Reduction of energy consumption in low rise residential space conditioning by retrofitting with evaporative condenser
This work presents an experimental investigation of the application of direct evaporative cooling to reduce energy consumption in a residential sized split Air Conditioning system. Direct evaporative cooling is employed at the air-cooled condenser of a split air-conditioning system to pre-cool the ambient air flowing over the condenser coils. Different ambient conditions of air were simulated using a heater to mimic typical high temperature environments. Rigid cellulose pads with thickness ranging from 2-6inches (5.1cm-15.2cm) served as the heat exchange medium for air-water interaction, and were tested to determine the influence of the pad thickness in pre-cooling the ambient air before it flows over the condenser coils to extract heat from the refrigerant in the condenser. It was observed that a 1°C drop in ambient air temperature causes the condensing temperature of the refrigerant to drop by 0.6°C. This drop in condensing temperature of the refrigerant causes a decrease in power consumption of the unit, accompanied by an increase in Coefficient of Performance (COP). Results obtained shows that up to 44% increase in COP, and a 20% decrease in power consumption can be achieved by employing evaporative cooling. Additionally, the COP was found to increase by 4% for every 1°C drop in refrigerant condensing temperature. The water consumption pattern of the hybrid system is monitored to provide a realistic estimate of the operating cost, and profitability of the hybrid system. It was observed that 0.34liters of water is consumed for every percent increase in COP. To provide a realistic estimate of the daily water consumption of the hybrid system, the operation time was increased from 1-4hours, in step increments of 1hour. The volume of water consumed was found to increase by a factor of 1.8, 2.5, and 3.2, for 2hrs, 3hrs and 4hrs of operation respectively. This shows that as the operating hours of the hybrid system in a day increases, the volume of water consumed will decrease. Intermittent operation of the water pump was also investigated and found to be beneficial to the system in terms of reduction in energy associated with the pump operation, and also prevention of water buildup in the flutes of the pad. Studies on water quality shows that water of high salinity (up to 35ppt), and turbidity (up to 30NTU) did not affect the evaporative cooling process, over the duration of usage. However, it is expected that over time, accumulation of salts, or other foreign materials on the pad surface will reduce the pad performance.
Nnanna, Purdue University.
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