Design and evaluation of a control circuit to improve cooling efficiency in solar refrigerated evaporatively cooled structure

Refrigerated storage is often considered to be the best method for preserving fresh fruits and vegetables. The Indian Agricultural Research Institute in New Delhi has designed a solar refrigerated evaporatively cooled (SREC) structure which is off-grid and battery-free, that can be constructed directly on the farm and operates without the need for electricity. To maintain a pre-set room temperature, the SREC system typically has a coil thermistor and an air thermistor which automatically cuts off the compressor. The minimum temperature that can be achieved is 16°C, which is a pre-set temperature by the refrigeration system manufacturer. In order to improve the efficiency of the refrigeration system, the control system is connected to a coil thermistor and an air thermistor of the refrigeration system. The SREC structure operated on on-grid and hybrid types of inverters with varied combination of coil thermistor resistances and air thermistor resistances. There were twelve treatments with a combination of inverter, coil and air thermistor resistance performed on the SREC structure. The cooling capacity, cooling efficiency, energy efficiency ratio and coefficient of performance (COP) were studied. The control system's connection helped lower the SREC structure's temperature from 16°C to 4°C. Hence, the cooling efficiency of the refrigeration system improved by 1.61 times. The highest cooling efficiency improvement of 2.29 times was found in the off-grid/ hybrid inverter with coil and air thermistor resistances of 39.4 kΩ and 21 kΩ, respectively. Highest COP value of 7.40 was found in on-grid inverter, coil and air thermistor resistances of 45 kΩ and 18.91 kΩ, respectively. The average improvement of COP was 0.79 times among the twelve treatments. The control system with an off-grid inverter refrigeration system is beneficial in enhancing the cooling performance of the SREC structure and establishing cold storage at remote locations.