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

Publication date: October 2013
Source:Building and Environment, Volume 68
Author(s): Erica R. McKenzie , Theresa E. Pistochini , Frank J. Loge , Mark P. Modera
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 unit's 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.