Savings from Variable Refrigerant Flow Systems

By Peter Criscione - Research Manager 

I’ve been studying heating and cooling technologies for many years, and variable refrigerant flow (VRF) systems are one of the more interesting efficiency opportunities that I’ve seen in a while. Instead of circulating conditioned air, VRF systems circulate refrigerant to multiple fan-coil units in the building. I’m often asked how they stack up against traditional heating and cooling systems. Unfortunately, I haven’t found an easy answer to this question—but some help is available. The main difficulty is that although these systems have an efficiency rating for both full- and part-load performance, these metrics don’t account for all of the technology’s capabilities. VRF systems can do simultaneous heating and cooling with heat recovery, a significant advantage over traditional systems. Some VRF heat pumps also perform better than traditional heat pumps at low outdoor air temperatures, and these systems can be configured with different numbers of indoor units. All of these factors make an apples-to-apples energy-use comparison with traditional equipment difficult at best.

To help evaluate VRF systems, a few options are available or emerging. The Consortium for Energy Efficiency (CEE) released a revised specification that, for the first time, includes VRF systems to guide utility program incentive levels for commercial air conditioning: CEE Commercial Unitary AC and HP Specification (PDF; effective January 6, 2012). Likewise, a new metric was developed for the VRF performance rating specification, ANSI/AHRI Standard 1230 with Addendum 1 (PDF), to account for simultaneous cooling and heating efficiency (SCHE). The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) won’t be releasing SCHE data on manufacturer’s products for about another year, but when it becomes available it will help to differentiate the performance of the available VRF units. Also, the Bonneville Power Administration has just launched a field study in 10 buildings to attempt to capture the total heating, cooling, and ventilation system savings for VRF systems, but data will not be available for at least three years. Southern California Edison (SCE) is conducting a field test on one of its own buildings that should be completed this year.

To estimate savings from VRF systems compared to traditional air conditioners and heat pumps at this point, though, it seems that all roads are pointing to the need to do modeling. Currently, the EnergyPro software can model VRF units with heat recovery. In addition, the Electric Power Research Institute is working with several organizations, including SCE, to perform field and laboratory tests to develop performance maps for VRF systems that will be put into two other modeling platforms, eQuest and EnergyPlus, this year. Though not as quick as just comparing the energy-efficiency ratios of two rooftop units, these modeling tools at least provide designers a path to compare the savings from VRF systems to those of other options.

I’d like to hear your thoughts on variable refrigerant flow systems. If you’re using them, what savings are you seeing? Aside from the difficulty in estimating their savings potential, do you have other concerns with this equipment?