Performance Evaluation of an Evaporatively-Cooled Split-System Air Conditioner

Water cooled air conditioners have been around for several years and have an excellent performance rating out of the box, an EER of about 17. However, the experience has been that water-cooled condensers can become fouled in a very short time, circumventing their performance and become a maintenance. The technology involves a typical vapor compression refrigeration cycle with a water-cooled condenser instead of an air-cooled condenser. The primary objectives are to verify the energy and water performance of the units, and to evaluate/simulate performance in California climate zones.

It has long been known that evaporatively-cooled condensers in air-conditioning systems provide increased efficiency over air cooled condenser technology. The increased efficiency is especially effective during peak demand periods that correspond with the hottest part of the day. Some of the unknowns are the performance of these units over a wide range of ambient conditions, the comparative performance to air cooled units, and information about water consumption due to purging and evaporation. The primary goal of this project is to evaluate the performance of an evaporatively-cooled condensing unit as part of a residential split-system air conditioner in some of the climate zone conditions found in Southern California Edison’s (SCEs) service territory. Additional goals are to determine the performance degradation of the unit with increasingly harsh climate conditions, look at general water consumption of the unit in these different climate conditions, and to compare normalized performance data to existing information on aircooled condenser type air conditioning units from previous lab research conducted at SCEs Technology Test Centers (TTC). The evaporatively-cooled condensing unit of the residential split-system was installed in a controlled environment room of the TTC and every major component was instrumented for data collection. Likewise, the indoor unit of the split-system was installed in a separate controlled environment room and every major component instrumented for data collection. Baseline tests were then conducted where a minimum of two hours of test data was collected under established indoor and outdoor conditions. These respective temperatures and humidities derive from the rating conditions required by the Air-Conditioning, Heating & Refrigeration Institute’s Standard 210/240-2003 for Unitary Air-Conditioning and Air-Source Heat Pump Equipment. The results of the Technology Test Center’s baseline data were then compared to the results of the baseline tests previously conducted by the manufacturer at identical test conditions. The closely matching results of this comparison established confidence in the results of these independently conducted tests. After the results were confirmed to be in close agreement, further tests were conducted at various outdoor climate zone conditions. Each different climate zone test was conducted under steady-state operation with the appropriate constant temperature and humidity in each of the indoor and outdoor test chambers. Data was collected for a minimum of two hours under several outdoor conditions representative of climate zones within SCE service territory. Measured parameters were later compared for performance variations across the different climate zone conditions. The findings show that evaporatively-cooled condenser technology is able to produce the same cooling capacity at lower energy consumption than current air-cooled condenser technology. The efficiency of the evaporatively-cooled condenser decreased slightly (approximately 10%) at the extreme climate zone conditions of high dry bulb and low wet bulb but was largely unchanged across less extreme climate zone conditions. By contrast, the efficiency of previously tested air cooled condensing units decreased severely (a drop of 34%) while increasing energy consumption at similar high dry bulb conditions.