Electric water heater designs for load shifting and control of bacterial contamination

This study examines the performance of three electric water heater designs for electric load management and control of bacterial contamination. The thermal behavior of the water heaters is simulated numerically using the TRNSYS computer program. The first design consists of a standard water heater to which various minor modifications were made. The results of the simulations reveal a benefit in large capacity water heaters (350 and 540 L) equipped with a vertical heating element and a time clock. The second design consists in a high temperature water heater equipped with a heat exchanger or a mixing valve. Although capable of storing more heat and better able to impede bacterial growth, these water heaters consume more electricity, are more prone to scaling and often have a limited service life. The third design consists in connecting in series two 175-L or two 270-L water heaters equipped with a time clock. The results indicate that such a system is capable of meeting load management requirements and eliminating bacterial contamination. Enough heat can be stored overnight so that the heating elements need not be operated during the day, and in addition, the temperature of the water in the service tank remains high, thus preventing the growth of bacteria. This design is most attractive for Canadian manufacturers, since it only requires minor modifications to be made to existing water-heater systems. It is estimated that such a system could save the five Canadian electric utilities considered in this study up to 1819 MW in power, with potential annual energy savings for the utility customer ranging from Cdn$150 to 360. (C) 1999 Elsevier Science Ltd. All rights reserved.