An experimental study on a novel defrosting method for cold room

Abstract

Refrigeration systems can be blocked by frost accumulating on the evaporator, when they operate at a temperature below the dew point of air and the freezing point of water. Therefore, a defrost process that consumes extra energy needs to be started from time to time. Conventional defrosting methods require energy and time to complete, which reduce the refrigeration efficiency and cause a temperature fluctuation in the storage room during the defrosting process. In this study, a new type of defrosting is used in order to reduce the energy needed for defrosting, improve refrigeration efficiency and decrease temperature fluctuations, which utilize the heat from the liquid refrigerant to defrost the evaporator using two evaporators and a four-way valve. When one of the evaporators cools the room, the other is used for sub-cooling the refrigerant before entering the cooler evaporator. The sub-cooling process provides defrosting of the second evaporator. When the cooler evaporator requires defrosting, the four-way valve reverses the cycle, and the second evaporator becomes cooler. The first evaporator then becomes the sub-cooler to be defrosted. A cold room with this concept was built and tested experimentally together with a conventional cooling system. Energy, exergy, economic and environmental (4E) analyses of both systems were made and the results were compared. The results show that the new method can perform the defrosting process using the energy dissipated from the sub-cooling refrigerant without using any external power source and improve refrigeration efficiency by 12%. Moreover, this new system does not interrupt the cooling process during defrosting process as the conventional systems do. Temperature fluctuations also decrease by about 60% following this method.