## Performance measurements

There are a number of metrics that can be used to compare the efficiency performance of various HVAC systems. The Air-Conditioning & Refrigeration Institute (ARI) defines standardized test procedures to determine the efficiency metrics for a limited scope of HVAC systems.3 The tests used to evaluate the performance vary based on the HVAC equipment being tested. The following list summarizes major HVAC performance metrics:

**Cooling capacity** is rated as the amount of heat energy a cooling unit can remove from a space per hour, expressed in BTU per hour.

**Energy Efficiency Ratio (EER)** is the ratio of the cooling capacity (BTU/h) to the power input value (watts) at any given set of rating conditions expressed in BTU/watt-hour. The current standard is an energy efficiency ratio (EER) of 8.9 for systems with a capacity of 65 to 135 thousand BTU per hour (kBTU/hr).

**Coefficient of Performance (COP)** is defined differently depending on function. For cooling, COP describes the ratio of the rate of heat removal to the rate of energy input in consistent units, for a complete cooling system as tested under a nationally recognized standard. For heating, it is the ratio of the rate of heat delivered to the rate of energy input in consistent units, for a complete heat pump system as tested

under designated operation conditions. Conversion: COP = EER * 3.4.

Note that both COP and EER are calculated under controlled laboratory conditions and usually do not reflect the efficiency of performance under actual use. The seasonal energy efficiency ratio (SEER) and the heating season performance factor (HSPF) address the need to reflect actual use by measuring efficiency in field situations.

**Seasonal Energy Efficiency Ratio (SEER)** is the total heat removed from the conditioned space during the annual cooling season, expressed in BTU, divided by the total electrical energy consumed by the air conditioner or heat pump during the same season, expressed in watt-hours. Federal appliance efficiency standards currently require minimum SEER ratings of 13. The highest efficiency models available can

have SEER ratings up to 23 for central air units.

**Heating Season Performance Factor (HSPF)** is the total heat added to the conditioned space during the annual heating season (expressed in BTU), divided by the total electrical energy consumed by the air conditioner or heat pump during the same season (expressed in watt-hours).

**Integrated Part-Load Value (IPLV)** is a seasonal efficiency rating method for representative loads from 65,000 BTU per hour and up. This rating applies to units that have stated partial capacities, such as units with staged compressors. Units are tested at full capacity and at each stated partial capacity, and those values are then used to calculate IPLV.

## Additional information

For additional information on lighting design optimization, see:

• Nontechnical introduction to H VAC: N CDENR . 2003. “Energy Efficiency in Industrial HVAC Systems.” Accessible at http://www.p2pays.org/ref/26/25985.pdf

• Technical discussion of HVAC systems: Benjamin, Reynolds, Grondzic, and Kwok. Mechanical and Electrical Equipment for Buildings, 10th Edition. John Wiley & Sons, Inc. New York

Notes: Air-Conditioning and Refrigeration Institute. (2006). 2006 Standard for Performance Rating of Unitary Air-Conditioning Equipment and Air Source Heat Equipment.