*>ILE COPY

IMBSIR 77-1271

Method of Testing, Rating and

Estimating the Seasonal

Performance of Central AirConditioners and Heat Pumps

Operating in the Cooling Mode

Mechanical Systems Program

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington. D C 20234

April 1978

Final Report

Sponsored by

The Department of Energy

12th and Pennsylvania Ave.. NW

Washington, D.C. 20461

G E Kelly

W H. Parken, Jr

NBSIR 77-1271

METHOD OF TESTING, RATING AND

ESTIMATING THE SEASONAL

PERFORMANCE OF CENTRAL AIRCONDITIONERS AND HEAT PUMPS

OPERATING IN THE COOLING MODE

G. E. Kelly

W. H. Parken, Jr.

Mechanical Systems Program

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, D C 20234

April 1978

Final Report

Sponsored by

The Department of Energy

12th and Pennsylvania Ave., NW

Washington, D.C. 20461

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kraps, Secretary

Dr. Sidney Harman. Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Director

Table of Contents

Section Page

1 . Scope and Purpose 1

1.1 Development of Recommended Test Procedures 2

1.1.1 Development of Recommended Test Procedures

for Determining Cyclic Performance 3

1.1.2 Development of Test Procedures which Allow

for Variations in Unit Design 6

1.2 Development of the Calculation Procedure for

Estimating Seasonal Performance and Seasonal

Cost of Operation 8

2. Recommended Testing and Rating Requirements 14

2.1 General 14

2.1.1 Requirements for Units with Single-Speed Compressors

and Single-Speed Condenser Fans 17

2.1.2 Requirements for Units with Single-Speed Compressors

and Multiple-Speed Condenser Fans 19

2.1.3 Requirements for Units with Two-Speed Compressors

or Two-Compressors 20

2.1.4 Requirements for Units with Two-Speed Compressors

or Two Compressors Capable of Varying the Sensible

to Total Capacity (S/T) Ratio 22

2.1.5 Requirements for Split Systems 22

2.1.6 Additional Requirements 23

2.2 Recommended Test Procedures

2.2.1 Selection of Test Methods for Steady-State and

Cyclic Operation 24

2.2.2 Test Room Requirements and Equipment Installation 25

2.2.3 Air Quantity Measurement 25

2.2.4 Test Operating Procedure and Results 25

i
Table of Contents (continued)

Section Page

2.2.5 Instrumentation and Data to be Recorded 29

2.2.6 Test Tolerances 30

2.2.7 Reduction of Data 31

3. Product Rating for the Seasonal Performance 36

3.1 Background 36

3.2.1 Recommended Procedure for Calculating an SEER

for Units with Single-Speed Compressor and

Single-Speed Condenser Fans 37

3.2.2 Recommended Procedure for Calculating an SEER

for Units with Single-Speed Compressor and

Multiple-Speed Condenser Fans 38

3.2.3 Recommended Procedure for Calculating an SEER

for Units with Two-Speed Compressors or Two

Compressors 39

3.2.4 Recommended Procedure for Calculating an SEER

for Units with Two-Speed Compressors or Two

Compressors Capable of Varying the Sensible

to Total Capacity Ratio 46

3.2.5 Recommended Procedure for Calculating the Seasonal

Cost of Operation in Different Climatic Regions of

the Country 46

4. Limitations of the Recommended Test and Rating

Procedures and Future Work 49

4.1 Limitations of the Recommended Test and Rating

Procedures 49

4.2 Additional Research Required 51

Nomenclature 53

Attachment A: Sample Calculations 59

Attachment B: General Considerations in Conducting the

Cyclic Dry-Coil Tests.

i i

67
List of Tables and Figures

Page

Figure 1 Schematic of the Various Modes of Operation for Units

with Two-Speed Compressor or Two-Compressors. 45

Figure 2 Distribution of Cooling Load Hours Throughout the

United States. 48

Table la and lb

Summary of Test and Rating Requirements 15, 16

Table 2 Test Operating and Test Condition Tolerances for

Cyclic Dry-Coil Tests 32

Table 3 Distribution of Fractional Hours i n Temperature Bins

to be Used for Calculation of the SEER for Two-Speed

Compressor and Two-Compressor Units. 44

iii

1 . Scope and Purpose

The recommended test methods and the rating and calculation

procedures proposed herein apply to air-cooled electrically-driven

unitary air conditioners and heat pumps operating in the cooling mode

as defined by the Air Conditioning and Refrigeration Institute (AR1)

Standards 210-75 and 240-76. The purpose of the test and calculation

procedures is to provide an estimate for the expected seasonal performance

including the seasonal cost of operation for the above described units.

Currently, testing and rating requirements for unitary air

conditioners are described in ARI Standard 210-75 and for heat pumps

in ARI Standard 240-76. Test procedures used to evaluate this

equipment are given in the American Society of Heating, Refriqerating

and Air Conditioning Engineers (ASHRAE) Standard 37-69. For air-source

units the current rating requirements are based on a steady-state test

conducted at indoor dry-bulb and wet-bulb temperatures of 80°F (26.7°C)

and 67°F (19.4°C), respectively, and an outdoor dry-bulb temperature

of 95°F (35°C). In addition, for units which reject condensate to an

outdoor condenser, an outdoor wet-bulb temperature of 75°F (23.9°C)

is specified.

In order to estimate the seasonal performance of an air conditioner

or heat pump operating in the cooling mode, its capacity and input

power must be known at outdoor temperatures other than 95°F (35°C). This

1
information is required since air conditioners and heat pumps are

utilized at such temperatures for many hours in various regions

throughout the United States. Furthermore, experimental investigations

have been conducted which indicate that the cycling "on" and "off" that

these units undergo to satisfy comfort requirements also may have

significant effect on the performance of the unit. The test procedure

recommended in the following sections addresses the above factors;

it does not however take into account the effect of consumer usage

patterns on annual energy consumption since very little information

is currently available on how consumers use central air conditioning

equipment.

1 .1 Development of Recommended Test Procedures

The recommended test methods are, for the most part, modifications

of ASHRAE Standard 37-69. The steady-state tests are conducted

and evaluated in a manner similar to that described in the ASHRAE

Standard. In addition to the currently required test for rating at

an outdoor dry-bulb temperature of 95°F (35°C), the recommended test

method requires a steady-state test at an outdoor dry-bulb temperature

of 82°F (27.8°C), which more closely typifies the average operating

temperature for the country. A procedure has also been included to

evaluate the cyclic performance of central cooling equipment.

Facility Design and Construction Engineering Weather Data, AFM 88-8

Chapter 6, TM5-785, NAVFAC p-89., Depts . of the Air Force, the Army and

the Navy, Washington, D.C. 1967.

2
1.1.1 Development of Recommended Test Procedures for Determining

Cyclic Performance

Indoor and outdoor ambient conditions are, for a large fraction

of the time in regions throughout the country, such that an air

conditioning unit must operate cyclically and with a wet evaporator

coil. It would therefore seem appropriate to test for the performance

under these cyclic, wet coil conditions. Laboratory tests have been

conducted to determine the performance under these conditions.

It was found that constant room ambient conditions are difficult

to maintain and errors associated with the measurement of dry-bulb

and wet-bulb temperatures can lead to large uncertainties in the cyclic

sensible and latent capacities.

Results from laboratory tests, however, have indicated that cyclic

wet-coil tests may be replaced by simpler and more accurate dry-coil

tests. The dry-coil tests are conducted at a low indoor relative

humidity, resulting in no generation of condensate. Specifically,

the laboratory results indicate that when steady-state and cyclic

dry-coil tests are conducted, the ratio of the cyclic energy efficiency

ratio (EER . ) to the steady-state energy efficiency ratio

eye, dry

(EER

ss ,dry) i s essentially the same as the ratio of the EER 1 s determined

from cyclic and steady-state wet-coil tests at the same cooling load factor.

The cooling load factor, CLF, is defined by the following expression:

3
cl f = w

^°yc ’ dry— 1 .1

Q t

_ xyc ,dry t on

Q . T ss ,dry

The quantity Q denotes the total cyclic cooling (sensible

cyl. and latent) done by the unit over n complete cycles of equal periods

i, each consisting of a compressor on-time, t , and compressor

off-time. The quantity Q

ss denotes the steady-state total cooling

capacity of the unit evaluated at the same ambient conditions as used

in the cyclic test, while Qcyc

represents the average cyclic cooling

capacity during an on-period and is equal to Qcyc (j ry/ nton

-

A degradation coefficient, Cq, defined by the following expression

is determined from dry-coil tests:

EER

1 - EER

C D 1 - CLF

eye, dry

ss ,dry 1 .2

Laboratory tests have indicated that is constant for cooling load

factors ranging from approximately 0.1 to 1.0 and is also independent

of ambient conditions.

