CHAPTER 7. ENERGY USE CHARACTERIZATION

TABLE OF CONTENTS

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

7.2 OVERVIEW OF ENERGY SIMULATION APPROACH................................................ 7­1
 

7.2.1 Overview of Energy Simulation Inputs ............................................................... 7­2
 

7.2.2 CBECS Building and Energy Use Data Sets....................................................... 7­2
 

7.2.3 Prototypical Building Selection ........................................................................... 7­4
 

7.2.4 Simulation Tool Description................................................................................ 7­6
 

7.2.5 Equipment Classes and Efficiency Levels Analyzed........................................... 7­6
 

7.3 BUILDING ENVELOPE CHARACTERISTICS .............................................................. 7­7
 

7.3.1 Building Shape and Building Aspect Ratio ......................................................... 7­9
 

7.3.2 Exterior Opaque Wall ........................................................................................ 7­10
 

7.3.3 Roof.................................................................................................................... 7­11
 

7.3.4 Fenestration........................................................................................................ 7­12
 

7.3.5 Air Infiltration.................................................................................................... 7­14
 

7.4 BUILDING INTERNAL LOADS AND SCHEDULES .................................................. 7­14
 

7.4.1 Building Occupancy, Lighting and Plug Load Schedules................................. 7­15
 

7.4.2 Building Occupancy Peak Densities.................................................................. 7­17
 

7.4.3 Building Lighting Peak Power Densities........................................................... 7­18
 

7.4.4 Building Plug Load Peak Power Densities........................................................ 7­20
 

7.5 BUILDING MECHANICAL SYSTEMS AND EQUIPMENT....................................... 7­20
 

7.5.1 Building Air Conditioning Operating Schedules............................................... 7­20
 

7.5.2 Heating and Cooling Set Points......................................................................... 7­20
 

7.5.3 Equipment Sizing and Efficiency ...................................................................... 7­21
 

7.5.4 Part­Load Performance Curves Development ................................................... 7­22
 

7.5.5 Fan Power Assumptions .................................................................................... 7­23
 

7.5.6 Ventilation Rates................................................................................................ 7­23
 

7.6 SUMMARY OF RESULTS ............................................................................................. 7­24
 

7.6.1 Annual Energy Use Results............................................................................... 7­24
 

7.6.2 Comparison of Simulation Results to CBECS Calculated Data........................ 7­28
 

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LIST OF TABLES
 

Table 7.2.1 Summary of Energy Simulation Inputs for Hotel/Motel Building Simulation........ 7­2

Table 7.2.2 2003 CBECS Variables Used in the Characterization Process............................... 7­4

Table 7.2.3 Equipment Classes and Efficiency Levels Directly Analyzed in the Energy

Use Analysis ........................................................................................................... 7­6
 

Table 7.3.1 Building Envelope Characteristic Variables in 20003 CBECS Survey................... 7­7
 

Table 7.3.2 Shape Categories in 2003 CBECS for 79 Buildings................................................ 7­9
 

Table 7.3.3 Wall Construction Categories in 2003 CBECS for 79 Buildings.......................... 7­10
 

Table 7.3.4 Roof Construction Categories in 2003 CBECS for 79 Buildings.......................... 7­11
 

Table 7.3.5 “Percent Exterior Glass” Categories in 2003 CBECS for 79 Buildings................ 7­12
 

Table 7.3.6 Estimated Probability of Low­E Glass in Commercial Building Fenestration...... 7­13
 

Table 7.3.7 Window U­Factor and Shading Coefficient Combinations................................... 7­14
 

Table 7.4.1 Lighting Peak Power Densities for Prototypical Hotel/Motel Building................ 7­19
 

Table 7.5.1 PTAC and PTHP Full­Load Supply Fan Flow Rate and Power Consumption ..... 7­23
 

Table 7.5.2 PTAC and PTHP Ventilation Air Flow Rate......................................................... 7­23
 

Table 7.6.1 Annual National Average Energy Use for PTAC and PTHP Unit........................ 7­24
 

LIST OF FIGURES

Figure 7.4.1 Guest Room Occupancy Schedules...................................................................... 7­16

Figure 7.4.2 Guest Room Lighting Schedules.......................................................................... 7­16

Figure 7.4.3 Guest Room Plug Load Schedules....................................................................... 7­17

Figure 7.5.1 Comparison of Old and New Degradation Factor for PTAC............................... 7­22

Figure 7.6.2 National Average Energy Use for PTHP at Various Efficiency Levels............... 7­26

Figure 7.6.3 National Average Building Electric Energy Use Intensity by Major End­Use.... 7­27

Figure 7.6.4 Frequency Distribution of State Average Energy Use for PTAC and

Baseline Efficiency Level..................................................................................... 7­28

Figure 7.6.5 Frequency Distribution of State Average Energy Use for PTHP and Baseline

Efficiency Level.................................................................................................... 7­28
 

Figure 7.6.6 Comparison of EUI between Simulation and 2003 CBECS ................................ 7­29
 

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CHAPTER 7. ENERGY USE CHARACTERIZATION
 

7.1 INTRODUCTION
 

This chapter presents the energy use characterization analysis for packaged terminal air

conditioners (PTAC) and packaged terminal heat pumps (PTHP). The purpose of the building

energy use characterization analysis is to assess the energy savings potential at different PTAC

and PTHP equipment efficiency levels for key commercial building types and across a range of

climate zones. The energy use characterization estimates the energy use of the PTAC or the

PTHP at specified energy­efficiency levels through the use of commercial building energy

simulations. The energy simulations yielded hourly estimates of the building electric loads that

included lighting, plug, and air­conditioning equipment. The energy­use estimates enabled

evaluation of energy savings from PTAC and PTHP operation at various efficiency levels. The

annual energy consumption of PTACs and PTHPs are used in subsequent analyses include the

life­cycle cost (LCC) and payback period (PBP) analyses (Chapter 8 of the TSD) and the

national impacts analysis (Chapter 11 of the TSD).

Energy savings from PTACs and PTHPs vary according to the efficiency level and

various other factors, including climate, commercial building construction, and building usage

patterns. The U.S. Department of Energy (DOE) performed the energy analysis for a

prototypical hotel/motel building in multiple climate locations in order to capture some of the

diversity of use and performance of PTACs and PTHPs.

PTAC and PTHP units are often selected as low­cost heating and cooling systems for

hotel/motel rooms, assisted living homes, dormitories, or any application that require individual

zone heating and cooling. According to the analysis by Ducker Worldwide (2001), PTAC and

PTHP units are primarily used in hotels/motels with less than 125 rooms and three stories.1

Therefore, DOE assessed the energy use of PTAC and PTHP units by selecting a single

representative building type – hotel/motel building. While DOE realizes that PTACs and PTHPs

are found in other building types, DOE believes that, based on engineering judgment and

consultation with industry experts, the cooling and heating loads of an individual room served by

a single PTAC or PTHP unit are independent of the building type in which the room is situated.

7.2 OVERVIEW OF ENERGY SIMULATION APPROACH

DOE used a whole­building hourly simulation program, DOE­2.1E (also refer to DOE­2

in this chapter), to estimate the energy use in a representative hotel/motel building for various

efficiency levels and equipment classes at 239 TMY2 climate locations.2 The DOE­2.1E

program has a built­in PTAC/PTHP module in its HVAC system components. DOE used the

Energy Information Agency (EIA) 2003 Commercial Building Energy Consumption Survey

(2003 CBECS) as the primary source of data to develop the representative building size and

other building characteristics for this analysis (i.e., aspect ratio, building construction type, etc.).3

DOE modeled hotel/motel guest rooms facing in all orientations by rotating a symmetrical

rectangular floor plan prototype building 90 degrees to capture the orientation­driven changes in

annual energy use of the PTAC and PTHP. The Ducker Worldwide market analysis estimated

that PTHP represents approximately 45 percent of the total market for packaged terminal

equipment. Therefore, DOE estimated the annual energy use per unit using a PTHP as well as a

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PTAC in each climate location. DOE assumed that generally the building would use a PTAC or

PTHP unit. DOE calculated the weighted­average annual energy use for each PTAC and PTHP

equipment class in each State through the population weighting of the representative climate

location(s) within the state. DOE further aggregated the energy use at the State level to national

average energy use using the 2000 Census population data, published by the U. S. Census

Bureau.

DOE estimated the annual energy use for each equipment class at the baseline efficiency

level (i.e., the efficiency level specified by ASHRAE/IESNA Standard 90.1­1999) plus five

higher efficiency levels. As is to be expected, annual energy use of PTAC and PTHP units

decreases as the efficiency level increases from the baseline efficiency level to the highest

efficiency level analyzed. The result of the whole­building simulation was the annual end­use

energy use of the space cooling and heating, lights, plug loads and fan.

