Stratification analysis of domestic hot water storage tanks: A comprehensive review

Abstract

To assure high quality thermal storage and high efficiency of its acquisition, thermal stratification is often employed in domestic hot water tanks. The whole motivation of stratification lies in the fact that mixing effect can be minimized during operational cycle of the tank so that high temperature water could be taken at the load end, thus maintaining high thermal efficiency at demand side, while low-temperature water can be drawn at lower bottom, thus maintaining the high efficiency at energy collection side. The study of stratification entails the assessment of a wide variety of concepts to be embodied around the central theme of the tank – its design and modelling. This paper presents a systematic review pertaining to various such concepts. For instance, multi-node and plug-flow approach to model various temperature distribution models are considered. These models are categorized in paper as linear, stepped, continuous-linear and general three-zone temperature distribution models. Subsequently, the dynamics of thermocline decay and influencing parameters both during standby and dynamic mode will be demonstrated. In addition, a survey of state of the art methods and practices to ascertain the performance improvement and its quantification will be illustrated. This includes geometrical parameters – such as, structural design incorporation, essentially – inlet design, tank aspect ratio and wall material specification, and also, operational parameters to curb down the inlet mixing. Practice techniques and methods which are presented here in a novel way, extend towards the ground of practical application and research procedures.