Quote:
Originally Posted by solarguy
Air to air, typical of mini splits, are much less expensive to install than ground source heat pumps. Traditionally, they performed poorly when temps went much below freezing because the evaporator/expansion coils would freeze up outside. So they resorted to resistance heating until they were frost free. When they are in resistance heat mode, they are no more efficient that the cheapest resistance heat.
troy
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When the outside evaporator coil freezes up, it doesn't run resistance heat to thaw the ice. Rather the heat pump runs in AC mode (pumps some house heat outdoors, but with the outside coil fan off) for a few minutes to melt the ice that forms on the outside coils. The outside coils form ice on them since their temp is below freezing when it is pumping heat into the house. It then switches back to heat pump mode to continue heating the house and blows out an massive cloud of "steam" when the outside fan is turned on after running the defrost cycle. My old Goodman heat pump used to defrost on a fixed schedule when running as a heat pump. Not sure how my new Mitsubishi mini-split decides when to initiate a defrost cycle, but its not on a fixed schedule.