Strategies for Energy Conservation

for A Large Retail Store

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Washington, DC 20234

September 1982

100

, 1)56

02-2580

1982

Prepared for: ce of Buildings Energy Research and Development

ce of Conservation and Renewable Energy

. Department of Energy

NBSIR 82-2580

STRATEGIES FOR ENERGY CONSERVATION

FOR A LARGE RETAIL STORE

fiational 0or8«u of Standards 0Cr ® 1982

GlCL, \oo

sa - ssio

James Y. Kao

Walter H. Parken

E. Thomas Pierce

U S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Equipment Division

Washington, DC 20234

September 1982

Prepared for: Office of Buildings Energy Research and Development

Office of Conservation and Renewable Energy

U.S. Department of Energy

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

PREFACE

This report is one of a series documenting NBS research and analysis efforts

in developing energy and cost data to support the Department of Energy/National

Bureau of Standards Building Energy Conservation Criteria Program. The work

reported in this document was performed under the Energy Analysis of Control

Strategies project, a part of the controls program element managed by Building

Systems Division, Office of Building Energy Research and Development, U.S.

Department of Energy. The NBS effort was supported by DoE/NBS Task Order

A008-BCS under Interagency Agreement No. EA77A 01-6010.

iii
ABSTRACT

A comparative analysis is made of the thermal performance of selected HVAC

systems and control strategies commonly employed in large retail stores. The

comparisons are made for six geographical locations representing wide climatic

variations within the continental United States.

Hour-by-hour simulations with the BLAST computer program are used to obtain

the yearly heating, cooling, and fan energy consumption of a two-story large

retail store. The HVAC systems simulated are constant volume reheat, variable air volume, and with direct expansion coils. The control strategies

tested are dry bulb temperature economy cycle, enthalpy economy cycle, supply

air temperature resetting, lowered space heating temperature, VAV zoning variations, and the combinations of these strategies. The results of these simulations are presented and discussed. Substantial energy consumption differences

are shown.

Key words: building control strategies; building energy conservation; building

thermal performance; HVAC systems
TABLE OF CONTENTS

Page

PREFACE iii

ABSTRACT iv

LIST OF TABLES vi

LIST OF FIGURES vii

1. INTRODUCTION 1

2. ENERGY SIMULATION 1

2.1 Building Model 1

2.2 Weather Data 2

2.3 HVAC System Simulation and Control Strategies 2

3. RESULTS AND DISCUSSION 6

3.1 Energy Consumption Results 6

3.2 Using Degree-Days as Energy Consumption Parameters 6

3.3 Comparison of Strategies 7

4. SUMMARY 12

REFERENCES 14

v
LIST OF TABLES

Page

Table I. Annual energy consumption - Lake Charles, LA 15

Table 2. Annual energy consumption - Madison, WI 15

Table 3. Annual energy consumption - Nashville, TN 16

Table 4. Annual energy consumption - Santa Maria, CA 16

Table 5. Annual energy consumption - Seattle, WA 17

Table 6. Annual energy consumption - Washington, DC 17

Table 7. Comparative annual energy consumption - Lake Charles, LA ..... 18

Table 8. Comparative annual energy consumption - Madison, WI 19

Table 9. Comparative annual energy consumption - Nashville, TN 20

Table 10. Comparative annual energy consumption - Santa Maria, CA 21

Table 11. Comparative annual energy consumption - Seattle, WA 22

Table 12. Comparative annual energy consumption - Washington, DC ....... 23
LIST OF FIGURES

Page

Figure 1. Large retail store model 24

Figure 2. Internal load profiles 25

Figure 3. Thermal zone diagrams 26

Figure 4. Cooling energy consumption of base case (Case 1) 27

Figure 5. Cooling energy consumption of applying temperature economy

cycle (Case 2) 27

Figure 6. Cooling energy consumption of applying enthalpy economy

cycle (Case 3) 28

Figure 7. Cooling energy consumption of applying outside air resetting

supply air temperature (Case 4) 28

Figure 8. Cooling energy consumption of base case with lowered space

heating temperature (Case 5) 29

Figure 9. Cooling energy consumption of applying VAV to perimeter

zones (Case 6) 29

Figure 10. Cooling energy consumption of applying VAV to all zones

(Case 7) 30

Figure 11. Cooling energy consumption of applying lowered space heating

temperature and temperature economy cycle (Case 8) 30

Figure 12. Cooling energy consumption of applying lowered space heating

temperature, temperature economy cycle, and outside air

resetting supply air temperature (Case 9) 31

Figure 13. Cooling energy consumption of applying lowered space heating

temperature, enthalpy economy cycle, and outside air

resetting supply air temperature (Case 10) 31

Figure 14. Cooling energy consumption of applying lowered space heating

temperature, enthalpy economy cycle, outside air resetting

supply air temperature, and VAV to perimeter zones

(Case 11) 32

Figure 15. Cooling energy consumption of applying lowered space heating

temperature, enthalpy economy cycle, outside air resetting

supply air temperature, and VAV to all zones (Case 12) 32

Figure 16. Cooling energy consumption of DX system (Case 13) 33

Figure 17. Cooling energy consumption of DX system applying enthalpy

economy cycle (Case 14) 33

Figure 18. Cooling energy consumption of all single control strategy

cases 34

Figure 19. Cooling energy consumption of all combined control strategy

cases and DX cases 35

Figure 20. Heating energy consumption of base case (Case 1) 36

Figure 21. Heating energy consumption of applying temperature economy

cycle (Case 2) 36

Figure 22. Heating energy consumption of applying enthalpy economy

cycle (Case 3) 37

Figure 23. Heating energy consumption of applying outside air resetting

supply air temperature (Case 4) 37

Figure 24. Heating energy consumption of base case with lowered space

heating temperature (Case 5) 38

vii
LIST OF FIGURES (Continued)

Figure 25. Heating energy consumption of applying VAV to perimeter

zones (Case 6) 38

Figure 26. Heating energy consumption of applying VAV to all zones

(Case 7) 39

Figure 27. Heating energy consumption of applying lowered space heating

temperature and temperature economy cycle (Case 8) 39

Figure 28. Heating energy consumption of applying lowered space heating

temperature, temperature economy cycle, and outside air

resetting supply air temperature (Case 9) 40

Figure 29. Heating energy consumption of applying lowered space heating

temperature, enthalpy economy cycle, and outside air

resetting supply air temperature (Case 10) 40

Figure 30. Heating energy consumption of applying lowered space heating

temperature, enthalpy economy cycle, outside air resetting

supply air temperature, and VAV to perimeter zones

(Case 11) 41

Figure 31. Heating energy consumption of applying lowered space heating

temperature, enthalpy economy cycle, outside air resetting

supply air temperature, and VAV to all zones (Case 12) 41

Figure 32. Heating energy consumption of DX system and DX system applying

enthalpy economy cycle (Cases 13 and 14) 42

Figure 33. Heating energy consumption of all single control strategy

cases 43

Figure 34. Heating energy consumption of all combined control strategy

cases 44

viii
1 . INTRODUCTION

This report is the second of a series of reports [1] to compare the energy

savings of heating, ventilating and air conditioning (HVAC) systems and control

strategies for commercial buildings. A large retail store of heavy architectural construction was used as a sample building for energy consumption comparisons in this study. According to a recent national survey [2], for buildings

over 25,000 square feet of floor area, retail sales and services occupy 18

percent of the total floor area of commercial buildings. The large retail

store of this study represents a department store or a variety store which is

either independently situated or is attached to a large shopping complex.

Buildings of this kind, as compared to small stores having unitary heating/

cooling equipment with simple thermostatic on-off type temperature controls,

are usually engineered by professional designers and operated by full-time

trained operating personnel. Therefore, this study was intended to give com- parative quantitative data and some guidelines to assist building designers

and system operators with HVAC system and control strategy selections as well

as with setting system operating conditions, using energy consumption of the

HVAC system as a parameter. Of course, the energy consumption of a particular store is a function of many factors, such as the building geometric shape

and orientation, space arrangement, building construction, climatic conditions,

internal load variations, etc. It is not the intention of this study to negate

the importance and necessity of having a thorough energy analysis and life

cycle cost study for cost-effective HVAC system and control strategy determination. The scope of the energy analysis of this study is limited to the air

handling systems. The heating/cooling plant energy consumption as well as the energy used for distributing the cooling and heating media from plant to

air handling equipment are not included. Furthermore, simple assumptions of

the fan and air distribution systems were made for the air handling system

simulations. Consequently, readers are cautioned to use care in applying

these data to their particular buildings.

The localities used for the energy consumption comparisons in this study are six cities representing various climatic conditions of the United States.

