Evaluation of VRF Systems with Comparisons to Traditional HVAC Systems (ST-16-C068)

Variable refrigerant flow (VRF) systems have been gaining popularity globally, particularly in Asia and Europe for cooling and heating in the built environment in the last two decades. In recent years, VRF systems are starting to fill a growing niche in renovation projects in the U.S. This paper describes the design and evaluation of a large scale installation of VRF systems with comparisons to traditional HVAC systems.  These VRF systems are part of a mega HVAC project that includes design, installation, commissioning, and operation of HVAC systems for 6 almost identical building complexes located in Seoul, Republic of Korea. The building complexes, with 10 above-ground floors and 4 subterranean floors, primarily house offices, conference rooms, auditoria, R&D labs, cafeteria, restaurants, utility, and machine rooms. Four of these buildings, Complex A, B, D, and E are equipped with a mélange of HVAC systems consisting of centrifugal chillers and absorption chillers, and VRF systems for their cooling and heating needs, while Complex C is 100% served by VRF systems and Complex F is 100% covered by traditional HVAC systems. The total installed HVAC equipment includes 2,000 tons of centrifugal chillers, 4,000 tons absorption chillers, 2,145 tons of geothermal VRF systems, and 6,335 tons of air- and water-cooled VRFs. Thanks to the similarities in architecture, construction, occupancy, and thermal load of these 6 building complexes, the mega project provides a unique opportunity to conduct objective evaluations and comparisons between VRF systems and traditional HVAC systems over a wide range of aspects: energy, comfort, maintenance costs, and initial investments.  The objectives of this study are (1) to evaluate the energy performance and other benefits of VRF systems in comparison with traditional HVAC systems, and (2) to evaluate if VRF is a technically and economically viable solution for large building complexes. The paper also presents several new technologies implemented in this project including (1) variable air volume (VAV) discharge temperature control technology, (2) VAV movable diffuser. The discharge temperature controls technology regulates the air flow to maintain the discharge air temperature instead of directly controlling the returning air temperature resulting in much less temperature swings. The movable diffuser utilizes Coanda effect to achieve optimal temperature distribution in air conditioned spaces. Lastly, an in-situ approach for determining the Coefficient of Performance (COP) of VRF systems is proposed for real-time energy performance evaluation.