7-i

CHAPTER 7. ENERGY USE ANALYSIS

TABLE OF CONTENTS

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

7.2 SURVEY SAMPLES....................................................................................................... 7-2

7.2.1 Sample for Residential Applications ............................................................................... 7-2

7.2.2 Sample for Commercial Applications.............................................................................. 7-3

7.3 ESTIMATES OF ENERGY USE.................................................................................... 7-3

7.3.1 Weather Station Assignment............................................................................................ 7-5

7.3.2 Baseline Operating Hours................................................................................................ 7-5

7.3.2.1 Residential Applications................................................................................ 7-5

7.3.2.2 Commercial Applications .............................................................................. 7-6

7.3.3 Operating Hours at a Higher Efficiency Level ................................................................ 7-8

7.3.4 Upper Limit on Total Operating Hours ........................................................................... 7-9

7.3.5 Variability in Annual Energy Consumption .................................................................... 7-9

7.3.6 Average Annual Energy Consumption by Efficiency Level ......................................... 7-11

7.3.7 Estimating Energy Use by Month.................................................................................. 7-11

LIST OF TABLES

Table 7.2.1 RECS 2009 Records Used for Residential Portable AC Sample......................... 7-2

Table 7.2.2 CBECS 2003 Records Used for Commercial Portable AC Sample .................... 7-3

Table 7.3.1 Regression Equations........................................................................................... 7-8

Table 7.3.2 Portable Air Conditioners: Average Annual Energy Use .................................. 7-11

LIST OF FIGURES

Figure 7.3.1 Number of Hours that Exceed ANSI/ASHRAE Standard 55 as a Function 

of Cooling Degree-Days...................................................................................... 7-7

Figure 7.3.2 Range of Annual Energy Use for Portable Air Conditioners in the 

Residential Sector .............................................................................................. 7-10

Figure 7.3.3 Range of Annual Energy Use for Portable Air Conditioners in the 

Commercial Sector............................................................................................. 7-10
7-1

CHAPTER 7. ENERGY USE ANALYSIS

7.1 INTRODUCTION

When the U.S. Department of Energy (DOE) carries out a life-cycle cost (LCC) and 

payback period (PBP) analysis, it must determine the operating cost savings consumers will 

derive from more efficient products. This chapter describes how DOE calculated the annual 

energy consumption of portable ACs for use in the LCC and PBP analysis, which is described in 

chapter 8.

The engineering analysis summarized in chapter 5 reports portable AC energy use based 

on the proposed DOE test procedure. The test procedure provides standardized results that help

compare the performance of various units operating under the same conditions. A unit’s usage in 

the field, however, will differ from the test procedure results depending on the conditions in 

which the appliance is operated. To establish a reasonable range of real-world energy 

consumption for portable ACs in residential applications, DOE relied largely on data from the 

Energy Information Administration (EIA)’s 2009 Residential Energy Consumption Survey

(RECS 2009).1 The RECS survey is a national sample of housing units to collect statistical 

information on residential energy consumption and expenditures across the nation, along with 

data on energy-related characteristics of the housing units and occupants. The EIA constructed 

RECS 2009, which collected energy-related data for 12,083 housing units, to represent the 

household population of the United States.

Although almost all portable ACs are used in residences, a few are used in commercial 

settings. To calculate the energy use patterns of portable ACs in commercial applications, DOE 

relied largely on data from the EIA’s 2003 Commercial Building Energy Consumption Survey

(CBECS 2003).

2 The EIA constructed CBECS 2003, which collected energy-related data for 

5,215 buildings, to represent the commercial building stock in the United States.

Although RECS 2009 and CBECS 2003 collected no data on portable ACs, both surveys 

collected data on room air-conditioners. For this preliminary analysis, DOE assumed that the 

subsample of users who own and operate room ACs are representative of owners of portable air 

conditioning units. The details of each survey sample are described in the following sections.
7-2

7.2 SURVEY SAMPLES

The following sections describe the data DOE examined to develop an understanding of 

portable AC usage and energy use in both residential and commercial applications. The data 

represent window- or wall-mounted room ACs, which DOE assumes are used in the same way as 

are portable ACs.

7.2.1 Sample for Residential Applications

DOE assumed that the ownership of a window- or wall- mounted AC in RECS 2009 

could be used to approximate ownership of a portable AC. DOE selected the subset of RECS 

2009 records that met the following criteria.

