IMAC TEAM 2 APPENDIX I

Procedure for measuring system COP [Coefficient of Performance] of a mobile air condtioning 

system on a test bench

DRAFT

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J2765

1.0 Purpose 

1.1 This Standard provides a method of testing the capacity (performance) and efficiency

(COP) of mobile air conditioning refrigerant systems under steady state conditions.

1.2 The procedure proposed is designed to give maximum repeatability and minimum error in 

determining cooling capacity (Q) and efficiency (COP – Coefficient of Performance) of the 

refrigeration system of the mobile air conditioner. For that reason a “breadboard” type 

facility is proposed in which components are assembled into a system and exposed to 

operating conditions in individual, separately controlled chambers. The facility should 

allow for three methods to determine system performance: refrigerant side, airside, and 

calorimetric chambers. Each side yields its own energy balance calculation to find the 

capacity of the system. With the three methods used, instead of two as typically required, 

redundancy will be maintained even when the evaporator refrigerant exit is two phase, or 

operation is unstable. In this case only the airside balance is available. The design 

should be made so that two independent methods could provide agreement of less than 

within 6.0% between two independent balances. 

2.0 Scope

2.1 This Standard applies to motor driven mobile air conditioning systems consisting of one 

in-car air coil (evaporator), a compressor, an expansion device, and one under-hood air 

coil (condenser). 

2.1.1 This standard can also be used for measuring systems that use electrically driven 

compressor if measurement of input power to compressor is carefully considered.

2.1.2 This standard can also be used for measuring systems that include the entire air 

handling system if air side pressure drop for the entire vehicle system is carefully

considered.

2.1.3 This standard can also be used for measuring systems that include the entire 

front end cooling module if air side pressure drop for the entire vehicle system is 

carefully considered.

2.1.4 This standard can also be used for measuring systems that include a secondary

cooling loop if the power to drive the pumps in this system is carefully considered.

2.2 This Standard specifies procedures, apparatus, and instrumentation that will produce 

accurate steady state capacity and efficiency data for refrigerant components.
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2.3 This Standard does not:

2.3.1 Specify tests for dual evaporator systems,

2.3.2 Specify transient test methods, 

2.3.3 Make recommendations for safety

2.3.4 Specify tests for production, specification compliance, or field testing of mobile air 

conditioning systems. 

3.0 Definitions 

3.1 air, standard: dry air having a mass density of 1.204 kg/m

3

(0.075 lb/ft3). 

3.2 apparatus: as used in this standard, this term refers exclusively to test room facilities and 

instrumentation. 

3.3 capacity, total cooling: the rate, expressed in watts (Btu/hr), at which the equipment 

removes heat from the air passing through it under specified conditions of operation. 

3.4 COP, coefficient of performance: a measure of the efficiency of an air conditioning

system, defined as the average heat removed through the evaporator divided by the 

average work input to the compressor

3.4.1 Adjustments to this calculation may be necessary for electrically driven 

compressors, in case the air handling system is used, in the case of front end 

cooling module is used, and for secondary cooling loop systems.

3.5 equipment: as used in this standard, this term refers exclusively to the mobile air 

conditioning equipment to be tested. 

3.6 pressure, standard barometric: 101.325 kPa (14.696 psi).

3.7 refrigerant, : a refrigerant that changes from the liquid to the vapor state in the process of 

absorbing heat. 

3.8 shall or shall not is used to indicate a provision that is mandatory if compliance with the 

standard is claimed.

3.9 should, recommended or it is recommended is used to indicate provisions which are 

not mandatory but which are desirable as good practice.

4.0 Instrumentation

4.1 Temperature Measuring Instruments

4.1.1 All temperature measurements (with the exception of dew point temperature) 

shall be made in accordance with ANSI/ASHRAE Standard 41.1-1986 (RA 

2001).1

4.1.2 If used in determining the water vapor content of the air, dew point hygrometers 

shall be applied as specified in ANSI/ASHRAE Standard 41.6-1994 (RA 2001)2

and shall be accurate to within ±0.2 °C (0.4 °F). 

4.1.3 Inlet air temperature measurements are to be taken upstream of static pressure 

taps on the inlet duct (if installed). Outlet air temperature measurements shall be 

taken downstream of the static pressure taps on the outlet. 

4.2 Pressure Measuring Instruments
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4.2.1 Pressure measurements shall be made with any device meeting the requirements 

of ASHRAE 41.3-1989.3

4.2.2 The accuracy of pressure measuring instruments shall permit measurement to 

within ±2.5% of the reading. 

4.3 Air Differential Pressure and Airflow Measurements4

4.3.1 The static pressure difference across nozzles and velocity pressures at nozzle 

throats shall be measured with manometers or electronic pressure transducers 

that have been calibrated against a pressure standard to within ±1.0% of the 

reading. The resolution of the device shall be equal to or less than 2.0% of the 

reading. 

4.3.2 Areas of nozzles shall be determined by measuring their diameters to within 

±0.20% in four places approximately equally spaced around the nozzle in each of 

two planes through the nozzle throat, one at the outlet and the other in the 

straight section near the radius.

