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ABSTRACT
Heat recovery technologies of variable refrigerant flow (VRF) systems have good potential to reduce the building energy consumption and maintain good thermal comfort in many commercial building types by allowing individual indoor units to heat or cool as required while the compressor load benefits from the internal heat recovery. This study investigates an integrated heat recovery system design of a VRF system with a domestic hot water (DHW) loop using a hydraulic heat exchanger. With the integrated heat recovery VRF configuration, the condensing heat from vapor compression cycles can be recovered and used for space heating and/or DHW production when space cooling is simultaneously required. This strategy could potentially improve the energy savings of the existing heat recovery VRF technology and minimize waste heat through VRF outdoor units. The hydraulic heat exchanger linked to the VRF refrigerant circuit box in this VRF system is connected to the water tank and is able to increase the heat recovery potential on the domestic hot water side. To evaluate energy savings potential of the proposed VRF system, a case study of a nine-story hotel building with 395 guest rooms is carried out in this study using DOE-2.2 in 6 U.S. climate zones. Based on simulated hourly building loads, a calculation tool is also developed to estimate heating/cooling and DHW energy usages. The results from the study show that the annual energy savings of the proposed VRF system can be around 22% to 24% and around 0.3% to 1.4% in cooling and heating main mode, respectively. In terms of annual DHW energy savings, the proposed VRF system can achieve around 54% to 91% of annual DHW energy savings when compared to the baseline VRF in 6 U.S. climate zones.
INTRODUCTION
The building sector is responsible for about 40% of the entire energy consumption in the U.S. (EIA 2015), and the energy consumed by heating, ventilation and air conditioning (HVAC) systems represents approximately 50% of the total energy usage of the building sector (Roth et al. 2002). Improving the energy efficiency of building HVAC systems is considered as an effective mean to achieve the reduction of building energy consumption (Pérez-Lombard et al. 2008). Variable refrigerant flow (VRF) systems have attracted increasing attention in recent years in U.S. and...