Old-timers in the HVAC industry remember the days when we rated the efficiency of equipment according to its EER (energy efficiency ratio) rating. This was calculated by dividing the BTU capacity of a unit by the wattage consumed by it. This was a steady-state rating however, and did not recognize a units seasonality or real-life consumption. Therefore, AHRI (Air-Conditioning Heating & Refrigeration Institute) developed the rating we use today known as SEER. This is calculated by taking the cooling output of a unit during a typical cooling season and dividing it by the total electrical energy input during that same time. This rating is only applicable to units under 6 tons.
Larger capacity units than this were rated according to their IPLV or integrated part load value. This was a single figure based on part load EER, designed to reflect the operating efficiency of equipment under real-world rather than ideal laboratory conditions. On January 1, 2010 a new methodology was adopted and defined as integrated energy efficiency ratio. (IEER) This rating methodology was developed by AHRI as an improvement for unitary equipment, and covers all units, even if single stage. It takes into account constant fan usage in commercial applications and includes mechanical cooling operation only. Economizer’s and energy recovery is not factored into this rating. IEER is defined as the weighted average of a units efficiency at four load points – 100%, 75%, 50%, and 25% of full load capacity. More specifically, this is determined as follows.
IEER = (.02*A) + (.617*B) + (.238*C) + (.125*D)
A = EER at 100% net capacity
B = EER at 75% net capacity
C = EER at 50% net capacity
D = EER at 25% net capacity
Weather modeling for cities representing 15 US climate zones was used in developing this calculation and included the percent of time operating in the four net capacity load bins listed above. Three end use sectors were chosen, office buildings at 40%, schools at 30% and retail spaces at 30%. The 15 cities defining US climate zones included Miami, Houston, Phoenix, Memphis, El Paso, San Francisco, Baltimore, Albuquerque, Salem, Oregon, Chicago, Boise, Burlington, Vermont, Helena, Duluth and Fairbanks.
This rating provides a comprehensive view of larger capacity systems, and a units IEER rating should never be compared to its EER rating. For more information, please refer to AHRI Standard 340/360, Performance Rating Of Commercial And Industrial Unitary Air-Conditioning And Heat Pump Equipment.