 At least one room AC was present in the household.

 The energy consumption of the room AC was greater than zero.

 The capacity of the room AC was less than 14,000 Btu/hr (a cooling capacity

comparable to portable ACs as measured by industry test methods).

 The room being cooled measured no more than 1,000 square feet.

0 provides details about the RECS 2009 records used to represent portable ACs. DOE 

used EIA’s weightings for each RECS 2009 household in the sample. The weightings indicate 

how frequently each household configuration occurs in the general population. Although the 

total number of households and portable ACs presented in 0 correspond to room ACs in RECS 

2009, DOE believes the weightings associated with each household represent the relative 

frequency of a household with a potential portable AC installation.

0 RECS 2009 Records Used for Residential Portable AC Sample

No. of 

Records

No. of U.S. 

Households 

Represented 

million

No. of Portable

ACs

Represented 

million

2,378 23.2 46.4

Sizing charts provided by vendors indicate that portable ACs are intended to cool rooms 

having an area as large as approximately 525 to 600 square feet.3, 4 A review of retail websites, 

however, indicated portable ACs may be used in rooms as large as 1,000 square feet. DOE 

assumed 1,000 square feet to be the maximum room size a user would attempt to cool using a 

portable AC. In practice, only 60 records in the RECS 2009 sample (about 2 percent) represent

rooms between 600 and 1,000 square feet.
7-3

7.2.2 Sample for Commercial Applications

DOE assumed that the ownership of a window- or wall- mounted room AC in CBECS 

2003 could be used to approximate ownership of a portable AC. DOE selected the subset of 

CBECS 2003 records that met all of the following criteria.

 A room AC served as a source of air conditioning.a

 The building was not vacant.

 A room AC was used as the primary equipment to cool at least part of the 

building.

 The area being cooled measured less than 1,000 square feet.

CBECS 2003 provides the total air conditioned square footage and the fraction of 

conditioning provided by a room AC for each building record, but it does not provide the number 

of room ACs in a given building. DOE therefore used the total conditioned square footage to 

determine its sample. DOE assumed that a residential room AC would be used only in rooms

measuring less than 1,000 square feet. 0 shows the number of CBECS 2003 records DOE used in 

its sample. DOE used EIA’s weightings for each CBECS 2003 building in the sample. The 

weightings indicate how frequently each building configuration occurs throughout the United 

States.

0 CBECS 2003 Records Used for Commercial Portable AC Sample

No. of 

Records

No. of U.S. Buildings 

Represented million

91 0.12

7.3 ESTIMATES OF ENERGY USE 

DOE calculated the annual energy consumption of a portable AC using the following 

equation.

PACENERGY = (

Total Hours of Use

Year ) ×

[(

Capacity × XCOOL

EER ) (

1

1000) + (XFan × kWFan) + (XStby × kWstby)]

Where:

 

a Packaged terminal air conditioning (PTAC) systems also could be listed as room ACs, so DOE focused on

selecting buildings having only room ACs. A building was considered to have a room AC if it did not have a PTAC 

type of heating system.
7-4

PACENERGY = annual energy consumption of portable AC (kWh/year),

Total Hours of Use

Year

= number of hours the portable AC is used per year (at > 0 W),

Capacity = rated capacity in Btu/hr as measured by the test procedure for 

portable ACs,

EER = energy efficiency ratio (Btu/hr/W),

XCool = fraction of time in cooling mode,

XFan = fraction of time in fan-only mode,

XStby = fraction of time in standby mode,

kWFan = power consumption (in kW) of fan-only mode, and

kWStby = power consumption (in kW) of standby/off mode.

For this preliminary analysis, DOE lacked data on operating hours associated with 

portable ACs. To estimate those operating hours, DOE utilized data for room ACs as presented 

in its Final Rule for Room Air Conditioners (2011).5 Furthermore, DOE made the following 

assumptions for its energy use analysis.

 The portable AC was installed according to manufacturer instructions (for example, a 

dual-duct unit would have both ducts properly installed and insulated).

 The number of operating hours spent in cooling mode for a window- or wall-mounted 

room AC in a RECS household or a CBECS enterprise could be used to approximate 

the hours a baseline portable AC spends in cooling mode.

