Highly efficient heat pumps for centralized electric heating and cooling in multifamily buildings.

Variable Refrigerant Flow (VRF) is an efficient heating and cooling technology that saves energy and reduces greenhouse gas emissions while greatly improving resident comfort. VRF systems offer multifamily buildings a path to electrification.

Variable Refrigerant Flow (VRF) is an air-source heat pump (ASHP) technology that can be used to heat and cool spaces. ASHPs are high-efficiency electric appliances that add or remove heat from an indoor space as needed. Because they transfer heat rather than generate it, ASHPs are extremely efficient.

Commonly used to provide air conditioning by transferring heat from the air inside to the air outside, ASHPs can also function in reverse to provide effective heating in climates as cold as that of NYC. VRF is a type of centralized ASHP system suitable for many building types. This tech primer focuses on VRF applications for large multifamily buildings. See our Mini-Split Tech Primer to learn more about other ASHP options.

VRF components are modular, allowing multiple indoor units to be connected to a single outdoor unit via refrigerant lines (see Fig 1). This refrigerant piping requires minimal exterior wall penetrations compared to through-wall or packaged terminal ACs, reducing porosity that allows for heat loss or gain through the building envelope.

Outdoor units have variable speed drives that allow them to operate at the optimal rate, instead of simply at “on” or “off” functions. This reduces energy consumption and delivers greater consistency and control of interior temperature. VRF systems can be programmed with smart controls that respond to indoor and outdoor temperatures and can be adjusted to accommodate future changes to the building use or occupancy. Occupants can also adjust room temperature to their personal comfort levels using thermostatic controls on indoor units.

The VRF control system can meter individual indoor units based on refrigerant flow, enabling residents to be billed for their personal heating and cooling consumption.

how to upgrade to VRF systems

Due to the high costs of replacing heating and cooling systems, the best time to consider this upgrade is during a major renovation or at the time of equipment replacement.

There are multiple steps to retrofitting a building with a VRF system:

Plan– When planning for a VRF system, consideration should be given to how refrigerant lines will run through the building, if and how the building should be divided into heating and cooling zones, where outdoor units will be located, and where indoor units will be installed. In buildings that require simultaneous heating and cooling, VRF offers the ability to recover heat from one side of the system and provide it to the other. Called heat recovery, this VRF option requires additional controls and refrigerant lines.

Determine Unit Locations– Outdoor units can be clustered together on the roof or at ground level. Indoor units can serve one room or can be ducted to serve multiple rooms.

The placement of indoor units should avoid creating hot or cold spots in the room and ensure spaces near windows are not too cold.

Forced air systems move air in a way that can make a room feel colder than the thermostat reads, so the placement and operation of the indoor units should not direct high-speed air onto a spot where occupants will linger, making that spot feel drafty.

Install– Installation should be carried out by contractors with significant VRF system experience. Poor installation can result in refrigerant leaks and an underperforming system.

Refrigerant lines must run from the outdoor unit to each indoor unit. The refrigerant can be a highly potent greenhouse gas so preventing leaks through careful installation is a top priority.

VRF systems have maximum vertical and horizonal lengths of refrigerant piping runs. For taller buildings it may be necessary to locate outdoor units at multiple levels to service the entire height of the building.

Condensate formed at the indoor units must be collected and piped to a drain.