Evaporative coolers: affordable comfort that's easy on the grid

Larry Kinney, Southwest Energy Efficiency Project (SWEEP)

Keywords

air conditioning; climate change; comfort; electric grid; efficiency; energy savings; evaporative cooling; peak shaving

Abstract

The calamitous heat wave of the summer of 2003 may be a precursor of the consequences of global warming. In all events, it sparked a new and large demand for air conditioning (A/C) in the residential sector in areas of Europe that have traditionally done without. Compressor-based space cooling can produce comfort, but it is associated with high first cost, substantial energy bills, and bothersome noise. Most important from the societal perspective, air conditioning loads on hot summer days threaten to cause unprecedented peak demand problems for European electric grids. Modern evaporative coolers produce good thermal comfort at lower first costs. Except under conditions of high relative humidity, comfort is better than with compressor-based A/C because with evaporative cooling, high volumes of fresh air are circulated into conditioned spaces. Both compressor-based A/C and evaporative cooling systems are becoming more efficient, but on a unit-of-cooling-per-kWh-of-electricity basis, evaporative cooling is at least four times more efficient than A/C and demand is less by a factor of five or more.

This paper examines:

New technologies and trends in upgrading existing technologies in evaporative cooling--direct, indirect, and indirect/direct;
Climate zones in Europe that favor evaporative cooling (most do);
The cost-effectiveness of evaporative cooling versus compressor-based cooling for new and retrofit residential applications from the perspectives of both end users and utility systems; and
Policy and program options for promoting evaporative cooling systems and related energy-efficiency measures tailored to the European community.

Water use by evaporative coolers is quite moderate, typically less than the amount of water that can be saved by the installation of a low-flow shower head or a water-conserving toilet. In addition, water use at the power plant is less by a factor of 5 than that required to generate additional electricity for a conventional A/C unit.