30 May 2005

MODELING OF AVOIDING WINDOW-TYPE HEAT PUMP FROST THROUGH HEAT RECOVERY SYSTEM


An ideal mathematic model is developed for widow-type air-conditioner evaporator with heat
recovery system under frosting condition. The exhaust hot indoor air passing through the heat recovery
system would be fed to the evaporator, which could increase the total air source mixture temperature, and
mixed air characteristics would be calculated through mass and energy conservation. A parametric
analysis is performed to investigate the effects of air inlet temperature, relative humidity and air mass
flow rate on total heat transfer coefficient, frost thickness and airside pressure drop separately. That
rationalizing ratio and characteristics of indoor air and outdoor air could prolong frosting time and reduce
the frost thickness greatly. Total heat transfer, frost thickness and airside pressure drop will increase with
the time diminishes. They increase non-linearly with frosting time, fast increase at the start and gradually
slowing down afterwards. A higher air mass flow rate would result in less frost accumulation. However,
this could increase the resistance to airflow, and the airside pressure drop.