Quote:
Originally Posted by Battlebasset
My unit is newer and I just had it serviced, and my electric heat coil came on. Heat pumps, at least the ones the builder installs, struggle once temps go below about 40 degrees. And if you set back your thermostat at night (like I do) and it is having to raise the temp vs just maintain, it will have to work even harder.
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AS VT state,d keeping a constant heat setpoint helps to minimize the need for the aux heating to come on during normal heat mode.
See Altavia post #3 for a link to a good description of auxiliary heating uses in a heat pump system.
IMHO, ALL heat pumps struggle when temperatures are below 40F since the heat pump is using a reverse air conditioning cycle to take heat from the outside air and eject it to the inside air and actually heating it. The cooling occurring at the outside condenser now acting as an evaporator now causes water in the outside air to freeze on the coils. The HVAC system senses this and goes into defrost mode.
1. The system goes back to AC.
2. Warm inside air now goes through the inside heat exchanger and evaporates the refrigerant.
3. The refrigerant vapor gets compressed in the outside compressor and increases in temperature.
4 The hot refrigerant vapor now goes to the condenser and rejects heat to the coil and melts the ice/frost.
5. The auxiliary heater now comes on to avoid cooling the air inside the house.
6. When defrosting complete, the system goes back to the original heating using the heat pump.