by Kevin G. Angle, PE, LEED Green Assoc.
Having three young children at home, I hear all kinds of music in the car and in the house. Lately, my kids have become excited when Meghan Trainor’s “All About the Bass” comes on the radio – I regularly listen to all three of them in the backseat of the car screaming the lyrics. While writing this post, I was tempted to title it “VRF – It’s All About the Application.” VRF, which is also called VRV, has gained popularity as a newer technology in the United States. This type of air conditioning system utilizes Variable Refrigerant Flow (or Volume).
VRF systems are often viewed as an enhanced version of ductless split systems, which have been successfully installed for many decades. The term “variable refrigerant flow” refers to changing the flow of refrigerant to each indoor unit. The Variable Refrigerant Flow enhancement comes with multiple indoor unit evaporators or condensers, up to 16 with various manufacturers, utilized with a single outdoor condensing unit or heat pump. Due to the advanced use of variable speed compressors, drives, and inverter-driven fans, many manufacturers of these systems are capable of providing simultaneous heating and cooling through their indoor units. Most manufacturers refer to these as heat recovery systems, and they have various methods of recovering the heat through either a two-pipe or three-pipe system.
Now that we know the capabilities of a VRF system, when does it make sense to use it? It’s all about the application (queue the music!). On the renovation of a relatively small government housing project (5,000 sq. ft.), we were tasked within the design criteria to provide a central HVAC system that also provided individual temperature control within each dormitory room. In addition, we had to meet the design requirements of a LEED-certified building, which requires energy savings of 30% compared to the baseline system. Those two criteria limited our options and led us in the direction of VRF. In the end, VRF and geothermal systems were the only two systems able to meet the energy savings.
So we know that the application of VRF works for a smaller building, but is it an option for larger buildings? I would say yes – but again, it’s about finding the right application. VRF systems are good for potential high-rise buildings, which have varying exposures and varying loads throughout the building. VRF heat recovery systems will perform well where one space may need heating, while the adjacent space may need cooling. VRF systems are expensive in terms of first cost – in many cases 2 to 2.5 times compared to a traditional packaged DX system. However, our energy models are indicating that in some cases, as much as 50% energy savings may be achieved when compared to baseline systems. Also, it is important to note that VRF systems do require a dedicated outdoor air system to meet ventilation codes, which in many cases adds to the first cost. Buildings with operable windows or natural ventilation are prime candidates for VRF. VRF also makes sense for historic renovation projects, where it is easier and less invasive to install refrigerant piping than larger hot or chilled water piping, along with associated ductwork.
VRF systems have been used with some success for larger assembly spaces; however, indoor units are typically limited in capacity to approximately 3-5 tons of cooling. As a result, VRF systems may not be the best solution for this application or for any type of industrial or manufacturing building. Albeit a newer technology with many uncertainties surrounding the reliability of energy models, actual savings in labor, and first cost, VRF systems have proven to have a spot in the marketplace with the right application. VRF systems are not new to Europe, and have been successfully used there for more than twenty years, which must say something.
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