This paper describes a simplified computer software program for evaluating energy consumption and operating costs for water heaters under a variety of operating conditions (EPRI 1996). Water heaters addressed include resistance units, heat pump water heaters, and fossil-fired options. The software tool was developed to meet the need for a simple means of estimating energy consumption and operating cost at various conditions for specific applications. Utility rates and operating conditions vary greatly throughout the country. In addition, overall efficiency is quite different for hot water usage that differs significantly from the 64.3 gpd figure assumed in the U. S. Department of Energy (U.S.DOE) energy factor rating (FR 1990). The use of energy factor based on nationwide average conditions for decision making is inappropriate and can result in poor decisions. With the software, users can quickly estimate energy consumption and cost at the conditions and parameters specific to a particular application to be used in lieu of nationwide average values. The software offers both a simple, intuitive graphical user interface that presents single cases for evaluation and a table view for comparison of several cases. Energy factor rating is used as an input to simplify the user inputs required to describe tank heat loss characteristics. A detailed help system provides an extensive reference that includes background information and typical values for all inputs. The result is a program that can be used immediately by most users without training or reliance on the user's manual. Features include the ability to save libraries of previous evaluation cases, printed output in graphical and tabular form, and exporting of results to spreadsheets and word processor documents. Typical applications include

• estimating efficiency and operating cost figures for specific local conditions for use in lieu of nationwide averages presented on energy guide labels;
• evaluating alternative water heater choices;
• designing and evaluating utility programs;
• creating tables of unit performance for manufacturer product literature.

The currently released version of the software makes calculations based on fixed operating conditions. A later version, now under development, will provide the capability to evaluate periodic changes in operating conditions and parameters, such as seasonal utility rates or monthly changes in cold water inlet temperature.

Units: I-P