A field study on the impacts of cold island effect on operating performances of air source heat pump array for space heating

Connecting multiple air source heat pump units in parallel to form an air source heat pump array (ASHP-A) is an important heating approach for central heating in small areas. At a low wind speed, the colder air stream exhausted by outdoor coils of ASHP units cannot effectively mixed with the ambient air and repeatedly return to the outdoor coil for heat exchange, resulting in the local air temperature inside the ASHP-A lower and lower and forming the cold island effect (CIE). CIE may seriously deteriorate the heating efficiency of ASHP units in buildings. However, the impacts of CIE on the operating performances of an ASHP-A were insufficiently studied in existing studies but necessary for developing a reasonable installation standard and efficient control strategy. Therefore, to reveal the impacts of CIE on the operating performances of ASHP units in ASHP-A, the characteristics of CIE, and its impacts on the operating performances of the field ASHP-A were experimentally carried out. The results demonstrated that CIE significantly existed in the field ASHP-A and resulted in frequent defrosting operations and lower heating performances. The defrosting frequency of Unit 1 having a more severe CIE was increased by 243.5 %. The averaged output heating capacity and COP in Unit 1 declined by 27 % and 27.7 %, and these for Unit 2 by 13.6 % and 14.8 %, respectively. The frosting-defrosting loss coefficient for Unit 1 was increased by 519 % relative to Unit 2. This study is valuable to promote the development of installation standards by taking the CIE into consideration for improving heating efficiency of ASHP-A in buildings.