Which type of heat pump does not require a defrost cycle?

The selected answer accurately identifies that a water source heat pump does not require a defrost cycle. Water source heat pumps typically operate with a constant temperature supply from a body of water, such as a lake, river, or underground aquifer. These bodies of water maintain relatively stable temperatures throughout the year, which minimizes the potential for freezing and eliminates the need for defrosting, unlike air source heat pumps that can encounter frost build-up in low temperatures.

Ground source and geothermal heat pumps, while also more stable in temperature compared to air source systems, may still operate in conditions where frost can form on their outdoor loops if part of the system is exposed to low air temperatures. Thus, they can sometimes require defrost cycles, particularly in harsh winter climates.

Air source heat pumps are significantly more susceptible to frost in colder conditions because they extract heat from the outside air, leading to ice accumulation on the coils. This necessitates regular defrost cycles to clear the frost and maintain efficient operation.

In summary, the inherent characteristics of a water source heat pump, utilizing stable water temperatures, mean it operates effectively without the defrosting challenges faced by air source and some ground source systems.