Identification and analysis of psychometric methods for enhancing air conditioner efficiency and capacity

摘要

Air conditioning is vital to the comforts of modem life. It is an energy conversion process that cools the inside space by removing heat and releasing this heat plus the driving energy to the outside. It is also electric power intensive, and times of highest an conditioning load typically correspond with the peak demand on the electric utility. Due to some electric power and fuel shortages during the last year and corresponding increased prices, there is renewed interest in methods for increasing the energy efficiency and performance of all energy use devices. Improvements in air conditioning efficiency is a specific part of the May, 2001 national energy plan presented by President Bush. The obvious possibilities for increasing air conditioning are better heat exchangers and compressors and possibly replacing the throttle with a power producing expander. The ideal or minimum power is a function of the difference between the temperatures on the inside and outside as defined by the Carnot cycle. Thus, another possibility for improving efficiency along with capacity is to lower the temperature of the outside heat sink. This is typically done with cooling towers for large air conditioners with the hot side condenser water cooled. The cooling tower can nominally decrease the water temperature to the wet bulb temperature of the air. This paper investigates methods to obtain a comparable improvement for systems with air cooled condensers. One possibility is to evaporatively cool the outside an that cools the condenser down to the wet bulb temperature. The second possibility is to first dehumidify the outside air with a desiccant, and then evaporatively cool to an even lower temperature. For example if the outside dry bulb temperature is 100 F and the relative humidity is 60%, the air can be evaporatively cooled to 87 F. Alternatively, if the 100 F outside air is first dehumidified to 40% relative humidity, it can then be evaporatively cooled to 79 F. This paper will first examine the ideal and actual performance of a conventional air cooled air conditioner using 1st and 2nd law analysis and then identify the efficiency improvement from psychometric and desiccant techniques for cooling the hot side air.