They are Lake Charles, Louisiana; Madison, Wisconsin; Nashville, Tennessee;

Santa Maria, California; Seattle, Washington; and Washington, D.C.

The energy program used in this study for simulation was the Building Loads

Analysis and System Thermodynamics Program (BLAST) [3]. This program was used because it was recognized as one of the best building energy programs

available commercially. The control loop dynamics of the control system

components which may also impact significantly on the building energy con- sumption was not investigated in this study.

2. ENERGY SIMULATION

2.1 BUILDING MODEL

The building used for this study is a two-story, 320 feet (97.5 m) long by

240 feet (73.2m) wide, heavy masonry structure with its short axis coinciding

with the true north-south orientation. There is no fenestration except glass

1
entrance doors on all walls of the lower level. The building dimensions and

pertinent construction data are as shown in figure 1. The architectural

specification of this building was modified from a model building of a state

energy performance standard [ 4 ]. The daily internal load profiles are shown

in figure 2. It was assumed that 30 percent of the light load was removed

directly by the return air stream. The 1.0 watt per square foot (10.8 W/m^)

equipment load included all appliances for sales and display, elevator and

escalator loads as well as other incidental equipment loads. The infiltration

load was assumed to be nil during the system-on hours and was assumed to be

0.6 air change per hour for the perimeter zones during the system-off hours.

The contents of the store, which may be important for both thermal capacitance

and thermal radiation heat exchange between the surfaces for a retail store, were simulated by using 4" (.102 m) thick concrete masonry unit partitions.

The building was divided into ten thermal zones for the constant volume (CV)

and variable air volume (VAV) systems using chilled water as the cooling

medium. The first and second floors had separate thermal zones because of the

space load differences contributed by the roof, ground and the entrance doors.

The interior and perimeter spaces of different exposures had separate thermal

zones. Zone multipliers were used to multiply the equally divided zone areas

of 1920 square feet (178.4 m^) to simplify the calculations. The entire building was modeled by using one air handling system. The heating and cooling

energy consumptions should remain the same, should more than one system be

used on account of system size limitations.

For the simulation of the direct expansion (DX) system, the building was divided into 12 thermal zones, differentiating between upper and lower floors,

interior and perimeter spaces, as well as exposures, with four interior zones

as contrasted to two interior zones of the chilled water system. The floor

areas of the zones were made larger than those of the chilled water system and

zone multipliers were not used. It was felt that, in actual system design,

the 12 zone arrangement was more realistic for the DX system than having ten

zones composed of 80 multipliers as was used for the chilled water system.

The thermal zone arrangement of both chilled water and DX systems are shown in

figure 3.

2 . 2 WEATHER DATA

The weather data used for the simulations were from Typical Meteorological

Year (TMY) climate tapes.

2.3 HVAC SYSTEM SIMULATION AND CONTROL STRATEGIES

Three types of HVAC system were simulated.

A. One constant volume system with ten thermal zones. Eight of the ten

zones had reheat controls to serve the perimeter.

B. One variable air volume reheat system with variable air volume for both

eight perimeter zones only and for all ten zones.

2
C. Twelve direct expansion constant volume systems for twelve thermal

zones. Each system had a pair of heating and cooling coils with

controls preventing them from operating simultaneously.

Although the use of constant volume reheat systems is generally discouraged

for energy conservation reasons, this study makes no judgment as to the

overall suitability of system selection. Furthermore, reheat systems were

used extensively during the past and some of these existing systems may need

to be retrofitted for energy conservation. The results of these simulations

may be useful in those applications.

During the zone load simulation stage, the heating and cooling capacities of

all zones were sized to take into account the climatic differences among the

six cities. The hourly load simulation results indicated that the maximum

zone temperatures at peak cooling hours were no more than 1°F (.56°C) above

the design temperature of 78°F (25.6°C). The indoor temperature during

heating operations varied depending on the control strategies. The details

will be described under the control strategy paragraphs later in this report.

The supply air to the spaces was about 0.73 CFM per square foot (3.71 x 10“^

m^/s per m^) of floor area. A ventilation air quantity of 5 CFM (2.36 x 10“^m^/s) per person at peak occupancy hours was assumed, which amounted

to 17 percent to 22 percent of the space supply air.

The following approach was used in comparing the control strategies. A base

case was first established and simulated. Then, the base case was modified

by single control strategies. This means that only one control strategy was used in each simulation run, so that the effect of energy savings of this

particular strategy may be compared with the base case and with other strategies. Finally, combined strategies were simulated to find the combined effect

on energy consumption. For the chilled water system, the control strategies

included dry-bulb temperature economy cycle, enthalpy economy cycle, reset

supply air temperature by outside temperature, lower reheat temperature, applying VAV to perimeter zones and applying VAV to all zones. For the DX system,

only enthalpy economy cycle was simulated to compare with the base DX strategy.

A. Base Case (Case 1).

The fan system ran continuously from 8 a.m. to 11 p.m. every day. At

night, the fan ran intermittently and tried to satisfy the set-back

temperatures of 52°F (11.1°C) minimum and 85 °F (29.4°C) maximum.

The minimum outside damper position was fixed to give minimum ventilation air. The supply air temperature at fan discharge was set to

maintain 60°F (15.6°C). The cooling coil controller throttling range

was assumed to be 3°F (1.7°C) from 60°F (15.6°C) to 57°F (13.9°C).

The daytime reheat controls were set to provide 72°F (22.2°C) minimum

space temperature for the perimeter zones. The heating coil controller

throttling range was also assumed to be 3°F (1.7°C). Except for peak

cooling load hours, these cooling and heating temperature settings

satisfied the recommended indoor design conditions for comfort air

conditioning of the American Society for Heating, Refrigerating, and

Air-Conditioning Engineers (ASHRAE) Standard 90-75, Energy Conservation

in New Building Design. As stated previously, only the eight perimeter

zones had reheat coils.

3
B. Base Case with Temperature Economy Cycle (Case 2)

In this case, the mixed air temperature downstream of the return and

outside air dampers was maintained by modulating the dampers to satisfy

the cooling coil thermostat setting of 54.9°F (12.7°C) to 57.9°F

(14.4°C) on account of 2.1°F (1.2°C) fan heat gain. When the outside

air temperature rose to above the cooling coil thermostat setting,

the outside air damper stayed at the minimum outside air position and

the cooling was achieved by mechanical cooling.

C. Base Case with Enthalpy Economy Cycle (Case 3)

Enthalpy sensors were added to both the return air and outside air

streams. When the outside air enthalpy was lower than the return air

enthalpy, the outside air and return air dampers were modulated to

maintain the desired cooling coil thermostat setting. When the enthalpy

comparison was reversed, the system admitted only the required minimum

outside air. Mechanical cooling was used to supplement the balance of

the cooling load.

D. Base Case with Supply Air Temperature Reset (Case 4)

This strategy takes advantage of the space cooling load variations. It

is generally achieved by two ways: to set the discharge air temperature

to satisfy the highest cooling load zone, or set the discharge air temperature according to a fixed schedule using the outside air temperature

as the parameter. Since this building has no window and is of heavy

construction, it should not be sensitive to the hourly external load

change. Therefore, it was felt that setting the cooling coil discharge

air temperature by the outside air temperature would be advantageous.

The discharge air temperature setting varied from 60°F (15.6°C) to

62°F (16.7°C) inversely with the outside air temperature of 75°F

(23.9°C) to 32 °F (0°C). This reset schedule was determined rather

arbitrarily. No attempt was made to find the optimum reset schedule

for energy savings.

E. Base Case with Lowered Space Temperature (Case 5)

The minimum space temperature for the reheat was lowered from 72°F

(22.2°C) of the base case to 68°F (20°C) during the store hours.

During 1979 to 1981 the U.S. Department of Energy regulations required

that 65°F (18.3°C) be used as the space temperature for heating in

retail stores. It was evident that a space temperature lower than the

72°F (22.2°C) as recommended by ASHRAE Standard 90-75 was generally

acceptable.

F. Base Case with Perimeter Zones Converting to VAV (Case 6)

In this case, the eight perimeter zones were converted to a reheat VAV

system with a minimum supply air volume at 40 percent of the peak supply

air. The air volume variations not only adjusted to the load

4
shifting due to the external factors such as solar and outside air

temperature changes, it also tried to match the internal load changes

during off-peak hours. No detailed analysis was performed to determine

the minimum supply air volume, and the 40 percent ratio was used for

all six cities.

G. Base Case with All Zones Converting to VAV (Case 7)

This case is an extension of the previous case. The two large interior zones were also provided with 40 percent minimum supply air VAV

controls. There was no reheat in interior zones. By adding these

two zones to the VAV system, the interior zone roof load and internal

load variations were also matched by reducing the supply air.

