions Amount per Unit of 

Electricity Generated 

lb/kWh (kg/kWh)

CO2 (carbon dioxide) 2.1 (0.95) 

SO2 (sulfur dioxide) 0.001 (0.0005) 

NOX (oxides of nitrogen) 0.004 (0.002) 

The evaluators estimated that the Visitor Center Complex saves 181 tons (164,000 kg) of CO2, 160 lbs 

(73 kg) of SO2, and 680 lbs (308 kg) of NOX annually as compared to emissions resulting from source 

energy consumption in the base case, as shown in Table 5.12. For this calculation, a 10% transmission 

loss is assumed from delivering electricity from the point of generation to the site. 

Table 5-12 Emissions Reduction Summary 

Base-case 

Emissions 

tons (kg)

November 2001–October 

2002 Emissions 

tons (kg)

Emissions Reductions 

(Amount Saved) 

tons (kg)

CO2 279 (253,000) 98 (89,000) 181 (164,000) 

SO2 0.13 (118) 0.05 (45) 0.08 (73) 

NOX 0.53 (480) 0.19 (172) 0.34 (308) 
63 

6 Subsystem Evaluations 

NREL evaluated the unique subsystems of the building, including the HVAC system, lighting, 

daylighting, and PV system. In addition, a comfort evaluation of occupants and an energy analysis of the 

Comfort Station were also performed. 

6.1 HVAC Evaluation 

We evaluated two years of indoor and outdoor dry-bulb temperature data from 2001 to 2003 and 

organized the years into seasons. We defined winter as October 1 through April 30 and summer as May 1 

through September 30. The comfort data starts in May 1, 2001, whereas the energy performance data 

starts in November 1, 2001. A histogram of the outdoor dry-bulb temperature is shown in Figure 6-1. 

The averages and standard deviations were similar for each year, but the histogram shows that there were 

43% more hours of outdoor dry-bulb temperatures above 95°F (35°C) in 2002 than in 2001. In addition, 

the temperatures in the winter of 2001–2002 were colder than the winter of 2002–2003. 

0

50

100

150

200

250

300

350

10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 More

Temperature (°F)

Hours

2001-2002

2002-2003

There are 43% more hours above 95°F during

2002 than during 2001.

Mean (2001-2002) = 65.3°F

StdDev (2001-2002) = 20.2°F

Mean (2002-2003) = 65.6°F

StdDev (2002-2003) = 19.5°F

Figure 6-1 Histogram of outdoor dry-bulb temperatures during occupied hours 

Further analysis of the outdoor temperatures show that the heating degree days at 65°F (HDD) between 

the two years of analysis did not change significantly; however, the cooling degree days at 75°F (CDD) in 

2002–2003 increased by 30% compared to 2001–2002, see Table 6-1. Note that these values do not 

match the values for the Zion measured data in Table 5-4 because the range of the datasets is different. 

Table 6-1 Heating and Cooling Degree Days for 2001–2002 and 2002–2003 

Data 

HDD 

(65°F/18°C) 

CDD 

(75°F/24°C) 

2001–2002 Data 3,508 728 

2002–2003 Data 3,505 946 
64 

This increase in outdoor temperature over the two-year monitoring period created many challenges on 

how to effectively cool the space. As seen in subsequent sections, the temperatures were easier to 

maintain during 2001, when the outdoor temperatures were lower. During the winter, the heating set 

point was controlled by the occupants. There is sufficient heating capacity to maintain set point 

temperatures at 72°F (22°C) or below. The only limitation of heating was the demand limiting controls to 

help control costs (Section 5.2.3.1). 

The majority of the energy used for the HVAC system went to the heating panels, while the cooling 

system used very little energy, as shown in Figure 6-2. When the outdoor temperature was between 60–

75°F (16–24°C), the building used very little energy for heating or cooling. The thermal envelope 

contributes to large heating and cooling energy reductions during the swing seasons. 

0

50

100

150

200

250

300

350

400

450

20 30 40 50 60 70 80 90 100

Average Daily Outdoor Temperature (°F)

Total Daily HVAC Consumption (kWh)

Figure 6-2 HVAC energy consumption as a function of outdoor temperature 

6.1.1 Heating Evaluation Methods 

The heating system includes Trombe walls and electric radiant ceiling panels. We calculated the energy 

consumption of the electric radiant panels by the BAS based on run time and a one-time load 

measurement of each panel. We compared the energy use to the base-case values reported in Section 

5.4.2. We also compared the energy use between the two winters of collected data. 

We measured the thermal gradient through the Trombe wall to approximate the performance. 

Thermocouples placed in the wall during construction, combined with portable data loggers, measured the 

temperature at three locations in the wall from November 29, 2000 to January 25, 2003 (Figure 6-3). The 

interior temperature sensor is not a measurement of surface temperature, but rather the measurement of 

the air temperature very close to the surface of the interior Trombe wall. Based on an evaluation of area 

and temperatures within the wall, we estimated the energy supplied from the Trombe wall to the Visitor 

Center space. We chose the data set from November 9, 2002 to January 14, 2003. It was also important 
65 

to determine how often the Trombe wall was being a net positive influence on the building, and when it 

was negatively impacting the building. 

Figure 6-3 Cross section of Trombe wall showing location of temperature sensors 

6.1.2 Heating Evaluation Results 

The Visitor Center heating system is a combination of electric radiant heating and passive solar. The 

occupants have control over the temperatures during the winter, so it is assumed that if they are 

uncomfortable, they will adjust the heating set point accordingly. More on comfort is seen in Section 6.4. 

The electric heating during the winter of 2001–2002 used 24,571 kWh compared to only 11,442 kWh 

during the winter of 2002–2003. The base case used 20,608 kW. During the winter of 2001–2002, the 

Visitor Center used 19% more energy than the base case, an increase of 3,963 kWh. However, during the 

winter of 2002–2003, the building used 44% less energy than the base case, a decrease of 9,166 kWh. 

The difference can be attributed to many factors, including a warmer winter in 2002–2003, demand 

controls implementation, and a reduced set point. The average daily monthly energy consumption is 

shown in Figure 6-4. 

Tinterior

TZone7

Tinner Tmiddle Texterior

Toutdoor

8-in.Grout Filled 

CMU Wall

Selective 

Surface 

2-in.Air 

Gap

5/32-in. 

Glazing

Shotcrete 

Wall Finish
66 

0

50

100

150

200

250

300

Oct Nov Dec Jan Feb Mar Apr May

Average Daily Heating Energy Consumption (kWh)

2001-2002

2002-2003

Figure 6-4 Average daily heating energy consumption by month 

The electric radiant system provides a large portion of heat to the Visitor Center; however, the Trombe 

wall is an integral part of the building’s heating system as well. To perform the heat transfer calculation 

on the Trombe wall, several assumptions had to be made, including: a homogeneous wall, a constant 

density of 130 lbs/ft3

 (2,080 kg/m3), a constant capacitance of 0.22 Btu/lb·°F (0.92 kJ/kg·K), and the 

temperature sensors within the wall were equally spaced (ASHRAE 2001). In addition, the heat flow was 

assumed one-dimensional. 

To confirm that the material and temperature homogeneity assumptions were valid, an infrared picture 

was taken of the Trombe wall during the middle of the heating season (see Figure 6-5). The temperature 

range across the Trombe wall was around 4°F (2.2°C). The edges of the wall have slightly larger 

temperature drops, but the majority of the 1,040-ft2

 (96.6-m2) wall was within the 4°F (2.2°C) range. This 

range was assumed reasonable for the homogeneous assumption of even distribution. Note the uneven 

temperature distribution in the middle of the interior wall caused by the external shading of the Trombe 

wall by the window mullions and other exterior wall shading. Also, note the heat bridge in the corner of 

the building—a typical problem spot. Even with careful detail to make certain the insulation was 

installed properly, losses from edge affects are still evident. More extensive modeling could be done, but 

it is beyond the scope of this project. 

 
67 

Figure 6-5 Infrared picture of Trombe wall during heating season 2/9/2000 at 

6:00 p.m. 

Using the stated assumption and the internal temperature measurements, we calculated the Trombe wall 

energy supplied to the building based on published heat flux calculation methods (Balcomb 1998). The 

objective was to calculate the middle temperature using the previous measured temperatures of the wall 

using the equations below. We then adjusted the thermal conductivity of the wall until the calculated 

middle temperature was comparable to the measured middle temperature. We found that the wall had a 

conductivity of 0.5 Btu/hr·ft·°F (0.86 W/m·K). Figure 6-6 shows the comparison between the calculation 

and measured temperatures after adjusting the thermal conductivity. 

( )

H G

H T T T G T T inner exterior middle middle

middle −

⋅ ′ + ′ − ′ − ⋅ ′ =

 x

k H

∆ = t

C x

G p

∆

∆ = ρ

Where: ρ = density 

 k = thermal conductivity 

 x = thickness of slice 

 T = Temperature 

 T′ = Previous Temperature 

 Cp = heat capacity 

 t = time 

Radiant 

Heating 

Panel 

Trombe Wall

Window

Lighting 

Bookshelf

Window 

Mullion Affects
68 

60

70

80

90

100

110

120

130

140

150

01/04/02

07:00

01/04/02

09:00

01/04/02

11:00

01/04/02

13:00

01/04/02

15:00

01/04/02

17:00

01/04/02

19:00

01/04/02

21:00

01/04/02

23:00

01/05/02

01:00

01/05/02

03:00

01/05/02

05:00

01/05/02

07:00

Temperature (°F)

Outer Trombe Wall Middle Trombe Wall

Inner Trombe Wall Interior Surface

Calculated Middle Trombe Wall

Figure 6-6 Verification of middle Trombe wall temperature after adjusting thermal 

conductivity 

The amount of energy delivered to the space could be calculated after determining the actual thermal 

conductivity of the Trombe wall. Visitor Center Trombe wall daily performance during the 2001–2002 

heating season is shown in Figure 6-7. During the period of evaluation of the Trombe Wall, the electric 

radiant heating system used 22,680 kWh (81,600 MJ), with the Trombe wall contributing 20% of the total 

heating to the building. The Trombe wall imposed a heating load on the building for only two of the 151 

days of the 2001–2002 heating season. For the other 149 heating days, the wall was net positive. The 

peak heat flux through the wall was 11.2 W/ft2

 (89 W/m2), or 8.3 kW over the entire Trombe wall area. 

The average efficiency of the wall over the 2001–2002 heating season (defined as the heat delivered to 

the building from the Trombe wall divided by the total solar radiation incident on the exterior of the wall) 

was 13%. 

During the first three months of the 2002–2003 heating season, the total electrical heating energy used 

was 5,389 kWh, while the Trombe wall provided approximately 41% of the energy or 3,800 kWh. This 

percentage was greater than the previous 2001–2002 heating season of only 20% due to improved 

controls of the electrical heating system and differences in weather. 
69 

0

50

100

150

200

250

300

350

400

11/01/200111/08/200111/15/200111/22/200111/29/200112/06/200112/13/200112/20/200112/27/200101/03/200201/10/200201/17/200201/24/200201/31/200202/07/200202/14/200202/21/200202/28/200203/07/200203/14/200203/21/200203/28/2002

Daily Heating Energy Supplied to Visitor Center (kWh/day)

Heat Added by the

Trombe Wall

Heating System Use

2001-2002 Heating Season:

»5,470 kWh added by 

 Trombe Wall

»22,680 kWh added by

 Trombe Wall 

»20% of heating from 

 Trombe Wall

»8.3 kW Peak heating 

 from Trombe Wall

»17.2 kW Peak heating 

 from Heating System

Figure 6-7 Trombe wall and heating system performance, 2001–2002 heating season 

The heat added to the Visitor Center from the Trombe wall during cooling months is a concern, especially 

in the enclosed offices on the south side of the Visitor Center. Although the Trombe wall is shaded by 

overhangs, diffuse radiation hitting the wall is transferred to the building. Because of the evaporative 

cooling system, this load is not generally seen by the building, although specific zones suffer from 

insufficient ventilation. We recommend that further research be completed in determining the summer 

Trombe wall loads and ways of reducing the impact. External shade cloths in the summer are a possible 

option. 

In the initial design, these offices were on the north side of the building and summer Trombe wall heat 

gain to the offices was not a concern. With the offices located directly next to the Trombe walls in the 

As-built design and separated from the cool air sources, overheating in these spaces can be a problem. 

This is discussed further in the next section. For buildings with conventional air-conditioning systems, 

careful Trombe wall design is essential so that summer gains are minimized. If buildings are flushed with 

evaporative cooling, the summertime cooling loads generated by the Trombe walls are not a problem. 

We conducted a further analysis to determine the delay of heat gain into the space because of the Trombe 

wall. The analysis involved measuring the temperature distribution through the wall as a function of time. 

A day was chosen that had very large insolation to preheat the wall, while the previous day had little 

insolation so the wall started with as little “charge” as possible. In addition, the outdoor temperature was 

relatively low to show the passive solar component of the Trombe wall. Figure 6-8 shows how the heat is 

slowly transferred into the building. The shifting of the temperature profile peaks shows the time delay of 

the heat transfer from the exterior of the Trombe wall to the interior. It takes approximately 4 hours for 

the heat to migrate from the exterior wall surface to the interior wall surface. In this case, the interior 

surface of the Trombe wall provided the most heating from 5:00–7:00 p.m. Temperatures at the interior 
70 

surface can reach over 100°F (37.7°C) during certain times of the year. This warm surface provides 

radiant heating to the occupants. The result is that occupants in the building with a view factor of the 

radiant surface should be comfortable at lower space temperatures. No attempt was made in this study to 

quantify the radiant effects of the wall on comfort. The NPS staff can control the temperature of the 

building via the thermostats, so savings from radiant comfort would be connected with the heating 

consumption of the building. 

0

20

40

60

80

100

120

140

12/15/2001 06:00 12/15/2001 12:00 12/15/2001 18:00 12/16/2001 00:00 12/16/2001 06:00 Temperature (°F)

0

200

400

600

800

1000

1200

1400

Insolation (W/m2

)

T exterior

T middle

T inner

T interior

T Zone 7 

T outdoor

Vertical Insolation

Figure 6-8 Trombe wall temperature transients over a 24-hour period 

6.1.3 Cooling Systems Evaluation Methods 

NREL determined cooltower performance by evaluating energy use, water consumption, and the ability 

of the natural ventilation, the cooltowers, and the fans to cool the space. We calculated the energy 

consumed by water pumps in the cooltowers and circulation with the BAS based on a one-time power 

measurement and run time. Water consumption was determined by measuring the water flow to and from 

the cooltowers during operation. We measured the ability of the clerestory windows, the cooltowers, and 

the fans to cool the space by collecting indoor zone temperatures and through occupant feedback. This 

data is reported in the comfort analysis section. 

6.1.4 Cooling Systems Evaluation Results 

The cooltowers cool the building using only a small circulation pump. Circulation fans were added in 

August 2001 to help push cool air into the office areas of the building. The total cooling energy (both 

cooltower pumps and circulation fans) for the Visitor Center Complex during 2001 was 4,940 kWh, or 

7.5% of the total consumed energy, whereas for 2002, the total cooling energy consumed was 7,300 kWh, 

or 8.4% of the total consumed energy. (The differences between the numbers can be attributed to many 

variables including the warmer summer during 2002.) The cooling energy intensity was 1.28 kBtu/ft2

·yr 
71 

(14.5 MJ/m2

·yr), which was 77% less than a typical building in the western United States that uses 

5.5 kBtu/ft2

·yr (62.5 MJ/m2·yr) (EIA 2002). 

The building uses control algorithms to precool the building during nighttime periods if certain conditions 

are met. The controls check the high temperature for the current day and the previous day. If the highs 

are greater than 90°F (32.2°C), then the building will perform night cooling for the next day. The purpose 

of the night cooling is to remove any excess heat in the building, such as Trombe wall heat, during the 

night while the temperatures are cooler. In addition, less energy is needed to cool the building because 

the internal loads are smaller. In some cases, the cost of energy is less during nighttime hours because of 

lower demands. The day following the night cooling period allows the building to “float” to the 

temperature set point instead of having to drop to the cooling set point. 

The next metric in determining the cooling system performance was to evaluate the amount of water 

consumed in the evaporative cooling process. Water consumption is a concern because of the semi-desert 

climate and the scarcity of water resources. From the installed water meters, 111,200 gallons (420,938 

liters) of water were consumed during 2002 for the two cooltowers in the Visitor Center. The water 

consumption was related to many variables such as temperature, relative humidity, and wind speed, with a 

loose correlation to the outdoor dry-bulb temperature shown in Figure 6-9. Due to flaws in the design of 

the cooltower plumbing, there was unnecessary water use, which occurred when the sump pit would 

overflow during on/off cycling of the pumps. The cycling of the pumps and sump pit overflow resulted in 

a 10% increase of water consumption. The cycling occurred during the swing season when the cooling 

was not required all the time. During this time, the pumps would run and saturate the pads and the sump 

pit would fill up. The pumps would turn off because cooling was no longer needed and all the water in 

the pads would drain into the full sump pit causing the pit to overflow. 

