CHAPTER 7. ENERGY USE CHARACTERIZATION

TABLE OF CONTENTS

7.1	 INTRODUCTION ........................................................................................................... 7­1
 

7.2	 OVERVIEW OF ENERGY USE FOR COMMERCIAL REFRIGERATION
 

EQUIPMENT .................................................................................................................. 7­1
 

7.2.1	 Direct Energy Consumption ................................................................................ 7­2
 

7.2.1.1	 Lighting Energy Consumption.............................................................. 7­2
 

7.2.1.2	 Evaporator Fan Motors......................................................................... 7­3
 

7.2.1.3	 Anti­Sweat Heaters and Condensate Pan Heaters ................................ 7­3
 

7.2.1.4	 Defrost and Drain Heaters .................................................................... 7­3
 

7.2.2	 Refrigeration Load and Compressor Energy Consumption................................. 7­3
 

7.3	 ENERGY ANALYSIS APPROACHES.......................................................................... 7­5
 

7.4	 WHOLE­BUILDING ANNUAL ENERGY SIMULATION ......................................... 7­7
 

7.4.1	 Modeling Tool ..................................................................................................... 7­7
 

7.4.2	 Climate Locations for Simulation........................................................................ 7­8
 

7.4.3	 Typical Supermarket Model ................................................................................ 7­8
 

7.4.3.1	 Building Description............................................................................. 7­8
 

7.4.3.2	 Refrigeration System Model................................................................. 7­8
 

7.4.4	 Summary of Simulation Results........................................................................ 7­12
 

7.4.4.1	 Comparison of Case Refrigeration Load between Simulation
 

Results and Engineering Analysis ...................................................... 7­12
 

7.4.4.2	 Impact of Climate on Daily Energy Consumption ............................. 7­13
 

7.4.4.3	 Comparison of Daily Energy Consumption between Simulation
 

and Engineering Analysis................................................................... 7­14
 

7.4.4.4	 Energy Savings Comparison at Different Efficiency Levels and
 

Climates.............................................................................................. 7­15
 

7.4.4.5	 Impacts of Display Case Improvements on Whole­Building Energy
 

Consumption....................................................................................... 7­16
 

7.5	 SENSITIVITY TO DISPLAY CASE LIGHTING OPERATING HOURS ................. 7­18
 

7.6 CONCLUSIONS............................................................................................................ 7­22
 

REFERENCES .......................................................................................................................... 7­24
 

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LIST OF TABLES
 

Table 7.4.1 Summary of Energy Model Assumptions for Building Envelope, Internal
 

Loads and HVAC System....................................................................................... 7­9
 

Table 7.4.2 Line­up Length of Modeled Display Cases........................................................... 7­10
 

Table 7.4.3 Modeled Design Options and Efficiency Levels................................................... 7­11
 

Table 7.4.4 Mapping of the Efficiency Levels for the Whole Building Analysis.................... 7­16
 

Table 7.4.5 Summary of Energy Savings for Refrigeration System and Whole Building ....... 7­17
 

Table 7.5.1 Average Reported Hours Open – Commercial Buildings Energy Consumption
 

Survey 2003 .......................................................................................................... 7­19
 

LIST OF FIGURES

Figure 7.4.1 Internal Load Schedule Assumptions in Energy Model....................................... 7­10

Figure 7.4.2 Case Refrigeration Load for Vertical Open, Remote Condensing, Medium

Temperature Equipment Class.............................................................................. 7­12

Figure 7.4.3 Baseline Daily Energy Consumption for Vertical Open, Remote Condensing,

Medium Temperature Equipment Class for Five Climate Locations................... 7­14

Figure 7.4.4 Daily Energy Consumption for Vertical Open, Remote Condensing, Medium

Temperature Equipment Class at Baltimore......................................................... 7­14

Figure 7.4.5 Daily Energy Savings for Vertical Open, Remote Condensing, Medium

Temperature Equipment Class.............................................................................. 7­16

Figure 7.4.6 Energy Savings for Baltimore (Refrigeration System versus Whole Building)... 7­17

Figure 7.5.1 Energy Savings versus Case Lighting Operating Hours for Efficiency Level

AD4....................................................................................................................... 7­20

Figure 7.5.2 Energy Savings versus Case Lighting Operating Hours for Highest Efficiency

Level Analyzed ..................................................................................................... 7­21
 

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CHAPTER 7. ENERGY USE CHARACTERIZATION
 

7.1 INTRODUCTION
 

The energy use characterization provides estimates of annual energy consumption for

commercial refrigeration equipment (CRE), which are used in the subsequent life­cycle cost

(LCC) and payback period (PBP) analyses (Chapter 8 of the TSD) and national impacts analyses

(Chapter 11 of the TSD). The U.S. Department of Energy (DOE) estimated the energy

consumption for the 15 equipment classes analyzed in the engineering analysis (Chapter 5 of the

TSD). These energy consumption estimates were then validated with annual simulation

modeling of selected equipment classes and efficiency levels.

7.2	 OVERVIEW OF ENERGY USE FOR COMMERCIAL REFRIGERATION

EQUIPMENT

American National Standards Institute (ANSI)/Air­Conditioning and Refrigeration

Institute (ARI) Standard 1200­2006 (ARI 1200­2006),1 which references ANSI/American

Society of Heating, Refrigerating, and Air­Conditioning Engineers (ASHRAE) Standard

72­2005,2 is an industry­developed test procedure for determining the energy consumption of

commercial refrigeration equipment. ARI 1200­2006 provides a method for estimating the daily

energy consumption for a display case under steady­state conditions. The use of daily energy

consumption is an appropriate approach for commercial refrigeration equipment for several

reasons. First, because the useful output of commercial refrigeration equipment is the ability to

display a product while maintaining that product at an adequate temperature, there is no easily

quantifiable output metric (such as British thermal units (Btu) of cooling provided). Second,

commercial refrigeration equipment typically provide both cold storage and lighting of product

with, varying, but often on the same order of magnitude, energy consumption. DOE’s need for a

single metric to describe both makes defining a useful output metric difficult.

DOE used ARI 1200­2006 as the basis for the engineering analysis calculations. ARI

1200­2006 treats remote condensing and self­contained commercial refrigeration equipment

differently. In the case of remote condensing equipment, the test procedure measures the energy

use of each component (e.g., fans and lights) as well as the total refrigeration load of the

equipment. The total refrigeration load is used to calculate compressor energy consumption

based on a standardized relationship of evaporator temperature and compressor energy efficiency

ratio. In the case of self­contained equipment, the test procedure measures the total energy use

of the equipment as a whole, including both component energy use and compressor energy use.

The resulting daily energy consumption estimate is either calculated daily energy consumption

(CDEC) for remote condensing equipment or total daily energy consumption (TDEC) for

self­contained equipment. Both metrics represent the sum of compressor energy consumption

and direct energy consumption used by evaporator fan motors, lighting, anti­sweat heaters,

defrost and drain heaters, and condensate evaporator pan heaters. This sum is represented in Eqs.

7.1 and 7.2; however, it is only calculated from individual components for remote condensing

equipment. For self­contained equipment, the TDEC is based on the measured total power draw.

CDEC = CEC + FEC + LEC + AEC + DEC + PEC Eq. 7.1

TDEC = CEC + FEC + LEC + AEC + DEC + PEC Eq. 7.2

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where

CDEC = Calculated daily energy consumption for remote condensing equipment in
 

kilowatt hours per foot per day (kWh/ft per day),
 

TDEC = Total daily energy consumption for self­contained equipment (kWh/ft per day),
 

CEC = Compressor energy consumption (kWh/ft per day),
 

FEC = Fan energy consumption (kWh/ft per day),
 

LEC = Lighting energy consumption (kWh/ft per day),
 

AEC = Anti­sweat heater energy consumption (kWh/ft per day),
 

DEC = Defrost and drain heater energy consumption (kWh/ft per day),
 

PEC = Condensate evaporator pan energy consumption (kWh/ft per day)
 

The primary difference between the CDEC and TDEC metrics is the way compressor

energy consumption is determined. In the CDEC metric, the cooling load (in Btu/hour) is

measured, and the compressor energy consumption is calculated using a compressor energy

efficiency ratio (EER) table provided in ARI 1200­2006. In the TDEC metric, the compressor

energy consumption is directly measured as a power draw during testing.