H. Base Case with Temperature Economy Cycle and Lowered Space Temperature

(Case 8)

This case and the following four cases are the combination cases of the

previous described cases. This case combines cases 2 and 5.

I. Base Case with Temperature Economy Cycle, Lowered Space Temperature,

and Supply Air Temperature Reset (Case 9)

This case combines cases 2, 4, and 5.

J. Base Case with Enthalpy Economy Cycle, Lowered Space Temperature, and

Supply Air Temperature Reset (Case 10)

This case combines cases 3, 4, and 5.

K. Base Case with Enthalpy Economy Cycle, Lowered Space Temperature, Supply

Air Temperature Reset, and Perimeter VAV (Case 11)

This case combines cases 3, 4, 5, and 6.

L. Base Case with Enthalpy Economy Cycle, Lowered Space Temperature, Supply

Air Temperature Reset, and All VAV (Case 12)

This case combines cases 3, 4, 5, and 7.

M. Direct Expansion Cooling Systems (Case 13)

As stated previously, 12 packaged air handling units with direct expansion refrigerant coils supplied air to each of the 12 thermal zones. The

input data of the cooling coil capacities were sized to satisfy the zone temperature profiles. Since this study compares the energy consumption

levels at the coil input (not at the plant input, unitary or central),

no distinction should be made as to the heating media—electric, hot

water or gas heat. During store hours, 66°F (18.9°C) was maintained

as the minimum space temperature.

5
N. Direct Expansion Cooling Systems with Enthalpy Economy Cycles

(Case 14)

This case had exactly the same input data as case 13 except that

enthalpy economy cycle was added to compare the outside air and

return air enthalpies to set the outside and return air damper

positions as described in case 3 previously.

3. RESULTS AND DISCUSSION

3.1 ENERGY CONSUMPTION RESULTS*

Tables 1 through 6 list the yearly heating, cooling, and fan energy consumptions of all the 14 control strategy cases for the six cities. In comparing

the strategies, it should be noted again, that not all the cases were based

on the same space temperature. Case 1 is the base case for chilled water

systems. Cases 2 through 7 are simple strategy cases and cases 8 through 12 are combined strategy cases. Between the hours of 8 a.m. to 11 p.m. during

the heating season, cases 1 through 4 and cases 6 and 7 (all single strategy

cases) tried to maintain space temperature at 72°F (22.2°C), while case 5

(single strategy), cases 8 through 12 (all combined strategy cases), and cases

13 and 14 (DX cases ) tried to maintain space temperature at 68°F (20°C).

The input total pressure data were 0.5, 4.0, and 2.0 inches of H2 O for the

return air fans, chilled water system supply air fans, and DX system supply

air fans, respectively. Since the required fan pressures were duct layout

dependent and these input data were quite arbitrary, it would be difficult

to have meaningful comparisons between the fan energy consumptions between the

chilled water units and the DX units. Therefore, the fan energy consumption

data for the DX systems are not provided in tables 1 to 6. The fan energy

consumption data for the chilled water systems are listed so that comparisons

may be made between constant volume and VAV systems. If more DX systems of

smaller sizes are compared to larger chilled water systems, the total fan

energy consumption of the DX systems should be less than that of the chilled

water systems. However, this study did not try to verify it.

Tables 7 through 12 give the yearly average heating, cooling, and fan energy

consumptions per square foot of gross floor area of the retail store for the

six cities. These figures may provide the readers with energy budget comparisons. Of course, the readers must take into account the building construction,

internal loading and other factors which affect the energy consumption of this

particular building. Also listed in these tables are the comparative energy

consumption ratios of the individual cases to those of the base case.

3.2 USING DEGREE-DAYS AS ENERGY CONSUMPTION PARAMETERS

The yearly energy consumption of a building with a fixed internal load pattern

depends on many external factors such as solar radiation, ambient temperature

*Energy consumption results are presented in English units only, for clarity.

6
and humidity, wind characteristics, etc., and their frequency of occurrence

during the year. It is always desirable, from the application point of view,

to have some parameters to correlate with the energy consumption data of one building so that the data may be applied to similar buildings of different

climatic conditions. The authors of this paper realize the difficulty of

finding these parameters to apply to commercial buildings such as the large

retail store of this study. However, a parameter, even a crude one, may give

HVAC designers assistance in deciding system and control strategies during the

early course of the building design and provide budget figures for comparisons.

This is not to say that the correlated data should be used indiscriminately.

Detailed energy calculations with an appropriate method must be performed for

a building in order to have accurate energy consumption values.

Evidently one of the most influential parameters affecting a building energy

consumption is the outdoor ambient dry-bulb temperature. The dry-bulb temperature changes the building energy consumption through ventilation air and building structure thermal conductance directly, and through ambient humidity

indirectly. Some measures of the dry-bulb temperature for a climatic location

are daily average temperature, monthly average temperature, degree-hour data,

frequency data (BINs), etc. However, the most available data for most of the

cities in the United States are the heating and cooling degree-days. Therefore,

in this study the energy consumption data of the six cities were correlated to

the degree-day data provided in the Local Climatological Data [5]. Figures ^ through 10 show the least square regression lines of the single strategy yearly

cooling energy consumptions of the six cities using 65°F based cooling degreedays as the independent variable. Figures 11 through 15 shows these lines for

various combinations of control strategies. These individual cooling consumption lines are put on the same diagram in figures 18 and 19 for easier comparisons. Figures 20 through 34 are similar diagrams, except that they show the

heating energy consumption plotted against 65°F based heating degree-days.

As mentioned previously, the ambient humidity level also affect the building

energy consumption. It may be shown that parabolic curves may represent the

cooling energy consumptions better than the straight lines because of the

ambient humidity effects through the ventilation air and infiltration. For

simplifying data analysis and application, only straight lines were used in

the regression curve fitting,

3.3 COMPARISON OF STRATEGIES

A. Temperature economy cycle and enthalpy economy cycle

The energy consumption results and comparisons for these strategies

may be seen from table 1 through 12. For single control strategies,

temperature economy cycles were applied in two cases. Case 2 (figures

5 and 21) and case 8 (figures 11 and 24) were based on indoor heating

design temperatures of 72°F (22.2°C) and 68 °F (20°C), respectively.

The energy consumptions of these two cases should be compared to those

of case l.base case, (figures 4 and 20) and case 5 (figures 11 and 27)

respectively. Case 3 (figures 6 and 22) was the result of applying

enthalpy economy cycles to the base case. Figures 18 and 19 indicate

7
that substantial cooling energy were saved and that these strategies

were especially beneficial in low cooling degree-day areas. However,

figures 33 and 34 show that the opposite is true: these strategies

caused more heating energy to be used, especially for higher heating

degree-day areas. Cases 9 and 10 were combined strategy cases where

temperature and enthalpy economy cycles were applied respectively to

lowered space temperature of 68°F (20°C) and varying discharge air

temperature according to outside air temperature (see paragraph, 3.2.B).

The following table lists the energy comparison ratio of these cases as com- pared to cases 1 (base case, 72°F heating) and 5 (68°F heating).

Lake

Charles Madison Nashville

Santa

Maria Seattle

Washington,

DC

Temperature economy (Case 2 vs Case 1, 72 °F heating)

Heating 1.06 1.30 1.12 1.09 1.14 1.17

Cooling .89 .57 .75 .69 .45 .67

Enthalpy economy (Case 3 vs Case 1

,

72 °F heating)

Heating 1.09 1.32 1.16 1.20 1.19 1.19

Cooling .89 .46 .65 .35 .24 .56

Temperature economy (Case 8 vs Case 5, 68 °F heating)

Heating 1.09 1.51 1.22 1.16 1.25 1.31

Cooling .89 .60 .76 .69 .46 .68

Temperature economy with supply air temperature reset (Case 9 vs Case 5, 68 °F

heating)

Heating .95 1.21 .99 .90 .93 1.06

Cooling .86 .58 .74 .62 .42 .66

Enthalpy economy with supply air temperature reset (Case 10 vs Case 5, 68 °F

heating)

Heating .99 1.24 1.04 1.06 1.00 1.09

Cooling .81 .47 .66 .34 .24 .58

By applying the temperature economy cycles at different indoor heating design

temperatures of 72°F (22.2°C) and 68°F (20°C) the cooling energy saving percentage were quite similar for cases 2 and 8. The heating energy increase which

appeared in all single strategy economy cycles (cases 2, 3, and 8), was mainly

caused by the decreased supply air temperature due to lowered cooling loads.

