Variable Refrigerant Flow (VRF) systems are gaining popularity in multizone commercial buildings due to comfort advantages owing to modulation and tighter temperature control. However, their actual installed performance in terms of energy efficiency, economic and environmental benefits relative to conventional heating, ventilating, and air conditioning (HVAC) systems are not well documented. It has become crucial to develop a validated methodology to accurately predict their seasonal performance to support facility owners and designers in decision-making and equipment sizing. Gas Engine-driven Heat Pump VRF (GVRF) systems are relatively new in the North American market and there are limited data on their installed performance characteristics across a wide range of conditions. Heat pump specifications are typically based on single-point rating conditions, whereas the actual installed performance of all air-source heat pumps, both gas-fired and electric, are dependent on ambient conditions and part-load operation. The efficiencies of these equipment are best defined by performance maps ranging across a broad range of operating conditions. The objective of this paper is to describe the development of EVRF (Electric VRF) and GVRF EnergyPlus models using the System Curve-based Model approach based on multiple custom performance curves. The study also highlights the current limitations of modeling VRF performance using manufacturer performance data as they inherently operate at part-loads below 50% when sized to meet the heating load in cold climates, but manufacturer specified performance data are frequently not specified below part-loads of 60%. The modeled performance curves were compared with measured performance data generated in field demonstrations.

These preliminary models were used to predict seasonal performance and operating cost savings of GVRF systems paired with dedicated outdoor air system (DOAS) relative to electric VRF/DOAS systems and baseline variable-air-volume (VAV) systems. This comparison was done for two commercial Department of Energy (DOE) reference building types across five ASHRAE climate zones in North America. Results indicate that the GVRF/DOAS may reduce peak electric demand by 24%-96% in all simulated applications and lower annual energy costs. Due to high-efficiency heating and cooling, GVRF/DOAS also has potential to reduce GHG emissions compared to conventional VAV systems given the current electricity generation mix. The results of these studies show the potential for VRF heat pumps, but also point to a need for additional measured field data for both EVRF and GVRF to build confidence in the predictions of the current VRF models.