Analysis of the Design and 

Energy Performance of the 

Pennsylvania Department of 

Environmental Protection 

Cambria Office Building 

March 2005 • NREL/TP-550-34931 

M. Deru and P. Torcellini 

National Renewable Energy Laboratory

M. Sheffer and A. Lau 

7group 

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

March 2005 • NREL/TP-550-34931 

Analysis of the Design and 

Energy Performance of the 

Pennsylvania Department of 

Environmental Protection 

Cambria Office Building 

M. Deru and P. Torcellini 

National Renewable Energy Laboratory

M. Sheffer and A. Lau 

7group 

Prepared under Task No. BEC3.4004 amd BEC3.1001 
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iii 

Acknowledgments 

The U.S. Department of Energy’s High Performance Buildings initiative (HPBi) made this work possible. 

We appreciate the support and guidance of Dru Crawley, Program Manager of the HPBi. The authors 

would also like to thank others who reviewed this document: Terry Logee of DOE; Ron Judkoff, (Center 

Director for Buildings Research), Brent Griffith, and Peter Ellis of NREL. John Boecker, the building 

architect from Robert Kimball & Associates, also reviewed this document prior to publication. 

Ed Hancock of Mountain Energy Partnership was critical to the success of the monitoring project for his 

efforts at specifying, installing, and programming the data acquisition system. 

The authors would also like to thank the Pennsylvania Department of Environmental Protection for 

allowing NREL to study this building and for assisting with this research. Tammy Ford-Hanna of the 

Cambria office has been especially instrumental in facilitating research needs. 
iv 

Contents 

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

EXECUTIVE SUMMARY ........................................................................................................IX

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

1.1 BUILDING EVALUATION SCOPE........................................................................................ 2 

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

2.1 ENERGY USE IN COMMERCIAL BUILDINGS IN THE UNITED STATES ................................. 3 

2.2 NREL RESEARCH OBJECTIVES ........................................................................................ 4 

2.3 PENNSYLVANIA DEP GREEN BUILDING EFFORTS............................................................ 4 

3 DESIGN PROCESS .............................................................................................................. 6

3.1 PROJECT PERFORMANCE OBJECTIVES .............................................................................. 6 

3.2 ENERGY DESIGN PROCESS ............................................................................................... 7 

3.3 THERMAL ENVELOPE ....................................................................................................... 7 

3.4 LIGHTING AND DAYLIGHTING.......................................................................................... 8 

3.5 HEATING, VENTILATION, AND AIR CONDITIONING .......................................................... 9 

3.6 DESIGN PHASE ENERGY MODELING .............................................................................. 10 

3.7 PHOTOVOLTAIC SYSTEM................................................................................................ 12 

4 CONSTRUCTION AND COMMISSIONING ................................................................. 14

5 CAMBRIA BUILDING DESCRIPTION.......................................................................... 15

5.1 BUILDING ENVELOPE ..................................................................................................... 16 

5.2 LIGHTING AND DAYLIGHTING........................................................................................ 17 

5.3 MECHANICAL SYSTEMS ................................................................................................. 17 

5.4 PHOTOVOLTAIC SYSTEM................................................................................................ 20 

6 WHOLE-BUILDING ENERGY EVALUATION............................................................ 21

6.1 PERFORMANCE MONITORING PLAN ............................................................................... 21 

6.2 MEASURED ENERGY PERFORMANCE.............................................................................. 23 

6.2.1 Annual Energy Performance.................................................................................................23

6.2.2 Monthly Energy Performance by End Use............................................................................25

6.2.3 Average Daily Profiles..........................................................................................................29

6.3 WHOLE-BUILDING ENERGY SIMULATION ANALYSIS ..................................................... 31 

6.3.1 Model Calibration.................................................................................................................31

6.4 WHOLE-BUILDING ENERGY PERFORMANCE RESULTS ................................................... 35 

6.5 ENERGY STAR PERFORMANCE RATING ..................................................................... 35 

7 SYSTEM EVALUATIONS ................................................................................................ 37

7.1 ANALYSIS OF THE HEATING, VENTILATION, AND AIR CONDITIONING SYSTEMS............ 37 

7.1.1 Impact of Heating, Ventilation, and Air Conditioning Controls on Energy Use ..................37

7.1.2 Heating, Ventilation, and Air Conditioning Sizing ...............................................................42

7.1.3 Groundwater Circulation Pumps..........................................................................................42

7.1.4 Outside Air ............................................................................................................................43

7.1.5 Thermal Comfort...................................................................................................................44

7.2 LIGHTING AND DAYLIGHTING EVALUATION.................................................................. 46 
v 

7.2.1 Illuminance Measurements ...................................................................................................47

7.2.2 Lighting System Energy Consumption ..................................................................................53

7.3 ANALYSIS OF BUILDING PLUG LOADS ........................................................................... 54 

7.4 PHOTOVOLTAIC SYSTEM EVALUATION.......................................................................... 56 

7.4.1 Photovoltaic System Measured Energy Production..............................................................57

7.4.2 Photovoltaic System Performance Analysis..........................................................................59

8 CONCLUSIONS.................................................................................................................. 61

8.1 LESSONS LEARNED ........................................................................................................ 61 

8.1.1 Design, Construction, and Commissioning Lessons Learned...............................................61

8.1.2 Technical Lessons Learned ...................................................................................................62

8.1.3 Building Operation Lessons Learned....................................................................................63

8.1.4 Energy Monitoring Lessons Learned ....................................................................................64

8.2 RECOMMENDATIONS...................................................................................................... 64 

REFERENCES............................................................................................................................ 65

APPENDIX A – PROJECT TIME LINE................................................................................. 67

APPENDIX B – HEATING, VENTILATION, AND AIR CONDITIONING CONTROL 

CHANGES................................................................................................................................... 68

APPENDIX C – WEATHER FILE CREATION .................................................................... 69

APPENDIX D – SITE-TO-SOURCE ENERGY CONVERSION ......................................... 71
 vi 

Figures 

Figure ES-1 Annual site energy consumption for the As-Built Baseline Model and As-Built Model.........x

Figure 1-1 South-facing view of the Pennsylvania DEP Cambria building ..............................................1

Figure 2-1 Typical site EUIs by end use for office buildings (kBtu/ft2·yr) (DOE 2004)...........................3

Figure 2-2 Cover page of the Model Green Office Leasing Specifications (1999)....................................5

Figure 3-1 Daylighting design features of the Cambria building ..............................................................9

Figure 3-2 Rendering of the Cambria office building used for energy simulation..................................11

Figure 3-3 Comparison of the energy cost performance of the Design Building Model to the Design 

Baseline Building Model .......................................................................................................12

Figure 5-1 Illustration of the high-performance features of the Cambria building..................................15

Figure 5-2 Floor plans of the Cambria building ......................................................................................16

Figure 5-3 HVAC waterside schematic ...................................................................................................19

Figure 5-4 HVAC airside schematic........................................................................................................20

Figure 5-5 Components of the raised floor system..................................................................................20

Figure 6-1 Comparison of the monthly daily average total energy consumption....................................25

Figure 6-2 Monthly HDDs (base 55°F [13°C]) .......................................................................................26

Figure 6-3 Monthly CDDs (base 55°F [13°C]) .......................................................................................26

Figure 6-4 Daily average energy use and PV production for weekdays from July 2001 to June 2003 

(PV system monitoring began in June 2002) .........................................................................27

Figure 6-5 Daily average energy use and PV production for weekends/holidays from July 2001 to 

June 2003 (PV system monitoring began in June 2002)........................................................28

Figure 6-6 Average daily building load profile for weekdays (2001–2002) ...........................................30

Figure 6-7 Average daily building load profile for weekdays (2002–2003) ...........................................30

Figure 6-8 Energy use from the calibrated simulation model and measurements for five months in 

2002........................................................................................................................................34

Figure 7-1 Average daily HVAC load profile for weekdays (2001–2002) .............................................38

Figure 7-2 Average daily HVAC load profile for weekdays (2002–2003) .............................................38

Figure 7-3 Hourly HVAC energy versus outdoor temperature (July–December 2001)..........................40

Figure 7-4 Hourly HVAC energy versus outdoor temperature (January–October 2002)........................41

Figure 7-5 Hourly HVAC energy versus outdoor temperature (January–June 2003) .............................41

Figure 7-6 Office space CO2 concentrations with the west ERV off during August...............................43

Figure 7-7 Office and outdoor temperatures for the summer of 2002 .....................................................44

Figure 7-8 Office and outdoor temperatures for the winter of 2002........................................................45

Figure 7-9 Average daily RH levels in the second-floor offices .............................................................46

Figure 7-11 Photometer placement in the first-floor, southwest corner of the building............................48

Figure 7-12 Photometer placement in the second-floor, west end of the building ....................................48

Figure 7-13 Placement of two photometers (shown circled) on the working plane of a cubicle...............49

Figure 7-14 Illuminance measurements at workstations for the first-floor, southwest office area from 

July 13–16, 2001 (task lights used in cubicle 10 ft [3 m] from outside wall)........................50

Figure 7-15 Lighting conditions on the first floor on June 7, 2001...........................................................50

Figure 7-17 Daylighting measurements at workstations for the second-floor, northwest office area on 

July 13–16, 2001 (task lights used in cubicle 18 ft [5.5 m] from outside wall).....................52

Figure 7-18 Lighting conditions in the second-floor, northwest office area on June 7, 2001, with the 

overhead electric lights on .....................................................................................................53

Figure 7-19 Daily interior lighting load profiles for weekdays .................................................................54

Figure 7-20 Daily plug load profiles for weekdays ...................................................................................55

Figure 7-21 Average daily purchased energy and PV system performance for June 2001 to August 

2003........................................................................................................................................57

Figure 7-22 Average daily purchased energy and PV system performance for January 2004 to 

December 2004 (a new inverter was installed in late February)............................................58
 vii 

Figure 7-23 Daily PV system energy production, parasitic load, and horizontal solar radiation ..............59

Figure 7-24 Simulated and measured PV performance for 2002...............................................................60

Figure A-1 Project time line from publication of RFPs to end of energy monitoring..............................67

Figure D-1 Energy flow diagram for electricity generation for 2002 (EIA 2003) ...................................72
 viii 

Tables 

Table ES-1 Energy and Energy Cost Performance Metrics.......................................................................xi

Table 3-1 Estimated Energy and Cost Savings ......................................................................................11

Table 5-1 Cambria Office Heat Pump Schedule ....................................................................................18

Table 6-1 Electrical Panels on the Electrical Monitoring System..........................................................22

Table 6-2 Monitoring Points and Frequency on the Campbell Scientific Data Logger .........................23

Table 6-3 Annual Energy Use from Utility Bills ...................................................................................24

Table 6-4 Energy Use Intensity Results from Utility Bills.....................................................................24

Table 6-5 Comparison of Measured Power Levels with the Design Building Model (before 

calibration) .............................................................................................................................32

Table 6-6 Calibrated Hourly Schedules for the As-Built Model............................................................33

Table 6-7 Percentage Difference between the Calibrated Model Energy Use and the Measured 

Energy Use.............................................................................................................................34

Table 6-8 Facility Energy Performance from Calibrated As-Built Models with Pittsburgh TMY2 

Weather File...........................................................................................................................35

Table 6-9 ENERGY STAR Rating of the Cambria Building.................................................................36

Table 7-1 Monthly HVAC Energy Comparison.....................................................................................39

Table 7-2 Energy Impacts of Changes to the ERV Control ...................................................................42

Table 7-3 Number of Office Area Plug Loads on July 13, 2001............................................................56

Table 8-1 Cost, Site, and Source Energy Savings Summary..................................................................61

Table B-1 Summary of HVAC Control Changes....................................................................................68

Table C-1 Weather Stations ....................................................................................................................69

Table C-2 Missing Data and Filling Source............................................................................................70

Table C-3 Calculated Weather Data .......................................................................................................70

Table D-1 Site-to-Source Energy Conversion.........................................................................................71
 ix 

Executive Summary 

Introduction 

The Commonwealth of Pennsylvania established the Governor’s Green Government Council (GGGC 

1998) to encourage environmental sustainability through its policymaking and in its government agencies. 

One of those agencies is the Pennsylvania Department of Environmental Protection (DEP), which has 

established itself as a leader in this endeavor by building and operating several high-performance, green 

buildings. One of DEP’s green buildings is its Cambria office building in Ebensburg, Pennsylvania, 

which was completed in the fall of 2000. 

DEP used an integrated design process for its Cambria building to meet its goal of producing a highperforming, environmentally sound building. The building features efficient wall and roof insulation, 

high-performance windows, ground-source heat pumps, an underfloor air distribution system, energy 

recovery ventilators, daylighting, motion sensors on restroom lights, and an 18.2-kW photovoltaic (PV) 

system for on-site electricity production. In addition to the energy efficiency measures, DEP chose paints 

and adhesives with low-level volatile organic compounds and finish materials based on their origination, 

recycled content, and their potential for being recycled in the future. The effort was successful in 

achieving a LEED (Leadership in Energy and Environmental Design) 2.0 Gold Certification for the 

building from the U.S. Green Building Council. 

DEP then asked the National Renewable Energy Laboratory (NREL) to evaluate the energy performance 

of the Cambria building to determine if it had met design goals. The focus of this report is the analysis of 

an integrated design process used to construct the facility and the postoccupancy energy performance. 

NREL collected energy use and other performance data and compared those data with a standard baseline 

computer model compliant with the minimum levels of Standard 90.1-2001 from the American Society of 

Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE 2001). NREL used the metered data 

and analysis to formulate recommendations to further improve building performance. 

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 compared the 

design process to a 10-step low-energy design process that we had previously developed and continue to 

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

building energy simulation, and 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. 

NREL established the following goals for working with the Cambria building: 

• Monitor and analyze the performance of the building and its subsystems for at least two years. 

• Implement improvements to the building operation based on monitoring and analysis. 

• Document lessons learned to improve future low-energy buildings. 

DEP installed a building energy monitoring system for the major end uses during construction. A second 

monitoring system for indoor air quality that measures temperature, relative humidity, and carbon dioxide 

levels was also added by DEP. NREL installed additional instrumentation to monitor the energy 
 x 

production of the PV systems and the weather conditions. Information from these systems and from the 

utility bills was used to analyze the building energy performance over three years. Based on initial 

results, NREL made changes to the building’s operation and control sequences to improve the energy 

performance. Performance metrics for site energy, source energy, and energy cost savings were 

determined with the energy consumption data. 

Results 

The Cambria building is an example of a high-performance building produced at a reasonable cost of 

$93/ft2

 ($1,000/m2). The building (without the PV systems) shows an estimated 40% energy saving and a 

43% energy cost saving. These savings are for the total building energy use and were determined with 

whole-building energy simulations that were calibrated with measured data. The As-Built Baseline 

Model was compliant with ASHRAE 90.1-2001. The annual energy consumption for the As-Built 

Baseline Model and As-Built Model is shown in Figure ES-1. Most of the energy savings are from a 

reduction in the heating and lighting energy. Table ES-1 shows the annual energy performance for site 

energy, source energy, and energy cost. 

0

100

200

300

400

500

600

Baseline As-Built

Annual Energy Consumption (MWh)

Ext Lights

DHW

Plug

Lights

Pumps

Fans

Cooling

Heating

40% Energy Saving

43% Energy Cost Saving

Figure ES-1 Annual site energy consumption for the As-Built Baseline Model and As-Built Model 
 xi 

Table ES-1 Energy and Energy Cost Performance Metrics 

Cost Total Site Energy Total Source Energy 

$/ft2·yr 

($/m2·yr) 

Percent 

Savings 

kBtu/ft2·yr 

(MJ/m2·yr)

Percent 

Savings

kBtu/ft2·yr 

(MJ/m2·yr)

Percent 

Savings

Baseline $1.80 

($19.38) 

57 

(642) 

180 

(1,800) 

As-Built $1.02 

($10.89) 

43% 

34 

(386) 

40% 

108 

(1,226) 

40% 
 1 

1 Introduction 

As a result of a new state policy instituted by the Governor of Pennsylvania to encourage green building 

practices, the Pennsylvania Department of Environmental Protection (DEP) set a goal to create new 

buildings that advance the concept of high-performance green buildings. The first building under this 

initiative was completed in the spring of 1998 and is DEP’s regional headquarters building in Harrisburg. 

The second building is the Cambria building in Ebensburg, which was completed in the fall of 2000. 

Most of the building’s 34,500 ft2

 (3,205 m2) is used for office space. The main objectives for this 

building were to provide a comfortable and productive work environment and minimize its environmental 

impacts. 

For the Cambria building, DEP integrated high-performance building features into its design process from 

the beginning to meet its goal of producing a high-performance, environmentally sound building. Among 

the high-performance design features chosen for this building were efficient wall and roof insulation, 

high-performance windows, ground-source heat pumps, an underfloor air distribution system (UFAD), 

energy recovery ventilators (ERVs), daylighting, motion sensors on restroom lights, and an 18.2-kW 

photovoltaic (PV) system for on-site electricity production. (Figure 1-1 shows the main entrance of the 

building and the building’s PV system.) DEP extended the sustainable design concepts used for the 

Cambria building to the building’s interior by choosing paints and adhesives with low-level volatile 

organic compounds (VOCs) and finish materials based on their origination, recycled content, and their 

potential for being recycled in the future. The Cambria design team performed a life-cycle analysis to 

estimate the costs and environmental impacts of the building construction and operation. The effort was 

successful in achieving a LEED (Leadership in Energy and Environmental Design) 2.0 Gold Certification 

for the building from the U.S. Green Building Council (USGBC 2004). 

In the spring of 2001, the National Renewable Energy Laboratory (NREL) was invited to evaluate the 

energy performance of the Cambria building. NREL evaluated both the integrated design process used to 

construct the building and the building’s postoccupancy energy performance. The results of that analysis 

are the focus of this report, which 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. This process 

covers predesign through postoccupancy, relies heavily on building energy simulation, and 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 

Figure 1-1 South-facing view of the Pennsylvania DEP Cambria building 

NREL PIX #10138
 2 

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. 

1.1 Building Evaluation Scope 

NREL’s participation with the Cambria building was established with the following goals: 

• Monitor and analyze the performance of the building and its subsystems for a period of at least 

two years 

• Implement improvements to the building operation based on the monitoring and analysis 

• Document lessons learned and determine which of the energy-efficient features could be applied 

to other office buildings 

• Develop and test standardized monitoring protocols developed by NREL as part of the 

Performance Metrics Research Project. 

NREL measured energy use compared to a simulated ASHRAE 90.1-2001 baseline building. Energy and 

water use were normalized by area and occupancy. A comparison was also made between this building 

and the Energy Information Administration’s (EIA) Commercial Buildings’ Energy Consumption Survey 

(CBECS). 

In collaboration with 7group and the staff at Cambria, NREL evaluated the design process and monitored, 

evaluated, and documented the building’s energy performance. The evaluation period was July 2001 

through June 2003. 

