การเลือกขนาดของบ่อแบบเปิดสำหรับระบายความร้อนในเครื่องปรับอากาศแบบระบายความร้อนด้วยน้ำ

Abstract

An open pond has a potential to be heat sink of water-cooled air conditioner instead of cooling tower. The pond has cooling mechanism which can absorb heat from condenser unit then reject to surrounding ambient. However, when the pond size is not appropriate with number of air conditioner, the total heat capacity of the pond cannot absorb total heat from the air conditioner condenser and the pond temperature will keep increasing which result in lower energy efficient ratio (EER) of the air conditioner. In this research, performance of open pond as heat sink of water-cooled condenser instead of cooling tower was considered. Experimental test of a 3.4 kW R32 air conditioner with 3m × 3m × 1.1m open pond was performed and the unit was running between 8 a.m. - 6 p.m. on a clear sky day. It could be seen that The EER was found to be in a range of 4.2 - 5.3 during the daytime which was higher than that of the air-cooled condenser unit which was around 3.8 quoted by the manufacturer and models to predict the average pond temperature and EER of the air conditioner were developed and the simulated results agreed well with those of the experiments with average error with in 5.23%. After that, the model was used to find out the suitable pond size that could keep the air conditioner EER over 4.1 when the number of air-conditioner were changed from 1 - 3 units on the hottest day of 4 provinces in Thailand The results showed that the EER increased with the increase of pond volume since increase of the pond volume retarded the increase in the pond temperature during the daytime then the condensing temperature was also low which resulted in high EER. However, Increase of the pond volume also retarded the decrease in the pond temperature during the nighttime because of its higher total heat capacity, the total heat absorbed could not be totally released and its temperature might not be lower than the initial temperature on the previous day then the potential on the heat absorption by the pond was deteriorated. An effective way to reduce the pond temperature on the next day to be lower than the initial temperature was to increase ratio of pond surface area and pond depth (A/D) since during the nighttime, more surface area resulted in higher heat loss to the surrounding ambient and the pond temperature could be reduced significantly. By adjusting the appropriate A/D, the pond temperature on the next day could be lower or equal to that on the previous day then the air-conditioner EER should be at least similar to that on the previous day. As for the climate in each province, it affected the EER of the air conditioning system and the temperature of the pond water as well. In the province that had high solar radiation, relative humidity and ambient temperature but the wind speed is low need to adjust the pond volume and the A/D ratio than other provinces.