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Evaporative cooling systems in buildings have been criticized for their water use and acclaimed for their low energy consumption, especially when compared to typical cooling systems. In order to determine the overall effectiveness of cooling systems in buildings, both water and energy need to be considered; however, there must be a metric to compare the amount of energy used at the site to the amount of water used at the power plant.A study of power plants and their respective water consumption was completed to effectively analyze evaporative cooling systems. Eighty-nine percent of electricity in the United States is produced with thermally driven water-cooled energy conversion cycles. Thermoelectric power plants withdraw a tremendous amount of water, but only a small percentage is evaporated. The evaporative or consumptive use1 is approximately 2.5% or 3,310 million gal per day (MGD) (12,530 x 10 6 L/d). Moreover, hydroelectric plants produce approximately 9% of the nation's electricity. Evaporative water loss from the reservoir surfaces also results in water being evaporated for electrical production.In thermoelectric plants, 0.47 gal (1.8 L) of fresh water is evaporated per kWh of electricity consumed at the point of end use. Hydroelectric plants evaporate an average of 18 gal (68 L) of fresh water per kWh used by the consumer. The national weighted average for thermoelectric and hydroelectric water use is 2.0 gal (7.6 L) of evaporated water per kWh of electricity consumed at the point of end use. From this information, different types of building cooling systems can be compared for relative water consumption. This paper will aid in High Performance Building research by providing a metric in determining water efficiency in building cooling systems. Further analysis is planned to determine the overall water efficiency of evaporative cooling systems compared to conventional direct expansion systems and chiller systems with cooling towers.

This report uses EnergyPlus simulations of each building in the 2003 Commercial Buildings Energy Consumption Survey (CBECS) to document and demonstrate bottom-up methods of modeling the entire U.S. commercial buildings sector (EIA 2006). The ability to use a whole-building simulation tool to model the entire sector is of interest because the energy models enable us to answer subsequent "what-if" questions that involve technologies and practices related to energy. This report documents how the whole-building models were generated from the building characteristics in 2003 CBECS and compares the simulation results to the survey data for energy use.

Commercial buildings have a significant impact on energy use and the environment. They account for approximately 18% (17.9 quads) of the total primary energy consumption in the United States (DOE 2005). The energy used by the building sector continues to increase, primarily because new buildings are added to the national building stock faster than old buildings are retired. Energy consumption by commercial buildings will continue to increase until buildings can be designed to produce more energy than they consume. As a result, the U.S. Department of Energy's (DOE) Building Technologies Program has established a goal to create the technology and knowledgebase for marketable zero-energy commercial buildings (ZEBs) by 2025. To help DOE reach its ZEB goal, the Buildings and Thermal Systems Center at the National Renewable Energy Laboratory (NREL) studied six buildings in detail over the past four years to understand the issues related to the design, construction, operation, and evaluation of the current generation of lowenergy commercial buildings. These buildings and the lessons learned from them help inform a set of best practices-beneficial design elements, technologies, and techniques that should be encouraged in future buildings, as well as pitfalls to be avoided. The lessons learned from these six buildings are also used to guide future research on commercial buildings to meet DOE's goal for facilitating marketable ZEBs by 2025. The six buildings are:

online ordering: http://www.ntis.gov/ordering.htm Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste ForewordThis is a publication of work that was almost completed in August 1983. Final publication was never completed at that time because of funding issues. There was, however, a limited distribution of the final draft to leading experts in the field, and the report has been referenced in a number of documents nationally and internationally. Since that time great strides have been made in computer hardware. It is now possible for a building design practitioner to run a full-blown simulation of building energy performance on a laptop computer, and there are literally hundreds of such computer programs throughout the world. Thus, there is renewed interest in the theory of how to validate building energy simulation programs. We have therefore cleaned up the few cosmetic edits that remained in the previous final draft and formally published it as NREL/TP-550-42059 (originally SERI/TR-254-1508). Although the simulation programs referred to in this report have long since been replaced by many subsequent versions of software, the underlying theory of how to validate, diagnose, and design good validation experiments has remained substantially unchanged since we first proposed this methodology.i Executive SummaryObjective To develop a validation methodology for building energy analysis simulations (BEAS), collect high-quality, unambiguous empirical data for validation, and apply the validation methodology to the DOE-2.1, BLAST-2MRT, BLAST-3.0, DEROB-3, DEROB-4, and SUNCAT 2.4 computer programs. DiscussionThis report covers background information, literature survey, validation methodology, comparative studies, analytical verification, empirical validation, comparative evaluation of codes, and conclusions. Section 1.0 establishes the historical context in which the Solar Energy Research Institute (SERI) studies evolved. The history of computerized building energy analysis is traced and the case is made that earlier methods do not contain algorithms that can accurately determine all heat flow quantities, especially for natural heating and cooling applications. These programs, though versatile for conventional buildings, are highly questionable for analyzing innovative design options. Newer state-of-the-art programs, such as DOE-2.I, BLAST-3.0, DEROB-4, and SUNCAT-2.4, have not yet been sufficiently validated over a wide enough range of parameters to be used with confidence. Researchers, representatives of the building industry, and several government-sponsored planning groups have expressed the need for a systematic approach to the validation issue. Section 2.0 reviews a sampling of the literature on the validation of building energy analysis simulations, which shows that previous validation studies left four areas needing further investigation:• Validation with empirical data from full-scale buildings: In previous studies there generally have not been sufficient data to understand observe...