4
The energy efficiency ratio for cyclic wet-coil operation,

(EER ) at any cooling load factor can therefore be determined from

Lyl

the steady-state wet coil energy efficiency ratio and the value of the

degradation factor by the following expression:

EER

cyc

= EER

ss PLF(CLE)

where the part-load factor, PLF is defined as follows:

PLF(CLF) = [1 - C

D

(1 - CLF)] 1 .4

In succeeding sections, test methods are given to evaluate the

cyclic performance and degradation coefficient, C

Q

. The cyclic dry-coil

tests and steady-state dry-coil tests are referred to throughout the

proposed test procedures as tests D and C, respectively. While NBS

does not believe tests C and D to be any more difficult to perform than

the current test procedure required for ARI certification, they each

require a minimum testing period of one and one half hours. It was

therefore felt that allowing manufacturers to choose between performing

tests C and D or accepting an assigned degradation coefficient, C^,

equal to 0.25 would not, at this time, have a significant effect on the

labeling of residential central cooling equipment, and would go a long

way toward making the new recommended testing and rating procedures

acceptable to the unitary air conditioner industry.

5
1.1.2 Development of Test Procedures which Allow for Variations

in Unit Design

Currently, there is a variety of central air conditioning systems,

many having unique modes of operation which affect their performance

characteri sties. The recommended test procedures have been developed

and classified according to several design features in order to incorporate those features which may substantially change the unit's performance. The unit design features for which test procedures have been

developed are given in Sections 2.1.1 through 2.1.5. Future additions

and modifications of the recommended test procedures may be required in

order to accurately reflect the performance of innovative central air

conditioning equipment.

It is recognized that while test procedures should accurately

reflect a particular unit's performance they may also be unduly burdensome to perform. The relative improvement in performance of a unit

must therefore be weighed against complicated test procedures which

accurately reflect such improvement. For example, in order to limit

extensive testing, manufacturers of units designed to provide an adjustable latent cooling capacity by employing, as an installed item, controls

which alter the effective evaporator coil size, may operate those controls in such a manner which results in the most effective evaporator

coil size to be employed in the tests. The mode of operation for these

units undergoing tests, must however, result in a system which would normally be encountered in residential use. Another example of the attempt

to limit extensive testing while maintaining a reasonably accurate estima

6
of the seasonal energy efficiency ratio, is found in the recommended test

procedure for units with single-speed compressor and multi -speed condenser

fans. Rather than conducting tests at all condenser fan speeds, the

recommended procedures require testing at a single condenser fan speed.

The recommended test procedures described herein should be reviewed

in the future and judged according to their efficiency. Research is

needed (see Section 4) to evaluate relative improvements in performance

of innovative equipment and to develop simpler less time-consuming

test procedures which will accurately reflect the improvement in

performance.

7
1 .2 Development of the Calculation Procedure for Estimating

Seasonal Performance and Seasonal Cost of Operation

The determination of seasonal performance and cost of operation

for unitary air conditioners and heat pumps operating in the cooling

mode, included herein, is based upon a temperature bin method. This

method, which is described in more detail below, establishes temperature

bins at 5 degree F increments, with the lower bound of the first bin

established at 65°F (18.3°C). The number of hours in a cooling season

in each temperature bin for different geographic locations may be

* determined from weather data. For a particular climate of interest,

the seasonal cooling requirement of a residence is determined for each

temperature bin and the requirements are then summed over all temperature

bins. The energy usage for each temperature bin is obtained by multiplying

the number of hours of operation of the unit by the power input to the unit

in that temperature bin. The seasonal energy usage may then be

obtained by summing up the energy used in each temperature bin.

The capacity and power input to various central air conditioning

units may not be a unique function of the outdoor temperature but is

dependent additionally on the mode of operation of the unit. Various

operating modes are utilized with units having two-speed compressors,

two compressors, and having multi -speed condenser fans, etc. In the

temperature bin method of analyses described in these recommended

test procedures, allowance has been made for some of the effects

*For example: Facility Design and Construction Engineering Weather Data,

AFM 88-8 Chapter 6, TM5-785, NAVFAC P-89., Depts. of the Air Force, the

Army and the Navy, Washington, D.C. 1967.

8
on performance due to modes of operation related to equipment characteristics.

However, for purposes of discussion, the following analysis omits the

effect of different operating modes and considers only an air

conditioning system employing a single-speed compressor and a

single-speed condenser fan.

The residential cooling requirements are determined by assuming:

1) a linear relationship between building cooling load, BL(T-), and outdoor

J dry-bulb temperature, T. (= 5j +62, in degrees F); 2) a zero load

J point of 65°F (18.3°C); 3) a cooling unit oversizing factor of 10°l

at an outdoor temperature of 95°F (35°C). The dependence of building

cooling load on the outdoor temperature is expressed by the following

equation:

5, . 3 Q ss (95°F)

BL < Tj>

= ' -*h K5

where j is the temperature bin number having integer values ranging

from 1 to 8.

The steady-state total cooling capacity of the central air

conditioning unit at an outdoor temperature of 95°F (35°C) is denoted by

Q (95). The total seasonal cooling consumption, Q, is then obtained by

ss multiplying the number of hours, n^ , in each temperature bin by the

building cooling load at temperature T., and is expressed as follows:

J 8 n Q = N E [nJ-] BL(T.)

j=l

N J

1 .6

where n. is the number of cooling season hours that occurred in temperature

J bin j and N is the total of all cooling season hours in the eight

temperature bins.

9
In order to determine the seasonal energy usage of central air

conditioning units, several definitions are introduced. A load

factor, X(T.) is first defined by the following expression:

J

X <V

Bl( V

«SS<V

BL <V<Qss'V

BL ( Tj)>Qss

( T

j)

1 .7

At an outdoor temperature T. , the central cooling unit is generally

J cycling "on" and "off", with a capacity Q ( T - ) , and having an on-time,

eye j

t , and an off-time. The total period in one cycle is the sum of the

on-time and off-time and is denoted by t. With proper sizing of the

cooling unit capacity to the building load, the unit will meet most,

if not all, the cooling requirements throughout the cooling season.

Such conditions may be expressed mathematically as follows:

t BL(T . ) = Q (T.) — 1.8

' j' xyc v j' r

Utilizing equations 1.1, 1.7 and 1.8,the following relationship

between the cooling load factor, CLF, and the load factor X(T.) is

J obtained:

CLF = X(T - )

1 .9

vJ

10
The total energy used in temperature bin j is the ratio of the

total cooling done in temperature bin j to the energy efficiency ratio.

The total energy used in temperature bin j is expressed as follows:

BL(T ) E( V eer cry

n

j

1J0

cyc

v j'

Utilizing equation 1.7, the above equation may be re-expressed

in terms of the load factor as follows:

X(T.) Qss ( T

i) E(T.) = ^ s

-s

- - ^ n.

J EER (T.) J

1 .11

eye' j

Employing equations 1.3, 1.9 and the definition of energy efficiency

ratio, equation 1.11 may be expressed as:

x(T

j

) Q ss( T

j

) E( V

= PLF(X(T

j

))EER

ss

(T

j

) n

j

. X(T

j?

E ss (V n PLF(X(Tj)) n

j

where E gs(Tj) denotes the steady-state power input to the unit at

temperature T .

.

J

11
The total electrical energy usage over the cooling season is then

the sum of the energy usage in each temperature bin. This is expressed

as follows:

8

E = r E(T .) 1.13

j-1 J

8

= N 2 j-1 “pcwjn 1 .14

The seasonal energy efficiency ratio, SEER, is then expressed

as follows:

= 9- 1.15

When the above described method for the determination of seasonal

performance is followed for single-speed compressor and single-speed

condenser fan units for different climates throughout the U.S., the

results in SEER do not vary by more than 10%. Seasonal performance

results using the temperature bin method have also been calculated

by several manufacturers for two-speed compressor (with and without

latent capacity control) and multi -speed condenser fan systems. The

variations in seasonal performance of these units in different climates

throughout the U.S. also appear to be less than 10%. Moreover, it is

likely that the variations in seasonal performance of identical units

placed in similar residences with the same climate will show variations

that are considerably larger than this (due to consumer usage patterns

and variations in the performance of identical units).

12
Since the variations in the seasonal performance of central

cooling units due to individual usage patterns and model idiosyncrasies

are estimated to be greater than the variations in performance due

to climate, a normalized climate was generated. Generated temperature

bin data is used in place of specific weather data (see Table 3, Section

3.2.3). The fraction of the cooling season hours, n./N, in the various

J temperature bins used in the calculation of the seasonal performance

corresponds to a distribution which is believed to approximate a national

average and which results in an average operating outdoor temperature

of 82°F (27.8°C). The average operating outdoor temperature was obtained

by determining the average temperature in different regions of the nation

(averaged with respect to the hours of compressor operation of a typical

single-speed unit) and weighting these temperatures according to the

number of central cooling units in each region. The seasonal energy

efficiency ratios obtained with the above method agree within 10% of

the results obtained with specific temperature bin data for different

regions of the country when applied to units with single- and two-speed

compressors with single- or multi -speed condenser fans.

