Concrete façade panels with enhanced thermal energy storage capacity

Abstract

The escalating global climate change crises is motivating governments to seek solutions for reducing non-renewable energy consumption. Buildings are responsible for more than 40% of the total global energy consumption and over 30% of greenhouse gas emissions, and hence the improvement of the energy efficiency of buildings, particularly during their operational phase, is an active area of research. One of the commonly proposed methods of enhancing the energy performance of a building is to use the mass of the building envelope as a thermal energy storage system. The absorption and storage of heat during the day can reduce overheating of the internal environment in a building and hence reduce the energy demand of the air conditioning system. The stored heat is then dissipated into the internal environment at night when the temperature of the building naturally reduces.

The thermal energy storage capacity of a building material can be enhanced by incorporating phase change materials (PCMs), which are materials that absorb or release a high amount of heat energy while changing phase from solid to liquid or vice versa while remaining at the same temperature. Previous laboratory research by the author has shown that the incorporation of PCMs into concrete enhances its thermal storage capacity by up to 50%. However, it cannot be assumed that this thermal mass benefit will be replicated in a full-scale actual scenario. There is a scarcity of full-scale research studies in the literature as previous studies were largely on numerical studies validated by laboratory experiments. To address these gaps in the research this study, after initial laboratory investigations to develop an appropriate PCM-concrete composite material, manufactured precast cladding sandwich panels with a PCM-concrete inner leaf. The panels were tested thermally and structurally in the laboratory. Three full-scale demonstration huts were constructed using the panels and instrumented to record both internal thermal data and local climate data over an 18 month period. Analysis of this data showed that when the internal air temperature fluctuated above and below the phase change temperature of the PCM within a 24 hour period, the PCM-concrete composite was effective at reducing the air temperature in the huts by up to 16% if overnight ventilation was provided and up to 12% without overnight ventilation in a temperate climate.

The potential of the PCM-concrete composite to provide a beneficial thermal mass effect in a building depends on many variable factors including geographical location, the local climate, building geometry and use of the building. As all buildings differ, each building will require a unique optimal solution for the application of a PCM composite material as a thermal energy storage system. For this reason, the development of numerical simulation tools is necessary to achieve a practical and economic application of this technology. In this study, a 3D finite element model was developed using COMSOL Multiphysics which replicates the thermal behaviour of the PCM-concrete composite in the full-scale huts. The model was validated by comparing the simulated temperatures in the model with the actual temperatures recorded in the huts. The validated model was used to investigate the influence of geographical location, that is, latitude, on the performance of the PCM-concrete composite. This `scenario? modelling concluded that during the summer in the Northern hemisphere, the PCM-concrete provided more beneficial thermal mass effect at higher latitudes. It was also demonstrated that the PCM-concrete was more effective when placed in a floor rather than a North wall under summer conditions. In contrast, in winter conditions the PCM-concrete composite was more effective in lower latitudes when positioned in the walls.