Evaluation of the performance of water-cooled VRF system for heat exchanger geometry under part-load operation

• Published in: Applied thermal engineering 2022-10, Vol.215, p.118921, Article 118921
• Main Authors: Choi, Jiyeon, Oh, Been, Na, Sangkyung, Min, Byeongchae, Park, Yeseul, Choi, Gyungmin
• Format: Article
• Language: English
• Subjects: Geometry optimization; Heat exchanger design; Numerical analysis; Variable refrigerant flow system; Water-cooled heat exchanger
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2022.118921

•The geometry of heat exchanger is optimized for water-cooled VRF system.•The heat transfer efficiency is best achieved with 20° of the chevron angle.•The optimal vertical length of full-load operation is 1.7 m.•Considering part-load, the optimal length is 1.2 m in cooling and 1.0 m in heating.•Compared to the experiment, IEER improved by 6.2% and COP improved by 2.87%. In this study, static numerical simulation was used to evaluate the performance of a water-cooled variable refrigerant flow (VRF) system for geometry of plate-type outdoor heat exchanger. In general, heat exchanger is designed based on full-load operating condition. Since most of operation for VRF system is part-load operation, part-load operating characteristics should be considered to optimize entire system. The geometry characteristics are divided into chevron angle and vertical length. Numerical models of cooling and heating modes were developed for the VRF system, system performance was represented by integrated energy efficiency ratio (IEER) for the cooling system and coefficient of performance (COP) for the heating system by AHRI standard 1230. Regardless of operating mode, 20° of chevron angle among 20°, 35° and 45° is the optimal angle of outdoor heat exchanger. The energy efficiency was proportional to the vertical length of the plate heat exchanger and inversely proportional to the chevron angle. In the cooling mode, the energy efficiency ratio (EER) calculation converged at a shorter vertical length of the heat exchanger with a decrease in operating loads. The optimal vertical length is 1.7 m with only considering full-load, and 1.2 m with considering part-load operation. In the heating mode, the tendency of energy efficiency was similar to that of the cooling mode. The optimal vertical length is 1 m which is 0.2 m shorter than the optimal length in cooling mode.