4.4 Electrical Instruments

4.4.1 Electrical measurements shall be made with indicating or integrating instruments. 

4.4.2 Instruments used for measuring the electrical power input to fan motors or other 

equipment accessories shall be accurate to within ±2.0% of the reading. 

4.4.3 Voltages shall be measured at the equipment terminals. Instruments used for 

measuring voltage shall be accurate to within ±1.0% of the reading. 

4.5 Refrigerant Flow Measurement 

4.5.1 Refrigerant flow shall be measured with an integrating flow measuring system 

that is accurate to within ±1.0% of the reading

4.6 Condensate Quantity Measurement 

4.6.1 Condensate collection rates shall be determined using a liquid quantity meter that 

is accurate to within ±1.0% of the reading. 

4.7 Speed Measuring Instruments 

4.7.1 Speed measurements shall be made with a revolution counter, tachometer, 

stroboscope, or oscilloscope that is accurate to within ±1.0% of the reading. 

4.8 Time and Mass Measurements 

4.8.1 Time interval measurements shall be made with an instrument that is accurate to 

within ±0.2% of reading.

4.8.2 Mass Measurement shall be made with an apparatus that is accurate to within 

±1.0% of reading. 

4.9 Torque Measurements 

4.9.1 Torque measurements shall be made with an instrument that is accurate to within 

±2.0% of reading. 

4.10 Refrigerant mass composition measurements for refrigerant mixtures shall be made 

using an instrument that is in accordance with ARI Standard 700-2004.5 
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5.0 Test Facility and Measuring Apparatus

5.1 Test Facility (Figure 1) Recommended configurations for the test facility are provided 

below. In all cases, suitable means for determining the dry-bulb temperature and water 

vapor content of the air entering and leaving the heat exchangers shall be provided. 

B - Blower, CP - Compressor, CC - Cooling Coil, CH - Glycol Chiller, Cond - Condenser, Dp - Differential Pressure Transducer, Evap - Evaporator, FS -

Flow Straightener, H - Heater, Hu - Humidifier, mg - Glycol Mass Flow Meter, mr - Refrigerant mass Flow Meter, Mtr - Motor, N - Nozzle, P - Pressure

Transducer, RH - Relative Humidity Probe, Sc - Condensate Scale, Sp - Speed Controller and Tachometer, T - Thermocouple, TC - Temperature Controller,

TG - Thermocouple Grid, Tor - Torque Transducer, W - Watt Transducer, TXV - Thermal Expansion Valve

Indices : a - air, c - condenser, cp - comp ressor, e - evaporator, g - glycol, I - inlet, n - nozzle, o - outlet, r - refrigerant,

Evaporator

Chamber

Condenser

Chamber

Tgo

Sc

Tgi Glycol

Chiller

mr

R&D

Txri

Tero

CP

Tcpri, Pcpri

Tcpro, Pcpro

Mtr

 Tor

TXV

TC

W

H

B

Teai TG

Hu

N

Ten 1

Tdpen

Tdpei

RH

 Peri

Dper

Sp

FS

Teao TG

Steam

M

mg

TH Compressor

Chamber

B

H

CC

N

Tcn 1

TC

Tcai TG

Sp

Dpcn

W

Tcro,

Pcro

Tcri

Dpcr

Tcao TG

M T

Ten 2

Dpca Dpen Dpea

Tcn 2

DPcd

Cond.

Evap

Figure 1 Sample Test Facility

5.2 Test Room Requirements

5.2.1 Typically, two test rooms are required; an in car room and an under-hood room. 

If desired, a third room may be used for the compressor to simulate under-hood 

conditions. 

5.2.2 An in car condition test room is required. This may be any room or space in 

which the desired test conditions can be maintained within the tolerances given in 

Table 1. 
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5.2.3 An under-hood test room is required. This may be any room or space in which 

the desired test conditions can be maintained within the tolerances given in Table 

1. A condenser wind tunnel may be substituted for the under-hood test room 

provided it is capable of maintaining the conditions given in Table 1. 

Table 1 Permissible Variations in Test Conditions

Test Operating Tolerance(1) Test Condition Tolerance(2)

Evaporator dry-bulb temperature (°C) 1.0 0.3

Evaporator wet-bulb temperature (C) 0.5 --

Condenser dry-bulb temperature (°C) 1.0 0.3

Condenser wet-bulb temperature (°C) 0.5 --

Saturated refrigerant temperature (°C) 1.7 0.3

Liquid temperature if not otherwise specified (°C) 0.3 0.1

External resistance to airflow (Pa) 12.5 --

Electrical voltage (% of reading) 2.0 --

Condensate flow (% of reading) 2.0 --

Nozzle pressure drop (% of reading) 2.0 --

High Side Refrigerant Pressure [kPa]

Low side Refrigerant Pressure [kPa]

Refrigerant Flow [g/s]

Refrigerant Differential Pressure [kPa]

(1) Test Operating Tolerance is the maximum permissible range of any measurement.