Many of the individual high-performance building components incorporated into the design were also 

studied in detail. The evaluation presented in this report focuses on the whole building performance; 

however, additional analysis was done for the PV, mechanical, and daylighting systems. 
 3 

2 Background 

2.1 Energy Use in Commercial Buildings in the United States 

The operation of commercial buildings accounts for approximately 18% of the total primary energy 

consumption in the United States. The total for all buildings is more than one-third of the primary energy 

consumption and more than 70% of the electricity consumption. The operation of buildings in the United 

States results in 38% of U.S. and 9% of global carbon dioxide (CO2) emissions. Electricity consumption 

in the commercial building sector doubled between 1980 and 2002; it is expected to increase another 50% 

by 2025 (DOE 2004). Reducing site energy consumption in commercial buildings through energyefficient and renewable building technologies would significantly reduce primary energy consumption in 

the United States. Site energy is also a concern for the building owner or those responsible for paying the 

utility bills. 

Typical site energy consumption by end use for office buildings is shown in Figure 2-1 (DOE 2004). The 

average building site energy use intensity (EUI) is 97.2 kBtu/ft2

·yr. These numbers are based on 1995 

data collected by EIA. Most of the space heating, water heating, and cooking use natural gas; the rest of 

the energy consumption is electricity. The primary energy consumed to generate and distribute the 

electricity is approximately three times the energy used on site. Lighting is the largest primary energy 

end use; therefore, reduction in lighting loads should be a primary objective in office buildings. 

24.3

9.1

5.2

8.7

28.1

1.1

0.4

15.1

5.2

Space Cooling

Space Heating

Other

Ventilation

Water Heating

Lighting

Cooking

Refrigeration

Office Equipment

Figure 2-1 Typical site EUIs by end use for office buildings (kBtu/ft2·yr) (DOE 2004) 
 4 

2.2 NREL Research Objectives 

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

Buildings initiative. NREL evaluates commercial buildings from a whole-building perspective to 

understand the impact of integrated design issues on energy use and costs in commercial buildings. By 

documenting analysis methodologies and results on new commercial design, NREL is providing direct 

assistance to industry. NREL’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 

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

2.3 Pennsylvania DEP Green Building Efforts 

Pennsylvania DEP took its first steps in creating and operating high-performance green buildings with the 

construction of the South Central Regional Office Building (SCROB) located in Harrisburg, 

Pennsylvania. The goals for this building included the identification and incorporation of sustainable 

building practices and energy efficiency into a cost-effective facility located on a semiurban brownfield 

site. DEP staff used the lessons learned from this first project to rewrite their agency building 

specifications to include and enhance their sustainable building practices, energy efficiency, and 

integrated design practices. The primary objectives were to use green technology to: 

• Significantly reduce energy consumption and operational costs. 

• Maximize the use of sustainable materials. 

• Improve the health, motivation, and productivity of the work force with improved air quality and 

the use of natural light. 

In July 1997, using the new building specifications that resulted from SCROB lessons learned as a guide, 

DEP requested that the Department of General Services obtain proposals for the Cambria project as an 

office facility that would be leased to the Commonwealth of Pennsylvania. The Cambria building was the 

next step in what later evolved into the Commonwealth’s Building Green in Pennsylvania Program. In 

September 1998, the final execution of the lease for the Cambria building was awarded to a developer that 

had proposed the lowest annual lease, and the design was initiated. 

As the Cambria project progressed, a series of additional goals were identified and negotiated into the 

project proposal. These goals later become the initial performance standards criteria for the Model Green 

Office Leasing Specifications published in May 1999 (Figure 2-5) (GGGC 1999). 
 5 

Figure 2-2 Cover page of the Model Green Office Leasing Specifications (1999) 
 6 

3 Design Process 

Because an integrated design approach was used successfully for the first green building project in 

Harrisburg, DEP used the same design approach for the Cambria building. An integrated design approach 

encourages all of the participants (owner, architect, engineers, contractors, etc.) to work together and find 

optimal solutions early in the design process to meet energy goals. This process targets downsizing or 

eliminating systems components, minimizing redundancies, improving performance, and reducing energy 

consumption. Including the contractors in the integrated design process improves their buy-in because 

contractors are able to understand design decisions. Contractor buy-in provides a smoother transition 

from design to construction and helps to control costs. 

The Cambria building is owned by a third party and leased to DEP. DEP developed, as part of the 

requirements of the building, green specifications that were incorporated into the design. The owner had 

an incentive to incorporate the features in a manner that was consistent with a positive cash flow based on 

the lease cost. This arrangement forced a truly integrated design process to meet green standards. It also 

required that the costs be minimized to make the project financially viable to the third party. 

In addition to the integrated design process, the project followed a design-build scenario in which the 

design and construction phases of a project are performed under a single contract. A design-build concept 

provides a single point of contact and streamlines the design process, which can save time and money. In 

a design-build process, the need for value engineering is eliminated because the project costs are 

estimated throughout the design. Therefore, economic values are considered with the systems 

optimizations. For example, much of the design focused on identifying optimized system solutions that 

lowered first costs and operating costs. By continually searching for these opportunities, many of which 

are identified in this report, the project design team was able to incorporate significant green building 

features into the design and deliver a building at conventional construction costs. One potential drawback 

of using the design-build approach is that some of the design occurs during construction with little 

consideration about systems integration and sometimes no documentation. 

The project developer assembled the design and construction teams subject to DEP approval. The 

following companies participated in the project design and construction: 

• Contractor/Developer: Miller Brothers Construction 

• Owner: MBC Properties 

• Architect: Kulp Boecker Architects, P.C. 

• Mechanical Engineer: Phoenix GeoThermal Services 

• Mechanical Contractor: Climate Comfort Heating & Air Conditioning, Inc. 

• Civil Engineer: WJP Engineers 

• Energy Modeling/Consulting: Energy Opportunities, Inc. 

3.1 Project Performance Objectives 

Energy consumption, cost, and environmental impact were primary concerns of the Cambria project. 

Many of the project goals were related to energy issues and initially included the following: 

1. A maximum site energy budget of 40 kBtu/ft2

/yr (450 MJ/m2/yr), not including plug loads and 

PV system contributions. 

2. A lighting budget not to exceed 0.9 W/ft2

 (9.7 W/m2) for ambient lighting. 

3. The indoor surface temperature of glazing shall not be less than 62°F (17°C) when the outdoor 

temperature is 20°F (−6.7°C). 
 7 

4. The indoor surface temperature of opaque wall surfaces shall not be less than 70°F (21°C) when 

the outdoor temperature is 20°F (−6.7°C). 

Additional project goals were established as the design progressed: 

1. Heating, ventilating, and air conditioning (HVAC) chiller size shall not exceed 600 ft2

/ton (15.8 

m2

/kW). 

2. The ventilation system must provide fresh air to maintain indoor air at less than 700 ppm CO2

during hours of occupancy. 

3. Cooling season indoor relative humidity (RH) shall not exceed 45% at established design 

conditions. 

4. Heating season humidity shall be no less than 25% at established design conditions. 

In addition to these specific performance-based goals, the team committed to achieving a LEED Gold 

rating, and established additional performance targets required for earning LEED credits related to site 

issues, water use, energy efficiency, materials, and indoor environmental quality (IAQ). As the project 

team worked its way through the LEED certification process, such targeted goals defined minimum 

performance thresholds for limiting site wetlands disturbance; using alternative transportation; 

implementing effective stormwater management; reducing heat island effects; limiting potable water 

consumption; maximizing energy efficiency; utilizing high percentages of recycled, local, and renewable 

materials; monitoring indoor air quality; increasing ventilation effectiveness, minimizing the use of offgassing materials and VOCs; augmenting controllability; maintaining thermal comfort ranges; 

incorporating daylighting strategies; and providing occupants with access to views. These targeted LEED 

performance goals informed all design decisions. 

3.2 Energy Design Process 

With the project goals well defined by the Commonwealth’s Model Lease Office Specifications, the early 

phases of design focused on building orientation, form, and required functions. As a result, the design 

concept originally conceived by the developer was modified significantly. The original plan envisioned a 

relatively square box with a flat roof and an orientation that responded to the road along the property’s 

edge in order to maximize curb appeal. The resulting building would have been poorly oriented with 

limited ability to capture solar energy and daylight. This concept came from an initial assumption that 

such a configuration would minimize construction costs. 

The original location of the building on the site was changed to optimize solar orientation and preserve 

wetlands on the property. Further design modifications to the building and the parking lots enabled the 

project to protect all of the pre-existing wetlands while meeting the programmatic requirements. The 

adjusted site plan also minimized the building along the street line, preserving a natural setting along the 

street. 

3.3 Thermal Envelope 

The contractor suggested to the design team the use of insulated concrete forms (ICFs) for the majority of 

the exterior wall construction. They had used ICFs on a previous project and found them to save labor 

and time compared to other wall construction systems. Following evaluation by the architect, owner, and 

energy consultant, ICFs were incorporated into the design from the foundation up to the sill height of the 

second-floor windows. Steel frame walls were used above this point. For the purposes of ensuring 

similar thermal performance with this wall system to the ICFs, a 1-in. (2.5-cm) layer of rigid board 

insulation was added to the exterior of the steel studs to mitigate thermal bridging through the studs and 

cellulose was used in the stud cavities. 

The design team target for the thermal performance of the roof was a minimum of R-30 hr⋅ft2

⋅°F/Btu (5.3 

m2

⋅K/W). Additional considerations included improving the daylighting and providing good acoustical 
 8 

performance. The roofing system originally envisioned comprised a steel deck supported by steel bar 

joists, with rigid insulation sandwiched between the deck and a standing-seam metal roof. The final 

design consisted of a series of products: wood/steel trusses, reflective roof decking composed of 100% 

postconsumer recycled waste paper along with a nail base, and recycled steel shingles. This roof 

assembly, which exceeded the performance criteria, provided additional environmental benefits, and 

offered better acoustical properties. 

The building fenestration design consisted of a combination of punched opening windows and storefront 

windows (primarily in the core near the front entrance). In order to comply with the project’s 

performance requirement of an interior glazing surface temperature of 62°F (17°C) when the outdoor 

temperature is 20°F (−6.7°C), two options were considered. The first option was to use radiative or 

convective perimeter heating. This approach had an initial cost estimate of $25,000. The second option, 

recommended by the design team as an integrated design solution, was to use triple-glazed windows and 

attempt to eliminate the perimeter heating system. An analysis completed by the design team, which 

included the use of Window 4.1 (Arasteh et al. 1994), demonstrated that low-e, triple-glazed windows 

would exceed the performance requirement, allow for the elimination of perimeter heating, contribute to 

energy savings via reduced heat gain and loss loads, and in turn, allow for HVAC system downsizing. 

The owner initially balked at the extra cost of these windows (about $15,000), but further analysis 

demonstrated that the use of these windows was the least expensive way to meet the project’s 

performance requirement. Overall, building performance was improved and first costs were reduced, a 

key integrated design solution. 

3.4 Lighting and Daylighting 

Because reduced energy use for electric lighting was identified as a critical issue to be addressed during 

the early stages of design, the building configuration was elongated along an east-west axis to gain better 

solar access and optimize daylight penetration into the building. The rooflines were sloped in order to 

allow the use of north- and south-facing clerestory windows on the second floor for daylighting, which 

also provided an angled surface for mounting PV panels. Light shelves were added on the south side of 

the first floor to help direct some daylight deeper into the office space. These daylighting features are 

illustrated in Figure 3-1. To improve the success of the daylighting, the second floor plan was designed 

to place the large open office spaces adjacent to exterior walls and locate enclosed offices in the center of 

the building rather than at the perimeter. As a result, these private offices do not block access to daylight, 

and the vast majority of occupants are afforded access to this daylight and views. In addition, a major 

programming effort was undertaken to ensure that most of the occupants were located in these large open 

office spaces on the second floor because of their access to daylighting. The first floor was designed to 

accommodate meeting spaces, storage, support functions, and workspace for field staff who spend the 

majority of their time away from the office. 

As is common in a design-build scenario, an independent lighting designer was not included on the design 

team. Lighting design was a combined effort by the architect, electrical contractor, energy consultant, 

and a product sales representative. DEP decided on the use of a lighting system that provided 30 fc (foot 

candles) of ambient light with undercabinet task lighting at workstations for supplemental light. 

Daylighting was an important part of the design and resulted in the use of clerestory windows, overhangs, 

light shelves, and a dimming system. 

The initial lighting design called for a lighting power density (LPD) of 0.82 W/ft2

 (8.8 W/m2). 

Subsequent refinement of the lighting system resulted in a final design LPD of 0.75 W/ft2

 (8 W/m2), not 

including task lighting. The LPD of the task lighting in the office areas is approximately 0.5 W/ft2

 (5.4 

W/m2

). 
 9 

Figure 3-1 Daylighting design features of the Cambria building 

The exterior lighting design was also modified. The original parking lot lighting design contained 14 cutoff fixtures with 400-W standard metal halide lamps mounted on nine poles. Additional analysis resulted 

in a final design of five cut-off fixtures with 400-W pulse start metal halide lamps each mounted on its 

own pole. The final design met the illumination recommendations of the Illuminating Engineering 

Society of North America (IESNA 2000) while reducing the first cost by more than $3,600 and reducing 

the energy costs by more than $1,800 per year compared to the original design. 

3.5 Heating, Ventilation, and Air Conditioning 

Initial HVAC selection for the Cambria building focused on the use of the gas boiler/absorption airconditioner system used at SCROB. It was determined that the Cambria building and its loads were too 

small for this type of equipment. Recommendations by the contractor centered on packaged rooftop 

units. However, it became clear early in the design process that the HVAC system proposed by the 

contractor would not be able to meet all of the performance criteria, and an investigation ensued to 

analyze alternatives. An analysis of the mechanical systems was completed that compared a packaged 

rooftop system with ground-source heat pumps with ERVs. A DOE-2 energy model was used as input 

for a life-cycle costing analysis, which included first cost, maintenance cost, energy cost, and depreciation 

over a 25-year time frame. The ground-source heat pump system was shown to save more than $500,000 

over the 25-year period. 

Following this report, another analysis was conducted comparing seven different HVAC options 

including packaged rooftop units, conventional boiler/chiller systems, various gas-fired chiller options, 

and ground-source heat pumps. The report included a professional cost estimate of each system, annual 

maintenance costs, and estimated energy costs using the DOE-2 energy model constructed for the first 

study. The results showed the ground-source heat pumps had the lowest operating cost and lowest annual 

maintenance costs. The chiller based systems were shown to have significantly higher maintenance costs 

based on data from the 1995 ASHRAE HVAC Applications Handbook (ASHRAE 1995). Maintenance 

problems with the HVAC system at SCROB were a key factor in selecting a system with low 

maintenance. 

Based on the analyses described above, ground-source heat pumps were selected as the system with the 

lowest operating costs that fit the maintenance capabilities of the developer and lessee. However, the first 

Diffuse north light

Summer

Winter
 10 

costs of this system were the highest of those considered. The decision was still made to pursue the 

ground-source heat pump system and investigate changes in the building design, which would allow the 

system first costs to be offset. 

Subsequent consultations and discussions between DEP, the mechanical contractor, the project architect 

and the building owner resulted in the retention of a mechanical engineer to design a ground-source heat 

pump system with ERVs. The use of an experienced ground-source heat pump system designer combined 

with two integrated design solutions (described below), contributed to keeping the cost of the system 

within an affordable range. 

One of the project goals inherent in the Model Lease Office Specs was an HVAC system area-capacity 

ratio of greater than 600 ft2

/ton (15.8 m2/kW). Typical office building HVAC design in this climate 

ranges from 250 to 400 ft2

/ton (6.6 to 10.6 m2/kW). To achieve this goal, the design team had to work 

together to optimize all the building systems in order to achieve significant load reductions. 

Collaboration with the mechanical designer is of vital importance in the development of the loads 

calculations to ensure that they accurately reflect the loads and the capabilities of the HVAC system. The 

result of the combined team effort produced an important integrated design solution, which produced an 

HVAC system area-capacity ratio of 663 ft2

/ton (17.5 m2/kW). The key ingredients to the design solution 

were the building orientation, augmented thermal envelope, lower LPD, and thermal energy recovery, 

which combined to reduce the cooling loads by approximately 50%. The overall result was smaller 

HVAC equipment and fewer ground-source heat pump wells, reducing the total project cost by an 

estimated $60,000. 

DEP specified a raised access flooring system for a UFAD system and modular electrical, telephone, and 

data distribution for the Cambria building. The system was specified because of the improved IAQ, 

reduced churn cost for reconfiguring workspaces, greater flexibility, ease of cabling access, and improved 

energy efficiency. DEP renegotiated the lease agreement with the building owner to compensate for the 

increased first costs of the raised floor system. 

An additional integrated design solution was discovered during a design meeting on the mechanical 

systems. Team members in attendance included the architect, mechanical engineer, mechanical 

contractor, energy modeler, developer, and lessee. The architect had initially predetermined that the 

location of the mechanical equipment would be in a penthouse. The meeting began with a discussion 

about how to coordinate the installation of the piping, ductwork, etc. from the penthouse out into the 

building. The architect realized the inefficiencies and asked where the mechanical space would optimally 

be located to reduce installation cost and simplify the system design. After a long pause, the mechanical 

engineer (who indicated that he had never been asked that question) suggested that the optimum solution 

would be to divide the central mechanical space into two rooms located on the first floor, one in each 

wing of the building. The ductwork for the UFAD system could then feed directly into the first floor. To 

serve the second floor, the ductwork would only have to go up about 6 ft (1.8 m) to connect to the raised 

floor. The only ducts from the roof would be the much smaller ventilation air ducts. 

The developer raised the issue that this design change would eliminate prime leasable space that would 

have to be added elsewhere. To accommodate this request, the architect added 1.5 ft and 2 ft (0.46 m and 

0.61 m) to the west and east ends of the building. The savings to the project resulting from the 

elimination of the mechanical penthouse and the reduced duct and pipe runs (including the increased cost 

of adding space to the building) were estimated at $40,000. In addition, HVAC system performance was 

enhanced due to the minimal turns in the duct system, and maintenance personnel have easier access to 

the mechanical equipment. 

3.6 Design Phase Energy Modeling 

Hourly energy simulations with DOE-2 were used at various stages in the project. Energy simulations 

formed a significant part of the HVAC analysis, which resulted in the selection of the ground-source heat 
 11 

pump system. This analysis used a simplified building model for the purposes of comparing the HVAC 

systems. A more detailed model was created and used to validate and measure the results of design 

decisions (i.e., the detailed model was not used as a design tool) and was called the Design Building 

Model. Figure 3-2 shows a rendering of the detailed building model used in DOE-2. The simulations 

used the ASHRAE WYEC (Weather Year for Energy Calculation) weather data file for Pittsburgh, 

Pennsylvania, the closest site to Ebensburg, Pennsylvania. WYEC data were used because the simulation 

appeared unstable when using the preferred TMY2 weather files. An error was later discovered in the 

DOE-2 default values that caused the instabilities, which is explained in Section 6.3. 