Switching to enthalpy economy cycle from temperature economy cycle at 72°F

(22.2°C) indoor design temperature increased cooling energy savings, compared

to base case, from 31 percent in Santa Maria and 55 percent in Seattle to 65

percent and 76 percent, respectively. As pointed out in reference [1], Santa

Maria and Seattle had many hours available for economy cycle operation. On

the other hand, the cooling energy savings remained the same at 11 percent in

Lake Charles

.

8
When the control strategies were combined, heating energy were reduced

substantially with further benefit of cooling energy reduction.

B. Supply Air Temperature Reset by Outside Air Temperature

Supply air temperatures were reset by the outside air temperatures in case 4

(fig. 7) to compare with case 1 (base case) and in case 9 (fig. 12) to compare

with case 8 (lowered indoor heating design temperature with temperature economy

cycle). In both cases, 4 and 9, the supply air temperatures varied between

60°F (15.6°C) and 62°F (16.7°C) in a linear relationship to the outside temperature of 75°F (23.9°C) and 32°F (0°C) respectively. Figures 7 and 23 show the

cooling and heating consumptions of the former case and figures 12 and 28 depict

those of the latter case. These comparisons are also shown in the following

table.

Lake

Charles Madison

Santa

Nashville Maria

Washington,

Seattle DC

Supply air temperature reset (Case 4 vs Case 1, 72°F heating;

Heating 1.18 1.00 1.09 1.09 1.01 1.04

Cooling 1.01 .99 1.00 1.00 .98 .99

Supply air temperature reset (Case 9 vs Case 8, 68°F heating)

Heating .87 .80 .81 .99 .74 .31

Cooling .98 .96 .97 .89 .91 .97

When the heating design temperature was 72°F (22.2°C) and no economy cycles were

used, the cooling savings were minimum because of the small reset schedule

2°F (1.1°C). A larger reset schedule is difficult to achieve for this building,

since the internal load is the dominant load of the building and the internal

zones have larger floor areas. The heating energy consumption of this case

(case 4) increased in most cities ranging from about even in Madison to 18

percent in Lake Charles. This increase was induced from higher space temperature of the reset strategy during the cooling seasons. When the heating design

temperature was lowered to 68°F (20°C) and temperature economy cycles were used as for case 9, the cooling energy was reduced from 11 percent in Santa

Maria to 2 percent in Lake Charles, the heating energy was reduced from 26

percent in Seattle to 13 percent in Lake Charles. Better results were obtained

for case 9 than for case 4 mostly during the milder and cooler months when

the economy cycle was in operation which lowered the cooling requirement and

the cold deck temperature. Thus, more benefits were obtained by resetting.

C. Lower Space Heating Temperature

The following table show the ratio's of heating and cooling energy ratios of

lowering space heating temperature from 72°F (22. °C) to 68°F (20°C).

9
Lake

Charles Madison

Santa

Nashville Maria Seattle

Washington,

DC

Lower space heating temperature from 72°F to 68 °F (Case 5 vs Case 0

Heating .62 .62 .60 .55 .57 .62

Cooling .96 .92 .95 .95 .94 .94

It is obvious that substantial heating energy was saved when the space

temperature was lowered. Cooling energy was also reduced during low heating

periods of the year when the cooling coil loads were decreased by having lower

coil entering temperature. From tables 7 through 12, it can be seen that the

air handling system fan energy was slightly increased for Madison (2 percent),

Nashville (1 percent), and Washington, DC (1 percent), when the space temperatures were lowered. For these cities, because less heat was stored in daytime,

longer fan operating hours at night in the heating season were needed to keep

the space temperature above the night setback temperature.

D. Variable Air Volume (VAV) System

VAV systems were applied in several cases. Case 6 had VAV for perimeter zones only and case 7 applied VAV to all zones. Both cases 6 and 7 were based on 72°F (22.2°C) space reheat temperature. Therefore, they should be compared to case 1 (base case). Cases 11 and 12 were also for perimeter zone VAV and all

zone VAV respectively, but they were added to case 10 which had 68 °F (20°C)

space reheat temperature and used enthalpy economy cycle and supply air reset

by outside temperature. These comparisons are as follows.

Lake

Charles Madison Nashville

Santa

Maria Seattle

Washington,

DC

Perimeter zone VAV (Case 6 vs Case 1, 72° F heating)

Heating .56 .61 .60 .55 .57 .62

Cooling .92 .80 .87 .95 .94 .94

All zone VAV (Case 7 vs Case 1, 72°F heating)

Heating .08 .23 .11 .08 .51 .57

Cooling .78 .63 .72 .69 .80 .85

Perimeter zone VAV added to case 10 (Case 11 vs Case 10)

Heating 1.11 1.02 1.02 1.00 .97 1.00

Cooling .98 .93 .96 .85 .87 .95

All zone VAV added to case 10 (Case 12 vs Case 10)

Heating .11 .40 .20 .14 .22 .25

Cooling .85 .78 .82 .72 .74 .80

Dramatic savings, for cases 6 and 7 were obtained by applying VAV's to the

building. This was especially true when the entire building was under the

VAV systems to take advantage of the internal load diversification. Less

than 10 percent of the base heating energy were enough for Lake Charles and

Santa Maria, if VAV's were used in all zones. Mixed results were evident for

10
case 11. Further cooling energy reduction (case 11 vs case 10) were achieved

by adding VAV's to the perimeter zones. However, some cities had more heating

energy consumed, even though the increased values were small. This increased

heating consumption was caused by the higher reheater discharge air temperature

of the VAV zones, due to reduced air flow and heating coil loads. Among the

six cities, from 18 percent to 25 percent of fan energy were saved for the

all VAV case. It should be noted that these results were based on a minimum

zone supply air of 40 percent of the constant volume system for all the six

cities. No attempt was made to optimize the minimum air ratio or to compare

the energy savings using the minimum air ratio as a parameter.

E. Direct Expansion (DX) Systems and DX Systems with Enthalpy Economy Cycle

The cooling energy consumption ratios of DX system with enthalpy economy

cycles to those without economy cycles are listed below.

Lake

Charles Madison Nashville

Santa

Maria

Washington,

Seattle DC

Enthalpy economy (Case 14 vs Case 13, DX Systems)

Cooling .86 .61 .75 .25 .26 .70

Similar to chilled water systems, the cooling consumption in lower cooling

degree-day cities benefited more percentage-wise than higher cooling degree-day

areas. The heating energy was the same in both cases. This was different from

the chilled water reheat systems where heating energy was increased when economy

cycles were used to reheat the lowered cooling coil discharge air temperature

to the desired room temperature. A close comparison between DX system and the

chilled water system may not be appropriate, since the zoning arrangement and

the sizing of cooling coils were not exactly the same, although the same internal loading input data were used in both cases. The closest comparison of

cooling energy between the two types of systems are case 12 (space temperature

at 68°F (20°C) during the heating season with enthalpy economy cycle, supply

air resetting by outside temperature, and all zones under VAV) and case 14 (DX

with enthalpy economy cycle). If the cooling energy of case 12 is represented

by unity, then the ratio of the two cases are as follows.

Lake Santa Washington,

Charles Madison Nashville Maria Seattle DC

Case 12 (all zone VAV with enthalpy economy, supply air temperature reset, and

68°F heating) vs Case 14 (DX with enthalpy economy)

1.12 .91 .97 .63 .72 .96

In theory, the cooling energy consumption of these two cases should be close,

since both cases try to match the system capacities to the space loads. The

bottom two lines in figure 19 show this relationship. The larger difference in

lower degree-day cities was probably caused by using the same minimum supply

air ratio (.4) for all cities. Except for Santa Maria and Seattle, the difference in energy consumption (as well as savings) between the two strategies

were within 3 percent as compared to the base case. Heating energy comparison

11
between these two strategies is not appropriate, since there was a 2°F (1.1°C)

difference in input data for the space temperature during heating season.

4. SUMMARY

The BLAST computer program was used to compute the yearly energy consumption

of a large two-story retail store of heavy architectural construction. The

mechanical systems modeled were reheat, VAV, and DX systems. The control stratategies tested were temperature and enthalpy economy cycles, supply air temperature reset by outside temperature, lowering space temperature during heating

season, applying VAV systems to perimeter and all thermal zones, and a few

combination strategies. Cities modeled covered a variety of climatic conditions. Tables 1 through 6 list the yearly heating, cooling, and electric

energy consumptions of the six cities. Tables 7 through 14 list these energy

consumptions per unit gross floor area of the store as well as the normalized

energy consumptions for all these strategies using the base case consumption

as unity.

The cooling degree-days of these cities range from 84 in Santa Maria, CA to

2739 in Lake Charles, LA. The heating degree-days range from 1498 in Lake

Charles to 7730 in Madison, WI. The cooling and heating energy consumptions

of all the strategies were also plotted in figures 4 through 17 and from 20

through 32, respectively, using degree-days as parameters.

