Thermal stratification and temperature variation in horizontal electric water heaters: A characterisation platform

Abstract

Electric water heaters, which have the capacity to act as thermal energy storage, are well suited to demand management strategies in smart grid applications. But finding the balance between managing power load, reducing thermal energy losses, user's convenience, and bacterial growth control, requires requires accurate modelling of the internal thermal dynamics of the tank. As a black box, this unknown is dependent on a multitude of environmental factors (e.g., ambient temperature and inlet temperature), water draw patterns, scheduling, set temperatures and orientation of the vessel. The latter affects the stratification and temperature variation inside the tank, and therefore has a direct bearing on the balancing act of demand management. Although these have been assessed inside vertically oriented tanks, what happens inside the horizontal variety – ubiquitous in developing countries -- is currently left to the guesswork. In this paper we present the development of a platform with which the temperature variations inside a horizontal water heater can be characterised under numerous environmental and usage conditions. The importance of doing so is highlighted by the results, which clearly show substantial temperature variation along the vertical axis, and interesting phenomena along the longitudinal and transverse axes, for both static (no water draw) and dynamic (with water draw) conditions. We conclude by highlighting potential for further research.