A method for sizing air source heat pump considering the joint effect of outdoor air temperature and relative humidity. (15th April 2023) - Li, Zhaoyang
Abstract: When operated in a highly humid environment, frost may accumulate on the surface of the outdoor coil in air source heat pump units (ASHPs), leading to a reduction in its output heating capacity. Currently, the existing methods for sizing ASHPs only considered the effect of outdoor air temperature, T a, without taking into account the effect of relative humidity, RH, on output heating capacity. This often resulted in an insufficient heating capacity from an ASHP selected. To resolve this issue, a model for predicting the output heating capacity of ASHPs, Q h, was established firstly. Then, considering the variation in the rated output heating capacity of ASHPs, a method for sizing ASHPs considering the joint effect of T a and RH has been developed. Besides, for practical application, a capacity design correction factor, K, was proposed, evaluated, and plotted as a cloud picture. Evaluating results indicated that K can be used for sizing ASHPs accurately. When the effect of frosting on Q h was considered, the maximum rates of decrease in the output heating capacity correction factor, K Q, was between 43.8% and 50.0%, and the outdoor air design temperatures for space heating in six typical Chinese cities were decreased by 1.8–3.5 °C, with the average of 2.8 °C. For highly humid cities, such as Qiannan area China, even if its outdoor air design temperature was 1.4 °C higher than that in Chongqing City, the K value was 0.24 lower. Highlights: A sizing method considering the joint effect of T a and RH was developed. A capacity design correction factor ( K ) was proposed and evaluated. Frosting caused the outdoor air design temperature for space heating to drop by 1.8–3.5 °C. Maximum decrease rates of output heating capacity caused by frosting was 43.8%–50.0%. A cloud picture was given by using the values of K in 278 Chinese cities.