Figure 18 compares cooling energy consumption of single strategy cases 1 through 7. Ranking energy savings, from the least to the most, were base case,

lowering space heating temperature to 68°F (20°C), applying VAV system

(40 percent minimum) to perimeter zones, temperature economy cycle, and enthalpy

economy cycle. Applying the VAV system (40 percent minimum) to all zones saved

considerable amounts of energy across all cities by roughly equal amounts.

Resetting of supply air temperature by outside air temperatures from 60°F

( 15 . 6°C) to 62°F (16.7°C) corresponding to 75°F (23.9°C) to 32°F (0°C) outside

temperature gave about the same cooling consumption as the base case. Figure 19

compares the the combination strategy cases and the DX systems. The best

cooling energy saving strategies were the combination of 68°F (20°C) space

temperature for heating, resetting supply air temperature by outside air

temperatures, enthalpy economy cycle, and applying VAV to all zones for the

chilled water system (case 12) and enthalpy economy cycled DX system. Except

for Lake Charles, DX system cooling energy was slightly lower than the chilled

water system. At Lake Charles, the cooling consumption difference between the

two systems was less than two percent. For the chilled water system alone,

the least energy consuming strategies (case 12) could reduce the cooling

energy consumption from 35 percent in Lake Charles to 83 percent in Seattle,

as compared to the base case.

As to heating energy consumption (see figures 33 and 34), temperature and

enthalpy economy cycles alone caused it to increase. Lowering space heating

temperature and applying VAV to perimeter and all zones saved a great deal

of energy. With VAV applied to all zones alone, heating savings were from 77

percent in Madison to 92 percent in Lake Charles and Santa Maria. Resetting

of supply air temperature caused most cities to use more energy with the exception of Madison which had about the same consumption as the base case. The

12
most beneficial combination of strategies for heating was case 12 which reduced

the yearly heating energy, as compared to the base case, from 69 percent in

Madison to 93 percent in Lake Charles. At lower degree day areas, cases 12,

13, and 14 all had very low heating energy consumptions.

The most favored strategy for reducing fan energy consumption was the all zone

VAV. The savings ranged from 33 percent in Lake Charles to 41 percent in

Madison. As stated in section 3.1, no comparison was made for the DX systems.

It should be stated again that the effect of energy consumption resulting from

the control loop dynamics were not considered in this study and that the data

presented in this report was based on a particular building with a particular

set of orientation, construction, internal loading, and schedules. One should

keep this in mind when using these data for preliminary design purposes or for

comparative control strategy selections. The control strategy and system

selections also depend on the relative costs of the energy sources, plant

efficiencies, transmission losses, etc. There is no substitute for determining

building energy consumptions by a detailed energy and economics analysis using

final design drawings.

13
REFERENCES

[1] Parken, W. H. , Kao, J. Y., and Kelly, G. E. Strategies for Energy

Conservation in Small Office Buildings, U.S. National Bureau of Standards

NBSIR 82-2489, 1982 June.

[2] Nonresidential Buildings Energy Consumption Survey: Building

Characteristics, U.S. Department of Energy DOE/E2A-0246 , 1981 March.

[3] Kittle, D. C., The Building Loads Analysis System Thermodynamics (BLAST)

Program, Version 2.0: Users Manual. Technical report E-153. U.S. Army

Construction Engineering Research Laboratory, Champaign, IL, 1979 June.

[4] Development of Building Models for Energy Budgets for Building Energy

Performance Standards, Volume III, Appendix II, Title 24 Building Model

Specifications; Ayres Associates, Los Angeles, CA, 1977 October.

[5] Local Climatological Data, Annual Summaries for 1975; U.S. National Oceanic

and Atmospheric Administration, Ashville, N.C.

14
Table 1. Annual energy consumption - Lake Charles, LA

CASE STRATEGY

HEATING ENERGY

Btu x 109

COOLING ENERGY

Btu x 109

FAN ENERGY

Btu x 109

1 Base (72°F heating) 1.81 13.23 2.41

2 Case 1 + temperature economy 1.91 11.71 2.41

3 Case 1 + enthalpy economy 1.98 10.68 2.41

4 Case 1 + supply air temperature

reset by outside air 2.15 13.41 2.41

5 Case 1 + 68 °F heating temperature 1.12 12.76 2.41

6 Case 1 + perimeter zone VAV 1.01 12.15 1.98

7 Case 1 + all zone VAV 0.14 10.31 1.61

8 Case 5 + temperature economy 1.22 11.40 2.31

9 Case 8 + supply air temperature

reset by outside air 1.06 11.17 2.41

10 Case 5 + enthalpy economy + supply

air temperature reset by outside air 1.11 10.36 2.41

11 Case 10 + perimeter zone VAV 1.23 10.16 1.98

12 Case 10 + all zone VAV 0.12 8.63 1.62

13 DX (66°F heating) 0.05 10.25 N.A.

14 DX + enthalpy economy 0.05 8.77 N.A.

Table 2. Annual energy consumption - Madison, WI

HEATING ENERGY COOLING ENERGY FAN ENERGY

CASE STRATEGY Btu x 109 Btu x 109 Btu x 109

1 Base (72°F heating) 3.22 9.30 2.64

2 Case 1 + temperature economy 4.17 5.33 2.64

3 Case 1 + enthalpy economy 4.2A 4.24 2.64

4 Case 1 + supply air temperature

reset by outside air 3.21 8.98 2.64

5 Case 1 + 68 °F heating temperature 2.01 8.57 2.70

6 Case 1 + perimeter zone VAV 1.97 7.46 1.99

7 Case 1 + all zone VAV 0.74 5.86 1.54

8 Case 5 + temperature economy 3.04 5.14 2.70

9 Case 8 + supply air temperature

reset by outside air 2.44 4.94 2.70

10 Case 5 + enthalpy economy + supply

air temperature reset by outside air 2.49 4.07 2.70

11 Case 10 + perimeter zone VAV 2.53 3.77 2.01

12 Case 10 + all zone VAV 1.00 3.16 1.57

13 DX (66°F heating) 1.79 4.72 N.A.

14 DX + enthalpy economy 1.79 2.89 N.A.

15
Table 3. Annual energy consumption - Nashville, TN

HEATING ENERGY COOLING ENERGY FAN ENERG?

CASE STRATEGY Btu x 109 Btu x 109 Btu x 10 9

1 Base (72°F heating) 2.22 11.33 2.39

2 Case 1 + temperature economy 2.49 8.45 2.39

3 Case 1 + enthalpy economy 2.57 7.31 2.39

4 Case 1 + supply air temperature

reset by outside air 2.41 11.30 2.39

5 Case 1 + 68 °F heating temperature 1.34 10.77 2.42

6 Case 1 + perimeter zone VAV 1.21 9.89 1.90

7 Case 1 + all zone VAV 0.25 8.19 1.53

8 Case 5 + temperature economy 1.64 8.19 2.42

9 Case 8 + supply air temperature

reset by outside air 1.33 7.97 2.42

10 Case 5 + enthalpy economy + supply

air temperature reset by outside air 1.39 7.09 2.42

11 Case 10 + perimeter zone VAV 1.42 6.82 1.90

12 Case 10 + all zone VAV 0.28 5.82 1.54

13 DX (66°F heating) 0.33 7.46 N.A.

14 DX + enthalpy economy 0.33 5.62 N.A.

Table 4. Annual energy consumption - Santa Maria, CA

HEATING ENERGY COOLING ENERGY FAN ENERGY

CASE STRATEGY Btu x 109 Btu x 109 Btu x 109

1 Base (72°F heating) 1.81 9.51 2.21

2 Case 1 + temperature economy 1.97 6.56 2.21

3 Case 1 + enthalpy economy 2.18 3.35 2.21

4 Case 1 + supply air temperature

reset by outside air 1.98 9.51 2.21

3 Case 1 + 68 °F heating temperature 0.99 9.06 2.21

6 Case 1 + perimeter zone VAV 0.85 7.96 1.74

7 Case 1 + all zone VAV 0.14 6.58 1.41

8 Case 5 + temperature economy 1.15 6.27 2.21

9 Case 8 + supply air temperature

reset by outside air 0.89 5.61 2.21

10 Case 5 + enthalpy economy + supply

air temperature reset by outside air 1.05 3.10 2.21

11 Case 10 + perimeter zone VAV 1.05 2.63 1.72

12 Case 10 + all zone VAV 0.15 2.24 1.41

13 DX (66°F heating) 0.07 5.56 N.A.

14 DX + enthalpy economy 0.07 1.41 N.A.

16
Table 5. Annual energy consumption - Seattle, WA

CASE STRATEGY

HEATING ENERGY

Btu x 10^

COOLING ENERGY

Btu x 10^

FAN ENERGY

Btu x 10'