7.2.1 Direct Energy Consumption

Direct electric energy consumption is the total energy consumption of evaporator fan

motors, lighting, anti­sweat heaters, defrost and drain heaters, and condensate pan heaters.

7.2.1.1 Lighting Energy Consumption

Commercial refrigeration equipment is generally outfitted with lighting to illuminate the

products it refrigerates. For most equipment, lighting represents a significant fraction of the total

energy consumption. Lighting configuration can vary significantly for different types of cases.

Lamps and ballasts can be located inside the refrigerated space and/or outside the refrigerated

space. For vertical open (VOP) type of refrigerated equipmenta

, standard lighting consists of 1

or 2 rows of lamps located in the top canopy. Additional lighting is sometimes placed along the

lower rail of the case and on the bottom of each shelf to illuminate the shelf below it. Lighting in

frozen food reach­in cases is located in the vertical mullions between the doors. Cases with solid

doors usually have no lighting.3

a Equipment class designations consist of a combination (in sequential order separated by periods) of a equipment

family code (VOP=vertical open, SVO=semivertical open, HZO=horizontal open, VCT=vertical transparent doors,

VCS=vertical solid doors, HCT=horizontal transparent doors, HCS=horizontal solid doors, or SOC=service over

counter), an operating mode code (RC=remote condensing or SC=self­contained), and a rating temperature code

(M=medium temperature (38°F), L=low temperature (0°F), or I=ice­cream temperature (­15°F)). For example,

"VOP.RC.M refers to the "vertical open, remote condensing, medium temperature" equipment class. See Chapter 3,

market and technology assessment, for a more detailed explanation of the equipment class terminology

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As described in the engineering analysis (Chapter 5), there are three types of lighting

technologies (T­8, T­8S and LED) for the horizontal configuration in the VOP, semi­vertical

open (SVO), horizontal open (HZO), and service over counter (SOC) equipment families, and

two types of lighting technologies (T­8 and LED) for the vertical configuration in the vertical

closed transparent (VCT) equipment family that were considered by DOE. Each type of

technology was implemented in a way to provide similar lighting of products in a display case,

but with different levels of electric power consumption.

7.2.1.2 Evaporator Fan Motors

Evaporator fans are used to circulate chilled air through the refrigerated compartments of

commercial refrigeration equipment. Most fan motors used in commercial refrigeration

applications are inexpensive and inefficient single­phase shaded pole motors (SPM). The

efficiency of permanent split capacitor (PSC) or electronically commutated motors (ECM) is

significantly better. Estimates of efficiency and power requirements for these three motor types

are compared in Chapter 5.

7.2.1.3 Anti­Sweat Heaters and Condensate Pan Heaters

In some equipment, anti­sweat heaters are energized continuously and no anti­sweat

control is provided. This results in a steady contribution of heat to the cooling load (and thus the

CEC) and of energy to the direct energy consumption of the refrigeration equipment. Retrofit of

conventional glass doors with high performance doors can reduce the power requirement of

heaters for low­temperature cases and eliminate the anti­sweat heaters for medium­temperature

cases. Power estimates for two levels of door types, thermal performance and corresponding

anti­sweat heaters used, on the equipment covered in this rulemaking are described in Chapter 5.

Condensate pan heaters are installed in commercial refrigeration equipment to evaporate

defrost­melt water. These heaters are usually used in self­contained equipment because

self­contained units are designed to be mobile and used where there is no drain available.

7.2.1.4 Defrost and Drain Heaters

Off­cycle defrost is commonly used for medium temperature equipment, while electric

defrost or hot gas defrost is used for low temperature equipment. The number of defrost cycles

required for a display case is dependent upon its type and design. For remote condensing

equipment, a drain heater is usually installed to heat the drain pipe during defrost to prevent

freezing. As discussed in Chapter 5, hot­gas defrost, defrost cycle control, and defrost

mechanism were not considered as design options. Power requirements and run time of defrost

and drain heaters are provided in Table B.2.2 of Appendix B, and these values are used in the

energy modeling.

7.2.2 Refrigeration Load and Compressor Energy Consumption

Lighting, evaporator fan motors, anti­sweat heaters, and defrost and drain heaters

contribute to the refrigeration load of the display case as well as directly consuming electricity.

To maintain the temperature of refrigerated products, the compressor and condenser

(collectively, the condensing unit) of the refrigeration system needs to remove heat from display

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cases. The amount of heat that must be removed from a given display case is called the total

refrigeration load. In addition to the load contributed by direct electric use equipment, the display

case refrigeration load also consists of heat conduction through case panels and walls, thermal

radiation from the ambient to the refrigerated product and display case interior, and air

infiltration through the open front of the case.

The characteristics of refrigeration load components are different for each equipment

class. The VOP family has a large portion (roughly 80 percent) of the refrigeration load

attributable to ambient air entrainment through the display case air curtain.3 The SVO and HZO

families have a significant load component that is due to radiation exchange with the surrounding

environment. The refrigeration load of the VCT and HCT families is significantly influenced by

the use of anti­sweat heaters. DOE made necessary assumptions to estimate the refrigeration

load in terms of radiation, conduction and infiltration loads as well as refrigeration load due to

direct energy consumption based on the rating conditions. Refer to Chapter 5, Engineering

Analysis, for detailed models and assumptions.

The electricity consumed by the condensing unit to remove the heat from the case can be

determined by the total refrigeration load of the case and compressor EER. However, there are

five issues regarding the accuracy of using ARI 1200­2006 to estimate case refrigeration load

and compressor energy consumption that should be noted.

(1)	 In the engineering analysis, lighting is assumed to be on for 24 hours for all cases

that are equipped with lighting. In practice, the lighting may be running for less time

depending on store operation hours and lighting control practices, which may cause

the case load to be less than the refrigeration load determined from the test

procedure.

(2)	 The relative humidity in the test chamber is maintained at 55 percent and this value

influences the case infiltration load for the test. In reality, the relative humidity of

store space will fluctuate, which results in the actual cooling load deviating from the

estimated load. This is particularly important for open display cases and VCT cases

with anti­sweat heaters.

(3)	 For remote condensing equipment, the condensing unit must be capable of removing

the total refrigeration load from the cases and rejecting it to the outdoor environment

via the condensers. ARI 1200­2006 uses a refrigeration performance map (Table 1

in ARI 1200­2006 provides EER as a function of suction temperature) to calculate

the compressor energy consumption. This map assumes a constant EER for the

condensing unit for a given suction temperature. A single condensing temperature

rating point of 90°F was assumed in ARI 1200­2006 for the condensing unit.4 In

practice, the EER of the condensing unit will vary with each installation and system

design as well as with climate.

(4)	 For remote condensing systems, there are additional system heat gains and other

system effects that may result in additional “superheat load” on the compressor.

These result from the difference in temperature between the vapor leaving the

evaporator and the vapor entering the compressor. This additional load is due to heat

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gain in the long refrigerant piping runs typically found in a supermarket or grocery

store and is not accounted for in ARI 1200­2006. However, a 65°F return­gas

temperature is implied as the basis of ARI 1200­2006 Table 1 values, which are

derived from ARI ratings of specific compressors according to ARI Standard

540­2004.5 ARI Standard 540­2004 assumes a 65°F return­gas temperature for all

external drive and accessible­hermetic type compressors. This return­gas

temperature is higher than the temperature of refrigerant vapor leaving a typical

display case (which is typically only 5°F to 10°F higher than the saturated suction

temperature – as controlled by the expansion device). The ARI 1200­2006 test

procedure was intended to provide relative comparisons of energy use for different

cases. It was not intended to define the actual energy consumption for any case.