For central cooling units with single-speed compressors, a

further simplification is possible in estimating the SEER. The SEER

is taken to be equal to the energy efficiency ratio of a cooling unit

operating cyclically at a cooling load factor, CLF, equal to 0.5 and at

an outdoor temperature of 82°F (27.8°C). This estimate of the SEER yields

essentially the same results as the temperature bin method, employing

temperature bin hours as specified in Table 3 in Section 3.2.3.

13
2. Recommended Testing and Rating Requirements

The test and rating requirements for unitary central air conditioners

and heat pumps operating in the cooling mode have been classified

according to several basic design features. These design features

are described in Sections 2.1.1 through 2.1.5. This classification

can be expanded or modified as knowledge of the performance of these

units increases, and provides a means for obtaining credit for

improved performance of innovative equipment.

2 . 1 General

The test requirements generally consist of two steady-state

wet-coil tests, labeled "A" and "B", and the selection of one of two

methods for determining the dynamic performance. Tests A and B are

referred to as "wet-coil" tests since virtually all present-day central

air conditioners and heat pumps operating in the cooling mode will

remove a considerable amount of water vapor from the indoor air at

test A and test B ambient conditions, resulting in a wet evaporator coil.

The first method for determining the dynamic performance (method 1) is

to conduct steady-state and cyclic dry-coil tests. The second method

(method 2) is to use an assigned degradation factor which describes the

dynamic (cyclic) performance. The cooling equipment is then rated

according to results of test A and calculation of the SEER. A summary

of the test and rating requirements is presented in Tables la and lb.

14
Table la

Summary of Test and Rating Requirements

Single-Speed

Compressor With

Single-Speed

Condenser

Fan

Single-Speed

Compressor With

Multi

-Speed

Condenser

Fan

i

2-Speed

Compressor

or

2-Compressor

Units

2-Speed

Compressor or

2-Compressor

wi

th Variable

S/T

Number of Tests - Type "A" 1 1 2 2

Number of Tests - Type "B" 1 1 2 2

Option 1 - Number- Type "C"

and "D" tests 1 1 2 2

Option 2

- Assigned Degradation

Factor

C

d

=0.25 C

d

=0.25 C^

=1 =0.25

Cq

=2

-0.25

Cp

=1 =0.25

C^

=2

=0. 25

Test and Rating

Requi rements

Section

2.1 .1 Section

2.1 .2 Section

2.1 .3 Section

2.1 .4 Procedure for

Calculating SEER

Section

3.2.1

Section

3.2.2

Section

3.2.3

Section

3.2.4

*Split Systems - The portion of the unit containing the compressor and indoor or outdoor

coil shall be rated with each coil which the manufacturer sells

together with the compressor portion of the unit as a matched pair.

The applicable test and rating requirements described in Section

2.1.1 through 2.1.4 shall be used.

15
Table IB

Summary of Test and Rating Requirements;

Indoor and Outdoor Entering Air Temperature

and Mode of Operation

Indoor

Dry-Bul

b

Temperature

Indoor

Wet-Bulb

Temperature

Outdoor

Dry-Bulb

Temperature

Outdoor Mode of

Wet-Bulb /

1

x. Operation

Temperature j

Test A 80°F (26.7°C) 67°F (19.4°C) 95°F ( 35°C) 75°F (23.9°C) steady-state

Test B 80°F (26.7°C) 67°F (19.4°C) 82°F (27.8°C) 65°F (18.3°C) steady-state

| Test C 80°F (26.7°C) See Note

(2)

82° F (27.8°C) — 1 steady-state

i Test D 80°F (26.7°C) See Note

(2)

82°F (27 .8°C) — j cyclic

j 6 min .on-time

|24 mi n .off-time

(1) Applies only to those units which reject condensate

to the outdoor coil.

(2) Shall at nc time exceed that value of the wet-bulb

temperature which results in the production of condensate

by the indoor coil at the dry-bulb temperatures existing

for the air entering the indoor portion of the unit.

16
2.1.1 Requirements for Units with Single-Speed Compressors and

Single-Speed Condenser Fans

Two steady-state wet-coil tests, referred to as test A and

test B, shall be performed according to the test procedures outlined

in Section 2.2. Test A and Test B shall be performed with the air

entering the indoor portion of the unit having a dry-bulb temperature

of 80°F (26.7°C) and a wet-bulb temperature of 67°F (19.4°C). The

dry-bulb temperature of the air entering the outdoor portion of the

unit in Test A shall be 95°F (35°C); in Test B it shall be 82°F (27.8°C).

The temperature of the air surrounding the outdoor portion of the

unit in each test shall be the same as the outdoor entering air

temperature, except for units or portions thereof intended to be

installed only indoors, in which case the dry-bulb temperature

surrounding that indoor portion of the unit shall be 80°F (26.7°C).

For those units which reject condensate to the condenser, located

in the outdoor portion of the unit, the outdoor wet-bulb temperature

surrounding the outdoor portion of the unit shall be 75°F (23.9°C) in

test A and 65°F (18.3°C) in test B.

The cyclic performance shall be determined by either of the two

following methods.

Method 1

Steady-state and cyclic dry-coil tests, referred to as test C

and test D respectively, shall be conducted according to the test

procedures outlined in Section 2.2. The indoor dry-bulb temperature

for tests C and D shall be 80°F (26.7°C). The indoor wet-bulb temperature

17
for tests C and D shall be a value which does not result in formation

of condensate on the indoor coil. It is recommended that an indoor

wet-bulb temperature of 57°F (13.9°C) or less be used. The dry-bulb

temperature of the air entering the outdoor portion of the unit shall

be 82°F (27.8°C). The temperature of the air surrounding the outdoor

portion of the unit shall be subject to the same conditions as the

requirements for conducting test B.

Test C shall be conducted with the unit operating steadily.

Test D shall be conducted by manually cycling the unit "on" and "off".

The unit shall cycle with the compressor "on" for 6 minutes and "off"

for 24 minutes. The indoor fan shall also cycle "on" and "off", the

duration of the indoor fan "on" and "off" periods being governed by

the controls which the manufacturer normally supplies with the unit.

The results of tests C and D shall be used to calculate a degradation

factor, Crj, by the procedures outlined in Section 2.2.

Method 2

As an alternative to conducting tests C and D, a value of C D

= 0.25

is assigned to the degradation coefficient.

The capacity and power input of the unit determined from test A,

the SEER and seasonal cost of operation shall be made available at the

time of purchase to assist the consumer in selecting a unit which

meets the design cooling requirements of his residence. The SEER and

seasonal cost of operation shall be determined as described in Sections

18
3.2.1 and 3.2.5 using the results of test B, the capacity measured in

test A, and either method 1 or method 2 to evaluate the cyclic performance.

2.1.2 Requirements for Units with Single-Speed Compressors and

Multiple-Speed Condenser Fans

The test requirements for multiple-speed condenser fan units

shall be the same as the test requirements described in Section 2.1.1

for single-speed condenser fan units. Briefly, this requires that the

two steady-state wet-coil tests A and B be conducted and either method 1

(conducting dry-coil tests C and D) or method 2 (assigned degradation

factor) be used to evaluate the cyclic performance. In addition, the

condenser fan speed to be used in test A shall be that speed which

normally exists at an outdoor temperature of 95°F (35°C), and for tests

B, C and D the fan speed shall be that which normally exists at an

outdoor temperature of 82°F (27.8°C).

The values of capacity and power input of the unit determined

from test A, the SEER and seasonal cost of operation shall be made

available at the time of purchase to assist the consumer in selecting

a unit which meets the design cooling requirements of his residence.

The SEER and seasonal cost of operation shall be determined as described

in Section 3.2.2 and 3.2.5 using the results of test B, the capacity

measured in test A, and method 1 or method 2 to evaluate the cyclic

performance

.

19
2.1.3 Requirements for Units with Two-Speed Compressors or Two Compressors

Test requirements are the same as described in Section 2.1.1

for single-speed compressor and condenser fan units, except that test

A and test B shall be performed at each compressor speed. The condenser

fan speed used in conducting test A at each compressor speed shall

be that which normally occurs at an outdoor dry-bulb temperature of

95°F (35°C). For test B, the condenser fan speed at each compressor

speed shall be that which normally occurs at an outdoor dry-bulb

temperature of 82°F (27.8°C).

The cyclic performance of the unit shall be determined by either

of the two following methods which are similar to the methods described

in the requirements for single-speed units.

Method 1

Tests C and D shall be conducted at the low compressor speed

with the same condenser fan speed as occurs in performance of test B.

For those two-speed units in which the normal mode of operation involves

the cycling "on" and "off" of the compressor at high speed, tests

C and D must also be performed with the compressor operating at high

speed and at a condenser fan speed that is normally encountered at

test A ambient conditions.

20
Method 2

If tests C and D are not elected to be performed, then the

following degradation factors shall be assigned:

1 = 0.25 low compressor speed (k=l)

k=2

Cp = 0.25 high compressor speed (k=2)

Units consisting of 2 compressors are subject to the same

requirements as those units containing 2-speed compressors. "High

speed" for 2-compressor units shall mean operation with both compressors,

whereas "low speed" shall mean operation with the one compressor which

normally operates at an outdoor temperature of 82°F (27.8°C).

