IMAC TEAM 2 APPENDIX J

J2766 Standard for Annualized Climate Calculation of System Power Consumption of a mobile air 

conditioning refrigerant system

DRAFT

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1. Scope

This recommended best practice outlines a method for annualizing the energy consumption of a mobile air 

conditioning system, given a specified ambient profile range, measured data on compressor torque as a 

function of speed and ambient, and a specified speed profile. 

2. References

J2765 Procedure for measuring system COP [Coefficient of Performance] of a mobile air 

conditioning system on a test bench

web sites for climate data

http://rredc.nrel.gov/solar/pubs/tmy2/tmy2_index.html. 

Federal Highway Administration, Nationwide Personal Transportation Survey, 1995. 

http://www-cta.ornl.gov/npts/1995/Doc/index.shtml

US Dept. of Energy, Typical Meteorological Year Data (TMY2), 1995.[preferred source]

http://www.eren.doe.gov/buildings/energy_tools/energyplus/energyplus_weatherdata.html 

National Renewable Energy Laboratory, TMY2 User’s Manual, 1995. 

http://rredc.nrel.gov/solar/old_data/nsrdb/tmy2/

Environmental Systems Research Institute (ESRI), USA Population by County, 1999.

http://www.esri.com

web sites for registration data [Ward’s Auto]

3. Capacity and COP data

Reference data for Capacity and COP shall be collected as described in SAE J2765-Procedure for 

measuring system COP [Coefficient of Performance] of a mobile air conditioning system on a test bench. 

The results shall be weighted as outlined in the following paragraphs.

4. Weighting factors for ambient temperature profile

Decide on the geographic area for which analysis is desired and select specific weather station locations 

close to the major metropolitan regions in this area. Assign vehicle populations based in these regions to 

each of these weather stations. The number of weather stations selected should be determined by the 

range of climate that exists in the geographic region being studied the the vehicle population density

variation in this region.
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Obtain data by time of day, by month [or by day] for each weather station from the appropriate reference 

noted above. Due to shifts in climate data over the recent years, it is recommended that the climate 

history be between 5 and 10 years and as recent as available. Remove the ambient data from 12:00 

midnight to 6:00AM and create temperature bins in 10 degree C increments showing the frequency that 

each temperature occurs in one year.

Add a table to show an example...

Weather

station 1

Weather 

station 2

Weather 

station 3

Weather 

station 4

Weighted 

average

>40 C

30-39 C

20-29 C

10-19 C

1-9 C

<0 C

5. Weighting for vehicle registrations

Obtain vehicle registrations for each area from the website referenced above. Organize and analyze the 

weather data as shown in the table below:

Percent of Vehicle 

registrations in 

region

Weather station 1

Weather station 2

Weather station 3

Weather station 4

6.
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7. Weighting for compressor RPM profile

Collect engine RPM data from the recommended drive shedule shown in the table below for a 

representative vehicle that is chosen for analysis. Multiple engine RPM data by the compressor to engine 

drive ratio. Curve fit the data from SAE J2765 to fit COP vs RPM for each ambient. These curves should 

have a R

2

value of greater than 0.90. [need more description here] These curves will then be added to 

the spreadsheet to predict COP as a function of compressor RPM for each second of the drvie cycle 

chosen.

7.1 Elevated idle temperatures at idle

To compensate for elevated temperatures at the condenser/gas cooler, the COP at speeds less than Idle 

RPM+50 should use the COP that is measured during SAE J2765 at +15 C temperature at the inlet.
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8. Cooling capacity requirement to achieve comfort

For cooling capacity, it is recommended to use the values shown below. If the capacity data from SAE 

J2765 supports that the system cannot achieve these values, then the values should be adjusted 

according to the data that was measured.

8.1 Correction for idle capacity capacity vs the stabilized comfort capacity

8.2 Correction for humidity impact on evaporator capacity

Organize weather data with associated humidity and sort the data by temperature. Partition the data in 10 

degree bins and determine the average humidity for each temperature bin. Correct the evaporator 

capacity for the difference between the tested humidity in J2765 and the average humidity calculated as 

explained above. Determine the enthalpy at each of the humidities and correction factor becomes the 

ratio of the average humidity to the test humidity. [this needs something that addresses the ratio to outlet 

enthalpy as well...]

8.3 Correction for Solar load impact on evaporator capacity

Organize weather data with associated solar load and sort the data by temperature. Partition the data in 

10 degree bins and determine the average solar load for each temperature bin. Correct the evaporator 

capacity for the difference between the tested solar load in J2765 and the average solar load calculated as

explained above. Determine the evaporator load difference by simulation or test at different the solar 

loads and correction factor becomes the ratio of the capacity required for comfort at the average solar 

load to the test solar load.

9. Correction for elevated temperature in front of condenser or gas cooler
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10. Annual Calculation
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Rationale

This standard can be used to compare different refrigerant systems.

Relationship of SAE Standard to ISO Standard

This standard can be submitted to ISO

Reference Section 

SAE J551—The RefItems style tag is used to list the documents.

Developed By 

Team two of the SAE Improved Mobile Air Conditioning Cooperative Research Program

Sponsored By 

SAE Interior Climate Control Committee