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Heat Pumps: The Outdoor Unit

A photo of the outdoor unit of a heat pump outside of a building, with a small covering to protect the unit from weather elements

A blog post from Steven Winter Associates

Key Takeaways

  • Carefully consider the location of the outdoor unit to avoid coil freezing, excessive defrost cycles, and other harmful weather conditions.

Executive Summary

During the winter, the outdoor unit of an air source heat pump removes heat from air blowing through it. But if the outdoor unit is encased in snow and ice, it is not able to remove heat from the air.Heat pumps have built-in defrost mechanisms, as some coil freezing is to be expected. However, when heat pumps are subject to extraordinary levels of moisture, the systems defrost a lot. Defrost cycles don’t generally use a tremendous amount of energy, but the time spent in defrost mode reduces the capacity of the system, as the unit cannot actively provide heat during those cycles. Also, when heat pumps defrost, liquid water drips out. If multiple outdoor units are stacked on top of each other, that liquid will drip down and freeze on the lower units. It’s important to carefully consider the location of the outdoor unit to avoid coil freezing, excessive defrost cycles, and other harmful weather conditions.

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