Ask the Expert: When Does VRF Make Sense?

When Does a Variable Refrigerant Flow System Make Sense?

Chris Zimbelman and Adam Allington for Zondits, June 2, 2015

In order to understand what the best applications are for variable refrigerant flow (VRF) systems, we should back up and discuss their operation and benefits first.

VRF systems are a sophisticated type of air-source (or occasionally water-source) heat pump. They have the ability to vary the flow of the refrigerant through the use of an inverter-driven compressor in order to match the refrigerant flow more closely to the heating and cooling load at part-load conditions, as opposed to a more traditional heat pump where the compressor operates at a single speed and is either on or off. This ability can improve the system efficiency when operating at these part loads. Some VRF systems can also use the refrigerant as a cooling and heating medium while still being served by a single outdoor inverter-driven condensing unit. If installed in an application that can take advantage of this ability, VRF systems can be very energy efficient and cost-effective.

A number of factors make the potential operating efficiencies of these systems very high compared to traditional cooling and heating systems. Some of these are improvements in compressor technologies, inverter drives on compressors, and the fact that the heat recovery systems can recover heat from one space that is in cooling mode to dump into a space that requires heating (or vice versa). The typical cooling efficiencies of these units range from 10 to 30 IEER, and heating efficiency ranges from 2 to 5 coefficient of performance (COP).

So, to (finally) answer the initial question:

VRF systems work in many environments but are ideal in buildings with different rooms or zones with different occupancy schedules, activities, and temperature setpoints. VRF systems have been found to be well suited in hotels, hospitals, nursing facilities, strip malls, schools, offices, and historical buildings. Taking advantage of these multiple zones with varying heating and cooling requirements is the best application for these systems, and if they are designed correctly, can allow them to reach the higher end of their efficiency range. They do not tend to work as well in large, open spaces such as large conference rooms.

These systems are complex, and there are many factors to consider prior to installation including (but not limited to) the heating season utility rates, overall heating hours required, and the fact that a supplemental ventilation system will be required.

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