EER

EER stands for Energy Efficiency Ratio — a measure of cooling equipment efficiency expressed as BTU of cooling output divided by watts of electrical input at a single, standardized operating condition (typically 95°F outdoor / 80°F indoor for air-cooled equipment). Higher EER means more cooling per watt of electricity consumed.

For chillers specifically, EER is the right metric for comparing units operating at peak design conditions — for example, a 500-ton water-cooled chiller running at full load on a 95°F afternoon. A current-generation high-efficiency centrifugal chiller will typically deliver an EER in the 14-to-17 range at full load. Older units may rate 9 to 11.

EER alone can be misleading because most commercial chillers spend the majority of their operating hours at part load, not full load. For that reason, ASHRAE and AHRI publish a separate Integrated Part-Load Value (IPLV) rating that weighs efficiency across a representative load profile. When comparing chillers, look at both numbers — a unit can have an excellent EER but a mediocre IPLV if it doesn't modulate well.

ASHRAE 90.1 specifies minimum EER thresholds by equipment category and tonnage; current state energy codes typically reference 90.1 by year (e.g., 90.1-2019), so check the threshold your local jurisdiction enforces before specifying replacement equipment.