The values of capacity and power input of the unit as determined

from test A at high compressor speed shall be made available at the

time of purchase to assist the consumer in selecting a unit which meets

the design cooling requirements of his residence. The SEER and

seasonal cost of operation, determined from the results of tests A

and B and either of the two methods for determining the degradation

factor, shall be calculated according to the procedures outlined in

Section 3.2.3 and 3.2.5. The SEER and seasonal cost of performance

shall also be made available at the time of purchase.

21
2.1.4 Requirements for Units with Two-Speed Compressors or Two Compressors

Capable of Varying the Sensible to Total Capacity (S/T) Ratio

Some units employing a two-speed compressor or 2 compressors

may also provide a method of varying the ratio of the sensible

cooling capacity to the total cooling capacity (S/T). For such units

the test and rating requirements are the same as for two-speed

compressor units, described in Section 2.1.3. The mode of operation

selected for controlling the S/T ratio in the performance of tests A

and B at each compressor speed shall be at the discretion of the

manufacturer, subject to the condition that it does not result in an

operating configuration which is atypical of a normal residential

installation. If method 1 is elected to be performed, tests C and D

shall be conducted at low compressor speed (single compressor operating)

with the same S/T control mode as used in test B performed with the low

compressor speed (single compressor operating). Likewise, if the normal

mode of operation involves cycling at high speed (two-compressor cycling),

then tests C and D shall also be conducted at high compressor speed, (two

compressor operating), and with the same S/T control mode as in test A

performed with the high compressor speed (two compressor operating).

2.1.5 Requirements for Split Systems

The applicable test and rating requirements described in Sections

2.1.1 through 2.1.4 shall be used for split systems as well as for

single package units. The portion of the unit containing the compressor

and indoor or outdoor coil shall be rated with each coil which the manufacturer sells together with the compressor portion of the unit as a

matched pair. 22
Split systems shall be rated with the length and size of enterconnecting tubing specified in ARI Standard 210-75.

2.1.6 Additional Requirements

The following additional requirements shall apply to central

air conditioners and heat pumps operating in the cooling mode. These

additional requirements are listed in the Air Conditioning and

Refrigeration Institute (ARI) Standard 210-75 under the titles and

section numbers listed below.

5.1.1 Values of the Standard Capacity Ratings

5.1.2 Values of the Standard Input Ratings

5.1.3 Values of the Standard Energy Efficiency Ratios

5. 1.4. 2 Voltage and Frequency

5. 1.4. 3 Cooling Coil Air Quantity.

23
2.2 Recommended Test Procedures

For the most part, the following test procedures for central air

conditioners and heat pumps operating in the cooling mode are

modifications and additions to ASHRAE Standard 37-69. The following

test procedures shall be utilized in conducting cyclic performance

tests C and D. Steady-state performance tests A and B shall be

conducted as described in ASHRAE Standard 37-69 except where noted

throughout this Section.

2.2.1 Selection of Test Methods for Steady-State and Cyclic Operation

Sections 3, 4, and 5 of ASHRAE Standard 37-69 describe the following

four test methods that may be employed to evaluate the performance

of unitary air conditioners and unitary heat pumps operating in the

cooling mode:

a. Air-Enthalpy Method, Indoor Side

b. Air-Enthalpy Method, Outdoor Side

c. Compressor Calibration Method

d. Volatile Refrigerant Flow Method.

All steady-state wet- and dry-coil performance tests on single

package units shall simultaneously employ the Air-Enthalpy Method on

the Indoor Side and one other method consisting of either the Air-Enthalpy

Method on the Outdoor Side or the Compressor Calibration Method. All

steady-state wet- and dry-coil performance tests on split systems shall

simultaneously employ the Air-Enthalpy Method on the Indoor Side and

24
one other method selected from those listed above. All cyclic

dry-coil performance tests shall employ only the Air-Enthalpy Method,

Indoor Side.

2.2.2 Test Room Requirements and Equipment Installation

The test room requirements and equipment installation procedures

are the same as those specified in Sections 11.1 and 11.2 of

ASHRAE Standard 37-69. All tests shall be performed at the nameplate

rated voltage and frequency. For central air conditioning equipment

with dual nameplate voltage ratings, the tests shall be performed

at both voltages or at the lower of the two voltages if only a single

rating is to be published.

2.2.3 Air Quantity and Measurement

Units shall be installed and tested in such a manner that when

operated under steady-state conditions the cooling coil and condenser

airflows meet the requirements of Sections 5. 1.4. 3, 6. 1.4. 4, and

5.1 .4.6 of ARI Standard 210-75.

2.2.4 Test Operating Procedures and Results

All steady-state wet-coil performance tests (tests A and B) shall

be conducted in accordance with the procedures described for cooling

tests in Section 11.3 of ASHRAE Standard 37-69. The results from

the wet-coil tests shall be analyzed in accordance with the coolingrelated requirements of Section 12 of ASHRAE Standard 37-69.

25
For the steady-state wet-coil tests and the steady-state and

cyclic dry-coil tests, those units which do not have indoor-air

circulating fans furnished as part of the model shall have their

sensible and total cyclic and steady-state capacities calculated as

described in Section 2.2.7.

For each of the steady-state and cyclic dry-coil tests (tests C

and D) the following test operating procedures and test results shall

apply:

1. The test room reconditioning apparatus and the equipment

under test shall be operated until equilibrium conditions are attained,

but for not less than one hour before data for the steady-state test

C are recorded.

2. Test C (steady-state) shall then be performed with data

recorded at ten minute intervals until four consecutive sets of

readings are attained within the tolerances prescribed in Section 11.6

of ASHRAE Standard 37-69.

3. When the outdoor air-enthalpy method is used for test C the

above two requirements apply to both the preliminary test and the

regular equipment test (see ASHRAE Standard 37-69, Section 3.6). When

the compressor calibration method is employed, the above two requirements

apply to both the equipment test and the compressor calibration test

(see ASHRAE Standard 37-69, Section 4).

26
4. For test C, the steady-state dry-coil capacity test results

using the Indoor-Air Enthalpy Method shall agree within 6.0% with the

results from one other simultaneously-conducted test method. The results

of only the Indoor-Air Enthalpy Method shall then be used.

5. The cyclic dry-coil test D shall be conducted immediately

after the completion of the steady-state dry-coil test subject to

item 4 listed above. The indoor average dry-bulb temperature for the

steady-state and cyclic dry-coil tests shall be within 1 .0°F (0.56°C) of

each other. Likewise the outdoor average dry-bulb temperature for the

steady-state and cyclic dry-coil tests shall be within 1 .0°F (0.56°C)

of each other.

6. Immediately after the steady-state dry-coil test is completed,

the test unit shall be manually cycled "off" and "on" (using the "off"

and "on" time periods specified in Section 2.1.1) until steadily

repeating ambient conditions are again achieved in both the indoor

and outdoor test chambers, but for not less than 2 complete "off"/"on"

cycles. Without a break in the cycling pattern, the unit shall be run

through an additional "off"/"on" cycle during which the required test

data shall be recorded. During this last cycle, which is referred to

as the test cycle, the indoor and outdoor test room ambient conditions

shall remain within the tolerances specified in Section 2.2.6.

27
7. During the cyclic dry-coil tests the condenser fan shall cycle

"on" and "off" when the compressor cycles "on" and "off". The indoor

air moving equipment shall also cycle "on" when the compressor cycles

"on" and shall cycle "off" as governed by any automatic controls normally

installed with the unit. This last requirement applied to units having

an indoor fan time-delay. Units not supplied with an indoor-fan time

delay shall have the indoor-air moving equipment cycle "on" and "off"

as the compressor cycles "on" and "off".

8. The test installation shall be designed such that there will

be no airflow through the cooling coil due to natural or forced

convection while the indoor fan is "off".

9. For both the steady-state and cyclic dry-coil tests, the test

results shall include the following quantities, calculated by the

procedures outlined in Section 2.2.7:

a) Total cooling capacity, Btu/h

b) Indoor-side air flowrate, cfm of standard air

c) External resistance to indoor airflow, inches of water

d) Total energy input to equipment or energy input to all

equipment components over the test cycle, watt-h.

e) Power input to the indoor fan for those units having an indoor fan as part of the model .

f) Degradation coefficient, Cp, to the nearest .02.

10.

Sections 12.1.5, 12.1.6, 12.1.7 of ASHRAE Standard

37-69 shall apply for both tests C and D.

28
2.2.5 Instrumentation and Data to be Recorded

The steady-state and cyclic performance tests shall have the same

requirements pertaining to instrumentation and data as those specified

in Section 10 and Table II of ASHRAE Standard 37-69. The following

additional requirements shall apply only to the cyclic dry-coil

performance tests.

(1) The dry-bulb temperatures of the air entering and leaving

the cooling coil or the difference between these two dry-bulb

temperatures shall be continuously recorded with instrumentation

having a total system accuracy and precision of + .3°F (+.17°C).

