An experimental investigation of the heat transfer and energy storage characteristics of a compact latent heat thermal energy storage system for domestic hot water applications

Abstract

This paper presents the experimental performance analysis of a latent heat thermal energy storage system (LHTESS) designed for domestic hot water (DHW) applications. The designed, fabricated and characterised thermal store comprised of a vertically oriented multi-pass tube heat exchanger in a rectangular cross-section container filled with phase change material (PCM) paraffin wax RT44HC. The experimental investigation evaluated the heat transfer within the system, measured the transient temperature distribution, determined the cumulative thermal energy stored, charging and discharging time and the instantaneous charging and discharging power. The experimental work was conducted under controlled experimental conditions using different heat transfer fluid (HTF) inlet temperatures and different volume flow rates for store charging and discharging. It was found that during charging natural convection in the melt played a significant role. During discharging thermal conduction dominates and natural convection has an insignificant impact on the LHTESS performance. This is due to the development of a solid layer of PCM around the heat transfer tubes which increases the thermal resistance and reduces heat transfer to the liquid PCM. Higher HTF inlet temperature during charging significantly decreased store charging time. Increasing HTF inlet temperature from 60 to 70 o C shortened the charging time by 3.5 hours, a further increase to 80 o C decreased melting time by a further 2 hours. This study illustrates the extent to which LHTESS, and heat exchanger designs need to be improved to meet the desired charge/discharge time requirements for most short-term storage applications and that a broad range of domestic and commercial heat demands can be fulfilled by assembling several LHTESS units to operate in parallel.

Thermal Performance Analysis of the Charging/Discharging Process of a Shell and Horizontally Oriented Multi-Tube Latent Heat Storage System

“…The experimental test program presented in this paper was performed at the Low-Temperature Lab-Scale Thermal Energy Storage Test Facility at Loughborough University [24,25]. A schematic diagram of the experimental system is presented in Figure 1.…”

“…The time-varying thermal power input/output to/from the PCM, and the total heat input/release are calculated using Equations ( 1) and (2) [6,24].…”

“…The store design could be optimized for use with a solar thermal system with heat collected by solar panels, used to directly charge a PCM filled latent heat storage system, which would be discharged at a later time to meet heat loads. Another potential application is in conjunction with an air source heat pump, allowing the heat pump to be operated using low-cost off-peak electricity, charging the store which can subsequently be discharged at times of peak heat demand [23,24].…”

A review on phase change materials for thermal energy storage in buildings: Heating and hybrid applications

“…However, both methods showed efficient predictions in the case of air outlet temperature simulations. M. Fadl and Eames [140] prepared a multi-pass tube heat exchanger oriented vertically adopted to a PCM container filled with RT44HC, used for domestic hot water in buildings. The study aimed to analyze the experimental results related to the variation of the heat transfer fluid (HTF) inlet temperature and its effect on charging/discharging rates of PCM.…”

Heat Transfer Analysis of a High-Temperature Heat Pipe-Assisted Latent Heat Thermal Energy Storage System Enhanced by Metal Foam

“…Latent heat thermal energy storage (LHTES) systems are one the most promising solutions to resolve the intermittency problem of concentrated solar power generation systems. They are also widely used in electronics cooling and heating and hot water systems [1,2]. These systems can store significantly higher amount of thermal energy in comparison to a sensible heat thermal energy storage system of the same size due to large latent heat of fusion of the phase change materials (PCM) used in them.…”