(120e) Comparing Evaporative Cooling to the Alternatives: Methodology, Data and Preliminary Results

In the United States, residential and commercial buildings account for 39% of total energy use and 73% of electricity use. About 13% of the primary energy used by buildings is consumed by space cooling, nearly all of which is used to produce electricity (DOE 2009). Evaporative cooling uses significantly less electricity than typical cooling systems; however, this class of technologies has been criticized for excessive water use. It remains an open question as to whether this criticism is valid.

An often overlooked aspect of electricity use is that a significant amount of water is evaporated by many power plants. Torcellini et al. (2003) found that, on average, U.S. thermoelectric plants use 0.47 gal (1.8 L), and hydroelectric plants use 18 gal (68 L) of fresh water per kWh of electricity consumed at the point of end use. That paper also establishes state and regional averages for consumptive water use by power plants?-numbers that vary quite widely from the national metrics.

The minimum amount of water used by evaporative cooling is 1.37 gal/ton?h (1.47 L/kWh) of cooling. Inefficiencies, and the electricity to power fans and pumps adds to the total (Modera 2008). Thus, evaporative cooling may be competitive with typical cooling systems (direct expansion coils and chillers) with regards to water as well as energy use in some buildings and climates. By coupling the estimates of water consumption per kWh of Torcellini et al. (2003) and results from annual building energy simulations it is possible to directly compare evaporative technologies with the alternatives across both dimensions.

This talk will give an overview of Torcellini et al.'s 2003 work, describe how those data can be used in conjunction with the building energy simulation program EnergyPlus (DOE 2008) to calculate the site and source energy and water use of a given cooling technology, and present preliminary results concerning particular technologies and locations using the commercial building benchmark models (Deru et al. 2008).

Deru, M.; Griffith, B.; Long, N.; Halverson, M.; Winiarski, D.; Huang, J.; Crawley, D. (2008). "DOE Commercial Building Research Benchmarks for Commercial Buildings." In preparation. U.S. DOE.

DOE (2008). "EnergyPlus Energy Simulation Software." Washington, D.C., U.S. Department of Energy. http://www.eere.energy.gov/buildings/energyplus/.

DOE (2009). "2008 Buildings Energy Data Book." Prepared by D&R International, Ltd. for the U.S. DOE EERE Building Technologies Program under contract to the National Energy Technology Laboratory.

Modera, M. (2008). "Minimizing Water Use in Non-Compressor Cooling Applications." 2008 ASHRAE Annual Conference, Salt Lake City, Utah.

Torcellini, P.; Long, N.; Judkoff, R. (2003). "Consumptive Water Use for U.S. Power Production." NREL/TP-550-33905. Golden, Colorado: National Renewable Energy Laboratory.