Figure 3-2 Rendering of the Cambria office building used for energy simulation 

The Design Building Model was compared to a budget or Design Baseline Building Model that was 

compliant with ASHRAE 90.1-1989. These initial results showed that the Design Building Model had an 

energy cost reduction of more than 55% compared to the Design Baseline Building Model. The Design 

Baseline Building Model was refined in March and April 2000 to comply with the requirements of 

ASHRAE 90.1-1999. The results remained the same, showing a 55% cost reduction. 

The final Design Building Model submitted for LEED certification included the utility rate structure and 

the purchasing of green power. The adjusted results demonstrated a 50% cost reduction. With the 

inclusion of the estimated revenue from the PV system, the overall energy cost reduction was projected to 

be 66%, as shown in Table 3-1. Figure 3-3 shows a breakdown of the energy consumption by end use. 

The lighting showed the most significant energy cost saving at 61% and the total HVAC energy cost 

saving was 49%. 

Table 3-1 Estimated Energy and Cost Savings 

% Savings 

Fuel 

Design 

Use 

(kBtu)

Design 

Cost 

($/ft2) 

Baseline 

Use 

(kBtu) 

Baseline 

Cost 

($/ft2) Energy Cost 

Total building energy use 851 0.77 1,597 1.54 47% 50% 

PV energy production 82 0.25 0 0 

Net building energy use 768 0.52 1,597 1.54 52% 66% 
 12 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Baseline Building Design Building

Annual Energy Cost ($/ft2

)

Exterior Lights

Fans

Pumps & Aux

Cooling

Heating

Equipment

Lights

Figure 3-3 Comparison of the energy cost performance of the Design Building Model to the 

Design Baseline Building Model 

3.7 Photovoltaic System 

During the summer of 1999, DEP began to express serious interest in a renewable energy system for the 

building. Early analysis quickly centered on a PV system. The architect initially envisioned a small PV 

array to be placed on the roof of the second-floor conference room element. 

Energy Opportunities, Inc., conducted a preliminary analysis in September 1999 on the design 

implications and optimum system size of a PV array. At the same time, an analysis of options for 

purchasing green power was conducted. The goal of these analyses was to determine the feasibility and 

potential cost implications of adding a PV system to the building. The study looked at many options and 

showed reasonable economic returns depending on three assumptions. First, the emergency generator 

would have to be eliminated and replaced by a PV system with battery backup. Second, federal tax 

savings were identified that would reduce the system first costs. Finally, a green power provider (Green 

Mountain Energy) was identified that was willing to pay a premium price for the all the electricity 

produced by the system. This study showed DEP that a system in the range of 15 kW was potentially 

feasible and additional analysis was conducted. 

A firm price estimate and design for the PV system was obtained from the installer. As the design 

progressed, the battery component of the system was eliminated because of maintenance concerns, which 

meant that the emergency generator had to be included in the building design. The installer identified PV 

panels available through a DOE-sponsored buy-down program that significantly reduced the cost estimate 

for the system. An agreement was negotiated with Green Mountain Energy to sell all the power generated 

by the PV system to Green Mountain Energy at a premium price and purchase green power to meet all the 

electricity loads for the building at a lower rate. The green power purchased for the building energy 

consumption is from a mixture of wind and solar production and is slightly more expensive than the rates 

charged by the local utility. After a lengthy review process, a two-year contract was executed with Green 

Mountain Energy effective February 26, 2002. 
 13 

The final analysis showed a total installed system cost of $50,000 after the buy-down and tax benefits. 

Annual energy savings would amount to $1,400 and revenue from the sale of the power generated by the 

system would amount to $7,200. Total savings of $8,600 were projected to result in a simple payback of 

5.8 years. 

The final design consisted of a 17.2-kW PV system mounted on the roof with a 15-kW three-phase 

inverter tied directly to the building’s main distribution panel. An additional 1-kW PV system is mounted 

on two single-axis tracking devices near the main entrance of the building. This system has a singlephase inverter and is tied into the east heating power panel. The larger system is the only one that is 

monitored as part of the agreement with Green Mountain Energy. 
 14 

4 Construction and Commissioning 

As is typically the case with a design-build project, the construction of the project began before design 

was complete. The project construction was completed in phases and coincided with the development of 

the design to a certain extent. 

During construction, the design team continued to develop energy-efficient features and integrate them 

into the project. Some of these decisions would have been better served had they been addressed more 

comprehensively in the design stage. One of the weaknesses of the design-build process is that the 

“design-as-you-go” concept does not always result in a thorough design. 

Commissioning was undertaken during the latter stages of construction. 7group was hired to perform 

commissioning as required by LEED. The commissioning agent participated in major systems start-ups 

and was on site to conduct prefunctional tests on the HVAC system. 

The commissioning process was able to identify several issues during the final stages of construction, 

including: 

• Identifying improper location of the temperature sensors. (They were moved from the return air 

stream to wall mounting within the space.) 

• Discovering a possible issue with the enclosure of the transformer for the PV system. 

• Identifying that the PV system was experiencing functional problems. 

• Finding faulty piping installation in the west mechanical room, which failed during system 

testing. 

• Discovering a potential sprinkler pipe freezing issue in the stairwell and recommending a 

solution. 

• Identifying the cause of ERV failure first noted when DEP reviewed the IAQ monitoring results 

and CO2 levels were very high. 

• Discovering that the 1 in. (2.5 cm) of rigid insulation was not installed over all areas of the steel 

stud portions of the building’s exterior walls. (The insulation was added and the siding reinstalled.) 

The overall effectiveness of the commissioning process on this project was limited by several factors. 

Commissioning did not begin until late in construction. The project was not fully documented, which is 

common in a design-build scenario. Mechanical drawings and specifications were limited to single-line 

duct and pipe drawings. Electrical drawings did not exist. The commissioning agent ended up serving as 

a third party referee at times and as system designer on occasion. 

Following occupancy, a couple of minor issues arose with regard to HVAC and lighting. A heat pump 

was added to the main telecommunications room to address a higher than anticipated cooling load. Three 

areas were identified which required additional illumination: 

• The file room lighting system was supplemented with three continuous rows of surface mount, 

two-tube fluorescent fixtures controlled by a timer switch, and the existing three-tube parabolic 

fluorescent fixtures were moved to the corridors on either side of the files. 

• An additional row of indirect fixtures (removed from the file room) was installed in a secondfloor conference room. 

• Additional compact fluorescent task lighting was purchased for the tables in the supervisor 

offices and the draft tables in a few of the cubicles. 
 15 

5 Cambria Building Description 

The Cambria building is a two-story, 34,500-ft2 (3,205-m2) structure oriented on a long east-west axis, as 

shown in Figures 5-1 and 5-2. The building contains office space for approximately 100 people, a large 

file storage area, two small laboratory areas, conference rooms, a break room, and general storage areas. 

Figure 5-1 Illustration of the high-performance features of the Cambria building 

 
 16 

Figure 5-2 Floor plans of the Cambria building 

5.1 Building Envelope 

The building rests on a slab-on-grade with 2 in. (5 cm) of horizontal perimeter insulation extending in 4 ft 

(1.2 m) from the exterior wall. The walls are primarily constructed of ICFs with an insulating value of R27 hr⋅ft2

⋅°F/Btu (4.8 m2⋅K/W). Remaining walls are 6-in. (15-cm) steel frame with spray cellulose 

insulation in the cavity and 1-in. (2.5-cm) rigid insulation on the exterior. The roof consists of decking 

and insulation with a total insulating value of R-33 hr⋅ft2

⋅°F/Btu (5.8 m2⋅K/W). Windows are triple-pane 

with aluminum frame for the entryways and triple-pane, wood frame for all other windows. Window 

insulating values are U-0.24 Btu/hr⋅ft2

⋅°F (1.4 W/m2⋅K) and U-0.26 Btu/hr⋅ft2⋅°F (1.5 W/m2⋅K), 

respectively. 

2nd Floor (Open Office Space) 

1st Floor 

Open Office File Storage 

Meeting Rm. Break 

Room 

Mech.

Room

Mech.

Room Storage 

Labs 

Telecom Room

Library
 17 

5.2 Lighting and Daylighting 

The luminaires in the open office areas are indirect fixtures with 32-W T-8 fluorescent lamps with an 

installed capacity of 0.75 W/ft2

 (8.1 W/m2). The LPD of the task lighting in the office areas is 

approximately 0.5 W/ft2

 (5.4 W/m2). The luminaires in the second-floor offices have dimmable ballasts 

controlled by lighting sensors in each of the office areas. Undercabinet task lighting in each cubicle is 

controlled by a motion sensor connected to a power strip. Compact fluorescent lamps are used in other 

areas of the building such as the restrooms and lobby. Occupancy sensors are installed on the restroom 

lighting. Timing circuits in the breaker boxes control the building ambient and exterior lighting systems 

with override switches near the main entrance. 

Daylighting features were incorporated into the design beginning with the building orientation on an eastwest axis (see Figure 5-1). Virtually all fenestration faces either north or south. The second floor is 

primarily open office plan and houses the majority of building occupants. The daylighting design 

incorporates clerestory windows facing north and south along the center of the building. The south-facing 

clerestory windows are equipped with motorized sunscreens controlled by a photosensor to block directbeam radiation. Overhangs shade the second floor windows on the south elevation. Light shelves are 

installed on the south-facing, first-floor windows. The interior finishes were selected to improve the light 

reflection and provide contrast. The first-floor ceiling tiles have a light reflectance of 89%, the second 

floor has high vaulted white ceilings with an open truss construction, the bottom 2.5 ft (0.8 m) of the 

walls are a light, natural wood color, the top portion of the walls are painted off-white (light reflectance of 

75%), and the cubicle dividers are off-white. The carpet and the desktops are black. The IESNA Lighting 

Handbook recommends the following light reflectances for surfaces in offices: ceilings, 80% or more; 

floors, 20%–40%; walls, 50%–70%; partitions, 40%–70%; and furniture, 25%–45% (IESNA 2000). 

The use of the task-ambient lighting scheme, light-colored surfaces, and lighting design resulted in a 

reduced first cost for the lighting system of approximately $20,000 compared to the original design. The 

lighting system saving does not include the additional first cost saving related to downsizing the HVAC 

system because of reduced heat gain from the lights. 

Immediately after the building was occupied, the lighting in the file storage area was noted to be 

inadequate. The files are stored in tall rows of moveable shelves that block much of the light, making it 

difficult to read the files. Thirty light fixtures were added in this space in order to provide adequate 

lighting. The light fixtures used two T-8 lamps. 

5.3 Mechanical Systems 

Ground-source heat pumps with ERVs are the primary heating and cooling sources. All of the heat 

pumps, except number 16, are located in two mechanical rooms serving the east and west wings of the 

building. Table 5-1 lists the heat pump capacities and areas served. Heat pump 16 was installed in the 

telecommunications room after the first year of operation because heat pump 13 did not provide adequate 

cooling to this space. Heat pump 13 provides cooling to the entire northeast quadrant of the building, 

which is used mostly for storage and laboratory space. The telecommunications room has very different 

space conditioning requirements than the other areas, and the temperature sensor for controlling the heat 

pump is located in the storage area. Total rated cooling capacity for the building is 53.7 tons (189 kW), 

which is 640 ft2

/ton (2.6 m2/kW). 

Electric resistance heaters provide auxiliary heating for the heat pumps. Nine units have integral singlestage heaters and heat pumps 5 and 6 have duct-mounted, two-stage heaters. Electrical power was never 

wired to the duct-mounted heaters. 

A schematic of the waterside loop for the HVAC systems is shown in Figure 5-3. Each heat pump has a 

dedicated series of one to three 1⁄4-hp (190-W) pumps for groundwater circulation, which run 

continuously. The pumps are connected to common supply and return headers in each mechanical room. 
 18 

Table 5-1 Cambria Office Heat Pump Schedule 

Heat 

Pump 

Area Served Cooling 

Capacity 

kBtu/hr (kW)

Auxiliary 

Heater 

kBtu/hr (kW)

Flow 

CFM (l/s)

Circulation 

Pumps 

1 1st-floor lunch 

and storage 

26 (7.6) 25.6 (7.5) 800 (378) 1 

2 1st-floor meeting 

room 

60 (17.6) 51.2 (15) 2,000 (944) 2 

3 1st-floor south 

offices 

42 (12.3) 25.6 (7.5) 1,400 (661) 2 

4 1st-floor 

reception, copy 

room, and 

conference room 

22 (6.4) 25.6 (7.5) 800 (378) 1 

5 2nd-floor north 96 (28.1) * 3,200 (1,510) 3 

West Side 

6 2nd-floor south 72 (21.1) * 2,400 (1,133) 2 

11 1st- and 2nd-floor 

lobby 

54 (15.8) 51.2 (15) 1,800 (849) 2 

12 Central files and 

library 

54 (15.8) 51.2 (15) 1,800 (849) 2 

13 1st-floor labs, 

storage, and 

telecom room 

70 (20.5) 51.2 (15) 2,400 (1,133) 2 

14 2nd-floor south 48 (14.1) 25.6 (7.5) 1,600 (755) 2 

15 2nd-floor north 70 (20.5) 51.2 (15) 2,400 (1,133) 2 

East Side 

16 ** Telecom room 30 (8.8) 24 (7.0) 1,000 (472) 1 

 Total 644 (189) 382 (113) 21,600 (10,193) 22 

*Heat pumps 5 and 6 have duct-mounted auxiliary heaters of unknown size with no power supplied to 

them. 

**Heat pump 16 was added after the first year of operation to provide cooling directly to the Telecom 

room. 
 19 

Figure 5-3 HVAC waterside schematic 

A schematic of the airside loop for the HVAC systems is shown in Figure 5-4. Two ERVs, one for each 

wing, supply ventilation and exhaust air and are located on the roof. Each uses a fixed-plate, enthalpic 

heat-exchange core for both latent and sensible thermal energy recovery. They use constant volume 

supply and exhaust fans. The west ERV fans draw 8.5 kW and supply 3,000 cfm (1,400 l/s) of outside 

air, and the east ERV fans draw 4.5 kW and supply 1,500 cfm (700 l/s) of outside air. The outside air is 

preconditioned by the ERVs, then supplied to the mechanical rooms, which act as supply air plenums for 

the heat pumps. The constant volume fans in the heat pumps draw return air from central return air ducts 

for each floor and mix this with the preconditioned outside air in the mechanical rooms. Heat pump 16 is 

located in the telecommunications room, and therefore cannot use outside air from the ERVs. 

The ERVs have simple on-off controllers located in the ERVs. Daily schedules can be input to the 

controllers. The design intent was to run the ERVs during operating hours and turn them off during 

nights and weekends. The heat pumps are separately controlled by dedicated programmable thermostats. 

The thermostats are located in the mechanical rooms and connected to temperature sensors located in the 

zones served by each heat pump. The design intent was to maintain constant temperature set points, and 

run the heat pump fans continuously during the day and as needed during nights and weekends to 

maintain temperature set points. There were no temperature setbacks or setups because it was thought 

that it would be difficult for the systems to recover and that there would be little or no energy savings. 

The majority of the building uses a UFAD system with swirl diffusers mounted in the raised floor. The 

swirl diffusers are located in the common areas and in each office area, and they can be manually adjusted 

by the occupant to control the amount of air entering his or her workspace. Return air registers are 

located high in the spaces. The system uses a displacement ventilation principle by supplying fresh air 

near the occupants and removing the older stale air high in the space. Figure 5-5 shows the components 

of the raised floor system including a view of the manually operated swirl diffuser. 

Heat 

Pump

Ground wells

Groundwater 

circulation pumps

Heat pumps

1-6 west side

11-16 east side

Heat 

Pump

Heat 

Pump
 20 

Figure 5-4 HVAC airside schematic 

Figure 5-5 Components of the raised floor system 

5.4 Photovoltaic System 

There are two PV systems on the building. A 17.2-kW system is mounted on the roof with a 15-kW, 

three-phase commercial grid-tied inverter; there is a 1-kW system mounted on two single-axis trackers in 

front of the building (Figures 1-1 and 5-1). Both systems use 43-W, amorphous-silicon PV panels to 

produce electricity. The large system feeds into the main distribution panel through a utility-grade power 

meter. The output of the inverter for the large system requires an isolation transformer to connect to the 

power grid. The transformer reduces the output of the system by approximately 3% when the system is 

operating, and it draws approximately 370 W of power when the PV system is not producing power. The 

small PV system has a single-phase, 1-kW inverter and feeds into the heating panel on the east side of the 

building. The energy output of only the large PV system is metered for the purposes of generating 

revenue. 

NREL PIX #11001 

Ground Source Loop 

Heat Pump 

ERV 

Supply Air 

to Zones 

Return Air 

From Zones

Outdoor Air 

Exhaust Air 

Mechanical Room 

DX
 21 

6 Whole-Building Energy Evaluation 

NREL evaluated the energy performance of the Cambria building with continuous end-use monitoring, 

analysis of utility bills, walk-through inspections of the building, spot measurements, and computer 

simulations. This section describes the monitoring plan and equipment, results, and comparison used to 

model baseline predictions. Guidance for monitoring and reporting the energy performance of 

commercial buildings can be found in Procedure for Measuring and Reporting Commercial Building 

Energy Performance (NREL 2005a). 

6.1 Performance Monitoring Plan 

The overall goal of the energy monitoring activity was to measure the building energy use patterns and 

evaluate the performance. This goal was broken down into the following objectives for the energy 

monitoring plan: 

1. Determine the energy use in the building systems. 

2. Verify that the design performance objectives are being met. 

3. Improve the performance of the building energy systems where possible. 

4. Track systems to ensure long-term performance of the building. 

5. Evaluate the lighting system performance including the effects of daylighting. 

6. Evaluate the PV system performance. 

7. Compare the building energy performance to an energy code-compliant building and to the 

typical building stock for this region. 

8. Meet requirements of the LEED Green Building Rating SystemTM Version 2.0 Energy Credit 5 – 

Measurement and Verification, the intent of which is to “provide for the ongoing accountability 

and optimization of building energy and water consumption performance over time.” 

In order to satisfy these objectives the following measurements were taken: 

1. Surveys of electrical equipment in the building including spot measurements of power or current 

2. Monthly building utility bills for electricity 

3. Total electrical power at 15-minute increments 

4. Electrical power of major end uses at 15-minute increments 

5. Electrical energy delivered to the building by the PV system in 15-minute increments 

6. Weather data including dry-bulb temperature, RH, horizontal and PV plane solar radiation, and 

PV system cell temperature. 

There are four energy-monitoring systems in the Cambria building. The building’s net electrical energy 

use is measured by the utility power meter. Another utility grade meter monitors the energy production of 

the large PV system. A SquareD PowerLogic® monitoring system monitors the energy use in each of the 

10 major electrical panels. Finally, a Campbell Scientific CR10X data logger is used to monitor the space 

temperatures, RH and CO2 levels, the weather station, and both PV systems. 