0

200

400

600

800

1,000

1,200

1,400

1,600

40 50 60 70 80 90 100

Daily Average Outdoor Temperature (°F)

Total Water Consumption (gallons/day)

111,200 gallons used annually

10% of annual consumption lost due 

to cycling of pumps and pit overflow

Figure 6-9 Water consumption versus daily average outdoor temperature 

(Summer 2002) 
72 

Another measure of cooltower success and excess water consumption is the effectiveness of delivering 

the evaporative cooled air to the building. By design, the dry air enters the building and picks up 

moisture. This air enters the building. However, some of the air may exit through the pads into the 

environment driven by evaporation on the exterior of the pads or cross-flow through the top of the tower, 

which results in more evaporation of water than would be expected with traditional evaporative 

technologies. The towers contained a simple internal diagonal blocking device to minimize this effect 

(see Figure 6-10). The tower pads are not shaded from direct sunlight, which increases the evaporation 

rate and as well as degrading the pads by UV exposure. 

To estimate the effects of water evaporation, a hot-wire flow meter was used to estimate airflows from the 

towers. These values are highly variable and difficult to capture. The inlet air conditions were also 

computed as well as the flow rates. As an estimate, 50% of the water is not used for cooling within the 

building; however, much more detailed measurements would be needed to validate and fine-tune this 

number. It does result in the conclusion that the efficiency of the towers could be improved with respect 

to water consumption. Several recommendations regarding the cooltowers emerged from this analysis as 

seen in Section 7.2.4. 

Figure 6-10 Plastic blocking device for cooltowers 

The natural ventilation and cooltowers have provided adequate cooling for the Visitor Center Complex, 

with occasional periods of overheating and low flow rates. There were several days when the cooltowers 

could not meet the desired comfort range. This is typical of direct evaporative cooling. The system 

performed as well as a conventional direct evaporative cooling system. The limitation of the system is 

that the air outdoors must be dry, which is the case the majority of the time. 

There were problems interfacing the automatic windows in the building with the BAS. If the windows 

fail to open, the evaporative cooler has no relief and hence no airflow. The window operation technology 

was a weak point in the system. It is essential that the windows are open for air to flow. The actuators 

did not have feedback so the state of the windows could not be determined. This was fixed by running an 

open/close cycle every night to make sure the windows are synchronized with the BAS. 
73 

6.2 PV System Evaluation 

6.2.1 PV System Evaluation Method 

The evaluators used a PV simulation tool to determine the expected performance of the array. The 

expected PV production was compared with the actual data collected by the BAS to determine the system 

performance. NREL monitored the performance of the PV system by measuring horizontal and vertical 

insolation, PV system AC production, and outdoor weather conditions. 

We used a PV system simulation tool called PVSyst v3.2 (Mermoud 1996) to calculate expected annual 

performance of the PV system. Inputs to this model include PV panel size and operational characteristics, 

inverter size and operational characteristics, array configuration and wiring details, array tilt and azimuth, 

and hourly weather data. System specific inputs, such as shading and array wiring losses, are also 

simulated. The simulation approximated the cell temperatures based on the default thermal properties of 

the specific mounting configuration. The procedure used for simulating array shading from trees and the 

canyon walls is included in Appendix D. 

We used the Sandia Photovoltaic Performance I-V Curve Tracer (King et al. 1998) to evaluate the effects 

of operating voltage on PV production. We used this model to create (I-V) and power-voltage (P-V) 

curve traces for a complete subarray at varying cell temperatures and insolation levels. With a specified 

array wiring configuration and the manufacturer’s PV panel ratings at standard test conditions of 1000 

W/m2

 and 77°F (25°C) cell temperature, expected I-V and P-V curve traces were generated with the 

Sandia I-V Curve Tracer model. 

6.2.2 PV System Evaluation Results 

6.2.2.1 Measured Data Results 

The PV system offsets approximately 15% of the loads during the spring and summer months. It offsets 

less than 5% of the load during the winter because of the higher electrical loads from heating and reduced 

PV production. During the monitored year, the PV system produced a net 7,861 kWh (building 

normalized to 2.3 kBtu/ft2

·yr (26.1 MJ/m2·yr), or 1,092 kWh/kW of installed capacity. The PV system 

offsets about 8% of the total annual energy load. Table 6-2 provides a tabular summary of the monthly 

consumption, production, net purchased, maximum production, and percent load met by PV. The total 

electricity consumed is a summation of all the electrical end uses in the Visitor Center, Comfort Station, 

and the Fee Station. The net purchased electricity is the difference between the total electricity consumed 

in the building for a month and the total PV electricity produced for the month. The maximum 15-minute 

averaged PV production of 5.43 kW occurred in March during a cool period with good solar resources. 
74 

Table 6-2 PV Performance: November 1, 2001 through October 31, 2002 

Total 

Consumption 

(kWh) 

PV 

Production 

(kWh) 

Net 

Purchased 

(kWh) 

Max PV 

Power 

(kW) 

% Load Met 

by PV 

Nov-01 6,286 355 5,930 3.95 5.6% 

Dec-01 12,191 319 11,872 3.88 2.6% 

Jan-02 12,947 428 12,519 4.13 3.3% 

Feb-02 8,160 561 7,600 4.93 6.9% 

Mar-02 7,592 785 6,807 5.43 10.3% 

Apr-02 5,880 779 5,101 5.15 13.2% 

May-02 5,766 965 4,801 5.39 16.7% 

Jun-02 6,192 919 5,273 5.16 14.8% 

Jul-02 7,257 850 6,407 4.83 11.7% 

Aug-02 6,950 826 6,124 4.94 11.9% 

Sep-02 6,217 571 5,646 4.64 9.2% 

Oct-02 7,440 503 6,937 4.22 6.8% 

YTD 

Totals 92,878 7,861 85,017 5.43 8.5% 

The PV system is a high-value feature to the building even though it displaces a small part of the total 

energy load. During daylit hours, the system can provide power for business operations without relying 

on power stored in the UPS system battery bank. This system met 40 power outages ranging from 

1 second to 8 hours during the monitoring period. 

Figure 6-11 shows the average hourly power profile for AC PV production for each month from 

November 2001 through October 2002. The monthly comparison of PV production profiles demonstrates 

the drastic reduction in PV production from summer to winter months. The maximum 15-minute average 

AC PV production varies from 4.7 kW in May to 2.2 kW in December. The primary cause of this is the 

reduced solar radiation in the winter. Also evident in Figure 6-11 is the nonsymmetrical power profile for 

each of the months. The time is Mountain Standard Time and does not include the daylight savings time 

change. Generally, the afternoon AC PV production is less than the morning production because of the 

afternoon shading from the trees. 
75 

0

1

2

3

4

5

6

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

AC PV Production (kW)

November-01

December-01

January-02

February-02

March-02

April-02

May-02

June-02

July-02

August-02

September-02

October-02

Annual Maximum

Figure 6-11 Average hourly AC power profile by month for PV production, November 

2001 through October 2002 

6.2.2.2 PV System Simulations 

The PVSyst simulated system losses are summarized in Figure 6-12 and detailed in Table 6-3. The 

expected maximum DC power point (Pmpp) is 7.2 kW for global insolation at 92.9 W/ft2

 (1000 W/m2) 

and cell temperatures of 77°F (25°C). The modeled system losses include wiring and connection 

resistance, diode losses, thermal inefficiencies, and panel parameter mismatches. The incidence angle 

reflectance losses are accounted for in the simulation by the incidence angle modifier (IAM). The 

thermal inefficiencies are determined based on simulated module temperatures, with losses totaling 

11.9%. The expected maximum DC power point at a cell temperature of 126°F (52°C) and global 

insolation of 92.9 W/ft2

 (1000 W/m2) is 5.7 kW. This number corresponds to an overall simulated system 

loss of 20.9% at these conditions. 
76 

Figure 6-12 Modeled array losses 

Table 6-3 Summary of PV System Losses at 1000 W/m2

, 77°F (25°C) 

Category Percent 

Loss 

Module Quality Loss 3.0 

Module mismatch 2.9 

IAM (Diffuse, beam 40°) 1.8 

Modules Temperature = 51.2°C 11.9 

Wiring Resistance (10 mΩ) 1.8 

Series Diode Loss (V=0.7V) 1.0 

Global Loss (Pmpp = 5.71kW) 20.9% 

To model the expected annual performance, we used a typical meteorological year weather dataset for 

Cedar City, Utah (60 miles north of Zion). An array tilt angle of 18.3° at a southern azimuth was 

modeled. We modeled the PV array operating voltage at 53.6 VDC (direct-current voltage) because this 

was the float voltage set point of the inverters. 

The Sandia Photovoltaic Performance I-V Curve Trace results are shown in Figure 6-13. This figure 

gives an example of the Curve Tracer model. The Curve Tracer model calculated instantaneous I-V and 

P-V traces for a complete subarray at varying weather conditions, cell temperatures, and insolation levels, 

as shown in Figure 6-13. Inputs included PV module size and type, array wiring configuration, and 

environmental conditions. NREL researchers used the Curve Tracer model to evaluate DC operating 

voltages. The effect of fixed array operating voltage was evaluated by comparing the voltage set point to 

7.2-kW DC maximum 

power point 

5.7-kW DC maximum 

power point at 52°C, 

1000 W/m2

Array Losses for 1000 W/m2:

T mod. = 25°C, Pmpp Array = 7.2 kW 

Module quality loss (per spec) 

Module mismatch: 

IAM: (diffuse, beam 10°) 

Modules temperature = 52°C 

Wiring resistance (10 mΩ): 

Series diode loss (V=0.7 V): 

Resultant: Pmpp Array = 5.7 kW
77 

a simulated maximum power point. The PVSyst model was also used to evaluate the annual 

consequences of a fixed voltage PV system as compared to a maximum power-point tracking system. 

Figure 6-13 Sandia PV performance model I-V curve tracer model for the Zion PV 

system 

Figure 6-14 provides a monthly summary of the effects of horizon and tree shading. Horizon shading is a 

result of the canyon walls. The tree shading can be seen in an actual photo in Figure 6-15 and in the 

simulation photo in Figure 6-16. 
78 

0

200

400

600

800

1,000

1,200

January

February

March

April

May

June

July

August

September

October

November

December

PV Production (kWh)

Unshaded Simulation

Horizon Shaded Simulation

Horizon and Tree Shaded Simulation

Figure 6-14 PV production for unshaded, horizon shaded, and horizon and tree 

shaded simulations 

For a typical meteorological year in Cedar City without any array shading, the estimated production is 

9,535 kWh/yr. The simulated annual performance of this model is 16% greater than the measured 

production. When the canyon wall horizon shading is considered, the array would produce 8,912 kWh/yr. 

Annual losses of 7% are expected because of canyon wall shading. The simulated annual production for 

the model that includes Cedar City weather data, canyon shading, and tree shading is 8,278 kWh/yr. 

Annual losses of 7% are expected because of tree shading. This model represents the expected 

performance for this system for a typical weather year. With all losses accounted for, the model predicts 

4% more production than was measured from November 2001 through October 2002. 

Figure 6-15 Photo of shaded PV panels (left side of photo) 
79 

Figure 6-16 Model of tree shading of PV array, 3:30 p.m. July 9, 2000 

To provide an accurate comparison of measured annual PV performance to the simulated PV 

performance, the typical meteorological year at Cedar City, Utah, is considered. In Cedar City, there is an 

average of 173.2 kWh/ft2

 (1,967 MJ/m2) of global horizontal radiation per year. Note that the measured 

values at the Visitor Center include the effects from the canyon walls shading the sensor; however, the 

sensor is not shaded by any foliage. 

During the measurement period, there was 163.8 kWh/ft2 (1,860 MJ/m2

) of global radiation available. 

This amount is 5% less solar radiation than a typical year in Cedar City. To determine this effect on the 

simulated performance, a weather file based on measured environmental conditions at the Visitor Center 

was used to generate a model that would adequately represent the PV performance from November 2001 

through October 2002. The simulated PV production using the measured weather file and the horizon and 

tree shading models were simulated to be 8,092 kWh/yr or 1% more than the measured PV production. 

The close match between simulated PV performance and measured PV production suggests that the PV 

system has operated with minimum unaccounted for system losses. 

6.2.2.3 Maximum Power Point Tracking 

A potential performance-limiting feature of the Zion PV system is the fixed-array voltage control. The 

PV array operating voltage is set at 53.6 VDC, as this is the float-voltage set point of the inverters. The 

maximum power point of the array is often greater than the fixed-voltage set point, as shown in the 

power-voltage curves in Figure 6-17 and Figure 6-18. 

For summer weather conditions of 104°F (40°C) and a wind speed of 3.28 ft/s (1 m/s), the Sandia Curve 

Tracer predicts a maximum power point of 54 VDC to 59 VDC, depending on insolation (Ic) and cell 
80 

temperature (Tc). For winter weather conditions of 32°F (0°C) and a wind speed of 9.8 ft/s (3 m/s), the 

Sandia Curve Tracer predicts a maximum power point of 69 VDC to 73 VDC, depending on insolation 

and cell temperature. 

A maximum power-point tracker was simulated with PVSyst to determine the potential PV production if 

this type of voltage control was used. The predicted annual production of the PV system with a 

maximum power-point tracker and current shading issues would be 9,826 kWh/yr. This number 

corresponds to a production increase of 16% due to maximum power-point control as compared to the 

fixed 53.6 VDC control. 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0 10 20 30 40 50 60 70 80

PV Array Operating Voltage (VDC)

PV Array DC Power (W)

Ic=1,000 Tc=69

Ic=800 Tc=63

Ic=600 Tc=58

Ic=400 Tc=52

Ic=200 Tc=46

Fixed 

operating 

voltage

Figure 6-17 Simulated power-voltage curve traces for summer weather conditions 
81 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0 10 20 30 40 50 60 70 80 90

PV Operating Voltage (VDC)

PV Array DC Power (W)

Ic=800 Tc=21

Ic=600 Tc=15

Ic=400 Tc=10

Ic=200 Tc=5

Fixed 

operating 

voltage

Figure 6-18 Simulated power-voltage curve traces for winter weather conditions 

Also simulated for voltage control was the optimal fixed voltage. The annual PV production is optimized 

at a fixed voltage of 61 VDC, as shown in Figure 6-19. Although this operating voltage results in the 

optimal annual PV production, it is not practical for charging the nominal 48 VDC battery backup system. 

8,824

8,278

0

2,000

4,000

6,000

8,000

10,000

12,000

45 50 55 60 65 70 75

Operating Voltage (VDC)

Annual PV Production (kWh)

actual 

fixed 

voltage

Optimal 

fixed voltage

Maximum 

powerpoint 

tracking

Figure 6-19 Simulated annual PV production: Best fixed voltage, actual fixed voltage, 

and maximum power-point tracking 
82 

The annual performance is degraded by 7% because of the tree that partially shades the west set of 

modules late in the afternoon. While the measured PV system production is expected and all system 

losses accounted for, the net annual production could be increased with a maximum power-point tracker. 

A maximum power-point tracking voltage controller would increase typical performance by 16% as 

compared to the fixed operating voltage control of 53.6 VDC. Unfortunately, the inverter will not allow 

maximum power-point tracking. Figure 6-20 provides a comparison of the annual PV production for the 

shading models, maximum power-point control model, and measured insolation model using the TMY2 

data to the measured performance. Table 6-4 shows the performance degradation results for the PV 

system and the estimated impact on actual PV production. 

9,826 9,535

8,912

8,278 8,092 7,861

0

2,000

4,000

6,000

8,000

10,000

12,000

Simulated with

MPPT;

Horizon and

tree shading

Simulated at

54VDC; No

shading

Simulated at

54VDC;

Horizon

shading

Simulated at

54VDC;

Horizon and

tree shading

Simulated at

54VDC;

Horizon and

tree shading;

Measured

weather file

Measured

Annual PV Production (kWh)

Figure 6-20 Simulated annual PV production comparisons to measured PV 

production 

Table 6-4 Performance Degradation Results 

Type of Fault 

Estimated PV 

Production Lost 

(kWh) 

Percent of Total 

Measured PV 

Production 

Horizon Shading (Canyon Walls) 623 7.9% 

Tree Shading 634 8.1% 

Unknown (Maintenance, Battery inefficiency, 

modeling and measurement uncertainty) 221 2.8% 

6.2.2.4 PV UPS and Simulated Failure 

The UPS circuit allows the building to remain operational during daylight hours when no power is 

available. The UPS powers the computer equipment, cash registers, window actuators, cooltower pumps, 

telephone switch, and BAS. The UPS system contains 200 Ah of battery capacity. 
83 

The poor power quality from thunderstorms causes the power to cycle off and on through many sequences 

in a short time period. For example, brownouts occurred several times on the day before the test day. 