1 Base (72°F heating) 2.37 8.88 2.25

2 Case 1 + temperature economy 2.71 3.98 2.25

3 Case 1 + enthalpy economy 2.82 2.16 2.25

4 Case 1 +

reset by

supply air temperature

outside air 2.40 8.71 2.25

5 Case 1 + 68 °F heating temperature 1.34 8.34 2.26

6 Case 1 + perimeter zone VAV 1.20 7.14 1.71

7 Case 1 + all zone VAV 0.30 5.72 1.36

8 Case 5 + temperature economy 1.68 3,82 2.26

9 Case 8 +

reset by

supply air temperature

outside air 1.25 3.49 2.26

10 Case 5 + enthalpy economy + supply

air temperature reset by outside air 1.34 2.03 2.26

11 Case 10 + perimeter zone VAV 1.30 1.77 1.70

12 Case 10 + all zone VAV 0.30 1.51 1.38

13 DX (66°F heating) 0.38 4.15 N.A.

14 DX + enthalpy economy 0.38 1.08 N.A.

Table 6. Annual energy consumption - Washington, DC

CASE STRATEGY

HEATING ENERGY

Btu x 10^

COOLING ENERGY

Btu x 10^

FAN ENERGY

Btu x 10^

1 Base (72°F heating) 2.65 10.67 2.47

2 Case 1 + temperature economy 3.09 7.10 2.47

3 Case 1 + enthalpy economy 3.16 6.01 2.47

4 Case 1 +

reset by

supply air temperature

outside air 2.76 10.53 2.47

5 Case 1 + 68 °F heating temperature 1.63 10.03 2.51

6 Case 1 + perimeter zone VAV 1.50 9.02 1.91

7 Case 1 + all zone VAV 0.38 7.27 1.51

8 Case 5 + temperature economy 2.13 6.87 2.51

9 Case 8 +

reset by

supply air temperature

outside air 1.72 6.65 2.51

10 Case 5 + enthalpy economy + supply

air temperature reset by outside air 1.77 5.79 2.51

11 Case 10 + perimeter zone VAV 1.77 5.51 1.92

12 Case 10 + all zone VAV 0.45 4.63 1.53

13 DX (66°F heating) 0.64 6.33 N.A.

14 DX + enthalpy economy 0.64 4.46 N.A.

17
Table 7. Comparative annual energy consumption - Lake Charles, LA

CASE STRATEGY HEATING ENERGY COOLING ENERGY FAN ENERGY

Consumption, 10J Btu/f

Ratio-relative to Case 1

1 Base (72°F heating) 11.78 86.13 15.69

1.00 1.00 1.00

2 Case 1 + temperature economy 12.43 76.24 15.69

1.06 0.89 1.00

3 Case 1 + enthalpy economy 12.89 69.53 15.69

1.09 0.81 1.00

4 Case 1 + supply air temperature 14.00 87.30 15.69

reset by outside air 1.19 1.01 1.00

5 Case 1 + 68 °F heating temperature 7.29 83.07 15.69

0.62 0.96 1.00

6 Case 1 + perimeter zone VAV 6.58 79.10 12.89

0.56 0.92 0.82

7 Case 1 + all zone VAV 0.91 67.12 10.48

0.08 0.78 0.67

8 Case 5 + temperature economy 7.94 74.22 15.69

0.67 0.86 1.00

9 Case 8 + supply air temperature 6.90 72.72 15.69

reset by outside air 0.59 0.84 1.00

10 Case 5 + enthalpy economy + supply 7.23 67.45 15.69

air temperature reset by outside air 0.61 0.78 1.00

11 Case 10 + perimeter zone VAV 8.01 66.15 12.89

0.68 0.77 0.82

12 Case 10 + all zone VAV 0.781 56.18 10.55

0.65 0.67

0.07

13 DX (66° F heating) 0.33 66.73 N.A.

0.03 0.78

14 DX + enthalpy economy 0.33 57.10 N.A.

0.03 0.66

18
Table 8. Comparative annual energy consumption - Madison, Wisconsin

CASE STRATEGY HEATING ENERGY COOLING ENERGY FAN ENERGY

Consumption, 10^ Btu/ft^

Ratio-relative to Case 1

1 Base (72°F heating) 20.96

1.00

60.55

1.00

17.19

1.00

2 Case 1 + temperature economy 27.15

1.30

34.70

0.57

17.19

1.00

3 Case 1 + enthalpy economy 27.60

1.32

20.60

0.46

17.19

1.00

4 Case 1 reset +

by

supply air temperature

outside air

20.90

1.00

58.46

0.97

17.19

1.00

5 Case 1 + 68 °F heating temperature 13.09

0.62

55.79

0.92

17.58

1.02

6 Case 1 + perimeter zone VAV 12.83

0.61

48.57

0.80

12.96

0.75

7 Case 1 + all zone VAV 4.82

0.23

38.15

0.63

10.03

0.58

8 Case 5 + temperature economy 19.79

0.94

33.46

0.55

17.19

1.00

9 Case 8

reset +by

supply air temperature

outside air

15.89

0.76

32.16

0.53

17.19

1.00

10 Case 5 + enthalpy economy + supply

air temperature reset by outside air

16.21

0.77

26.50

0.44

17.19

1.00

11 Case 10 + perimeter zone VAV 16.47

0.79

24.54

0.41

13.09

0.76

12 Case 10 + all zone VAV 6.51

0.31

20.57

0.34

10.22

0.59

13 DX (66° F heating) 11.65

0.56

30.73

0.51

N.A.

14 DX + enthalpy economy 11.65

0.56

18.81

0.31

N.A.

