Key Considerations for Cold-Climate Ductless Heat Pumps

Mar 12, 2020

Manufacturers designed cold-climate ductless heat pumps to produce an adequate volume of heat at very low temperatures. Some models maintain their full capacity at temperatures as low as -15˚F. Due to increased interest in these models throughout the region, in 2019 the NW Ductless Heat Pump Project, along with regional and extra-regional subject matter experts, developed a recommended Northwest specification for cold-climate ductless heat pumps (that resource is available here). In colder areas of the Northwest, these modern heat pumps are ideally suited to displace electric resistance heat.

Key considerations:

1. Increased output capacity: If a consumer primarily uses the system for heating (not cooling), then installers can size a cold-climate system smaller than a standard ductless system. Recent capacity and performance lab testing of over a dozen cold-climate systems shows that in many cases a 1-ton cold-climate system can provide better capacity than a 1.5-ton standard ductless system when outdoor temperature is below 10˚F. It is essential that installers use the manufacturer extended capacity tables to optimize the system size for its application.

2. Improved efficiency at low outdoor temperatures: Systems selected for cold-climate conditions are capable of producing anywhere from 1.75 to 2.25 COP at 5˚F. In comparison, a standard ductless heat pump may have both a lower COP and lower capacity, increasing the reliance on electric resistance heat in the home.

3. Performance at moderate temperatures: It is recommended practice to ensure that all variable capacity equipment can operate at a wide range of its rated capacity. For example, a system with a minimum capacity that is less than a quarter of the maximum capacity should reduce short cycling at moderate temperatures.

Making the most of a cold-climate ductless heat pump system requires understanding the climate conditions and heating needs of the home and designing the system according to load calculation results. For heat displacement applications, a system should be designed to displace 40%–70% of the calculated load. In order to properly size the systems, installers can use the new HVAC Sizing Tool or the Cold-Climate Heat Pump Specifications and Recommendations document. Cold-climate systems are a good choice for climates where winter ambient temperatures regularly drop into the 20’s.

NEEA, Canada, and Purdue University are co-developing a new load-based test procedure. The procedure reveals that installers need better part-load performance data so they can more accurately select ductless equipment for the specific climate it will operate in. Stay tuned for more information about this new test procedure.