Performance of water-source variable refrigerant flow: measurement and verification of two installed systems

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Variable Refrigerant Flow (VRF) systems have developed into a promising emerging technology. While popular in some places in the world, these systems are quite new to the upper Midwest. The systems are an innovative version of a simple split system air conditioner that utilizes variable speed compressors, multiple zone refrigerant distribution, heat recovery, and low energy fan coils to cool and heat commercial buildings more efficiently than standard split systems and heat pumps. VRF systems save energy in four primary ways: distribution of heating/cooling using refrigerant instead of air, variable speed compressors (and fans), zone-level heating and cooling, and recovery of heat from cooling zones to heating zones.

Most VRF systems are air-source, meaning the outdoor unit is cooled (or heated) by air blowing across an air-to-refrigerant heat exchanger. But these systems perform much better in milder climates because their capacity decreases rapidly at very low ambient temperatures (beginning somewhere between 15 degrees F and -10 degrees F). In colder climates these systems often use supplemental heat to provide heat at these temperatures. Alternately, the system can be upgraded to water or ground-source, thereby saving even more energy in colder climates, but at significant additional first cost. But performance of VRF systems is even less understood than that of air-source systems. To fill this knowledge gap, we have completed a study of the energy savings from two water-source VRF systems.