Heat pipe integration in vapor compression systems for building energy efficiency: A critical review

Vapor compression systems (VCSs) dominate building heating and cooling and account for a large share of building energy use and peak electricity demand. Although heat pipes (HPs) have been widely studied for heat recovery, subcooling, dehumidification, and free cooling, existing reviews largely focus on device behavior or isolated applications rather than building-scale energy relevance. This review addresses that gap by examining more than 85 studies on HP integration into VCSs across central HVAC, vapor-compression heating, residential and unitary air conditioning, data center and telecommunications cooling, and building-related thermal energy storage. Using a common building-oriented framework based on performance mechanism, energy boundary, and deployment practicality, the applications are grouped into three classes. High-yield applications, such as HP-assisted free cooling and heat-pipe radiator heating, report the largest savings (46–89%) by reducing or displacing active compression under favorable climates. Moderate-yield applications, especially air-side heat recovery and latent-load management in central HVAC, typically achieve savings of 22–45%, though these are often offset partly by fan or pump energy. Residential integrations generally provide smaller gains (