Implicit in the ARI assumption of using the compressor rated coefficient of

performance (COP) is that this additional superheat load from the piping is not

attributed to the case. For instance, this might be true if the additional superheat load

would be unaffected by improvements to the case, treating it effectively as a constant

load (for cases of the same suction temperature), and therefore the energy needed to

satisfy this load (additional superheat load divided by total COP) would also be

constant. In comparing any two cases, the tacit assumption is that the energy savings

from a reduction in case load does not need to take into account the “additional

superheat load.” Practically, additional superheat load needed to get to the 65°F

return­gas temperature implicit in the compressor efficiencies is not a constant. If

one assumes the same temperatures for refrigerant leaving the case and entering the

compressor, but reduced refrigerant mass flow rate resulting from reduced case load,

the additional superheat load must vary in proportion to the mass flow rate change.

This reduced additional superheat load for more efficient cases apparently reduces

the compressor energy consumption as well, which is not accounted for in ARI

Standard 1200­2006. Annual energy simulation accounting for this “additional

superheat load” would give some insights into this issue.

(5)	 Heat­recovery systems are commonly used for water heating and supplemental

space­heating in supermarkets. These systems transfer heat from the condenser to

the building heating, ventilating and air­conditioning (HVAC) and/or water­heating

system. Heat recovered in this way is “free” in the sense that it would otherwise be

rejected to the outdoor environment. The implementations of lower energy

consumption display cases in a supermarket refrigeration system can reduce the

amount of heat rejected to the condensing unit, and would, therefore, reduce the

amount of heat available for recovery.

7.3 ENERGY ANALYSIS APPROACHES

Several options were considered for providing estimates of CRE energy consumption.

These options included: using the ARI 1200­2006 test procedure; using an existing simulation

program that would analyze display case and compressor energy use on an annual basis; and

using a whole­building simulation which would analyze case, compressor, and HVAC impacts.

DOE’s approach for the advance notice of proposed rulemaking (ANOPR) analysis was to use

the engineering analysis estimates of energy consumption directly in the LCC analysis, but to

also run selected design options for the equipment through whole­building simulation software,

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which included the simulation of refrigeration systems, to provide a check on the engineering

analysis estimates of the annual energy consumption of the equipment.

Whole­building simulation with whole­building energy impact analyzed was the option

first considered by DOE and discussed during DOE’s Framework public meeting. During that

meeting, several stakeholders commented that a whole­building analysis is the desired

approach,b others were concerned about the additional difficulty and complexity of the analysis.c

DOE decided to use energy consumption estimates developed from the engineering analysis and

to validate the estimates with whole­building simulation of supermarkets which included

simulation of the refrigeration system. Reasons for adopting this approach included:

1.	 The energy consumption ratings provided by ARI 1200­2006 do not distinguish between

energy consumption by the compressor (which may vary as a function of environmental

conditions) and energy consumption by other components in the case (e.g., lighting)

which do not vary as a function of environmental conditions. These two types of energy

consumption are roughly similar in magnitude, and it is difficult to assess where the

energy savings are coming from or what the impact on a building HVAC load might be.

2.	 The initial engineering analysis (see Chapter 5 of the TSD) did not suggest design options

that would provide significant changes to the building load relative to the commercial

refrigeration system energy consumption.

3.	 The net interaction between the refrigeration system and HVAC energy consumption is a

function of the variation in HVAC designs. HVAC system designs for food sales

buildings, like supermarkets, may incorporate such features as separate dehumidification

and refrigerant condenser reheat systems, which make assessing overall HVAC impact

complicated. Also, detailed data on the relative prevalence of different HVAC system

designs incorporating these features is not readily available.

4.	 The interaction between the refrigeration and overall HVAC energy consumption is a

function of the ratio of the total heat removed from the space by the display cases relative

to the other internal loads (lighting, occupancy, and plug load) and external loads

(building envelope and ventilation driven) in the building. This ratio determines the

fraction of the year that the building is either in heating or cooling mode. However, the

balance of refrigeration­driven space loads to the other space loads is impacted by the

efficiency levels for all CRE equipment classes, complicating the analysis of each

equipment class individually.

A second option was to simulate the performance of commercial refrigeration equipment

using available software and to report the simulation program’s results. However, unlike most

other equipment regulated by DOE, the majority of commercial refrigeration equipment covered

b Southern Company, Commercial Refrigeration Equipment Framework Public Meeting Transcript, No. 9 at pp.
 

151; Air­Conditioning and Refrigeration Institute, Commercial Refrigeration Equipment Framework Public Meeting
 

Transcript, No. 16 at pp. 151.
 c Northwest Power Planning Council, Commercial Refrigeration Equipment Framework Public Meeting Transcript,
 

No. 2 at pp. 161; Appliance Standards Awareness Project, Commercial Refrigeration Equipment Framework Public
 

Meeting Transcript, No. 14 at pp. 155.
 

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under this rulemaking is of the remote condensing type where the actual efficiency of the

condensing unit is not regulated. Finally, commercial refrigeration equipment operating over a

range of refrigerant suction temperatures is commonly assigned to operate with compressor racks

that operate at a single temperature. This is accomplished through the use of evaporator pressure

regulator (EPR) valves which provide for a drop in line suction pressure from that used to

maintain temperature for a specific group of CRE cases down to that of the compressor rack.

This system allows all cases in a large supermarket refrigerant system, with all its varied

operating temperatures, to be served by two refrigerant racks (a medium­temperature and a

low­temperature rack). In addition, performance of the refrigeration system can be impacted by

decisions that provide heat exchange (primarily for subcooling) between the medium­ and

low­temperature racks.

The third option considered was to rely on estimates of the CRE energy consumption for

various categories of equipment as were developed during the engineering analysis. This would

provide energy consumption estimates for the wide range of equipment types covered under the

rulemaking and was the most expeditious option. However, there were concerns over the

reliance on the test procedure and its accuracy. DOE’s primary concern was that the test

procedure did not take into account the building space conditions that might impact the load on

the commercial refrigeration equipment and, in particular, space­humidity loads in open cases.

Nor was it certain that the annual energy efficiency of a typical compressor rack would be the

same as the single point efficiencies used in the test procedure.

As discussed, DOE’s approach for the ANOPR analysis was to use the engineering

analysis estimates of energy consumption directly in the LCC analysis, but to also run selected

design options for the equipment through whole­building simulation software, which included

the simulation of refrigeration systems, to provide a check on the engineering analysis estimates

of the annual energy consumption of the equipment. Refrigeration load and relative energy

consumption for different types of commercial refrigeration equipment as a function of climate

and energy consumption level were examined and simulation results were compared with

engineering analysis estimates.

7.4 WHOLE­BUILDING ANNUAL ENERGY SIMULATION

The annual energy simulation of refrigeration equipment involved building a typical

supermarket energy model with a realistic refrigeration system and selection of representative

climate locations.

7.4.1 Modeling Tool

DOE used a whole­building simulation tool, DOE­2.2 refrigeration version (DOE­2.2R),

to model a typical supermarket.6 DOE­2.2R uses an extension of the circulation loop concept of

DOE­2.2 for refrigeration systems. This tool is capable of simulating supermarket and industrial

refrigeration systems in detail, as well as their interactions with the building and HVAC systems

on an hourly basis. The refrigeration simulation model in DOE­2.2R is component­based, which

allows users to build up a refrigeration system model out of individual components such as

display cases, compressors, condensers and refrigerant circuits.

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7.4.2 Climate Locations for Simulation

DOE selected five representative climate locations to simulate annual energy

consumption of commercial refrigeration equipment: Baltimore, Chicago, Houston, Los Angeles

and Memphis. DOE considered these climates as representative of the five large climates zones

it uses in its building energy codes development work,7 and together the five climate zones

encompass about three­fourths of the U.S. population. These climate zones capture the

significant variability of both outside air temperature and humidity in these climates. Chicago

has cold and dry winters and represents the single most populous climate zone. Los Angeles is

warm and dry during most of the year and represents the southwestern U.S. maritime region.