19
Table 9. Comparative annual energy consumption - Nashville, TN

CASE STRATEGY HEATING ENERGY COOLING ENERGY FAN ENERGY

Consumption, 10 J Btu/f t 2 Ratio-relative to Case 1

1 Base (72°F heating) 14.45 73.76 15.56

1.00 1.00 1.00

2 Case 1 + temperature economy 16.21 55.01 15.56

1.12 0.75 1.00

3 Case 1 + enthalpy economy 16.73 47.59 1.00

1.16 0.65 1.00

4 Case 1 + supply air temperature 15.69 73.57 15.56

reset by outside air 1.09 1.00 1.00

5 Case 1 + 68 °F heating temperature 8.72 70.12 15.76

0 . 60 0.95 1.01

6 Case 1 + perimeter zone VAV 7.88 64.39 12.37

0.55 0.87 0.79

7 Case 1 + all zone VAV 1.63 53.32 9.96

0.11 0.72 0.64

8 Case 5 + temperature economy 10.68 53.32 15.76

0.74 0.72 1.01

9 Case 8 + supply air temperature 8.66 51.89 15.76

reset by outside air 0.60 0.70 1.01

10 Case 5 + enthalpy economy + supply 9.05 46.16 15.76

air temperature reset by outside air 0.63 0.63 1.01

11 Case 10 + perimeter zone VAV 9.24 44.40 12.37

0.64 0.60 0.79

12 Case 10 + all zone VAV 1.82 37.89 10.03

0.13 0.51 0.64

13 DX (66° F heating) 2.15 48.57 N.A

0.15 0 . 66

14 DX + enthalpy economy 2.15 36.59 N.A

0.15 0.50

20
Table 10. Comparative annual energy consumption - Santa Maria, CA

CASE STRATEGY HEATING ENERGY COOLING ENERGY FAN ENERGY

Consumption

,

10 J Btu/f t 2 Ratio-relative to Case 1

1 Base (72°F heating) 11.78 61.91 14.39

1.00 1.00 1.00

2 Case 1 + temperature economy 12.83 42.71 14.39

1.09 0.69 1.00

3 Case 1 + enthalpy economy 14.19 21.81 14.39

1.20 0.35 1.00

4 Case 1 + supply air temperature 12.89 61.91 14.39

reset by outside air 1.09 1.00 1.00

5 Case 1 + 68 °F heating temperature 6.45 58.98 14.39

0.55 0.95 1.00

6 Case 1 + perimeter zone VAV 5.53 51.82 11.33

0.47 0.84 0.79

7 Case 1 + all zone VAV 0.91 42.84 9.18

0.08 0.69 0.64

8 Case 5 + temperature economy 7.49 40.82 14.39

0.64 0.66 0.65

9 Case 8 + supply air temperature 5.79 36.52 14.39.

reset by outside air 0.49 0.59 0.65

10 Case 5 + enthalpy economy + supply 6.84 20.18 14.39

air temperature reset by outside air 0.58 0.33 0.65

11 Case 10 + perimeter zone VAV 6.84 17.12 11.20

0.58 0.28 U • 78

12 Case 10 + all zone VAV 0.98 14.58 9.31

0.08 0.24 0.64

13 DX (66° F heating) 0.46 36.20 N. A.

0.04 0.58

14 DX + enthalpy economy 0.46 9.18 N.A.

0.04 0. 15

21
Table 11. Comparative annual energy consumption - Seattle, WA

CASE STRATEGY HEATING ENERGY COOLING ENERGY FAN ENERGY

Consumption, 10 J Btu/f t 2

Ratio-relative to Case 1

15.43 57.81 14.65

1 Base (72°F heating) 1.00 1.00 1.00

17.64 25.91 14.65

2 Case 1 + temperature economy 1.14 0.45 1.00

18.36 14.06 14.65

3 Case 1 + enthalpy economy 1.19 0.24 1.00

4 Case 1 + supply air temperature 15.63 56.71 14.65

reset by outside air 1.01 0.98 1.00

8.72 54.30 14.71

5 Case 1 + 68 °F heating temperature 0.57 0.94 1.00

7.81 46.48 11.13

6 Case 1 + perimeter zone VAV 0.51 0.80 0.76

1.95 37.24 8.85

7 Case 1 + all zone VAV 0.13 0.64 0.60

10.94 24.87 14.71

8 Case 5

-4

- temperature economy 0.71 0.43 1.00

9 Case 8 + supply air temperature 8.14 22.72 14.71

reset by outside air 0.53 0.39 1.00

10 Case 5 + enthalpy economy + supply 8.72 13.22 14.71

air temperature reset by outside air 0.57 0.23 1.00

8.46 11.52 11.07

11 Case 10 + perimeter zone VAV 0.55 0.20 0.76

1.95 9.83 8.98

12 Case 10 + all zone VAV 0.13 0.17 0.61

2.47 27.02

13 DX (66°1 heating) 0.16 0.47 N.A

2.47 7.03

14 DX + enthalpy economy 0.16 0.12 N.A.

22
Table 12. Comparative annual energy consumption - Washington, DC

CASE STRATEGY HEATING ENERGY COOLING ENERGY FAN ENERGY

Consumption, 10 J Btu/f t 2 Ratio-relative to Case 1

17.25 69.47 16.08

1 Base (72°F heating) 1.00 1.00 1.00

20.12 46.22 16.08

2 Case 1 + temperature economy 1.17 0.67 1.00

20.57 39.13 16.08

3 Case 1 + enthalpy economy 1.19 0.56 1.00

4 Case 1 + supply air temperature 17.97 68.55 16.08

reset by outside air 1.04 0.99 1.00

10.61 65.30 16.34

5 Case 1 + 68 °F heating temperature 0.62 0.94 1.02

9.77 58.72 12.43

6 Case 1 + perimeter zone VAV 0.57 0.85 0.77

2.47 47.33 9.83

7 Case 1 + all zone VAV 0.14 0.68 0.61

2.47 47.33 9.83

8 Case 5 + temperature economy 0.14 0.68 0.61

9 Case 8 + supply air temperature 11.20 43.29 16.34

reset by outside air 0.65 0.62 1.02

10 Case 5 + enthalpy economy + supply 11.52 37.70 16.34

air temperature reset by outside air 0.67 0.54 1.02

11.52 35.87 12.50

11 Case 10 + perimeter zone VAV 0.67 0.52 0.78

2.93 30.14 9.96

12 Case 10 + all zone VAV 0.17 0.43 0.62

4.17 41.21

13 DX (66° F heating) 0.24 0.59 N.A.

4.17 29.04

14 DX + enthalpy economy 0.24 0.42 N. A.

23
l

st

fl.

2

nd

fl.

320 ft

Exterior Walls:

1st floor: 12" (.3m) concrete masonry units, 2" (.05m)

insulation K = 0.27 Btu/h • ft • °F (.00389 w/m • °K)

,

and 1/2 M (.013m) gypsum board

2nd floor: same as 1st floor except 8" (.2m) concrete masonry units.

Roof

:

Built-up roof, 3" (.07m) insulation K = 0.158 Btu/h • ft • °F

(.00228 w/m • °K) , 3 1/2" (.09m) light weight concrete, metal deck,

air space, and 1/2" (.01m) ceiling panels. Ceiling height 12' (3.66m).

Floor

:

1st floor: 5" (.13m) concrete slab on grade and carpeting

2nd floor: 9" (.23m) concrete base, 3 1/2" (.09m) light weight

concrete and carpeting

Door

:

Tempered glass doors

Figure 1. Large retail store model

24
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Figure 2. Internal load profiles

25

Sunday

Weekday

and

Saturday

Lighting

and

equipment

schedules—

peak

lighting:

3.1

W/ft 2

9

(33.4

W/m 2

peak

equipment:

1.0

W/ft^

(10.8

W/m :
4-1 0

«r r-

• • m r-» cm

zone 9—1st floor

zone 10—2nd floor.

1920 ft2 (178.4 m

2

) x 2 multipliers for

each floor

17.9 ft (5.5 m)

zone 3—1st floor zone 4-x2nd floor

1920 ft (178.4 m

2

) x 4 multipliers for each floor

zone 1—1st floor zone 2—2nd floor

1920 ft2 (178, 4 m2

) x 28 multipliers

for each floor

IZZ

zone 7—1st floor zone 8—2nd floor

1920 ft 2 (178.4 m2

) x 2 multipliers for

each floor

17.9 ft (5.5 m)

01 zone 5—1st floor ^ zone 6—2nd floor

JQ 1920 ft 2 (178.4 m2

) x 4 multipliers for each floor

Reheat and VAV systems

zone 11—1st floor

zone 12—2nd floor

9500 ft 2 (883 m2 ) each zone

7 zone 5—1st floor /

zone 6—2nd floor /

NS,13500 ft2 (1254 m2

) each zone /

zones 1 & 2—1st floor

zones 3 & 4—2nd floor

15400 ft2 (1431 m2 ) each zone

zone 9—1st floor

zone 10—2nd floor

9500 ft2 (883 m2 ) each zone

50 ft

(15.2 m) zone 7 —1st floor

zone 8—2nd floor

13500 ft2 (1254 m2) each zone

50 ft

(15.2 m)

DX systems

Figure 3. Thermal zone diagrams

26
Yearly

cooling

energy,

10"

Btu

Yearly

cooling

energy,

10

Btu

Figure 4. Cooling energy consumption of base case (Case 1)

Figure 5. Cooling energy consumption of applying temperature

economy cycle (Case 2)

27

Yearly

cooling

energy,

10 3

Btu/ft

2

.

Yearly

cooling

energy,

10 3

Btu/ft
Yearly

cooling

energy,

10'

Btu

Yearly

cooling

energy,

10'

Btu

Cooling degree-day

Figure 6. Cooling energy consumption of applying enthalpy

economy cycle (Case 3)

Cooling degree-day

Figure 7. Cooling energy consumption of applying outside air

resetting supply air temperature (Case 4)

28

Yearly

cooling

energy,

10

Btu/ft
Yearly

cooling

energy,

10

Btu

Yearly

cooling

energy,

10

Btu

Cooling degree-day

Figure 8. Cooling energy consumption of base case with lowered

space heating temperature (Case 5)

Cooling degree-day

Figure 9. Cooling energy consumption of applying VAV to

perimeter zones (Case 6)

29

Yearly

cooling

energy,

10 3

Btu/ft

2

Yearly

cooling

energy,

10

Btu/ft
Yearly

cooling

energy,

10'

Btu

Yearly

cooling

energy,

10

Btu

15 . &

90.0 14 , 13 . 12 . 11 . 10 . 9 .

e.7 . 6 . 5 . 4 . 3 . 2 .

1 . 0 .

CDD CITY — 40.0

84 Santa Maria

129 Seattle — - 30.0

460 Madison

1415 Washington _ - 20.0

1694 Nashville

2739 Lake Charles - 10.0

0-

• B0 .