7.2.1 Overview of Energy Simulation Inputs

To estimate the energy use of a prototypical building, DOE estimated the inputs for

building envelope characteristics, building internal loads and operating schedules, ventilation

rates and schedules, HVAC equipment efficiency, operation, control and sizing, and fan power

assumptions. Table 7.2.1 summarizes these inputs used in the energy analysis. The processes by

which the values for these inputs were developed are described below.

Table 7.2.1 Summary of Energy Simulation Inputs for Hotel/Motel Building Simulation

Building Envelope

Configuration/Shape Exterior Opaque Wall Roof Floor Fenestration

• Aspect ratio

• Number of floors

• Number of guest rooms

• Floor­to­floor height

• Floor­to­ceiling height

• Structure type

• Insulation

• Structure type

• Insulation

• Structure type

• Insulation

• Window type

• Window­to­wall ratio

• Exterior shading

• Interior shading

Building Internal Loads and Schedules

Occupancy Lighting Plug Load

• Occupancy density

• Occupancy schedule

• Occupant sensible and latent heat gain

• Peak lighting power density

• Lighting schedule

• Peak plug load power density

• Plug load schedule

HVAC System

• HVAC system type

• Number of thermal zones

• Space heating and cooling set points and schedules

• PTAC and PTHP equipment efficiency

• Fan supply air flow rate and power consumption

• Fan control type

• Fan operation schedule

• Ventilation air rate

7.2.2 CBECS Building and Energy Use Data Sets

DOE used the 2003 CBECS data set as the primary data source to develop the

assumptions for building characteristics for the purpose of modeling. DOE supplemented this

data with the New Commercial Construction Characteristics (NC3

) database as well as other

sources when CBECS 2003 did not contain the needed data for the energy simulations.4 The

CBECS data sets are publicly available and provide statistically valid results from a periodic

national survey of commercial buildings and their energy suppliers performed by DOE’s Energy

Information Administration (EIA). The results of the surveys are available as downloadable

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reports and micro­data files from the EIA website (http://www.eia.doe.gov/emeu/cbecs/). The

2003 CBECS is the most recent data set available. NC3 is an internal Pacific Northwest National

Laboratory (PNNL) database of nationwide commercial construction energy­related

characteristics developed based on building characteristics taken from McGraw Hill/F.W. Dodge

commercial building plans submitted for construction bids. The current database includes over

160 commercial buildings.

In the 2003 CBECS survey, 4,859 buildings were surveyed, and the sampled buildings

were given base weights (CBECS adjusted weight field identifier “ADJWT8”) that relate the

sampled buildings to the entire stock of commercial buildings in the United States. DOE used a

subset of hotel/motel buildings to characterize the prototypical building to be simulated. The

buildings chosen in the CBECS database were hotel/motel buildings that use PTAC or PTHP as

main cooling and heating equipment. Because PTAC and PTHP are not clearly defined as one of

main cooling and heating equipment categories, a set of criteria, described in detail in section

7.2.2, were developed to extract buildings that most likely use PTAC and PTHP for space

cooling and heating. Table 7.2.22 gives a list of the variables used in the characterization

process.

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Table 7.2.2 2003 CBECS Variables Used in the Characterization Process
 

Field Identifier Description

PUBID8 Building identifier

REGION8 Census region

CENDIV8 Census division

ADJWT8 Adjusted weight

SQFT8 Square footage

YRCON8 Year of construction

PBA8 Principal building activity

PBAPLUS8 More specific building activity

MAINHT8 Main heating equipment

PKGHPS8 Packaged unit heat pump for heating

SPLHPS8 Split system heat pump for heating

RMHPS8 Individual room heat pump for heating

AIRHPT8 Air source heat pump for heating

GRDHPT8 Ground source heat pump for heating

WTRHPT8 Water loop heat pump for heating

MAINCL8 Main cooling equipment

PKGCPS8 Packaged unit heat pump for cooling

SPLCPS8 Split system heat pump for cooling

RMCPS8 Individual room heat pump for cooling

AIRCPT8 Air source heat pump for cooling

GRDCPT8 Ground source heat pump for cooling

WTRCPT8 Water loop heat pump for cooling

VAV8 VAV system

ECN8 Economizer cycle

ELHT18 Electricity used for main heating

WLCNS8 Wall construction material

RFCNS8 Roof construction material

GLSSPC8 Percent exterior glass

EQGLSS8 Equal glass on all sides

WINTYP8 Window glass type

TINT8 Tinted window glass

REFL8 Reflective window glass

AWN8 External overhangs or awnings

SKYLT8 Skylights/atriums designed for lighting

BLDSHP8 Building shape

NFLOOR8 Number of floors

LODGRM8 Number of guest rooms

7.2.3 Prototypical Building Selection

PTAC and PTHP are often selected as a low­cost cooling and heating system for

hotel/motel rooms, assisted living homes, dormitories or any application that requires individual

zone space cooling and heating. DOE decided that PTAC and PTHP are primarily used in

hotels/motels.1 Therefore, DOE assessed the electric energy use for PTAC and PTHP equipment

by simulating a prototypical hotel/motel building. DOE used the 2003 CBECS as the primary

source of data to develop the representative building characteristics. Because PTAC and PTHP

are not clearly defined as one of the main heating and cooling equipment categories, a set of

criteria were developed to extract building characteristics that most likely use PTAC and PTHP

for space cooling and heating.

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In the 2003 CBECS, the main heating and cooling equipment is characterized by

variables “MAINHT8” and “MAINCL8” respectively. The values for these two variables are the

following:

Main Heating

1 = Furnaces that heat air directly

2 = Boilers inside the building

3 = Packaged heating units

4 = Individual space heaters

5 = Heat pumps for heating

6 = District steam or hot water

7 = Other heating equipment

Main Cooling

1 = Packaged air conditioning units

2 = Residential type central air conditioners

3 = Individual room air conditioners

4 = Heat pumps for cooling

5 = District chilled water

6 = Central chillers inside the building

7 = Swamp coolers or evaporative coolers

8 = Other cooling equipment

Where heat pumps are utilized, the survey asks further questions of the type of heat

pumps (e.g., water source, ground source, air source, packaged, split system, individual room)

used for heating and cooling the building. CBECS also includes data on whether a variable airvolume (VAV) system and economizer are used in the building, as well as the main and

secondary heating or cooling fuel types.

Unfortunately, not all the 2003 CBECS responses regarding equipment categories are

mutually exclusive, particularly in the categories of packaged heating units, individual space

heaters, packaged air conditioning units, individual room air conditioners and heat pumps.,

PTAC units can be categorized as packaged air conditioning units or individual room air

conditioner. Similarly, PTHP units could potentially also be interpreted as packaged heating

units, or individual space heaters. Based on these definitions, it is clear that a large overlap exists

between the categories of packaged heating units and individual space heaters for main heating,

and packaged air conditioning units and individual room air conditioners for main cooling. This

overlap cannot be easily disaggregated through other survey responses.

DOE assumed that PTAC and PTHP could be categorized as either one of the above

categories by the survey respondents, and extracted hotel/motel buildings using packaged air

conditioning units, individual room air conditioners or heat pump as main cooling equipment and

using packaged heating units, individual space heaters or heat pumps as main heating equipment.

Furthermore, buildings using split system heat pumps, ground source heat pumps, water loop

heat pumps, VAV systems or economizers are excluded. DOE also used the variable “ELHT18”

(electricity used for main heating) to exclude those buildings using fuel sources other than

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electricity for space heating, because PTAC and PTHP equipment using electricity are the only

equipment considered in this rulemaking.

After applying the above­mentioned criteria, DOE identified 79 buildings of the 4,859

surveyed buildings from 2003 CBECS to base the building envelope characteristics of the

prototypical building to be simulated. Hereafter, when referring to the data from 2003 CBECS,

DOE means only the data for these 79 buildings.

7.2.4 Simulation Tool Description

DOE chose to use DOE­2.1E as the primary simulation tool for the energy analysis.

DOE­2.1E is one of the most widely used programs for whole­building energy simulation

analysis and has been validated by comparing its results with thermal and energy use

measurements on actual buildings and with calculations. DOE­2.1E predicts the hourly energy

use and energy cost of a building given hourly weather information and a description of the

building and its heating, ventilation and air­conditioning (HVAC) equipment. DOE­2 has one

subprogram for translation of input file (BDL Processor), and four simulation subprograms

(LOADS, SYSTEMS, PLANT and ECON). LOADS, SYSTEMS and PLANT are executed in

sequence, with the output of LOADS becoming the input of SYSTEMS, etc. The output of

PLANT then becomes the input to ECON. Each of the simulation subprograms also produces

printed reports of the results.