(2) Test Condition Tolerance is the maximum permissible variation of the average value of the measurement from 

the specified test condition.

5.3 Wind tunnels for heat exchangers

5.3.1 To produce repeatable and comparable results, it is recommended to control the 

inlet air temperature and velocity profile across the face of the test heat 

exchangers.

5.3.2 Below is an example of one setup that has been used to accomplish this end.

5.3.2.1 Each test heat exchanger shall be mounted in a wind tunnel inside their 

respective test room. The wind tunnel may be constructed from any

suitable duct material. The illustration of a duct sections for the test heat

exchanger in a wind tunnel are shown in Figure 2.
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5.3.2.2 Air enters over the flow straightener (1) and inlet thermocouple grid (2) to 

the test heat exchanger (evaporator, condenser, or gas cooler). At the 

exit of the test heat exchanger is the outlet thermocouple grid (3) before 

the flow measuring devices – nozzles (4). After the nozzles, average air 

stream temperature is measured by a thermocouple or other appropriate 

thermometer (5). Reconditioning of the air (cooling or heating) is done in 

the conditioning test facility heat exchanger (6). For control purposes, an 

electrical heater is recommended. The test facility Blower (7) provides air 

circulation for the test heat exchanger.

Figure 2 Possible Air Loop [re-draw to show straightener and identify necessary insulation]

5.4 Airflow Measuring Apparatus

5.4.1 A suitable means of measuring heat exchanger air flow shall be provided. One 

such method is given in ANSI/ASHRAE Standard 41.2-1987 (RA 92).6 As shown 

in Figure 4, the nozzle airflow measuring apparatus consists of a receiving 

chamber and a discharge chamber separated by a partition in which one or more 

nozzles are located. 

5.4.2 The nozzles used to measure air flow shall comply with ANSI/ASHRAE Standard 

41.2-1987 (RA 92)5or suitable alternative (ASME, ISO, JIS, etc.). The discharge 

coefficient shall be calculated and evaluated as given in ANSI/ASHRAE Standard 

51-19997or ASME Fluid Meters.4

Add references to figure 3? Do we need ASHRAE approval to use?
SAE J2765 Issued Proposed Draft 23MAR2006

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Figure 3 Nozzle Airflow Measuring Apparatus (ANSI/ASHRAE Standard 37-20058)

Figure 4 Flow Nozzle Construction (ANSI/ASHRAE Standard 37-2005)

5.4.3 The velocity profile when measured at not less than nine (9) grid points should be 

within ±10%. Additional means shall be used when needed to improve uniformity

of the air velocity profile. Consult ANSI/ASHRAE Standard 41.2-1987 (RA 92)6

for methods of flow straightening to achieve the desired velocity profile.

5.4.4 Temperature measurements shall be made at not less than the same nine (9) 

locations as in 5.4.3. at the center of equal segments of cross-sectional area 

throughout the duct. Inlet air temperature should be uniform within ±0.5 °C. 

Consult ANSI/ASHRAE Standard 41.1-1986 (RA 2001)1for methods of mixing 

the air stream to achieve the desired uniformity of temperature. 
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5.5 Refrigerant loop (Figure 5)

5.5.1 The refrigerant loop should mimic as much as possible conditions encountered in 

the reference vehicle environment. The components used in the vehicle should 

be used in the test loop if possible. Alteration of the piping (lines, hoses, and 

fittings) from the real application should be fully documented. 

5.5.1.1 Suction line pressure drop should be +/- 10% of the reference vehicle 

application

5.5.1.2 If a Internal Heat Exchanger [IHX] or suction line heat exchanger is used 

in the system, it should be located in the same ambient environment as 

the compressor.

5.5.1.3 Relative height of the components should be located within +/- 25 mm of 

the reference vehicle system. If no reference vehicle is defined, the 

bottom of compressor should be located at bottom of condenser and 

bottom of evaporator shall be located at top of condenser. [Figure 5a]

5.5.1.4 System refrigerant charge amount should not be greater than 125% of 

the reference vehicle system.

5.5.1.5 Oil amount should be revised based on charge amount to approximate 

the same ratio of refrigerant to oil ratio as the reference vehicle system.

5.5.1.6 Oil in circulation shall meet the compressor manufacturer’s requirements.

5.5.2 Instrumentation shall be installed so as to minimize their effect on system 

operation or performance. 

Add nozzle temperatures, additional instrumentation, show 2nd view that illustrates height 

of components

TM

Air in

Air in

SG

Mr

MF

IRD

Cond.

Evap.

Evaporator Chamber Wall Condenser Chamber Wall

Dpen

Comp.

Compressor Chamber

Motor

Tor

Tcao

Tcai

Dpcn Teai

Teao

Sp

Pcpro Pcpri

Tcpro Tcpri

Tcri Tcro

Pcro

TG

TG

TG

TG

DPcr

Tero

Pero

DPer

Ten 1

NZ

Ten 2

NZ

Tcn1 Tcn2

Tcph

Teri

EXV

Pxri

Txri

Figure 5 Typical Refrigerant Loop
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Figure 5a Illustration of component heights.

