Experimental and numerical study on thermal performances of a modular hydronic thermal barrier wall with heat injection system in filler cavities

Abstract

The hydronic thermal barriers with dynamically adjustable thermal performance have become one of the highly anticipated solutions for opaque envelope insulation while improving the efficiency of the use of low-grade energy. In response to the technical constraints encountered by conventional hydronic thermal barrier walls (i.e., CHTBs) when it comes to enhancing heat transfer, the concept of modular hydronic thermal barrier walls (i.e., MHTBs) was introduced. The MHTB incorporates a heat injection system within its filler cavities, a feature designed to promote the overall thermal performance of the opaque enclosure structure. The performance enhancement described is mainly achieved through active management of the thermal conductivity of the filling material within the vicinity of fluid pipes. In this study, field thermal performance assessments were carried out during winter conditions in three reduced-scale experimental rooms. The southern boundary of these test rooms adopts walls with different configurations, i.e., MHTB, CHTB, and traditional thermal insulation wall. Subsequently, a comprehensive investigation regarding the impacts of filling materials on the energy performances of MHTB was conducted through numerical simulations. The outcomes demonstrated a substantial reduction in heat loss through the south wall by using MHTB, leading to reduced room thermal discomfort. In particular, with a charging temperature set at 35.0 °C, the inner surface temperature of MHTB displayed a noteworthy increase of 10.3 °C compared to that of the traditional thermal insulation wall, resulting in a significant reduction in heat load by a factor of 7.4. Additionally, it was observed that the filler material within the pipe cavity played a vital role in shaping MHTB's thermal performance. For instance, considering the case with a heat injection temperature of 25.0 °C, a doubling of thermal conductivity resulted in an enhancement of 0.24 W/m2 in heat gain on the outer surface and an overall increase of 0.04 MJ in total injected heat. This study demonstrated the positive effect of MHTB on optimizing the efficiency of hydronic thermal barriers and guided their further application and research.