The PowerLogic electrical monitoring system was part of the building design and was installed by the 

building contractor. The system consists of 10 Enercept power meters and a personal computer that polls 

the meters and records the data every 15 minutes. Table 6-1 shows the electrical panels and the loads 

monitored by this system. The personal computer has remote control software and is connected to a 

phone line to allow remote access for data retrieval. The system began storing monitored data near the 

end of June 2001. 
 22 

Table 6-1 Electrical Panels on the Electrical Monitoring System 

Electrical Panel Loads 

1st E heat panel heat pumps, fans, circulation pumps, water heater 

1st E light panel lights 

1st E rec panel telephones, water cooler, freezer, receptacles 

1st W heat panel heat pumps, fans, circulation pumps 

1st W light panel lights 

1st W rec panel receptacles, break room loads 

2nd light panel lights, water cooler, sprinkler compressor 

2nd rec panel receptacles 

Elevator elevator 

EMR panel egress lights, exit signs, fire panel 

The electrical monitoring system and the associated computer has proven to be difficult to use and not 

very reliable. The meters have no memory and can only relay instantaneous readings; therefore, only the 

instantaneous power is known at 15-minute increments and not the energy consumed. If the personal 

computer fails, there is a loss of data until the computer is manually rebooted. The downtime of the 

personal computer has resulted in a loss of more than 30% of the data for the two-year monitoring period. 

Some months have no missing data; two months have no data. In addition, the data are stored in 

weeklong increments in database files. These files are large and fill up the hard drive space quickly, and 

they make data retrieval difficult because only one week at a time can be accessed. The computer 

assigned to this system was old, and its small hard drive filled up near the end of June 2003. The 

computer was not maintained or replaced; therefore, no archived data were available from this system 

starting in July 2003. 

The Campbell Scientific data logger was installed by a DEP contractor to monitor the space conditions in 

each of the four quadrants on the second floor and the southwest quadrant and main conference room on 

the first floor. These measurements consist of the temperature, RH, and CO2. Originally, the data logger 

was programmed to record data every 10 minutes. NREL installed additional instrumentation to monitor 

the PV systems and the weather and connected them to this data logger. The data logger was 

reprogrammed to record the totals or averages of each variable every 15 minutes and record the total PV 

power every minute. A personal computer is dedicated to poll the data logger every two hours to collect 

the new data. The data logger has enough memory to go for approximately one month without 

overwriting the 15-minute data. An external memory module is also attached to the data logger that can 

store nearly two years of 15-minute data. A description of the data points and monitoring frequency on 

the data logger are shown in Table 6-2. 
 23 

Table 6-2 Monitoring Points and Frequency on the Campbell Scientific Data Logger 

Data Point Frequency 

Space temperature (6 points, time averaged) 15 min 

Space RH (6 points, time averaged) 15 min 

Space CO2 (6 points, time averaged) 15 min 

Space CO2 (6 points, maximum) 15 min 

Outdoor temperature 15 min 

Outdoor RH 15 min 

Global horizontal solar radiation 15 min 

Global PV-plane solar radiation 15 min 

PV cell temperature 15 min 

Main PV system AC voltage (3 phases) 15 min 

Main PV system power production 15 min and 1 min 

Main PV system power consumption 15 min and 1 min 

Small PV system power production 15 min and 1 min 

Several performance metrics are used to examine the energy performance of the building. The Procedure 

for Measuring and Reporting Commercial Building Energy Performance (NREL 2005a) describes these 

metrics and the methods of determining them in detail. This section uses these performance metrics to 

analyze the energy performance at various levels. The first level of analysis is on an annual basis from 

the utility bills. Monthly energy consumption by end use is used to examine the energy distribution and 

the seasonal variations. Average daily profiles are used to analyze the daily energy use patterns. Wholebuilding energy simulations are used to determine the performance compared to an energy codecompliant building for typical weather. The simulations are used to examine the effects of changing the 

energy systems in the building. Finally, the building is rated using the ENERGY STAR® Portfolio 

Manager. 

6.2 Measured Energy Performance 

6.2.1 Annual Energy Performance 

Analyzing utility bills was the only method available for determining total energy use before July 2001. 

Table 6-3 summarizes energy use and peak demand for the Cambria building from 2001 to 2003 using the 

utility bills and PV monitoring. Net site energy use gives credit for electricity generated on site by the PV 

system; total site energy use is the total electricity consumed. The heating degree-days (HDDs) and 

cooling degree-days (CDDs) are also included for comparison of the weather years. 
 24 

Table 6-3 Annual Energy Use from Utility Bills 

Performance Metric 2001 2002 2003 

Net site electrical energy – MMBtu/yr 

(GJ/yr) 

1,446 

(1,526) 

1,242 

(1,310) 

1,243 

(1,311) 

Total site electrical energy – MMBtu/yr 

(GJ/yr)

1,496 

(1,578) 

1,269 

(1,339) 

1,262 

(1,331) 

Net PV energy production – MMBtu/yr 

(GJ/yr)

50 

(53) 

27 

(28) 

19 

(20) 

Percent total energy from PV system 3.3% 2.2% 1.5% 

Average monthly peak demand (kW) 80 82 83 

Maximum peak demand (kW) (Feb) 90 (Dec) 99 (Jan) 95 

Average load factor 59% 50% 50% 

Net site purchased energy cost $28,120 $29,919 $35,197 

HDDs (55°F [13°C]) 6,117 5,886 6,554 

CDDs (55°F [13°C]) 2,469 2,885 2,501 

Source energy is a measure of the energy required to supply the energy in the form it is used at the site. 

Appropriate source energy conversion factors for the Cambria building are difficult to determine because 

electricity is provided through an energy contract from a supplier that specializes in distributing electricity 

generated by renewable sources. The contract leads to a real increase in energy costs, but in theory, 

should reduce the source energy use attributed to operating the Cambria building. If we assume that only 

transmission losses apply and a source energy conversion factor of 90% is applicable, the annual net 

source energy use was 1,607 MMBtu/yr (1,695 GJ/yr) for 2001 and 1,379 MMBtu/yr (1,455 GJ) for 

2002. However, if we assume that a national average source energy conversion factor of 31.6% applies, 

the annual net source energy use was 4,580 MMBtu/yr (4,832 GJ) for 2001 and 3,935 MMBtu/yr (4,150 

GJ) for 2002 and 2003. The details of how the conversion factor was calculated are included in Appendix 

D. 

The EUI, which is the annual energy use per square foot, provides a succinct method of representing 

energy performance. Table 6-4 lists results for EUI and energy cost intensity based on a building area of 

34,500 ft2

 (3205 m2). 

Table 6-4 Energy Use Intensity Results from Utility Bills 

Performance Metric 2001 2002 2003 

Net Site EUI – kBtu/ft2·yr (MJ/m2·yr) 42 

(477) 

36 

(409) 

36 

(409) 

Total Site EUI – kBtu/ft2·yr (MJ/m2·yr) 43 

(488) 

37 

(420) 

37 

(420) 

90% Net Source EUI – kBtu/ft2·yr (MJ/m2·yr) 47 

(534) 

40 

(454) 

40 

(454) 

31.6% Net Source EUI – kBtu/ft2·yr (MJ/m2·yr) 133 

(1,510) 

114 

(1,295) 

114 

(1,295) 

Net Site Energy Cost Intensity – $/ft2·yr ($/m2·yr) 0.82 

(8.83) 

0.87 

(9.36) 

1.02 

(10.98) 
 25 

6.2.2 Monthly Energy Performance by End Use 

The monthly daily average energy consumption by end use was calculated from the 15-minute 

instantaneous power readings from the electrical monitoring system assuming an average power for the 

previous 15-minute period. There are two potential errors with this method. The first is that almost onethird of the data were missing due to failures in the monitoring system, and the second is the assumption 

that the average power over a 15-minute period may not be represented well by one instantaneous 

reading. Fortunately, the power levels in this building are relatively constant during the occupied and 

unoccupied periods, and averaging the values over the period of a month should produce reasonable 

results. NREL checked this method of predicting the monthly daily average energy totals by comparing 

the total building energy consumption from the electrical monitoring system to the utility bills plus the 

energy produced from the PV systems. This comparison is shown in Figure 6-1. The average difference 

is −1.7% and the largest monthly difference is −7.3%. Therefore, it is reasonable to use the values from 

the PowerLogic system to estimate the monthly daily average energy consumption of the major end uses 

for comparison purposes. Note that the data are completely missing for November and December 2002. 

0

200

400

600

800

1000

1200

1400

Jul-01

Aug-01Sep-01

Oct-01

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

Jun-03

Average Daily Electricity Use (kWh)

Utility Bills

Electrical Monitoring System

Figure 6-1 Comparison of the monthly daily average total energy consumption 

The weather conditions are important drivers of the energy use in buildings. The monthly HDD (base 

55°F [13°C]) and CDD (base 55°F [13°C]) are shown in Figures 6-2 and 6-3. The data for January 2001 

to June 2001 is adjusted from a Federal Aviation Administration weather station at the Blair County 

Airport in Altoona, Pennsylvania (Appendix C). Starting in July 2001, weather data were measured at the 

building site. Notice that the summer of 2002 was much warmer than the summers of 2001 and 2003, 

with 1,850oF·days (1,028oC·days) CDD from May to September 2002 versus 1,446oF·days (803oC·days) 

CDD for 2001, and 1,455oF·days (808oC·days) CDD for 2003. In addition, the winter of 2002–2003 was 

colder than the winter of 2001–2002, with 3,256oF·days (1,809oC·days) HDD for December to March 

2002–2003 versus 2,445oF·days (1,358oC·days) HDD for December to March 2001–2002. 
 26 

0

200

400

600

800

1000

1200

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

Monthly Heating Degree Days (55°F)

2001

2002

2003

Figure 6-2 Monthly HDDs (base 55°F [13°C]) 

0

100

200

300

400

500

600

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

Monthly Cooling Degree Days (55°F)

2001

2002

2003

Figure 6-3 Monthly CDDs (base 55°F [13°C]) 
 27 

The breakdown of energy consumption by end use is shown in Figures 6-4 and 6-19, for weekdays and 

weekends/holidays. These figures show the average daily energy use by month for the HVAC, lighting, 

and plug loads for July 2001 through June 2003. These graphs also show the energy production by the 

PV systems. The PV system monitoring began in June 2002 on the Campbell data logger system. In 

addition, the average monthly outdoor dry-bulb temperature is shown on the graphs. 

-200

0

200

400

600

800

1000

1200

1400

Jul-01

Aug-01Sep-01

Oct-01

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

Jun-03

Average Daily Electrical Energy Use (kWh)

0

10

20

30

40

50

60

70

80

Average Outdoor Air Temperature (°F)

PV Plug Lights HVAC Temperature

Figure 6-4 Daily average energy use and PV production for weekdays from July 2001 to 

June 2003 (PV system monitoring began in June 2002) 
 28 

-200

0

200

400

600

800

1000

1200

1400

Jul-01

Aug-01Sep-01

Oct-01

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

Jun-03

Average Daily Electrical Energy Use (kWh)

0

10

20

30

40

50

60

70

80

Average Outdoor Air Temperature (°F)

PV Plug Lights HVAC Temperature

Figure 6-5 Daily average energy use and PV production for weekends/holidays from July 2001 

to June 2003 (PV system monitoring began in June 2002) 

The energy use for plug loads is similar from month to month, which is expected in an office building 

with consistent schedules. The lighting loads show a slight increase in the winter, which is mostly due to 

increased use of exterior and manually controlled interior lights. Overall, the HVAC systems consume 

approximately 55% of the total energy, the lights 21%, and the plug loads 24%. 

The weekday HVAC energy use had smaller than expected variations in weather conditions from July 

2001 to May 2002. An investigation of the HVAC controls revealed that the controller on the west ERV 

was incorrectly set. The schedule to turn the unit off was programmed correctly, but it was not activated, 

which left the unit running continuously. In addition, the heat pump fans ran continuously and there was 

no setback on the heat pump thermostats. The effect of these control problems can also been seen in the 

weekends/holidays HVAC energy use. The HVAC energy use for winter weekends/holidays was actually 

higher than the weekday energy use. This was due to the high amount of outside air being brought into 

the building by the west ERV when there were minimal internal gains to help heat the building. 

Changes were made to the HVAC controls at the beginning of June 2002. The controller on the west 

ERV was correctly programmed to turn on at 6:00 a.m., turn off at 5:00 p.m. Eastern Standard Time 

(EST), Monday through Friday, and stay off on the weekends. The east ERV was set to the same 

schedule. The thermostats were reprogrammed with cooling set points of 72°F (22°C) and 78°F (26°C) 

and heating set points of 70°F (21°C) and 66°F (19°C) during occupied and unoccupied periods. The 

occupied hours were set from 5:00 a.m. to 6:00 p.m. EST. In addition, the clock on HP11 was off by 12 

hours; therefore, reprogramming with a setback caused it to come on at night and turn off during the day. 

The clock was reset to the correct time. 

The effects of these changes are most noticeable in the weekend/holiday HVAC energy use in Figure 6-

19, which shows a large drop from May to June 2002. The weekend/holiday HVAC energy use for the 

remainder of the monitoring period remained lower than the previous year’s values despite a warmer 

summer and a colder winter. The lower energy use is also evident in the weekday graph in Figure 6-4. 
 29 

The average daily HVAC energy use for July 2002 is more than 100 kWh less than the July 2001 value, 

even with nearly twice as many CDDs in July 2002 as in July 2001. 

After the thermostats were adjusted, there were some comfort complaints in isolated parts of the building, 

which led DEP to remove the heating setbacks and cooling setups on all the thermostats. In one case, the 

thermostat was set with a higher heating temperature at night than during the day. The main heating 

problem was in the upstairs restrooms, which have an outside wall but no direct heating source. The 

restrooms rely on the exhaust fans drawing warm air from the main part of the building. All of the 

thermostats were reprogrammed in July of 2003 with less aggressive setback and setup schedules. The 

thermostats were reprogrammed with cooling set points of 72°F (22°C) and 76°F (24°C) and heating set 

points of 72°F (22°C) and 68°F (68°C), and the occupied hours were set to 4:00 a.m. to 6:00 p.m. EST. A 

more detailed examination of the HVAC systems is completed in Section 7.1. 

The plug loads remain high during the weekend/holiday periods. The plug load power level during 

unoccupied periods is approximately half of the value during occupied periods. This is due to a large 

amount of electrical equipment being left on continuously. A more detailed examination of the plug loads 

is completed in Section 7.3. 

The PV systems provided between –0.7% and 4% of the overall monthly energy consumption in the 

building. The inconsistent system performance is mainly due to the poor performance of the inverter on 

the large PV system. The negative percentage is due to the energy consumption by the isolation 

transformer when the system is not producing power. A more detailed analysis of the PV systems is 

contained in Section 7.4. 

6.2.3 Average Daily Profiles 

Another way to examine energy use is to plot the average daily load profiles by month. This aggregates 

the monthly data into one graph and allows a view of the daily and seasonal variations. Daily load 

profiles were created from the PowerLogic data for weekdays and for weekends/holidays for every month 

during the data-monitoring period. The seasonal variations in the building daily load profiles from 2001 

to 2003 are shown in Figures 6-6 and 6-7. The dates for the graphs were set because July 2001 was the 

first full month of data collection and changes were made to the HVAC control systems in June 2002 that 

had a significant impact on the energy consumption. The most noticeable differences between the two 

figures is that the nighttime loads are higher in Figure 6-6 and the daytime loads for July and January are 

higher in Figure 6-7. Changes to the HVAC control settings (Section 7.1) lowered the nighttime loads. 

Some of these changes were reversed by January 2003, resulting in an increase in the nighttime loads. 

The daytime loads are higher in Figure 6-7 because the weather in July and January was more severe 

(hotter or colder) than in the months in Figure 6-6. The weather differences are seen in the HDD and 

CDD as shown in Figures 6-2 and 6-3. 
 30 

0

10

20

30

40

50

60

70

80

90

0 3 6 9 12 15 18 21 24

Hour

Building Weekday Electrical Power (kW)

Jul 2001

Oct 2001

Jan 2002

Apr 2002

Figure 6-6 Average daily building load profile for weekdays (2001–2002) 

0

10

20

30

40

50

60

70

80

90

0 3 6 9 12 15 18 21 24

Hour

Building Weekday Electrical Power (kW)

Jul 2002

Oct 2002

Jan 2003

Apr 2003

Figure 6-7 Average daily building load profile for weekdays (2002–2003) 
 31 

6.3 Whole-Building Energy Simulation Analysis 

Computer modeling was used to provide a means of comparing the actual performance of the Cambria 

building to what it would have been were it built to meet the minimum standards of the energy code. The 

simulation models used in the design phase were updated and calibrated to match the as-built building. A 

baseline energy model was developed to meet the minimum standards of ASHRAE Standard 90.1-2001 

(ASHRAE 2001). An informative addition to the standard, Addendum e, was developed that provides a 

method of applying the Energy Cost Budget method to rating buildings that perform better than required 

by the standard (ASHRAE 2002 and 2003). This addendum is included in Standard 90.1-2004 as 

Appendix G. The Baseline Building Model used a packaged heat pump for heating because natural gas is 

not available at the building. The models were calibrated using measured weather and energy 

consumption data for 2002 and used schedules for occupancy and receptacles developed from 

measurements. Then the calibrated As-built and As-Built Baseline Models were run with a “typical” year 

weather file from Pittsburgh, which is the closest location with a TMY2 weather file. 

The simulation models used in the design phase used ASHRAE’s WYEC weather data for Pittsburgh, 

Pennsylvania. WYEC data were used because the simulation appeared unstable when the preferred 

TMY2 weather files were used. While using the model to develop the calibrated version, an error was 

found in the performance curves for the cooling operation of the ground-source heat pumps. One of the 

points in the performance curve was far out of range. The cooling performance curves were reset to the 

library values for water-loop heat pumps. Subsequent runs with Pittsburgh TMY2 weather data showed 

no instabilities, and the TMY2 weather data were used for the remaining simulations. 

6.3.1 Model Calibration 

The Design Building Model and the Design Baseline Building Model were calibrated to more accurately 

describe the actual equipment loads and building use, and hence, provide better prediction of actual 

energy use. The calibrated model is called the As-Built Model. The information for adjusting the AsBuilt Model came from several sources: 

• Ongoing measured electricity use from three sources: 1) the total metered utility electricity use 

(kWh and monthly peak kW), 2) the total roof-mounted PV array electricity production (monthly 

kWh), and 3) the PowerLogic system that monitors power in each of 10 major electrical panels 

(15-minute kW) 

• Hand measurements of typical electrical loads connected to the panels 

• Observations of occupancy patterns, thermostat settings, time clock settings, and other operating 

characteristics 

• Ongoing measurements of local weather data, including horizontal solar radiation, outside drybulb temperature, and outside RH. 

The simulation model was calibrated using data from 2002. One problem in the calibration process is 

selecting a period with good data, few changes in operations, and that represents seasonal variations. The 

year 2002 was selected because the building had been in use for slightly more than a year and most of the 

operations were consistent. The period between January and May was selected because there were no 

changes in the operation of the building. Starting in June 2002, NREL changed the thermostats and 

reprogrammed the west ERV to turn off at night. 

