Variable refrigerant flow (VRF) systems (also known as VRV) have been successfully used for over 25 years, first in Asia, then in Europe. VRF systems allow multiple indoor fan coil units to be served from a single condensing unit, with some systems capable of simultaneous cooling and heating. Systems are known for high efficiency and application flexibility. Indoor fan coil units use Sirrocco type fans, which have a low acoustic footprint. Designers must use care to provide sufficient access to fan coil units for filter change and also consider ASHRAE 15 refrigeration safety requirements. The Mitsubishi system uses a two-pipe refrigerant piping network; other manufacturers use a three-pipe system. WRL will provide commentary on two-pipe versus three-pipe systems as a separate blog post. Units are available in water-source or air-source configurations.
Application note (March 2013): designers should use care when specifying twinned water-source VRF units in a variable condenser water flow application. Units are not able to natively modulate an associated control valve. Previously published application guides incorrectly indicated this as a design feature. For designers looking for variable flow applications, consider units by LG or Daikin, which are available with a specialized control module.