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This paper investigates the total environmental impacts of a thermal caisson (TC) system by implementing a life cycle assessment methodology. The total environmental impacts consider the comprehensive effect on the environment across two life cycle stages: manufacturing and operation. A comparison between the TC results and two different HVAC systems, including air-conditioning/furnace and conventional ground-source heat pump (GSHP) systems, was made by adopting the ReCiPe 2016 methodology. This study reveals that the operation phase is the predominant contributor to environmental impacts across systems, mainly due to its extended duration. Specifically, the operational impacts of GSHPs are substantial, accounting for approximately 87% of total environmental impacts. A TC GSHP system demonstrates a notable environmental advantage, achieving a 79% reduction in total environmental impact when compared to traditional AC/furnace systems. This represents a 21% improvement over conventional GSHP systems. Despite this substantial reduction in total environmental impact, the TC GSHP system shows an almost 5% increase in the resource availability damage category relative to the conventional GSHP, which is attributed to its higher material consumption. These results highlight the TC GSHP system's superior efficiency in reducing environmental impacts and its potential as a more sustainable alternative in residential heating and cooling applications. [ABSTRACT FROM AUTHOR]

This paper investigates the total environmental impacts of a thermal caisson (TC) system by implementing a life cycle assessment methodology. The total environmental impacts consider the comprehensive effect on the environment across two life cycle stages: manufacturing and operation. A comparison between the TC results and two different HVAC systems, including air-conditioning/furnace and conventional ground-source heat pump (GSHP) systems, was made by adopting the ReCiPe 2016 methodology. This study reveals that the operation phase is the predominant contributor to environmental impacts across systems, mainly due to its extended duration. Specifically, the operational impacts of GSHPs are substantial, accounting for approximately 87% of total environmental impacts. A TC GSHP system demonstrates a notable environmental advantage, achieving a 79% reduction in total environmental impact when compared to traditional AC/furnace systems. This represents a 21% improvement over conventional GSHP systems. Despite this substantial reduction in total environmental impact, the TC GSHP system shows an almost 5% increase in the resource availability damage category relative to the conventional GSHP, which is attributed to its higher material consumption. These results highlight the TC GSHP system’s superior efficiency in reducing environmental impacts and its potential as a more sustainable alternative in residential heating and cooling applications.

• Thermal caissons (TCs) can provide cheaper and more efficient HVAC systems for the studied building. • TCs not only considerably reduce capital costs of GSHP systems, but also mitigate efficiency degradation over time. • The energy performance of TCs is found to be heavily influenced by the use of phase change materials (PCMs). In Canada, buildings account for a considerable portion of energy use and contribute heavily to Canada's greenhouse gas (GHG) emissions. As such, a transition towards energy-efficient heating and cooling systems is important. Sustainable ground-source heat pumps (GSHPs) are one type of energy-efficient heating and cooling systems. But, they have high capital costs and often decline in efficiency over time. In this study, we further develop a phase change material (PCM)-based thermal caisson (TC) system, and extend a numerical algorithm previously developed in the same research group to assess the long-term energy performance of these systems. Dual-purpose and low-cost TCs not only provide structural support to a building, but also provide high efficiency geothermal heating and cooling, through ground heat exchanger U-tubes and embedded PCMs. Linear regression analyses are also performed to formulate how values of the coefficient of performance (COP) of TC systems change over time based on results from the literature and the current model. The results show that the long-term energy performance of TCs is significantly influenced by the use of a PCM, which can improve the long-term COP of GSHP systems, by 22% on average. For the small residential building investigated in this study, the capital cost and the net present value (NPV) of a TC system can be up to 50% and 32% lower, respectively, than the corresponding values for a conventional GSHP system. In addition, the TC system has a return on investment (ROI) of 65% which is significantly higher compared to the conventional GSHP system. Furthermore, over the heat pump system lifetime (assumed 20 years in this work), the CO 2 emissions of the TC-based system are approximately 19% lower than conventional GSHP systems. Overall, the techniques used in this study can be extended and applied to larger buildings and potentially lead to greater energy savings for these buildings, if TCs are widely adopted in the building sector [ABSTRACT FROM AUTHOR]

• Thermal caissons (TCs) can provide cheaper and more efficient building HVAC. • TCs require HDPE pipes and a carefully chosen PCM attached to a caisson and a GSHP. • TCs are over 49% cheaper than GSHPs and can improve their COP by 16% on average. • TC design is sensitive to the selection of PCM and the caisson configuration. • TCs can be adopted in HVAC systems of various buildings for heating and cooling. 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. [ABSTRACT FROM AUTHOR]