From Winter’s Rain to Summer Breeze
Evaporative cooling systems are an energy-efficient cooling solution for hot, arid climates. They are approximately 30% more energy efficient than conventional cooling systems. For example, compared to a baseline home with an air-cooled condensing unit, the residential buildings in the western part of the US would achieve annual electricity savings of about 27 trillion Btu of total site energy by using evaporative condenser units in all single-family homes. This corresponds to preventing 5X106 tons of CO2 emissions per year.
However, evaporative processes lead to accumulation of mineral scale on the heat exchanger, whose performance thereby degrades over time, which generally means that additional water is consumed to mitigate this scaling process. Therefore, water management for evaporative cooling systems is essential, and particular care must be taken to reduce the effects of hard water and the overall water consumption of the systems. Several strategies have been put forward by Western Cooling Efficiency Center, UC Davis, to improve water-use efficiency and/or minimize scale formation in evaporative cooling systems. By investigating the impacts of using harvested rainwater instead of tap water, this project could enable the use of evaporative cooling systems in hard-water areas. It is expected that the lower hardness in rainwater compared to municipal tap water will minimize scale formation, which extends the system life and increases system efficiency. This results in reduced consumption of water, electricity, and chemicals, as well as reduced water treatment needs (e.g. water softening). In addition, rainwater harvesting reduces the need for piping to convey water to its point of use and reduces energy consumption for tap-water treatment and distribution, thereby reducing regional energy and climate consequences. Rainwater harvesting can also help reduce storm water runoff, which consequently reduces soil erosion and can mitigate floods. This project received the 2014 ASCE-Sacramento “Improvement Energy Project” award by focusing on the development of carbon-neutral-alternative-energy solutions.
This work was supported by the California Energy Commission under contract 500-08-042, and is part of Nasim Tajmand’s PhD thesis for the Civil and Environmental Engineering department at UC Davis. Professor Mark Modera, Professor Tom Young, Professor Roger Bolton, as well as Theresa Pistochini (an engineer at the WCEC) have been Nasim’s advisors on this work.