We used weather data measured on site and from nearby weather stations to create a TMY2 style weather 

file for 2002. The weather file was used to calibrate the As-Built Model against measured building 

energy performance. The details of how this file was created are contained in Appendix C. 
 32 

The first step in calibrating the models is to make sure that the model parameters match the as-built 

building. Several adjustments were made to the models based on the all the available information 

regarding the building construction and operation. 

• Energy consumption of major components, including the circulation pumps for the ground loop, 

HVAC fans, ERV fans, lights, and plug loads 

• Hourly schedules that describe energy use, or occupancy, changes over the course of a weekday 

and a weekend/holiday day 

• Operating set points, such as thermostat settings and supply air temperature. 

Component Power Levels

The power levels for major building components as measured and as simulated in the Design Building 

Model are listed in Table 6-5. In most cases, the model had significantly lower power levels than the 

actual building. The lower power levels are especially significant for the ERVs, which also had longer 

run times than anticipated in the model. The power levels for all of these components were adjusted in 

the As-Built Model to match the measured values. 

Table 6-5 Comparison of Measured Power Levels with the Design Building Model 

(before calibration) 

Item Measured 

(kW) 

Design 

Building 

Model 

(kW) 

Model 

Difference 

(%) 

Pumps-ground loop 4.06 2.60 −36.0 

Fans-HVAC 8.60 9.23 7.3 

ERVs 13.00 5.22 −59.8 

Lights 21.90 18.64 −14.9 

Equipment (plug) 17.80 17.80 0.0 

Hourly Schedules

The Design Building Model had a maximum occupancy of 120 people with a maximum scheduled 

diversity of 0.8 or 96 people. Observations reported by DEP staff indicated a maximum typical 

occupancy of 70 people (maximum scheduled diversity 0.58 based on 120 people). Total weekday 

occupancy-hours are 743 modeled versus 706 reported. The As-Built Model was adjusted to use the 

reported weekday profile as shown in Table 6-6. For Saturdays, three occupants are assumed from 

8:00 a.m. until 12:00 p.m. For Sundays and holidays, occupancy is assumed to be zero. The domestic hot 

water schedule was changed to reflect the occupancy schedule. 

The Design Building Model had a maximum lighting power of 23.3 kW with a maximum scheduled 

diversity of 0.80, or 18.6 kW. The measured average maximum was 21.9 kW. Average daily usage in 

the Design Building Model was 226 kWh, and the measured value is 310 kWh (37.4% more). The AsBuilt Model weekday lighting schedule shown in Table 6-6 was generated using the measured data for 

January through October 2002. The lighting load profile varied little from month to month as can be seen 

in Figure 7-19. The measured lighting energy use for weekends and holidays is not consistent due to the 

number of holidays that fall on a weekday and the inconsistent use of the building on the weekends. The 

weekend and holiday lighting schedule for the As-Built Model was set to be nearly constant and was 

created to match the average daily total measured energy use of 69 kWh. 

The Design Building Model had a maximum equipment power of 22.2 kW with a maximum scheduled 

diversity of 0.8, or 17.8 kW. The measured average maximum was also 17.8 kW. However, the Design 
 33 

Building Model assumed an average daily consumption of 138 kWh, but the measured value is 292 kWh 

(112% more). The weekday plug load schedules shown in Table 6-6 were created to match the measured 

load profiles shown in Figure 7-20. The Design Building Model assumed zero energy consumption for 

plug loads on the weekends and holidays; however, the measured value is 207 kWh. The As-Built Model 

schedule was modified to produce a flat profile that matches the measured average daily energy use. 

Table 6-6 Calibrated Hourly Schedules for the As-Built Model 

Fraction of Max Value for Hours 1–12 

Schedule Max 

Value 1 2 3 4 5 6 7 8 9 10 11 12 

Occupancy WD 120 0.0 0.0 0.0 0.0 0.0 0.0 0.04 0.50 0.58 0.58 0.58 0.58

Lights WD 23.3 0.13 0.13 0.13 0.15 0.24 0.72 0.90 0.92 0.94 0.94 0.94 0.94

Lights WEH 23.3 0.13 0.13 0.13 0.13 0.13 0.13 0.12 0.12 0.12 0.13 0.14 0.15

Plugs WD 22.2 0.40 0.40 0.40 0.40 0.40 0.42 0.53 0.73 0.80 0.80 0.80 0.75 

Plugs WEH 22.2 0.39 0.39 0.39 0.39 0.39 0.39 0.39 0.38 0.39 0.39 0.39 0.39 

Fraction of Max Value for Hours 13–24 

Schedule Max 

Value 13 14 15 16 17 18 19 20 21 22 23 24 

Occupancy WD 120 0.42 0.58 0.58 0.58 0.50 0.25 0.08 0.00 0.00 0.00 0.00 0.00

Lights WD 23.3 0.93 0.93 0.94 0.9 0.83 0.66 0.40 0.11 0.12 0.14 0.14 0.13

Lights WEH 23.3 0.14 0.13 0.13 0.13 0.11 0.08 0.08 0.07 0.11 0.14 0.13 0.13

Plugs WD 22.2 0.74 0.78 0.77 0.64 0.51 0.44 0.42 0.41 0.41 0.41 0.41 0.41 

Plugs WEH 22.2 0.39 0.39 0.39 0.39 0.39 0.38 0.39 0.39 0.38 0.39 0.39 0.38 

Set Points and Other Changes to the Model

A few other changes were made to the model based on observations made by NREL and 7group during 

site visits: 

• Thermostats in the original model were 72°F (22°C) heating, 74°F (23°C) cooling, with no 

setback or setup. These were changed in the calibrated model to 70°F (21°C) heating, 72°F 

(22°C) cooling to match the building thermostat set points. The set points during the period used 

for calibration were constant. 

• The original model used a supply air temperature for cooling of 63°F (17°C), as representative of 

UFAD systems. However, the supply air temperature in the building was measured to be closer 

to 55°F (13°C). 

The next step in the calibration process was to run the simulation and compare the results with the 

measured data. As stated earlier, the period from January to May 2002 was selected as the calibration 

period. The plug load and lighting profiles were adjusted to match the measured data from January to 

May 2002. Using these adjusted profiles, the As-Built Model was compared to the energy use measured 

by the PowerLogic system. The energy use from the calibrated model was compared to the measured 

energy use from the PowerLogic system and the utility bills in Figure 6-8 and Table 6-7. 
 34 

0

5

10

15

20

25

30

35

40

Jan Feb Mar Apr May

Monthly Energy Use (kWh)

As-Built Model

PowerLogic Data

Utility Bills + PV

Figure 6-8 Energy use from the calibrated simulation model and measurements for 

five months in 2002. 

Table 6-7 Percentage Difference between the Calibrated Model Energy Use and the 

Measured Energy Use 

Utility Bills1 PowerLogic Data Month 

Total Total HVAC Lights Plug 

Jan −2.7% 0.5% 4.1% −3.6% −3.8% 

Feb −0.9% −1.5% −0.6% −3.4% −1.7% 

Mar −0.9% 1.6% 1.9% 0.9% 1.4% 

Apr 3.2% 3.0% 6.6% −4.6% 2.5% 

May 3.7% 7.1% 7.7% 12.2% 1.8% 

Total 0.4% 2.1% 3.8% 0.1% 0.0% 

1

The utility bill energy use is the sum of the utility bill adjusted to the calendar month plus the separately 

metered contribution from the roof-mounted PV array. 

The utility bills are the best reference for calibration because of the high accuracy of the utility meter and 

the large number of missing data from the PowerLogic system. There is fair agreement between the AsBuilt Model and the utility bills, with the As-Built Model only 0.4% higher for the five months and the 

largest monthly difference is only 3.7% higher. However, there is a tendency to underpredict the energy 

in the heating months and overpredict the energy in the cooling months. Looking at the comparison of 

the end-use data from the PowerLogic system, there is no clear answer for the behavior of the model. 

The lighting energy in the simulation model follows the same schedule for the entire year, but the lighting 

energy in the building has variations due to cleaning crew and occupant behaviors. The modeled HVAC 
 35 

energy varies the most from the PowerLogic data. The HVAC system is complex from a heat transfer 

point of view. The pumps and fans are simple to model because they are constant speed and ran 

continuously during the calibration period, except for the east ERV fans, which only ran during the day. 

The ground-source loop is difficult to model because of the many unknowns and complex heat and 

moisture transfer in the soil. The compressor model is the default one and not that of the actual 

compressor operation. The UFAD system is also difficult to simulate because the mathematical models 

assume a well-mixed zone at a single temperature. Some of the variation in the HVAC loads is caused by 

the difference in the lighting and plug loads. The underprediction of the lighting and plug loads in 

January means that more heat will have to come from the HVAC system. The overprediction of the 

lighting and plug loads in May requires more cooling from the HVAC system. 

The next step was to update the Design Baseline Model to reflect the calibration used in the As-Built 

Model. This process was completed in accordance with ASHRAE 90.1-2001 Addendum e. The building 

size and schedules were changed to match the As-Built Model, and the new model was named the AsBuilt Baseline Model. 

6.4 Whole-Building Energy Performance Results 

Once the energy simulation models were calibrated, they were run with the Pittsburgh TMY2 weather file 

to predict the energy performance of the building with typical year weather data. Results from this 

modeling are shown in Table 6-8. Note that these numbers represent the energy consumption in the 

building and do not include the energy supplied by the PV systems. 

Table 6-8 Facility Energy Performance from Calibrated As-Built Models with 

Pittsburgh TMY2 Weather File 

Performance Metric Baseline As-Built Savings 

Total Site EUI – kBtu/ft2·yr (MJ/m2·yr) 57 

(642) 

34 

(386) 

40% 

90% Total Source EUI – kBtu/ft2·yr (MJ/m2·yr) 63 

(715) 

38 

(428) 

40% 

31% Total Source EUI – kBtu/ft2·yr (MJ/m2·yr) 180 

(2,044) 

108 

(1,226) 

40% 

Total Site Energy Cost Intensity – $/ft2·yr ($/m2·yr) 1.80 

(19.38) 

1.02 

(10.98) 

43% 

The baseline modeling allows the energy performance of the Cambria building to be characterized as a 

percent level of savings. The results for 2002 indicate that the building is 40% better in terms of total 

energy use and 43% better in terms of energy cost than the energy code-compliant building. 

6.5 ENERGY STAR Performance Rating 

The U.S. Environmental Protection Agency (EPA) has developed a method of rating the performance of 

commercial buildings (EPA 2004). The ENERGY STAR Portfolio Manager can be used to rate the 

performance of a building based on basic information about its size, location, function, and utility bills. 

The rating is on a scale from 1 to 100 representing the percentile ranking of the building energy 

performance with other commercial buildings of the same type. Buildings must receive a rating greater 

than 75 to earn an ENERGY STAR certification. ENERGY STAR uses a statistical analysis of the 

CBECS data from EIA as the basis for the rating. CBECS contains information from more than 5,000 

buildings from all commercial building sectors across the United States. 

We rated the Cambria building using the energy consumption from the utility bills with the Portfolio 

Manager. The ENERGY STAR ranking for the building from 2001 to 2003 is shown in Table 6-9. The 
 36 

ENERGY STAR rating of 88 states that this building would rank 88 out of 100 in energy performance 

compared to the building stock adjusted for size, function, use patterns, number of occupants, and climate. 

The Cambria building’s EUI is shown in the third column, and the EUI for an ENERGY STAR rating of 

50 for the same building is shown in the fourth column. An ENERGY STAR rating of 50 represents 

average performance. The Cambria building performs 40% better than the average office building, which 

is the same performance predicted from the energy simulations in Table 6-8. 

Table 6-9 ENERGY STAR Rating of the Cambria Building 

Year ENERGY STAR 

Rating 

Measured EUI 

kBtu/ft2·yr 

(MJ/m2·yr) 

EUI for ENERGY STAR 

Rating of 50 

kBtu/ft2·yr 

(MJ/m2·yr)

2001 80 42 (480) 60 (680) 

2002 88 36 (410) 60 (680)

2003 88 36 (410) 60 (680)
 37 

7 System Evaluations 

NREL evaluated the energy systems at the Cambria building to determine their individual performance. 

The mechanical systems, lighting, plug loads, and PV systems were evaluated to determine the 

performance at a detailed level. 

7.1 Analysis of the Heating, Ventilation, and Air Conditioning Systems 

NREL evaluated the mechanical systems to determine if they were properly sized and operated optimally 

for comfort and energy efficiency. In addition, we evaluated the system design to see if changes could be 

made to improve performance. 

NREL first inspected and initiated monitoring of the HVAC systems in July 2001. Several issues were 

noted from visual inspections, spot power measurements, and evaluation of the 15-minute power data. 

1. ERV Control: The west ERV ran continuously. The controller for the east ERV was off by one 

day, ran Tuesday through Saturday, and was off Sunday and Monday. 

2. Heat pump control: The thermostats for the heat pump control ran the fans continuously and the 

temperature set points were constant with no setbacks or setups for unoccupied periods. 

3. Groundwater Circulation Pumps: Each heat pump has its own bank of groundwater circulation 

pumps that are mounted in series of one, two, or three pumps and run continuously. 

4. Excessive Ventilation Air: The outside air from the ERVs is constant and more than is required 

by the number of occupants in the building. 

5. No Option for Economizer: There is no way to get outside air into the building except through 

the ERVs. 

7.1.1 Impact of Heating, Ventilation, and Air Conditioning Controls on Energy Use 

As shown in Section 6.2.2, the HVAC systems consume about 55% of the total energy; therefore, 

operational changes can have a large impact on the building energy performance. The average daily 

HVAC load profiles for July 2001 to April 2002 and July 2002 to April 2003 are shown in Figures 7-1 

and 7-2. The differences in the load profiles from Figure 7-1 to Figure 7-2 are mainly caused by changes 

in the control strategies and somewhat by weather differences. Table B-1 presents a summary of changes 

to the control settings. 
 38 

0

5

10

15

20

25

30

35

40

45

0 3 6 9 12 15 18 21 24

Hour

HVAC Weekday Electrical Power (kW)

Jul 2001

Oct 2001

Jan 2002

Apr 2002

Figure 7-1 Average daily HVAC load profile for weekdays (2001–2002) 

0

5

10

15

20

25

30

35

40

45

0 3 6 9 12 15 18 21 24

Hour

HVAC Weekday Electrical Power (kW)

Jul 2002

Oct 2002

Jan 2003

Apr 2003

Figure 7-2 Average daily HVAC load profile for weekdays (2002–2003) 

When the building was first occupied, the west ERV ran continuously, the heat pump fans ran 

continuously, and the heat pump thermostats were controlled to constant temperatures. The west ERV 

ran continuously because the controller was not set correctly, the thermostats for the heat pumps were not 
 39 

set correctly to allow the heat pump fans to cycle on demand during unoccupied periods, and the 

temperature set points were constant because it was thought the system would not respond well to 

temperature setbacks. This control scheme led to very high nighttime loads as seen in Figure 7-1. The 

winter weekday daytime loads were smaller than nighttime and weekend loads as the heat pumps had to 

heat large amounts of cold air brought into the building by the ERV when there were little internal gains. 

The heat pump fans were set to cycle-on-demand during unoccupied periods in December 2001. 

However, this setting had little effect because the west ERV ran continuously and the temperature set 

points were constant. At the end of May 2002, we programmed the west ERV controller to run from 

5:00 a.m. to 5:00 p.m. EST Monday through Friday. In addition, we reprogrammed all of the thermostats 

to have heating set points of 70°F and 66°F (21°C and 19°C) and cooling set points of 72°F and 78°F 

(22°C and 26°C) during occupied and unoccupied periods. The occupied period was set from 5:00 a.m. 

to 6:00 p.m. EST Monday through Friday. These time settings were set to provide adequate conditioning 

for both standard and daylight saving times. The thermostat and ERV controller clocks should stay on 

EST. 

The thermostat settings were changed multiple times between November 2002 and June 2003 in response 

to comfort complaints from the occupants. The occupants complained that the second-floor women’s 

restroom was too cold in the mornings and that some offices were too hot on Monday mornings during 

hot weather. The exact changes are unknown, but the temperature setbacks and setups were removed and 

some of the thermostats had higher unoccupied heating set points. In addition, all of the heat pump fans 

were set to run continuously. In July 2003, we reset the clock on the west ERV, which was off by 

approximately three hours, and reset the thermostat set points and heat pump fan control. The 

temperature setbacks and setups were set to smaller values than were set in May 2002, and the occupied 

period was set to start an hour earlier to allow more time to recover before occupants arrive. 

The effects of changing the ERV controller and the thermostat set points are immediately apparent in the 

July and October profiles. The nighttime loads for July and October 2002 are much lower than for 2001, 

and the daytime load profiles are similar. January 2002 and January 2003 have very different profiles 

because of the control changes and weather differences. The nighttime loads were much higher in 2002 

than 2003 because the west ERV ran continuously in 2002. The daytime load was higher in 2003 than in 

2002 because 2003 was significantly colder than 2002 (1,084 HDD versus 667 HDD base 55°F [602 

versus 370 base 13°C]). There was a 63% increase in the HDDs for January from 2002 to 2003 but less 

than a 1% increase in the HVAC energy consumption. A summary of the differences in the HVAC 

energy and total heating and CDDs for each period is presented in Table 7-1. There were many changes 

in the thermostat set points during the two years; however, the main difference was turning the west ERV 

off during unoccupied periods. This change shows the large energy penalty for running the ERV 

continuously, especially in the winter. 

Table 7-1 Monthly HVAC Energy Comparison 

Comparison Months % Change in 

HVAC 

Energy 

% Change in 

HDD + CDD 

July 2001 to July 2002 −31% 54% 

October 2001 to October 2002 −38% 17% 

January 2002 to January 2003 0.5% 62% 

April 2002 to April 2003 −17% -15% 
 40 

The hourly HVAC energy plotted against the outdoor temperature for 2001, 2002, and 2003 is shown in 

Figures 7-3 to 7-5. The data are separated by weekdays and weekends/holidays. The 2001 and 2002 

graphs show a minimum in energy use between 50°F and 55°F (10°C and 13°C); below this temperature 

range, the building is predominately heating, and above this temperature range, the building is 

predominately cooling. In 2001, the building ran with a constant temperature control and the west ERV 

ran continuously. Therefore, the weekend/holiday heating loads were similar to the weekday heating 

loads. The weekend/holiday cooling loads were smaller because the internal heat gains were smaller. 

The west ERV was reprogrammed beginning in June 2002 to turn off during unoccupied periods. The 

effect of reprogramming the west ERV is evident in Figure 7-4 for June to October (there were no data 

for November and December). The hourly energy requirement during most of the unoccupied hours 

drops below 2 kWh when there are moderate outdoor temperatures. The building requires heating during 

unoccupied periods when the weather is cold. 

The data for 2003, shown in Figure 7-5, are more scattered than 2001 and 2002 for a number of reasons. 

