Which statement best describes the energy efficiency ratio (EER) under designated operating conditions?

• A. A ratio of cooling energy to air volume flow.
• B. A ratio of energy cost to cooling energy.
• C. A ratio of heating load to fuel input.
• D. A ratio of net cooling capacity in Btu/h to total electric input in watts.

Answer: (D)

Energy efficiency ratio measures how effectively a cooling system converts electrical power into cooling under fixed operating conditions. Under designated operating conditions, it is defined as the net cooling capacity (in BTU per hour) divided by the total electric input (in watts). A higher ratio means more cooling per unit of electrical power, indicating greater efficiency. This differs from seasonal metrics like SEER because DOC uses a specific, standardized set of indoor and outdoor conditions rather than averaging performance over a season. The other statements mix different concepts—cooling energy relative to air flow, energy cost relative to cooling energy, or heating load relative to fuel input—none of which represent the standard efficiency rating for cooling under designated conditions.