CHAPTER 7. ENERGY USE ANALYSIS

TABLE OF CONTENTS

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

7.2 EQUIPMENT ENERGY USE SAVINGS DETERMINATION.......................................7-1

7.2.1 Splitting Heating and Cooling Energy................................................................7-1

7.2.2 Adjusting for Climate Change ............................................................................7-2

7.2.3 Adjusting for Capacity and Energy Efficiency Ratio ........................................7-4

7.3 PTAC AND PTHP EQUIPMENT ENERGY USE RESULTS .........................................7-5

LIST OF TABLES

Table 7.3.1 Annual Energy Use by Equipment Class and Efficiency Level for PTACs.................. 7-6

Table 7.3.2 Annual Energy Use by Equipment Class and Efficiency Level for PTHPs.................. 7-6

LIST OF FIGURES

Figure 7.2.1 Comparison of cooling degree days by state for TMY3 and TMY2 ......................... 7-3

7-i 
CHAPTER 7. ENERGY USE ANALYSIS

7.1 INTRODUCTION 

Whole-building simulations from the 2008 packaged terminal air conditioning (PTAC) and 

packaged terminal heat pump (PTHP) equipment rulemaking provided annual unit energy consumption 

(UEC) data by cooling capacity and energy efficiency ratio (EER).1 These data are used for those 

equipment classes and efficiency levels that are the same in this rulemaking and adjusted for those that 

are different. This chapter describes the methodology used to adjust the unit energy consumption of 

PTAC and PTHP equipment for this rulemaking.

7.2 EQUIPMENT ENERGY USE SAVINGS DETERMINATION 

Whole-building simulations in the previous rulemaking were performed on PTACs and PTHPs for

four equipment classes, six efficiency levels, and 51 locations (the U.S. States and the District of 

Columbia). The four equipment classes consist of combinations of PTAC and PTHP equipment and of 

representative cooling capacities, namely 9,000 Btu/h and 12,000 Btu/h. As whole-building simulations 

are an excellent approach to obtain UEC data, the 1,224 annual UECs data points were leveraged for this 

rulemaking.

The current rulemaking considers a set of capacities and efficiency levels that differs from that in 

the previous rulemaking. In order to make relevant the UECs, three transformations were performed: 

splitting heating and cooling energy, adjusting for climate change, and adjusting for capacity and EER.

7.2.1 Splitting Heating and Cooling Energy

The first transformation prepares the UEC for the following two transformations. As the total 

annual UECs, UECtotal, capture both a cooling and heating energy portion, the UEC was split into 

UECcooling and UECheating. The U.S. Department of Energy (DOE) is aware that PTACs and PTHPs have 

slight differences in function and performance. However, PTACs and PTHPs have a similar functionality 

other than a reversing valve. In addition, insufficient data exist highlighting substantial differences in 

cooling energy consumption. For these reasons, DOE assumed that the UEC of a PTAC is equal to the 

energy expended during a PTHP’s operation in cooling mode, assuming that the equipment has the 

same efficiency level and capacity, as shown in Eq. 7.2.1. The remaining energy of a PTHP, which is the 

difference between the total UEC and the cooling energy, as shown in Eq. 7.2.2, is the heating energy:

7-1 
UECPTAC = UECPTHP_cooling Eq. 7.2.1

UECtotal = UECheating + UECcooling Eq. 7.2.2

It was assumed that the fan energy during periods of cooling was included with the cooling 

energy and the fan energy during periods of heating was included with the heating energy. It was also 

assumed that the fan energy during periods of cooling scaled with the cooling energy and the fan energy 

during periods of heating scaled with the heating energy. 

7.2.2 Adjusting for Climate Change

The second transformation adjusts for the projected impact of global warming on hotter 

summer days and warmer winter days. An adjustment to the unit cooling energy consumption and unit 

heating energy consumption was made based on the change in cooling degree days (CDD) and heating 

degree days (HDD) from an older TMY2 (Typical Meteorological Year) weather dataset to a newer TMY3 

weather dataset, which was updated in 2008.

2,3 A comparison of the two datasets showed that total 

annual CDD have increased by 5% and total annual HDD have increased by 2% at all locations used in 

this analysis, as shown in Figure 7.2.1. 

7-2 
Figure 7.2.1 Comparison of cooling degree days by state for TMY3 and TMY2

The figure shows the cooling degree days (CDD) relative to 65 °F computed from the TMY3 data 

vs. the CDD for TMY2. The calculation is done separately for day time (8 am to 8pm) and night time 

hours. Each point corresponds to a state; in cases where there are multiple stations in a single state the 

data are averaged. As the TMY3 data are considered to be more representative of current weather, the 

total annual CDD increase and total annual HDD increase were assigned to the weather multipliers, Wc

and Wh, for cooling and heating, respectively, and were applied to the separated cooling and heating 

UECs in the manner as shown in Eq. 7.2.3 and Eq. 7.2.4: 

UECcooling_weather = (1 + Wc) ∙ UECcooling Eq. 7.2.3

UECheating_weather = (1 + Wh) ∙ UECheating Eq. 7.2.4

7-3 
7.2.3 Adjusting for Capacity and Energy Efficiency Ratio 

The third transformation accounts for adjustments of cooling capacity and/or EER values that 

differ from those in the previous rulemaking (source) to those considered in the current rulemaking 

(target). UECcooling_weather for each equipment class and each efficiency level was linearly scaled from 

source to target cooling capacity and/or EER. If the UEC only changed with cooling capacity, DOE 

performed a linear interpolation across a constant EER value; this operation is highlighted in Eq. 7.2.5. If 

the UEC only changed with EER, DOE performed a linear interpolation across a constant cooling capacity 

value; this operation is highlighted in Eq. 7.2.6. If the UEC changed with both cooling capacity and EER, 

DOE performed a linear interpolation across both variables, one at a time, one after another, using the 

equations as already set forth in Eq. 7.2.5 and Eq. 7.2.6. Similarly, for heating energy, DOE accounted for 

differences in coefficient of performance (COP) by linearly scaling UECheating_weather, at a constant 

cooling capacity, for each equipment class and each efficiency level, from source to target COP, as 

shown in Eq. 7.2.7. 

