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The New Variable Refrigerant Flow System Models in EnergyPlus: Development, Implementation and Validation

Variable Refrigerant Flow (VRF) systems provide more flexible controls and better thermal comfort while saving energy. There are two types of VRF systems: the Heat Pump (HP) and the Heat Recovery (HR). The VRF-HP system can provide either cooling or heating, but not simultaneous cooling and heating; while the VRF-HR system can deliver simultaneous heating and cooling to different zones by recovering heat from cooling zones to heating zones. For VRF models in a number of building simulation tools, a large number of system-level curves are used to describe the operational performance of the overall system. These models can generate satisfactory results for VRF-HP systems with simple controls (e.g., constant evaporative temperature), but for VRF-HP or VRF-HR systems with more complex controls under a wider range of operational conditions, there exist significant discrepancies between the simulated and measured energy use. This paper presents algorithms development and implementation of a new VRF-HP model and a new VRF-HR model in EnergyPlus. The two VRF models were successfully validated with measured performance data from real buildings and laboratory experiments.