This was the first winter with the west ERV off at night and weekends, and it was much colder than the 

previous winter. There are some weekday nighttime hours and weekend hours with cold temperatures 

that required no heating and some hours that required a small amount of heating. In addition, the 

thermostat settings were changed (probably more than once) during this period. At some point, the heat 

pump fans were set to run continuously and the temperature set points were set to constant values, or, in 

some cases, to higher heating set points at night. Finally, the time clock on the west ERV was off by 

three hours, causing the system to come on earlier in the morning. 

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60 70 80 90 100

Outdoor Temperature (oF)

HVAC Energy (kWh)

Weekday

Weekend/Holiday

Figure 7-3 Hourly HVAC energy versus outdoor temperature (July–December 2001) 
 41 

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60 70 80 90 100

Outdoor Temperature (oF)

HVAC Energy (kWh)

Weekday (Jan-May)

Weekend/Holiday (Jan-May)

Weekday (Jun-Oct)

Weekend/Holiday (Jun-Oct)

Figure 7-4 Hourly HVAC energy versus outdoor temperature (January–October 2002) 

0

2

4

6

8

10

12

14

0 10 20 30 40 50 60 70 80 90 100

Outdoor Temperature (oF)

HVAC Energy (kWh)

Weekday

Weekend/Holiday

Figure 7-5 Hourly HVAC energy versus outdoor temperature (January–June 2003) 
 42 

The calibrated As-Built Model was used to examine the energy impacts of ERV controls. One simulation 

was completed with both ERVs running continuously and another was run with the ERVs replaced by 

airside economizers. The results of these simulations, along with the As-Built Model with Pittsburgh 

TMY2 data, are shown in Table 7-2. Running the ERVs continuously increased the energy cost by 

$4,260, replacing the ERVs with airside economizers saved $2,940. There were more hours outside of 

the throttling range with the economizers because the heat pumps were not resized to make up for the lost 

energy recovery. If the heat pumps were sized correctly, the energy costs would have gone up slightly for 

the economizer case. The best option would be to use smaller ERVs (half the current size) with bypass 

dampers for economizer operation. For 2002 and 2003, there were 440 and 390 hours when the outside 

air temperature was 50°F–60°F (10°C–16°C) on weekdays between 5:00 a.m. and 5:00 p.m., which is 

when economizer operation could be used. This represents approximately 13% of the weekday hours 

between 5:00 a.m. and 5:00 p.m. Above 55°F (13°C), the heat pumps may have to provide some cooling, 

but the ERV fans would not have to be used. Above 60°F (16°C), the outside air may have high moisture 

levels that would have to be removed by the heat pumps. Enthalpy control on the economizer would 

expand the economizer operation range and provide more hours for using outside air for cooling. The 

outside air temperature range at which ERV operation recovers more energy than the fans use is probably 

below 50°F (10°C) and above 60°F (16°C). 

Table 7-2 Energy Impacts of Changes to the ERV Control 

Model Annual 

Energy 

(MWh) 

Annual 

Energy Cost 

Energy 

Savings 

Cost 

Savings 

As-Built Model 344 $35,473 

As-Built Model with ERVs running 

continuously 397 $39,737 −15.7% −$4,260 

As-Built Model with ERVs replaced 

by airside economizers 315 $32,533 8.2% $2,940 

7.1.2 Heating, Ventilation, and Air Conditioning Sizing 

Another question about the HVAC systems was whether they were properly sized. The heat pump 

cooling capacity is 54 tons (189 kW), which may be slightly undersized because they take a long time to 

recover from a setback condition. This situation is compounded by the control of the ERVs, which 

should not be used on cold winter mornings until occupants arrive and could be used in warmer weather 

to help cool the building before occupants arrive. However, the ERV controllers are very simple and only 

allow a fixed time schedule. The one area of the building that was definitely undercooled was the 

telecommunications room, which contains the telephone switchgear, computer servers, and two personal 

computers for energy monitoring. This room was cooled by a heat pump serving other areas with very 

low internal gains. The heat pump was controlled by the conditions in the areas with low internal gains, 

which was very different from the telecommunications room. The solution was to install a 2.5-ton (9-

kW) heat pump directly to the telecommunications room, which is about 100 ft2

/ton (2.5 m2/kW). This 

was probably a little oversized, but it keeps the room cool and is more efficient than running the larger 

heat pump just to keep this room cool. It also allows more electronic equipment to be added in the future. 

7.1.3 Groundwater Circulation Pumps 

The groundwater circulation pumps are mounted in series to match the flow and head requirements of 

each heat pump. This configuration is not the most efficient, but it is often used because pump sizes may 

have limited availability and many contractors want to use only one type of pump. The pumps are rated 

at 230 W each, but they were measured to draw approximately 200 W each. The pumps run 
 43 

continuously; however, they only need to operate when the compressor is running. There was a concern 

that the capacitance effects of the ground might adversely affect the system when the pumps run in a 

cycling mode. According to a study done by Kavanaugh and Rafferty (1997), this is not a concern, and 

the best method of operating the circulation pumps is to tie them to the compressor operation. A 

conservative estimate is that the compressors run an average of 50% of the time. The annual saving of 

linking the pumps with the compressor operation would be 18 MWh and approximately $1,300. 

7.1.4 Outside Air 

The ERVs represent one of the largest factors in the HVAC energy use. The ERV fans consume a 

considerable amount of energy to bring in large amounts of outside air, which must be conditioned. 

According to ASHRAE Standard 62-1999 (ASHRAE 1999), the minimum outside air for an office is 20 

cfm/person (10 l/s·person). When both ERVs are running, there are 4,500 cfm (2,125 l/s) of outside air. 

The average daily peak occupancy is approximately 70 people. A conservative estimate of the design 

maximum is 100 occupants. At 100 occupants, the ERVs deliver 45 cfm/person (21 l/s·person), more 

than double the minimum required. An accidental test of the amount of outside air required occurred 

when the west ERV was inadvertently turned off on July 30 and left off until August 29, 2002. The 

measured CO2 levels during the month before, during, and after the ERV was turned off are shown in 

Figure 7-6. 

Figure 7-6 Office space CO2 concentrations with the west ERV off during August 

The west side was affected the most, but the CO2 levels on the east side also increased. ASHRAE 62-

1999 recommends that the CO2 concentrations should remain below 700 ppm above the ambient CO2

levels to maintain comfort with respect to human bioeffluents. The ambient CO2 concentration is 

approximately 380 ppm, so the recommended maximum is approximately 1,100 ppm. The second-floor, 

southwest sensor exceeded 1,100 ppm CO2, a total of 10 hours during the 23 working days when the west 

ERV was off. The first-floor, southwest CO2 sensor exceeded 1,100 ppm for 3 hours, and the secondfloor, northwest CO2 sensor never exceeded 1,100. The east ERV is half the size of the west unit and 

provides about 21 cfm/person (10 l/s·person) for 70 people, which meets the minimum standard for 

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

7/1 7/8 7/15 7/22 7/29 8/5 8/12 8/19 8/26 9/2 9/9 9/16 9/23 9/30

Date (2002)

Office Area CO2 (ppm)

Second Floor Southwest

Second Floor Southeast
 44 

normal occupancy, but the outside air is not evenly distributed throughout the building when it runs on 

only one ERV. 

There was also a noticeable difference in the energy consumption when the west ERV was turned off. 

We used a linear regression of the weekday HVAC energy use and daily outdoor temperatures in June, 

July, and September to estimate the weekday HVAC energy use in August with the west ERV in normal 

operation. Energy data were missing for 7 of the 24 weekdays when the west ERV was off, so another 

linear regression was used to estimate the actual weekday HVAC energy use during this period. The 

estimated HVAC energy saving during the 30 days that the west ERV was off is 2.2 MWh ± 0.05 MWh, 

which is approximately $250 in energy and demand savings. This number represents approximately 8% 

of the total building energy during this period. 

7.1.5 Thermal Comfort 

The space temperatures for the second-floor, southwest and southeast quadrants are shown in Figures 7-7 

and 7-8 for summer and winter periods. Figure 7-7 shows the performance during the warmest day in 

2002, and Figure 7-8 shows the space temperatures during one of the coldest periods in 2002. These 

temperature readings were taken from the permanent monitoring system. The data from this system were 

checked and compared with data from a hand-held sensor during the summer of 2002. The permanent 

system consistently logged temperatures that were 1°F–2°F (0.5°C–1°C) higher than the hand-held 

system. The temperatures shown were adjusted to more closely match the temperatures measured on the 

hand-held system. 

Figure 7-7 Office and outdoor temperatures for the summer of 2002 

70

71

72

73

74

75

76

77

78

79

80

8/9 8/10 8/11 8/12 8/13 8/14 8/15 8/16 

Date (2002)

Office Area Temperature (oF)

0

10

20

30

40

50

60

70

80

90

100

Outdoor Temperature (oF)

Second-Floor Southwest

Second-Floor Southeast

Outdoor

Thru Fri Sat Sun Mon Tue Wed
 45 

Figure 7-8 Office and outdoor temperatures for the winter of 2002 

The recommended thermal comfort limits for light office work are approximately 70°F–80°F (21°C–

27°C) (ASHRAE 2004). The range depends on the amount of clothing, activity level, air movement, and 

RH. This comfort range assumes that the occupants are dressed in light clothes at the high end and 

warmer clothes at the low end. A more likely acceptable comfort range is 72°F–76°F (22°C–24°C) in the 

summer and 70°F–76°F (21°C–24°C) in the winter. For the summer week in Figure 7-7, the temperature 

in the southwest sensor never exceeded 76°F (24°C) hours during normal working hours, and the 

temperature in the southeast sensor exceeded this comfort limit by less than 0.5°F (0.25°C) on Monday 

and Tuesday. In the winter week in Figure 7-8, the temperature from the southwest sensor was below 

70°F (21°C) for one to two hours every weekday morning, and the temperature from the southeast sensor 

was below 70°F (21°C) for one hour on December 4. 

Interior humidity also influences thermal comfort; however, the comfort range from ASHRAE Standard 

55-2004 is quite broad. The upper limit is stated as a humidity ratio of 0.012, which is approximately 

80% RH at 70°F (21°C) and 55% at 80°F (27°C). There is no lower limit, but experience has shown that 

people in humid climates expect a higher humidity level and may be dissatisfied below 20% RH. The 

average daily RH levels in the office spaces are shown in Figure 7-9 for July through December 2002. 

The summer RH levels for the southwest space are 30%–40%, which is low, but acceptable. The 

southeast summertime RH levels are consistently 40%–50%, which provides a comfortable environment. 

The RH levels from both sensors start dropping in October and reach levels below 20% in December. 

The cold winter air has a low moisture content, and when the air is warmed to the building temperature, it 

has a low RH. There have been some complaints in this building about the dry air in the winter. 

Reducing the amount of outside air introduced to the building in the winter would help keep the humidity 

levels higher. 

60

62

64

66

68

70

72

74

76

78

80

11/28 11/29 11/30 12/1 12/2 12/3 12/4 12/5 

Date (2002)

Office Area Temperature (oF)

0

10

20

30

40

50

60

70

80

90

100

Outdoor Temperature (oF)

Second-Floor Southwest

Second-Floor Southeast

Outdoor

Thru Fri Sat Sun Mon Tue Wed
 46 

Figure 7-9 Average daily RH levels in the second-floor offices 

A study of the effectiveness of the UFAD system was completed by Lawrence Berkeley National 

Laboratory researchers in 2004 (Fisk et al. 2004). They found that the air change effectiveness was about 

the same as a zone with well-mixed air, but the pollutant removal efficiency for CO2 was 13% better than 

expected in a zone with well-mixed air. The thermal stratification in the zones during cooling mode 

operation was only 2°F–4°F (1°C–2°C) between just above the floor and the return air registers. This low 

thermal stratification is caused by low internal gains (partially occupied building) and higher than 

necessary supply airflow rates. It is expected that the thermal stratification would increase if the building 

were fully occupied or if there was a variable air volume system that reduced airflow with reduced zone 

loads. Thermal stratification is desirable because it can lead to energy savings during cooling. 

7.2 Lighting and Daylighting Evaluation 

The lighting systems at the Cambria building were evaluated to determine the illuminance distribution 

delivered by the lighting design and to determine the energy performance. The Procedure to Measure 

Indoor Lighting Energy Performance (NREL 2005b) provides performance metrics and procedures for 

evaluating lighting designs including the effects of daylighting. In addition, procedures were followed 

from the International Energy Agency (IEA) protocol established under Daylight in Buildings Task 21 

(Atif et al. 1997). The goals of the monitoring plan were the following: 

1. Quantitatively assess the illumination distribution. 

2. Determine the energy savings due to the lighting design without daylighting controls. 

3. Determine the amount of electric lighting offset by daylighting and the energy saved in lighting. 

4. Analyze the operation of the daylighting design and optimize its performance. 

5. Document successes and weakness of the lighting design. 

0

10

20

30

40

50

60

6/28 7/26 8/23 9/20 10/18 11/15 12/13 

Date (2002)

Average Daily Relative Humidity (%)

Second-Floor Southwest

Second-Floor Southeast
 47 

Figure 7-10 Outdoor illuminance for July 13–16, 2001 

7.2.1 Illuminance Measurements 

NREL monitored the outdoor and indoor illumination levels continuously from Friday to Monday, July 

13–16, 2001. Figure 7-10 shows the outdoor illuminance. The first three days were mostly sunny with 

occasional cumulus clouds, and the final day was cloudy in the morning with some clearing by the 

afternoon. 

The indoor light levels were measured on the working surfaces in cubicles along a north-south cross 

section in the first-floor, southwest quadrant and the second-floor, southwest and northwest quadrants. 

On the first floor, three photometers were placed in each cubicle—one in front of the keyboard and one 

on the working surfaces on either side of the cubicle (see Figure 7-11). The three photometers in front of 

the keyboards were 10, 18, and 26 ft (3.0, 5.5, and 7.9 m) from the inside surface of the outside wall. On 

the second floor, two photometers were placed in each cubicle—one in front of the keyboard and one on 

the working surface to the left of the keyboard (see Figures 7-12 and 7-13). The photometers in front of 

the keyboards were again 10, 18, and 26 ft (3.0, 5.5, and 7.9 m) from the inside surface of the outside 

wall. Measurement of the illuminance from the electric lights only was taken between 9:00 p.m. and 

10:00 p.m. on Friday, July 13. The recommended minimum illuminance level on a horizontal surface for 

open offices is 30 to 50 fc (300 to 500 lux), depending on the task (IESNA 2000). For general reading of 

handwriting with a pen or printed materials in 8–10 point font, the recommended minimum illuminance is 

30 fc (300 lux). For reading lighter copies or smaller fonts, the recommended minimum illuminance is 50 

fc (500 lux). 

0

5

10

15

20

25

30

35

40

45

50

0 600 1200 1800 0 600 1200 1800 0 600 1200 1800 0 600 1200

Hour for Friday–Monday July 13–16, 2001

Illuminance (fc)

0

50

100

150

200

250

300

350

400

450

500

Illuminance (lux)

26 ft (7.9 m)

18 ft (5.5 m)

10 ft (3.0 m)

Distance from outside wall
 48 

10’

18’

26’

Distance from 

outside wall 

Photometers

Figure 7-11 Photometer placement in the first-floor, southwest corner of the building 

26’

Photometers

18’

10’

Figure 7-12 Photometer placement in the second-floor, west end of the building 
 49 

Figure 7-13 Placement of two photometers (shown circled) on the working plane of a cubicle 

Measured illuminance levels in the first-floor office area are shown in Figure 7-14. The ambient electric 

lights were on Friday and Monday during working hours and Friday evening for testing. The task lights 

were off in the cubicles 18 and 26 ft (5.5 and 7.9 m) from the south wall, and they were on for part of the 

testing period in the cubicle 10 ft (3.0 m) from the south wall. The ambient electric lights provided 25–

35 fc (250–350 lux) on the working planes. The natural light added 10 fc (100 lux) at the cubicle closest 

to the outside wall to 3 fc (30 lux) at the cubicle furthest from the outside wall. These light levels are at 

the minimum levels for working at a computer terminal and performing easy reading tasks; however, 

some individuals prefer more light for reading. The task lights raise the light levels on the side working 

surfaces to 60–100 fc (600–1,000 lux). 

Figure 7-15 shows the lighting conditions near midday on June 7, 2001, which had similar sky conditions 

to those during the illuminance measurements. The reflected light from the light shelves only penetrates 

approximately 3 ft (1 m) along the ceiling. The light shelves are not effective because of the small 

amount of glass area (the wide window frames block much of the light), low reflectance off the light 

shelves, and the high angle of the summer sun. There was no useful daylighting (i.e., dimming of electric 

lighting) in the first-floor office area during this testing period. 
 50 

Figure 7-14 Illuminance measurements at workstations for the first-floor, southwest office area 

from July 13–16, 2001 (task lights used in cubicle 10 ft [3 m] from outside wall) 

Figure 7-15 Lighting conditions on the first floor on June 7, 2001 

NREL PIX #11000 

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 51 

The measured illuminance for the second-floor, southwest and northwest office areas from Friday to 

Monday, July 13–16, 2001 is shown in Figures 7-16 and 7-17. The task lights were off except in the 

cubicle that is 18 ft (5.5 m) from the north wall in the northwest office area. The electric lights were off 

over the weekend, except for the period between 5:30 a.m. and 9:00 a.m. on Saturday in the northwest 

office area. The natural light levels on the north side were slightly reduced because the east half of the 

clerestory sun shades was in the down position for maintenance. The light levels with daylighting and the 

ambient electric lights are below the recommended minimum levels in all the areas except for the cubicles 

on the south side that are 10 and 26 ft (3.0 and 7.9 m) away from the outside wall. Therefore, task 

lighting would probably be used to increase the illuminance on the working surfaces. We determined 

from an informal walk-through survey that approximately half of the task lights are used at any given 

time. 

Illuminance from the ambient electric lights was measured Friday evening between 9:00 p.m. and 

10:00 p.m. Illuminance levels at the workstations with only the ambient electric lights were 

approximately 15 fc (150 lux). This is lower than the first floor because the indirect luminaires do not 

reflect well off the high ceiling with trusses. The combination of the ambient electric lights and 

daylighting provided 20–40 fc (200–400 lux) at midday. The natural light levels over the weekend were 

10–25 fc (100–250 lux) on the working surfaces and 20–30 fc (200–300 lux) in the open circulation areas. 

The daylighting on the second floor is reduced because of the poor reflection off the high ceiling, 

blockage by the roof trusses, the dark floor, and the windows on the outside walls are too low to provide 

light beyond the first row of cubicles. In addition, the illuminance levels on the second floor would be 

improved with direct lighting luminaires. 

