VRF foundation laid for growth

Codes, standards, and modeling software developments for variable refrigerant flow technology makes life easier for engineers.


Although variable refrigerant flow (VRF) systems have been used for 25 years in commercial and residential buildings overseas, the technology has been slow to take off in the United States. Reasons for this include concerns about refrigerant leaks in occupied spaces, perceptions of higher first costs, and unfamiliarity with VRF systems.

VRF stalwarts Daikin and Mitsubishi Electric have been educating the industry, investing in R&D, and refining their product lines to move the market forward. This has softened the ground for other manufacturers, such as LG Electronics, Sanyo, and Toshiba Carrier, to join the fray. With time and experience, concerns will be allayed, costs will come down, and engineers and owners will have greater familiarity and trust in VRF systems.

These are the above-ground market dynamics of new HVAC technologies breaking into a conservative U.S. construction market. A lot of foundational work has also been going on in three key areas.

First, VRF systems have not been covered by a certified rating standard by the Air-Conditioning, Heating, and Refrigeration Institute (AHRI), like chillers have, for example. Certified products provide a level playing field for comparing like products from different manufacturers and assurance that products will meet design intent.

Also, VRF systems were not covered explicitly in ASHRAE Standard 90.1, which is adopted directly as the energy code for many states, or indirectly as a compliance path to state energy codes based on the ICC International Energy Conservation Code.

And, energy-modeling results are often required for documenting compliance with codes such as California Title 24, and for voluntary (or involuntary) U.S. Green Building Council LEED ratings. Energy modeling may also be required for realizing tax incentives and participating in utility rebate programs, such as California’s Savings By Design, where incentives are based on how much a building’s modeled energy usage exceeds Title 24.

But all of these things have changed.

In 2008, manufacturers were granted waivers from the existing federal Energy Policy and Conservation Policy Act testing procedures and provided an alternative test method so that efficiency numbers could be used in marketing their products. The alternative testing is based on a procedure agreed upon by AHRI, VRF manufacturers, and the Dept. of Energy (DOE).

In July 2009, AHRI published Standard 1230, Performance Rating of Variable Refrigerant Flow (VRF) Multi-Split Air-Conditioning and Heat Pump Equipment.

In July 2010, ASHRAE adopted Addendum cp to Standard 90.1-2007, which adopted AHRI Standard 1230 and established efficiency requirements for VRF systems. Interestingly, the Institute for Energy and Environment Research targets are 10% higher for VRF systems than for the unitary systems since the part-load performance for VRF systems will be greater.

Since 2008, EnergyPro software, sold by Energy Soft (www.energysoft.com), has been providing a module for VRF systems. At ASHRAE’s 2010 summer meeting VRF seminar in Albuquerque, N.M., it was said that VRF algorithms have been developed for EnergyPlus, the free modeling software provided by DOE; however, the user interface has not been completed. (Isn’t there some stimulus money floating around that can move that along?)

All together, with product testing standards, energy standards, and modeling software catching up, VRF systems can be designed and specified more quickly and with greater confidence. A good next step would be a new section in ARCOM’s MasterSpec library providing standard guideline specifications for VRF systems.

Michael IvanovichIvanovich is the president of The Ivanovich Group, which provides research, analysis, and consulting services to the buildings industry. Ivanovich is a former chief editor of Consulting-Specifying Engineer and HPAC Engineering.


Word on the street

Addendum cp encountered some resistance during the public review process because the critical operations power systems (COPs) in the Addendum are so low that manufacturers won’t break a sweat meeting them. However, the 90.1 committee felt that because AHRI 1230 is so new and manufacturers are still getting their arms around it, ASHRAE didn’t want to push too hard—yet. Expect VRF efficiency requirements to get incrementally tougher via future addenda.

Design tip

I picked up from the ASHRAE VRF seminar that while VRF systems can provide simultaneous heating and cooling by scavenging heat from cooling coils and other methods, in very cold climates where outside temperatures drop to 5 F and below, they need auxiliary heat from in-duct electrical resistance or hot-water coils to meet indoor temperature setpoints.

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