Proposal of a PCM Underfloor Heating System Using a Web Construction Method

Abstract

Apartment buildings in Korea have adopted underfloor heating systems using web construction methods based on concrete and hot water systems. However, since such systems consume significant amounts of energy for heating owing to their low thermal storage performance, it is necessary to develop a new system that can minimize energy consumption by improving concrete thermal storage performance. This study proposes a phase-change material (PCM) underfloor heating system to reduce energy consumption in apartment buildings. An optimal design for a PCM underfloor heating system is proposed, and thermal storage performance of the proposed system is evaluated experimentally. The temperature range of the PCM for underfloor heating is also calculated considering the proposed design and comfortable heating conditions for domestic apartment buildings. Results indicate that a PCM underfloor heating system can be constructed in the following order: (1) a 210 mm concrete slab, (2) a 20 mm cushioning material, (3) 40 mm of mortar including a 10 mm PCM thermal storage container, and (4) 40 mm of finishing mortar including wire mesh and hot water pipes. The temperature range of the PCM used for underfloor heating in domestic apartment buildings is 32–45°C. Experimental tests reveal that thermal storage performance of underfloor heating systems that apply 35, 37, 41, and 44°C as representative PCM temperatures is superior to existing systems.

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

“…Through this time-lag phenomenon, surface-temperature decrease is delayed relative to the conventional system, and the reoperation time is, therefore, extended via the latent heat exchange of the PCM. Furthermore, as demonstrated by previous small-module experiments, PCM also demonstrates better sensible-heat storage and discharge performance compared to mortar [13], and therefore, even after the latent heat has been discharged, the surface temperature decreases more slowly, when compared to a conventional system, through loss of sensible heat. These features allow the PCM radiant floor-heating system to be operated intermittently whilst suppressing the rapid reduction in floor-surface temperature, thereby reducing hot water as well as energy consumption.…”

“…The (b) panel in Figure 1 depicts a schematic of the proposed radiant floor-heating system, wherein a PCM is inserted into an existing floor system that demonstrates sensible as well as latent heat exchanges [13]. Because this system can maintain the floor-surface and indoor-air temperatures at a pre-set value via the supply of isothermal energy from PCM, without the need for continuous hot-water supply, energy consumption can be reduced through intermittent operation of the heat-source system.…”

“…Prior to PCM insertion into a floor structure, it must be contained within a structure inside which it could safely undergo phase change from solid to liquid. Figure 3 depicts a PCM container fabricated for use in an extant study and its construction process [13]. Given the high thermal conductivity and durability of the floor, the container was fabricated using a thin aluminum sheet to accommodate the 10 mm thick PCM, specified in Section 2.1.1.…”

“…In the proposed and extant studies, the authors propose a design and system structure and describe methods for constructing a PCM container. In addition, the range of PCM melting-point temperatures required to maintain comfortable indoor-air and floor-surface temperatures has also been calculated [12][13][14].However, because floors between stories in an apartment housing must meet basic, legally prescribed performance requirements in terms of noise transmission between stories, waterproofing, and structural safety [15,16], it is, in practice, nearly impossible to completely change an existing floor structure to insert PCMs. For this reason, it is more effective to replace part of the existing floor material and subsequently employ the reheating storage method, wherein the heat storage and discharge cycles of PCMs are repeated via circulation of hot water during heating periods.…”

“…In the proposed and extant studies, the authors propose a design and system structure and describe methods for constructing a PCM container. In addition, the range of PCM melting-point temperatures required to maintain comfortable indoor-air and floor-surface temperatures has also been calculated [12][13][14].…”