5.5.3 Compressor Test Stand and Chamber 

5.5.3.1 The compressor is placed inside a third chamber that provides and 

controls specified conditions. The temperature should be maintained 

within 2

oC. 

5.5.3.2 The torque meter should be located between the compressor and the 

clutch in order to measure compressor power at the shaft. 

Drive

Motor

Belt

Idler

Pulley

Compressor

Clutch

Torque

Meter

A/C

Compressor

Shaft

Coupler

Figure 5b Torque meter location
SAE J2765 Issued Proposed Draft 23MAR2006

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6.0 Test Conditions

6.1 To allow for variation of specified compressor speeds for different drive ratios or 

compressor types RPM of compressor should be adjusted as necessary based to match 

the system capacity at L35 test conditions.

6.2 The test matrix is shown in Table 2. The conditions cover a significant range of typical 

vehicle air conditioning operation.

6.3 Performance can be determined with the system operating at full capacity or at a reduced 

capacity to limit evaporator air outlet temperature (measured at the outlet of the airflow 

nozzles). Limiting evaporator air outlet temperature allows comparisons at approximately

equal capacity, allows simulation of smart variable temperature control, and can provide 

evaporator icing prevention. Depending on the compressor, capacity can be controlled by

varying displacement, cycling rates/temperature swings, etc. Precisely achieving a target 

temperature can sometimes be difficult due to resolution in the controls. Specification of 

the target temperature should be consistent across systems to be compared.
SAE J2765 Issued Proposed Draft 23MAR2006

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Table 2 Test Matrix

Ambient 

temp.

[

oC]

Comp 

speed

[rpm]

Condenser Conditions Evaporator Conditions Dew 

point 

[°C]

Inlet air temp 

[

oC]

Face velocity 

[m/s]

Inlet air temp 

[

oC]

Face velocity 

[m/s]

45 900 60 1.5 35 2.0 12

“ 900 45 1.5 “ 2.0 “

“ 1500 “ 3.0 “ 2.5 “

“ 2500 “ 4.5 “ 2.5 “

“ 4000 “ 4.5 “ 2.5 “

35 900 50 1.5 35 2.0 19.4

“ 900 35 1.5 “ 2.0 “

“ 1500 “ 3.0 “ 2.5 “

“ 2500 “ 4.5 “ 2.5 “

“ 4000 “ 4.5 “ 2.5 “

35 900 35 1.5 35 1.5 19.4

“ 1500 “ 3.0 “ 1.0 “

“ 2500 “ 4.5 “ 1.0 “

“ 4000 “ 4.5 “ 1.0 “

25 900 40 1.5 25 1.5 21.3

“ 900 25 1.5 “ 1.5 “

“ 1500 “ 3.0 “ 1.0 “

“ 2500 “ 4.5 “ 1.0 “

“ 4000 “ 4.5 “ 1.0 “

25 900 40 1.5 25 1.5 13.9

“ 900 25 1.5 “ 1.5 “

“ 1500 “ 3.0 “ 1.0 “

“ 2500 “ 4.5 “ 1.0 “

“ 4000 “ 4.5 “ 1.0 “

25 900 25 1.5 25 1.0 13.9

“ 1500 “ 3.0 “ 0.7 “

“ 2500 “ 4.5 “ 0.7 “

“ 4000 “ 4.5 “ 0.7 “

15 900 30 1.5 15 1.0 11.6

“ 900 15 1.5 “ 1.0 “

“ 1500 “ 3.0 “ 0.7 “

“ 2500 “ 4.5 “ 0.7 “

“ 4000 “ 4.5 “ 0.7 “
SAE J2765 Issued Proposed Draft 23MAR2006

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6.4 System setup tests

6.4.1 A typical Refrigerant charge determination procedure is shown below. Other 

procedures may be used based on user preferences.

6.4.1.1 A charge determination shall be performed at the following conditions: 

6.4.1.1.1 The charging condition should be: compressor speed 2000 

rpm, full displacement, 

6.4.1.1.2 Compressor chamber temperature 70oC; 

6.4.1.1.3 Air temperature inlet to the gas cooler/condenser 40oC, 

6.4.1.1.4 Air velocity through the gas cooler/condenser 3.7 m/s

6.4.1.1.5 air temperature inlet to evaporator 40oC, 

6.4.1.1.6 Air velocity through the evaporator 2.5 m/s

6.4.1.1.7 Relative humidity at evaporator inlet of 40%. 

6.4.1.1.8 Other conditions in adddition to this are permited. 

6.4.1.1.9 Compressor RPM may be adjusted based on equalizing 

capacity.

6.4.1.2 The system shall be operated for a minimum of ten (10) minutes at the 

above conditions before starting the charge determination. This is to 

insure stable operation during the charge determination. 

6.4.1.3 Select the initial amount of refrigerant based on system size. In no case 

should be system be operated with less than 1/2 the expected total 

charge. 

