Improving the energy storage capability of hot water tanks through wall material specification

Abstract

Domestic hot water tanks represent a significant potential demand side management asset within energy systems. To operate effectively as energy storage devices, it is crucial that a stratified temperature distribution is maintained during operation; this paper details experimental and numerical work conducted to understand the influence that wall material specification has on de-stratification within domestic hot water tanks. A 2d axisymmetric CFD (Computational Fluid Dynamic) model was consistent with experiments which showed that switching from copper to stainless steel resulted in a 2.7 fold reduction in useable hot water loss through reduced de-stratification for a 74 L UK domestic hot water tank over a 48 h period. During simulation, a counter rotating convection system, with peak velocities of 0.005 m/s, was observed above and below the thermocline. Minimizing de-stratification, through appropriate wall material selection, increases the performance of hot water tanks and scope for their use in demand side management applications. Given the inconclusive evidence surrounding copper's efficacy as a sanitizing agent, along with the low tensile strength of polyethylene, this paper advocates the use of stainless steel in hot water tank walls and further exploration of alternative materials and composites which have low cost and low thermal conductivity along with high strength and manufacturability.