7.2.5 Equipment Classes and Efficiency Levels Analyzed

DOE estimated the annual energy consumption of the prototypical hotel/motel building

for six representative equipment capacities at the baseline efficiency level plus four increasing

efficiency levels, which were identified from the engineering analysis (Chapter 5). Table 7.2.3

lists these six PTAC and PTHP representative equipment capacities and all the efficiency levels

analyzed.

Table 7.2.3 Equipment Classes and Efficiency Levels Directly Analyzed in the Energy

Use Analysis

Equipment Category

Representative

Cooling

Capacity

Efficiency Level

Baseline Level 1 Level 2 Level 3 Level 4

Standard 9,000 Btu/h 10.6 EER 10.9 EER 11.1 EER 11.3 EER 11.5 EER

PTAC

Size 12,000 Btu/h 9.9 EER 10.2 EER 10.4 EER 10.6 EER 10.8 EER

NonStandard 11,000 Btu/h 8.6 EER 9.4 EER 9.7 EER 10.0 EER NA

Size

Standard 9,000 Btu/h 10.4 EER

3.0 COP

10.9 EER

3.1 COP

11.1 EER

3.2 COP

11.3 EER

3.3 COP

11.5 EER

3.3 COP

PTHP

Size 12,000 Btu/h 9.7 EER

2.9 COP

10.2 EER

3.0 COP

10.4 EER

3.1 COP

10.6 EER

3.1 COP

10.8 EER

3.1 COP

NonStandard

Size

11,000 Btu/h 8.5 EER

2.6 COP

9.4 EER

2.8 COP

9.7 EER

2.8 COP

10.0 EER

2.9 COP NA

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Standard size PTACs and PTHPs, as defined in the market and technology assessment

(MTA) (Chapter 3), refer to units with wall sleeve dimensions greater than or equal to 16 inches

high or greater than or equal to 42 inches wide. Non­standard size PTAC and PTHP, as defined

in the MTA, refer to units with wall sleeve dimensions less than 16 inches high and less than 42

inches wide. As mentioned in the engineering analysis, the energy conservation standards for

PTAC and PTHP equipment are measured and expressed in terms of energy­efficiency ratioa

(EER) and coefficient of performanceb (COP). DOE defined baseline efficiency level, as shown

in Table 7.2.3, as the efficiency level specified in the ASHRAE/IESNA Standard 90.1­1999. 5

Efficiency level 4 for the standard size equipment and efficiency level 3 for the non­standard size

equipment, also called as “Max Tech”, in the last column of Table 7.2.3 refers to the maximum

technologically feasible design as established by the engineering analysis (Chapter 5).

7.3 BUILDING ENVELOPE CHARACTERISTICS

This section describes the process by which the assumptions and inputs of the building

envelope characteristics were developed for the prototypical hotel/model building. As described

in section 7.2 of this Chapter, DOE used the 2003 CBECS data set as the primary data source to

develop the representative building characteristics and supplemented this with NC3 database as

well as other sources, when CBECS 2003 did not contain the needed data for the energy

simulations. Following the list of variables used in the characterization process in Table 7.2.2,

Table 7.3.1 details the variables and corresponding values in 2003 CBECS that describe

the building envelope characteristics.

Table 7.3.1 Building Envelope Characteristic Variables in 20003 CBECS Survey

2003 CBECS Variable CBECS Description Values

WLCNS8 Wall construction

1=Brick, stone, or stucco

2=Pre­cast concrete panels

3=Concrete block or poured concrete

4=Siding, shingles, tiles, or shakes

5=Sheet metal panels

6=Window or vision glass

7=Decorative or construction glass

8=No one major type

9=Other

RFCNS8 Roof construction

1=Built­up

2=Slate or tile shingles

3=Wood shingles/shakes/other wood

4=Asphalt/fiberglass/other shingles

5=Metal surfacing

6=Plastic/rubber/synthetic sheeting

a According to the ARI 310/380­2004 Standard for Packaged Terminal Air­Conditioners and Heat Pumps (ARI

310/380­2004) test procedure, EER is defined as “the ratio of the produced cooling effect of an air conditioner or

heat pump to its net work input, expressed in Btu/watt­hour.”

b COP is defined by ARI 310/380­2004 as “the ratio of the produced cooling effect of an air conditioner or heat

pump (or its produced heating effect, depending on the mode of operation) to its net work input, when both the

cooling (or heating) effect and the net work input are expressed in identical units of measurement.”

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2003 CBECS Variable CBECS Description Values

7=Concrete

8=No one major type

9=Other

WINTYP8 Window glass type

1=Single layer glass

2=Multi­layer glass

3=Combination of both

4=No windows

GLSSPC8 Percent exterior glass

1=10 percent or less

2=11 to 25 percent

3=26 to 50 percent

4=51 to 75 percent

5=76 to 100 percent

BLDSHP8 Building shape

1=Square

2=Wide rectangle

3=Narrow rectangle

4=Rectangle/square with courtyard

5="H" shaped

6="U" shaped

7="E" shaped

8="T" shaped

9="L" shaped

10="+" or cross shaped

11=Other shape

NFLOOR8 Number of floors

0­14 = 0­14

991 = 15 to 25

992 = Over 25

LODGRM8 Number of guest rooms

0­999996 = 0­999996

999997 = Not ascertained

999998 = Refused

999999 = Don’t know

TINT8 Tinted window glass

1=Yes

2=No

7=Not Ascertained

8=Refused

9=Don’t Know

REFL8 Reflective window

glass

1=Yes

2=No

7=Not Ascertained

8=Refused

9=Don’t Know

The average floor area is 17,316 ft2 for the 79 hotel/motel buildings in 2003 CBECS.4

The CBECS data also shows that 50 percent of the buildings are two­story buildings and 33

percent of them are one­story buildings. The floor areas of a one­story (Economy Inn) and three3 2 2 story (Sleep Inn & Suites prototype) motel buildings in NC are 10,958 ft and 36,602 ft ,

respectively. Therefore, DOE assumed that the prototypical building to be simulated is a 20,000

ft2

, two­story, hotel/motel building.

DOE also assumed that the prototypical building has 44 guest rooms, approximately

75 percent of the building total floor area. These guest rooms include 10 suites with a floor area

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of 462 ft2 per suite and 34 standard guest rooms with a room floor area of 308 ft2. This

assumption is based on the CBECS data, the NC3 database and the 2000 Screening Analysis for

EPACT­Covered Commercial HVAC and Water­Heating Equipment.6 The CBECS 2003

reported the average number of guest rooms as 34. The Sleep Inn & Suites in the NC3 database

has 77 guest rooms that have 55 standard guest rooms with the room area of 280 ft2, 12 suites

with room area of 415 ft2

. In the DOE’s Screening Analysis7 conducted in 2000, an assumption

of 300 ft2 per guest room was used.

7.3.1 Building Shape and Building Aspect Ratio

The CBECS survey asks questions regarding the building shape (square, wide rectangle,

other) and found 52.7 percent of buildings, which use PTAC or PTHP as the main cooling and

heating equipment, are wide rectangular shape. Therefore, DOE assumed the prototypical

building to be a wide rectangle. Table 7.3.2 shows the 2003 CBECS shape categories, as well as

the fraction of buildings in the data set in each shape category based on the data for the 79

buildings.

Aspect ratios are important in determining the relative amount of perimeter area

(responsive to the outdoor environment and with window daylighting potential) to core area for a

given building. Aspect ratio information coupled with orientation and self­shading is also

relevant in determining solar loading in a real building.

The aspect ratio is defined as the reported building length divided by the building width:

Building Length Aspect Ratio = Eq. 7.1

Building Width

Table 7.3.2 Shape Categories in 2003 CBECS for 79 Buildings

Shape Categories Fraction of Building Population (%)

Square 0.0

Wide rectangle 52.7

Narrow rectangle 8.2

Rectangle/square with courtyard 2.3

"H" shaped 0.0

"U" shaped 10.3

"E" shaped 1.4

"T" shaped 3.0

"L" shaped 24.0

"+" or cross shaped 0.8

Other shape 0.0

Total 100

Unfortunately, aspect ratio information has not been collected in the CBECS since 1995,

so general information on actual aspect ratios has been limited. What information was collected

in these early CBECS distributions is building length and width for rectangular and square

buildings. The rectangle with courtyard buildings did not have the length and width reported.