0

70.0

60.0

50.0

1—7 1 I |—T——I I I |

1 1

1 •—I — 1 1 I I 1

|

I 1 I

1

1

‘ ' * * ****** 0 500 1000 1500 2000 2500 3000

Cooling degree-day

Figure 10. Cooling energy consumption of applying VAV to all zones (Case 7)

0.0

Figure 11. Cooling energy consumption of applying lowered space

heating temperature and temperature economy cycle

(Case 8)

30

Yearly

cooling

energy,

10

Btu/ft

Yearly

cooling

energy,

10

Btu/ft
Yearly

cooling

energy,

10'

Btu

Yearly

cooling

energy,

10

Btu

Cooling degree-day

Figure 12. Cooling energy consumption of applying lowered space

heating temperature, temperature economy cycle, and

outside air resetting supply air temperature (Case 9)

Figure 13. Cooling energy consumption of applying lowered space

heating temperature, enthalpy economy cycle, and outside air resetting supply air temperature (Case 10)

31
Yearly

cooling

energy,

10

Btu

Yearly

cooling

energy,

10

Btu

Figure 14. Cooling energy consumption of applying lowered space

heating temperature, enthalpy economy cycle, outside

air resetting supply air temperature, and VAV to

perimeter zones (Case 11)

Cooling degree-day

Figure 15. Cooling energy consumption of applying lowered space

heating temperature, enthalpy economy cycle, outside

air resetting supply air temperature, and VAV to all zones (Case 11)

32

Yearly

cooling

energy,

10

Btu/ft

Yearly

cooling

energy,

10

Btu/

ft
Yearly

cooling

energy,

10

Btu

Yearly

cooling

energy,

10

Btu

Figure 17. Cooling energy consumption of DX system applying

enthalpy economy cycle (Case 14)

33

Yearly

cooling

energy,

10 3

Btu/ft

2

Yearly

C

°°

Un8

energy

’

103

Btu/ft2
n 39 ,0T

o

‘ ASaaua Sutjood

34

Figure

18.

Cooling

energy

consumption

of

all

single

control

strategy

cases
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3 £

CD CD 0 0 0 0 0 0 0

CD 0 CD CD 0 0 0 CD CD 0

cn 00 N UD in m OJ rH

1ft cn (\i rH rH

tH

rH Q (T> CD to in cn oj CD

nig 0T ‘^§J9ua guTjooo Ajaea^

6

S

Q

<S

CO

Q

Q

in

(\J

<sQ

Q

OJ

(S0

in

rH

0

0

0

0

0

in

0

>.

(3 T3

I0)

(1) u

SOo

'O

o

o

CJ

35

Figure

19.

Cooling

energy

consumption

o!"

all

combined

control

strategy

cases

and

DX

cases
Yearly

heating

energy,

10

Btu

Yearly

heating

energy,

10

Btu

5.0

. HDD CITY

1498 Lake Charle;

4 . 0- _ 3053 Santa Maria

3696 Nashville

- 4211 Washington

5185 Seattle

3 . 0-

7730 Madison

0.0

1000 2000

Figure 20.

30.0

CM

25.0

(* 20.0

15.0

10.0

5.0

0.0

3000 4000 5000 6000 7000 0000

Heating degree-day

Heating energy consumption of base case (Case 1)

Figure 21. Heating energy consumption of applying temperature

economy cycle (Case 2)

36

Yearly

heating

energy,

10

Btu/ft

Yearly

heating

energy,

10

Btu/ft
Yearly

heating

energy,

10

Btu

Yearly

heating

energy,

. 10

Btu

Figure 22. Heating energy consumption of applying enthalpy

economy cycle (Case 3)

Heating degree-day

Figure 23. Heating energy consumption of applying outside air

resetting supply air temperature (Case 4)

37

Yearly

heating

energy,

10 J

Btu/ft

Yearly

heating

energy,

10

Btu/ft
Yearly

heating

energy,

10'

Btu

Yearly

heating

energy,

10

Btu

5.C*

HDD CITY

1498 Lake Charle

3053 Santa Maria

3696 Nashville

4211 Washington

5185 Seattle

7730 Madison

30.0

- 25.0

- 20.0

0.0-] . 1

. J

. 1

. 11 1

«

1

' 1000 2000 3000 4000 5000 6000 7000 0000

Heating degree-day

Figure 24. Heating energy consumption of base case with

lowered space heating temperature (Case 5)

0.0

Heating degree-day

Figure 25. Heating energy consumption of applying VAV to

perimeter zones (Case 6)

38

Yearly

heating

energy,

10

Btu/ft

Yearly

heating

energy,

10 J

Btu/ft
Yearly

heating

energy,

10

Btu

Yearly

heating

energy,

10

Btu

5 . 0-

2 .

1 .

0 .

HDD CITY

1498 Lake Charle*

3053 Santa Maria

3696 Nashville

4211 Washington

5185 Seattle

7730 Madison

1000 2000 3000 4000 5000 6000 7000

30.0

• 25.0

• 20.0

15.0

10.0

5.0

0.0

0000

Heating degree-day

Figure 26. Heating energy consumption of applying VAV to all zones (Case 7)

Figure 27. Heating energy consumption of applying lowered space

heating temperature and temperature economy cycle

(Case 8)

39

Yearly

beating

energy.

10 3

Btu/ft

2

Yearl *

heatlu

6

energy,

10

Btu/ft
Yearly

heating

energy,

10

Btu

Yearly

heating

energy,

10

Btu

Heating degree-day

Figure 28. Heating energy consumption of applying lowered space

heating temperature, temperature economy cycle, and

outside air resetting supply air temperature (Case 9)

Figure 29. Heating energy consumption of applying lowered space

heating temperature, enthalpy economy cycle, and outside air resetting supply air temperature (Case 19)

\

40

Yearly

heating

energy,

10

Btu/ft

Yearly

heating

energy,

10

Btu/ft
Yearly

heating

energy,

10

Btu

Yearly

heating

energy,

10

Btu

Figure 30. Heating energy consumption of applying lowered space

heating temperature, enthalpy economy cycle, outside

air resetting supply air temperature, and VAV to

perimeter zones (Case 11)

CN

heating temperature, enthalpy economy cycle, outside

air resetting supply air temperature, and VAV to all zones (Case 12)

41

Yearly

heating

energy,

10

Btu/ft

Yearly

heating

energy,

10 3

Rtu/ft
Yearly

heating

energy,

10

Btu

Figure 32. Heating energy consumption of DX system and DX

system applying enthalpy economy cycle (Cases 13

and 14)

42

Yearly

heating

energy,

10 J

Btu/ft
£ 0T ‘ ASxaua Suxqeaii Ajaea^

0 0 0 0 0 0 0

0 in 0 in 0 in 0

m OJ 0J rH 0

0

0

CD

0

0

0

N

0

0

0

kD

0

0

0

in

0

0

Q

''T

0

0

0

m

0

0

0

f\J

0

0

c3

IGJ

CUu*. r oT -o

fc£ C

in m OJ 0

n 39 ,01 ‘4§xaua 3ut^B9ij Ajjaa^

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43

Figure

33.

Heating

energy

consumption

of

all

single

control

strategy

cases
01 ‘4Sjaua gujrjeaq /qaea*

c t 0 0 0 0 0

0 in 0 in 0

m (\j (VJ rH 0

0

0

0

0

0

0

N

0

0

0

0

0

0

0

in

0

0

0

0

0

0

n

0

0

0

(\j

0

0

0

(0»

cfl "3

I <U0)

t-i 60

01 "Oto

(TJ 0)

n^9 OT

6

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44

Figure

34.

Heating

energy

consumption

of

all

combined

control

strategy

cases
NBS-1I4A (REV. 2-80) U.S. DEPT. OF COMM. 1 . BIBLIOGRAPHIC DATA

SHEET (See instructions)

PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. NBSIR 82-2580

3. Publication Date September 1982

4. TITLE AND SUBTITLE

STRATEGIES FOR ENERGY CONSERVATION FOR A LARGE RETAIL STORE

5. AUTHOR(S)

James Y. Kao. Walter H. Par ken, and Thomas E. Pierce

6. PERFORMING ORGANIZATION (If joint or other than N BS, see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Reoort & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State, ZIP)

Office of Buildings Energy Research and Development

Office of Conservation and Renewable Energy

U.S. Department of Energy

Washington, D.C. 20585

10. SUPPLEMENTARY NOTES

| | Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bi bl icgraphy or literature survey, mention it here)

A comparative analysis is made of the thermal performance of selected HVAC systems

and control strategies commonly employed in large retail stores. The comparisons

are made for six geographical locations representing wide climatic variations within

the continental United States. Hour-by-hour simulations with the BLAST computer

program were used to obtain the yearly heating, cooling and fan energy consumption

of a two-story large retail store. The HVAC systems simulated were constant volume

reheat, variable air volume, and with direct expansion coils. The control stragegies

tested were dry bulb temperature economy cycle, enthalpy economy cycle, supply air

temperature resetting, lowered space heating temperature, VAV zoning variations, and

the combinations of these strategies. The results of these simulations were given

and discussed. Substantial energy consumption differences were shown.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Building control strategies; building energy conservation; building thermal

performance; HVAC systems

13. AVAILABILITY

[x] Uni imlted

Q3) For Official Distribution. Do Not Release to NTIS rn Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

[xf] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

52

15. Price

$9.00

USCOMM-DC 6043-P80