Humidity and Variable Refrigerant Flow Operation in Multifamily Buildings

In climates where summers are warm and humid, high indoor humidity is a growing concern for multifamily developers and building owners. The challenge is exacerbated in efficient buildings because efficient envelopes (especially glazing) reduce sensible loads, but latent loads generated by occupants are unchanged. This study was led by Steven Winter Associates, Inc. (SWA) and focused on three new multifamily buildings in New York, NY. Variable refrigerant flow (VRF) systems have become very common in large, new multifamily buildings. As with many other cooling systems, designers often rely on VRF systems to control humidity during summer months. The three new, large, multifamily buildings in New York City all used VRF systems to provide heating, cooling, and humidity control (at least in part). SWA installed instruments to collect humidity data from dozens of apartments in each building (between 24 and 67 apartments per building). At Buildings A and C, SWA also connected to VRF systems via BACnet to collect key system performance parameters. The primary focus of this research was evaluating humidity control strategies in these buildings, including humidity control provided by the VRF systems. A secondary goal was to characterize energy performance and efficiency of the VRF systems.