Memphis and Baltimore have mild weather and represent the middle latitudes of the U. S.

Houston represents the hot and humid climates found along the U.S. Gulf Coast.

7.4.3 Typical Supermarket Model

A whole­building energy model of supermarkets requires modeling the building

envelope, internal loads and schedules, HVAC system and refrigeration system.

7.4.3.1 Building Description

Data from the Food Marketing Industry shows median average supermarket size in 2005

2 8 2 is 48,058 ft . Based on this data, DOE modeled a typical 45,000 ft supermarket with an aspect

ratio of 1.0. The exterior walls of the building were modeled as 8­inch solid concrete block with

R­5.7 insulation. The roof material was modeled as steel deck with rigid insulation and the floor

was modeled as 12­inch soil and 6 inches of 140­pound heavyweight concrete.

DOE assumed that the supermarket was operated from 8 am to 12 am (16 hours/day). The

lighting density and plug load density in sales area were assumed to be 1.5 W/ft2 and 0.4 W/ft2

,

respectively. The lighting power density was based on ASHRAE Standard 90.1­2004

Table 9.5.1.9 Sensible load and latent load from occupants are 250 Btu/hr­person and

200 Btu/hr­person.10 A constant volume packaged rooftop unit with electric direct expansion

(DX) cooling and gas­fired furnace provided space­cooling and space­heating needs,

respectively, in the sales area. The space thermostat set point was set at 70°F for heating and

75°F for cooling. Set­back controls and economizers were not used in the HVAC system. A

summary of model assumptions for the building envelope, internal loads and HVAC system is

provided in Table 7.4.1 and Figure 7.4.1.

7.4.3.2 Refrigeration System Model

A typical supermarket contains several compressor racks, each with multiple

compressors, which are piped either in a loop or direct circuit to display cases, and walk­in

coolers and freezers. The racks accommodate the evaporators by maintaining the lowest suction

temperatures for the group. Typically, three to five compressor racks will be employed to

provide all refrigeration in the supermarket. Each compressor rack may have from 3 to 5

compressors serving a series of loads with nearly identical evaporator temperature. A typical

supermarket will have about 60 to 80 display cases.11 About 60 percent of these are mediumtemperature cases and 40 percent are low­temperature cases. Most of the medium­temperature

cases are open display cases.

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In total, seven equipment classes of remote condensing equipment were modeled in this

study, representing most ARI shipments (shipments data are given in Chapter 3, Market and

Technology Assessment) and different characteristics. Figure 7.4.2 summarizes the main features

of these display cases. Number of cases for each modeled equipment class was chosen to

Table 7.4.1 Summary of Energy Model Assumptions for Building Envelope, Internal

Loads and HVAC System

Characteristic Model Assumptions

Building Envelope

Gross Area, ft2

Aspect Ratio

Number of Floors

Window to Wall Ratio

Floor­to­Ceiling Height, ft

Floor­to­Floor Height, ft

Exterior Wall

Structure

Insulation

Roof

Structure

Insulation

Floor

Structure

Floor Insulation

Floor F­factor

Window/Door

Window Type

Low­e

Actual DOE­2 Glazing Input

Window Overhangs/Interior Shading

45,000

1.0

1

13%

15

18

8 in. solid concrete block

R­5.7

Steel deck with rigid insulation

R­15 ci

Slab­on­grade

None

0.73

Double­pane clear glass w/alum. frame

No

Glazing Code = 2000, U=0.57, SHGC=0.76

None

Internal Loads

Number of Occupancy

Occupancy Schedule

People Sensible Heat Gain, Btu/h­person

People Latent Heat Gain, Btu/h­person

Peak Lighting Power, w/ ft2

Lighting Schedule

Peak Load, w/ ft2

Equipment Schedule

675

See Figure 7.4.1

250

200

1.5

See Figure 7.4.1

0.4

See Figure 7.4.1

HVAC System

HVAC System Type

Number of Thermal Zones

Number of HVAC Units

Space T­stat Set Point

Ventilation Control Mode

Fan Schedule

Outside Air Supply, cfm

Return Air Path

Economizer

Single­package rooftop unit, constant air volume system,

electric DX cooling with gas­fired furnace

1

1

75°F cooling / 70°F heating

Outside air damper remains open at minimum position

Always on

6000

Plenum return

No

7­9

 EE-2006-STD-0126 COMMENT 23.2
   

                  

                

           

                        

                         

                              

                         

                     

                       

                       

                        

                             

                            

                           

                            

                       

       

                           

                             

Internal Load Schedules
 

Ratio
 

1

0.8

0.6

0.4

0.2

0

Occupancy Mon­Fri

Occupancy Sat&Sun

Lighting

Equipment

1 3 5 7 9 11 13 15 17 19 21 23

Hour

Figure 7.4.1 Internal Load Schedule Assumptions in Energy Model
 

Table 7.4.2 Line­up Length of Modeled Display Cases
 

Equipment Class Unit Length (ft) Line­Up Length (ft)

VOP.RC.M 12 384

SVO.RC.M 12 84

VCT.RC.M 12.7 25.4

HZO.RC.M 12 24

SOC.RC.M 12 24

VOP.RC.L 12 24

VCT.RC.L 12.7 266.7

represent the distribution of display cases in a typical supermarket. Self­contained equipment

were not included in this energy analysis because the compressor energy use of self­contained

unit is only a function of refrigeration load and not dependent on climate conditions. Therefore,

the energy consumption behavior of the self­contained equipment has similar features to remote

condensing equipment with the same configuration at a specified climate location.

For each equipment class, DOE selected four representative efficiency levels from the

engineering analysis and modeled them to compare simulated annual energy consumption with

energy consumption derived from the engineering analysis. DOE simulated the four sets of

efficiency levels for display cases one by one. Therefore, twenty runs (for five climate locations)

were performed in the simulation. Table 7.4.3 lists the selected efficiency levels and design

options and Tables D.2.1 through D.2.8 in appendix D.2 provide more detailed information on

these design options, as well as corresponding input parameters in the DOE­2.2R model. The

chosen design options were changes in lighting power, fan power, saturated evaporator

temperature, and case door­type.

In an actual supermarket, different types of cases can be attached to a common

compressor rack. However, the model assumes only one rack for each equipment class to

7­10

 EE-2006-STD-0126 COMMENT 23.2
                

   

       

                             

                                

                           

                            

                

                   

                          

                           

                           

                            

                 

  

Table 7.4.3 Modeled Design Options and Efficiency Levels
 

Equipment

Class

Efficiency

Levels from

Engineering

Analysis

Design Options

Lighting

Saturated Evaporator

Temperature

(°F)

Evaporator

Fan MotorType Door­Type

AD1 T­8 15.0 SPM —

VOP.RC.M AD3 T­8 15.5 ECM —

AD5 T­8S 21.0 ECM —

AD7 LED 21.3 ECM —

AD1 T­8 15.0 SPM —

SVO.RC.M AD3 T­8 15.4 ECM —

AD5 T­8S 21.0 ECM —

AD6 LED 21.2 ECM —

AD1 T­8 27.0 SPM Standard

VCT.RC.M AD3 T­8 27.5 ECM Standard

AD4 T­8 28.5 ECM high­performance

AD6 LED 29.1 ECM high­performance

AD1 — 15.0 SPM —

HZO.RC.M AD2 — 15.4 PSC —

AD3 — 15.9 ECM —

AD4 — 21.2 ECM —

AD1 T­8 20.0 SPM Standard

SOC.RC.M AD3 T­8 21.0 ECM Standard

AD4 T­8S 21.3 ECM Standard

AD8 LED 27.2 ECM high­performance

AD1 T­8 ­20.0 SPM —

VOP.RC.L AD3 T­8 ­19.2 ECM —

AD5 T­8S ­14.2 ECM —

AD7 LED ­14.0 ECM —

AD1 T­8 ­11.0 SPM Standard

VCT.RC.L AD3 T­8 ­10.7 ECM Standard

AD4 T­8 ­8.6 ECM high­performance

AD6 LED ­8.2 ECM high­performance

facilitate data extraction by equipment class and limit interactions that might occur in real life

due to cases with different suction temperatures used on the same racks. For example, an EPR

valve is usually used to maintain evaporator/temperature control in different cases on the same

refrigeration circuit. DOE chose compressors in the model to match those used in the

