Dew Point Fluid Coolers

Cooling loads constitute approximately 13% of the total demand for the United States, and in California, the hot dry summers drive cooling loads and peak demand throughout the season. Currently, the market is driven by compressor-based systems, which are inherently limited in efficiency. In California, because the climate is hot and dry, there is potential to expand the market to incorporate evaporative cooling. Most ordinary evaporative systems, such as cooling towers, are limited to cooling to the ambient wet-bulb, which limits their cooling capacity, and their ability to be used in a radiant system. The sub wet-bulb evaporative cooling (SWEC) technology has a significant advantage over other evaporative technologies because of its ability to cool below the ambient wet-bulb. Several unique designs exist that are considered sub wet-bulb evaporative chillers, and this report focuses on one such design. The SWEC utilizes a two stage evaporative cooling system to chill water below the web-bulb temperature of the outdoor air. The theoretical limit for the supply water temperature is the dew point of the outdoor air. The third-party laboratory (aka lab) tested the SWEC in an environmental control chamber in order to map its performance characteristics. The SWEC was instrumented such that the load, energy consumption, and water-use can be determined. Outdoor air conditions and return water temperature were held at a steady state. The lab performed a comparative analysis of the SWEC tested in this evaluation to another SWEC design subsequently tested and highlighted strengths and weaknesses of each system. The SWEC chiller tested for this report was able to consistently provide cooling loads efficiently, while operating under a variety of environmental, operational, and load-based conditions. The unit consistently provided anywhere from 0.7 to 2.6 tons of cooling, with 1-2 tons being consistently typical and average. The variation in coefficient of performance (COP) ranged from 8.5 to 33, with 15 to 25 being an average and typical value. The unit was able to consistently provide chilled water as low as 58°F, which is low enough to be used in a radiant system. The results of the lab evaluation of the SWEC technology show that it has great potential to reduce energy use in hot dry climates. Although the technology shows great potential, there are also some significant barriers that need to be overcome. In general, radiant panels add significant costs to any installation, and don’t have great market penetration. A fan coil unit can potentially replace a traditional evaporator coil, and therefore be more cost-effective than a radiant system. It is recommended that further research be done in order to determine the cost-effectiveness of a SWEC with a thermal storage system and thermal distribution system using fan coil units in a residential building. The analysis should determine if a fan coil thermal distribution system can meet the load in a residential building in California climate zones. The analysis should also determine whether the addition of a thermal storage system makes economic sense as a peak demand reduction strategy.