Variable refrigerant flow (VRF) systems, like air conditioners, aim to cool the air in one or more rooms by taking the indoor heat from the home and discharging it to the outside. Some of these VRFs may also be used in heating mode.
Unlike air conditioners for domestic use, VRFs can be connected to a multitude of indoor units. They are generally used in shopping malls, office buildings, hotels, hospitals, etc.
The VRF is a category of air conditioning systems using the same thermodynamic laws and the same components as air conditioners.
A VRF is composed of 5 elements:
- A liquid refrigerant circulating inside the VRF. This fluid changes state in each component in order to convert the energy taken from the home and discharge it as heat to the exterior.
- By recovering the calories present in the indoor air, an evaporator, also called “exchanger”, converts the liquid refrigerant into a gaseous state by evaporation.
- A compressor, powered by a motor (electric). It increases the temperature of the fluid coming out the evaporator, while increasing its pressure.
- A condenser, also called “exchanger”, transfers the energy produced during the change of state of the fluid to the outside environment. Condensation converts the gas coming out of the compressor into a liquid.
- An expansion valve reduces the pressure of the liquid, which comes out of the condenser, so that the liquid refrigerant can start a new cycle.
The operation can in some cases be reversed:
The device thus captures the heat from the outdoor air and releases it to the indoor air. This is called a reversible unit.
VRFs can operate:
The outdoor unit draws/releases calories from/into the air, but some models can also be installed on a water loop.
Certified indoor units can be in a cassette or be ducted:
Unlike conventional air conditioners:
It is very easy to make the right choice: just compare the products. But when product performance is not certified, this becomes impossible.
Certification makes it possible to compare objectively.
Following new European regulations promoting the sale of high-performance heating equipment, the performance of VRFs is changing: their efficiency long characterised by instantaneous efficiency called EER for “cooling” mode and COP for “heating” mode is now characterised by a performance that reflects the efficiency of the VRF throughout the year. This is known as SEER (seasonal energy efficiency ratio for cooling mode) or ηsc and SCOP (seasonal coefficient of performance for heating mode) or ηsh. The higher this performance, the more efficient the VRF will be.
Thermal comfort for buildings