ARI 1200­2006.5 Both compressors for medium­temperature application and low­temperature

application are Copeland discus compressors, which are typical in commercial refrigeration

systems. Furthermore, DOE did not examine the impacts of compressor choices for modeled

remote condensing equipment in this energy analysis, because DOE believes that using the same

compressors as those in ARI 1200­2006 will give a fair comparison between the simulated

energy use and the energy use based on the engineering analysis. The compressor model

numbers for medium­temperature and low­temperature applications are 3DB3A100E and

3DB3A075E, respectively.

7­11

 EE-2006-STD-0126 COMMENT 23.2
                         

                          

                         

                             

                        

                    

                     

                        

        

                         

                    

                             

                          

                          

       

                         

                      

                       

                     

                         

                             

                      

           

                 

   

                     

                        

                   

                 

   

                     

     

DOE modeled air­cooled condensers located outside of the store because they are the

most common type.12 Evaporative condensers are also used in some supermarkets, primarily in

hot, dry climates where a substantial difference in dry­bulb and wet­bulb temperatures exist.

Water­cooled condensers are used primarily in urban stores where easy access to the outside for

condensers does not exist. The model captured the difference in design condensing temperatures

between medium­ and low­temperature racks. For air­cooled condenser systems, the

medium­temperature rack often operates with a 15°F temperature difference between saturated

condensing temperature and design dry­bulb temperature. For the low­temperature rack, a 10°F

temperature difference is common.9

DOE used floating­head pressure control in the model, which is standard on many

refrigeration systems. In outdoor air­cooled condensers, floating­head pressure controls take

advantage of low air temperatures to reduce the amount of compressor work by allowing the

head pressure to vary with outdoor conditions. This reduces compressor load and energy

consumption and can extend compressor life. DOE did not model condenser heat recovery.

7.4.4 Summary of Simulation Results

DOE simulated annual energy use for seven equipment classes was simulated at four

representative efficiency levels. To examine the impacts of space relative humidity, refrigeration

piping system thermal loss and climate locations on energy consumption of commercial

refrigeration equipment, annual simulation data was compared with the consumption values

calculated in the engineering analysis. The annual energy use and refrigeration load data

extracted from the model were divided by 365 to provide average daily energy consumption and

refrigeration load. Also, DOE assessed the magnitude of interactions between the refrigeration

system and the building HVAC system.

7.4.4.1	 Comparison of Case Refrigeration Load between Simulation Results and

Engineering Analysis

Appendix D.4 summarizes the comparison of case refrigeration load between the

simulation and engineering analyses at different climates and efficiency levels. Figure 7.4.2

gives an example of the comparison for VOP.RC.M equipment class.

VOP.RC.M

Case Refrigeration Load (Btu/hr)25000

20000

15000

10000

5000

0

Annual Sim._Baltimore Annual Sim._Houston Annual Sim._Memphis

Annual Sim._Chicago Annual Sim._Los Angeles Engineering

Eff Level AD1 Eff Level AD3 Eff Level AD5 Eff Level AD6

Figure 7.4.2	 Case Refrigeration Load for Vertical Open, Remote Condensing, Medium

Temperature Equipment Class

7­12

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From appendix D.4, DOE notes the following:

(1) In general, simulated case refrigeration load is lower than the load determined from the

engineering analysis, because during most of the year, space relative humidity in the

model is lower than that assumed in the test procedure. Space relative humidity is

determined by HVAC­system humidity control and climate. In the building model, as in

most supermarkets, there is no dedicated humidity control in the HVAC system. Instead,

space dehumidification is solely driven by the space­cooling load.

(2) The difference between the simulation results and engineering analysis is greater for

open equipment than closed equipment. Open equipment have much greater infiltration

loads than closed equipment. Consequently, space humidity has a larger impact on open

equipment.

(3) Case refrigeration load decreases with increased levels of efficiency. The percentage of

load reduction in closed equipment is greater than for open equipment, and is depicted by

the relatively flat curves in appendix D.4. The refrigeration load in open equipment is

largely attributable to infiltration. However, reduction in infiltration load was not a

design option and DOE did not analyze it. Instead, DOE assumed that the infiltration

load was constant at all efficiency levels, which caused the load reduction in open

equipment to be less significant in comparison to that in closed equipment.

(4) For closed equipment, SOC.RC.M, VCT.RC.M and VCT.RC.L, climate location has

only minimal impact on case load. This is because infiltration load, which is driven by

space relative humidity, which is in turn driven by climate, is relatively small at all

efficiency levels.

7.4.4.2 Impact of Climate on Daily Energy Consumption

To assess the impact of climate conditions on display case energy consumption, DOE

compared case daily energy consumption data (at the baseline efficiency level) for the five

climate locations, ranging from cold and dry climate to hot and humid climate. Figures D.5.1 to

D.5.7 in appendix D summarize the results, and Figure 7.4.3 provides an example for the

VOP.RC.M equipment class.

In view of the results, DOE notes that climate locations have no influence on case energy

consumption for all equipment classes and have only little influence on compressor energy

consumption for equipment classes with doors. As expected, climate conditions have significant

impact on compressor energy consumption for open equipment. Compressor energy

consumption is determined by total refrigeration load and compressor efficiency, and both are

affected by climate conditions for remote condensing equipment. An outdoor air­cooled

condenser with floating­head pressure control operates more efficiently than at rated conditions,

which reduces compressor energy consumption.

7­13

 EE-2006-STD-0126 COMMENT 23.2
   

                   

             

               

   

                         

                        

                          

      

                 

                     

         

                           

                            

                                 

                             

                           

                             

                       

                         

VOP.RC.M­Eff Level AD1

80

Energy Consumption (kWh/Day) 60

40

20

0

CompElec

CaseDirElec

Baltimore Chicago Houston Los Angeles Memphis

Figure 7.4.3	 Baseline Daily Energy Consumption for Vertical Open, Remote Condensing,

Medium Temperature Equipment Class for Five Climate Locations

7.4.4.3	 Comparison of Daily Energy Consumption between Simulation and

Engineering Analysis

Case daily energy consumption is comprised of case direct electric use and compressor

electric use. Appendix D.6 shows comparisons of daily energy consumption between simulation

and engineering analysis at different efficiency levels. Figure 7.4.4 gives an example for

VOP.RC.M equipment class.

HZO.RC.M­Baltimore

0

5

10

15

20

25

Annual

Sim.

Engineering

Annual

Sim.

Engineering

Annual

Sim.

Engineering

Annual

Sim.

Engineering

Eff Level AD1 Eff Level AD2 Eff Level AD3 Eff Level AD5

Energy Consumption (kWh/Day)

CompElec

CaseDirElec

Figure 7.4.4	 Daily Energy Consumption for Vertical Open, Remote Condensing, Medium

Temperature Equipment Class at Baltimore

For a given efficiency level, case direct energy consumption is essentially the same for

the simulation and engineering analysis. This is because case direct energy consumption is not

dependent on space humidity and climate condition, and it does not change over the year or from

location to location and because time based defrost termination was used. For HZO.RC.M, the

case direct energy consumption was from 0­9 percent points higher in the simulation as

additional defrost energy was required during some periods of the year in some climates.