DOE calculated the actual aspect ratio based on the 1992 CBECS data from the reported length

and width of the building.7 An average of aspect ratio was calculated to be 2.84 for 1992

7­9

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CBECS lodging (hotel/motel/dorm) buildings that possibly using PTAC and PTHP (the same

criteria for extracting buildings using PTAC and PTHP was applied). DOE determined the

aspect ratio of the prototypical building to be 3.0 based on the 1992 CBECS data and verified

this value with the sampled floor plans in NC3 database.

7.3.2 Exterior Opaque Wall

The description of the wall construction and roof construction variables in 2003 CBECS

primarily describes the surface material for these portions of the building envelope and not the

actual construction. Table 7.3.3 shows the CBECS wall construction categories and fraction of

building population for the hotel/motel buildings using PTAC and PTHP.

Table 7.3.3 Wall Construction Categories in 2003 CBECS for 79 Buildings

Wall Construction Categories Fraction of Building Population (%)

Brick, stone, or stucco 54.2

Pre­cast concrete panels 0.0

Concrete block or poured concrete 18.1

Siding, shingles, tiles, or shakes 27.4

Sheet metal panels 0.0

Window or vision glass 0.3

Decorative or construction glass 0.0

No one major type 0.0

Other 0.0

Total 100.0

The most common opaque wall category in 2003 CBECS is “brick, stone, and stucco”.

Brick, stone, and stucco are all commonly used as materials to dress up the façade of a building,

and while brick and stone can both be the primary supporting construction material used in a

building, that is believed to be a less common approach for recent buildings due to cost. It is

expected that the relative fraction of brick or stone over metal building construction would be

small, and the primary question is whether these brick, stone, or stucco façades are over masonry

or frame walls. DOE also reviewed data in NC3 database in an attempt to provide a better insight

into wall construction. However, due to a very small number of samples in the database (two

motels in the current database with Economy Inn using wood frame wall and Sleep Inn & Suites

using frame wall), the information that can be used in this analysis is very limited. Based on the

CBECS and NC3 data, as well as general practice, DOE assumed that the wall construction in the

simulated prototypical building is steel­framed with 1­inch stucco.

The resistance or the R­value of the wall insulation is important for thermal performance

of the wall. There are few other studies of wall and roof insulation characteristics in existing

commercial buildings. DOE identified two studies. The first study was a 1986 Pacific Gas &

Electric survey of on­site construction characteristics in existing buildings in California. The

results of this survey are reported in Akbari et al.8 The second study was a review of commercial

building characteristics undertaken in 2000 by New Jersey Electric and Gas Utilities to

understand typical construction and renovation practices in their service area.9 This study

observed building characteristics for a large number of newly constructed buildings and a

smaller number of building retrofits, and provided the frequency of occurrences for different wall

and roof R­values (thermal resistance values) from those observations. The study showed the

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predominance of three insulation levels—R­6, R­11, and some R­19—for wall insulation and it

also reported that the average insulation level for lodging is R­13.8 for new construction.

Unfortunately, the New Jersey Electric and Gas Utilities study did not clearly define the type of

construction corresponding to the predominated insulation levels.

DOE reviewed these studies but, because of their localized nature it was recognized that

it would be difficult to categorize either of their results as representative of U.S. construction

practices. Given the unavailability of national data, DOE assumed that the insulation level on a

steel­framed wall would be R­13 cavity insulation. R­13 is believed to be a common R­value for

standard frame wall construction; its thickness is designed to fill wall cavities created by

standard 3.5­inch thick wall construction.

In summary, DOE assumed the steel­framed wall construction to have an exterior

surface with a 1­inch stucco and R­13 cavity insulation. The effective R­value for the steel

frame wall with R­13 cavity insulation is equivalent to R­6.0. The steel­framed wall includes the

following layers:

• Exterior air film (R­0.17)

• 1 inch stucco (R­0.08)

• 5/8 inch gypsum board (R­0.56)

• Steel frame/cavity (R­6.0)

• 5/8 inch gypsum board (R­0.56)

• Interior air film (R­0.68)

The overall U­factor (thermal transmission factor) which is the inverse of the resistance

(or R­value) for the exterior opaque wall is 0.124 Btu/hr­ft2­°F.

7.3.3 Roof

2003 CBECS provides seven categories of roof construction material, plus an “other”

category and a “not one major type” category. Table 7.3.4 shows the CBECS roof construction

categories and fraction of building population for the lodging buildings using PTAC and PTHP.

The data shows 55.5 percent of the buildings have asphalt/fiberglass/other shingles roof surface.

The study by New Jersey Electric and Gas Utilities shows the predominance of R­19 or R­20

levels for roof insulation in new construction or retrofit buildings.

Table 7.3.4 Roof Construction Categories in 2003 CBECS for 79 Buildings

Roof Construction Categories Fraction of Building Population (%)

Built­up 16.6

Slate or tile shingles 4.2

Wood shingles/shakes/other wood 2.2

Asphalt/fiberglass/other shingles 55.5

Metal surfacing 8.7

Plastic/rubber/synthetic sheeting 9.5

Concrete 3.4

No one major type 0

Other 0

Total 100

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For this analysis, DOE assumed the roof construction to have an asphalt shingles, wood

sheathing, R­19 batt insulation and gypsum board. The sloped frame roof includes the following

layers:

• Exterior air film (R­0.17)

• Asphalt shingles (R­0.44)

• Wood sheathing (R­2.06)

• R­19 batt insulation

• 5/8 in. gypsum board (R­0.56)

• Interior air film (R­0.92)

The overall U­factor for the roof is 0.043 Btu/hr­ft2­°F, corresponding to the mass of

7.1 lb/ft2 and thermal capacity of 2.3 Btu/ft2­°F.

7.3.4 Fenestration

In the 2003 CBECS data, a “percent exterior glass” variable was reported for each

building in one of the five bins shown in Table 7.3.5. DOE used this data for estimating the

window­to­wall ratio (WWR) for the prototypical building. The data showed that 31.7 percent

of the buildings fall into “10 percent or less” category while 42.0 percent fall in the “11–25

percent” category. DOE assumed the window size to be a 4 ft 8 in. by 4 ft 8 in. square and

calculated the WWR of the prototypical building to be 10.3 percent.

Table 7.3.5 “Percent Exterior Glass” Categories in 2003 CBECS for 79 Buildings

“Percent Exterior Glass” Categories Fraction of Building Population (%)

10 percent or less 31.7

11–25 percent 42.0

26–50 percent 14.5

51–75 percent 4.7

76 –100 percent 1.6

Total 100.0

The window characteristics of concern for the energy analysis are primarily the overall

window U­factors and the window shading coefficient (SC). These characterize the performance

of the windows in the building once the WWR has been established. The 2003 CBECS contains

information on window glass type (variable “WINTYP8”), whether windows in the building use

tinted or reflective glass (variables “TINT8” and “REFL8”) and whether either external

overhangs or awnings are present (variable “AWN8”).

The window glass type variable “WINTYP8” provides three categories: single­pane glass,

multi­pane glass, and combination of both. Because very little triple­pane glass is used in

commercial buildings in the U.S., DOE characterized the multi­pane glass as double­pane glass.

The 2003 CBECS data reported that about the same fraction of buildings use single­pane glass

and multi­pane glass. Therefore, DOE decided that the prototypical building to be simulated

uses single­pane glass at half of TMY2 climate locations, and uses double­pane glass at the other

half of TMY2 locations. The Microsoft (MS) Excel random number generator is used to

randomly assign the window glass type to the 239 TMY2 climate locations.

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The variables “TINT8” and “REFL8” are used to report on whether the window glass is

tinted or reflective. The 2003 CBECS data reported that most of the buildings do not have tinted

or reflective glass (87 percent of the buildings do not use tinted glass and 90 percent of the

buildings do not use reflective glass). DOE characterized the window glass to be clear in the

prototypical building.

An important step in estimating both the U­factor and the SC for glazing is determining

whether a low­emissivity (low­e) surface is used in the glazing. This attribute is not

characterized by the CBECS data, and would typically be found only in newer construction (post

1980), or in replaced windows. DOE adopted the same approach as used in the energy analysis

of the commercial unitary air conditioners and heat pumps rulemaking to estimate the fraction of

low­e coating used in commercial buildings over the last 20 years (refer to the Technical Support

Document: Energy Efficiency Program for Commercial and Industrial Equipment: Commercial

Unitary Air Conditioners and Heat Pumps, Chapter 6, Building Energy Use and End­Use Load

Characterization Analysis).10 It was estimated that approximately 20 percent of the glazing sold

for commercial buildings used low­e coating in 2000.11 Virtually all of this low­e coated glass is

double­pane to ensure longevity of the low­e coating. DOE assumed a linear growth for the

commercial low­e glass market, from initial product availability in 1985 through providing for

20 percent of the double­pane market in 2000 and afterwards. Table 7.3.6 shows DOE’s

estimates of the probability of any double­pane windows in buildings constructed between 1985

and 2006 having a low­e coating.