6.4.1.4 After allowing system to stabilize, record data for ten (10) minutes. 

Average the data to obtain average readings. 

6.4.1.5 Add refrigerant in increments of no more than 50 g. 

6.4.1.6 The system shall be allowed to stabilize for a minimum of ten (10) 

minutes after adding charge and before recording data. 

6.4.1.7 Figure 8 shows a typical charge determination result for a non-subcooled 

condenser R134a system. The recommended criteria for R134a is: 

[other fluids may have different criteria]

6.4.1.7.1 Minimum of 5 K subcool 

6.4.1.7.2 Compressor out pressure not to exceed 1800 kPa
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SAE R134a charge determination test

Note: evaporator exit DTsuperheat kept = 6~8 K 

0

5

10

15

20

25

30

35

40

400 500 600 700 800 900 1000 1100 1200 1300

Charge [g]

COP [-] / Qe [kW] / DT [K] / T [C]

0

500

1000

1500

2000

Prcpo [kPa] / Prcpi [kPa]

COP_avg Q_avg DTsubcool Teao_at_nozzle

DTsuperheat Proper Charge 1125g Prcpo Prcpi

Figure 6 Sample Charge Determination

Legend: COP_avg – Coefficient Of Performance (average), Q_avg – Refrigeration capacity at evaporator (average), Teao -

Temperature of evaporator air out measured at nozzle, DTsubcool – Condenser outlet subcool, DTsuperheat – Evaporator outlet 

superheat, Prcpo – Compressor outlet (discharge) pressure, Prcpi – Compressor inlet (suction) pressure

6.4.2 Oil in circulation rate

6.4.2.1 Using test conditions as specified in Table 2 at 45oC and 900 RPM and 

45oC and 2500 RPM, a sample of the circulating refrigerant and oil 

mixture should be taken from the equipment and the percentage of oil 

measured in accordance with ANSI/ASHRAE Standard 41.4-1996.9

[Except sample amount is 30 grams.] The total indicated flow rate should 

then be corrected for the amount of circulating oil. Adjust oil amount to 

obtain compressor supplier recommended oil in circulation. [Other 

methods are acceptable based on user preferences]

6.4.3 Temperature and air velocity uniformity

6.4.3.1 To provide equal conditions for all systems to be tested and insure 

reproducibility of the test results, uniformity of air velocity and 

temperature at the inlet to the heat exchangers must be verified prior to 

starting the refrigeration system performance test. Each test should be 

performed for both heat exchangers (condenser/gas cooler and 

evaporator) and over a relevant range of air velocities and inlet air 

temperatures. 
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6.4.4 Air side pressure drop [dry]

6.4.4.1 At room temperature, change airflow rate to cover the range of operation 

in Table 2 and record the pressure drop from inlet to outlet of each heat 

exchanger with the compressor turned off.

6.4.5 Suction line pressure drop

6.4.5.1 Check refrigerant pressure drop from evaporator out to compressor inlet 

and verify that the requirements in 5.5.1.1 are met.

6.4.6 Refrigerant control strategies

6.4.6.1 Verify that all control strategies that would normally be used in the 

refrigerant system are duplicated per the reference vehicle that is being 

simulated. [For example: superheat control, compressor out pressure 

control]

6.5 Operating procedure

6.5.1 The facility operating procedures for the steady state tests procedure elements 

are: 

6.5.1.1 Pre-set test condition parameters.

6.5.1.2 Warm up or cool down the test chambers and adjust the parameters as 

needed until a stable condition is reached.

6.5.2 Establish and maintain stable conditions for at least twenty [20] minutes prior to 

taking data. Steady state conditions are characterized by no more than +/- 0.2

oC 

variation of heat exchanger inlet air and +/- 0.1oC for dew point temperatures

recorded at the beginning and after ten (10) minutes. Trend in temperatures shall 

not be downward or upward by greater than 0.2oC.

6.5.3 Once stable conditions are achieved, data shall be collected for a minimum of 10 

additional minutes with a minimum frequency of 0.1 Hz. [In the case of cycling 

system operation, measurements should be taken with a minimum frequency of 

10Hz for compressor torque and speed. Torque will be time averaged.]

7.0 Calculations 

7.1 Evaporator Capacity shall be measured using three independent methods [See Figure 7]

7.1.1 Air Capacity = dry air mass flow rate * air enthalpy difference – condensate 

enthalpy (small): Additional factors should be added to compensate for any heat 

loss in the duct from the heat exchanger outlet to the nozzle outlet.

Qindoorair = Maindoor,dry · ( heai – hean ) + Qleakduct – Maindoor,dry · ( Wei – Wen ) · h ( 'SteamNBS' , T =Ten , x =0 )

7.1.2 Refrigerant capacity shall be calculated using the following:

Refrigerant Capacity = refrigerant mass flow rate * refrigerant enthalpy difference

Qindoorref = Mr · ( 1 – Xoil ) ·

hero – heri

1000

+ Mr ·

Xoil

1000

· 2.0499 · ( Tero – Terisat) +

0.002261

2

· ( Tero

2 – Terisat2

)
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7.1.3 Chamber capacity = electric heat + steam supplied energy +/- heat gain/loss 

through the chamber walls (small). 

