While Variable Refrigerant Flow (VRF) HVAC systems have been used extensively in Japan over the past 20 years and have been increasing in popularity in Europe, VRF systems still have yet to make a significant dent in the U.S. HVAC market. So I want to ask the simple question: Why is this?

A VRF system is basically an enhanced version of a ductless multi-split system, which have multiple indoor evaporator units connected to one outdoor condensing unit (some ducting may be required for ventilation air). What makes this system different from traditional ducted systems is that heat is transferred to or from the space by circulating refrigerant to and from the evaporators in the conditioned space. Traditional systems transfer heat from the space to the refrigerant by circulating air through ducts or water throughout the building (Goetzler, 2008).

So what are the advantages of a VRF system? They are more energy efficient than traditional ducted systems as there are no duct losses, and also due to the lower sink temperature over the condenser coil. The compressors also typically employ variable speed drives (VSDs). Energy savings of 30-40% over traditional chiller and VAV systems have been found in numerous studies (Amarnath and Blatt, 2008). However, some of the efficiencies gained during the cooling season may be lost in the heating season in particularly cold climates, so be cautious of this while reviewing manufacturer data. VRF systems are typically easier to install because they are lightweight and modular, which in theory should reduce installation costs. These systems also use less square footage in a facility because the condensing unit sits outside the building. VRF systems are particularly good choices for retrofit and renovation projects, especially in older buildings with no air conditioning where duct installation would be difficult or expensive (Goetzler, 2002 and 2008).

If an HVAC technology is more energy efficient yet easier and more cost effective to install, then why isn’t it universally accepted in the U.S.?

Well although in theory the cost to install should be less, American contractors are not yet familiar with the new VRF technology available, therefore their bids are likely a bit higher to manage that uncertainty. Also, facility managers and maintenance technicians are not familiar with the technology, which results in some push back from the owners side on incorporating a technology that their maintenance personnel don’t feel comfortable maintaining. There is also a perceived refrigerant leakage problem, which is undocumented and unwarranted. Lastly, there may be more maintenance involved as each indoor unit would have to be serviced as well as other unknown maintenance issues and life expectancy. Due to this, the total life cycle cost of the VRF technology is unknown and is difficult to compare to other energy efficient HVAC options on the market today.

In the end, most of the cons against VRF technology are due to the “unknown” factor. Like anything else in the world, people are resistant to change and the unknown. I see VRF systems as a wonderful energy efficient alternative to the conventional chiller/VAV system, that are particularly well suited for retrofits and renovations of older buildings that never had air conditioning systems installed. I think the foundation is now being laid, and it is only a matter of time until the VRF system will be considered traditional, and there will be a new technology vying to take its place.

REFERENCES:

Goetzler, William, "Variable Refrigerant Flow Systems," ASHRAE Journal, April 2007.

http://www.ashrae.org/doclib/20070327_goetzler.pdf

Amarnath, Ammi and Blatt, Morton, “Variable Refrigerant Flow: Where, Why and How,” Engineered Systems, February 2008

http://findarticles.com/p/articles/mi_m0BPR/is_2_25/ai_n24265416/

Roth, Kurt and Goetzler, William, et al. "Energy Consumption Characteristics of Commercial Building HVAC Systems Volume III: Energy Savings Potential," TIAX LLC for DOE, 2002

http://doas-radiant.psu.edu/DOE_report.pdf