Table 7.3.6 Estimated Probability of Low­E Glass in Commercial Building Fenestration

Year Probability of Low­E

Percentage (%)

1984 and before 0.00

1985 1.25

1986 2.50

1987 3.75

1988 5.00

1989 6.25

1990 7.50

1991 8.75

1992 10.00

1993 11.25

1994 12.50

1995 13.75

1996 15.0

1997 16.25

1998 17.50

1999 18.75

2000 to 2006 20.00

DOE used the estimated percentages in Table 7.3.6 to calculate a weighted average

fraction of using low­e coating in the prototypical building. This approach resulted in only

approximately 4 percent of probability for the prototypical building having low­e glazing. The

low percentage of low­e glazing was due to the fact that majority of the selected buildings (i.e.,

75 percent of the buildings among the 79 selected buildings) were constructed prior to 1990,

corresponding to a very low probability of low­e glazing. Similarly, DOE used the MS Excel

7­13

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random number generator to randomly select 4 percent of the buildings (TMY2 climate locations)

that use double­pane glass to have low­e coating. Table 7.3.7 shows the selected glass types in

the simulation.

Table 7.3.7 Window U­Factor and Shading Coefficient Combinations

Glass Type

Tinted or

Reflective Glass Low­E

Assumed Characteristics DOE­2.1E Glass

Window U­Factor Window SC Type Code

Single­pane No No 1.09 0.95 1001

Double­pane No No 0.49 0.89 2001

No e=0.10 0.32 0.69 2631

The CBECS information with respect to the presence of overhangs and awnings provided

virtually no detail on the size or shading capability of overhangs or awnings. Because 2003

CBECS reported about the same fraction of buildings have overhangs or awnings as those that

do not, and no other source of information on this feature could be identified, DOE did not try to

characterize the performance of awnings and assumed that the prototypical building has no

overhangs or awnings.

The CBECS survey did not capture any information about window interior shading.

Since moveable interior shading devices such as mini blinds and draperies are usually used in

hotel/motel buildings, DOE assumed windows are equipped with medium color and semi­open

weave draperies, which has an interior solar attenuation coefficient of 0.63. DOE obtained this

value from the American Society of Heating, Refrigeration and Air­Conditioning Engineers, Inc.

(ASHRAE) 2005 Handbook of Fundamentals, Chapter 31, Table 22.12 DOE also assumed a

probability of 0.5 for opening the draperies from 7 a.m. to 7 p.m. and that the draperies are

closed during the rest of the day.

7.3.5 Air Infiltration

Building envelope tightness is important based on its relevance to the estimation of

building ventilation rates as they impact building energy use and indoor air quality. Existing

data sources and literature for commercial building infiltration rates are limited. A study by

Persily provided some data for the air tightness of 139 commercial and institutional buildings.13

The study concluded that no correlations between building age and air tightness, or building type

and air tightness exist. It also examined the effect of wall construction types on infiltration and

found that masonry, masonry/frame, concrete, metal buildings were similar in air tightness while

frame buildings were somewhat leakier.

DOE assumed an infiltration rate of 0.038 cubic foot per minute (cfm)/ft2 of the gross

exterior wall based on ASHRAE Standard 90.1­1989, Section 13.7.3.2.14

7.4 BUILDING INTERNAL LOADS AND SCHEDULES

Building internal loads include occupancy thermal load, lighting and plug loads.

Modeling the commercial building energy use using whole­building energy simulation tools such

as DOE­2.1E required assumptions about the building’s internal load characteristics in order to

help establish the estimated energy use for the lighting, plug loads, and HVAC systems. This

7­14

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section describes the building internal load characteristics that DOE used to estimate the HVAC

loads and schedules for the prototypical building.

Typically, these loads are represented by peak occupancy density for occupancy thermal

load (in ft2

/person) and peak power density (in W/ft2) for lighting and plug loads and a schedule

that describes the hourly magnitude (usually given in terms of fractions of the peak). These

fractions multiplied by the peak load density give the actual load density for each hour.

7.4.1 Building Occupancy, Lighting and Plug Load Schedules

The peak load and schedule are unique for each commercial building, but there are

similarities between buildings of the same type and with comparable occupancy patterns. For

this analysis, occupancy, lighting, and plug load schedules for the guest rooms were developed

from the schedules used in the 2000 Screening Analysis. Occupancy, lighting, and plug load

schedules for other spaces such as lobby, corridors, stairs, vending and laundry rooms, storage,

and utility rooms were developed based on engineering design practice.

The occupancy, lighting and plug load schedules in the 2000 Screening Analysis, which

were also used in the energy analysis for the commercial unitary air conditioners rulemaking,

were developed from recommendations by ASHRAE for each of the building types considered.

Where metered data were available, observed peak and base loads were used to scale the

schedules to reflect loads observed in “real” buildings. For the lodging building type in the 2000

Screening Analysis, the peak and base loads for plugs and lighting were the values provided by

ASHRAE because metered data were unavailable.

ASHRAE’s Standing Standards Project Committee 90.1 has developed several typical

profiles for use in its energy cost budget (ECB) compliance method, which estimates the annual

energy consumption of a design building. The lighting and plug load profiles in Standard 90.1­

1989 were modified through ASHRAE’s addenda process. Addendum 90.lj to Standard 90.1­

1989 (referred to as “Addendum 90.1j”) revised several of these profiles by increasing the

magnitude of off­hour loads. These “modified” ASHRAE load profiles formed the basis for the

previous 2000 Screening Analysis work and, therefore, are used for this analysis, as well.

Figure 7.4.1, Figure 7.4.2, and Figure 7.4.3 show the hourly occupancy, lighting and plug

load schedules, respectively, for a typical hotel/motel guest room on weekdays, Saturdays, and

Sundays/holidays. Appendix B summarizes the occupancy, lighting and plug load schedules and

peak densities for other spaces in the prototypical hotel/motel building.

7­15

 EERE-2007-BT-STD-0012 COMMENT 32
   

     

            

     

     

            

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Percent of Peak Power Density

Weekday

Sat.

Sun./Hol.

Guest Room Occupancy Schedules

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2 Weekday

Sat. 0.1 Sun./Hol.

0.0

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

Hour of the Day

Figure 7.4.1 Guest Room Occupancy Schedules

Guest Room Lighting Schedules

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

Hour of the Day

Figure 7.4.2 Guest Room Lighting Schedules

Percent of Peak Occupancy

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Guest Room Plug Load Schedules

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Percent of Peak Power Density

Weekday

Sat.

Sun./Hol.

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

Hour of the Day

Figure 7.4.3 Guest Room Plug Load Schedules

7.4.2 Building Occupancy Peak Densities

For the occupancy loads, the occupancy peak density refers to the maximum occupancy

at the peak time of a typical day. The 2006 U.S. lodging industry profile shows that average

occupancy rate for properties with 15 or more rooms was 63.1 percent for year 2005.15 The

lodging report by Smith Travel Research, Inc. shows that in the year 2006, lodging industry

occupancy was 63.4 percent.16 DOE assumed that the occupancy rate of the prototypical

hotel/motel building is 63 percent (28 guest rooms) and used the Excel random number generator

to randomly assign 37 percent (16 guest rooms) to be vacant.

In the 2000 Screening Analysis, DOE assumed the occupancy density of 300 ft2 per

person based on the End­Use Load and Consumer Assessment Program (ELCAP) and 1995

CBECS data, with maximum occupancy numbers from Standard 62­1989 and the Uniform

17, 18, 19, 20, 21 2 Building Code (UBC). ELCAP reported 300 ft per person and 1995 CBECS

reported 565 ft2 per room (approximately 1.9 persons per room) for weekdays (peak).

ASHRAE’s Addendum 90.lj to Standard 90.1­1989 had 278 ft2 per person.

For this analysis, DOE assumed the occupancy peak densities were 1 person per occupied

standard guest room (308 ft2 per person) and 2 persons per occupied suite room (231 ft2 per

person). For the lobby/lounge space, DOE assumed the occupancy peak density to be 28 persons

(33 ft2 per person); this value was derived from data in ASHRAE Standard 62.1­2004.22

DOE assumed the occupant activity level to be 245 Btu/h per person, including Btu/h

sensible heat gain and 155 Btu/h latent heat gain; DOE derived these values from data in the

ASHRAE 2005 Handbook of Fundamentals and did not vary the occupant activity levels with

climate.

