Experimental study of sensible heat recovery of heat pump during heating and ventilation

Indoor space requires heating, cooling and ventilating for maintaining human occupant space to a comfortable level. Heat pump system is now widely used since it has the capabilities of providing both cooling and heating with a single unit. Ventilation, which exhausts the contaminated indoor air and brings in the fresh outdoor air is essential for maintaining pleasant indoor air quality. Ventilation, however, causes energy loss since air-conditioning is necessary to change the state of outdoor air to that of indoor. When outdoor air is introduced into the interior space, it must be cooled or heated to bring it to the indoor space condition. In this work, three methods of recovering sensible heat during heating and ventilation process of heat pump have been studied experimentally. Those methods are by a separate sensible heat exchanger, introduction of indoor air to the evaporator (single heat recovery), and finally a combination of fore-mentioned two methods (double heat recovery). An air-source heat pump system with none, single and double heat recovery capabilities has been built and tested in two constant-temperature and constant-humidity thermal chambers that simulate the indoor and outdoor environments. From the experiment performed under standard heating condition with a ventilation ratio of 23.1%, coefficient of performance for none, sensible heat exchanger, single and double heat recoveries were 2.88, 3.20, 3.18 and 3.28, respectively. Double heat recovery heat pump that has the ventilation and double heat recovery functions integrated into a single unit showed the best COP performance.