What is VRF
VRV Variable Refrigerant Volume systems were invented in Japan in 1982 by Daikin and brought to the United States in 2004. These systems are used worldwide. Daikin VRV (Variable Refrigerant Volume) is their trademarked name, that’s why all other manufactures use the acronym VRF.
Major Components of a VRF System
VRF systems include two major components, a compressor with outdoor coil and multiple indoor fan coil units. The outdoor unit houses the compressor which acts as a pump pushing refrigerant through piping to the indoor coils and back.
A third component is the VRF Branch Selector Box which is the traffic cop of the refrigerant, based on the demand of the system. See our article on VRF Single Port versus Multiport Branch Selector Boxes.
The outdoor coil is most often air cooled, or in some cases water-cooled with a connected cooling tower and boiler to maintain a minimum range of temperature. The compressor provides a variable flow of refrigerant by using an inverter rated motor that varies the speed of the compressor, allowing for reduced energy consumption and varying loads within the building.
Types of VRF Systems
VRF comes in three common system types, cooling only, VRF heat pump and VRF heat recovery. Cooling only is just as the name implies with no way of providing heat.
The heat pump system can provide cooling and heating, but only one method at a time, meaning all zones need to be either cooling or heating, not simultaneously.
The third type is the heat recovery system which allows for simultaneous cooling and heating, and provides for some great energy savings the more balanced the cooling and heating loads are. VRF Heat recovery units basically take heat from one space that wants to be cooled and gives it to another space that wants heating.
Also, within these VRF system types there are air-cooled and water-cooled outdoor units.
Types of VRF Fan Coils
The indoor units are called fan coils because they contain a fan and a coil. The coil can be used for cooling or heating depending on the type of system installed as indicated above. The indoor fan coils come in a variety of configurations and are either visible or hidden behind the construction.
The air can be ducted or un-ducted, meaning the air travels through a piece of sheet metal before reaching the conditioned space or the fan coil is exposed within the room and requires no ductwork.
The fan coils can be recessed mounted on the ceiling or they can protrude down from the ceiling, they can be floor mounted in the space with a manufactured cover or floor mounted and hidden behind construction materials, or hung exposed on the wall.
VRF Ventilation Requirements
Since these VRF fan coils are split from their outdoor units they need a source of fresh air which is important for air quality, unless you live in a heavily polluted city. ASHRAE and most codes require some form of outside air for ventilation, whether by natural means, such as operable windows or more commonly by a dedicated outside air system (DOAS).
This HVAC (Heating, Ventilating and Air Conditioning) unit can be fitted with a cooling or heating coil depending on the geographic climate conditions. The DOAS unit is not intended to cool or heat the space, but to provide fresh outside air that is tempered close to room conditions so that the outside air doesn’t add additional load to the indoor fan coils.
The load for this ventilation requirement should be handled by the DOAS. There are several methods or system configurations in the design of the DOAS that we’ll cover in another article.
VRF Energy Recovery
Working in conjunction with the DOAS unit can be some form of ERV (energy recovery ventilation) unit, that recovers heat from air being exhausted as in winter or from outside air when cooling.
In summer when the hot outside air that is required for ventilation is being brought into the building it can be run through the ERV energy recovery ventilation unit which has cooler indoor air being exhausted through it, effectively pre-cooling the hotter fresh air.
Conversely in winter when colder outside air is being brought in for fresh ventilation requirements, the warmer air being exhausted can be put through the ERV energy recovery ventilation unit to recover some of the heat energy to pre-heat the colder air.
The control of these systems range from a simple remote to complete integration into the buildings energy management system. The great thing about the VRF control system is that it doesn’t need any other automation systems, as it uses its own controllers and interface module with web access capabilities. See our comparison between VRF Manufactures.
How have you used ERV or DOAS in a VRF System, and did everything function smoothly?
Please leave us a comment below, and tell us about your experience with these systems.
Get this great book that goes in depth about VRF Systems.