VRF Loops

A VRF system is an air-conditioning system that varies the refrigerant flow rate using variable speed compressor(s) in the outdoor unit, and the electronic expansion valves (EEVs) located in each indoor unit. The system meets the space cooling or heating load requirements by maintaining the zone air temperature at the setpoint. The ability to control the refrigerant mass flow rate according to the cooling and/or heating load enables the use of as many as 60 or more indoor units with differing capacities in conjunction with one single outdoor unit. This unlocks the possibility of having individualized comfort control, simultaneous heating and cooling in different zones, and heat recovery from one zone to another. It may also lead to more efficient operations during part-load conditions.

There are two alternative VRF models in EnergyPlus:

• The system provided in DesignBuilder is the system curve based model (VRF-SysCurve). In this model, a number of system level curves are used to describe the VRF system performance. This model corresponds to the AirConditioner:VariableRefrigerantFlow object.
• Physics based model (VRF-FluidTCtrl) has been recently introduced into EnergyPlus. It is able to consider the dynamics of more operational parameters and is applicable for fluid temperature control. This model corresponds to the AirConditioner:VariableRefrigerantFlow:FluidTemperatureControl object.

Refer to the Engineering reference for more technical details of the two models.

VRF indoor units are placed within HVAC zones like other zone forced air units. They include pre-configured direct-expansion cooling and/or heating coils.

VRF loops are not like other loops in DesignBuilder HVAC as they consist simply of a single VRF outdoor unit connected to one or more VRF indoor units through a dotted line.

There is no data associated with the VRF loop itself - it mainly serves as a container for the VRF outdoor unit and the connections to the indoor units.