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Method for Estimating the Energy Efficiency Ratio of Mixed System Air Conditioners and Heat Pumps (NISTIR 6045)



Piotr A. Domanski, B. S. Kim


In lieu of testing each split system air conditioner and heat pump combination, an empirically based calculation procedure may be used for estimating a unit's Energy Efficiency Ratio at the 35 deg C (95 deg F) rating condition, EER(95). The procedure accounts for performance changes caused by using different indoor sections with the same condensing unit. The procedure is applicable to all electric units having rated cooling capacities less than 19 kW (65,000 Btu/h) and charged with Refrigerant 22. To estimate the EER(95) of one or more combinations that use the same condensing unit, a lab-measured EER(95) for one combination must be known. Typically, the known EER(95) will correspond to the indoor section most frequently sold with the given condensing unit-termed the matched system--because the testing of this combination is mandated by federal regulation. In addition to the lab-measured EER(95), select information on the hardware used in the indoor sections of the matched system and the system(s) for which EER(95) is sought, hereafter referred to as the mixed system, must also be known.
NIST Interagency/Internal Report (NISTIR) - 6045
Report Number


air conditioning equipment, air conditioner, building technology, heat pumps, mixed system, rating procedure


Domanski, P. and Kim, B. (1997), Method for Estimating the Energy Efficiency Ratio of Mixed System Air Conditioners and Heat Pumps (NISTIR 6045), NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed July 18, 2024)


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Created September 1, 1997, Updated November 10, 2018