This article first appeared in Engineered Systems. View the original post in its entirety here.

Variable refrigerant flow (VRF) systems were first introduced to the HVAC community in Japan in 1980 as a highly efficient heating and cooling option in multi-zone comfort applications. It took the U.S. about 25 years to first embrace VRF concepts. Before VRF, engineers opted for the more traditional and less energy-efficient direct expansion (DX) cooling and heat pump (C&HP) options or costlier air- and water-cooled chilled water systems for multiple occupant comfort zones using either 2- or 4-pipe fan coil units.