Qhx := Qsteam + Qsteam2 +

W

1000

– Qtrans

Figure 7 Capacity Measurement Schematic for all three methods

7.1.4 Properties of refrigerants shall be obtained from 2001 ASHRAE HandbookFundamentals10

or from an established refrigerant property database.10

7.1.5 Air enthalpies shall be determined in accordance with ANSI/ASHRAE Standard 

41.6-1994 (RA 2001).2or other established database.

7.2 Reported Capacity Calculation

7.2.1 The reported capacity is used to calculate COP. At least two of these 

independent capacities measurements shall be within 5% and the reported 

capacity shall be the average of these two values.

7.3 Compressor Power Calculation

7.3.1 Compressor power is calculated as given below:

T

60

2π

Wcomp  rpm  

7.3.2 In the case of cycling compressors, the average compressor power is calculated 

by integrating the power over complete cycles during the stabilized ten minute 

measurement.

7.3.3 For variable compressors, the average power over the stabilized ten minute 

measurement is used.

7.4 Refrigerant system Coefficient of Performance (COP) Calculation

7.4.1 Coefficient of performance shall be calculated as follows:

COPindoor,avg =

Qindooravg

Wcomp
SAE J2765 Issued Proposed Draft 23MAR2006

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7.4.2 Condenser/gas cooler fan and evaporator blower power is not included in this 

COP calculation. This calculation shall be modified if configurations described in 

paragraph 2.1 are being evaluated.

8.0 Data to be Recorded

8.1 System description

8.1.1 The system and test conditions should be described, as far as possible, 

specifying:

8.1.1.1 Size and weight of components.

8.1.1.2 Air pressure drop through the evaporator and condenser/gas cooler.

8.1.1.3 Uniformity of airflow velocity and inlet air temperature to the evaporator 

and condenser.

8.1.1.4 Line lengths (should be similar in length and diameters to real system).

8.1.1.5 Charge determination criteria.

8.1.1.6 Oil type, charge, and concentration in circulation.

8.1.1.7 Expansion device.

8.1.2 Control of evaporator air outlet temperature should be described. Some systems 

use variable displacement compressors whose capacity is controlled to maintain 

the desired air outlet temperature (if the system could reach that temperature), 

some are clutch cycling, some have other ways of reducing capacity. All systems 

typically exhibit some oscillation at very low loads and these should be reported. 
SAE J2765 Issued Proposed Draft 23MAR2006

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9.0 Symbols used in Equations

A nozzle throat area (m2)

C nozzle discharge coefficient (dimensionless)

Ei power input, evaporator side (W)

ha1 enthalpy, air entering evaporator (J/kg dry air)

ha2 enthalpy, air leaving evaporator side (J/kg dry air)

hr1 enthalpy, refrigerant entering evaporator (J/kg)

hr2 enthalpy, refrigerant leaving evaporator (J/kg)

Pcomp power, compressor (W)

Pv pressure drop across the nozzle (Pa)

qtci total cooling capacity, evaporator (W)

Qs air flow, standard air (m3/s)

Qv airflow rate (m3/s)

rpm revolutions per minute

T torque, compressor (N-m)

vn specific volume of the dry air portion of the mixture evaluated at the dry-bulb temperature 

and barometric pressure at the nozzle exit, and vapor content evaluated at the leaving 

conditions (m3/kg dry air)

v’n specific volume of air at nozzle (m3/kg)

vnsp specific volume of the dry air portion of the mixture evaluated at the dry-bulb temperature 

at the nozzle exit and vapor content evaluated at the leaving conditions but at standard 

barometric pressure (m3/kg dry air)

Wn humidity ratio at the nozzle (kg water vapor/kg dry air)

wro mass flow rate, refrigerant oil mixture (kg/s)

x mass ratio, refrigerant to refrigerant oil mixture (deminsionless)

 density of refrigerant (kg/m3)
SAE J2765 Issued Proposed Draft 23MAR2006

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Appendix XXX Examples of calibration records

1. The UA value for calorimetric chambers.

2. Pressure calibration

3. Torque transducer calibration,...

Appendix FFF – supporting data

1. Uniformity of velocity profiles

2. Uniformity of temperature profiles

3. Air side Pressure drops
SAE J2765 Issued Proposed Draft 23MAR2006

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10.0 References

Table 3 List of Variable Names

AFR_scfm_indoor Total volumetric air flow rate, indoor [scfm]

AFR_scfm_outdoor Total volumetric air flow rate, outdoor [scfm]

COP_indoor_air Coefficient of performance based on air balance, indoor chamber

COP_indoor_chamber Coefficient of performance based on chamber balance, indoor chamber

COP_indoor_ref Coefficient of performance based on refrigerant balance, indoor chamber

COP_outdoor_air Coefficient of performance based on air balance, outdoor chamber

COP_outdoor_chamber Coefficient of performance based on chamber balance, outdoor chamber