During a power outage, the inverter would maintain the 1800-W emergency panel load and would drain 

the batteries within a few hours. At this point, the low-battery alarm point would trigger, but there was a 

15-minute delay before the loads were disconnected and the inverter shut down. It appears that during 

this time, the batteries continued to drain and the output voltage from the inverter was not stable. The 

result was partial loss of memory from the BAS. The BAS is critical to operation of all systems including 

lights and HVAC. The Comfort Station BAS panel did not experience any loss of memory because of 

clean power disconnect and reconnect. 

On the evening of August 18, 2001, we performed a power failure test on the emergency power system at 

the Visitor Center. Because only the inverter system was being tested, the test was performed by setting 

the main PV-utility disconnect to OFF. This disconnected the inverter system from the main distribution 

panel. A power meter was attached to panel “E.” 

The settings on the inverter were adjusted to disconnect and provide UPS power when the grid voltage 

drops below 110 V and will shutdown the inverter when the batteries drop below 46.0 V. The inverter 

will not delay after this low battery cut-off. In addition, a low-battery warning signal was set to trigger at 

a battery voltage of 46.6 V and below. From this test, the BAS panel in the Visitor Center on the UPS 

completely shutdown and recovered when power was restored to the system. 

The grid power was disconnected at 8:01:32 p.m. At 9:46:57 p.m., the inverter shut off, resulting in no 

emergency power. This time was 1:45:27 hours after the utility failure. During unoccupied hours, or 

when no solar radiation is available, this is enough time to operate the building and plan for an organized 

shutdown of computer equipment. Power was restored at approximately 10:18 p.m. The inverter started 

a few seconds later (10:18:06 p.m.) and restored power to the emergency panel. At 10:26:10 p.m., the 

pumps in the cooltowers were energized by the BAS. This equipment is on a delay start to prevent surges 

on power restoration. These pumps cycle on start-up, as needed, to provide water to the pads, resulting in 

fluctuations in power consumption. The total energy delivered by the UPS during power outage was 

3.028 kWh. Results from this test are shown in Figure 6-21. It is interesting to note the pattern of the 

voltage provided by the inverter and the variation of the utility power after the power was restored. 
84 

0

20

40

60

80

100

120

140

20:3020:4521:0021:1521:3021:4522:0022:1522:3022:4523:00

Time on 08/18/2001

Voltage (V)

0

500

1,000

1,500

2,000

2,500

Real Power (W)

RMS Voltage

RMS Power

Figure 6-21 Voltage and real power of emergency panel versus time for a utility grid 

power outage 

During February 2001 through May 2002, the building power was monitored to further verify the 

operation of the UPS system. Because of the unreliable power in the area, the power shut off many times. 

A couple of times, the UPS system was unable to maintain clean power. During the evaluation period, 

the grid disconnected 50 times for more than 0.5 seconds. If the grid shut down for less than 0.5 seconds, 

the scan rate on the BAS did not record the power failure. We believed that the panel had many split 

second disturbances, but it was unable to record the instances. The total time the grid was unavailable 

and the UPS system was functional during the evaluation period was 107.4 hours or 2.6% of the time. 

The UPS maintained power to the building and the BAS during all of these instances except two. 

The frequent outages are normally a quick disconnect and reconnect. For instance, on March 1, 2002, the 

power turned off and on 10 times in a 30-minute period with a typical outage ranging from 0.5 seconds to 

15 seconds. The power may have actually fluctuated more, but the resolution of the data logger was only 

0.5 seconds. The reason the UPS system did not catch a couple of the failures is still unknown. In these 

instances, the power was disconnected to the “E” panel for less than 0.5 seconds before battery power 

would be fed into the inverter. 

6.3 Lighting and Daylighting Evaluation 

6.3.1 Lighting and Daylighting Evaluation Methods 

The evaluation team performed the measurement segment of the Visitor Center daylighting analysis based 

on a monitoring protocol developed by the International Energy Agency Solar Heating and Cooling 

Programme (IEA/SHC) Task 21 (Atif 1997). This protocol offers guidelines for measuring daylighting 

performance, predicting performance, and evaluating control parameters. The performance measurement 

section of this protocol outlines recommended techniques for monitoring the daylighting contribution to 
85 

indoor illuminance and the corresponding electrical lighting displacement. These techniques include 

measurement of horizontal illuminance in selected daylit zones during varying sky conditions for typical 

summer, winter, and fall/spring seasons. Recommended illuminance levels for each lighting zone were 

analyzed in accordance with the Lighting Handbook of the Illuminating Engineering Society of North 

America (IESNA 2000). Simultaneous monitoring of external horizontal illuminance and electrical 

lighting consumption are required to complete the daylighting measurements. 

The goals of the daylighting evaluation were to: 

• determine the amount of electrical lighting offset by lighting design and daylighting when 

compared to a base case, 

• analyze the operation of lighting and daylighting controls and optimize their performance, 

• quantitatively and qualitatively assess the daylighting design, and 

• document successes and weaknesses of using daylighting as part of the lighting system. 

In accordance with the IEA/SHC Task 21 daylighting monitoring standards, we made short-term 

continuous measurements of illuminance at varying sky conditions for different seasons. These 

continuous measurements were performed in the ZNHA (Zion Natural History Association) bookstore 

area. The locations of illuminance measurements are shown in Figure 6-22. Illuminance was measured 

for 12 points on the top of the bookshelves at a height of 6 ft (1.82 m). Measurements were taken at 5-

second intervals and recorded as 5-minute averages. In addition, we also measured the outdoor 

illuminance (location 13). 

Because the protocol specifies that measurements be taken within 3 weeks of the beginning of each 

season, illuminance measurements were taken near the summer solstice (July 11–12, 2000), the fall 

equinox (September 20–22, 2000), and the winter solstice (December 14–16, 2000). The electric lights 

operated in the as-designed control scheme. 

In addition to continuous measurements, handheld measurements were made on a 10-ft (1.82 m) grid at a 

height of 48 in. (121.9 cm) over the interior of the Visitor Center. The locations of the handheld 

measurements are shown in Figure 6-22. The primary purpose for the handheld illuminance 

measurements was to determine discrete illuminance levels in lighting zones not considered by the 

continuous measurement system. The measurements were taken for varying sky conditions and times of 

day. 

The BAS measured electric lighting consumption from August 2000 to July 2003. The measured lighting 

energy consumption included all area and display lighting electricity used in the building and in the 

adjacent parking lot and sidewalks. End-use categories were measured as outdoor BAS controlled 

parking lot lights, indoor switch or motion controlled lights, and indoor BAS controlled space lights. The 

Comfort Station BAS controlled lighting consumption was measured as well, although a full daylighting 

analysis was not conducted in this building. 
86 

Figure 6-22 Continuous and handheld illuminance measurement locations 

6.3.2 Lighting and Daylighting Evaluation Results 

A principal metric in the evaluation of the lighting and daylighting systems is the energy consumption of 

these systems. The total installed interior and exterior lighting was responsible for 31% of the total site 

load, and consumed 28,957 kWh, or 8.4 kBtu/ft2

·yr (95 MJ/m2·yr). The outdoor and parking lot lights 

were responsible for 10% of the total lighting load for the site. These lights were in operation from dusk 

until 11:30 p.m. and from 5:30 a.m. to dawn. The building lighting end uses (Comfort Station and Visitor 

Center computer controlled, and Visitor Center switch controlled) used 26,157 kWh or 7.6 kBtu/ft2

·yr (86 

MJ/m2

·yr). In comparison, according to the CBECS database, the average lighting energy intensity for 

mercantile and service buildings was 23.4 kBtu/ft2

·yr (266 MJ/m2·yr), or 67% more than the measured 

lighting consumption. As a general lighting performance metric, this indicates high-performance lighting 

and daylighting design and operation. 

6.3.2.1 Calculated Energy Savings Resulting from Lighting and Daylighting Design 

To quantify the success of Zion’s lighting design coupled with daylighting, the evaluation team 

considered the conventional base-case building (the same base case discussed in previous sections). The 

base-case model predicts the indoor and outdoor lighting end use consumption in a conventional nondaylit building according to the Federal Energy Code 10 CFR 435. This code outlines upper limits for 

ZNHA Area 

Back Offices

NPS Counter 

1 

12

2 

4 3 

6 5 

11

10

13

8 7 

9 

• Numbered circles are continuous 

measurement locations 

• Dark gray unnumbered circles are 

handheld measurement locations 

recorded hourly. 

3 
87 

lighting power densities (LPD)4

 by zone type for federal buildings. The base case predicted that a 

conventional retail and display building would consume 107,781 kWh annually, or 31.4 kBtu/ft2

·yr (357 

MJ/m2

·yr), of total indoor and display lighting electricity. Every attempt was made to schedule the lights 

in the base case to estimate what the lighting load would have been without daylighting and occupancy 

controls, and with typical manual control. Atypical occupancy and manual control can provide a source 

of error in comparing measured lighting consumption to the simulated base case. 

Because the total lighting load for the base case and the actual building included 400 W of parking lot 

lighting not directly related to either building, the lighting savings without including the parking lot lights 

become relevant. In this case, the base case predicted that a conventional building would consume 

104,981 kWh in building-related lighting electricity. Compared to the measured indoor building annual 

lighting electricity consumption of 26,157 kWh, the building lighting loads were 75% less than a 

conventional building. These lighting consumption savings are attributed to improved lighting and 

daylighting design and operation, as ZNP incorporates a reduced LPD and daylighting design strategies 

with occupancy controls that are not included in the conventional base-case simulation. 

To investigate the savings from the reduced LPD, the evaluation team compared the base-case model, 

which included the LPD shown in Table 6-5, to a base-case model using the actual LPD. The only 

difference between the actual LPD base-case model and the code-compliant, base-case model was the 

difference in LPD as shown in Table 6-5. 

Table 6-5 Base-Case and Actual Lighting Power Density by Space 

Zone Base-Case LPD 

W/ft2 (W/m2)

Actual LPD 

W/ft2 (W/m2)

Percent 

Reduction 

Offices 1.4 

(15) 

0.96 

(10) 31.4% 

Retail and Display 2.2 

(24) 

0.90 

(9.7) 59.1% 

Comfort Station 1.0 

(11) 

1.00 

(10.8) 0.0% 

Outdoor and Parking Lot 400 W 400 W 0.0% 

When the actual LPD base-case model was simulated with the reduced LPD, the annual indoor lighting 

consumption was 52,130 kWh, which was 50% less than the code-compliant, base-case lighting upper 

limit. The reduced LPD resulted in the 50% lighting energy savings. The installed LPD is not as high as 

10 CFR 435 recommends because the lighting design accounts for a daylighting contribution during the 

day, includes efficient fluorescent lamps and ballast, and appropriate placement of task lighting. 

Nighttime illuminance levels can be a concern when the installed LPD is lower than the recommended 

levels, as the daylighting contribution is not available. To ensure that the LPD was not too low, the 

evaluators measured the quality of lighting and daylighting, which is discussed in the following sections 

and in Appendix F. 

A second type of lighting energy savings can be attributed to appropriate control of the installed 

luminaire. The Visitor Center and Comfort Station lighting control strategy involves multiple daylighting 

sensors combined with motion controlled switches. To evaluate the savings that accrue from the 

daylighting and occupancy control strategies, the measured building-related lighting consumption was 

compared to the base-case model with the actual LPD and no occupancy sensors or daylighting. The 

measured building lighting consumption was 50% less than the predicted actual LPD base case, as shown 

in Figure 6-23. NREL expected that occupancy sensors combined with daylighting controls would result 

in the displacement of 52,314 kWh of electrical lighting. 

 

4

 LPD refers to the installed lighting power per ft2 (m2). 
88 

Daily profiles of lighting consumption averaged over the year for the code-compliant base case, the actual 

LPD base case, and the measured consumption are shown in Figure 6-24. The 2.5 kW difference in peak 

morning consumption between the actual LPD base case and the measured lighting consumption is due to 

occupancy sensors only operating lights in occupied zones. 

0

20,000

40,000

60,000

80,000

100,000

120,000

10 CFR 435 LPD Base

Case

Actual LPD Base Case Measured

Annual Consumption (kWh)

Outdoor Lighting

Indoor Lighting

50% Savings 

Due to Lighting 

Design

75% Overall Indoor 

Savings Due to 

Lighting and 

Daylighting Design 

50% Savings 

Due to 

Daylighting 

Design

Figure 6-23 Lighting and daylighting design savings for indoor lighting 
89 

Figure 6-24 Measured, base case, and actual LPD annual lighting consumption 

profiles and savings (October 2001 to November 2002) 

6.3.2.2 Lighting and Daylighting Quality and Quantity 

The results of the continuous indoor retail and outdoor illuminance levels are shown in Figure 6-25 for 

typical days in each of the prescribed measurement periods. The south retail illuminance measurement is 

an average of measurement points in the bookstore next to the Trombe wall, while the north retail 

illuminance measurement is an average of the retail measurement points directly under the clerestory, as 

shown in Figure 6-22. As shown in the September and December measurements, the electrical lights are 

turned on for the cleaning staff at 6:00 a.m. As the outdoor illuminance levels increase, additional 

daylighting is provided to the space. Note that the daylighting contribution to the retail illuminance levels 

is greater in the winter than the summer, even with lower available outdoor illuminance. This difference 

is because the lower solar altitude angle in the winter results in better daylighting penetration into the 

retail area. Although not shown in Figure 6-25, direct solar penetration does result in glare during the fall 

and winter examples, which is not evident because the location of the continuous illuminance 

measurements. The overhang design typically blocks direct beam from entering the space in the summer, 

although early morning and late afternoon glare has been a problem. The early morning glare issue was 

due to the east clerestory windows. 

0

4

8

12

16

20

24

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Hour of the Day

Average Lighting Consumption (kW)

10 CFR 435 LPD Base Case

Actual LPD Base Case

Measured Total Site 
90 

0

100

200

300

400

500

600

700

800

900

1,000

5:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:00

5:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:00

5:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:00

July 12, 2000 September 22, 2000 December 16, 2000

Indoor Illuminance (Lux)

-250,000

-200,000

-150,000

-100,000

-50,000

0

50,000

100,000

150,000

200,000

250,000

Outdoor Illuminance (Lux)

South Retail Average

North Retail Average

Outdoor 

Early Morning 

Electrical Lighting 

Levels without 

Daylighting

Figure 6-25 Measured bookstore and outdoor illuminance levels, July 12, 2000; 

September 22, 2000; and December 16, 2000 

Examples of this glare problem are shown in Figure 6-26 and Figure 6-27. The first glare example shows 

excessive glare on the bookstore checkout counter and staff during an early morning in December. This 

was from direct solar gain through the clerestories. Due to the poor placement of the checkout stands 

with relation to direct solar gain, glare can overwhelm staff and customers. In the rest of the areas, direct 

solar gain and the resulting glare is not a problem. Occupants are not focused on a single area and any 

glare issues are compensated by occupant behavior (moving in/out of glare if it is a problem). Note that 

the location of the checkouts was not determined until just before occupancy, so provisions could not be 

made during the design phase. Glare and direct gain is acceptable in this space as long as people can 

control their location with respect to the glare. When the checkout counter glare was identified as a 

problem, direct solar gain through the clerestory was controlled using diffusing film placed on the 

clerestory glass. The diffusing film eliminated direct gain and the resulting glare. 

The second glare example, Figure 6-27, shows excessive direct solar gain in the southeast office on a 

December afternoon. This glare is the result of direct gain through the unshaded southern windows above 

the Trombe wall. The occupants typically utilize a temporary shading device (cardboard) when the glare 

is a problem. Adjustable blinds or diffusing film would provide a permanent glare management solution. 
91 

Figure 6-26 NPS bookstore checkout counter glare from clerestories 

Figure 6-27 Southeast office afternoon glare 

Figure 6-25 also shows illuminance measurements without a daylighting contribution. Nighttime 

illuminance levels at the continuous measurement location points in the bookstore are about 100 Lux. 

Figure 6-28 shows nighttime illuminance levels over the Visitor Center, taken from handheld illuminance 

measurements. 
92 

146 185

172

165

150

101

305 62 83 96

96

91 178

302 71

63

60 71

72 143

75

58

78 133

62

147 234 238

95

895

82

176

75

65 100

63

288

94

660

608

126

87

305

119

106

73

346

155

134

75

386

215

101

39

0

100

200

300

400

500

600

700

800

900

1,000

Illuminance (Lux)

Figure 6-28 Illuminance points over the floor plan from electrical lights without 

daylighting on July 10, 2000, 10:00 p.m. 

The 0.9 W/ft2 (9.9 W/m2) of installed electrical lighting in the retail area results in nighttime illuminance 

levels as shown in Figure 6-28. Low nighttime illuminance levels in the circulation spaces and in the 

retail spaces are evident. Areas directly under spotlights or display lighting are uncharacteristically 

higher than the general space lighting levels. The measured nighttime illuminance levels with all the 

lights on are lower than expected at 0.9 W/ft2 (9.9 W/m2

). The Illuminating Engineering Society of North 

America recommends luminance levels of 500 Lux in retail spaces (IESNA 2000). A primary reason for 

low nighttime illuminance levels is due to the uplighting design combined with tall, dark ceilings. The 

space lighting fixtures provide 88% uplighting, which is absorbed in the ceiling and dark beams, and 

limited amounts are reflected back to the space. 

