Transient and Rate-Dependent Performance of Conventional Electric Storage Water Heating Systems


Electric resistance water heaters are relatively simple and are therefore one of the most common water heating configurations. Due to constraints on the allowable instantaneous electrical power draw, most electric water heating systems incorporate a sizable thermal storage component. The inherently unsteady storage component therefore has an overwhelming impact on the system behavior. In this investigation, a residential-scale electric storage water heater was tested across a range of flow rates for both powered and nonpowered discharge processes as well as for charge processes with no throughflow. The flow dynamics internal to the storage volume is shown to be strongly multidimensional and transient, especially when the internal heating elements are energized. Comparison of the measured data to the performance limits of a system with a fully mixed or a perfectly stratified storage element reveals that the conventional system operates relatively near to the fully mixed limit. As a result, there appears to be significant potential for improvements in system performance through reductions in the level of thermal mixing internal to the storage volume.


Mechanical and Aerospace Engineering


University of Missouri Research Board

Keywords and Phrases

Mixed Convection; Thermal Energy Storage; Water Heating; Heat storage

International Standard Serial Number (ISSN)


Document Type

Article - Journal

Document Version


File Type





© 2005 American Society of Mechanical Engineers (ASME), All rights reserved.

Publication Date

01 Jan 2005