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Winter Heat Pump Inspections

Heat pumps are the same as a/c units, so we don’t operate them when it’s cold outside (below 60°F). We do, however, operate them in the heating mode since that is what would be in use when it’s cold out. The temperature differential at the supply vs. return should be equal to roughly half of the outside temperature, e.g. 50°F outside temperature, the split would be 25°F, 40F outside the split would be 20°F, etc.

Let’s think about that, a heat pump in the heat mode is trying to draw heat from the outside, but it’s cold out. That being the case, the warmer it is outside the easier it will be
to draw heat from the outside air into the refrigerant in the “outdoor coil” and the colder it is the more difficult. The point where the heat pump can no longer keep up is called the balance point. This is the point at which the “emergency / auxiliary / supplemental / back-up” (depending on what you call it) heat is turned on. This is done automatically and the source would typically be electric heat strips or a gas furnace depending on the climate.

There is another factor involved with heat pumps in the winter, which is a bit more complicated. It is the COP or coefficient of performance. This is the amount of electricity put into the compressor vs. the amount of heat out. When the COP is 1 or less, then the back-up heat (even heat strips) is more economical to operate. Remember heat strips are 100% efficient, gas furnaces are only 98% at best, but compressors are typically putting out over 200% efficiency. That is two times the heat for the same amount of electricity. Balance point settings must be set correctly!

 

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