Water-Source Heat Pumps


Water-source heat pumps (WSHPs) are commercial equipment that are typically installed in commercial buildings as part of a system where multiple heat pumps are connected to a common water loop. Water-source heat pump systems typically also include a boiler and cooling tower for times when it is necessary to add additional heat to the water loop or reject heat from the loop. Applications of WSHPs include water-loop and ground-loop systems. 

WSHPs are a category of ASHRAE equipment.


The current standards for water-source heat pumps took effect in 2015. The standard levels are equivalent to the levels specified in the 2013 version of ASHRAE Standard 90.1. The cooling energy efficiency ratio (EER) standards are 12.2 EER for the smallest WSHPs (less than 17,000 Btu/h) and 13.0 EER for WSHPs with cooling capacities of at least 17,000 and less than 135,000 Btu/h. The heating efficiency standard is 4.3 COP for all equipment types. 

In 2020, DOE initiated a rulemaking to consider amended standards for WSHPs. 

*The cooling energy efficiency metric, energy efficiency ratio (EER), is expressed as cooling capacity at a single entering water temperature (86 °F) divided by the power input. It is expressed in Btu/Wh. The heating energy efficiency metric, the heating coefficient of performance (COP), is a ratio of the heating capacity (at 68 °F entering water temperature) to the power input. It is expressed in W/W.


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, known as simultaneous heating and cooling. 

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



Federal Date States
Potential Effective Date of Updated Standard 2026
Updated DOE Standard Due 2023
Potential Effective Date of Updated Standard 2018
Updated DOE Standard Due 2016
2nd Federal Standard Effective 2015
2nd Federal Standard Adopted (DOE) 2015
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.