COP_outdoor_ref Coefficient of performance based on refrigerant balance, outdoor chamber

DPca Air pressure difference across gas cooler/condenser

DPcd

Air pressure difference between condenser 

air inlet and nozzle air inlet, for flow restriction simulation test 

DPcn Air pressure difference across condenser nozzle

DPcr Refrigerant pressure drop across condenser

DPea Airside pressure drop across evaporator

DPen Air pressure drop across evaporator nozzle

DPer Refrigerant pressure drop across evaporator

DPersl

Refrigerant pressure drop across evaporator and 

suction line, DPersl=DPer+DPsl

Dslope Slope of condensate for evaporator, condensate rate [lbm/s]

Dslope2 Slope of condensed steam after entering indoor chamber [lbm/s]

DT_desup_cp_out Desuperheat compressor outlet [degC]

DT_sub Subcooling condenser out [degC]

DT_sup Superheat evap out [degC]

DT_sup_cp_in Superheat compressor inlet [degC]

ErrIndoor_air Percent difference between air and indoor chamber energy balances

ErrIndoor_ref Percent difference between refrigerant and indoor chamber energy balances

ErrOutdoor_air Percent difference between air and outdoor chamber energy balances

ErrOutdoor_ref Percent difference between refrigerant and outdoor chamber energy balances

eta_c Isentropic efficiency

eta_v Volumetric efficiency

Fc Torque of compressor [N-m / lbf-in]

hcai Moist air enthalpy at condenser inlet

hcan Moist air enthalpy at condenser nozzle

hcri Refrigerant enthalpy at condenser inlet

hcro Refrigerant enthalpy at condenser outlet

heai Air enthalpy at evaporator inlet

heai_dry Dry air enthalpy at evaporator inlet

hean Air enthalpy at evaporator nozzle

hean_dry Dry air enthalpy at evaporator nozzle

heri Refrigerant enthalpy at evaporator inlet

hero Refrigerant enthalpy at evaporator outlet

hvin Water vapor inlet enthalpy
SAE J2765 Issued Proposed Draft 23MAR2006

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hvout Water vapor nozzle enthalpy

h_compin Refrigerant enthalpy at compressor inlet

h_compout Refrigerant enthalpy at compressor outlet

h_fg Latent heat of vaporization

h_liq_in Saturated liquid enthalpy at inlet state

h_liq_out Saturated liquid enthalpy at outlet state

h_vap_in Saturated vapor enthalpy at inlet state

h_vap_out Saturated vapor enthalpy at outlet state

Ma_indoor_dry Dry air mass flow rate across evaporator

Ma_indoor_wet Det air mass flow rate across evaporator

Ma_outdoor Det air mass flow rate across condenser

Ma_outdoor_dry Dry air mass flow rate across condenser

Mr Refrigerant flow [g/s]

Mw_kgps Condensate rate [kg/s]

Mw_kgps2 Condensate rate from steam line inside evaporator duct [kg/s]

Patm Atmospheric air pressure

Pcn Pressure at condenser nozzles

Pcri Refrigerant pressure at condenser inlet

Pcro Refrigerant pressure at condenser out

Pen Air pressure at nozzle entrance

Peri Refrigerant pressure at evaporator inlet

Pero Refrigerant pressure at evaporator out

Prcpi Refrigerant pressure at compressor inlet

Prcpo Refrigerant pressure at compressor out

P_ratio Compression ratio [Prcpo/Prcpi]

Qindoor_air Indoor cooling capacity based on air balance

Qindoor_chamber Indoor cooling capacity based on chamber balance

Qindoor_latent_cond Indoor chamber latent heat based on condensate rate calc.

Qindoor_latent_psych Indoor chamber latent heat based on psychrometric calc.

Qindoor_ref Indoor cooling capacity based on refrigerant balance

Qindoor_sensible_cond Indoor chamber sensible heat based on condensate rate calc.

Qindoor_sensible_psych Indoor chamber sensible heat based on psychrometric calc.

Qoutdoor_air Outdoor capacity based on air balance

Qoutdoor_chamber Outdoor capacity based on chamber balance

Qoutdoor_ref Outdoor capacity based on refrigerant balance

Rhci Relative humidity at condenser inlet

Rhei Relative humidity at evaporator inlet

Rhen Relative humidity after nozzle in evaporator

Tcai Air inlet temperature at condenser 

Tcao Air outlet temperature at condenser 

Tcic Temperature condenser chamber inside ceiling

Tcif Temperature condenser chamber inside floor

Tciw Temperature condenser chamber inside wall

Tcn Average nozzle temperature in condenser

Tcn1 Air temperature at condenser nozzle 1

Tcn2 Air temperature at condenser nozzle 2
SAE J2765 Issued Proposed Draft 23MAR2006

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Tcoc Temperature condenser chamber outside ceiling