(2) Instrumentation used to measure the dry-bulb temperatures

entering and leaving the coil or the difference between these two

temperatures shall have a response time of 2.5 seconds or less. Response

time is defined as the time required for the instrumentation to attain

63% of the final steady-state temperature difference when subjected

to a step change in temperature difference of 15°F (8.3°C) or more.

(3) The electric energy used by a test unit shall be measured

with a watt-hour meter that is accurate to within +0.5%.

Suggested instrumentation is described in Attachment B, ASHRAE Standard

37-69 and ASHRAE Standard 41

.

29
2.2.6 Test Tolerances

All steady-state wet- and dry-coil performance tests shall be

performed within the applicable operating and test condition tolerances

specified in Section 11.6 and Table III of ASHRAE Standard 37-69.

Two exceptions to these requirements shall apply to the steady-state

dry-coil tests; these are 1) that the wet-bulb temperature of the air

surrounding and entering the indoor portion of the unit shall not, at

the dry-bulb temperature existing in the indoor section, exceed that

value of the wet-bulb temperature that results in the formation of

condensate on the indoor coil 2) the tolerances on the wet-bulb

temperature of the air discharging from the indoor and outdoor portions

of the unit shall not be specified.

The test condition and test operating tolerances for conducting

the cyclic dry-coil test D are given in Table 2. Test condition

tolerance is defined as the maximum permissible variation of the

average of the test observation from the desired test condition. Test

operating tolerance is defined as the greatest permissible difference

between maximum and minimum instrument observation during a test.

When expressed as a percentage, the maximum allowable variation is

the specified percentage of the arithmetical average of the observations.

Variation in test conditions greater than the tolerances prescribed

in Table 2 shall invalidate the test.

30
In order to meet the required air temperature tolerances specified

in Table 2 for the cyclic dry-coil tests, it is suggested that an electric

resistance heater having a heating capacity approximately equal to the

cooling capacity of the unit be installed and that it be cycled "on" and

"off" as the test unit cycles "on" and "off" in the indoor test room. A

similar heater with a heating capacity approximately equal to the sum of

the cooling capacity and compressor and condenser fan power input should

be installed and cycled "off" and "on" as the test unit cycles "on" and

"off", respectively. This results in the maintenance of a constant cooling

and heating load in the indoor and outdoor test chambers. Additional suggestions for conducting the cyclic dry-coil tests may be found in

Attachment B.

2.2.7 Reduction of Data

The steady-state performance test results for the test unit's capacity

shall be calculated using the equations specified in Section 3.7 of ASHRAE

Standard 37-69*

For steady-state performance tests, units which do not have indoorair circulating fans furnished as part of the model shall have their

measured total and sensible steady-state cooling capacities adjusted by

subtracting from these measured values 1250 Btu/h per 1000 SCFM (0.78

watts per dm /s) of indoor air flow and adding to the total steady-state

power input 365 watts per 1000 SCFM (0.78 watts per dm /s) of indoor air

handled. The steady-state energy efficiency ratio, EER

SS , is then the

ratio of this adjusted total capacity, in Btu/h, to this adjusted total

power input, in watts.

*The equation in Section 3 . 7 of ASHRAEStandard should read as follows:

*Vi - 60 V<h al - M/WiO+Wn)-

31
Table

2

Test

Operating

and

Test

Condition

Tolerance

for

Cyclic

Dry-Coil

Tests

32
The results of the cyclic and steady-state dry-coil performance

tests shall be used in the following equations to determine the

cyclic capacity, Qcyc>dry » cyclic power input, E cyCjdry » cyclic energy

efficiency ratio, EER

cyc dry > and degradation factor, Cp. The various

terms appearing in the following equations are defined in the Nomenclature.

60 V C r Qcyc,dry " [v^ (1+W'

n )]

2,1

^cyc,dry

~ ^cycjdry^on 2.2

(time indoor fan off)

r = /

[T

al

(t) ' T

a2 (t)]dt 2.3

(time indoor fan on)

CLF

^cyc ,dry

^ss ,dry

x T

EERcyc,dry

Qxcyc,dry

E cyc,dry

2.4

2.5

E eye, dry

= total electrical energy used during a test

cycle consisting of 1 compressor "off"

period and 1 compressor "on" period. 2.6

33
1 EER

eye, dry

C D 2.7

T Duration of time, in hours, for one

complete cycle consisting of one

compressor "on" time and one compressor

"off" time. 2.8

t

Qn - Duration of time, in hours, of the

compressor "on" time in one cycle

of duration x

2.9

For the cyclic performance tests, as in the steady-state performance

tests, units which do not have indoor-air circulating fans furnished

as part of the model shall have their total cooling done, Q . , and

eye ,ary

circulating indoor-air equipment power. The value to be used for the

circulating indoor air equipment power shall be 1250 Btu/h per 1000 SCFM

for indoor-air circulation during one cycle is the product of the circulating

indoor air equipment power and the duration of time in one cycle that the

circulating indoor air equipment is "on". The total cooling done shall

then be the measured cooling done in one complete cycle minus the

energy usage required in one complete cycle for indoor-air circulation.

The total energy usage shall then be the sum of the energy usage required

for indoor-air circulation in one complete cycle and the energy used by

energy used, E CyC ^y, in one complete cycle adjusted for the effect of

3

(.78 watts per dm /s) of circulating indoor air. The energy usage required

34
remaining equipment components in one complete cycle. The cyclic energy

efficiency ratio, EER „ , , shall then be the ratio of the total

eye, dry

cooling done in Btu, to the total energy usage, in watt-hours, where the

total cooling done and total energy usage have been adjusted by the

above-described procedures.

35
3. Product Rating for the Seasonal Performance

3.1 Background

Sections 3.2.1 through 3.2.4 describe how an average seasonal energy

efficiency ratio, SEER, shall be calculated for each type of central

cooling equipment for which testing and rating requirements and procedures

have been prescribed herein. After the SEER has been determined it is

used in Section 3.2.5 to estimate the seasonal cost of operating such

equipment in different climatic regions of the country.

Two different methods are employed to calculate seasonal energy

efficiency ratios. In the first method, which is used for units

with single speed compressors with single or multiple-speed condenser

fans, it is assumed that the SEER is equal to the energy efficiency ratio

of the cooling unit operating under cyclic conditions at an outdoor

temperature of 82°F (27.8°C). A temperature of 82°F (27.8°C) has been

estimated to be the average operating outdoor temperature for the country

during the period of the year requiring cooling. This value was obtained

by finding the average temperature in different regions of the country

(averaged with respect to the hours of operation of a typical single

speed unit) and weighting these average temperatures according to the

number of central residential cooling units in each region. The second

method, employed for units having two-speed compressors or two compressors,

utilizes the results of tests A and B to define the capacity and power

input requirements of the unit as a function of outdoor temperature.

36
A temperature bin method of analysis is then used to calculate a seasonal

energy efficiency ratio. The distribution of the fraction of cooling

hours in the various temperature bins used in the calculation corresponds

to a distribution which is believed to approximate a national average

and which results in an average operating outdoor temperature of 82°F

(27.8°C). Both methods yield results which are virtually identical

when they are applied to single-speed units.

3.2.1 Recommended Procedure for Calculating an SEER for Units with

Single-Speed Compressor and Single-Speed Condenser Fans

The seasonal energy efficiency ratio for units employing singlespeed compressors and single-speed condenser fans is based on the

results of test B and either of two methods outlined in Section 2.1.1

to account for the cyclic performance.

The seasonal energy efficiency ratio shall be determined by the

following equation:

SEER = [PLF(0.5)][EER

b

] 3.1

The part-load performance factor, PLF(0.5), at a cooling load

factor, CLF equal to 0.5 is determined from the following equation:

PLF(0 .5) = 1 - C

D

(1 - 0.5) 3.2

The value of the degradation coefficient C D is obtained by either

method 1 or method 2, as described in Section 2.1.2.

37
3.2.2 Recommended Procedure for Calculating an SEER for Units With

Single-Speed Compressors and Multiple Speed Condenser Fans

The seasonal energy efficiency ratio for units employing singlespeed compressors and multi-speed condenser fans is based on the energy

efficiency ratio obtained for test B and either of the two methods outlined in Section 2.1.2 to account for the performance under cyclic

conditions. The energy efficiency ratio for test B, EERg, is obtained

with the unit operating with a condenser fan speed normally encountered

with test B-type ambient conditions. If tests C and D are conducted

(i.e. method 1) to determine the cyclic degradation coefficient, Cg,

then the tests are to be performed with the unit operating at the same

condenser fan speed as encountered in test B.

The seasonal energy efficiency ratio shall be determined by the

following equation:

SEER = [PLF(0.5)] [EERg] 3.3

The part load performance factor, PLF (0.5), at a cooling load

factor, CLF, equal to 0.5 is determined by the following equation:

PLF(0 . 5) = 1 - C

D

(1 - 0.5) 3.4

The degradation coefficient, Cg, is evaluated by either conducting

tests C and D (method 1) or using an assigned value of Cg =0.25 (method 2)

as outlined in Section 2.1.2.