Figure 7-16 Illuminance measurements at workstations for the second-floor, southwest office 

area from July 13–16, 2001 (no task lighting) 

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Illuminance (lux)

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 52 

Figure 7-17 Daylighting measurements at workstations for the second-floor, northwest office 

area on July 13–16, 2001 (task lights used in cubicle 18 ft [5.5 m] from outside wall) 

Figure 7-18 shows the lighting conditions in the northwest office area near midday on June 7, 2001 with 

the ambient electric lights on. The light distribution is fairly even as expected from the illuminance 

measurements. The ceiling is bright near the clerestory windows and has a darker area in the middle. 

The south-facing clerestory windows can be the source of undesirable lighting conditions at times. At 

low sun angles, they can admit direct beam radiation, and they can be very bright at other times, causing 

contrast and glare problems. Automatic sunshades are installed on the interior of the windows to block 

the direct beam radiation. The sunshades are controlled by an exterior photosensor. The sunshades block 

an excessive amount of light and defeat the purpose of the clerestory windows. Other options for these 

windows are to diffuse the incoming light with frosted or patterned glass or a light-diffusing film on the 

glass or direct the beam radiation to the ceiling with a louver system. The drawback of these solutions is 

the view of the sky will be lost. 

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 53 

Figure 7-18 Lighting conditions in the second-floor, northwest office area on June 7, 2001, with 

the overhead electric lights on 

7.2.2 Lighting System Energy Consumption 

Average daily load profiles for the lighting loads are shown in Figure 7-19. The lighting loads exhibit 

very consistent patterns from month to month. The lighting loads consist of all the interior and exterior 

lights, exit signs, telephone system, and drinking fountains. 

The interior lights are on from approximately 5:00 a.m. to 6:00 p.m. Most of the interior lights are 

controlled by timer circuits in the breaker boxes to turn on at 6:00 a.m. and turn off at 6:00 p.m. 

However, the cleaning crew comes in every morning around 5:00 a.m. and manually turns most of the 

lights on in the building. Between 2 kW and 4 kW of interior lights are manually controlled in enclosed 

offices and storage spaces. The slight drop in the power between 3:30 p.m. and 4:00 p.m. is when many 

of the occupants leave and some of the manually controlled lights are turned off. The variation in the 

early evening is due to the operation of the parking lot lights, which are used more in the winter and fall. 

The 3-kW nighttime load is from exterior lights on the building and exit signs in the building. The 

ambient lighting in the open office areas on the second floor is dimmable with the daylighting controls. 

Very little, if any, savings are realized by the daylighting controls. The weekend/holiday lighting load 

profiles are inconsistent from month to month. The weekend nighttime load profile is the same as the 

weekday load profile, but the weekend daytime load profile varies between 0 and 7 kW because of 

holidays that occur during the weekdays and occupants who occasionally work on weekends. The 

lighting controls have no provision for a holiday schedule; therefore, all the building lights turn on for 

holidays that fall on weekdays. An alternative option that has worked well in other buildings is a manual 

on switch with a timer controlled off for the normally unoccupied periods. The duration of the timer 

would be set by the person turning on the lights. 

NREL PIX #10281 
 54 

Figure 7-19 Daily interior lighting load profiles for weekdays 

When NREL first monitored the building in July 2001, the lights were turned on between 3:00 a.m. and 

4:00 a.m. by the cleaning crew and were turned off at 7:00 p.m. by the lighting control circuits. In 

October 2001, the cleaning crew changed their schedule to start at 5:00 a.m. and the lighting control 

circuits were changed to run between 6:00 a.m. and 6:00 p.m. These changes save approximately 12,000 

kWh and $800 per year. Additional savings could be achieved by changing the cleaning schedule to start 

closer to normal business hours and turning the lights off earlier in the evening (most occupants leave by 

4:00 p.m.). 

Daylighting savings are defined as the fraction of the lighting electricity displaced by natural light 

contributions while maintaining the minimum illuminance levels (Atif et al. 1997). The illuminance 

measurements have shown that the light levels with the natural light and the electric lights are at or below 

the minimum illuminance level of 30 fc (300 lux) for a horizontal working surface in an office (IESNA 

2000). On the first floor, the natural light levels are extremely low and contribute little to the overall 

levels. The illuminance levels on the second floor with only the electric lights are below the minimum 

levels, and the combination of daylighting and electric lights on a sunny day is close to the minimum 

levels. According to this definition and these measurements, there are no daylighting savings. In 

addition, daylighting savings would show a dip in the lighting power consumption during the daylit 

hours; however, this is not evident in the measurements as shown in Figure 7-19. 

7.3 Analysis of Building Plug Loads 

The plug loads in the building consist mainly of computers, monitors, printers, task lights, and other 

office equipment. Daily load profiles for the plug loads are shown in Figure 7-20. The total load is very 

consistent and varies between 9 kW at night and on weekends to approximately 17 kW during the 

occupied hours. 

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 55 

Figure 7-20 Daily plug load profiles for weekdays 

The plug load profile closely reflects the occupant behavior. Most of the occupants arrive between 

7:00 a.m. and 8:00 a.m. and leave between 3:00 p.m. and 4:00 p.m. The lunch break is consistently from 

about 11:30 a.m. until 1:00 p.m. The nighttime load is approximately half the daytime load, which is 

much higher than was anticipated during the design phase of the building. The high nighttime load is due 

to electronic equipment that is being left on, including computers, monitors, printers, and copiers. Much 

of this equipment goes into a standby mode, which still consumes a significant amount of energy when 

combining all of the equipment in the building. The weekend/holiday plug daily load profile is flat and at 

the same level as the weekday nighttime load profile. 

NREL researchers conducted a survey of the plug loads in the office areas after business hours on the 

evening of Friday, July 13, 2001. Results are shown in Table 7-3. Some docking stations had no laptop 

computer attached; therefore, the actual number of laptop computers used in the building is higher than 

the total shown. 

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 56 

Table 7-3 Number of Office Area Plug Loads on July 13, 2001 

Load 1st Floor 2nd Floor Total On or 

Standby 

Desktop computers 13 72 85 54 

Laptop computers 5 6 11 0 

Monitors 17 82 99 90 

Printers/scanners 10 64 74 74 

Copiers 1 3 4 3 

Fax machines 1 1 2 2 

Plotters and misc. 0 4 4 1 

Refrigerators 1 

(break room, 

vol. ≈ 23 ft3

[651 cm3

]) 

4 

(vol. ≈ 6 ft3 

[170 cm3]) 

0 5 

Vending Machines 2 

(break room) 

 2 2 

The numbers and types of equipment left on or in standby mode were also noted during the survey. Most 

desktop computers were left on and were in standby mode. Their exact power draw is not known, but 

most desktop computers draw 40–80 W in normal operation. Most operating systems have a power 

management feature that will put the computer in standby after a certain period; however, these features 

only reduce the power consumption by about one-third when they are in operation. Many CRT monitors 

in standby mode use 3–10 W; however, older monitors do not have a standby mode and use around 40 W 

when turned on with a blank screen. The computer and monitor energy consumption can be reduced with 

manual or automatic control. Manual control relies on users to turn off their computers and monitors at 

night. If this approach is not successful, there are power management software options that can be 

implemented and controlled over a local network. Computer power management software can be very 

effective at reducing energy consumption during unoccupied periods. Energy savings have been shown 

to be an average of 200 kWh/yr per computer. 

Computers are not the only large plug load; there are a large number of printers in this building with a 

printer for nearly every occupant on the second floor. Each printer consumes energy even on standby. 

Replacing 80% of these printers with five central networked printers would save money in the purchasing, 

maintenance, and operation of the printers. Additionally, reducing the number of printers down to five 

would make it easier to configure the printers to perform duplex printing to save paper. One more 

opportunity to save energy is to put power control devices on the cold drink vending machines. These 

devices reduce energy consumption by 30%–50% and usually pay for themselves in less than two years. 

7.4 Photovoltaic System Evaluation 

The PV systems in the Cambria building were evaluated to determine the energy produced by the 

systems, the effect on the building purchased electrical energy, and the performance of the systems. The 

Procedure for Photovoltaic System Performance (NREL 2005c) provides guidance on evaluating the 

performance of PV systems in the built environment. Additional measurements were taken for a more 

detailed evaluation of the system performance. The goals of the monitoring plan were the following: 

1. Measure the delivered alternating current energy production by the PV systems. 

2. Determine the percentage of the building electrical energy consumption offset by the PV systems. 

3. Determine building electrical demand offset by the PV systems and the energy cost savings. 

4. Determine the performance of the PV systems compared to the expected performance. 
 57 

The large PV system is monitored by a utility-type meter that is manually read each month for billing 

purposes. This energy is sold as green power at a premium rate. NREL installed an additional 

instrumentation in June 2002 on both PV systems that records the total energy every 15 minutes. Data 

collection for this monitoring system is automated and is used for analysis purposes. Because of 

problems with the building end use 15-minute data, there were no detailed building electrical demand 

data, and the third goal could not be accomplished 

7.4.1 Photovoltaic System Measured Energy Production 

The average daily purchased energy from the utility bills and the average daily energy from the large PV 

system are shown in Figure 7-21 for June 2001 to August 2003 and Figure 7-22 for January 2004 to 

December 2004. The main PV system was turned off in August 2003 due to inverter problems, and the 

inverter was replaced in late February 2004. The PV data for June 2001 through May 2002 are from the 

PV utility meter readings, and the remaining PV data are from the NREL installed monitoring system. 

The data from the PV utility meter represent the net PV energy production of the large PV system, that is, 

the PV energy produced minus the energy consumed by the isolation transformer when the PV system is 

down. The data from the NREL installed monitoring system are also the net energy and include the 

energy produced by the small PV system. The height of the columns is the total energy consumption of 

the building. The percent of the total building load met by the PV system is included as a line graph. 

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Figure 7-21 Average daily purchased energy and PV system performance for 

June 2001 to August 2003 
 58 

Figure 7-22 Average daily purchased energy and PV system performance for January 2004 to 

December 2004 (a new inverter was installed in late February) 

Figure 7-23 shows the daily energy production and parasitic load for the main PV system for 2003. The 

daily global horizontal solar radiation is also shown as an area graph. The main PV system was shut 

down several times because of inverter faults and was finally disconnected from the grid on August 26, 

2003. The causes of the faults were a high AC voltage and high temperature. The high temperature fault 

was the most severe because the system would have to be manually reset. The inverter was removed and 

sent to the manufacturer in December 2003 and replaced with a new unit in February 2004. 

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 59 

Figure 7-23 Daily PV system energy production, parasitic load, and horizontal solar radiation 

During the period from May 31, 2002 to December 31, 2003, the main PV system produced no energy on 

50% of the days because of inverter problems. There were many other days when the system was only 

operational for part of the day because of inverter problems. From May 31, 2002 to December 31, 2003, 

the parasitic load on the PV system equaled 40% of the energy delivered to the building by the main PV 

system. Most of the parasitic load (37%) occurred when the PV system was down at night or due to an 

inverter fault; the other 3% were transformer losses during PV system operation. From the time that the 

inverter was replaced on February 20, 2004 to December 31, 2004, the main PV system was down only 

three days because the whole system was shut down. During this same period, the parasitic load of the 

isolation transformer was 18% of the total energy delivered to the building. The monthly parasitic load 

varies from 11% in the summer to over 50% in the winter. A circuit that automatically disconnects the 

PV system from the grid when the PV system is down and reconnects when the PV system is operational 

should be implemented. 

The small PV system has also experienced operational problems caused by blown fuses in the combiner 

box. From May 31, 2002 to August 31, 2004, the small PV system was operational only 103 days, which 

is 13% of the days. Most of the time, it has been operating on one-half of the panels. From February 8, 

2004 to the end of 2004, there was no measured output from this system. 

7.4.2 Photovoltaic System Performance Analysis 

A simulation using PVSYST v3.2 (Mermoud 1996) was conducted to estimate the performance of the 

large PV system. The simulation was completed for 2002 using a weather file constructed from weather 

data measured on site. Figure 7-24 shows the net energy production from the simulation and the 

measured data. 

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 60 

Figure 7-24 Simulated and measured PV performance for 2002 

The performance from March to May and October to November was only slightly lower than predicted. 

However, the other months showed very poor performance. The annual total production was only 60% of 

the simulated value, which is mainly because of the inverter problems that shut the system down for long 

periods. The performance in the winter was lower than the simulation because of snow cover and lower 

than expected performance in the low radiation conditions. 

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 61 

8 Conclusions 

At a construction cost of $93/ft2 ($1,000/m2), this building shows it is possible to pay extra attention to 

systems and materials to build a “green” office building within the same cost range as building a 

conventionally constructed office building. The building is economically viable in this location as it was 

developed by a private developer looking for a return on investment. This kept the costs in check. In 

many “green” buildings, other architectural elements add to the cost and it is difficult to separate 

amenities from the actual “green” elements. 

The estimated performance of the Cambria building from calibrated simulations is shown in Table 8-1. 

The detailed monitoring and analysis have shown that the building uses 40% less energy and has 43% 

lower energy costs than typical, minimally code-compliant office buildings of similar size. 

Table 8-1 Cost, Site, and Source Energy Savings Summary 

Cost Total Site Energy Total Source Energy 

$/ft2·yr 

($/m2·yr) 

Percent 

Savings 

kBtu/ft2·yr 

(MJ/m2·yr)

Percent 

Savings

kBtu/ft2·yr 

(MJ/m2·yr)

Percent 

Savings

Baseline $1.80 

($19.38) 

57 

(642) 

180 

(1,800) 

As-Built $1.02 

($10.89) 

43% 

34 

(386) 

40% 

108 

(1,226) 

40% 

8.1 Lessons Learned 

Many things went well and many things could have been improved with this project. NREL has already 

applied lessons learned from the Cambria building to other research projects and the lessons will continue 

to be valuable for future projects as well. 

In addition, the knowledge and information gained from the Cambria project have formed the basis for 

the Building Green in Pennsylvania program and they continue to provide baseline information for 

subsequent projects. Additional projects are the 21,000-ft2

 (1,900-m2) California Office Building with a 

small office at Philipsburg and an 110,000-ft2 (10,000-m2) office in downtown Norristown. These thirdphase projects started with established energy budgets, lighting budgets, as well as shell and glazing 

requirements, HVAC, and IAQ requirements that are required upon completion and that must be 

maintained during the life of the project. 

The lessons learned from this project can be divided in to four categories: design and construction 

processes, technical, building operation, and energy monitoring. 

8.1.1 Design, Construction, and Commissioning Lessons Learned 

1. Setting specific performance goals that the whole design team believes in is critical to producing 

a building that operates efficiently. The estimated energy cost saving compared to ASHRAE 

Standard 90.1-2001 is 40%. The high-level performance was achieved through a concerted effort 

by the owner, occupant, and entire design team. 

2. The design-build process can be efficient, saving time and money. In addition, the design-build 

process is dynamic and allows new ideas to be integrated quickly. New ideas can be evaluated at 

any time during the design and construction phases. 

3. The design-build process can develop so quickly that there is not enough time to fully evaluate 

design options. Construction may begin before some systems are fully designed, which limits the 

options that can be considered and can have a negative impact on systems integration. 
 62 

4. Documentation of the building process including plans, specifications, and operation sequences is 

not always fully completed in the design-build process. For example, there are no electrical 

drawings for the Cambria building, which makes it difficult to makes changes to the building 

electrical system or make monitoring plans. 

5. The design-build process involves the contractor in the design process and the designers in the 

construction process. Both sides learn valuable lessons from working together. The 

collaboration allows many construction issues to be worked out during the design process and 

integrates the full costs into design solutions. 

6. Integrated design solutions can lead to simpler, more effective, and lower cost systems. The 

building envelope and HVAC system went through many design iterations and resulted in a more 

effective, lower cost system because the architect, mechanical engineer, mechanical 

subcontractor, energy consultant, and owner worked together to find better solutions. 

7. Energy simulations played an important part in understanding the forces that drive energy 

performance and allowed design alternatives to be investigated. However, the quick pace of the 

design-build process does not always allow enough time to complete the energy simulations and 

to inform design decisions. 

8. Daylighting design should be analyzed carefully to ensure a high level of performance. The 

daylighting design at Cambria incorporated good daylighting design principles (i.e. orientation, 

clerestories, high reflectance ceilings, open office design), but the details were not analyzed to 

determine likely performance. Small changes could have improved the performance. 

9. The construction process should be monitored for energy use concerns. 

10. Commissioning is important, but it does not guarantee that the occupied building will operate 

efficiently. Monitoring building end use energy consumption provides valuable feedback to help 

maintain efficient performance of systems. Two main items missed during commissioning were 

the west ERV ran continuously and the HVAC fans ran continuously. These items may have 

been difficult to track without looking at the end use energy data. The end use energy data also 

allowed the timing of the lighting circuits and HVAC controls to be changed to save energy. 

8.1.2 Technical Lessons Learned 

11. The ERVs should include bypass dampers for economizer operation to use outside air for cooling 

without the overhead of the ERV fans. If bypass dampers for outside air were available, the 

ERVs should not be operated when its operating costs exceed the savings from the recovered 

energy. A conservative temperature range for not operating the ERVs is 50°F–60°F (10°C–

16°C), which represents about 13% of the weekday hours between 5:00 a.m. and 5:00 p.m. in 

2002 and 2003. Enthalpy control would expand this operating range. 

12. The ERVs are more than twice as big as they need to be for outside air requirements. 

13. Variable air volume fan control on the heat pumps would improve the energy performance as the 

system backs off supply air requirements with lower internal cooling or heating loads. The 

building is usually only partially occupied with approximately 70% of the designed occupancy. 

14. The groundwater circulation pumps should not run continuously, but should be linked to the heat 

pump compressor operation. This would save approximately half the energy consumed by the 

pumps or about 18 MWh/yr. 

15. There are trade-offs of using the simple thermostats on each heat pump. The thermostats are less 

expensive than a centralized control system and easier to program. However, it is difficult to 

keep the time and set points on all of them programmed correctly. The current system would 

work well, if only one or two people with proper training had access to the thermostats. 

16. The heat loads of data center rooms are often underestimated. In many cases, these rooms should 

have a dedicated HVAC system because the loads are very different from surrounding zones. In 

the Cambria building, the heat pump installed in the telecom room should have an outside air 

damper to take advantage of cooling with outside air. 
 63 

17. The illuminance levels are low due to lower than expected daylight contributions, low LPDs, 

indirect lighting used throughout the building, and high ceilings on the second floor. 

18. Indirect lighting should only be used close to highly reflective ceilings. The indirect lighting on 

the first floor works well, but the indirect lighting on the second floor does not work well because 

the light source is too far from the ceiling and the roof trusses obstruct some of the light. Direct 

lighting or a combination of direct and indirect lighting would work better for the second floor. 

19. The light shelves on the first floor are ineffective at providing light to the space. The ceilings are 

too low, there is not enough glass area, and the reflectance off the light shelves is too low to 

provide adequate light. 

20. On the second floor, light from the clerestory windows does not penetrate beyond the first row of 

cubicles. There is not enough light entering through the windows and the roof trusses block some 

of the light. The daylighting along the perimeter walls is not very good because the windows are 

not high enough, the glass area is too small, the large wood frames limit the glass area and block 

some of the light, and the first row cubicle walls are too high and block daylight entering these 

cubicles. 