The dark structural beams throughout the buildings were not considered when the daylighting features 

were designed. The dark beams absorb and block significant portions of the clerestory daylighting. This 

problem was identified during construction based on the proposed colors of the wood and the ceiling. 

The uplighting design and the daylighting would have functioned better if the ceilings had been a brighter 

color or a higher percentage of the light came from downlighting. 

The Visitor Center does not have visitors at night, so low electrical illuminance levels are adequate in this 

case. No complaints have been received for low light levels in the evening partly because of the contrast 

from the dark exterior to the interior of the building. People have adjusted to darker ambient conditions 

and seem to accept lower interior ambient levels. During the day, complaints have been received from 

bookstore staff as to the level of the lighting. This is in part due to the high exterior ambient lighting 

compared with inside. Part of the original intent was to use lower lighting levels in the building to make 

the space feel cooler compared to the bright, hot exterior. 

A sample of the quantity of daylighting under typical operation for a summer and winter period is shown 

in Figure 6-29 and Figure 6-30. Similar graphs of the illuminance levels due to daylighting with the 

lights turned off are included in Appendix F. Again, note the additional daylighting contribution in the 

winter months. The low illuminance levels in the summer led to installation of task lighting not 

connected to the daylighting controls, as illuminance levels were not adequate for detailed task work at 

the checkout stations. Task lighting in the form of linear T-5’s were installed over the cash register 

counters and the interpretation desks. This solution greatly reduced the issues of lower illuminance in the 

remainder of the space. The lighting levels in the bookstore were less than predicted because of reasons 

N 

Display Spot Light

Lighting 

ZNHA Area

NPS Counter 
93 

that were previously discussed. With additional task lighting, the low illuminance levels do seem to be 

adequate for this type of retail environment when augmented by the daylighting and appropriately located 

task lighting. The addition of these task lights significantly reduced the lighting issues. 

384

375

332 336

269 361 461

258

221 238

222 217 305 379

218

182

158 236

239

351

220

147

285

262

219

239 329 375

232

975

253

267

197

171 260 256

398

169

718

673

275

255

416

238

415

268

433

262 338

282

491

292

0

100

200

300

400

500

600

700

800

900

1,000

Illuminance (Lux)

Figure 6-29 Illuminance points across floor plan for a clear sky with lights on; July 

11, 2000 at 12:25 p.m. 

780

1180 1880 1370 1710 2280 1785

470

650

578

470

314

328

275

455

820

1640

885

456

317

390

103

280

187

275 326 386

318

185 205

355 384

370

340

261

572

195

725

653

281

250

380

135 240

285

395

168 257

458

518

195

0

100

200

300

400

500

600

700

800

900

1,000

Illuminance (Lux)

Figure 6-30 Illuminance points across floor plan for a partly cloudy sky with lights on 

as normal; December 14, 2000 at 12:15 p.m. 

The original daylighting analysis for the proposed building intended to have many more lights off, with 

daylighting significantly reducing the electrical lighting load. Although daylighting has reduced the 

lighting consumption compared to typical buildings that are not daylit, the success of the daylighting at 

Zion has been restricted due to several issues in the building’s design and implementation. Issues include 

the following: 

• The size of the specified clerestory visible glazing was not adequately communicated to the design 

team, reducing the daylighting from the clerestories. The frames, mullions, screens, and automation 

N 

N 

NPS Counter ZNHA Area

Display Spot Light

Lighting 

NPS Counter ZNHA Area
94 

mechanisms all reduce the amount of visible glazing in the clerestory windows and were not 

considered in the original daylighting design. This reduced the expected daylighting provided by the 

clerestories from the original design. It is important to specify the visible window area when 

transferring information from the energy consultant to the design team. It is also important to 

understand the impact of screens. 

• The dark structural beams throughout the buildings were not considered when the daylighting features 

were designed. These dark beams absorb and block significant portions of the clerestory daylighting 

and uplighting. (Daylighting is more effective with white ceilings.) 

• Stepped lighting controls work well as long as they are not in an area where detail work is occurring. 

Continuous task lighting would offset the on/off sequencing of the lights and provide additional 

lighting at critical locations. The stepped daylighting controls have been problematic, as the stepped 

control resulted in uneven distribution and occupant complaints of on-off sequencing. The design of 

the stepped operation called for every other fixture to be on a separate circuit. What was installed 

was every other row on a separate circuit, which resulted in uneven distribution during stepped 

control operation. Continuously dimming fixtures would allow for even distribution of the electric 

lights, resulting in further reduction of lighting consumption. 

Continuous monitoring of the lighting and daylighting systems have identified and addressed several 

problems. Clerestory glare problems were addressed with diffusing films, and adjustable blinds 

recommended for occasional glare in the offices. We added additional task lighting in critical areas, as 

the stepped controls, uplighting, and daylighting did not provide adequate illuminance levels for detailed 

work. Appropriate placement and use of occupant controlled task lighting is essential for daylit buildings 

with reduced LPD, especially for detailed task work. 

6.4 Comfort Evaluation 

6.4.1 Comfort Monitoring Methods 

A comfort analysis was performed to determine the ability of the energy-efficient heating and cooling 

systems to provide adequate comfort to building occupants. Ultimately, an energy-efficient HVAC 

system should maintain occupant comfort while minimizing energy costs. The Visitor Center and 

Comfort Station are monitored and controlled separately. Temperature measurement points in the Visitor 

Center consist of twelve temperature sensors located on the walls and three sensors located on the ceiling. 

Layout of the temperature sensors can be seen in Figure 6-31. The Visitor Center is organized in three 

main zones: the ZNHA Office, the NPS Counter, and the Back Offices. The BAS calculates the average 

temperature of these three zones and records the values. The BAS controls the spaces based on these 

temperatures. The Comfort Station has six temperature sensors total. The BAS averages all values in the 

Comfort Station and determines the appropriate actions needed to maintain comfort. 
95 

Figure 6-31 Layout of temperature sensors for Visitor Center 

For the comfort analysis, the Visitor Center was categorized into three different areas the ZNHA Area, 

NPS Counter, and the Back Offices. The zones for the areas are listed in Table 6-6. 

Table 6-6 Visitor Center Area Definitions 

Area Zone Temperature Sensor 

ZNHA Area 8,9,10,11,12 

NPS Counter 6,13 

Back Offices 1,2,3,4,5,7,14,15

For the analysis, the winter was defined as October 1 through April 30, while summer was from May 1 

through September 30. The occupied hours were defined from 8 a.m. to 5 p.m. 

6.4.2 Comfort Monitoring Results 

The outdoor temperatures for the winter of 2002–2003 were slightly higher than the temperatures for the 

winter of 2001–2002 (Section 6). In general, during the winter, the occupants were considered 

Zone Temperature Sensor 

Zone Temperature Sensor at Clerestory Ceiling

ZNHA Area 

Back Offices 

NPS Counter

ZN9 

ZN8

ZN7

ZN13

ZN15

ZN11

ZN10

ZN5

ZN6 

ZN4

ZN1 ZN2

ZN3

ZN14

ZN12

ZN# 

ZN# 
96 

comfortable because the occupants had control of the heating set point up to 74°F (23.3°C). During 

2002–2003, the temperatures were slightly cooler indoors partially due to a lower heating set point. 

Figure 6-32 shows the hours at the given temperature for the average Visitor Center temperature. 

0

50

100

150

200

250

300

350

400

450

60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

Temperature (°F)

Hours

2001-2002 NPS/ZNHA Average

2002-2003 NPS/ZNHA Average

Mean (2001-2002) = 69.4°F

StdDev (2001-2002) = 2.51°F

Mean (2002-2003) = 68.0°F

StdDev (2002-2003) = 2.35°F 

During Occupied Hours

Figure 6-32 Histogram of winter average temperature in the Visitor Center 

The temperatures below 65°F (18.3°C) typically occurred before noon; however there were a few days in 

2001 when the temperatures were below 65°F (18.3°C) all day. It is unknown why the temperatures were 

low, but it is assumed that the occupants could have increased the temperature if they were 

uncomfortable. 

Appendix E also contains histograms for the other zones during the winter along with a psychrometric 

plot. 

The average interior temperature of the Visitor Center during the summer of 2002 was slightly warmer 

than the summer of 2001 (see Figure 6-33). The average temperatures were collected in 15-minute 

intervals while the building was occupied. Figure 6-33 shows the number of hours at specific average 

temperatures for the Visitor Center. During 2001, the temperature was greater than 78°F (25.6°C), only 

2.6% of the hours. This percentage increased slightly to 3.7% during 2002. It is believed that during 

2002, the average temperature was slightly warmer mainly because of the warmer outdoor temperatures 

and partially because of the increased ventilation to the back offices. 
97 

0

50

100

150

200

250

300

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

Temperature (°F)

Hours

2001 NPS/ZNHA Average

2002 NPS/ZNHA Average

Mean (2001) = 72.3°F

StdDev (2001) = 2.62°F

Mean (2002) = 73.0°F

StdDev (2002) = 2.63°F 

During Occupied Hours

Figure 6-33 Histogram of hours at average temperature in the Visitor Center during 

summer 

There were several problems cooling two of the zones in the Visitor Center. These zones (Zone 2 and 

Zone 7) are offices located next to the Trombe wall. Both zones experienced the same overheating 

problems in the summer. This is partially due to the Trombe wall providing heat to the space. Although 

the Trombe walls are shaded during the summer, some diffuse solar gains transmit through the Trombe 

wall and add heat to the space. Overheating this area was compounded by the lack of ventilation of the 

enclosed offices. In addition, occupants typically do not use the operable windows even when outdoor 

conditions are favorable. 

During 2001, the temperatures in Zone 2 were unacceptable and action was needed to correct the 

situation. Figure 6-34 shows temperatures for Zone 2. During the winter of 2001–2002, small circulation 

fans were placed in the adjacent space and a door louver was installed to allow air to freely enter the 

space. This seemed to work effectively, as the average temperature in Zone 2 was decreased by 1.5°F 

(0.8°C) along with a smaller standard deviation compared to the summer of 2001 to 2002. 
98 

0

50

100

150

200

250

300

65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

Temperature (°F)

Hours

2001 Zone 2

2002 Zone 2

Mean (2001) = 79.4°F

StdDev (2001) = 3.90°F

Mean (2002) = 77.9°F

StdDev (2002) = 2.85°F 

During Occupied Hours

Figure 6-34 Visitor Center Zone 2 comfort histogram during summer 

Zone 7 had a similar situation. Zone 7 is the bookstore office also located next to the Trombe wall. A 

small, unconditioned stock room is next to the office. This storeroom often overheats due to dark brown 

double doors that collect heat during the morning. The internal temperature of the door radiates to the 

occupants working in the storeroom, as shown in Figure 6-35 and Figure 6-36. The metal doors could not 

simply be painted white because the exterior coloring of the building had to follow NPS standards, which 

is dark brown. To help cool these two zones, several small fans were installed along the floor vents to 

help with ventilation. These were installed at the end of 2001. Operating these fans provided additional 

cooling to the storeroom and office. However, it has not completely alleviated the problem. 
99 

0

20

40

60

80

100

120

140

160

00:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 18:00 20:00 22:00 00:00

Time of Day

Temperature (oF)

Outdoor Temperature

Temperature on Outer Surface

Temperature on Inner Surface

Figure 6-35 Zone 7 exterior door temperatures averaged over October 8, through 

October 19, 2001 

85.0°F

149.0°F

100

120

140

Figure 6-36 Infrared picture of the interior door in Zone 7, August 18, 2001 12:35 p.m. 
100 

6.5 Comfort Station Energy Evaluation 

The Comfort Station at ZNP is responsible for 15% of the total energy used at the Visitor Center 

Complex. The building uses 17.6 kBtu/ft2

·yr (200 MJ/m2·yr) of site energy, with heavy traffic during 

summer months. The building used 14,230 kWh. The energy use for the Comfort Station divided into 

each month is shown in Figure 6-37. 

0

10

20

30

40

50

60

Nov-01Dec-01

Jan-02

Feb-02Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Site Energy Consumption (kWh/day)

DHW

Cooling and Fans

Heating

Lighting

Plug Loads

Figure 6-37 Comfort Station end use monthly consumption per day, November 2001 

through October 2002 

The majority of the energy used in the Comfort Station was for lighting and plug loads. The Comfort 

Station lighting loads contain continuously charging back-up batteries that draw about 300 W for 

emergency lighting. 

The heating and cooling systems in the Comfort Station are similar to the systems in the Visitor Center. 

The Comfort Station uses a single cooltower for cooling. Heat from the radiant panels augments the 

Trombe wall heat to maintain set point temperatures. The designed comfort region for the Comfort 

Station was to maintain the facility between 55°F and 80°F (13–27°C) year round. 

The hot water in the Comfort Station is primarily used to clean the restrooms. As a result, hot water is 

provided to all sinks, but it is not an issue if there is not enough capacity. The peak visitor season is in the 

summer. During the winter, half of the restroom area is closed to save energy and cleaning costs. See 

Figure 4-4 for closed sections. 

Most of the heat for the Comfort Station is provided by the Trombe wall, except for the family restroom, 

because it does not have a southern exposed wall. The temperature histogram for the Comfort Station is 

seen in Figure 6-38. The graphs shows that the Comfort Station is maintained within the set point limits 

during the entire winter. The building overheated a few hours during the winter. 
101 

0

50

100

150

200

250

300

350

400

50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

Temperature (°F)

Hours

Winter 2001 - 2002

Winter 2002 - 2003

Mean (2001-2002) = 61.9°F

StdDev (2001-2002) = 5.87°F

Mean (2002-2003) = 60.9°F

StdDev (2002-2003) = 3.13°F 

Figure 6-38 Histogram of hours at average temperature in the Comfort Station during 

winter 

During the summer, the cooltower provides a reasonable temperature in the Comfort Station (see 

Figure 6-39). The temperatures in 2002 were much cooler than 2001. There was no design limit on the 

summer temperature. Eighteen percent of the hours in 2001 were above 80°F (27°C), while in 2002, 

there were no above hours above 80°F (27°C). 

0

50

100

150

200

250

300

350

400

450

500

60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90

Temperature (°F)

Hours

Summer 2001

Summer 2002

Mean (2001-2002) = 75.4°F

StdDev (2001-2002) = 3.77°F

Mean (2002-2003) = 72.5°F

StdDev (2002-2003) = 3.24°F 

Figure 6-39 Histogram of hours at average temperatures in the Comfort Station 

during summer 
102 

7 Recommendations 

We derived the recommendations listed below from lessons learned during the project. They are intended 

to assist designers for future projects. 

7.1 Low-Energy Design Process 

This section discusses recommendations developed from evaluating the process used to deliver lowenergy commercial buildings. 

Recommendation # 1: Set energy performance goals and remain committed to 

achieving them throughout the design process. 

Creating buildings with low-energy architecture requires the setting of clear, measurable energy 

performance goals and tracking progress toward that goal. Goals provide an energy saving target to 

achieve and a value to compare energy performance. For this project, an energy-cost saving goal of 70% 

(compared to minimum code) was adopted early in the design process (computer simulations showed that 

an energy saving goal of 80% was achievable). However, actual measured data indicated that the 

building energy cost saving was 67% because some construction and design changes were made before 

NREL could perform energy simulations to determine the energy impact of the changes. Nonetheless, by 

setting a high energy saving goal, remarkable savings were still achieved. 

Recommendation # 1A: Use the architectural design and envelope of the building to 

save energy and enhance comfort. 

Form, shading, daylighting, choice of materials, sizing, orientation, and specification of glass all have a 

major impact on building energy, lighting, and comfort performance. Use the mechanical system to make 

up for what cannot be accomplished by architecture and envelope alone, not to correct for an architectural 

design that is climatically ill conceived. 

Recommendation # 2: Apply a process that fosters a team approach to integrated 

design. 

It is important to involve the entire design team throughout the design process to reveal potential energy 

saving opportunities and to get a whole-team decision. By involving the whole design team from the 

predesign stage, team members that ordinarily are not involved until later can identify ways to improve 

the design before the building is constructed. Follow-up evaluations showed that participants in the 

Visitor Center Complex project agreed that the project benefited from the process adopted. Specifically, 

integrating the energy analyst directly into the process to guide architectural decisions created a building 

that worked well with the energy decisions. 

Recommendation # 3: Update energy models as design development progresses. 

There were important changes to the design and siting of the Visitor Center that occurred late in the 

design development stage. Changes to the orientation and location of offices reduced the energy 

performance of the building. For example, offices were located adjacent to the Trombe wall and far from 

the cooltowers, which led to comfort problems. Had each design change been reanalyzed with detailed 

simulations and updated zoning, the comfort problems may have been predicted and corrected (e.g., by 

adding back into design the cooltowers that had been removed or moving the offices). It is critical to 

maintain the simulations from predesign through occupancy. 

