Variable refrigerant flow VRF
It was first developed by Daikin Industries in Japan, under the trade name ‘variable refrigerant volume’ (VRV), but is now widely used throughout the world under the generic name ‘variable refrigerant flow’ (VRF). VRF systems are becoming increasingly popular as they can be more efficient, more compact and offer greater flexibility than other HVAC systems.
VRF systems are based on the flow of refrigerant between an external condensing unit and multiple internal evaporators (typically fan coil units). Each internal evaporator serves a different thermal zone within the building, and the flow of refrigerant to each evaporator is adjusted depending on the local requirement. This gives a great deal of flexibility, and as the output of the outdoor condenser adjusts to match the total internal demand, it allows the systems as a whole to operate at optimum efficiency.
Very broadly, VRF systems can be two-pipe or three pipe systems:
- Two pipe systems can provide either cooling or heating (heat pump systems) to all of the zones.
- Three pipe systems, can provide heating and cooling simultaneously, heating some zones and cooling others, with heat recovery enabling heat from zones requiring cooling to be used to heat zones that require heating. Whilst this has a greater capital cost, the heat recovery allows very efficient operation and so lower operating costs.
VRF systems are best suited to buildings with multiple spaces, varying heating and cooling demand and the need for good local control, such as hotels, where some rooms may be unoccupied whilst others have a very high thermal demand. Because of their limited space requirements (depending on how ventilation is provided) compared to some other systems, they may also be suited to retrofitting older buildings.
They may be less suited to large uniform spaces such as gymnasiums or theatres.
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