Use of variable refrigerant flow (VRF) technology, already popular in Japan and Europe, is growing in the United States. Developers are using VRF in many types of buildings, including multi-family residential, schools, and office buildings.
Because of its efficiency, VRF will save utility costs for the owner of an owner-occupied building. In buildings occupied by tenants, the technology can be advertised to tenants as a green feature that will reduce their utility bills.
Similar to air-cooled heat pumps, VRF systems use an outdoor condensing unit with copper refrigerant lines run to an indoor evaporator. The difference, however, is that VRF includes a branch controller that controls refrigerant flow between several evaporator units.
Estimates of cost savings vary from 10% to 60%, depending on the application and the baseline type of system and its efficiency. Installation costs are typically a little higher than conventional HVAC systems. Payback periods are reported to be five years or less, but an analysis should be done on a building-by-building basis.
Most manufacturers allow for up to 48 evaporators connected to a single condensing unit. The evaporators come in both ductless (wall-mounted, ceiling mounted, and acoustical ceiling tile hung) and ducted type, allowing for flexibility in design.
They can be used where you would use split system heat pumps, chilled and hot water systems.
VRF can be used in both new construction and renovations, and applies to almost any building use. By using a ductless VRF system, the above-ceiling space needed for MEP systems is greatly reduced.
This gives the developer the choice to reduce building costs by having a shorter height building with the same number of floors, or have higher ceilings, adding value to the space, or possibly adding another floor without changing the building height. It gives an added advantage to retrofit projects because installing refrigerant piping is much less invasive than ductwork.
Saving Compressor Energy
The biggest advantage in energy savings comes from the ability of the system to have zones connected to one condensing unit in heating and cooling simultaneously, while expending little or no compressor energy.
The branch controller varies refrigerant flow (hence the name) by distributing refrigerant to each branch based on the zone thermostat’s call for heating or cooling. It is essentially able to pass heat from the zone in cooling mode to the zone in heating mode. Therefore, the variable speed compressor (another way it saves energy) only handles the difference between all the heating and cooling calls.
VRF can also be used in conjunction with a ground source system for even greater savings by eliminating the outdoor unit. Another option is to use it to supply supplemental heat, via a heat exchanger, to a domestic water heating or a pool water heating system.
All these advantages add up to a good reason for you to consider using VRF in your new project or in retrofitting an older building. Some owners of existing buildings have reported a payback of less than a year for the added installation costs, resulting in energy savings will mount up over the life of the building.