An investigation of coupling evaporative cooling and decentralized graywater treatment in the residential sector

Total electricity and water burdens, including both direct and indirect uses, were modeled for newly constructed and 15-year-old homes in six California climate zones for three air conditioning systems: standard air-cooled condensing unit, evaporatively pre-cooled condensing unit, and an evaporative condensing unit. Compared to the air-cooled condensing unit, average annual direct electricity savings were 17.7% and 11.3% for an evaporatively pre-cooled condensing unit and an evaporative condensing unit, respectively. The evaporative condensing unit provided greater savings at peak load than the evaporatively pre-cooled condensing units (peak power savings were 30.9% and 23.8%, respectively), which is promising for hot arid climates. Total water burden reflected direct (e.g., evaporation) and indirect (i.e., electricity generation) water use. The standard air-cooled condensing unit, which had only an indirect water burden, exhibited the lowest total water burden; the evaporatively pre-cooled condensing unit and evaporative condensing unit had similar total water burdens, which were approximately double the air-cooled condensing unitʹs total water burden. This is because the evaporatively pre-cooled condensing unit and evaporative condensing unit both required a substantial volume of water (average 30.8 and 28.1 L/h, respectively; up to 8.5% increased water consumption for a typical household) to achieve their electricity-saving and peak power reduction benefits. This additional water burden can be offset by implementing an in-home decentralized graywater treatment and reuse plan, where shower and clothes-wash water is treated and recycled in-home for evaporative cooling as well as irrigation and toilet flushing.