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7.4.3 Building Lighting Peak Power Densities

Because of the importance of lighting energy use, which comprises about a quarter of the

total commercial building energy use, and the rapid changes in lighting technology, DOE

estimated the lighting power densities (LPD) for lodging buildings based on a projection of

future lighting power in year 2010. This section provides a brief description of how DOE

established these values.

The prediction of expected LPD for future building or space designs and common

practice depends primarily on the potential variables discussed here.

(1) Existing lighting technology efficiency improvements

Existing lighting technology will tend to make small incremental improvements over

time. The lighting market will, as current supplies are depleted, offer these products to users.

This will not be instantaneous but will depend greatly on manufacturers tooling and marketing

changes as well as consumer interest. These incremental changes are expected to have some,

albeit a minimal, effect on the overall change in LPD.

(2) New/improved lighting technology introductions

New or improved versions of technology such as the newer T5 and advanced T8 lamp

systems will have a greater effect on space type LPD as their introduction to the market is

generally advertised and embraced as a significant advantage to users. The T5 lamp system

employs higher efficiency lamps than the standard T8 technology but has some application

specifics that have slowed its adoption in typical U.S. applications. Both technologies offer

energy savings and efficiency improvements over the standard technology. Specifically, the

advanced T8 lamp systems currently offer efficiencies over standard T8 lamps in the range of

5 percent to 7 percent.

(3) Space design preference changes based on society or corporate preference

As design preferences change, the lighting in spaces will change, which can affect overall

efficiency and LPD. However, design preference cannot be predicted. Some simple changes can

be expected such as increased replacement of incandescent technology with compact fluorescent

technology. However, these are more related to energy cost concerns and code compliance

issues rather than design issues.

(4) Energy (and other) code adoption and compliance

Compliance with energy codes (as with other building codes) can have a definite and

consistent effect on building design and construction. The effect does depend on actual

compliance and enforcement and these are often a product of how entrenched the code is in

building practice. Recent changes in the stringency of energy codes and increased interest in the

Energy Policy Act (EPACT) rulings requiring energy codes for buildings are bolstering the

application of energy codes. The most current building energy standard, ASHRAE Standard

90.1­2004 and the commonly adopted 2003 International Energy Conservation Code (IECC)

include a similar set of LPD values for commercial buildings and are quickly becoming the

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common code for a majority of states in the United States. Currently 21 of the 30 states that

have adopted a nationally available energy code (ASHRAE 90.1, IECC) have adopted one with

the latest LPDs. The remaining states are in the process of considering new energy codes and

most are expected to adopt a code with these latest LPD values in the near future. This will bring

the majority of the country to a consistent level of required LPD limits for new construction and

alterations. It may take several more years for all new construction to meet the new code levels

and longer for existing building stock to be renovated, and therefore, meet the new limits as well.

There is also interest in proposing changes to the current 90.1 code that would include a change

in the basis for the LPD values (currently standard T8 systems) to advanced T8 lamp systems for

a general overall efficiency improvement of 5 percent to 7 percent.

Recent research work shows that LPD values for new buildings are quite mixed (low to

high) even when faced with applicable building energy codes. Therefore, pinpointing a

consistent LPD level for construction in the future will be necessarily problematic. However, it

also seems most probable that the modification and adoption of the newer energy codes will have

the most expected and documentable effect on building LPD and this might be the best metric for

predictions of the future.

Expected changes to the energy codes discussed above (advanced T8 lamp systems basis

for LPD values) could appear in the 2010 version of the ASHRAE Standard 90.1 and could then

soon appear in the IECC energy code as well. Adoption of these newer versions of the codes

would be expected within 5 years in many states with probable widespread application by 2010.

The LPD requirement in Standard 90.1­2004 for hotel/motel buildings is 1.0 W/ft2

.

A conservative 5 percent improvement in the stringency of the code would reduce this to

approximately 0.95 W/ft2

. It is reasonable to expect that by 2010, most states will have an

average requirement of 0.95 W/ft2 LPD for lodging facilities.

DOE derived the lighting peak power density estimates for the prototypical hotel/motel

building in the year 2010 based on the LPD values using the space­by­space method provided in

ASHRAE Standard 90.1­2004 and the estimate of 5 percent energy reduction by 2010.

Table 7.4.1 gives the LPD values used in the present analysis.

Table 7.4.1 Lighting Peak Power Densities for Prototypical Hotel/Motel Building

Space Type LPD in ASHRAE

Standard 90.1­2004 (W/ft2

)

Predicted LPD in Year

2010 (W/ft2)

Corridor 0.50 0.48

Guest Room 1.10 1.05

Laundry/Vending 0.60* 0.57

Lobby/Lounge 1.15** 1.10

Stair 0.60 0.57

Storage/Utility 1.15*** 1.10

* LPD for hospital laundry washing was used.
 

** LPD was the average of LPDs for lobby and lounge.
 

*** LPD was the average of LPDs for active storage and electrical/mechanical space.
 

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DOE did not consider the impact of building lighting controls. Because the installed

wattage would not change, no data existed to support an estimate of the impact of lighting

controls on overall HVAC system performance. The HVAC systems would likely be designed

for the full (undimmed) lighting load.

7.4.4 Building Plug Load Peak Power Densities

Commercial buildings generally have substantial plug loads, which increase the electrical

energy use of the building. Plug loads also contribute to the air conditioning load of the

commercial building, while offsetting the heating load. Plug loads represent electrical appliances

operated in the conditioned space, such as TV, microwave, coffee maker, and other equipment

plugged in to electrical outlets, hence the name “plug load”. In some cases, plug loads might be

directly wired into the electrical circuit, such as small motors.

DOE assumed the plug load peak power density for a typical guest room based on the

2000 Screening Analysis and derived the plug load peak power densities and schedules for other

spaces based on general practice and professional judgment. DOE calculated the peak power

densities by adding the peak power of all typically used appliances in that space and multiplying

the peak power by the appliance usage diversity factor. The peak power for common appliances

and office equipment were obtained from several sources including ASHRAE 2005 Handbook of

Fundamentals, residential clothes washer rulemaking technical support document, and Energy

23, 24 Star refrigerated beverage vending machines product specifications. The plug load peak

2 2 2 power densities are 0.23 W/ft for a guest room, 1.81 W/ft for lobby/lounge area, and 9.02 W/ft

for a laundry/vending room.

7.5 BUILDING MECHANICAL SYSTEMS AND EQUIPMENT

This section describes the development of the PTAC and PTHP operation schedules,

space heating and cooling setpoints, equipment part­load curves, as well as the ventilation rate

and schedules. The prototypical hotel/motel building is air conditioned by PTACs and PTHPs.

Each guest room has one PTAC or PTHP unit to meet the space­cooling and ­heating load, and

PTAC and PTHP units are also used in common areas to provide thermal comfort.

7.5.1 Building Air Conditioning Operating Schedules

DOE assumed the fan runs all the time in lodging buildings, consistent with the 2000

Screening Analysis. Only one fan schedule was used for all the PTAC and PTHP units in the

occupied guest rooms. For the vacant guest rooms, DOE assumed that the fans are controlled by

the room thermostat and only cycle on to maintain the room thermostat setback temperature.

7.5.2 Heating and Cooling Set Points

The 2003 CBECS data set contains no information on internal building operating

temperatures. For the purpose of this analysis, DOE assumed a 70°F heating setpoint and a 75°F

cooling setpoint for occupied rooms and lobby area. No temperature setback was assumed for

occupied rooms and lobby/lounge area. For vacant rooms, utility/storage rooms and

vending/laundry rooms, a 60°F heating setpoint and an 85°F cooling setpoint were assumed.

7­20

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The PTAC and PTHP equipment compressors and fans are cycled “on” and “off” based on the

thermostat control, which calls for cooling or heating to maintain the space temperature.

7.5.3 Equipment Sizing and Efficiency

Equipment sizing refers to the method used to determine the cooling and heating

capacities for a PTAC or PTHP selected for use in serving a given building thermal zone. It is

typically a two­step process. The first step is the mathematical determination of the cooling or

heating load on a given zone. This is commonly done by calculating the thermal load for a set of

environmental conditions. The second step is the selection of equipment that will meet the

calculated design thermal load from the discrete equipment capacities available for purchase. To

estimate the annual cooling and heating energy use in the prototypical building at various

efficiency levels, DOE simulated six representative PTAC and PTHP equipment at the efficiency

levels described in section 7.2.5. DOE also assumed that all the PTAC and PTHP units used in

the prototypical building had the same cooling capacity for each individual room. The heating

capacities of the electric resistance of the PTAC and supplemental electric resistance of the

PTHP were auto­sized by the DOE­2.1E program.

