Water-Source Heat Pumps



Water-source heat pumps (WSHPs), which are generally used in commercial buildings, are installed as part of a system where multiple heat pumps are connected to a common water loop. In heating mode, the heat pump transfers heat from the water loop to a space, while in cooling mode, the heat pump transfers heat from the space to the water loop. Water-source heat pump systems allow for moving heat from one area of a building to another during times when some spaces need cooling while others require heating.


DOE updated the standards for WSHPs in January 2001 by adopting the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) 90.1-1999 minimum efficiency levels. (ASHRAE 90.1 is a commercial building energy code.) The standards for WSHPs, which vary by capacity, include minimum efficiency levels for both cooling and heating performance. Cooling efficiency is measured by an Energy Efficiency Ratio (EER), which is the cooling capacity (in Btu/hr) divided by the power input (in watts). Heating efficiency is measured by the coefficient of performance (COP), which is the heat delivered (in Btu) divided by the energy input (in Btu). The current standards took effect in October 2003.

ASHRAE 90.1-2013 updated the minimum efficiency levels for WSHPs. DOE is required to either adopt the efficiency levels in 90.1-2013 as national standards or adopt more stringent standards if they would produce significant additional energy savings and be technologically feasible and economically justified.


Technology options for improving the efficiency of water-source heat pumps include higher-efficiency compressors and fan motors.


Federal Date State
Potential Effective Date of Updated Standard 2018
Updated DOE Standard Due 2016
1st Federal Standard Effective 2003
1st Federal Standard Adopted (DOE) 2001
EPACT Initial Federal Legislation Enacted 1992

Timeline reflects state standards from 2001 to present; federal standards from inception to present.

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