Recommendation # 3A: Watch out for “Transparency Creep” 

Glass has a very strong impact on energy, comfort, and lighting performance. These impacts can be 

positive or negative depending on many factors. Simulations allow us to optimize glass optical and 
103 

thermal properties, sizing, orientation, placement, and shading. Additional glass is often added because 

of trying to achieve transparency of the building. The additional glass really does not provide 

transparency of the building because of the strong exterior contrast from the sun. The result is that the 

building is not transparent even with lots of glass. This building is overglazed on the north façade. 

Recommendation # 4: Review architectural program with concern for energy 

performance. 

Altering the architectural program to move interpretive displays to an outside patio reduced the size of the 

building, resulting in enormous savings in first cost and overall energy use. Besides space area needs, 

establishing individual comfort ranges for the buildings and allowing for interruptible hot water further 

improved the building’s energy efficiency. It is beneficial to identify areas where generally accepted 

design criteria may be replaced with creative energy saving solutions that meet or exceed the functional 

requirements of the building. 

7.2 Visitor Center Complex Systems 

Several lessons were learned after construction and during initial occupancy about the performance of the 

following systems: demand responsive controls, cooltowers, Trombe walls, electric heating, lighting and 

daylighting systems, and the solar-electric system. 

7.2.1 Demand Responsive Controls 

This section presents recommendations developed from experiences implementing control strategies in 

the BAS that attempt to reduce the peak draw of electricity over a 15-minute period in any given billing 

cycle. 

Recommendation # 5: Develop stable demand controllers and strategies. 

Demand controlling for the Visitor Center Complex worked well in aggregate, but we found that isolated 

failure events lasting more than 15 minutes could instigate an excessive demand charge for that month. 

Software routines and hardware need to be reliable and default to appropriate settings after a system 

failure so that system resets are rare and not problematic. By the end of the monitoring period, the 

software was robust and provided good demand management. As with any system, improvements can 

still be made. 

Recommendation # 6: Include forecasted weather data in demand responsive controls. 

Experience with the Visitor Center Complex suggests that better performance could be obtained if 

forecasted data were used in addition to historic data in the demand control algorithms. Weather forecasts 

are readily available and can be used to make control decisions. 

Recommendation # 7: Investigate using short-term battery storage to offset peak 

demands. 

Although the existing battery storage at the Visitor Center Complex is probably not sufficient, the 

presence of all the needed components suggests that demand could be offset by using UPS systems. To 

do this, the inverter must be able to communicate with the BAS. 

Recommendation # 8: Reevaluate thermostat setup/setback strategies. 

High-thermal-mass buildings such as those in the Visitor Center Complex may show increased demand 

charges because of nighttime setback of the thermostats. Analysis should be performed to better 
104 

understand the interactions between energy use and demand charges in order to determine optimal setback 

strategies. 

Recommendation # 9: If PV is to be included in a project, use building energy simulation 

programs that model PV with demand interactions. 

Experience with Visitor Center Complex called attention to the need to model demand controlling and 

interactions with PV generation. The lack of modeling prevents researchers from determining the full 

effectiveness of the current demand control strategies. Using a building simulation program that includes 

PV will allow for analysis on demand responsive controls and integrated cost analysis. Simulation 

programs also need to have the ability to study demand-limiting controls. 

Recommendation # 10: Use EnergyStar® enabled computers and flat screen monitors. 

Parasitic loads are a problem in commercial buildings. Part of this load is idle computers. Energy 

savings can be realized by making the machines EnergyStar enabled to shut them down during periods of 

inactivity. Flat screen monitors should also be used for added energy savings. 

7.2.2 Trombe Walls 

This section provides recommendations related to the Trombe walls located along the south walls of the 

Visitor Center and Comfort Station. 

Recommendation # 11: Consider Trombe walls for passive heating of commercial 

buildings. 

Trombe walls were effective in providing a significant portion of the heating. It is clear that this building 

is heating dominated. Passive solar heating of commercial buildings has not been used very often 

because conventional wisdom indicates that such buildings need little heating. However, low-energy 

commercial buildings tend to require more heating because of reduced internal gains. 

Recommendation # 12: Provide effective shading and/or active control for Trombe walls 

during the cooling season. 

The Trombe wall with its overhang was effective in maximizing the heat gains in the winter. However, 

although reduced, the diffuse solar component still partially heats the wall in the summer when the heat is 

not desired (see Section 6.1.2). This problem was compounded by limited cooling capacities in the 

offices that were against the Trombe wall. Movable exterior shades are one possible means of mitigating 

unwanted heat during the cooling season. The walls should have been resized to better match the heating 

loads for these spaces. 

7.2.3 Electric Heating 

This section discusses recommendations related to the use of electric heat. 

Recommendation # 13: Consider electric radiant heating. 

An electric radiant heating system was used in the current project because it offered several advantages. 

The Visitor Center Complex’s buildings do not require a lot of heat and a ducted air system was not used 

for cooling. Therefore, it was considered too costly and complex to add a mechanical air system and the 

associated ductwork for a small amount of heating. We arranged electric radiant heaters to direct heat at 

the locations where staff would spend the most time. Results show that occupants allowed lower 

thermostat temperature set points; these results are most likely because the radiant heating can provide 

comfort at lower dry-bulb temperatures. Electric radiant heaters also allow for a more cost-effective and 
105 

precise temperature control because many thermal zones can be created. Although the electric heaters 

contribute to demand charges, they are simple to control. The cost of propane and transportation were 

key considerations in the creation of an all-electric building. The key is heating the building without 

incurring additional demand charges. Note that this decision is highly dependent on the metrics used to 

measure success. The solution was successful from a cost basis, but it is not as favorable on a source 

energy basis. 

Recommendation # 14: Consider air-source heat pump heating. 

Although the electric radiant panels have been successful, it may have been appropriate to install a small 

air-to-air heat pump to provide some heating with electricity. A unitary system located on the north side 

of the building (away from the Trombe walls) would probably have been a good choice. An air-source 

heat pump can provide COPs between about 1.0 and 3.0, depending on outside air temperatures, whereas 

electric resistance always has a COP of 1.0. 

7.2.4 Cooltowers 

This section lists recommendations related to the cooltowers. These architectural features combine direct 

evaporative cooling with natural ventilation. The cooltowers work well to provide cooling to the main 

area of the Visitor Center. Visitors find the towers fascinating and give them the type of attention often 

given to large fireplaces in public areas. The interaction of the visitors with the cooling system provides 

an amenity that normally would not be achieved with a traditional cooling system. This was not 

expected—that visitors would place value on the cooling system as an amenity for the building. 

Recommendation # 15: Provide multiple opportunities for passive airflow. 

As a special class of passive natural ventilation, the use of cooltowers requires careful design of interior 

partitions and fenestration to promote good circulation of cooled air. The enclosed offices in the building 

tend to overheat due to insufficient airflow and continual heat gains from the Trombe wall. Exhaust fans 

originally installed in the office area were not sufficient to move air through these spaces to counteract the 

heat gains from Trombe walls. As with many passive systems, moving air mechanically should be 

avoided. The Trombe wall is shaded in the summer, but the diffuse component of the solar radiation still 

heats the wall. In the initial building design, the Trombe walls were to be adjacent to open spaces, not the 

enclosed offices. Late in the design process, the interior layout of the building was changed to place 

enclosed offices on the south side of the building adjacent to the Trombe walls. Even in the winter, this 

Trombe wall provides more heat than needed to the office spaces. As a result, circulation fans were 

installed between the public and private spaces to help induce additional air flow. These fans improved 

the comfort of the office spaces; however, they also increased the fan energy use and noise, which is to be 

avoided in passive cooling and heating. 

Recommendation # 16: Use dampers on automatic controls rather than operable 

fenestration for natural ventilation. 

Operable windows are an important part of the natural ventilation system in the Visitor Center. Windows 

located near the ground are operated manually while clerestory windows are on automated actuators. 

Experience showed that occupants did a poor job of operating the manual windows. In addition, the 

motorized window actuators were prone to failure and were difficult to interface with th e BAS. 

Furthermore, the windows did not open much and the window screens reduced the effective opening. 

One suggestion is to separate the ventilation from the fenestration and use relief dampers for the passive 

ventilation. This would also increase the fenestration area and help with the daylighting. The control 

actuators would be typical HVAC controllers, reducing maintenance and integration issues. 
106 

Recommendation # 17: Provide solar shading of cooltower media. 

No shading was designed into the cooltowers to shade the media from direct exposure to sunlight. 

Although the consequences were not quantified, researchers suspect that solar shading would reduce 

water consumption. Reducing UV degradation of the exterior media surface is another advantage of 

shading as well as the visible dissolved solids that accumulate on the exterior of the surface. 

Recommendation # 18: Size sump pits to hold all the water in the system. 

To avoid wasting water, systems should be sized to avoid overflows. The Visitor Center Complex 

cooltowers include a sump pit that was not sized large enough to hold all the in-transit water. The 

installed sump pit has a 20-gallon (76 liter) capacity. The trays and media, when wetted, hold about 20–

30 gallons (76–114 liters) of water, which makes it possible for about 10–15 gallons (38–57 liters) of 

water to overflow the drain when the pump cycles off. This water is made up with fresh water when the 

pumps turn back on. 

Recommendation # 19: Consider using inlet scoops and/or louvers at the top of 

cooltowers. 

Although it cannot be determined from the current data, there are several possible mechanisms for 

moisture to be entrained into the air passing by the tower and transported away from the tower without 

providing cooling to the building. Better control of how winds interact with the openings of the 

cooltower may alleviate water waste and improve air circulation. Installing inlet louvers on the outside of 

the evaporative media may channel air straight into the tower and prevent air passing adjacent to the 

towers (but not entering tower) from coming into direct contact with the wetted exterior surface. Such 

louvers may also provide solar shading. The change could also enhance passive natural ventilation. 

Modeling should be done to determine if there are advantages to only using windward pads to coincide 

with the prevailing winds in the canyon. 

Recommendation # 20: Ensure that the plumbing system for the cooltowers is robust. 

Ensure that the plumbing system for the cooltowers is robust. The initial plan was changed after the first 

few weeks of operation to allow for additional drain flows and better fresh-water inlet control. Drains 

were poorly detailed and undersized resulting in overflows. 

Recommendation # 21: Detail water circulation system to handle air-borne debris. 

In the Visitor Center Complex cooltowers, the trays that collect water extend about 1.5 in. (3.8 cm) 

beyond the cooling media. Leaves are caught in the trays and then migrate past the cooling media at the 

corners and enter the water circulation system. The bleed valve has clogged on occasion because of 

leaves getting into the system. Although improved details may reduce the debris, the water circulation 

system needs to be robust enough to handle it. 

Recommendation # 22: Consider wind loads on cooltower components. 

The open, upper area of the towers is continuously exposed to wind. The water distribution components 

that wet the cooling media were not designed appropriately, causing the high winds to occasionally shift 

the water spraying components so that water misses the media. The distribution system for the water 

needs to be redesigned to be robust. 

Recommendation # 23: Detail inside of cooltower as if it were exterior facade. 

The inside walls of the cooltowers should be considered exterior to prevent water damage because they 

are constantly exposed to moist air. The interiors of the cooltowers were lined with drywall. As a result, 

they have had moderate damage (i.e, pealing paint) due to the high humidity, occasional water sprays 
107 

(high wind conditions), and improperly flashed or sealed tower tops. Rainwater can work its way onto 

the sills, seep between the bottom of the cooling media frames, and run down the inside of the wall. A 

suggestion is to build the towers from masonry block, rather than tubular steel. 

7.2.5 Lighting and Daylighting Systems 

This section discusses recommendations related to the lighting and daylighting systems in the Visitor 

Center Complex. Daylighting was significantly less than originally predicted. 

Recommendation # 24: Provide high reflectivity finishes to spaces that are daylit or 

have indirect light fixtures. 

Instead of NREL’s recommended white ceiling, a light-color pine, tongue-and-groove ceiling was 

installed in the Visitor Center. Designers intentionally chose the white ceiling to incorporate diffuse light 

in the space to reflect the lighting characteristics within the narrow slot canyon of ZNP, keep direct solar 

heat gain to a minimum, and make the building interior psychologically cooler. The darker ceiling that 

was installed appears to have decreased the daylighting effectiveness in the space. This decreased 

effectiveness is compounded by the use of 88% uplighting fixtures with the low reflectance ceiling. 

Recommendation # 25: Account for window screens, attachments, and actual view area 

in daylighting analyses. 

Experience with the Visitor Center suggests significant reductions in daylight entering fenestration 

because of screens, reduced window view area due to mullion thickness, and shading deployed to reduce 

glare problems. It is essential during the design phase to size the fenestration based on glass area and not 

the opening area, which would include the impact of the frame and screens. 

Recommendation # 26: Account for structural elements in daylighting analyses. 

Predictions related to daylighting during design development neglected the structural beams. The interior 

of the Visitor Center has a large number of dark-colored wood beams and researchers have determined 

that these contributed to the poorer-than-expected daylighting performance. Indirect lighting fixtures 

were installed level to the horizontal beams in the space, some distance below the ceiling. This also made 

the uplighting fixtures not as efficient as intended. This is an extension of the Recommendation #3 for 

using simulations throughout the design process to assess architectural finishes. 

Recommendation # 27: Provide lighting controls that dim in response to natural daylight. 

The lighting controls in the Visitor Center Complex are stepped controls. When the electric lights switch 

on or off, the occupants tend to be distracted. Dimming controls were added to minimize distractions 

from the cycling of lights. The dimming system can still be turned off. 

Recommendation # 28: Provide task lighting to augment daylighting. 

The absence of task lighting further decreased the effectiveness of the daylighting system because 

occupants required more use of overhead lighting to maintain sufficient lighting levels in work areas. 

Task lighting was installed in these areas after the building was occupied. Use of task lighting permitted 

building operators to decrease the ambient lighting threshold that controls the electric lighting. A similar 

problem existed in the Comfort Station where additional lighting was needed over the sinks. After 

occupancy, more lighting was provided over the sinks and the general lighting level could then be 

decreased. During the design phase, high priority areas should be identified for possible task lighting or 

increased daylighting. Tubular daylighting devices could have provided necessary lighting over the sink 

area in the Comfort Station. 
108 

Recommendation # 29: Consider separate emergency lighting. 

Fixtures with integral backup ballasts were selected for the Comfort Station. These back-up batteries 

draw 300 W even when the light fixtures are off. The Visitor Center used wall packs to achieve the same 

effect at a fraction of the power consumption. Lower power, self-contained wall pack light assemblies 

would have been a better choice and would have reduced the parasitic load. 

Recommendation # 30: Consider special controls for cleaning. 

Cleaning commercial buildings requires ample light and special control modes that accommodate 

cleaning crews should be considered. A cleaning override switch for the Comfort Station was successful. 

This switch enables the lights through the BAS for cleaning. When the cleaning crews leaves, the switch 

can be turned off to return to daylighting control. If the switch is not shut off, the BAS will return to the 

daylighting control scheme after 90 minutes. 

Recommendation # 31: Install easy to use switches for lighting controls. 

The main building lighting was controlled with an occupied/unoccupied button on the thermostat. It was 

difficult to train staff to use this control device for lighting. As a result, the system was programmed to 

turn on the lights at a set time each morning and to sequence down in the evening. User interfaces are 

critical for success of the BAS. It would have been better to provide an input resembling a traditional 

light switch. There has been some success in using the lighting control late in the project, allowing NPS 

staff to change the occupied time from 6:00 a.m. to 7:00 a.m. The impact of the user interface cannot be 

underestimated. 

Recommendation # 32: Reduce the lighting in the Comfort Station. 

The Comfort Station was overlit on both the LPD and the lighting intensity. Some fixtures could be 

eliminated, saving maintenance and energy costs. 

Recommendation # 33: Minimize the number of motion/occupancy sensors. 

The original plan had several motion sensors in the Comfort Station on the same lighting control, making 

it difficult to identify a single failed sensor. It is easiest to have a one-to-one correspondence between the 

sensors and the fixtures. The design was changed to just have one sensor in each half of the restroom 

with a 20-minute delay. This has worked well. In addition, at night, when occupancy is low, the sensor 

only turns lights on above the sink and in the hallway to minimize the glare and the contrast between 

inside and outside. 

7.2.6 PV and UPS System 

This section provides recommendations related to the PV and UPS systems. 

Recommendation # 34: Consider specifications for how a PV-based UPS system 

transitions to and from utility power. 

The reliability of electrical utility power at ZNP is poor, especially during the summer thunderstorm 

season. Sometimes power failures are not abrupt but include frequent cycling. For example, in one case, 

the power turned on and off 40 times in less than 5 seconds before disconnecting. Because of this, the 

main UPS system has had difficulties determining when to disconnect from and reconnect to the utility 

power. The reliability of the PV system itself has been excellent, but its use as a UPS has not been 

satisfactory. As a result, some smaller, self-contained UPS systems were installed on critical devices. 

Future efforts to use PV systems for building-wide UPS should carefully investigate how the equipment 

responds to the types of power failures the building is likely to experience. 
109 

Recommendation # 35: Plan for future addition of PV. 