21. The rows of electric lights should run parallel to the daylight sources and should be controlled 

separately so that they can be dimmed as necessary as the daylight levels vary with distance from 

the source. 

22. The isolation transformer on the large PV system consumes approximately 18% of the energy 

delivered by the system. An automatic disconnect circuit should be added to this system to avoid 

the large losses when the PV system is down, or an inverter system that does not have high 

parasitic loads should have been chosen. 

23. An automatic monitoring system for PV system operation should be installed. Poor operation of 

the PV system can currently be determined only if someone downloads and examines the power 

data from the detailed monitoring system. 

24. The use of compact fluorescent luminaires should be limited and linear fluorescent luminaires 

should be used in most areas. Linear fluorescents have a higher efficacy and longer life. 

8.1.3 Building Operation Lessons Learned 

25. The UFAD system appears to work well from a comfort point of view; however, it is only slightly 

better at removing occupant pollutants than a well-mixed air delivery system (Fisk, et al. 2004). 

26. This HVAC system has a slow response time; therefore, temperature setbacks should be small 

and have long startup periods. 

27. Spaces that do not have a direct supply of conditioned air are very slow to respond to changing 

conditions. The restrooms rely on the exhaust fans to bring in conditioned air from the rest of the 

building. Therefore, the restrooms with outside walls can be cold in the mornings. These 

restrooms should have a direct supply of conditioned air or supplemental heating systems for 

morning warmup. The supplemental heating systems may be too expensive to run in an all 

electric building. 

28. The ERVs should be controlled to operate only when the building is occupied. 

29. The ERV time clocks should be installed in an easily accessible location inside the building to 

facilitate adjustments. The current location inside the units on the roof is not convenient. 

30. The lights used during cleaning should not be all turned on at once. The cleaning crew should 

turn on the lights in only the sections they are cleaning and then turn them off when they have 

completed cleaning. 

31. Computers and other nonessential electronic equipment should be turned off at night. Standby 

modes can consume a substantial amount of energy. In this building, the nighttime plug loads are 

more than half the daytime loads. 

32. The building light controls have a manual on and off control; however, there should also be an 

automatic off switch controlled by a timer. The length of the timer would be set by the person 

turning on the lights. 
 64 

33. A substantial amount of energy can be consumed while the building is being cleaned. Cleaning 

crews typically turn on all the building lights and leave them on until they are finished. Cleaning 

could be partially done during normal building operation, and the other cleaning should be done 

by zone with the lights on only in the zone being cleaned. 

8.1.4 Energy Monitoring Lessons Learned 

34. Performance monitoring systems need to be very robust and maintained by someone locally or 

monitored remotely with someone local to handle problems. 

35. Electrical system monitoring should be performed with watt-hour (energy) meters or watt (power) 

meters with memory and not pure watt (power) meters. Watt meters that are read every 15 

minutes only provide a snap shot of the instantaneous power and do not give a true measure of the 

energy used over the previous 15 minutes. 

36. Personal computers should not be relied upon to be the only instrument of data retrieval and 

archiving. They are very unreliable compared to systems dedicated to data logging. 

37. Include a weather station for extensive monitoring projects. The weather station should include a 

minimum of dry-bulb temperature, RH, and global horizontal solar radiation. 

38. Carefully plan the monitoring system starting with an explicit list of questions to be answered. 

39. The most effective daylighting analysis includes measurements taken a minimum of three times a 

year: near the summer and winter solstices and near either the spring or the fall equinox. 

8.2 Recommendations 

Several actions could further improve and maintain the energy performance of the building. Our top 

recommendations are presented here. Most of these issues have been discussed previously, but they are 

presented here with information that is more specific. 

1. Install an automatic disconnect circuit on the large PV system to minimize the energy consumed 

by the isolation transformer, or install an inverter system that does not have the large parasitic 

loads. Annual energy savings would be approximately 2.3 MWh and $200. 

2. The thermostat and ERV settings should be set and checked regularly by qualified personnel to 

ensure that the proper settings are maintained. The ERV controllers have been shown to be 

unreliable, and the thermostat set points have been found to have higher nighttime settings and 

clock settings that are off by 12 hours. 

3. Reduce the airflow in the ERVs to approximately one-half of their current values. This could be 

accomplished with different pulley sizes, perhaps with different motor wiring, or new smaller fan 

motors. Reducing the ERV flow rate by one-half will reduce the fan energy consumption to 

about one-eighth of its current value because fan power is related to the cube of the fan flow rate. 

Additional energy savings would result from conditioning the lower amount of outside air. 

However, reducing the flow rate by half will adversely affect the energy recovery effectiveness. 

4. Continue to monitor the energy performance of the building each month. This should include 

comparing monthly total energy by end use to past and expected performances. Things to look 

for are sudden changes in energy consumption and gradual upward trends in energy consumption. 

In addition, track the monthly peak electrical demand to control utility costs. This will require 

staff to be trained and graphs to be generated automatically from the monthly data. 

5. Consider the energy demand and energy use implications of adding loads to the building. 

6. Install power management software on all computers. This type of program can be easily 

installed and controlled over a local area network. Annual energy savings have been shown to be 

100–300 kWh per computer. 

7. Install energy control devices on the cold drink vending machines. These units can reduce the 

energy consumption by one-third to one-half and typically pay for themselves in less than two 

years. 
 65 

References 

Arasteh, D. K., E. U. Finlayson, and C. Huizenga. (1994). Window-4.1 User’s Manual, LBL-35298, 

Windows and Daylighting Group, Berkeley, CA: Lawrence Berkeley National Laboratory.

ASHRAE. (1995). HVAC Applications Handbook. Atlanta, GA: American Society of Heating, 

Refrigerating and Air-Conditioning Engineers. 

ASHRAE. (1999). Ventilation for Acceptable Indoor Air Quality. ASHRAE Standard 62-1999. 

Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers. 

ASHRAE. (2001). Energy Standard for Buildings Except Low-Rise Residential Buildings. ANSI/ 

ASHRAE/IESNA Standard 90.1-2001. Atlanta, GA: American Society of Heating, Refrigerating and 

Air-Conditioning Engineers. 

ASHRAE. (2002). Addendum e to ANSI/ASHRAE/IESNA Standard 90.1-2001. First Public Review. 

July 2002. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers. 

ASHRAE. (2003). Addendum e to ANSI/ASHRAE/IESNA Standard 90.1-2001. Second Public 

Review. April 2003. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning 

Engineers. 

ASHRAE. (2004). Thermal Environmental Conditions for Human Occupancy. ANSI/ASHRAE 

Standard 55-2004. Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning 

Engineers. 

Atif, M. R., J. A. Love, and P. Littlefair. (1997). Daylighting Monitoring Protocols and Procedures for 

Buildings. A Report of IEA Task 21/Annex 29 Daylight in Buildings. T21/D2.1/97-01. Ottawa, Ontario, 

Canada: Institute for Research in Construction. 

DOE. (2004). 2004 Buildings Energy Databook. Washington, D.C.: U.S. Department of Energy. 

http://buildingsdatabook.eren.doe.gov/. Accessed September 2004. 

EIA. (2003). Annual Energy Review 2002. http://www.eia.doe.gov/emeu/aer/contents.html. 

Washington, DC: U.S. Department of Energy/Energy Information Administration. Accessed March 3, 

2004. 

EPA. (2004). ENERGY STAR Portfolio Manager, Washington, D.C.: U.S. Environmental Protection 

Agency. http://www.energystar.gov. Accessed September 2004. 

Fisk, W., D. Faulkner, D. Sullivan, C. Chao, M. P. Wan, L. Zagreus, and T. Webster. (2004). 

Performance of Underfloor Air Distribution: Results of a Field Study. LBNL-56257, Berkeley, CA: 

Lawrence Berkeley National Laboratory. 

GGGC. (1998). Pennsylvania Governor’s Green Government Council. Harrisburg, PA: 

http://www.gggc.state.pa.us. Accessed July 2004. 

GGGC. (1999). Model Green Office Leasing Specifications. Pennsylvania Governor’s Green 

Government Council. Harrisburg, PA:. http://www.gggc.state.pa.us/publictn/leaspecs.html. Accessed 

July 2004. 

IESNA. (2000). The IESNA Lighting Handbook: Reference & Application, ninth edition. New York: 

Illuminating Engineering Society of North America. 

Kavanaugh, S. P. and K. Rafferty. (1997). Ground Source Heat Pumps. Atlanta, GA: American Society 

of Heating, Refrigerating and Air-Conditioning Engineers. 
 66 

Mermoud, A. (1996). PVSYST Version 3.2. User's Manual. Geneva, Switzerland: University of 

Geneva, University Center for the Study of Energy Problems. http://www.pvsyst.com/. Accessed 

December 2002. 

NREL. (2005a). Procedure for Measuring and Reporting Commercial Building Energy Performance.

Publication expected September 2005. Golden, CO: National Renewable Energy Laboratory. 

NREL. (2005b). Procedure to Measure Indoor Lighting Energy Performance. Publication expected 

September 2005. Golden, CO: National Renewable Energy Laboratory. 

NREL. (2005c). Procedure for Measuring and Reporting the Performance of Photovoltaic Systems in 

Buildings. Expected publication date September 2005. Golden, CO: National Renewable Energy 

Laboratory. 

Torcellini, P. A., S. J. Hayter, and R. Judkoff, (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; pp. 802–810; NREL Report No. 26144. 

USGBC. (2004). LEED, Leadership in Energy and Environmental Design, United States Green Building 

Council. Washington, D.C.: http://www.usgbc.org. Accessed July 2004. 
 67 

Appendix A – Project Time Line 

Figure A-1 Project time line from publication of RFPs to end of energy monitoring 

7/1/1997 12/31/2000

8/6/1997

RFP published

10/21/1997

Proposals presented

to DEP 9/3/1998

Lease agreement

executed with

Miller Bros Construction

1/21/1999

“Green Building for

Commonwealth Real

Estate Staff” Publihsed

9/1/2000

Building accepted

by DEP

8/1/1999-8/31/2000

Building construction

1/1/2001 12/31/2004

9/8/2000

DEP occupies

the building

7/12/2001

First NREL visit

& daylighting

measurements

7/1/2001-6/30/2003

Building energy

end use data collection 6/1/2002-12/31/2004

PV system monitoring

2/20/2004

New PV inverter

installed
 68 

Appendix B – Heating, Ventilation, and Air Conditioning Control Changes 

Table B-1 Summary of HVAC Control Changes 

Date West ERV 

Operation 

East ERV 

Operation 

Heat Pump 

Fan 

Operation 

Heating Set Points Cooling Set Points 

Sep 

2000 

Continuous On Tues–

Sat1

 

6:00 a.m. to 

6:00 p.m. 

Continuous 70°F (21°C) 72oF (22°C) 

July 14, 

2001 

 On Mon-Fri 

6:00 a.m. to 

6:00 p.m. 

Continuous 70°F (21°C) 72oF (22°C) 

Dec 11, 

2001 

 Cycle-onDemand for 

Unoccupied 

6:00 p.m. to 

6:00 a.m. 

70°F (21°C) 72oF (22°C) 

May 30, 

2002 

On Mon–Fri 

5:00 a.m. to 

5:00 p.m. 

On Mon-Fri 

5:00 a.m. to 

5:00 p.m. 

Cycle-onDemand for 

Unoccupied 

6:00 p.m. to 

5:00 a.m. 

70°F (21°C) Occ. 

66°F (19°C) Unocc. 

Occupied: Mon–Fri 

5:00 a.m. to 6:00 p.m. 

72°F (22°C) Occ. 

78°F (26°C) Unocc. 

Occupied: Mon–Fri 

5:00 a.m. to 6:00 p.m.

Sep/Oct 

20022

 

Clock 3 

hours fast 

On Mon–Fri 

3:00 a.m. to 

6:00 p.m. 

 

Nov 

2002 to 

Jun 

20033 

 Continuous 70°F (21°C) Occ. 

72°F (22°C) Unocc.4

Occupied: Mon–Fri 

5:00 a.m. to 6:00 p.m. 

72°F (22°C) Occ. 

 72°F (22°C) Unocc.

Occupied: Mon–Fri 

5:00 a.m. to 6:00 p.m.

Jul 15, 

2003 

Clock reset 

On Mon–Fri 

5:00 a.m. to 

5:00 p.m. 

 Cycle-onDemand for 

Unoccupied 

6:00 p.m. to 

5:00 a.m. 

72°F (22°C) Occ. 

68°F (20°C) Unocc. 

Occupied: Mon–Fri 

4:00 a.m. to 6:00 p.m. 

72°F (22°C) Occ. 

76°F(24°C) Unocc. 

Occupied: Mon–Fri 

4:00 a.m. to 6:00 p.m.

1

 All times are EST. 

2

 The time clock on the west ERV changed to be approximately 3 hours fast. The cause is unknown. 

3

 Thermostats were changed to satisfy occupant complaints. 

4

 Some of the thermostats were changed to have a higher heating set point at night than during the day. 
 69 

Appendix C – Weather File Creation 

A weather data file was created for Ebensburg, Pennsylvania for the year 2002 for the purpose of building 

energy simulations of the Pennsylvania DEP Cambria building. The file format follows the TMY2 

format (http://rredc.nrel.gov/solar/old_data/nsrdb/tmy2/). The data for the file were taken from on-site 

weather data, nearby weather stations, and the TMY2 file for Pittsburgh. 

A weather station, which consists of horizontal and in the PV plane Li-Cor pyranometers and a Vaisala 

humitter, was installed and connected to a Campbell Scientific, Inc., CR10X data logger on the west roof. 

The humitter was only reading temperature; however, a T-RH Hobo data logger was left on the east side 

of the building to get RH. 

The missing data, sources of fill data, and reasons for the missing data are summarized in Table C-2. 

Most of the data were filled with measured data from nearby weather stations. Hourly data for the two 

weather stations were obtained from the Pennsylvania State Climatologist at 

http://pasc.met.psu.edu/PA_Climatologist/index.php. The weather stations are summarized in Table C-1. 

Table C-1 Weather Stations 

Station Organization Lat Long Elevation (ft) 

Cambria DEP Office NREL 40.47° −78.67° 2,000 

Johnstown (JST) – Cambria 

County Airport FAA 40.317° −78.834° 2,280 

Altoona (AOO) – Blair County 

Airport FAA 40.291° −78.319° 1,504 
 70 

Table C-2 Missing Data and Filling Source 

Period Hrs Data Fill Source Notes 

4/20 0400 to 4/21 0200 23 Tdb Data logger internal temperature 

adjusted to match Tdb

Unknown source of 

error 

4/21 0700 to 4/22 0200 20 Tdb Same Same 

5/03 1300 to 5/03 2000 8 Tdb Same Same 

5/28 1700 to 5/31 1000 66 Tdb Altoona FAA weather station, 

smoothed to match existing data 

Data logger moved 

from roof to IS room 

5/28 1700 to 5/31 1000 66 RH Same Same 

5/28 1700 to 5/31 1000 66 Igh Filled from days with similar 

weather according to cloud 

cover data taken at Altoona 

weather station. Data smoothed 

to match existing data. 

Same 

11/4 0700 to 11/27 1000 556 RH Altoona FAA weather station, 

smoothed to match existing data 

RH sensor out of range 

12/11 0900 to 12/14 2400 88 RH Altoona FAA weather station, 

smoothed to match existing data 

Same 

11/5 1600 to 11/9 1600 97 Tdb Altoona FAA weather station, 

smoothed to match existing data 

RH sensor out of range 

caused other readings 

to fail 

11/10 0300 to 11/10 1700 15 Tdb Altoona FAA weather station, 

smoothed to match existing data 

Same 

11/6 0800 to 11/9 1300 97 Igh Estimated from cloud cover data 

from Johnstown FAA weather 

station 

Same 

11/14 1000 to 11/14 1800 15 Igh Same Same 

12/15 0100 to 12/28 1100 323 Tdb Johnstown FAA weather station Computer down 

12/15 0100 to 12/28 1100 323 RH Johnstown FAA weather station Same 

12/15 0100 to 12/28 1100 323 Igh Estimated from cloud cover data 

from Johnstown FAA weather 

station 

Same 

Some of the weather variables in the final file were calculated from the measured data as summarized in 

Table C-3. 

Table C-3 Calculated Weather Data 

Variable Source Variables Method 

Tdp Tdb, RH ASHRAE Fundamentals Ch. 6 

Idn Igh Perez model 

Idf Igh, Idn, θz Idf = Igh – Idn cos( θz) 

TotalSkyCover Igh, Idf, θz TRNSYS Type 69 by Thomas Auer 

OpaqueSkyCover Assumed = TotalSkyCover 
 71 

Appendix D – Site-to-Source Energy Conversion 

It is difficult to compare the consumption of different forms of energy at the building site. For example, 

heating with gas, electricity, or district heat cannot be compared, because electricity and district heat are 

nearly 100% efficient. However, this comparison does not account for the energy used to generate and 

deliver the electricity or district heat. A better comparison is to calculate the source (or primary) energy 

used to generate and deliver the energy to the site. But many of the important issues necessary to 

calculate source energy are often unknown at the local utility level, including energy source mix, 

generation efficiencies, and distribution and transmission efficiencies. A solution is to use primary 

energy based on total energy generation and consumption data for the United States. Using national 

average data is a good approach because the energy distribution network in the United States is highly 

interconnected. National energy data are compiled by the EIA and can be accessed through its Web site 

(http://www.eia.doe.gov/). The site-to-source conversion efficiencies for electricity are shown in Table 

D-1.

The average generation and delivery efficiency of electricity for 2002 was approximately 31.57%, or 

source energy is 3.167 times site energy consumption. The national energy flow associated with the 

production of electricity is shown in Figure D-1. Electricity efficiency is calculated by dividing end use 

electricity by energy consumed to generate electricity and accounts for conversion, transmission, and 

distribution losses. It is based on the average of all sources of electricity generation and distribution in 

the nation, as reported by EIA in the 2002 Annual Energy Review (EIA 2003). This does not account for 

precombustion energy—energy to extract, transport, and process fuels used to generate electricity. 

 

Table D-1 Site-to-Source Energy Conversion 

Energy Source-to-Site 

Efficiency 

Site-to-Source 

Conversion 

Electricity 31.6% 3.167 
 72 

Figure D-1 Energy flow diagram for electricity generation for 2002 (EIA 2003) 
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5a. CONTRACT NUMBER

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4. TITLE AND SUBTITLE

Analysis of the Design and Energy Performance of the Pennsylvania 

Department of Environmental Protection Cambria Office Building 

5c. PROGRAM ELEMENT NUMBER

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NREL/TP-550-34931 

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BEC3.4004 and BEC3.1001 

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The Pennsylvania Department of Environmental Protection asked NREL to evaluate the energy performance of the 

Cambria Office Building to determine if it had met design goals. The focus of this report is the analysis of an 

integrated design process used to construct the facility and the postoccupancy energy performance. NREL collected 

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