INTRODUCTION Variable refrigerant flow (VRF) systems vary the flow of refrigerant to indoor units based on demand. This ability to control the amount of refrigerant that is provided to fan coil units located throughout a building makes the VRF technology ideal for applications with varying loads or where zoning is required.

VRF systems are available either as heat pump systems or as heat recovery systems for those applications where simultaneous heating and cooling is required.

In addition to providing superior comfort, VRF systems offer design flexibility, energy savings, and cost effective installation.

This paper will outline the benefits of a typical VRF system, describe the advantages offered by the most advanced outdoor units available, and provide general guidelines for selecting a heat pump system versus a heat recovery system.

Each indoor fan coil unit has its own metering device that is controlled by the indoor unit itself, or by the outdoor unit. As each indoor unit sends a demand to the outdoor unit, the outdoor unit delivers the amount of refrigerant needed to meet the individual requirements of each indoor unit (Fig. 1).

These features make the VRF system ideally suited for all applications that have part load requirements based on usage or building orientation, as well as applications that require zoning.