38
3.2.3 Recommended Procedure for Calculating an SEER for Units With

Two-Speed Compressors or Two Compressors

The calculation procedure described in this Section is based on

the performance of tests A and B at each of the compressor speeds for

two-speed compressor units, subject to the conditions on condenser fan

speed described in Section 2.1.3. If elected to be performed, the cyclic

performance tests C and D must be performed with the unit operating at

the low compressor speed and with a condenser fan speed (for multi -speed

fans) that is normally encountered at test B ambient conditions. For

those 2-speed units in which the compressor can cycle on and off at high

speed, tests C and D must also be performed with the compressor cycling

at high speed and at a condenser fan speed (for multi -speed fans) that is

normally encountered at test A ambient conditions.

Units operating with two compressors shall have the SEER calculated

in the same manner as described below for two-speed compressor units.

The superscripted index, k=l , (and the term "low speed") now designates

that compressor which normally operates at an outdoor temperature of

82°F (27.8°C), and the superscript k=2 (and the term "high speed") denotes

operation with both compressors.

The results from each set of the A and B-type tests, for each

compressor speed of the two-speed units shall be used in the following

equation for the calculation of the SEER.

39
SEER 3.5

8

z j=1

8

z j=l

«<V

E <V

The terms

Q(T,)

and

E(T,)

, summed over temperature bins numbered

N —“ N one through eight,are evaluated at each temperature bin according to

the four possible cases listed below. The four possible cases are also

shown diagrammatical ly in Figure 1.

Case I

Units operating at low compressor speed, i.e. k=l , for which the

. k=l

steady-state cooling capacity, Q ss (T^), is greater than or equal to

the building cooling load, BL(T-).

J

bl( v 4 C<v 3.6

X k=l

BL ‘V 3.7

Q(V

N

x k=l

‘ T

j) fT 3.8

40
3.9

E <V . Ess^Tj) "j

N PLF

k=1 R

~~

PLF

k=1

= 1 - C k=1

(1 - X k=1

) 3.10

Case II

Units alternating between high (k=2) and low (k=l) compressor

speeds to satisfy the building cooling load at temperature T.

vj

. k=l . k=2

Q (Tj) <BL(Tj ) < Q ss (Tj) 3.11

k=2

,k=l . ^ss < Tj> - BLf-V

~k=2

Qss <V - Qss <V

3.12

X

k 2 = 1 - X k 1 3.13

•) i-i .k=l . 0 .k=2 n • - = t x Q

ss <V + x Q

ss

(T

j

,] ir 3.14

E(T.) , n

. k=l , 9 .k=2 n

i E ss (Tj) + X

k - 2

E ss (Tj)] fp

3.15

41
Case III

Units cycling on and off (k=2) at high compressor speed in order

to satisfy the building cooling load at temperature T.

.

J

Ak=l .k=2

BL(Tj) < Q

ss (Tj) 3.16

,k=2 _ BL ‘V

Q

k_2

(T -

)

x

ss

v y

3.17

Q(T ). 2

. k=2 n. -/-= xk 2

q

ss

(Tj) 3.18

,k=2

,k=2

E ( T

j

) X E ss

< Tj> "j

N " ^JP2 N 3.19

PLF

k=2

= 1 - C

k 2

(1 - X

k ~

2

) 3.20

42
Case IV

Units operating continuously at high compressor speed (k=2) at

outdoor temperature T..

J

BL( V > «ss

2

'V 3.21

Q(T

i

)

• k=2 Hi

N gss u j' N 3.22

E(T

i)

- k=2 — naL- = WT 1 -j- 3 2?

N

t ss u

j

; N

The building cooling load, BL(T.) for the four cases described

J above for two-speed compressor, or two-compressor units, shall be obtained

from the following equation:

BL(T ) - ^2(95F ) BL(T

r 95 - 65 1.1

3.24

The fraction of hours, , in each temperature bin, j, shall be

obtained from Table 3.

In order to evaluate the steady-state capacity, Qg S (Tj), and

power input, E (T.), at temperature T. for each compressor speed,

s s j j

k=l,2, the results of tests A and B shall be used in the following

equations

:

k . k

• k .k 6 (82 F ) - Q (95F)

<WV qss (95f) +

ss - ^Tir (33 - 5j) 3.25

B ss<V E,

S <95F) +

k • k E_(82F) - E ss (95F)

ss 95 - 82

(33 - 5 j

)

3.26

43
Table 3

Distribution of Fractional Hours in Temperature

Bins to be Used for Calculation of the SEER for

Two-Speed Compressor and Two-Compressor Units

Fraction of Total

Representative Temperature Bin Hours

Bin Number, Bin Temperature Temperature Bin _j_

j Range (°F) (°F) N

1 65 - 69 67 .214

2 70 - 74 72 .231

3 75 - 79 77 .216

4 80 - 84 82 .161

5 85 - 89 87 .104

6 90 - 94 92 .052

7 95 - 99 97 .018

8 100 - 104 102 .004

44
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II

O'

PQ

O

COO.

CO O

M -o (!) s *

<u Xi

4-1 CO 4-1

GO CO

CD

cocO O

tioo co

LO

ON

CM

ON

c-. oo

CM

r»

r^.

CM

r--»

f'- VO

Oo

H 5

CMo

LOcn

oco

CM

o

CM

0)

V43

4J

CO

J-l Q.

0)a

it H

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PQ

IPo Q

l-i O

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45

Figure

1

Schematic

of

the

various

modes

of

operation

for

units

with

two-speed

compressors

or

two-compressors.

The

cross-marks

denote

the

rated

capacities

at

type

"A"

and

type

"B"

conditions.
k=l The value of the degradation coefficient, Cp for low compressor

k=2

speed cycling and Cp for high speed on/off compressor cycling is

determined by either method 1 or method 2, described in Section 2.1.3.

3.2.4 Recommended Procedure for Calculating an SEER for Units with

Two Speed Compressor or Two Compressors Capable of Varying the

Sensible to Total Capacity Ratio

Units with two-speed compressors or two compressors capable of

varying the sensible to total capacity ratio (S/T) shall have the

seasonal energy efficiency ratio determined as described in Section

3.2.3. For such units, the mode of operation selected to determine the

steady-state capacities, and power inputs Q^95), Q^ s (82 ) , E^

s

( 95 )

,

E ss (82) at each compressor speed k=l , 2, for tests A and B is outlined

in Section 2.1.4.

3.2.5 Recommended Procedure for Calculating the Seasonal Cost of

Operation in Different Climatic Regions of the Country

The following procedures shall be followed to estimate the cost of

operating a central air conditioner or heat pump during the cooling

season in various geographic locations of the United States:

1. Obtain the number of cooling load hours, CLH, from Figure 2

for the region of interest.

2. Determine the rated capacity, CAP(95), in Btu per hour, at

test A- type indoor and outdoor ambient conditions. For units with twospeed compressors or two compressors, the results from the A-type test

which gave the highest capacity shall be used.

46
3. By the procedures outlined in Sections 3.2.1 through 3.2.4,

determine the seasonal energy efficiency ratio, SEER.

4. The seasonal cost of operation shall be determined from the

following equation:

Seasonal Cost of Operation = CLH X X cos

^

-H 3.27

47
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48
4. Limitations of the Recommended Test and Rating Procedures and

Future Work

Several limitations are evident in the proposed test and rating

procedures which indicate the need for future work. It is also evident

from these limitations that test and rating procedures should not be

considered as fixed, but should be continually updated and improved

as our knowledge and understanding increases.

4.1 Limitations of the Recommended Test and Rating Procedures

In these proposed test and rating procedures, manufacturers of

units capable of varying the sensible to total capacity (S/T) ratio are

allowed to evaluate the performance of such units at the most favorable

S/T ratio. Because of the resulting better performance, this may create

an unfair advantage over other units whose S/T ratio is fixed at such a

value as to provide satisfactory comfort requirements for the consumer.

This limitation of the test and rating procedures arises from the fact

that the state-of-the-art knowledge of the cooling loads in residences

is not advanced enough to allow NBS to specify with any degree of

certainty, the latent cooling load that would be seen by an air

conditioner or heat pump at various indoor and outdoor conditions in

different types of homes and different climatic regions of the country.

In order to determine the cyclic performance of central airconditioning equipment, the proposed standard allows manufacturers the

option of conducting tests C and D and calculating the degradation

49
factor Cp, value equal to 0.25. This allows units whose actual cyclic

performance is worse than that indicated by the assigned degradation

factor to be rated with a higher cyclic performance than actually exists.

The procedures specified in Section 3 assume that a central air

conditioner or heat pump is used to meet the entire seasonal cooling

requirement of a house continuously inhabited and maintained at a

constant and reasonably comfortable indoor temperature. These assumptions

will therefore result in a conservative estimate of the seasonal operating

cost. Often, a consumer will use some sort of natural ventilation

(opening windows, employing window fans, etc.) or a device to automatically

adjust the daytime or nighttime thermostat setting, or simply to turn the

air conditioning unit off when no one is at home in order to reduce his

electricity bill. Under such circumstances, the recommended procedures

would result in an overestimate of the seasonal cost of operating the

central cooling equipment. On the other hand, if a consumer maintains a

very low indoor temperature, his seasonal cost of operation could be

appreciably greater than that calculated by the procedure outlined in

Section 3.2.5. This limitation of the recommended rating procedures will

be understood by the consumer if the label or brochure which is placed on

the product clearly states that the seasonal cost of operation will vary

with different usage patterns.