 The upper limit of total hours in either cooling or fan-only mode was estimated 

assuming that a portable AC would be operated only in months having 5 or more 

cooling-degree days that exceed 65 °F.

 For rooms measuring less than 250 square feet, the portable AC setpoint can be 

reached (the cooling load is constant), and operating hours would decrease with a 

higher-capacity portable AC.

 For rooms measuring 250 square feet or more, the cooling load could not be met by 

increasing the capacity of the portable AC and, therefore, cooling operation would 

continue until the user turned off the unit. The operating hours spent in cooling mode 

would remain constant for any portable AC operating at any efficiency level. 

 The average capacity at a given efficiency level can be used to represent the full 

range of capacities at that efficiency level.

CBECS 2003 does not report annual energy consumption of portable air conditioners, so 

DOE estimated the energy consumption using (1) variables specific to each building in the 

sample and (2) data on cooling degree-days. DOE used the calculation methodology described in 

its Final Rule for Room ACs (2011).

5

An additional factor in DOE’s energy use analysis was the square footage of the room the 

portable AC attempts to cool. In cases where the baseline portable AC adequately meets the 

cooling load of a room, a higher-capacity unit will reduce the hours of operation in cooling 
7-5

mode. If the baseline unit cannot handle the cooling load, however, field-metering data indicate 

the compressor will remain running until a user turns the unit off (Burke, et al., 2014).6

Below, DOE describes in greater detail the method used to calculate annual energy 

consumption of portable ACs.

7.3.1 Weather Station Assignment

DOE began by assigning each RECS household or CBECS enterprise that used a room 

AC to one of the 321 weather stations operated by the National Oceanic and Atmospheric 

Administration (NOAA).7 DOE identified the weather station that best matched the heating and 

cooling degree-days (CDD) of the RECS 2009 household or the CBECS 2003 building (see 

appendix 7-A for more details). The weather data were used to constrain the hours of AC 

operation. In addition, regional energy prices were weighted to summer months, when portable 

ACs likely would be used.

7.3.2 Baseline Operating Hours

This section describes DOE’s estimate of operating hours for baseline portable ACs used 

in both residential and commercial applications.

7.3.2.1 Residential Applications

DOE estimated the number of hours a baseline portable AC operates in cooling mode 

based on data for room ACs operating in cooling mode. DOE began with the data reported by 

RECS 2009 on the annual energy consumption (field energy consumption) for room air 

conditioning, referred to as FEC(all)RECS. The reported end-use quantities were not based on 

metering of individual appliances; rather, EIA used a regression technique to estimate how much 

of each household’s total annual electricity consumption was attributable to each end-use 

category.b

RECS 2009 reports the number of room ACs in each household. Of all homes that use a 

room AC, 32 percent have two room ACs, and 20 percent have three or more units. To estimate 

the energy consumption of a single room AC, referred to as FECRECS, DOE divided FEC(all)RECS 

by the reported number of room ACs. For houses having both central air conditioning and room

AC, DOE scaled FEC(all)RECS using a relative use factor. Although each portable AC in a home 

may be utilized for a different amount of time, DOE has no way to estimate such differences.

DOE calculated the annual cooling-mode operating hours for each portable AC in each 

residential sample using the following formula based on room AC methodology.

 

b The desire to use numerous independent variables without using a large number of interaction terms and the desire 

to adapt the regression procedures to account for heteroscedastic error terms led EIA to use a nonlinear regression 

technique. For more information, see: http://www.eia.doe.gov/pub/consumption/residential/append_c.pdf.
7-6

BldgShellAdj CDDAdj

Capacity

FEC EER OH RECS RECS * *



Where:

OH = operating hours per year,

FECRECS = estimated field energy consumption for the room AC,

EERRECS = estimated EER of the room AC,

Capacity = capacity of the room AC in Btu/hr,

BldgShellAdj = adjustment for building shell efficiency in 2019 (%), and

CDDAdj = adjustment for cooling degree days (Btu/hr).

The derivation of FECRECS was discussed above. The capacity of the room AC is given 

by the representative product class analyzed in the Room AC Final Rule (2011).

5 So that the 

estimated operating hours could represent future conditions, DOE used the 2019 building shell 

index factor of 0.97 for space cooling in all residences from the EIA’s Annual Energy Outlook

2014.8 DOE also used the 115-year historical average cooling degree-days (CDD) by census 

division. Applying the building shell index factor decreased energy use by 3 percent; the CDD 

adjustment factor decreased energy use by 10 percent on average. 

