An experimental study on defrost heaters applied to frost-free household refrigerators

In this study the performance of defrost systems applied to household refrigerators was experimentally evaluated through a purpose-built testing apparatus. The test bench is comprised of a calorimeter, a refrigerated cabinet and a humidifying system. Three distinct types of electrical heaters (distributed, calrod and glass tube) and three actuation modes (integral power, power steps and pulsating power) were investigated. The experiments were carried out under controlled conditions in order to ensure the same frost accumulation pattern over the evaporator. It was found that the defrost efficiency of the three types of heaters is practically the same for each operating mode. The highest efficiency of approximately 48% was obtained with the glass tube heater operating in power steps. However, this heater reached the highest temperature levels. The calrod heater seems to be the most appropriate not only because of its efficiency, which is compatible with the other options, but also due to its low cost and easy installation. However, standardized energy consumption tests need to be carried out before this finding can be generalized.