Frosting suppression performance enhancement of air source heat pump through improving relative capacity

Abstract

In practical projects, it is always observed that the frosting degree of two identical variable-frequency air source heat pumps (VFASHPs) in the same neighborhood varies a lot. When the building area they serve is smaller, their frosting speed is slower. This indicates the relative capacity of VFASHP, i.e. the ratio of heating capacity of VFASHP at rated speed to the space heating load at the outdoor design temperature for heating, has evident influence on the frosting suppression performance. However, the influence mechanism and degree are unclear. To reveal the quantitative influence of relative capacity on its frosting suppression performance, a mathematical model of VFASHP was established to reveal this phenomenon in this work. By changing the building area it served, the effect of relative capacities of VFASHP on frosting suppression performance was investigated through the method of developing frosting maps. Then combining the meteorological data, its frosting performance variations in Beijing (low humidity city) and Xi’an (high humidity city) were analyzed. Results indicate that with the increase of relative capacity, the frosting suppression performance of VFASHPs can be enhanced obviously. Specifically speaking, the upper limit temperature of frosting region of VFASHP decreases, while the critical relative humidity for frosting increases. Consequently, when the relative capacity increases by 10%–50%, the frosting duration in Beijing decreases by 3.29%–19.63%. Compared with that in Beijing, the decrease rate of frosting duration in Xi’an is 0.30%–3.07% greater.