DOE estimated the EER of the room AC in each sample household by matching the 

reported age of the unit with the average EER for the reported product class in the year of its 

vintage. DOE assumed a uniform distribution within each vintage bin, and assigned an age to the 

room AC in each RECS 2009 household. DOE calculated scalars for each year based on the ratio 

of the total shipments-weighted EER for that year to the calculated EER, then applied those 

scalars to the minimum efficiency required in each year. 

Based on an initial analysis of field-metering data, DOE assumed that hours of portable 

AC operation in fan-only mode were 30 percent of hours spent in cooling mode.6 The sum of the 

cooling-mode and fan-only mode hours of operation give the total hours a portable AC is in use.

The estimated mean operating hours for a portable AC is 586 in cooling mode and 176 in fanonly mode, for 762 total operating hours.

7.3.2.2 Commercial Applications

DOE calculated annual operating hours for portable ACs in the commercial sector using 

the method presented in the Room AC Final Rule (2011).5 DOE calculated the annual operating 

hours for each commercial-sector portable AC in its sample by establishing a relationship 

between CDD and operating hours for various combinations of building type and building

schedule. DOE assumed that a portable AC is operated when outdoor air conditions exceed the 

comfort zone described by ANSI/ASHRAE Standard 55-2004.9 To estimate how often those 

outdoor conditions are exceeded, DOE used the following equation.

OH55 = (a * CDD) + b
7-7

Where:

OH55 = average annual hours when outdoor air conditions exceed the ASHRAE 

Standard 55 comfort zone,

CDD = number of annual cooling degree-days (in excess of 65 °F) for a given 

location, and

a and b = linear fit parameters.

DOE used data on CDDs from the National Solar Radiation Database (NSRDB) for 

1991–2010.

10 This database is an hourly ground-based set of solar and meteorological fields for 

1,454 stations (see appendix 7-B for more details). There is a complete 15-year for 858 of the 

1,454 stations. After removing the NSRDB sites in Hawaii, Guam, and the Caribbean islands, 

DOE performed regressions to predict the hours per year that exceed ASHRAE Standard 55 

based on the number of CDDs for each year. The data points and regression lines are shown in 

Figure 7.3.1 for all hours of the year. Each data point represents 15 years’ of data for 842 

NSRDB sites in the continental United States.

Figure 7.3.1 Number of Hours that Exceed ANSI/ASHRAE 

Standard 55 as a Function of Cooling Degree-Days

As Figure 7.3.1 illustrates, the data patterns differ for desert locations, where humidity 

does not affect comfort. The regression equations developed from the data are presented in 0.

CLDD vs #hours > ASHRAE Std55 

all day, all year 1991-2005

y = 2.7592x + 127.99

R

2

 = 0.9224

y = 1.153x + 574.04

R

2

 = 0.8714

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 500 1000 1500 2000 2500 3000 3500

CLDD (base 65F)

hours/year above ASHRAE Std 55

non-desert

desert

Linear (non-desert)

Linear (desert)
7-8

0 Regression Equations

Region Equation R2 No. of Sites

Non-desert OH55 = 2.759 x CLDD + 127.99 0.9224 809

Desert OH55 = 1.153 x CLDD + 574.04 0.8714 33

For a given location, the annual number of hours that exceed the ASHRAE Standard 55 

comfort zone varies by building schedule, which indicates the time that a building is open or in 

use. DOE performed the regression for many combinations of building type and schedule, 

yielding somewhat different equations for each combination. The building types included were

assembly, education, food service, office, retail, and warehouse. For each building type, DOE 

estimated operating hours for the following schedules: (1) open 24 hours a day and 7 days a 

week; (2) open business hours Monday through Friday; (3) open business hours Monday through 

Saturday; (4) open business hours Monday through Friday and Sunday; (5) open business hours 

all week. Each schedule yielded a variation of the above equations.

To estimate the operating hours of room ACs for each building in the CBECS 2003

sample having a room AC, DOE identified the building type and schedule using information 

provided by CBECS, then used the appropriate equation (non-desert or desert) combined with 

the number of CDDs for the location of the building. DOE used a scaling factor to adjust the 

results to account for the difference between the number of building operating hours assumed for 

deriving the equations and the building operating hours reported by the CBECS 2003.

