When considering the best choices to heat and cool high-performance homes, my mind immediately goes to heat pumps. They are very efficient systems that facilitate electrification of homes. However, there are a variety of tradeoffs and considerations around types of systems, climate zone, size of heating and cooling loads, and installation. Some of these can have a substantial impact on the performance and ‘greenness’ of the system. Let’s review some of them.
Minisplits are probably the most familiar type of system. In heating mode, they extract heat from the outdoor air and pump it indoors via refrigerant. In cooling mode, it is the opposite, and they extract heat from the indoor air and pump it outside much like a typical central a/c system. (For a detailed review of the refrigerant cycle see Heat Pumps for Cold Climates.)
A wide variety of well-established manufacturers offer high-performance systems with multiple options including ductless wall-mounted, floor-mounted, and recessed ceiling systems, as well as a variety of ducted offerings with options for small to fully centralized distribution systems.
Cold-climate specific systems are suitable for homes in climate zone 6 since the practical lower operating limit is typically around -15°F. In climate zones 7 and 8, these systems can cover a substantial portion of heating loads but need to be supplemented with a secondary heat source such as electric resistance baseboard, cove heaters, or heat strips (in line with ducted systems).
However, progress is being made as the Carrier Infinity Series can maintain 75% output at -22°F. Additionally, the Department of Energy launched the Residential Cold Climate Heat Pump Technology Challenge that includes an optional goal of optimizing performance at -15°F. It will be interesting to see how…
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