Technical Study of Extracting Waste Cooling Energy from Air Conditioning System and Storage as Chilled Water

Abstract

The aim of this research was to perform a technical study on extraction of waste cooling energy from air conditioning system and storage as chilled water. The experimental unit consisted of a vapor compression refrigeration system with a capacity of 3.52 kW (12,000 BTU/hr), and an air-cooled condenser. R-22 refrigerant was used in the system. The cold energy storage tank was made from a 1 mm thick aluminum board and had a diameter of 330 mm and a height of 450 mm. This tank was filled with 23 L of water and wrapped with thermal insulation material. The coiled copper tube with an internal diameter of 15.87 mm, was entwined to a diameter of 260 mm with a 39 mm pitch spacing. The cold energy storage tank was installed between the evaporator and the compressor. During testing, the usual designed room temperature of 25^oC was used, and the air conditioning loads were adjusted to 900, 1,800 and 2,200 W, respectively. The results showed that when the initial water temperature at the beginning of the experiment was 25^oC, it decreased steadily until it reached a constant value that was maintained throughout the rest of the time period. In the cold energy storage tank, the average cool water temperatures were 18.73, 16.36 and 13.25^oC, respectively. The heat transfer rates of condenser were 4.10, 3.81 and 3.65 kW, respectively. The average power consumption of the air conditioning system was 1,062.42, 1,092.04 and 1,112.71 W, respectively. In terms of the coefficient of performance of the system, the values were 3.43, 3.22 and 3.04, respectively. Furthermore, this research has identified advantages of cold energy storage tank, including their uncomplicated equipment and minimal installation space requirements. These tanks operate on the principle of extracting waste cold energy from the refrigerant, with the water within the tank serving to absorb the waste cold energy from the refrigerant. Moreover, the findings from the experiments suggest potential applications for the chilled water stored in cold energy storage tank. For instance, this chilled water can be used to assist in reducing the indoor air temperature before the air conditioning system is turned on, thereby accelerating the cooling process, particularly when combined with evaporative cooling systems. Alternatively, the chilled water can be employed to lower the air temperature before it transfers heat to the condenser, aiming to enhance the efficiency of the air conditioning system. This approach requires the combination of a heat exchanger.