Experience with the Visitor Center Complex project showed that designing a building to be ready for the 

future addition of a PV system could add value. Although funds for a PV system were not originally 

available, the Visitor Center was configured for such a system, making it simple to install once funds 

were available. Although some buildings may never have the need for PV, those that do may benefit 

from roof angles and orientation designed for future installation of a PV system, including pre-installing 

conduit, roof penetrations, and anchoring points. 

Recommendation # 36: Install PV panels where they will not be shaded. 

PV panels should be located where they will not be shaded. The annual performance of the Visitor 

Center PV system is degraded by 7% because a tree partially shades the west set of modules late in the 

afternoon. Another option would be to remove the tree that is causing the shading. It is essential to 

understand the interactions between nature shading the PV panels and the environmental benefits of 

having additional PV production. 

Recommendation # 37: Install maximum power-point tracking controllers for PV. 

A maximum power-point tracking voltage controller would increase performance of the Visitor Center 

PV system by 16% as compared to the fixed operating voltage control of 53.6 VDC. 

7.3 Commissioning 

Recommendation # 38: Plan for continuous commissioning. 

Experience with the Visitor Center Complex confirms that continuous commissioning efforts are required 

to achieve and maintain low-energy buildings. Despite the inevitable problems, the lack of mechanical 

systems made the Visitor Center Complex relatively simple to commission. A partial list of findings 

during normal commissioning includes: clerestory glare, lack of appropriate task lighting, bathroom 

exhaust fan was blocked, PV system had various problems, operable cooltower doors and clerestory 

windows were difficult to interface with the BAS. Continuous commissioning was found to further 

improve the energy performance. The evaluator’s continuous postoccupancy monitoring, analysis, and 

improvements over many years have helped to realize a low-energy building. 

7.4 Postoccupancy Research Methods 

This section discusses recommendations for researchers engaged in similar postoccupancy studies. 

Recommendation # 39: Use dedicated, self-contained data acquisition equipment for 

monitoring energy performance. 

This study used the BAS to collect data on the performance. This method was found to be problematic 

and should be avoided. With current BAS and energy management systems, there appears to be a low 

probability of obtaining contiguous, error-free, measured data sets over a long period. A better solution is 

to use dedicated, self-contained data acquisitions systems designed for unattended remote operation that 

do not use operating systems designed for personal computers. 

Recommendation # 40: Provide researchers studying a particular building with direct 

access to the BAS. 

In the Visitor Center Complex project, researchers had access to and control of the BAS, which was 

helpful to understand and influence how the building was being controlled. Researchers were able to 

improve energy management strategies such as implementing and testing various demand responsive 
110 

strategies. Access to the BAS allowed us to reduce the demand charges to the building and facilitated 

continuous commissioning activities. Another advantage of BAS access and control is having a full 

understanding of the various set points and control strategies to use as inputs into building energy 

simulation. 

Recommendation # 41: Determine whole-building energy savings with as-built and 

base-case model comparisons. 

Ideally, the base-case site energy use, source energy use, and energy costs would be compared to an 

as-built model to calculate savings for a typical weather year. Energy savings uncertainties can be 

minimized when savings are determined from the comparison of one simulation to another simulation 

(e.g. base case to as-built). Because difficult-to-know inputs are held the same in both simulations, such 

comparisons remove much of the uncertainty inherent in an hourly building energy simulation. Variables 

that change throughout the year, such as inconsistent occupancy, set point changes, and equipment 

performance degradation, are difficult to account for in an annual building energy simulation. By 

comparing a base-case model to an as-built model with the same schedules, the uncertainty caused by 

these inconsistent variables is reduced. In the analysis of Zion, an as-built model of the Zion Visitor 

Center and Comfort Station was beyond the scope of this analysis due to limitations in the whole-building 

simulation tools. These limitations include nonexistent building integrated modeling techniques for the 

energy use and cooling capacity of cooltowers, difficulties modeling the as-built operation of subhourly 

demand limiting controls with integrated PV production, and uncertainties with Trombe wall thermal 

models. We attempted to account for the inherent uncertainty involved in comparing measured data to a 

simulation by calibrating the base-case model with measured weather data, measured equipment loads, 

and operation schedules. 
111 

8 Conclusions 

The Visitor Center Complex opened in May 2000 and includes an 8,800-ft2 (818-m2) Visitor Center (with 

interpretative displays, offices, and retail space for the ZNHA), a 2,756-ft2

 (256-m2) Comfort Station 

(with restrooms), and a 170-ft2 (15.8-m2) entrance Fee Station. The building was evaluated by comparing 

the measured energy use to the energy use of a simulated model. The major results of the performance 

are presented below and are divided into whole-building performance (both measured and simulated), PV 

performance, lessons learned, and future research. 

8.1 Measured Whole-building Performance 

From November 2001 through October 2002, the annual energy costs for the Visitor Center Complex 

were $5,094/yr or $0.43/ft2

·yr ($4.63/m2), net site energy use was 85,000 kWh/yr or 24.7 kBtu/ft2·yr (281 

MJ/m2

·yr), and source energy intensity was 80 kBtu/ft2·yr (909 MJ/m2·yr). The average daily energy use 

is presented in Figure 8-1. Table 8-1 summaries the energy use during the evaluation. 

0

50

100

150

200

250

300

350

400

450

Nov-01

Dec-01

Jan-02

Feb-02Mar-02

Apr-02

May-02

Jun-02

Jul-02

Aug-02Sep-02

Oct-02

Nov-02

Dec-02

Jan-03

Feb-03Mar-03

Apr-03

May-03

Daily Average Monthly Consumption and Production 

 (kWh/day)

PV Production Site Plug Loads

Site Lighting Site Heating

Site Cooling Site Fans

Site DHW Fee Station

Figure 8-1 End use daily average monthly consumption, November 2001 through 

May 2003 
112 

Table 8-1 Measured Whole-Building Results 

Measured Site 

Use Intensity 

kBtu/ft2·yr 

(MJ/m2·yr)

Measured PV 

Production 

Intensity 

kBtu/ft2·yr 

(MJ/m2·yr)

Percent of 

Building 

Load Met By 

PV 

Measured Net 

Site Use 

Intensity 

kBtu/ft2·yr 

(MJ/m2·yr)

Measured 

Source Use 

Intensity 

kBtu/ft2·yr 

(MJ/m2·yr)

Energy Cost 

Intensity 

$/ft2·yr 

($/m2·yr)

 27.0 

(307) 

 2.3 

(26) 8.5% 24.7 

(281) 

80 

(910) 

$0.43 

($4.63) 

8.2 Simulated Whole-Building Performance 

A base-case energy model, which used calibrated internal gains and weather data measured at the site for 

the same period, predicted energy costs of $15,250/yr or $1.30/ft2

·yr ($13.99/m2·yr). The base-case 

model predicted site energy use at 241,800 kWh/yr or 70.3 kBtu/ft2

·yr (798 MJ/m2·yr) and source energy 

intensity at 227 kBtu/ft2

·yr (2,580 MJ/m2·yr). This represents savings (including receptacle loads) of 67% 

for energy cost, 62% for site energy (not including on site generation), and 65% for source energy (see 

Figure 8-2 and Table 8-2). The measured energy cost savings shows that the original energy design goals 

are close to being met. 

0

500

1,000

1,500

2,000

2,500

3,000

Base Case Model Measured Data

Annual Source Energy (MBtu/yr)

PV

DHW

Fans

Cooling

Heating

Lighting

Equipment

70.3 kBtu/ft2

27.0 kBtu/ft2

62% Savings

Figure 8-2 Annual performance comparison 
113 

Table 8-2 Cost, Site, and Source Energy Savings, Nov. 2001 to Oct. 2002 

Cost Site Energy Source Energy 

$/ft2·yr 

($/m2·yr)

Percent 

Savings 

kBtu/ft2·yr 

(MJ/m2·yr)

Percent 

Savings

kBtu/ft2·yr 

(MJ/m2·yr)

Percent 

Savings

Base-case $1.30 

($13.99) 

70.3 

(798) 

227 

(2580) 

As-built $0.43 

($4.63) 

67% 27.0 

(307) 

62% 80 

(910) 

65% 

8.3 PV System 

The PV system offsets approximately 15% of the loads during the spring and summer months. It offsets 

less than 5% of the load during the winter because of the higher electrical loads from heating and reduced 

PV production. During the monitored year, the PV system produced a net 7,861 kWh (building 

normalized to 2.3 kBtu/ft2

·yr [26.1 MJ/m2·yr]). The PV system offsets about 8% of the total annual 

energy load. 

8.4 Lessons Learned 

Experience with the Visitor Center Complex project, from early conceptual design through three years of 

postoccupancy monitoring, led to the following prominent conclusions. Although the design can be 

replicated by the NPS for future visitor centers, many of the conclusions are applicable to commercial 

buildings in general, especially retail operations. The Comfort Station portion of the project is typical of 

many highway rest areas and state park facilities and concepts from this design could be easily replicated 

across many future buildings. 

• A multiple-use commercial building that includes retail, office, and public assembly spaces, can 

be constructed that uses 62% less site energy than an equivalent, minimally code-compliant 

building. 

• It is possible to actively control buildings to reduce electrical demand charges. 

• For the climate and scale of the Visitor Center Complex, it is possible to eliminate mechanical air 

systems and use simple localized heating systems to augment passive heating and cooling to 

provide occupant thermal comfort. 

• Cooltowers can effectively combine direct evaporative cooling and passive natural ventilation 

and deliver comfort comparable to mechanical direct evaporative cooling. 

• Daylighting can be used to augment electric lighting in retail spaces. 

• Dark ceilings must be avoided to fully take advantage of the daylighting and uplighting. 

• Solar-electric uninterruptible power systems can add value to commercial buildings in areas with 

poor power reliability. 

• A PV system can provide emergency power, offset peak loads, and reduce energy costs by 

reducing demand. 

• Changes in rate structures can change the design decisions and operating strategies. 

• Commercial buildings may shift from being cooling dominated to heating dominated because of 

low-energy design. 
114 

The probability that a low-energy building will be achieved is improved by adopting the low-energy 

design process described in this paper. That process includes: (1) setting energy performance goals early 

on and remaining committed to achieving them, (2) assembling a diverse design team and involving them 

in all phases of the project, (3) applying computer simulation to predict energy performance at multiple 

stages of the design process, (4) using the architecture of the building itself to reduce energy needs and 

enhance comfort, and (5) evaluating delivered performance and continuously commissioning systems to 

improve performance. For Zion, we learned that the low-energy design process enabled the building to 

achieve remarkable energy savings. 

8.5 Future Research 

As with any research project, future research topics are possible, as indicated below. 

• Continuous monitoring of building energy performance is essential to the long-term vision of the 

energy performance of the building. Identify areas of degrading performance with time. 

• Develop peak demand algorithms for minimizing electrical cost to fully benefit from energy 

efficiency devices (especially the daylighting) and the on-site generation capacity, including 

modeling the building and the PV system with a 15-minute time step in an integrated building 

simulation program. Study the ability for PV systems to minimize demand with controls. 

• Perform water consumption and cost analysis for the cooltowers compared to a typical airconditioning system. The analysis will include a simulation study on the energy and water use 

tradeoffs for cooling commercial buildings. 

• Identify better methods for natural ventilation systems or improve the robustness of the actuators. 

• Identify methods to reduce glare in the spaces. 

• Identify better methods of eliminating task lighting in the retail space. 

• Simulations are critical throughout the design process. Many of the issues resulted from lack of 

simulation during a portion of the design process. Development of automated building energy 

simulation optimization tools can make the simulation task faster and easier, and therefore more 

likely to be applied when needed. 

• Develop an as-built whole-building energy model of the Visitor Center that would include 

Trombe walls, cooltowers, subhourly demand limiting controls, and PV generation. An 

EnergyPlus model could be developed for further study of demand limiting controls with onsite 

generation, water use in evaporative cooling systems, and enable an as-built to base-case 

simulation comparison for determining energy and cost savings (EnergyPlus 2005). 
115 

9 References 

ASHRAE 1989. ANSI/ASHRAE/IES Standard 90.1-1989. Atlanta, GA: American Society of Heating, 

Refrigerating, and Air-Conditioning Engineers. 

ASHRAE 2001. ASHRAE Handbook Fundamentals. Atlanta, GA: American Society of Heating, 

Refrigerating, and Air-Conditioning Engineers. 

ASHRAE 2004. ASHRAE Standard 90.1-2001 Addendum E. Atlanta, GA: American Society of Heating, 

Refrigerating, and Air-Conditioning Engineers. 

Atif, M.R.; Love, J.; Littlefair, P. 1997. Daylighting Monitoring Protocols and Procedures for Buildings. 

A report of IEA Task 21/Annex 29 Daylight in Buildings. Paris, France: International Energy 

Agency. 

Balcomb, J.D.; Barker, G.; Hancock, C.E. 1998. “An Exemplary Building Case Study of the Grand 

Canyon South Rim Residence.” NREL/TP-550-24767. Golden, CO: National Renewable Energy 

Laboratory. 

Brager, G.; de Dear, R. 2000. “A Standard for Natural Ventilation.” ASHRAE Journal. Vol. 42, No. 10; 

pp. 21–28. 

Carlson, S.W. 2000. “Performance Monitoring of a Sustainable Residence Hall at Northland College.” 

Research Report 198-1. Madison, WI: Energy Center of Wisconsin. 

DOE 1995. Code of Federal Regulations 10 – Energy. Washington, D.C.: Office of the Federal Register 

National Archives and Records Administration. 

DOE 2003. 2003 Buildings Energy Databook. Washington, D.C.: U.S. Department of Energy. Pg. 1–1, 

Table 1.1.3. http://buildingsdatabook.eren.doe.gov/. Accessed July 2004. 

DOE 2004. High-Performance Buildings initiative Web site. Washington, D.C.: U.S. Department of 

Energy. www.highperformancebuildings.gov. Accessed August 2004. 

EIA 2000. Annual Energy Outlook. U.S. Department of Energy. Washington, DC: Energy Information 

Agency. Pg. 217, Diagram 5. 

EIA 2002. 1999 Commercial Buildings Energy Consumption Survey: Consumption and Expenditures 

Tables. Washington, DC: Energy Information Agency. 

EnergyPlus 2005. EnergyPlus User’s Manual, V1.2.1; December 2004. Engineering Document. 

Washington, DC: U.S. Department of Energy. http://www.energyplus.gov/. Last accessed February 

24, 2005. 

EPA 2003. Emissions and Generation Resource Integrated Database. Washington, DC: Environmental 

Protection Agency. http://www.epa.gov/cleanenergy/egrid/index.html. Accessed September 2003. 

Hicks, T.W.; von Neida, B. 2000. “An Evaluation of America’s First ENERGY STAR Buildings: The 

Class of 1999,” ACEEE Summer Study on Energy Efficiency in Buildings Proceedings; 2000, Pacific 

Grove, CA. Pg 4.181, Table 1. 

IESNA 2000. Lighting Handbook-Reference and Application Volume. New York: Illuminating 

Engineering Society of North America. 

King, D.L. Kratochvil, J.A. Boyson, W.E Bower, W.I. 1998. “Field Experience with a New Performance 

Characterization Procedure for Photovoltaic Arrays.” Proceedings of the 2nd World Conference and 

Exhibition on Photovoltaic Solar Energy Conversion; July 1998, Vienna, Austria. 
116 

Lindsey, G.; Todd, J.; Hayter, S. 2003. A Handbook for Planning and Conducting Charrettes for HighPerformance Projects. Golden, CO: National Renewable Energy Laboratory. NREL/BK-710-33425. 

Mermoud, A. 1996. PVSYST Version 3.2. User's Manual. Geneva, Switzerland: University of Geneva, 

University Center for the Study of Energy Problems. Available online at http://www.pvsyst.com/. 

Accessed December 2002. 

NPS 1995. “Zion Canyon Comprehensive Design.” Washington, D.C.: National Park Service. U.S. 

Department of Interior. 

NPS 2003. Zion National Park Map and Guide. Washington, D.C.: National Park Service. U.S. 

Department of Interior. www.nps.gov/zion/MapGuidesummer_2003.pdf. 

Pless, S; Torcellini, PA. 2004. “Energy Performance Evaluation of a Low Energy Academic Building” 

NREL/TP 550-33180. Golden, CO: National Renewable Energy Laboratory. 

Torcellini, P. A.; Hayter, S. J.; Judkoff, R. (1999). “Low-Energy Building Design—The Process and a 

Case Study.” ASHRAE Transactions, Vol. 105, Part 2. Atlanta, GA: American Society of Heating, 

Refrigerating and Air-Conditioning Engineers, Inc.; pp. 802-810; NREL Report No. 26144 

Winkelmann F.C.; Birdsall B.E.; Buhl W. F.; Ellington K. L.; Erdem, A. E.; Hirsch, J. J.; Gates, S. 1993. 

DOE2 Supplement, Version 2.1E, LBL-34947. Lawrence Berkeley National Laboratory. 

