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Variable Refrigerant Flow (VRF), or Variable Refrigerant Volume (VRV) systems offer a highly flexible and efficient alternative to traditional building heating, ventilation and air-conditioning (HVAC) systems. These modern systems are well suited to small to mid-sized buildings with multiple zones, each with different heating / cooling requirements.

What is a VRF / VRV system?

VRF systems are temperature control devices used for space heating and cooling. Similar to split HVAC systems, a VRF system consists of heat exchange units mounted outside and inside the building. In VRF systems, a single outside unit services multiple inside units as opposed to the 1:1 ratio in traditional split systems. Each inside unit provides thermal control to an individual building zone. A branch selector control system allows for precise control of the refrigerant flow rate to each inside unit.

How do VRF / VRV systems work?

VRF systems operate according to a refrigeration cycle in which a working fluid or refrigerant is circulated between an evaporator in each inside unit and a condenser in the outdoor unit. Heat is exchanged between the refrigerant and the indoor / ambient air in these components, allowing for heat to be “pumped” from one air mass to the other.

Heat transfer at the inside units is controlled by varying the refrigerant flow rate in the evaporators. The VRF branch selector allows for flow rate control at each inside unit and different heat loads can therefore be serviced simultaneously by each unit.

Benefits of VRF / VRV systems

The benefits of VRF systems relate largely to their flexibility. They provide rapid response to individual space heating / cooling requirements and can be used for simultaneous heating and cooling of separate zones. This ability makes it possible to use these systems for heat recovery from one zone to another, resulting in higher system efficiency.

The single outside unit in VRF systems offers some maintenance advantages over split HVAC systems in buildings with multiple zones. In addition, having only one outdoor unit means that more sophisticated condenser technology can be used at a similar total cost to an equivalent split HVAC system, resulting in higher energy efficiency. The installation of VRF systems is typically more complicated however, due to the refrigerant piping between the outdoor and indoor units.

VRF systems are far more flexible than traditional packaged or ducted HVAC systems (where a single outdoor unit circulates conditioned air or cold water throughout all zones of a building), offering individualized zone control and a high degree of decentralized controllability. VRF systems also eliminate the need for expensive ducting and offer higher efficiency than packaged HVAC systems due to the lower heat losses incurred during fluid transport between the outdoor and indoor units.

VRF systems are best for small to mid-scale buildings where their somewhat limited inside unit capacity (since a single outside unit must service all inside units) is sufficient.


By Michael Owen, PhD

Michael is a mechanical engineer working in academia. His research encompasses various aspects of fluid dynamics and heat transfer with a strong emphasis on industrial heat exchangers.



  1. https://patinstitute.ca/an-introduction-to-different-types-of-hvac-systems/
  2. https://www.swtc.edu/Ag_Power/air_conditioning/lecture/basic_cycle.htm
  3. https://www.sciencedaily.com/terms/refrigerant.htm
  4. https://www.swtc.edu/Ag_Power/air_conditioning/lecture/evaporator.htm
  5. https://www.swtc.edu/Ag_Power/air_conditioning/lecture/condenser.htm
  6. https://www.csemag.com/single-article/back-to-basics-vrf-systems.html
  7. http://www.seedengr.com/Variable%20Refrigerant%20Flow%20Systems.pdf
  8. http://www.betterbuildingspartnership.com.au/information/vrfvrv-systems/
  9. https://www.advantage-asl.co.uk/news/the-benefits-of-vrf-vrv-air-conditioning-systems