The above approach provides a ‘best guess’ of the operating hours for the portable AC in

a particular CBECS building. Operating hours are affected by some factors not included in the 

analysis, however, such as interior heat gains from equipment or people and solar gains. To 

develop a range for the number of operating hours for the portable AC in each sample building, 

DOE added an error band to the value derived using a regression equation. The error band 

includes values that are ± 10 percent from the regression line for the appropriate combination of 

building type and schedule. Operating hours for portable ACs in the commercial sector were 

estimated based on the cooling climate in 2003. To match the 115-year average CDD values, 

DOE decreased the estimated operating hours in the commercial sector by 2 percent on average.

Based on an initial analysis of field-metering data, hours of operation of portable ACs in 

fan-only mode were assumed to be 30 percent of the hours of operation in cooling mode (Burke

et al.).

6 DOE calculated the mean number of operating hours as 1,388 in cooling mode and 400 

in fan-mode only, for a total of 1,788 operating hours.

7.3.3 Operating Hours at a Higher Efficiency Level

DOE determined that a portable AC’s operating hours by mode at a higher efficiency 

level will depend on whether the baseline portable AC adequately cools the room in which it is 

located. If the baseline portable AC does not meet the cooling demand of the room, a highercapacity portable AC will not reduce the hours spent in cooling mode. A study conducted by 

Consumer Reports

11 found that portable ACs tested in a 250-square-foot room labored to provide 

adequate cooling. Based on that study, DOE assumed that households using a higher-efficiency 
7-9

(and thus higher-capacity) portable AC in a room measuring less than 250 square feet would 

experience a reduction in hours of operation in cooling mode, assuming a fixed cooling load. In 

areas that measure 250 square feet or more, the hours spent in each mode would not change at

any efficiency level, because no portable AC could cool the room adequately.

In cases where a baseline portable AC is cooling a space adequately (i.e., installations in 

rooms smaller than 250 square feet), DOE assumed that a higher-capacity unit would operate in 

cooling mode for a reduced number of hours based on the ratios of cooling capacity:

OHCooling,STD = OHCooling,BASE (

CapacityBASE

CapacitySTD

)

The hours of operation not spent in cooling mode were assigned to fan-only mode:

OHFan mode,STD = OHFan mode,BASE + (OHCooling,BASE − OHCooling,STD)

In cases where a baseline portable AC cannot cool a room adequately (i.e., installations in 

rooms measuring 250 square feet or more), DOE assumed that the hours of operation in all 

modes would remain the same no matter the capacity of the portable AC.

7.3.4 Upper Limit on Total Operating Hours

The climate data obtained from NOAA’s National Climatic Data Center helped DOE 

determine the maximum amount of time a portable AC would be operated annually. The data 

also helped DOE apportion the annual electricity use for portable ACs operating in various 

geographic areas among the months of the year. DOE assumed that a portable AC would be 

operated only in months having 5 or more cooling-degree days that exceed 65 °F. DOE 

confirmed that the calculated combined hours of operation in cooling and fan-only mode were 

less than the upper limit derived from months having 5 or more CDDs. In cases where the hours 

of operation exceeded the upper limit, DOE set the hours of operation equal to the upper limit.

7.3.5 Variability in Annual Energy Consumption

Error! Reference source not found. and Figure 7.3.3 show the range of average annual 

energy consumption by efficiency level for portable ACs within DOE’s residential and 

commercial samples. In the figures, the blue box represents values within 25 percent to 75

percent of the distribution, and the "whiskers" extend from 5 percent to 95 percent of the 

distribution. The red line indicates the median value, and the red circle indicates the average. The 

figures illustrate the greater utilization of portable ACs in the commercial sector.
7-10

Figure 7.3.2 Range of Annual Energy Use for Portable Air 

Conditioners in the Residential Sector

Figure 7.3.3 Range of Annual Energy Use for Portable Air

Conditioners in the Commercial Sector
7-11

7.3.6 Average Annual Energy Consumption by Efficiency Level

0 shows the efficiency levels of baseline portable ACs and the levels DOE is considering 

for potential standards. The considered efficiency levels are in terms of cooling energy efficiency 

ratio (EERcm). Also shown are the corresponding average annual energy consumptions calculated 

for both the residential and commercial sectors.