50
4.2 Additional Research Required

The following additional research is needed to improve upon the

recommended test and rating procedures and to remedy the limitations

discussed in Section 4.1.

1. More laboratory work is needed to determine how to simplify

and speed up the test procedures for evaluating steady-state and cyclic

performance. For example, if an accurate and reliable method could

be found for evaluating the cooling performance of central air

conditioners and heat pumps under cyclic wet-coil conditions, tests

B, C and D could be replaced by a single test for units with singlespeed compressors and single-speed condenser fans.

2. Research is needed to determine whether the degradation in

performance due to cyclic operation can be accurately predicted from

knowledge of a unit's design (e.g. capillary tube, expansion valve,

compressor EER, etc.). If the degradation can be predicted, then it

might be possible to eliminate all cyclic tests and assign a predicted

degradation factor, C^, to each type of unit.

3. Computer modeling and field studies are needed as quickly as

possible to improve our knowledge of the cooling loads in

residential buildings. Field studies are also needed to verify the

accuracy of the reconmended procedures for predicting annual operating

costs and to quantify the effects of different consumer usage patterns

on the annual energy consumption of central air conditioners and heat

pumps operating in the cooling mode.

51
4. Laboratory and field studies are needed to determine the best

method of testing and rating innovative equipment. This is true even

for two-speed compressor units, for which test and rating procedures

have been specified.

52
Nomenclature

BL <V

CAP (95)

CLF

CLH

dm3

E

E <V

E ss<V

Building cooling load at an outdoor dry-bulb temperature T.

,

[Btu/h]

Highest rated capacity at test A-type ambient conditions,

[Btu/h]

Degradation factor for cyclic operation, defined by equation 1.2

Cooling load factor, defined as the ratio of the total cyclic

cooling done in a complete cycle of specified period consisting

of an "on"-time and "off "-time to the steady-state cooling

done over the same time period at constant ambient conditions.

See equation 1.1.

Cooling load hours, defined as the number of hours in a cooling

season that a building requires cooling. See Figure 2.

Specific heat at constant pressure of air-water mixture per

pound of dry air, C

pa

= 0.24 + 0.444 W

n

, [Btu/lbF].

Cubic decimeter

Total seasonal energy usage, [watt-h]

Energy usage in temperature bin j [watt-h], see equations 1.12,

and 3.9

Total electrical energy usage over a test cycle consisting of one compressor "off" period and one compressor "on" period,

[watt-h]

Steady-state total power input at an outdoor temperature T .

,

[watts]

.

53
EER Energy efficiency ratio, defined as the ratio of total capacity

of the unit to the total power input at specified indoor and

outdoor ambient conditions, [Btu/watt-h]

EER

ss Steady-state energy-efficiency ratio [Btu/watt-h]

EER Cyclic energy efficiency ratio [Btu/watt-h]

j Outdoor dry-bulb temperature bin number, see Table 3

N Total number of temperature bin hours

n

i p- Fractional number of temperature bin hours, see Table 3

PLF Part-load factor, defined as the ratio of the cyclic energyefficiency ratio to the steady-state efficiency ratio, see equation 1 .4

Q Total seasonal cooling done, [Btu]

Total cooling done over a cycle consisting of one compressor

"off" period and one compressor "on" period, [Btu]

Q(T.) Total cooling done in temperature bin j, [Btu], see equation 3.8

J

Q ss (Tj) Total steady-state cooling capacity at an outdoor temperature

Tj,[Btu/h]

54
v( v

Cyclic total capacity at an outdoor temperature T

^

, [Btu/h ]

;

defined as the ratio of the total cooling done over a given

time period to the duration of time the compressor is on in

that period

5eTr Seasonal energy efficiency ratio, [Btu/watt-h] ; defined as the ratio of the total cooling done to the total energy

usage over a cooling season

T

j

Representative outdoor dry-bulb temperature for temperature

bin j , [°F] . See Table 3

Dry-bulb temperature of air entering the indoor coil, [°F]

T.2« l ) Dry-bulb temperature of air leaving the indoor coil, [°F]

t Time, [h]

ton Duration of time the compressor is on in one cycle consisting

of a compressor on-time and a compressor off-time, [h]

V Indoor air flowrate, [CFM] at the dry-bulb temperature,

humidity ratio and pressure existing in the region of

measurement

v

n Specific volume of air-water mixture, at the same dry-bulb

temperature, humidity ratio, and pressure used in the

3 determination of the indoor air flowrate, [ft /lb].

W

n Humidity ratio, [Ib/lb]

X( Tj ) Load factor at an outdoor dry-bulb temperature T . , defined

J by equation 1 .7

55
X Same as X ( T -

)

J

t Time period consisting of a compressor on-time and compressor

off-time [h]

r Defined by equation 2.3, in [F-h]

.

56
Subscripts and Superscripts

ss - steady-state

eye - cyclic

dry - dry- coil

B - Test B

j

- Temperature bin number, see Table 3

k - Compressor index parameter, defined for two-speed compressor

(or two-compressor) units, where k = 1 denotes low compressor

speed (single compressor operating) and k = 2 denotes high

compressor speed (2 compressors operating).

57

Attachment A

Sample Calculations

59
The following example is used to illustrate the calculation procedure

for determining the SEEfc and seasonal cost of operation of a central

air conditioning unit containing a two-speed compressor. Table A1

contains the capacity and power input results at the low (k=l) and high

(k=2) compressor speeds obtained from tests A and B. The degradation

k=l k=2 coefficients, , at low and high compressor speeds are also

listed and are assumed to have been determined from tests C and D.

Table A2 has been constructed to aid in the determination of the

SEER. The data in the first three columns in Table A2 list the temperature

bin data contained in Table 3. The data for each temperature bin in the

remaining columns is determined from Table A1 and equations listed in

Section 3.2.3 as described below.

1. (Column 4) Determine the building cooling load, Bl(T.), from

J equation (3.24) for the representative outdoor temperatures, T., in each

J temperature bin.

For example, at T. = 67°F, j = 1:

J

BL(67°F) = = 4363.6 Btu/h

2. (Columns 5, 6, 7, and 8) Using equations 3.25 and 3.26, determine

• k• k

the capacity, Q (T.), and total power input, E (T-), for each compressor

J ^ ^ J speed and each temperature bin.

60
For example, at T. = 92°F, j = 6:

J

Q^( 9 2-F) = 43000 + 51000 - 43000

95 - 82

(33 - 5 x 6) = 44846 Btu/h.

Q5 S

2 (92°F) = 72000 + 80000 - 72000

95 - 82

(33 - 5 x 6) = 73846 Btu/h.

E^(92-F) = 5300 + 5100 - 5300

"95 - 82 (33 - 5 x 6) = 5253.9 watts

E^~2(92°f) = 9300 + 8800 - 9300

95 - 82

(33 -5x6)= 9184.6 watts.

3. (Column 9) Determine the applicable mode of operation of the airconditioning unit described in Section 3.2.3, cases 1 through 4 for the

representative outdoor temperature in each temperature bin. For example,

at a representative outdoor temperature of 67°F the capacity at the low

compressor speed exceeds the building load and therefore case 1 is the

applicable mode of operation.

As another example, at a representative outdoor temperature of

92°F the building cooling load is greater than the capacity at the low

compressor speed and less than the capacity at the high compressor speed.

Depending on the controls normally installed in the unit, the compressor

may cycle between high and low speeds (case 2) or cycle "on" and "off"

at high compressor speed (case 3) to satisfy the building cooling load.

In this example, the air conditioning unit is assumed to operate in

the mode described in case 2.

61
4. (column 10 through 15) For each case and temperature bin listed

i/ in Table A2, determine where applicable the load factors, X , part load

k Q(Ti

) E(T

i

} factors, PLF , and the terms y

- ,

-

- .

The above-mentioned quantities are calculated using the equations listed

in each of the four possible cases described in Section 3.2.3.

Example : T. = 67°F, j = 1, case 1 J from equations 3.7, 3.8, 3.9, 3.10:

v k=l _ 4363.1 _

x ' 5U23TT

' - 0725

.0725 x 60231 . x .214 = 934.5 Btu/h

PLF

k 1 = 1 - 0.20(1 - .0725) = .815

EterF) . .0725 x 4869.2 x ,214 . 92>6g watts

Example : T. = 92°F, j = 6, case 2

from equations 3.12, 3.13, 3.14, 3.15:

v k=l 73846. - 58909. _ C1C

X 73846. - 44846. ,515

Q ^

2

°

- Fl = [.515 x 44846 + .485 x 73846] x .052 = 3063.4 Btu/h

E = [.515 x 5253.9 + .485 x 9184.6] x .052 = 372.3 watts

62
5. The seasonal energy efficiency ratio may be determined by summing

Q(T.) E(T.)

the individual terms — listed in the last two columns of

Table A2, over the eight temperature bins.