DOE simulated five efficiency levels for standard size equipment and four efficiency

levels for the non­standard size equipment as discussed in section 7.2.5 with different EER and

COP for each equipment type (i.e., PTACs and PTHPs). These two energy efficiency ratings at

Air­Conditioning and Refrigeration Institute (ARI) test conditions account for both compressor

and fan energy use of equipment. In DOE­2 program, compressor energy use and fan energy use

of equipment are calculated separately. Compressor energy use for cooling is calculated using

energy input ratio (EIR) and energy use for heating is calculated using heat input ratio (HIR).

EIR and HIR are the ratios of the power consumed by the compressor/condenser system to the

thermal cooling output at the cooling coil at full load conditions. Therefore, the following two

equations are used to calculate equipment EIR and HIR from EER and COP, and EIR and HIR

values are direct inputs to the DOE­2.1E simulation program.

(CAPc / EER) − ARIFanPower

EIR = Eq. 7.2 (CAPc / 3.413) + ARIFanPower

[CAPh /(COP×3.413)]− ARIFanPower

HIR = Eq. 7.3 (CAPh / 3.413) − ARIFanPower

where:

EIR = energy input ratio,

HIR = heating input ratio,

CAPc = cooling capacity at ARI rating conditions,

CAPh = heating capacity at ARI rating conditions,

EER = energy efficiency ratio

7­21

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COP = coefficient of performance

ARIFanPower = fan power at ARI rating conditions.

7.5.4 Part­Load Performance Curves Development

Several parameters are used to define the performance of the PTAC and PTHP at other

than full­load design conditions in DOE­2 program. These include a system performance curve

to determine the variation in cooling/heating capacity when deviating off of design­temperature

conditions, a system performance curve to determine the variation in hourly full­load power

consumption (e.g., maximum instantaneous power) at off­design cooling conditions, and a

system performance curve to determine actual power consumption at part­load conditions.

The updated system performance curves for PTAC and PTHP in DOE­2.1E, version 107

were used for this analysis.25 The cooling capacity and full­load power consumption for PTAC

at off­design conditions are bi­quadratic functions of entering coil wet­bulb temperature and

outside dry­bulb temperature. The heating capacity and full­load power consumption for PTHP

at off­design conditions are cubic functions of entering coil dry­bulb temperature. The part­load

performance curves for both PTAC and PTHP are cubic curves that calculate the fraction of fullload power consumed by the compressor under part­load conditions. Part­load conditions are

defined by the part­load ratio (PLR) variable; the ratio of the load to the capacity of the

compressor at the design operating conditions. Table B.1 in appendix B gives the equations and

coefficients of these curves. The part­load performance of a compressor is degraded when the

equipment cycles on and off. The degradation factor was used to predict part load effects. The

PTAC part­load was linear in earlier versions of DOE­2 program and was updated in DOE­2.1E

version 107 by Henderson et al.26 These degradation factors for PTAC are shown in Figure 7.5.1.

Figure 7.5.1 also shows this updated curve using the new DOE­2.1E with the old part­load

performance curve in DOE­2 for a PTAC.

Part Load Degradation

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

PLR (load/capacity)

Figure 7.5.1 Comparison of Old and New Degradation Factor for PTAC

0.0

0.2

0.4

0.6

0.8

1.0

Degradation Factor

Old (DOE­2 Supplement, DOE2.1E)

New (DOE­2.1E version 107)

7­22

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7.5.5 Fan Power Assumptions

The DOE­2.1E program can calculate the fan energy use by taking one parameter as

input to the PTAC and PTHP model, i.e., design full­load power of the supply fan per unit of

supply air flow rate in terms of Watts per cfm. To estimate the design full­load power of the

supply fan per unit of supply air flow rate, DOE reviewed major PTAC and PTHP

manufacturers’ catalogs. Table 7.5.1 summarizes the average PTAC and PTHP supply air flow

rate and supply fan power based on the review at full­load conditions, which was used in the

model.

DOE assumed the fan has two­speed control, low speed and high speed, based on the

manufacturers’ catalogs. In the energy model, a fan speed ratio of 0.83 was assumed for all

modeled representative equipment. This ratio was also based on the review of manufacturers’

catalogs.

Table 7.5.1 PTAC and PTHP Full­Load Supply Fan Flow Rate and Power Consumption

Representative Equipment Supply Air Flow Rate

(cfm)

Supply Fan Power

(W/cfm)

Standard Size PTAC and PTHP

9,000 Btu/h 275 0.27

Standard Size PTAC and PTHP

12,000 Btu/h 330 0.34

Non­Standard Size PTAC and

PTHP 395 0.44

7.5.6 Ventilation Rates

The chassis of the PTAC and PTHP has an outside air vent that supplies fresh air to the

space. DOE reviewed the manufacturers’ published vent air flow rate, as shown in terms of the

average vent air flow rate in Table 7.5.2. These values exceed the requirements in ASHRAE

Standard 62­2004, which sets a combined outside air rate of 5.0 cfm per person and 0.06 cfm/ft2

of the floor area for hotel/motel guest rooms. Because the manufacturers’ engineering

specifications indicate the outside air vent damper is fixed and not automatically adjustable for

the PTAC and PTHP equipment, DOE assumed the outside air flow rate in the model based on

the average manufacturers’ data in Table 7.5.2.

Table 7.5.2 PTAC and PTHP Ventilation Air Flow Rate

Representative Equipment Vent Air Flow Rate

(cfm)

Standard Size PTAC and PTHP

9,000 Btu/h 60

Standard Size PTAC and PTHP

12,000 Btu/h 65

Non­Standard Size PTAC and

PTHP 55

7­23

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7.6 SUMMARY OF RESULTS

For cooling and heating equipment, the annual energy use is a function of the heating and

cooling loads the equipment must meet. DOE used the DOE­2.1E hourly simulation program to

estimate building loads and annual energy use for the prototypical hotel/motel building for six

PTAC and PTHP representative equipment at various efficiency levels and all the 239 TMY2

stations in the United States.

7.6.1 Annual Energy Use Results

DOE weighted the annual energy consumption from the simulations for each of the

individual buildings at 239 TMY2 weather stations using weighting factors to scale the influence

of each TMY2 weather station on each state's results. The detailed methodology for developing

the weighting factors is discussed in appendix C. DOE further aggregated the energy use at state

level to national average energy use using the 2000 Census population data.27

The national average energy use estimates for each of the six representative equipment

analyzed is summarized in Table 7.6.1. The results shown here are for cooling and fan energy

use for PTACs and cooling, heating, and fan energy use for PTHPs, calculated in terms of kWh

of electric energy use per unit at various efficiency levels. The heating energy use for PTHPs

includes both compressor energy use for heating and heating energy use for supplemental

electric resistance. This metric allows examination of the improvement of equipment efficiency

on cooling and heating energy use for PTACs and PTHPs. Table 7.6.1 also shows the

percentage energy savings for each representative unit at maximum efficiency level (Level 5)

compared with baseline efficiency level. The savings range from 7.9 percent for 9,000 Btu/h

standard size PTAC unit to 12.2 percent for non­standard size PTAC unit.

Table 7.6.1 Annual National Average Energy Use for PTAC and PTHP Unit

Equipment Category

Representative

Cooling

Capacity

Annual National Average Energy Use per Unit

(kWh)*

Baseline Level 1 Level 2 Level 3 Level 4

Standard 9,000 Btu/h 1,045 1,026 1,013 1,001 990

PTAC

Size 12,000 Btu/h 1,317 1,294 1,279 1,264 1,251

NonStandard

Size

11,000 Btu/h 1,658 1,584 1,559 1,536 NA

Standard 9,000 Btu/h 2,063 2,013 1,984 1,957 1,945

PTHP

Size 12,000 Btu/h 2,467 2,406 2,370 2,356 2,343

NonStandard

Size

11,000 Btu/h 2,661 2,533 2,508 2,465 NA

* Annual national average energy use per unit refers to the cooling and fan electric energy use for PTAC unit, and

cooling, heating and fan electric energy use for PTHP unit.

