ABSTRACT
Heat pumps are reverse cycle building heating/cooling units or systems that can extract heat from a building and reject that heat to the environment, providing cooling for abuilding, and can switch from providing cooling to providing heating by extracting heat from the environment and rejecting that heat into a building. This heat transfer cycle can be accomplishedusing avapor-compression refrigeration cycle or an absorption refrigeration cycle; though by far, vapor-compression systems are more widely used (see Section 27.4 for more discussion of absorption cycle systems).
