Designing VRF Systems

The main advantage of a variable refrigerant flow (VRF) system is its ability to respond to fluctuations in space load conditions. By comparison, conventional direct expansion (DX) systems offer limited or no modulation in response to changes in the space load conditions. The problem worsens when conventional DX units are oversized or during part-load operation (because the compressors cycle frequently). A simple VRF system, comprised of an outdoor condensing unit and several indoor evaporators, which are interconnected by refrigerant pipes and sophisticated oil and refrigerant management controls, allows each individual thermostat to modulate its corresponding electronic expansion valve to maintain its space temperature setpoint. VRF systems have been used in Asia and Europe for almost twenty-five years. With a higher efficiency and increased controllability, the VRF system can help achieve a sustainable design. Unfortunately, the design of VRF systems is more complicated and requires additional work compared to designing a conventional DX system.