0 Portable Air Conditioners: Average Annual Energy Use 

Efficiency 

Level

Efficiency

EERcm

Residential

Sector kWh

Commercial

Sector kWh

Baseline 2.08 724 1,713

1 3.53 525 1,411

2 4.32 473 1,330

3 5.28 434 1,274

4 5.82 400 1,173

7.3.7 Estimating Energy Use by Month

Portable AC use occurs primarily in the warm months of the year. In conducting the LCC 

analysis for portable ACs (see chapter 8), DOE used monthly electricity prices because 

electricity tariffs show seasonal variation in many areas of the country. Therefore, to properly 

calculate operating costs for portable ACs, DOE needed to estimate how the annual portable AC

electricity use for each sample household or business is apportioned over the year.

To estimate portable AC electricity use by month, DOE utilized data on seasonal climate 

variation, as measured by cooling degree-days. RECS 2009 provides data on yearly heating and 

cooling degree-days for each household in the sample, but does not break down the information 

by month. To estimate monthly CDDs for the households in the RECS sample, DOE matched

each household with the NOAA weather station that had the most similar climate based on 

cooling and heating degree-days. After matching a household to a weather station, DOE utilized 

the monthly CDD data from the weather station to estimate the relative number of coolingdegree days by month (see appendix 7-B for more details). DOE divided the number of coolingdegree days in each month by the total number of CDDs in the year for that weather station. 

DOE assumed that each month’s percentage of cooling-degree days reflects the appropriate 

weighting of electricity usage and price for that month. 
7-12

REFERENCES

 

1 U.S. Department of Energy–Energy Information Administration. Residential Energy 

Consumption Survey:2009 RECS Survey Data. 2009. (Last accessed September 8, 2014.) 

<http://www.eia.gov/consumption/residential/data/2009/>

2 U.S. Department of Energy–Energy Information Administration. Commercial Buildings 

Energy Consumption Survey. 2003. (Last accessed September 8, 2014.) 

<http://www.eia.gov/consumption/commercial/data/2003/>

3 Air & Water, the Portable Appliance Experts. What Size Portable Air Conditioner do You 

Need? (Last accessed September 8, 2014.) <http://www.air-n-water.com/portable-acsize.htm>.

4 The Home Depot. (Last accessed September 3, 2014.) 

<http://www.homedepot.com/c/air_conditioners_HT_BG_AP>.

5 U.S. Department of Energy–Office of Energy Efficiency and Renewable Energy. Energy 

Conservation Program for Consumer Products: Energy Conservation Standards for 

Clothes Dryers and Room Air Conditioners; Final Rule. 10 CFR Part 430. Federal 

Register. August 19, 2011. Vol. 76, no.164: pp. 52854–52862. (Last accessed September 

8, 2014.) <http://www.regulations.gov/#!documentDetail;D=EERE-2007-BT-STD-0010-

0067>.

6 T. Burke, et al., Using Field-Metered Data to Quantify Annual Energy Use of Portable 

Air Conditioners, Lawrence Berkeley National Laboratory, Report No. LBNL-6868E 

(December 2014). Available at: <www.osti.gov/scitech/servlets/purl/1166989>.

7 NOAA Data. National Climatic Data Center (NCDC). <http://www.ncdc.noaa.gov/dataaccess/land-based-station-data/land-based-datasets/quality-controlled-localclimatological-data-qclcd>.

8 Energy Information Administration. Annual Energy Outlook 2014 with Projections to 

2014. Building Shell Index Factor. April 2014.

9 American National Standards Institute & American Society of Heating, Refrigeration, 

and Air-Conditioning Engineers, Inc. ANSI/ASHRAE 55-2004 Thermal Environmental 

Conditions for Human Occupancy. 2004.

10 National Renewable Energy Laboratory. National Solar Radiation Database 1991–2005 

Update: User’s Manual. 2007. <http://www.nrel.gov/docs/fy07osti/41364.pdf>.

11 Consumer Reports. Are Portable Air Conditioner Claims a Lot of Hot Air? Published 

online June 12, 2014. (Last accessed June 12, August 31, 2014.) 

<http://www.consumerreports.org/cro/news/2014/06/are-portableair-conditioner-claimsa-lot-of-hot-air/index.htm>.