HSPF (Heating Seasonal Performance Factor) is a term used in
the heating and cooling industry. HSPF is specifically used to measure the
efficiency of air source heat pumps.
The efficiency of air conditioners are often rated by the Heating Seasonal
Performance Factor (HSPF) as defined by the Air Conditioning, Heating, and
Refrigeration Institute in its standard 210/240 Performance Rating of Unitary
Air-Conditioning and Air-Source Heat Pump Equipment.
The higher the HSPF rating of a unit, the more energy efficient it is. HSPF
is a ratio of BTU heat output over the heating season to watt-hours of
electricity used. It has
units of BTU/watt-hr.
Depending on the system, an HSPF ≥ 8 can be considered high efficiency and
worthy of a US Energy Tax Credit.
The HSPF is related to the non-dimensional Coefficient
of Performance for a heat pump, which measures the ratio of heat
energy delivered to electrical energy supplied, independently of the units used
to measure energy. The HSPF can be converted to a seasonally-averaged COP by
converting both the BTU heat output and the electrical input to a common energy
unit (e.g. joules). Since 1 BTU = 1055 J, and 1 watt-hour = 3600 J, the
seasonally-averaged COP is given by:
Avg COP = Heat transferred / electrical energy supplied = HSPF * 1055 J/BTU /
3600 J/watt-hour = 0.293 HSPF.
Thus, a system which delivers an HSPF of 7.7 will transfer 2.25 times as much
heat as electricity consumed over a season.