Tcof Temperature condenser chamber outside floor

Tcow Temperature condenser chamber outside wall

Tcpc Air temperature of compressor chamber, sometimes Tcph

Tcri Refrigerant inlet temperature at condenser

Tcro Refrigerant outlet temperature at condenser

Tdpei Dew point temperature at evaporator inlet

Tdpen Dew point temperature at evaporator nozzle

Teai Air temperature at evaporator inlet

Teao1 Average of the first row of the matrix

Teao11 Matrix indices (row, column)

Teao12 Matrix indices (row, column)

Teao13 Matrix indices (row, column)

Teao14 Matrix indices (row, column)

Teao2 Average of the second row of the matrix

Teao21 Matrix indices (row, column)

Teao22 Matrix indices (row, column)

Teao23 Matrix indices (row, column)

Teao24 Matrix indices (row, column)

Teao3 Average of the third row of the matrix

Teao31 Matrix indices (row, column)

Teao32 Matrix indices (row, column)

Teao33 Matrix indices (row, column)

Teao34 Matrix indices (row, column)

Teao4 Average of the fourth row of the matrix

Teao41 Matrix indices (row, column)

Teao42 Matrix indices (row, column)

Teao43 Matrix indices (row, column)

Teao44 Matrix indices (row, column)

Teao_avg Average temperature of evaporator air out

Teic Temperature evaporator chamber inside ceiling

Teif Temperature evaporator chamber inside floor

Teiw Temperature evaporator chamber inside wall

Ten Average nozzle temperature

Ten1 Temp of evaporator air nozzle 1

Ten2 Temp of evaporator air nozzle 2

Teoc Temperature evaporator chamber outside ceiling

Teof Temperature evaporator chamber outside floor

Teow Temperature evaporator chamber outside wall

Teri Temperature of refrigerant at evaporator inlet

Tero Temperature of refrigerant at evaporator outlet

Tgi Outdoor glycol temp in

Tgi2 Indoor glycol temp in

Tgo Outdoor glycol temp out

Tgo2 Indoor glycol temp out

Tori Temperature before the expansion device
SAE J2765 Issued Proposed Draft 23MAR2006

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Trcpi Temperature of refrigerant at compressor inlet

Trcpo Temperature of refrigerant at compressor outlet

Ts Temperature of steam in indoor chamber

Tw Temperature of condensate (out of evaporator)

T_cond Condensing temperature

T_evap_in Evaporating temperature at inlet state

T_evap_out Evaporating temperature at outlet state

Vc Compressor speed [rpm]

Vn_c1 Specific volume at condenser nozzle 1

Vn_c2 Specific volume at condenser nozzle 2

Vn_e1 Specific volume at evaporator nozzle 1

Vn_e2 Specific volume at evaporator nozzle 2

Wc Power for 1st blower plus heaters - outdoor chamber [W]

Wc2 Power for 2nd blower - outdoor chamber [W]

Wci Humidity ratio at condenser inlet

We Power for blower and heater - indoor chamber [W]

Wei Evaporator inlet humidity ratio

Wen Humidity ratio after evaporator nozzles

W_comp Compressor power [W]

Xoil Oil circulation rate

x_in Evaporator inlet quality

x_out Evaporator exit quality
SAE J2765 Issued Proposed Draft 23MAR2006

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11. Standard References

1

ANSI/ASHRAE Standard 41.1-1986 (RA 2001), Standard Method for Temperature Measurement, 

American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

2

ANSI/ASHRAE Standard 41.6-1994 (RA 2001), Standard Method for Measurement of Moist Air 

Properties, American Society of Heating, Refrigerating, and Air-Conditioning Engineers. 

3

ASHRAE Standard 41.3-1989, Standard Method for Pressure Measurement, American Society of 

Heating, Refrigerating, and Air-Conditioning Engineers.

4

Fluid Meters-Their Theory and Application-Sixth Edition, 1971. American Society of Mechanical 

Engineers, New York, NY.

5

ARI Standard 700-2004, Specifications for fluorocarbon refrigerants. Air-Conditioning and Refrigeration 

Institute. 

6

ASHRAE Standard 41.2-1987 (RA 92), Standard Methods for Laboratory Airflow Measurement, 

American Society of Heating, Refrigerating, and Air-Conditioning Engineers.

7

ANSI/ASHRAE Standard 51-1999 - Laboratory Methods of Testing Fans for Aerodynamic Performance 

Rating (AMCA Standard 210-99), American Society of Heating, Refrigerating, and AirConditioning Engineers.

8

ANSI/ASHRAE Standard 37-2005, Methods of Testing for Rating Electrically Driven Unitary AirConditioning and Heat Pump Equipment, American Society of Heating, Refrigerating, and 

Air-Conditioning Engineers.

9

ANSI/ASHRAE Standard 41.4-1996, Standard Method for Measurement of Proportion of Lubricant in 

Liquid Refrigerant, American Society of Heating, Refrigerating, and Air-Conditioning 

Engineers. 

10 NIST Standard Reference Database 23, NIST Thermodynamic and Transport Properties of Refrigerants 

and Refrigerants and Refrigerant Mixtures – REFPROP 6. National Institute of Standards 

and Technology, Gaithersburg, MD