Assessment of a novel phase change material-based thermal caisson for geothermal heating and cooling

Abstract

Space heating and cooling account for major portions of the energy consumption in various types of buildings. Energy use that relies heavily on fossil fuels results in greenhouse gas emissions and ultimately contributes to climate change via global warming. As such, it is important to utilize clean and renewable technologies to meet building energy demands. One such technology is the ground-source heat pump (GSHP), which uses the free and abundant energy from the ground. However, GSHP systems are expensive to install and often suffer from declining efficiencies over time, especially when they are employed in buildings that have unbalanced heating and cooling loads, such as those in extreme Canadian climates. In this study, we introduce a novel concept, a thermal caisson (TC), which not only considerably reduces the capital costs of GSHP systems, but also mitigates their efficiency degradation over time. TCs serve a dual functionality as both structural components that support the building as well as energy system components that provide heating and cooling to buildings. The TC comprises ground heat exchanger loops and a carefully chosen phase change material (PCM), which stores and releases large quantities of latent heat when needed, connected to a high efficiency heat pump inside the building. Results show that TCs could reduce the capital costs of GSHP systems by up to 49% and increase their coefficients of performance by up to 16% (with a median change from 3.7 to 4.3 in January) resulting in much shorter payback periods as well as more stable and improved performance. Compared to fossil-fuel based systems, TCs offer a considerable reduction (close to 30% in this study) in annual operating costs for a much smaller corresponding increase in capital costs. The results suggest that TCs have promise to be widely incorporated in the heating, ventilation, and air-conditioning systems of numerous building types.