7­24

 EERE-2007-BT-STD-0012 COMMENT 32
                           

                          

                            

                               

                                

                                   

                                      

                       

                                

                             

                               

                               

         

     

     

                        

Figure 7.6.1 and Figure 7.6.2 present the change of cooling and heating energy use,

respectively, at various efficiency levels simulated. As expected, energy use decreases as the

EER increases for all representative equipment. Again, here the energy use for PTAC includes

both cooling and fan energy and energy use for PTHP includes cooling, heating and fan energy

use. Because DOE did not consider a high­performance fan as one of the design options (see

Chapter 4), the slopes of the curves in the figures are entirely determined by the EER changes for

the PTAC and both the EER and COP changes for the PTHP. For both the PTAC and the PTHP

representative equipment, non­standard size units consume most energy and standard size 9,000

Btu/h units consume least energy at all efficiency levels as a result of several observations. The

PTHP with a cooling capacity of 9,000 Btu/h have the highest EER and COP and non­standard

size units have the lowest EER and COP, which determines the compressor energy use; on the

other hand, fan energy is greater for non­standard size units compared with standard size units as

shown in Table 7.5.1.

1,800

Standard PTAC 9,000 Btu/h

Standard PTAC 12,000 Btu/h 1,700

Non­Standard PTAC

1,600

1,500

1,400

1,300

1,200

1,100

1,000

900

800

PTAC Energy Use Per Unit (kWh)

8 9 10 11 12

EER

Figure 7.6.1 National Average Energy Use for PTAC at Various Efficiency Levels

7­25

 EERE-2007-BT-STD-0012 COMMENT 32
)

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Wk(

t

i

n

U

r

e

P

e

s

U

y

gr

e

n

E

P

H

T

P

2,800
 Standard PTHP 9,000  Btu/h
 

2,700 Standard PTHP 12,000  Btu/h

Non­Standard  PTHP

2,600

2,500

2,400

2,300

2,200

2,100

2,000

1,900

1,800

1,700

1,600

8 9 10 11 12

EER

Figure 7.6.2  National Average Energy Use for PTHP at Various Efficiency Levels 

Figure 7.6.3 shows the national average building electric energy use intensity (EUI), in 

kWh/sf­year, for each of the five major energy end­uses at the baseline efficiency for each of the 

six representative equipment simulated in this analysis.  These five major energy end­uses are 

lighting, plug loads, space heating, space cooling and fan.  This figure also shows the fractions of 

the whole­ building energy consumption for each of the five major energy end uses.  Based on 

the figure, it is observed that: 

(a) Lighting energy use is 34 percent to 41 percent and plug load is 11 percent to 14 percent 

of total building electric energy use.   

(b) Heating energy use for buildings using PTHP units is less than from PTAC units, because 

the PTHP units have higher heating efficiency than PTAC units.   

(c) Standard Size PTAC 12,000 Btu/h units consume more heating energy than 9,000 Btu/h 

units and non­standard size units because the heating load due to outside air ventilation is 

greater for 12,000 Btu/h units.   

(d) Non­standard size PTAC and PTHP equipment consume more fan energy than standard 

size equipment; this can be explained based on Table 7.5.1 with non­standard units 

having more supply flow and higher fan power. 

7­26 

 EERE-2007-BT-STD-0012 COMMENT 32
                        

                           

                         

                                

                         

                            

                                      

                                     

       

Lighting Plug Loads Heating Cooling Fan

16

14

Whole Building EUI (kWh/sf­year) 12

10

8

6

4

2

0

Standard PTAC, Standard PTAC, Non­Standard Standard PTHP, Standard PTHP, Non­Standard

9000 Btu/h 12000 Btu/h PTAC 9000 Btu/h 12000 Btu/h PTHP

12%

30%

13%

8%

30%

34% 34% 41%

11%

13%

11%

11%

25%

14%

16%

14%

23%

15%

8%

38%

12%

24%

15%

36%

11%

12%

21%

15%

16%

37%

Figure 7.6.3 National Average Building Electric Energy Use Intensity by Major End­Use

Figure 7.6.4 and Figure 7.6.5 show the frequency distributions of average energy use for

all PTAC and PTHP representative equipment respectively at baseline efficiency for 50 states

(cooling and fan energy for PTAC, cooling, heating and fan energy for PTHP). The shapes of

the distributions for different product products are similar, but with peak shifted for different

representative equipment. For standard size PTAC 9,000 Btu/h, energy use for most states (47

out of 50 states) is between 600 kWh per unit and 1600 kWh per unit. For standard size PTHP

9,000 Btu/h, energy use for most states (38 out of 50 states) is between 1500 kWh per unit and

2700 kWh per unit.

7­27

 EERE-2007-BT-STD-0012 COMMENT 32
     

     

     

                       

   

     

     

     

                       

   

               

                           

                              

                              

                           

                                

0

4

8

12

16

20

Frequency

Standard PTAC, 9000 Btu/h

Standard PTAC, 12000 Btu/h

Non­Standard PTAC

400 600 800	 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000

PTAC Energy Use (kWh/Unit)

Figure 7.6.4	 Frequency Distribution of State Average Energy Use for PTAC and Baseline

Efficiency Level

0

4

8

12

16

20

Frequency

Standard PTHP, 9000 Btu/h

Standard PTHP, 12000 Btu/h

Non­Standard PTHP

1200 1500 1800 2100 2400 2700 3000 3300 3600 3900 4200 4500 4800 5100

PTHP Energy Use (kWh/Unit)

Figure 7.6.5	 Frequency Distribution of State Average Energy Use for PTHP and Baseline

Efficiency Level

7.6.2 Comparison of Simulation Results to CBECS Calculated Data

DOE compared the EUIs from the building model simulations with those from the 2003

CBECS data to determine how close simulations came to real building data. The EUI is

calculated based on the national energy use for each product at baseline efficiency. The average

EUI for hotel/motel buildings in 2003 CBECS is derived from the electricity consumption data

and floor spaces for the 79 identified buildings as described in section 7.2.2. As shown in

7­28

 EERE-2007-BT-STD-0012 COMMENT 32
                                

                                  

                           

                            

              

       

                  

Figure 7.6.6, EUIs of simulations are close to the CBECS data. For standard size PTAC 9,000

Btu/h, the EUI of simulation is about 2.7 percent less than that from CBECS data. For standard

size PTAC 12,000 Btu/h and non­standard size PTAC, the EUIs are approximately 5 percent

higher than CBECS. The EUIs for PTHP representative equipment are 1.3 percent to 12.8

percent less than that from CBECS data.

16
 

14
 2003 CBECS
 

12
 

10
 

8
 

6
 

4
 

2
 

0
 Standard PTAC, Standard PTAC, Non­Standard Standard PTHP, Standard PTHP, Non­Standard

9000 Btu/h 12000 Btu/h PTAC 9000 Btu/h 12000 Btu/h PTHP

Figure 7.6.6 Comparison of EUI between Simulation and 2003 CBECS Whole Building EUI (kWh/sf­year)

7­29

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S. Gates. 1993. DOE­2 Supplement, Version 2.1E, LBL­34947, Lawrence Berkeley National

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(Last accessed January 15, 2007.)

4.	 Pacific Northwest National Laboratory, National Commercial Construction Characteristics

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Buildings Except Low­Rise Residential Buildings.” Atlanta, Georgia.

6.	 Somasundaram, S., P.R. Armstrong, D.B. Belzer, S.C. Gaines, D.L. Hadley, S. Katipamula,

D.L. Smith, D.W. Winiarski. 2000. Screening Analysis for EPACT­Covered Commercial

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11. E­Source.	 2001. High­Performance Glazing in Commercial Buildings Growing But Still

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12. ASHRAE.	 2005. Handbook of Fundamentals, American Society of Heating, Refrigerating

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14. ASHRAE. 1989.	 ASHRAE Standard 90.1­1989, Energy Efficient Design of New Building

Except Low­Rise Residential Buildings, American Society of Heating, Ventilating and AirConditioning Engineers, Inc., Atlanta, Georgia.

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16. Smith Travel Research, 2007. 2006 U.S. Lodging Industry Results.

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18. Taylor, Z.T. and R.G. Pratt.	 1990. Comparison of ELCAP Data with Lighting and

Equipment Load Levels and Profiles Assumed in Regional Models. PNL­7449, Pacific

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Efficiency Standards for Consumer Products: Clothes Washers, December 2000.

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25. Lawrence Berkeley National Laboratory.	 2000. Documentation Update Package #2

DOE­2.1E, Version 107. Lawrence Berkeley National Laboratory, University of California

at Berkeley, Berkeley, California.

26. Henderson, H.I., Y.J. Huang, and D. Parker.	 1999. Residential Equipment Part­Load

Curves for Use in DOE­2. LBNL­42175, February 1999.

27. The U.S. Census Bureau, 2000 Census,

http://factfinder.census.gov/servlet/GCTTable?_bm=y&­geo_id=01000US&­

_box_head_nbr=GCT­PH1&­context=gct&­ds_name=DEC_2000_SF1_U&­tree_id=4001&­

format=US­9. (Accessed on March 25, 2007.)

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