Abstract
The energy performance of a variable refrigerant flow (VRF) system was evaluated using an occupancy-emulated research building in the southeastern region of the United States. Full- and part-load performance of the VRF system in heating and cooling seasons was compared with a conventional rooftop unit (RTU) variable-air-volume system with electric resistance heating. During both the heating and cooling seasons, full- and part-load conditions (i.e., 100%, 75%, and 50% thermal loads) were maintained alternately for 2 to 3 days each, and the energy use, thermal conditions, and coefficient of performance (COP) for the RTU and VRF system were measured. During the cooling season, the VRF system had an average COP of 4.2, 3.9, and 3.7 compared with 3.1, 3.0, and 2.5 for the RTU system under 100%, 75%, and 50% load conditions and resulted in estimated energy savings of 30%, 37%, and 47%, respectively. During the heating season, the VRF system had an average COP ranging from 1.2 to 2.0, substantially higher than the COPs of the RTU system, and resulted in estimated energy savings of 51%, 47%, and 27% under the three load conditions, respectively.
Highlights
In order to evaluate the performance of the two systems, three load conditions (i.e., 100%, 75%, and 50%) were applied to the test facility, and each system was operated alternately for 2 to 3 days, respectively [7, 8]. e three load conditions were applied to the entire building or selected zones, and the energy use, thermal conditions, and the coefficient of performance (COP) were measured
The rooftop unit (RTU) system was operated for 9 days at 50% load, 13 days at 75% load, and 8 days at 100% load. e variable refrigerant flow (VRF) system was operated for 9 days at 50% load, 9 days at 75% load, and 6 days at 100% load. e heating season analysis is based on measured data from December 30, 2015, through March 6, 2016
Evaluation Metrics. e performance of the RTU and VRF systems was compared in terms of (1) energy use, (2) ability to maintain room temperature, and (3) system e ciency. e energy use and thermal performance comparison were performed using measured hourly data for occupied hours only (i.e., 8 a.m. to 6 p.m.), excluding the startup hours. e coe cient of performance (COP) analysis was performed using both hourly and 1-minute data
Summary
VRF (Variable Refrigerant Flow) system has been used in many countries in Europe and Asia for more than 30 years since it was invented in Japan in 1982 [1]. ere are known benefits of VRF systems such as easier modular installation, space efficiency, responsiveness to fluctuating loads, and higher efficiency, but several studies [2–6] show that there are concerns regarding the application of VRF systems in the USA, including (1) lack of awareness of energy efficiency advantages, (2) higher first cost, and (3) lack of understanding about the suitability of the VRF system for the building operation profile in the USA. e performance of VRF systems in the USA has been measured mainly in chambers; performance measurement of VRF system in real buildings is challenging due to the complexity of the system and occupancy-related uncertainties. e present paper compared the performance of existing HVAC (RTU, Rooftop Unit) and VRF system in Oak Ridge National Laboratory (ORNL)’s two-story Flexible Research Platform (FRP) during the heating and cooling period. Ere are known benefits of VRF systems such as easier modular installation, space efficiency, responsiveness to fluctuating loads, and higher efficiency, but several studies [2–6] show that there are concerns regarding the application of VRF systems in the USA, including (1) lack of awareness of energy efficiency advantages, (2) higher first cost, and (3) lack of understanding about the suitability of the VRF system for the building operation profile in the USA. E present paper compared the performance of existing HVAC (RTU, Rooftop Unit) and VRF system in Oak Ridge National Laboratory (ORNL)’s two-story Flexible Research Platform (FRP) during the heating and cooling period. In order to evaluate the performance of the two systems, three load conditions (i.e., 100%, 75%, and 50%) were applied to the test facility, and each system was operated alternately for 2 to 3 days, respectively [7, 8]. E three load conditions were applied to the entire building or selected zones, and the energy use, thermal conditions, and the COP were measured In order to evaluate the performance of the two systems, three load conditions (i.e., 100%, 75%, and 50%) were applied to the test facility, and each system was operated alternately for 2 to 3 days, respectively [7, 8]. e three load conditions were applied to the entire building or selected zones, and the energy use, thermal conditions, and the COP were measured
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