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.
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.