(1) In Houston, compressor energy consumption is greater for the simulation for all

equipment classes although simulated refrigeration load is lower than load derived in the

7­14

 EE-2006-STD-0126 COMMENT 23.2
                       

                              

            

                     

                     

                      

                     

                          

                     

                     

                          

              

                   

                     

                         

                       

                     

                   

                                 

         

                 

                         

                                

       

                 

                       

                        

                     

                       

                       

                         

engineering analysis, and the simulated compressors are on average more efficient over

the year. This is because additional piping heat gains are dealt with in the simulation,

but not in ARI Standard 1200­2006.

(2) For VOP.RC.M and SVO.RC.M and HZO.RC.M equipment classes at all efficiency

levels, simulated compressor energy consumption is lower than engineering analysis data

in Baltimore, Chicago and Los Angeles. For VCT.RC.M and SOC.RC.M equipment

classes at higher efficiency levels, simulated compressor energy consumption is lower

than engineering analysis data at Chicago and Los Angeles. This is because the

simulated refrigeration load for these equipment classes is much lower than the

engineering analysis data and the average compressor efficiency is improved compared

to warmer climates. Therefore, even the inclusion of “additional superheat load” in the

simulation still requires less compressor energy use.

(3) For VOP.RC.L and VCT.RC.L equipment classes (Figures D.6.26 through D.6.35),

simulated compressor energy consumption is greater than the engineering analysis data

(except for VCT.RC.L at higher efficiency levels in Los Angeles) because the lower

refrigeration load (compared to the engineering analysis) seen with the simulation results

does not offset the “additional superheat load” calculated in the simulation.

(4) The difference in compressor energy consumption between the simulation and

engineering analysis data can be as much as 11 percent to 25 percent in the hot and

humid climate represented by Houston.

7.4.4.4 Energy Savings Comparison at Different Efficiency Levels and Climates

Appendix D.7 compares case energy savings (relative to a baseline efficiency level) for

the efficiency levels at five climate locations. Figure 7.4.5 is one example of appendix D.7 for

the VOP.RC.M equipment class.

(1) As expected, energy savings increases with higher efficiency levels.

(2) Generally, simulated average daily energy savings are somewhat greater than the savings

calculated by the engineering analysis. This is caused by underestimation of energy

savings in ARI Standard 1200­2006 due to “additional superheat load” issue.

(3) Warm and humid climates (Houston and Memphis) have greater energy savings than

relatively cooler and drier climates (Baltimore, Chicago and Los Angeles) at efficiency

level AD4 or higher, though the difference is not significant for closed cases

7­15

 EE-2006-STD-0126 COMMENT 23.2
                 

   

                     

     

               

               

                           

                         

                        

                        

                       

                          

                       

                 

                           

                         

                               

                                

                                

                             

               

                        

                   

VOP.RC.M

0

5

10

15

20

25

Energy Savings (kWh/Day)

Annual Sim._Baltimore

Annual Sim._Chicago Annual Sim._Houston

Annual Sim._Los Angeles Annual Sim._Memphis

Engineering

Eff Level AD1 Eff Level AD3 Eff Level AD5 Eff Level AD6

Figure 7.4.5	 Daily Energy Savings for Vertical Open, Remote Condensing, Medium

Temperature Equipment Class

7.4.4.5	 Impacts of Display Case Improvements on Whole­Building Energy

Consumption

DOE examined whole­building energy consumption and refrigeration­system energy

consumption for selected efficiency levels and climate locations to determine if the display case

improvements considered in the engineering analysis would have a significant effect on building

HVAC­system energy use. The influence of reduced display case energy consumption on

HVAC­system energy use varies depending on characteristics of design options. For example,

improved lighting efficiency would reduce energy consumptions of both refrigeration system and

potentially the space cooling load depending on lighting placement. By contrast, reduction in

conduction and radiation loads on refrigeration equipment would increase the space­cooling load

on the HVAC system while decreasing the space­heating load.

As discussed in section 7.4.3.2, DOE selected four efficiency levels for each type of

display case for its annual­energy simulation. To calculate whole building energy savings at

different sets of efficiency levels, DOE denoted the first set of efficiency levels (Level AD1 for

all equipment classes) in combination as Level A. The second, third and fourth sets of efficiency

levels selected for all products were combined as Levels B, C, and D respectively. Table 7.4.4

shows the mapping of the efficiency levels from the engineering analysis to the efficiency levels

used to calculate whole building energy savings.

Table 7.4.4 Mapping of the Efficiency Levels for the Whole Building Analysis

Equipment Class Level A Level B Level C Level D

VOP.RC.M AD1 AD3 AD5 AD7

SVO.RC.M AD1 AD3 AD5 AD6

VCT.RC.M AD1 AD3 AD4 AD6

HZO.RC.M AD1 AD2 AD3 AD4

SOC.RC.M AD1 AD3 AD4 AD8

VOP.RC.L AD1 AD3 AD5 AD7

VCT.RC.L AD1 AD3 AD4 AD6

7­16

 EE-2006-STD-0126 COMMENT 23.2
                                 

                        

                            

                       

                      

                 

                           

                                  

                           

      

                        

     

   

   

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

                      

The net energy savings at a specified level are shown as the percent of the difference in

energy consumption between a specified level and Level A (baseline). Table 7.4.5 summarizes

energy savings results of refrigeration systems and whole buildings for the five climate locations.

Also, appendix D.8 graphically compares energy savings between the refrigeration system and

the whole building. Figure 7.4.6 provides an example of these graphs.

Whole­building energy simulation results show that refrigeration system energy

consumption ranges from 42 percent to 57 percent of the whole­building energy consumption at

baseline (Level A) and 32 percent to 47 percent at the highest efficiency level (Level D). Results

also showed that the simulated supermarket is heating­load dominated with a small amount of

space­cooling energy consumption.

Table 7.4.5 Summary of Energy Savings for Refrigeration System and Whole Building

Location Level

Refrigeration

System Savings

(MBtu)

Whole Building Savings

(MBtu) Difference

Natural Gas Electricity Total (%)

Level B 460.9 ­9.6 461.2 451.6 ­2%

Baltimore Level C 1250.5 132.6 1246.4 1379.0 10%

Level D 1764.4 134.4 1760.1 1894.5 7%

Level B 456.0 ­10.0 456.0 446.0 ­2%

Chicago Level C 1223.0 134.3 1219.9 1354.2 11%

Level D 1736.6 135.1 1733.2 1868.3 8%

Level B 479.8 ­10.4 480.6 470.2 ­2%

Houston Level C 1352.4 121.9 1341.9 1463.8 8%

Level D 1896.5 124.4 1885.2 2009.6 6%

Los

Angeles

Level B 447.6 ­11.7 447.7 436.0 ­3%

Level C 1223.5 136.7 1222.5 1359.2 11%

Level D 1733.0 137.8 1731.9 1869.7 8%

Level B 467.4 ­8.4 467.9 459.5 ­2%

Memphis Level C 1298.9 124.6 1291.1 1415.7 9%

Level D 1827.0 127.0 1818.5 1945.5 6%

Energy Savings for Baltimore

(Ref. System versus Whole Building)

0

500

1000

1500

2000

2500

Energy Savings (MBtu)

Ref. System

Whole Building

Level B Level C Level D

Figure 7.4.6 Energy Savings for Baltimore (Refrigeration System versus Whole Building)
 

7­17

 EE-2006-STD-0126 COMMENT 23.2
                       

                       

                             

                          

                           

                       

                   

                     

                             

   

                         

                           

                             

                     

                          

                     

           

                     

                             

                       

                       

                            

                               

                        

                            

                   

                            

                            

                 

                           

                               

       

Some important observations of Table 7.4.5 and appendix D.8 are summarized as

follows:

(1) The difference in energy savings, between the refrigeration system and the whole

building, is less than 11 percent at all levels (with the whole building energy savings

averaging 7% at the highest level). This means that the whole­building energy savings

are mostly attributable to the energy savings of the refrigeration system and that the

interaction between the display cases changes and the HVAC system is small.