Springfield, Virginia: National Technical Information Service. 
117 

Appendix A The Low-Energy Design Process 

The Low-Energy Design Process 

In the traditional building design process, the architectural team first creates a building program. The 

program specifies the needs for the building and parameters that should be considered in the design. 

Based on this program of requirements, the architectural team then establishes the massing and form of 

the building facade, including orientation, color, window area, and window placement. The criteria by 

which the architectural team might evaluate energy efficiency improvements include first cost, simple 

payback, savings-to-investment ratio, life-cycle cost, or net present value of savings. 

After the building form and envelope are initially designed, the floor plans are passed to the engineering 

team, who designs the HVAC systems. Most engineers then work within the context of the building form 

and envelope as designed, focusing on improving the HVAC systems. However, because many important 

architectural decisions are set at this point, few changes can be made. The engineer also evaluates 

compliance with applicable energy codes and acceptable levels of environmental comfort for building 

occupants during this stage of the process. 

In contrast to the traditional process, in the low-energy design process the building owner, architect, 

engineer, and energy consultant form a collaborative design team focused on energy and energy cost 

savings for the building from the onset of the project. Once the design team commits to energy goals for 

the project, the low-energy design process will guide the team toward good decision-making and trade-off 

analysis without sacrificing the building’s programmatic requirements. 

Low-energy design must first meet or exceed all functional and comfort requirements of the building 

program. Low-energy design does not imply that building occupants must endure conditions considered 

unacceptable in traditional buildings. However, Brager and deDear (2000) have shown that some lowenergy design strategies result in occupants being more tolerant of varying indoor conditions, increasing 

opportunities for application of these approaches. 

The low-energy design process begins in predesign, where the building size, type, location, and use are 

known. The process then continues through design, construction, and commissioning according to the 

following steps. These steps assume a team committed to low-energy building design already has been 

formed (Torcellini et al 1999). 

Step 1: Predesign. During predesign, the design team develops a thorough understanding of the 

building site, local weather patterns, and building functional requirements. Examining these issues early 

often leads to potential solutions for minimizing building energy consumption. At this point, the design 

team should brainstorm energy solutions, especially those that affect the architecture. Refinements of the 

concepts will happen later in the design process. It must be noted that all buildings are unique and will 

have a different minimization strategy. Also at this stage, the team establishes preliminary metrics, which 

may include percent energy savings, percent energy cost savings, or emission reductions. It is critical that 

the entire team understand these goals and how design features impact those goals. 

Step 2: Create a Base-Case Building Model. The low-energy design process is a simulation-based, 

quantitative, and qualitative method to help architects and engineers create low-energy buildings. Lowenergy design is not intuitive. Building energy use and energy cost depend on the complex interaction of 

many parameters and variables. The problem is far too complex for rule-of-thumb or hand calculations. 

The interactions are best studied using computerized energy simulation software to thoroughly evaluate 

all interactions among the building envelope, HVAC system, and design features. 

To determine energy saving opportunities, the design team starts by simulating a base-case model of the 

building with a building-energy simulation program. In general terms, a base-case building is “solar 

neutral.” For ZNP, the base-case design was a square floor plan with windows distributed equally on 
118 

each facade. It has the same floor area as the proposed building and complies with the prescriptive 

standards of the applicable energy code for the building type and location. Based on the base-case model, 

the building energy program simulates annual loads and peak demands for heating, cooling, lighting, plug 

loads and HVAC system fans and pumps, providing an energy-use profile for the base-case building. 

Although not available at the time of design, ASHRAE Standard 90.1-2001 Appendix G (90.1 Addendum 

E) has standardized the base-case building definition (ASHRAE 2004). 

Step 3: Parametric Analysis. An elimination parametric analysis provides building designers with an 

understanding of the sensitivity of total building energy performance at specific loads. In a parametric 

analysis, loads such as conduction losses, people, solar gains, and plug loads are removed from the 

simulation one at a time. As each load is removed, the impact on the metric, such as energy costs, is 

recorded. For example, if eliminating all conductive heat transfer through the building envelope has a 

small affect on energy consumption and energy costs, there is little sense in increasing building insulation 

levels beyond those prescribed by code. Similarly, parametric modeling may demonstrate an upper limit 

to the amount of insulation before internal loads begin to increase air-conditioning loads. The design 

team may find that reducing insulation levels and using the money to reduce energy elsewhere has a 

larger impact on the total energy picture. If, however, eliminating all solar gains greatly affects energy 

performance, then it is worth exploring solar related issues such as window area, orientation, window 

solar heat gain coefficient (SHGC), and shading. Finally, the team establishes the energy goal for the 

climate and building type based on this analysis. All team members should agree on the feasibility of 

achieving this goal. 

Step 4: Brainstorm Design Solutions. In this stage, the design team brainstorms possible solutions to 

energy issues, focusing on solutions relating to building geometry. For example, daylighting might be a 

solution if lighting loads and associated cooling loads are a large percentage of building energy use. If 

winter heating loads are an important issue, passive solar heating may be desirable. These solutions 

significantly impact decisions on building geometry, siting, zoning, and orientation, which are all aspects 

of a building that are difficult or impossible to alter later in the design process. 

Step 5: Simulate Performance of Design Solutions. Simulations are performed on variants of the basecase building based on the list of possible solutions developed in Step 4. Issues that influence building 

architectural elements are explored first. The simulated building energy use of each variant is compared 

to the original base-case building and other variants. Daylighting systems, thermal issues, and building 

control strategies may be addressed by different building disciplines, but successful low-energy 

performance can only be achieved by examining the interrelation between these components through 

building energy simulation. 

Step 6: Conceptual Design. Conceptual design is the most difficult part of the energy design process. It 

is when important energy features must be integrated into the architectural design. The objective of lowenergy design is to use architectural and envelope features to minimize energy used for heating, cooling, 

and lighting. Often, energy features can also serve as major architectural features, thereby reducing first 

costs directly attributable to energy efficiency. If an energy feature increases construction costs, then the 

feature is reevaluated to ensure its effectiveness. 

In Step 6, the architectural team prepares a preliminary set of drawings based on the siting, orientation, 

and basic geometry of the building incorporating information from simulations performed in Step 5. The 

energy performance of this preliminary design is also modeled at this point. Variants of the preliminary 

design are then simulated to provide information to the architectural team about how the design should be 

refined. At this stage, energy use modifications will not affect the overall form, but may have a minor 

influence on building appearance. Important variables to evaluate include wall-to-window surface area 

for each building orientation, geometry of fixed shading devices, and light shelves on each facade. Other 

variables to consider include window optical and heat transfer characteristics on each facade, use of 

natural ventilation, resistance and capacitance of walls, and quantity of internal thermal mass. 
119 

Note that only the building envelope has been considered at this point in the design. After optimizing the 

energy efficiency of the building envelope, the design team then works on the HVAC design. Because 

slight changes in the envelope design can significantly affect total building energy loads, it is best to wait 

until the envelope design is well developed before considering the HVAC design so that it accurately 

reflects the needs of the building envelope. 

Step 7: Design Development. After the architectural features affecting energy use have been established, 

the model for the proposed building is updated to reflect those features. A set of simulations is then 

performed to guide decisions regarding the HVAC system and associated controls. These simulations are 

primarily used to optimize annual energy use, annual energy cost, and occupant comfort. Simulations can 

also be used to help properly size the equipment. Low-energy buildings can defy industry norms used for 

equipment sizing. Downsizing equipment can substantially reduce construction cost and the savings can 

often be used to pay for improved envelope energy features. At this point, there will be some trade-off 

between mechanical system decisions and architectural features. 

Step 8: Bid Documents and Specifications. Building design plans and specifications must be carefully 

reviewed to find areas where the design intent is not met and to catch unacceptable component 

substitutions. Examples include ensuring that there are no thermal bridges connecting conditioned space 

with the outdoors, window thermal and optical properties are sufficiently specified, HVAC equipment 

efficiency and performance are ample, control algorithms are adequately expressed, and R-values of 

insulation materials are specified. A final simulation is based on these plans and specifications to ensure 

a low-energy building and to show energy code compliance (e.g., the building should perform more than 

50% better than the code-compliant base-case building in most cases). In the case of high construction 

bids, the design may need modification to reduce costs. All modifications should be closely evaluated to 

ensure that the original energy savings goals are maintained and the impacts of changes are well 

understood. 

Step 9: Construction. At this phase, most of the simulation work has been completed, so simulations are 

performed only in response to unanticipated substitutions, changes, or additions made by the construction 

contractor, suppliers, architects, inspectors and others involved in building construction. Simulations at 

this time might include those needed to determine if a substitute component meets energy related 

specifications, or to review a construction detail that must be modified because of a problem at the 

construction site. Scheduled plan reviews and site inspections are crucial to ensure that specified details 

omitted from the plans do not compromise the energy design. A clear communication path between the 

contractor, building operator, and the design team will help ensure that components are installed properly. 

In many cases, once construction on a particular area is incorrectly completed, the building owner is often 

forced to live with the resulting energy performance consequences because correction may be impractical. 

Step 10: Commissioning and Postoccupancy Evaluation. The commissioning process includes testing 

all subsystems in the building to ensure that they operate as intended. For example, poorly calibrated 

economizer controls or daylight sensors may allow excess air to enter or cause lights to stay on for 

excessive periods. Occasionally, simulations are required to help solve problems that emerge during this 

final phase and to respond to changes in building use that may occur once the building is occupied. The 

key is to maintain controls that function in harmony with building design intent. A good building quickly 

becomes a “bad” building with improper control strategies. In addition, it is important to educate the 

building owner, occupants, and the maintenance staff about how to properly use the building systems as 

conceived by the design team. The building’s operating energy performance can only be optimized if 

individual occupants and/or building operators are able to understand how these systems interact. 
120 

Appendix B Design Process Questionnaire 

Questionnaire 

The following questionnaire was sent to those involved in the design of the Visitor Center Complex: 

Questionnaire and Round Table Meeting 

A questionnaire and a round table meeting will be used to capture and record what worked and what did 

not work in the design process. The questionnaire will be distributed and collected first, followed shortly 

thereafter by a round table meeting. 

This feedback will help inform future design teams of the critical elements involved in the design process. 

Please be frank and honest. All responses will be anonymous. Data will be compiled solely for aiding 

future design projects. 

You can write on the back of the page if insufficient space is provided for your answer. Do indicate the 

question number that you are addressing. 

Please print this document, answer the questions, and return to Patrick Shea by October 29, 1998. Thank 

you for your time and cooperation. 

Sincerely, 

Stefan Craine 

NREL Analyst 

Please call me at (303) 384-7566 if you have any questions regarding this questionnaire. 
121 

Date: ______________ 

1. What was your position on the design team? (Please select all that apply)

❍ Architect 

❍ Landscape Architect 

❍ Electrical Engineer 

❍ Mechanical Engineer 

❍ Project Manager 

❍ Owner 

❍ Building Operator 

❍ Building Occupant 

❍ Other __________________________________________________________ 

2. Please define your understanding of your role in the sustainable design plan. 

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

_____________________________ 

3. Do you think that the sustainable design plan was developed successfully? 

❍ Yes ❍ No 

4. What specifically helped the development of the sustainable design plan? 

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

_______________________________ 

5. What specifically inhibited the development of the sustainable design plan? 

________________________________________________________________________

________________________________________________________________________

________________________________ 

6. In your opinion, what are the critical elements that need to be addresses when 

developing a sustainable design plan? 

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

___________________________________ 
122 

7. Please rate how well informed you were of the project goals during the design plan. 

 ❍ Very informed ❍ Mildly informed ❍ Mildly misinformed ❍ Very misinformed ❍ N/A

8. I understood the goal of the design plan specific to the roles of the following stakeholder: 

(please check accordingly for each stakeholder. Included others at the "X" if necessary)

 Strongly Agree Mildly Agree Mildly Disagree Strongly Disagree

NPS 

ZION 

Federal Gov't 

NREL 

Cinnemax 

X 

X 

9. Please rate how well informed you were of project changes during the design plan. 

 ❍ Very informed ❍ Mildly informed ❍ Mildly misinformed ❍ Very misinformed ❍ N/A

10. I understood why changes occurred to the design plan specific to the roles of the 

following stakeholder: (please check accordingly for each stakeholder. Included others at 

the "X" if necessary)

 Strongly Agree Mildly Agree Mildly Disagree Strongly Disagree

NPS 

ZION 

Federal Gov't 

NREL 

Cinnemax 

X 

X 

11. I feel that I understood the role of the NPS team in the design process. 

 ❍ Strongly Agree ❍ Mildly Agree ❍ Mildly Disagree ❍ Strongly Disagree ❍ N/A

12. I feel that the NPS team members communicated clearly to each other. 

 ❍ Strongly Agree ❍ Mildly Agree ❍ Mildly Disagree ❍ Strongly Disagree ❍ N/A 
123 

13. I feel that the NPS team responded to each others needs promptly. 

 ❍ Strongly Agree ❍ Mildly Agree ❍ Mildly Disagree ❍ Strongly Disagree ❍ N/A

14. I feel that the NPS team was open to new ideas. 

❍ Yes ❍ No (Please Explain)

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

_______________________________ 

15. I feel that I understood the role of NREL in the design process. 

 ❍ Strongly Agree ❍ Mildly Agree ❍ Mildly Disagree ❍ Strongly Disagree ❍ N/A

16. I feel that NREL communicated their ideas clearly. 

 ❍ Strongly Agree ❍ Mildly Agree ❍ Mildly Disagree ❍ Strongly Disagree ❍ N/A

17. I feel that NREL responded to the design teams needs promptly. 

 

❍ Strongly Agree ❍ Mildly Agree ❍ Mildly Disagree ❍ Strongly Disagree ❍ N/A

18. I feel that NREL was open to ideas. 

 ❍ Yes ❍ No (Please Explain)

________________________________________________________________________

________________________________________________________________________

____________________________ 

19. Was NREL's participation beneficial to the design process? 

❍ Yes ❍ No (Please Explain)

________________________________________________________________________

________________________________________________________________________

___________________________

20. Did the design team interact and work well with each other? 

❍ Yes ❍ No (Please Explain) 

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

_______________________________ 
124 

21. How would you strengthen the team? 

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

__________________________ 

22. What would you have done differently if given the opportunity? 

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

___________________________ 

23. Additional comments: (Please write anything that you would like to discuss e.g. successes, 

frustrations, concerns, problems, solutions) 

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

__________________________________________________________ 
125 

Questionnaire Results 

Based on the questionnaire from Appendix A, survey results are summarized based on six responses. 

Do you think the sustainable design plan was developed successfully? 

 17% 66% 17% 

 K-----K -----K 

Not successfully [ -5 -4 -3 -2 -1 0 1 2 3 4 5 ] Very Successfully 

 

Please rate how well informed you were kept of the project goals during the design process. 

100% 

K 

( )Very informed ( )Mildly informed ( )Mildly misinformed ( )Very misinformed ( ) N/A 

Please rate how well informed you were kept of project changes during the design process. 

100% 

 K

 ( )Very informed ( )Mildly informed ( )Mildly misinformed ( )Very misinformed ( )N/A 

I feel that I understood the role of the design team during the design process. 

100% 

K

( )Strongly Agree ( )Mildly Agree ( ) Mildly Disagree ( ) Strongly Disagree ( ) N/A 

I feel that the design team members communicated clearly to each other. 

 

66% 17% 17% 

K ------K -------------K

 ( ) Strongly Agree ( ) Mildly Agree ( )Mildly Disagree ( )Strongly Disagree ( )N/A 

I feel that the design team responded to each others' needs promptly. 

66% 17% 17% 

K -----K -------------K 

( )Strongly Agree ( )Mildly Agree ( )Mildly Disagree ( )Strongly Disagree ( )N/A 
126 

The design team interacted and worked well with each other? 

100% 

 K

( ) Agree ( )Disagree 

I feel that NREL communicated their ideas clearly. 

 

100% 

K

( ) Strongly Agree ( )Mildly Agree ( )Mildly Disagree ( )Strongly Disagree ( )N/A 

I feel that NREL responded to the design teams' needs promptly. 

67%--33% 

K K

( ) Strongly Agree ( )Mildly Agree ( )Mildly Disagree ( )Strongly Disagree ( )N/A 

I feel that NREL was open to my ideas and thoughtfully listened to them. 

100% 

 K

( Yes ) ( No) 

NREL's participation benefited to the design process? 

100% 

 K

( Yes) ( No) 
127 

Results of specific questions are included below. The question, paraphrased answers, and a general 

summary of answers are provided. 

What promoted development of the sustainable design?

• Individual enthusiasm, genuine interest in project by NREL & design staff and by the NPS as 

well 

• Good policy & agency goals (design team pushing envelope of sustainable design) 

• Relocation of traditionally indoor visitor space to outdoor area 

• Team cohesiveness. 

The individual enthusiasm of NREL and architectural design staff as well as the motivation of NPS staff 

all contributed toward the development of a viable sustainable design for the Visitor Center. The project 

was viewed by many as an opportunity to push the envelope of sustainability, which led to a sense of 

team cohesiveness among the participants. During design and construction, many novel approaches were 

applied in an effort to conserve resources. One such approach involved relocating traditionally interior 

visitor functions to the outdoor environment, resulting in reduced facility dimensions with a comparable 

reduction in energy use. 

