Determination of Optimum Hot-Water Temperatures for PCM Radiant Floor-Heating Systems Based on the Wet Construction Method

Sanghoon Baek,Sangchul Kim

doi:10.3390/su10114004

Abstract

Owing to use of mortar, which demonstrates low heat storage and discharge performance, conventional radiant floor-heating systems, based on the wet construction method and hot-water circulation, consume large amounts of energy. This study proposes a new type of radiant floor-heating system that is capable of reducing energy consumption via use of the latent heat of a phase change material (PCM), whereby the phase change, which occurs within, is induced by the thermal energy supplied by hot water. Simulation analyses revealed that hot-water supply temperatures, required to maintain the floor-surface and indoor-air temperatures at the set point using PCM latent heat, were in the range 40–41 °C. At supply water temperatures measuring less than 39 °C or exceeding 42 °C, the latent-heat effect of the phase change of the PCM tended to fail, and the corresponding floor-surface temperature assumed a value different from that corresponding to the set point. By contrast, supply temperatures in the range 40–41 °C resulted in return temperatures measuring approximately 27.4–27.5 °C, which in turn corresponded to an indoor air temperature of 21.6–22.6 °C that was stably maintained within ±0.6 °C of the 22 °C set-point temperature.

Highlights

IntroductionMost materials undergo transition from one state (solid, liquid, or gas) to another via absorption or discharge of heat, and depending upon which state they lie in, with respect to their particular phase-change points (e.g., melting and boiling points), most substances undergo sensible or latent heat exchange [1]
Most materials undergo transition from one state to another via absorption or discharge of heat, and depending upon which state they lie in, with respect to their particular phase-change points, most substances undergo sensible or latent heat exchange [1]
Most materials absorb and discharge more heat during latent heat exchange compared to sensible heat exchange, and if a material continues to demonstrate latent heat exchange for a sufficient length of time, it can be used as a system for storing and supplying large quantities of heat

Summary

Introduction

Most materials undergo transition from one state (solid, liquid, or gas) to another via absorption or discharge of heat, and depending upon which state they lie in, with respect to their particular phase-change points (e.g., melting and boiling points), most substances undergo sensible or latent heat exchange [1]. During latent heat exchange, such as the transition from ice to water at 0 ◦C, the material state of a substance changes isothermally (at the same temperature). PCMs demonstrate extended durations of latent heat exchange during phase change, they are capable of storing and discharging large quantities of heat in an isothermal manner. These materials are being used in buildings as heat storage and discharge reservoirs for radiant floor-heating systems. Replacing conventional floor-heat-storage materials, which only demonstrate sensible heat exchange, with PCM enables radiant floor-heating systems to maintain indoor-air and floor-surface temperatures at a pre-set value without activating the heat-source system, thereby significantly reducing the energy consumed by the overall system. Many studies concerning PCM radiant floor-heating systems have been performed in recent times to explore appropriate PCM container shapes for floor insertion, and it has been demonstrated that use of a PCM can result in significant benefits in terms of reduced indoor-air and floor-surface temperature maintenance and increased energy savings

Methods

Results

Conclusion