(2) The improvements on equipment have little to no significant impact on space­cooling

and space­heating energy use, partially because case infiltration, which is the most

important factor for HVAC system loads, was not considered as a design option in the

engineering analysis.

(3) At Level B, the refrigeration system energy savings is slightly higher than the wholebuilding energy savings due to a slight change in the natural gas heating usage.

(4) The energy savings differences at Level C are relatively higher than at the other levels.

As shown in appendix D.2, saturated evaporator temperatures for equipment are

increased at this level. Thus, the energy savings are almost entirely from the

refrigeration system and without any interaction with the building HVAC system.

7.5 SENSITIVITY TO DISPLAY CASE LIGHTING OPERATING HOURS

In addition to its examination of the energy consumption calculations using wholebuilding simulation tool, DOE also undertook a sensitivity study of the energy savings for higher

efficiency levels as a function of the display case lighting operating hours.

In commercial refrigeration equipment with installed lighting, the operating hours of the

lighting system impact the total daily or annual energy consumption of the equipment. DOE

presumed a 24­hour lighting energy use for this equipment in the engineering analysis and in the

comparisons to whole­building simulation estimates discussed previously in this Chapter. In the

field, however, lighting operating hours can vary. DOE believes that a relatively small fraction

of supermarkets are open for business on a 24­hour basis.

A higher fraction of convenience stores do operate on a 24­hour basis. However, most

stores in both categories are open to customers fewer hours. Building operating­hours data from

the Energy Information Administration’s (EIA) 2003 Commercial Building Energy Consumption

Survey (CBECS)13 are shown in Table 7.5.1 as square­foot­averaged number of hours open per

week for each of the four building types which make up the CBECS “Food Sales Principal

Building Activity” category.

7­18

 EE-2006-STD-0126 COMMENT 23.2
                    

   

        

   

   

   

   

   

     

   

                           

                                

           

                        

                               

                              

           

                                 

                          

                      

              

                             

                                    

                                  

                                

                                     

               

                                 

                            

                         

                              

                          

                         

   

                         

                            

                            

                           

                 

                          

                                   

                         

Table 7.5.1 Average Reported Hours Open – Commercial Buildings Energy Consumption

Survey 2003

Convenience

store

Convenience

store with gas

station

Grocery

store/food

market

Other

food sales

Average All

Food Sales

Bldgs

Hours per

week

(Max 168) 121 135 107 64 112

Hours per day

(Max 24) 17.3 19.3 15.3 9.2 16.0

While a supermarket may be open a specified number of hours for customers, commonly

night hours are used for stocking purposes. During stocking, it is common to have some lighting

on in the display cases.

Some supermarkets and convenience stores operate on a 24­hour basis for customers. In

these stores, stocking of cases is done often at night when shoppers are less frequent and

stocking has less impact on these shoppers. DOE presumed that display case lighting is on

24 hours in these stores.

In other stores, display case lighting is on 24 hours per day even when customers are not

present. A common reason cited is potential or perceived difficulty of restarting fluorescent

lighting in low­temperature cases.14 Analysis of energy savings for display­case lighting

controls often presumes this mode of operation.

A second common operating mode is to reduce the display case lighting during hours the

store is not open. Case lighting may be operated at a 50 percent level during stocking, and then

shut off for the remainder of the evening.15 In yet another strategy, display case lighting may be

shut down to a 50 percent level, but not turned completely off during unoccupied periods. The

rationale here is that lighting may be left on for security reasons or to make sure that some lights

will be available when customers arrive the next morning. 16

DOE has no definitive data on the number or square footage of stores falling into any of

these categories. A survey undertaken by the Food Industry Center at the University of

Minnesota suggests that an automated energy management system either for lighting, HVAC, or

both exist in 44 percent of supermarkets.17 The survey found that these systems were more

prevalent in large chain stores than smaller independent stores. The survey neither contained

data on whether these systems actually controlled the display­case lighting, nor any after­hours

lighting strategy.

For the ANOPR, DOE based the energy consumption analysis on the assumption of

24­hour lighting. However, DOE recognized that this may overstate the energy savings for some

equipment classes and design options. DOE conducted a sensitivity study of the relative energy

consumption as a function of display­case lighting operating hours per day, and used the

spreadsheet­based engineering analysis tool and the analytically derived energy consumption

levels for the 15 equipment classes. (See Chapter 5, Engineering Analysis.) The display­case

lighting operating hours per day was varied from 16 hours to 24 hours to assess the daily energy

consumption savings calculated for each efficiency level (savings referenced to the Level 1

7­19

 EE-2006-STD-0126 COMMENT 23.2
                       

                              

                         

                            

                                

                                

                           

                               

                        

                        

   

   

   

                        

HCT.SC.I

HZO.RC.L

HZO.RC.M

HZO.SC.L

HZO.SC.M

SOC.RC.M

SVO.RC.M

SVO.SC.M

VCS.SC.I

VCT.RC.L

VCT.RC.M

VCT.SC.I

VOP.RC.L

VOP.RC.M

VOP.SC.M

baseline) relative to the daily energy consumption savings calculated assuming 24­hour display

case lighting. The results are shown in Figure 7.5.1 for each equipment class assuming an

intermediate efficiency level (Analytical Design Level 3), and in Figure 7.5.2 assuming the

highest (max tech) efficiency level developed for each equipment class. For the equipment class

with no case lighting, there is no impact on the energy consumption. For all other equipment

classes, a reduction in case lighting hours results in a reduction in daily energy savings. For

equipment classes with lighting but where the efficiency level uses the same lighting technology

as the baseline level, the relative reduction in energy savings can be very slight (Figure 7.5.1,

VCT.RC.L equipment class). However where a change in lighting technology occurs, the

difference in energy savings can be significant (Figure 7.5.1, SVO.RC.M equipment class).

24 Hour Lighting

20 Hour Lighting

16 Hour Lighting

120%

100%

80%

60%

40%

20%

0%

Relative Energy Savings from Baseline (Level 1)

Figure 7.5.1 Energy Savings versus Case Lighting Operating Hours for Efficiency Level

AD4

7­20

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HCT.SC.I

HZO.RC.L

HZO.RC.M

HZO.SC.L

HZO.SC.M

SOC.RC.M

SVO.RC.M

SVO.SC.M

VCS.SC.I

VCT.RC.L

VCT.RC.M

VCT.SC.I

VOP.RC.L

VOP.RC.M

VOP.SC.M

24 Hour Lighting

20 Hour Lighting

16 Hour Lighting

120%

100%

80%

60%

40%

20%

0%

Relative Energy Savings from Baseline (Level 1)

Figure 7.5.2	 Energy Savings versus Case Lighting Operating Hours for Highest Efficiency

Level Analyzed

The reduction in calculated energy saving across all levels considered in the engineering

analysis for the products with display­case lighting was between 0 percent and 4 percent at AD4

and at a 20 hours­per­day lighting use schedule (averaging 1.5 percent across all equipment

classes with installed lighting). It was between 0 and 7 percent at a 16 hours­per­day lighting use

schedule (average 3 percent reduction across all equipment with installed lighting). At the maxtech efficiency level, the reduction in energy savings for equipment with display­case lighting

was between 3 and 10 percent at 20 hours­per­day, averaging 5 percent. At 16 hours­per­day

lighting, the reduction in energy savings was between 5 and 19 percent, averaging 11 percent.

At the ANOPR public meeting, DOE presented its analysis of the energy impact of

differing lighting operating hour assumptions. Manufacturers at the meeting and industry trade

groups in follow­up comments stated that 24 hour cases lighting is a valid assumption for DOE’s

energy analysis, citing concerns by equipment owners with lighting restarts in low­temperature

display cases and moisture­related lighting maintenance issues. It was noted that these problems

didn’t exist with LED lighting.d Based on these comments, DOE continued to use the 24­hour

assumption of display case lighting operating hours for the NOPR analysis. Additional detail on

the energy use characterization can be found in Chapter 7 of the TSD.

d Hussman; Public Meeting Transcript, No. 13.5 at p. 118; Hill Phoenix Public Meeting Transcript, No. 13.5 at p.