From equation 3.5:

SEER = 25666.

2784. 9.22

Determination of the Seasonal Cost of Operation

In order to determine the seasonal cost of operation of the central

air conditioner in the present example, the procedure outlined in

Section 3.2.5 is followed. It is assumed that the central air conditioner

is installed in the Washington, D.C. area and that the cost of electricity

is $0,040 per KWH.

From Figure 1, the number of cooling load hours, CLH, for the

Washington, D.C. area is approximately 850. The highest measured

capacity obtained from test A, in this example unit is 72000 Btu/h and

the SEER has been determined to be 9.2.

The seasonal cost of operation is determined by equation 3.27:

Seasonal Cost of Operation = 850 x x = $266.
Table Al. Sample Data Required to Calculate the SEER for a Central

Air Conditioning Unit Containing a Two— Speed Compressor.

Low

compressor

speed

,

k=l

High

compressor

speed,

k=l

. k

Q (95F) , Btu/h

b O 43,000 72,000

. k

Q (82F), Btu/h

ss 51,000 80,000

. k

E (95F) , watts

s s 5300 9300

. k

E gg(82F) , watts 5100 8800

*Degradation

Factor, C^

0.20 0.20

* assumed to be obtained from

tests C and D.

64
Sample

Calculation

for

Determining

the

SEER

for

a

Central

Air

Conditioner

Containing

a

Two-Speed

Compressor

65

'OV> N M

«M N M

0\ M II

SEER

Attachment B

General Considerations in Conducting

the Cyclic Dry-Coil Tests

67
Suggested test facility design and instrumentation for determining

the performance of central air conditioning equipment are described

in ASHRAE Standard 37-69. Although intended for steady-state

testing, the suggestions given in the Standard are readily applicable

or adaptable to cyclic performance testing. The recommended test and

rating procedures require that the cyclic capacity be determined by

the Indoor-Air Enthalpy Method as stated in the above-mentioned Standard.

Since there is no independent simultaneously conducted test method

used to serve as a check on the determination of cyclic performance,

precautions should be taken to assure an accurate determination. The

following considerations are directed to alleviating a few potential

problems which may occur during the cyclic performance tests.

Control of Indoor-Side and Outdoor-Side Ambient Air Temperature

Supplementary air reconditioning equipment is generally required

to absorb the cooling and heating output of the air-conditioning

equipment to be tested and to control the surrounding and entering

ambient air temperatures . During cyclic performance testing, a

periodically fluctuating load is imposed on the air-reconditioning

equipment, making ambient conditions more difficult to control than

in steady-state testing. The air-reconditioning equipment should have

sufficient capacity to absorb the load, as well as to handle the air

flow imposed on it by the equipment under test.

68
One method of reducing the periodically fluctuating loads due to

cyclic operation is to install electric heaters in an appropriate

location on the discharge sides of both the indoor and outdoor portions

of the unit. The heating capacity of the indoor-side heater should

approximately equal the cooling capacity of the unit. The heating

capacity of the outdoor-side heater should approximately equal the

sum of the cooling capacity and power input to the compressor and

condenser fan.

ASHRAE Standard 37-69 requires a test room into which the

outdoor portion of the central air conditioning equipment to be tested

is installed and the entering air temperature is controlled. The air

within the outdoor-side test room should be well circulated, especially

when the test equipment is cycled "off", to prevent air temperature

stratification; however, air velocities in the vicinity of the unit should

be kept low. These remarks also apply to those installations utilizing

an indoor test room. Precautions should be taken to prevent air

discharging from the indoor and outdoor portions of the unit from

bypassing the supplementary air reconditioning equipment and re-entering

the respective portions of the unit.

Air Temperature Measurement

The important air temperatures to be measured in the determination

of the cyclic performance are the air temperatures entering the indoor

and outdoor portions of the test unit and the temperature difference

of the air entering and leaving the indoor portion of the unit. These

69
air temperature measurements should be made with suitable devices

having a precision, accuracy and response time within the tolerances

specified in the recommended test procedures.

A number of methods for measuring air temperatures, several of

which are described below, are described in ASHRAE Standard 41.

The air temperature entering portions of the unit can be measured by

utilizing several thermocouples connected electrically in parallel

and installed in an appropriate fashion across the air inlet portions

of the unit or in the entering air ducts. In order to measure the

temperature difference of the air entering and leaving the indoor portion

of the unit, a thermopile, consisting of a number of thermocouples

connected electrically in series, may be utilized. The thermopile is

appropriately installed in the entering-air and discharge-air ducts

attached to the indoor portion of the unit. The millivolt signal

generated by the thermocouples attached to the air-entering portions

of the unit may be directed to strip chart recorders. The signal

generated by the thermopile may also be directed to a strip chart

recorder and the determination of the capacity (see Section 2.2.6

equations 2.1 and 2.3) facilitated by measuring the area under the

curve generated by the recorder.

Several potential errors may occur in the measurement of air

temperature within ducts, especially during the cyclic testing of

central air conditioning equipment. In order to measure the temperature

difference across the indoor portion of the unit, or the temperature

of the supply air, a uniform air velocity and temperature distribution

70
must be assured. Sources causing possible nonuniformities in the supply

air temperature are poor mixing of the supply air, heat transfer through

the duct wall, and thermal storage effects of the duct. The latter source

of error is due to measuring the air temperature near the duct wall,

where the duct wall and air near the wall may exhibit a different

rate of temperature decrease than the mainstream supply air when the

unit is turned "on". Another source of error in the supply air

temperature measurement is the heat transfer through the thermocouple

wi re

.

A suitable mixing device may have to be installed in the supply

duct to reduce the nonuniformities in the air temperature and velocity

distribution. The supply air duct should be heavily insulated and

sealed from leaks and air temperatures within the duct measured

reasonably close to the unit. If thermocouples are used, several

inches of thermocouple wire beyond the junction should also be left

in the supply air duct to reduce the error associated with the heat

transfer through the wire.

Air Flowrate Measurement

ASHRAE Standard 37-69 describes in detail instrumentation and

calculation procedures which may be used to determine the indoor-side

air flow rate of the test unit. During the cyclic tests, static pressures

and temperatures needed to determine the air flow rate may be varying

and measurement of these data may be facilitated by taking these

measurements towards the end of the "on" period.

71
Measurement of Electrical Energy Usage

In order to determine the dry-coil cyclic and steady-state energy

efficiency ratios, the energy input to the indoor air circulating fan,

condenser fan, compressor, and control circuit must be determined. The

energy usage can be measured by a number of commercially available

watt-hour meters. These meters commonly utilize registers and/or pulse

generators which generate pulses proportional to the energy usage

and are of sufficient resolution and accuracy to be used in the cyclic

performance tests.

Additional Considerations

During cyclic testing, provisions should be made to prevent either

natural or forced convection through the indoor portion of the unit

when the unit is cycled "off". The unit should be installed and operated

in such a manner that the normal air circulating pattern around the

outdoor portion of the unit is maintained. Installation of the unit

should also be consistent with the manufacturer's recommendations.

72
NBS-II4A (Rev 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBSIR 77- 1271

2. Gov’t Accession

No.

3. Recipient’s Accession No.

4. TITLE AND SUBTITLE

Method of Testing, Rating and Estimating the Seasonal

Performance of Central Air Conditioners and Heat Pumps

Operating in the Cooling Mode

5. Publication Date April 1978

6. Performing Organization Code

7. A IJTHOR(S) Dr. George E. Kelly and Dr. Walter H. Parken, Jr.

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON. D.C. 20234

10. Project/Task/Work Unit No. A62 klhk

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Federal Energy Administration

12th and Pennsylvania Ave

New Post Office Building

Washingf-nn D.C. 20.461

15. SUPPLEMENTARY NOTES

13. Type of Report & Period Covered Final

14. Sponsoring Agency Code

16. ABSTRACT (A 200-word or less (actual summary ot most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The National Bureau of Standards has made a study of the part-load and seasonal

performance of residential central air conditioners and heat pumps operating in the

cooling mode. This document outlines methods for testing and rating these units which

account for the variation in performance due to part-load operation and change in

outdoor air temperature. A calculation procedure is presented which can be used to

estimate the seasonal performance and seasonal cost of operation of residential

central-cooling equipment.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

central air conditioners, heat pumps, rating proce

test method

18. AVAILABILITY |~yl Unlimited

l J For Official Distribution. Do Not Release to NTIS

j Order From Sup. of Doc., U.S. Government Printing Office Washington, D.C. 20402, SD Cat. No. Cl 3

IX I Order From National Technical Information Service (NTIS)

Springfield, Virginia 22151

e, seasonal cost of operation.

19. SECURITY CLASS 21. NO. OF PAGES

(THIS REPORT)

75

UNCL ASSIFIED

20. SECURITY CLASS 22. Price (THIS PAGE)

$5.25

UNCLASSIFIED

USCOMM-DC 29042* P 74

A
v .

1 ' :