The primary focus was on electrically driven air-to-air or air-to-water air-source heat pumps (ASHP), with air or hydronic heating systems, since these products suffer severe loss of heating capacity and efficiency at lower outdoor temperatures. Thermally activated (engine-driven, absorption, etc.) ASHPs and ground-source heat pumps (GSHP) was also included in individual country contributions if desired. The main technical objective was to identify solutions leading to ASHPs with heating SPF > 2.63 W/W, recognized as a renewable technology.

Start date: July 2012

End date: May 2017


  • Identify potential equipment & system options for detailed evaluation
  • Determine energy savings potential over range of cold climate locations
  • Develop final Annex report comparing various design options for cold climate heat pump applications on common basis

The main outcome of this Annex was information-sharing on viable means to improve ASHP performance in cold climate locations – defined for purposes of the Annex as locales with a significant number of hours having ambient temperatures < -7°C.

Project manager and participating countries

Austria, Canada, Japan, and the US (Operating Agent) were participating in the Annex.


The website of Annex 41 can be viewed here


Field News

New publications from Annex 41

Three new publications – the Final report, the Executive summary, and the Two-page summary – from the HPT TCP Annex 41...