118, Zero Zone, No. 17 at p.4, and ARI, No. 18 at p.4.

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7.6 CONCLUSIONS

DOE conducted annual simulations of the refrigeration system energy consumption

(including both direct case­energy use as well as compressor energy consumption) over four

efficiency levels selected to span the range of efficiency levels analyzed by DOE in its

engineering analysis. The inputs to the annual simulations reflected the engineering analysis

assumptions for these equipment classes. Simulations were done in five different climates to

ascertain the impact of climate on the case load, energy consumption, and energy savings.

In general, the refrigeration load was smaller than that predicted by the engineering

analysis, due to differences between the building­space conditions through the year and those

used for the steady­state test procedure. The simulated energy consumption of the compressors

was higher than that predicted by the engineering analysis for medium temperature cases in

warm and humid climates (Memphis, Houston) with all equipment classes and for low

temperature cases in general. The simulated energy consumption of the compressors was lower

than in the engineering analysis for medium temperature cases in colder/drier climates

(Baltimore, Chicago, Los Angeles). The difference in energy consumption between the

simulation and engineering analysis is due to the differences in refrigeration loads from the case,

the fact that the simulation accounts for changes in condensing temperatures over the year for

each climate location, and partly due to the additional superheat loads calculated by the

simulation software to bring the return refrigerant vapor up to the compressor inlet temperature

conditions (assumed to be 65°F).

Analysis of the annual refrigeration system energy savings for each of the three

efficiency levels above the baseline efficiency level (Level AD1) were within 14 percent of that

predicted by the engineering analysis for the 6 equipment classes examined, but averaged

4.2 percent higher for the highest efficiency level examined. For the VOP.RC.L equipment class

as discussed above, the annual energy savings deviated by as much as 21 percent. Shipments for

this equipment class are unknown, but are expected to be small. This suggests that for the

majority of the equipment classes, the energy savings predicted by the test procedure agreed

reasonably well with the annual simulation results, although the impact of individual design

options may differ.

The same simulations allowed DOE to examine the energy savings calculated for the

refrigeration system alone compared with energy savings for the whole building. For all

efficiency levels analyzed, the annual whole­building energy savings was within 11 percent of

that calculated for the refrigeration system alone. The widest deviations between whole building

and refrigeration­only energy savings appears at a mid­range efficiency level (Level C). At the

max­tech level the energy savings varied between 6 and 8 percent across the five climates. The

simulation results suggest that the overall impact of the design options when taken together had

only a minor effect on the overall HVAC energy consumption.

Based on the general agreement between the energy savings results from the annual

simulation modeling and the energy savings estimates from the spreadsheet­based engineering

estimates of energy use, DOE used the energy use estimates from the engineering analysis for the

LCC and subsequent analysis.

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A sensitivity analysis of the impact of reduced display case lighting hours from the

24 hours presumed in the engineering analysis showed that such reduction would also reduce the

energy savings calculated for all equipment with display­case lighting. The actual reduction in

energy savings is dependent on the equipment class and on design options incorporated at each

efficiency level but for equipment which utilize lighting the reduction in energy savings at the

max­tech level would typically vary between 3 percent and 10 percent at a 20­hour­per­day

lighting­use schedule (averaging 5 percent) and between 5 percent and 19 percent at a 16­hourper­day lighting­use schedule (averaging 11 percent).

DOE presents more detailed results and supporting data for the energy use

characterization in appendix D.

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REFERENCES
 

1 Air­Conditioning and Refrigeration Institute, ARI Standard 1200­2006, Performance Rating of

Commercial Refrigerated Display Merchandisers and Storage Cabinets, 2006, 4100 N. Fairfax

Drive, Suite 200, Arlington, VA 22203, U.S.A.

2 American Society of Heating, Refrigerating, and Air­Conditioning Engineers, Inc.

ANSI/ASHRAE Standard 72­2005, Method of Testing Commercial Refrigerators and Freezers,

2005, 1791 Tullie Circle N.E., Atlanta, GA 30329, U.S.A.

3 Walker, D.H., Faramarzi, R.T. and V.D. Baxter, Investigation of Energy­Efficient Supermarket

Display Cases, December 2004, Oak Ridge National Laboratory, ORNL/TM­2004/292.

4 Air­Conditioning and Refrigeration Institute, ARI Standard 540­2004, Performance Rating Of

Positive Displacement Refrigerant Compressors And Compressor Units, 2004, 4100 N. Fairfax

Drive, Suite 200, Arlington, VA 22203, U.S.A. ARI 2004.

5 Tanner, Robert. Personal communication. Hill Phoenix. Phone conversation and follow up

email to David Winiarski, PNNL. Aug 16, 2006

6 James J. Hirsch & Associates, Building Energy Use and Cost Analysis Program Volume 2r:

Dictionary – Refrigeration Simulation, November 2004, 12185 Presilla Road, Camarillo, CA

93012­9243.

7 Briggs, R.S., Lucas, R.G. and Z. Todd Taylor, 2002. Climate Classification for Building

Energy Codes and Standards. Pacific Northwest National Laboratory.

<http://www.energycodes.gov/implement/climatezones_04_faq.stm>

8 Food Market Institute, Supermarket Facts Industry Overview 2005

<http://www.fmi.org/facts_figs/superfact.htm>. (Last accessed December 19, 2006)

9 American Society of Heating, Refrigerating, and Air­Conditioning Engineers, Inc.

ANSI/ASHRAE/IESNA Standard 90.1­2004, Energy Standard for Buildings Except Low­Rise

Residential Buildings, 2004, 1791 Tullie Circle N.E., Atlanta, GA 30329, U.S.A.

10 American Society of Heating, Refrigerating, and Air­Conditioning Engineers, Inc. 2005

ASHRAE Handbook Fundamentals, 2005, 1791 Tullie Circle N.E., Atlanta, GA 30329, U.S.A.

11 Westphalen, D., Zogg, R.A., Varone, A.F. and M.A.Foran, Energy Savings Potential for

Commercial Refrigeration Equipment, Arthur D. Little, Inc. for DOE, June 1996, Acorn Park,

Cambridge, Massachusetts 02140­2390.

12 Walker, D.H., Development and Demonstration of an Advanced Supermarket

Refrigeration/HVAC System, Foster­Miller, Inc. for. Oak Ridge National Laboratory,

September 2001, 350 Second Avenue, Waltham, MA 02451.

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13 2003 Commercial Building Energy Consumption Survey (CBECS), 2003 CBECS Detailed

Tables. U.S. Department of Energy Energy Information Administration.

<http://www.eia.doe.gov/emeu/cbecs/cbecs2003/detailed_tables_2003/detailed_tables_2003.ht

ml#allbldg> (Accessed Dec 19, 2006).

14 LED Magazine LED Luminaires get Warm Welcome in Supermarket Freezers

http://ledsmagazine.com/articles/features/3/4/2/1 (Accessed January 2007)

15 Personal conversation with energy management personnel at Phoenix, Arizona Safeway during

Food Marketing institute tours. Cited typical hour stocking periods (10 pm­4 am) with case

lighting at 50%, with case lighting turned off for additional 4 hour period before store reopens.

Sept 12, 2006

16 Personal conversation with store personnel at Kennewick, Washington Fred Meyer on

November 13, 2006.

17 FIC, 2003. The 2001 Supermarket Panel Energy Management Study, Working Paper 03­03.

Prepared by Robert King, Jonathan Seltzer, and William Poppert.

http://foodindustrycenter.umn.edu/Food_Supply_Chain_Practices (Accessed January 2007)

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