UECtarget = UECsource1 + (UECsource2 − UECsource1) � Capacitytarget-Capacitysource1

Capacitysource2-Capacitysource1��

constant EER

 

Eq. 7.2.5

Where: 

UECtarget = interpolated unit energy consumption at the target cooling capacity, 

UECsource1= unit energy consumption at the source cooling capacity, for the first

point of the interpolation, 

UECsource2= unit energy consumption at the source cooling capacity, for the second 

point of the interpolation, 

Capacitytarget= target cooling capacity, 

Capacitysource1= source cooling capacity for the first point of the interpolation, and

Capacitysource2= source cooling capacity for the second point of the interpolation. 

UECtarget = UECsource1 + (UECsource2 − UECsource1) � EERtarget−EERsource1

EERsource2−EERsource1

��

constant cooling capacity

 

Eq. 7.2.6

Where: 

UECtarget = interpolated unit energy consumption at the target cooling capacity, 

7-4 
UECsource1= unit energy consumption at the source cooling capacity, for the first 

point of the interpolation,

UECsource2= unit energy consumption at the source cooling capacity, for the second 

point of the interpolation,

EERtarget= target EER,

EERsource1= source EER for the first point of the interpolation, and

EERsource2= source EER for the second point of the interpolation.

UECtarget = UECsource1 + (UECsource2 − UECsource1) � COPtarget−COPsource1

COPsource2−COPsource1

��

constant cooling capacity

 

Eq. 7.2.7

Where: 

UECtarget = interpolated unit energy consumption at the target cooling capacity, 

UECsource1= unit energy consumption at the source cooling capacity, for the first 

point of the interpolation,

UECsource2= unit energy consumption at the source cooling capacity, for the second 

point of the interpolation,

COPtarget= target COP,

COPsource1= source COP for the first point of the interpolation, and

COPsource2= source COP for the second point of the interpolation.

7.3 PTAC AND PTHP EQUIPMENT ENERGY USE RESULTS

DOE summed the cooling energy and heating energy, upon completion of the 

transformations, to give the total UEC. The U.S. average UECs for each of the considered

capacities and EERs are provided in Table 7.3.1 for PTACs and Table 7.3.2 for PTHPs. The 

UECs disaggregated by the 51 locations are presented in Appendix 7-A.

7-5 
Table 7.3.1 Annual Energy Use by Equipment Class and Efficiency Level for PTACs

Efficiency 

Level

>7,000 Btu/h >7,000 Btu/h and < 

15,000 Btu/h >15,000 Btu/h

EER

UEC

(kWh) EER

UEC

(kWh) EER

UEC

(kWh)

0* 11.7 892 11.1 1078 9.3 1688

1† 11.9 881 11.3 1066 9.5 1671

2 12.2 866 11.5 1050 9.7 1657

3 12.6 839 12.0 1022 10.0 1625

4 13.1 813 12.4 994 10.4 1594

5 13.6 786 12.9 966 10.8 1563

6 13.8 773 13.1 952 11.0 1547

* This level represents the Federal minimum. † This level represents the ANSI/ASHRAE/IES Standard 90.1-2013 minimum for this equipment type.

Table 7.3.2 Annual Energy Use by Equipment Class and Efficiency Level for PTHPs

Efficiency Level

>7,000 Btu/h >7,000 Btu/h and < 

15,000 Btu/h >15,000 Btu/h

EER

COP

UEC

(kWh)

EER

COP

UEC

(kWh)

EER

COP

UEC

(kWh)

0* 

11.9

3.3

1728

11.3

3.2

1985

9.5

2.9

2847

1 

12.2

3.5

1708

11.5

3.3

1956

9.7

2.9

2829

2 

12.6

3.5

1674

12

3.4

1918

10

3 

2778

3 

13.1

3.6

1639

12.4

3.5

1879

10.4

3.1

2727

4 

13.6

3.7

1605

12.9

3.6

1841

10.8

3.2

2676

5 

13.8

3.8

1588

13.1

3.6

1822

11

3.2

2651

* This level represents the Federal minimum and the ANSI/ASHRAE/IES Standard 90.1-2013 minimum for this 

equipment type.

7-6 
REFERENCES

1. U.S. Department of Energy – Office of Energy Efficiency and Renewable Energy, 

Energy Conservation Program for Commercial and Industrial Equipment: Packaged 

Terminal Air Conditioner and Packaged Terminal Heat Pump Energy Conservation 

Standards., 2007. (Last accessed June, 2014.) 

<http://www.regulations.gov/#!docketDetail;D=EERE-2007-BT-STD-0012>

2. National Renewable Energy Laboratory, National Solar Radiation Data Base 1961-1990: 

Typical Meterological Year 2, (Last accessed June, 2014.) 

<http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/tmy2/>

3. National Renewable Energy Laboratory, National Solar Radiation Data Base 1991-2005 

Update: Typical Meterological Year 3, (Last accessed June, 2014.) 

<http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/>

7-7