What inhibited development of a sustainable design?

• Traditional/limited materials, construction practices 

• High visitor expectations 

• Economic limitations (high cooltower cost) 

• Park service bureaucracy 

• Similar design failures of the past 

• Design personnel with no knowledge of arid climate or incorporated technologies 

• Pedestrian site flow produced less than optimum solar building orientation. 

However, the success of the design was also partially hindered by several other factors. Traditional 

expectation and cultural norms in materials selection and construction techniques were at the foremost of 

the problems addressed. Adapting to the deviation from standard procedure was found to be difficult for 

some individuals. In general, the unconventional nature of the building coupled with the high cost of the 

cooltowers was initially cause for apprehension because similar facilities built previously had failed to 

perform adequately. ”Quote” Optimum solar design was also somewhat compromised in order to 

accommodate pedestrian traffic through the site. Despite these issues, the structure’s energy savings have 

adequately surpassed that of its predecessors. 

What are the critical design processes that need to be addressed?

• Promote free flow of ideas and frequent communication with designers to promote fully 

integrated design 

• Attract laymen/stakeholders/decision makers by avoiding technical excess 

• Emphasize sustainability 

• Understanding of regional/social/cultural context (especially climate) 
128 

• Make sustainable materials selection, and other technology need to be made known at the early 

stages of project development (Contributes to integrated design). 

Several individuals felt the design process could be greatly optimized by making the available materials 

and technology selection known before project initiation. Because many features were implemented late 

in the design process, their appearance was of awkward additions to the original project. Increased 

communication with designers should be emphasized in the future in order to promote a more integrated 

design. Detailed information about the local environment should also be made available to reduce the 

chances of overcompensating the design mechanically. Communication should not use an excess of 

technical details, in order to avoid the possibility of alienating stakeholders and decision makers. 

The design team interacted and worked well with each other?

• Strong, cohesive project vision 

• Team captain played important role in organizing the work 

• All responders to the questionnaire unanimously felt that the design team interacted and worked 

well with each other. 

How would you strengthen the team? Why?

• Retain original team members if project continues 

• Be more open about researching and incorporating unapplied sustainable practices and 

technologies 

• Coordinate and streamline time usage amongst participating parties to taking longer than 

necessary. 

Team strength could potentially be improved upon by utilizing better time management. A strategy that 

coordinates the progress of all disciplines involved would be most beneficial. In addition, a deeper 

exploration of sustainable practices and technologies beyond those currently applied, and retention of 

current team members in future endeavors could also enhance team efficacy. 

What do you think NREL’s role is in the design process?

• Assist in creation of project vision, detailing material sources, advocating & presenting 

technologies 

• Concept testing, research, technical input 

• Review and comment on drawings and specifications 

• Evaluate facility after construction to determine success and recommend necessary modifications 

needed to increase efficiency 

• Provide energy use calculations before construction to assist design team in making decisions. 

NREL’s role in the project design process was felt to be best suited to providing the team with conceptual 

and technical input. Specifically, the most useful assistance arrived in the form of review and comment 

on drawings and proposed specifications, project vision creation, material source details, and the 

presentation of various renewable technologies. Energy use calculations provided before construction 

assisted in the design team decision-making process. No less important was the need to evaluate facility 

performance after construction to determine design success and recommend modifications needed to 

increase efficiency. 
129 

I feel that NREL communicated their ideas clearly.

• Explanations specially tailored for various audiences 

• Paul Torcellini effectively communicated ideas & recommendations as part of design team 

• Recommendations added value to the designer’s work (avoided detracting from it) 

• Paul Torcellini deserves credit for pitching the sustainable goals and concepts of the project and 

design team, which resulted in eventual funding of the project. 

Overall, communication took place successfully and problems encountered were virtually nonexistent. 

Paul Torcellini played an effective role in communicating ideas and recommendations to the design team, 

as well as selling the sustainable goals and concepts. This was largely responsible for eventual funding 

for the project, and was credited for adding value to the original design. 

I feel that NREL responded to the design team’s needs promptly.

• Single point of contact [Paul Torcellini & Mark Golnar (NPS Mechanical Engineer)] worked well 

for reducing time spent communicating amongst team members 

• Reviews, sub-consultants, technical info were all timely 

• Large NREL workload slowed response times occasionally, but did not present a problem. 

NREL responded to a majority of team requests with accuracy and speed. Paul Torcellini and Mark 

Golnar played a significant role in facilitating this by serving as a single point of contact for team 

communication. This structure allowed reviews, sub-consultants and technical information to be 

distributed very quickly. Occasionally, substantial demand for NREL’s services were cause for minor 

delay, but did not end up posing a significant threat toward the progression of ongoing activities. 

I feel that NREL was open to my ideas and thoughtfully listened to them.

• Common sense methods were always applied to accomplish project goals 

• Philosophical or technical differences were addressed in a professional manner 

• Ideas about backup heating in the visitor area were received well by NREL staff. 

It was generally felt that ideas were well accepted, and common sense methods were used to implement 

these goals. Cooperation amongst the design team was complemented with a marked professionalism in 

resolving group differences. A mechanical engineer involved with the project remarked about how well 

his proposal for heating the visitor area was received. 

Was NREL’s participation beneficial to the design process?

• Success achieved would not be as significant had NREL not been involved with the project 

• Critical input and information provided, even at early stages of development 

• Background, knowledge, and strength of vision all contributed toward a functional and visually 

appealing design 

• Helpful knowledge supplied, included information about calculating passive solar heating outputs 

and mass storage contributions with regard to design of the backup heating systems. 

NREL’s participation in the project was essential for achieving success in the design. The background and 

vision provided were useful in attaining both a functional as well as visually appealing design. This took 

the form of critical input regarding progress of the design process from early stages to project conclusion. 

Specifically, information about passive solar heating output and mass storage calculations were given to 

otherwise inexperienced members. 
130 

What would you have done differently if given the opportunity?

• Modifications to original procedure are unnecessary. Continue to use a project formulation that 

promotes the establishment of vision. 

• Exploring and utilizing a broader expanse of materials would positively complement design of 

the most sustainable facility. 

• Exploration could also have included looking further into solar electrical generation. 

• Design of the BAS could have been carried out during preliminary stages of the design process 

instead of the final phases. 

• Pressure to complete the project in a very short time period may have hindered sustainability and 

the design process as a whole. Organization suffered. 

• Some minor skepticism was relayed about the longevity of the digital building control 

mechanisms. 

In retrospect, original design procedures were considered very close to ideal, with changes being largely 

unnecessary. However, requests for a closer look at broadening materials selection practices have been a 

recurring theme. Concerns about the building control systems have taken a close second in line. Some 

feel longevity may become an issue in the next 5–10 years, while others are simply concerned about how 

late the system was conceived in the design process. This, combined with a short time period allotted for 

construction, may have pushed the limits of group organizational capabilities. 
131 

Appendix C Energy Summary Tables 

MEASURED DATA (kWh) Nov-01 Dec-01 Jan-02 Feb-02 Mar-02 Apr-02 May-02 Jun-02 Jul-02 A

Total Consumption 6,284 12,191 12,947 8,160 7,592 5,880 5,766 6,192 7,257 

PV Production 355 319 428 561 785 779 965 919 850 

Net Purchased 5,930 11,872 12,519 7,600 6,807 5,101 4,801 5,273 6,407 

HVAC 1,361 7,525 8,256 4,420 3,611 1,133 589 1,227 2,126 

Visitor Center Heating 997 6,957 7,554 4,022 3,150 774 87 0 0 Comfort Station Heating 47 278 341 182 182 0 0 0 0 Visitor Center Cooling 2 0 0 0 0 0 137 615 942 Comfort Station Cooling 0 0 0 0 0 0 7 196 304 Visitor Center and Comfort Station Ceiling and Exhaust Fans 314 290 362 216 279 360 358 416 880 

Lighting 2,269 2,094 2,224 1,871 1,775 2,301 2,483 2,261 2,322 

Visitor Center Computer Controlled 1,191 1,115 1,093 939 984 1,237 1,154 1,206 1,280 Visitor Center Switch Controlled 338 292 285 279 334 428 518 517 623 Comfort Station 459 459 634 497 330 396 596 351 213 Outdoor 281 228 212 156 126 240 214 188 206 

Equipment/Other 2,645 2,573 2,466 1,869 2,206 2,445 2,695 2,705 2,814 

Fee Station 590 768 747 306 201 304 264 218 266 Visitor Center Plug Loads 1,690 1,406 1,249 1,163 1,412 1,501 1,682 1,766 1,642 Comfort Station Plug Loads 158 247 286 255 420 450 372 265 464 Visitor Center Domestic Hot Water 55 57 72 70 81 84 82 74 60 Comfort Station Domestic Hot Water 153 95 113 75 92 107 294 383 382 

MEASURED WEATHER BASE CASE (kWh) Nov-01 Dec-01 Jan-02 Feb-02 Mar-02 Apr-02 May-02 Jun-02 Jul-02 A

Total Base-case Consumption 16,540 19,550 18,885 15,476 17,106 17,159 19,909 24,610 28,348 2

Base-case Heating 1,998 6,259 5,445 2,970 2,237 380 277 176 27 

Base-case Cooling 1,704 22 98 535 1,611 4,010 6,251 11,378 14,762 1

Base-case Fans 1,542 1,597 1,597 1,439 1,594 1,543 1,603 1,616 1,776 

Base-case Lighting 8,859 9,154 9,154 8,267 9,154 8,859 9,154 8,859 9,154 

Base-case Equipment 2,223 2,368 2,365 2,115 2,332 2,166 2,230 2,145 2,217 

Base-case DHW 214 150 226 150 178 201 394 436 412 

Figure B-1 Summary of measured and base-case energy use 
132 

Appendix D PV Shading Simulation Procedure 

To account for the mountain shading from the south of the PV array, the southern horizon line was 

modeled. Over the course of a year, the mountains of the southern canyon wall, as shown in Figure D-1, 

shade the building and the PV array in the morning and in the evening. 

Figure D-1 Photo of Visitor Center looking south showing southern horizon (canyon 

walls) accounted for in simulations 

The measured horizontal insolation, shown as monthly profiles in Figure D-2, demonstrates the morning 

and evening canyon wall shading. On average for the month of December, the building is shaded until 

9:30 a.m. and unshaded until the end of the day. On average for the month of June, the building is shaded 

until 7:00 a.m. and again at 6:00 p.m. The sun path diagram with a horizon line in Figure D-3 shows the 

modeled horizon that corresponds to the morning and evening canyon wall shading. 

Horizontal Insolation Load Shape

0

200

400

600

800

1,000

1,200

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

0:00

Global Horizontal Insolation (W/m2)

October-01

November-01

December-01

January-02

February-02

March-02

April-02

May-02

June-02

July-02

August-02

September-02

October-02

Figure D-2 Horizontal insolation monthly profile, October 2001 through October 2002 
133 

Figure D-3 Southern horizon model 

Another occurrence of PV array shading is apparent in the afternoon when the trees to the west of the PV 

array, as shown in Figure D-4, shade a portion of the array. A picture of the shaded array taken at 

3:30 p.m. on July 9, 2000, as shown in Figure D-4, demonstrates the tree shading. A 3-D representation 

of the tree in relation to the PV array was simulated, as shown in Figure D-5. It is possible to quantify the 

PV performance degradation due to this shading through simulation. 

Figure D-4 Tree shading of PV array, 3:30 p.m. July 09, 2000 
134 

Figure D-5 Model of tree shading of PV array, 3:30 p.m. July 9, 2000 
135 

Appendix E Extended HVAC and Comfort Analysis 

Portable Comfort Measurement 

During September 22, 2000 through November 29, 2000, a temperature and relative humidity sensor was 

placed by the cash register in the ZNHA area. According to ASHRAE Standard 55, only 5 hours were 

outside the comfort zone, as shown in Figure E-1. These data points occurred during the end of 

September and result from evaporative cooling. These temperatures are reasonable, but the humidity 

added because of the cooltowers resulted in a relative humidity outside of the comfort range. Again, 

values to the left of the comfort zone are considered comfortable because the occupants are able to control 

heating during the winter. 

0

0.002

0.004

0.006

0.008

0.01

0.012

0.014

0.016

50 55 60 65 70 75 80 85 90 95 100

Dry-Bulb Temperature (°F)

Humidity Ratio (lb Water/lb Dry Air)

Winter Comfort

Summer Comfort

Before Noon

After Noon

70°F

60°F

50°F

40°F

Reported from 

09/22/2000 to

11/29/2000, 

Occupied Hours 

Only

Relative Humidity 90%

70%

80%

60%

50%

40%

30%

20%

10%

100%

Figure E-1 Comfort chart of cash register area during occupied hours 
136 

Appendix F Extended Lighting Analysis 

Several other light readings were taking during the evaluation; see Figure F-1 and Figure F-2. Notice the 

higher illuminance near the windows during winter sky conditions. 

153 208 210

190

176 190

158

203

123 134

121

118

122

64

155

105

88 166

158 195

155

92

106 145

150

102

89 127 134

125 176

118

112

101 152 183

92

77

76 102 154

155 79 115 162 93 193 111 196

310

125

67

0

100

200

300

400

500

600

700

800

900

1,000

Illuminance (Lux)

Figure F-1 Illuminance for clear sky with lights OFF; July 11, 2000 at 12:05 p.m. 

606

790 828

692

635 648

825

507507

454

406

350 342

222

442 526

973

950

508 503 340

210

290 335

272

206

299 310

291 308

325

670

480

760

442 248 280

55 83 207 295

74 117

223273 83 102 236

410

185

54 0

100

200

300

400

500

600

700

800

900

1,000

Illuminance (Lux)

Figure F-2 Illuminance for clear sky with lights OFF on December 15, 2000 at 

11:15 a.m. 

ZNHA Area 

NPS Counter 

ZNHA Area

NPS Counter 

N 

N 
137 

Appendix G List of People Involved in Project 

Contracting Party: 

 Denver Service Center 

 National Park Service 

 United Stated Department of Interior 

Contractor: 

 Bud Mahas Construction, Inc 

 917 Duluth Ave. 

 Salt Lake City, UT 84116 

National Park Service Architect: 

 James Crockett, Larry Kilborn, Krista Copeland 

 National Park Service 

 SC-AR 

 P.O. Box 25287 

 Denver, CO 80225 

Predesign Energy Concept Generation 

 Ron Judkoff and Paul Torcellini 

 National Renewable Energy Laboratory 

 1617 Cole Blvd 

 Golden, CO 80401 

Energy Analysis: 

 National Renewable Energy Laboratory 

 Paul Torcellini, Ron Judkoff, Nick Long, Shanti Pless, Sheila Hayter 

 1617 Cole Blvd 

 Golden, CO 80401 

MechanicalEngineer: 

 Mark Golnar 

 National Park Service 

 DSC-EN 

 P.O. Box 25287 

 Denver, CO 80225 

Building Control Systems: 

 Setpoint Systems Corporation 

 Contact: Aaron Nahale 

 2680 South Platte River Drive 

 Denver, Colorado 80223-4208 

 Phone: 303-733-2300 

Post Occupancy Evaluation Team: 

 National Renewable Energy Laboratory 

 Contact: Paul Torcellini, Nicholas Long, Shanti Pless 

 1617 Cole Blvd 

 Golden, CO 80401 

Building Operators: 

 Jim Lutterman, Zion National Park 

 Jim Starling, Zion National Park 
138 

Building Occupants: 

 Zion National Park 

 Zion Natural History Association 

Cooltower Contact: 

 Martin Yoklic 

 University of Arizona 

 Environmental Research Laboratory 

 2601 E. Airport Drive 

 Tucson, AZ 85706 

 Phone: 520-626-3322
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents 

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

February 2005 

2. REPORT TYPE

Technical Report 

3. DATES COVERED (From - To)

 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Evaluation of the Low-Energy Design and Energy Performance of 

the Zion National Park Visitor Center 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/TP-550-34607 

5e. TASK NUMBER

BEC3.4005 and BEC2.4002 

6. AUTHOR(S)

P. Torcellini, N. Long, S. Pless, and R. Judkoff 

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

NREL/TP-550-34607 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

This report is part of a series of six case studies to develop, document, analyze, and evaluate the processes by 

which highly energy-efficient buildings can be reliably produced. NREL monitored the energy performance of the 

Visitor Center Complex at Zion National Park from September 1, 2000 to June 1, 2003. This evaluation was crucial 

to achieving and verifying the low-energy design goals of the building after post-occupancy. This report presents 

results from that multiyear performance monitoring. The Park’s new transportation system was not studied as part of 

the building evaluation. 

15. SUBJECT TERMS

Zion; Zion National Park; National Park; energy evaluation; energy performance evaluation; design; energy design; 

low-energy design; energy performance; high-performance buildings; commercial buildings 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18