Understanding Variable Refrigerant Flows

Common in Europe and Asia, VRF systems have recently become more popular in North America.  Its  ability to respond to fluctuation in space load conditions, means it can reduce energy costs significantly.

There are two basic systems--water-cooled and air-cooled.  A simple VRF system consists of an outdoor condensing unit and multiple indoor evaporators. The condenser and evaporators are connected by a complex set of oil and refrigerant pipes and governed by individual thermostat controls.

Installation 

While VRFs can help save on energy costs,  it is not suitable for all facilities.  Before installing an HVAC system, you should have a professional engineer determine if a VRF system is appropriate for your building.

If the engineer recommends the use of a VRF, the next decision is to determining whether you will need a water-cooled system or an air-cooled system. As the requirements for these two systems can vary and may impact architectural elements.

Air Cooled VRF

For air-cooled systems, an exterior space is required for the installation of a condenser. The space selected for the installation must be away from windows, accessible to maintenance and support weight of the units.  These units, can be unsightly and may need to be hidden from view with an architectural enclosure.

Water Cooled VRF 

For water cooled system is used, a small closet is often required to house the required water source units that compromise units.

In addition, for both air cooled and water cooled systems, a feasible path to route the refrigerant pipes is required.

Another challenge for specifying VRF systems is the provision of a separate outside air supply to each indoor unit to comply with ASHARE Standard 62.1 and building codes.  This requires larger facilities to have a separate outside air fan and control system, and in humid climates providing outside air to each indoor unit helps ensure good indoor air quality.

Negatives of VRF systems

Due to the limitation on the indoor coil maximum and minimum dry and wet bulb temperatures, the units are unsuitable for 100% air applications, particularly in hot and humid climates.   Another concern, is that the cooling capacity available to an indoor section is reduced when there are lower outdoor temperatures, which limits the use of the system in a cold climate to serve rooms that require year-round cooling, such as a server room.

That being said, VRF systems offer benefits beyond energy savings. Its ability to heat and cool separate space at the same time in the same building,  vary compressor speed to meet load condition, and its quieter operations are also other reasons why a VRF system should be considered.