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Browsing by Author "Agarwala, Prem"

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    Modeling and performance enhancement of thermo-active foundations for cold climates - Case of Minnesota
    (2023-07) Agarwala, Prem
    In the United States, building energy consumption accounts for approximately 40%, witha significant portion used to meet heating and cooling needs. The reliance on fossil fuels to meet space heating and hot water needs leads to substantial CO2 emissions. Therefore, there is an urgent need for clean and sustainable energy technologies to decarbonize building energy usage. Among these technologies, ground source heat pump (GSHP) systems have gained significant attention due to their high efficiency and consistent performance across different seasons. However, their widespread adoption is hindered by the high initial costs, despite their lower operation and maintenance expenses. One promising approach to mitigate this issue is coupling the GSHP system’s ground heat exchanger with the building foundation, known as the “thermo-active foundation (TAF).” By doing so, the capital cost and space requirements of the entire system can be reduced. Additionally, integrating the ground heat exchanger with the building foundation serves dual purposes of structural support and heat exchange with the ground. This study focuses on evaluating and enhancing the performance of a vertical U-loopground heat exchanger integrated into a 20-meter deep helical steel pile. A thoroughly validated and verified transient computational fluid dynamics numerical model is employed for this purpose. The model is utilized to investigate the short-term (one year) and long-term (five years) transient performance of the system in the cold climate of Minnesota, where there is a significant disparity between heating and cooling loads. A building energy model, representing a typical small residential house in Minnesota with an area of 2026 square feet, is developed using BEopt software to determine the annual heating and cooling loads. Three normalized building load cases (0.25, 0.33, and 0.4 tons) are then used to determine the capacity per pile. For the larger 0.4 tons load, detailed parametric studies are conducted to establish performance under different inlet fluid velocities (considering laminar and turbulent flow regimes), and the TAF’s location in relation to the building. The results demonstrate that the COP (coefficient of performance) remains constant at around 3.3 for all pile locations, indicating that the system’s performance is independent of the pile’s location. Moreover, for all flow velocities, the COP remains the same, around 3.3, with laminar flow being preferable due to lower pump power requirements. To enhance performance, thermal energy storage using phase change material (PCM), isincorporated inside the TAF. Two PCM tubes, each with a volume of 0.0053093 m3 (5.30 kg), are inserted beside both sides of the pile in the ground. The performance enhancement for different building loads (0.4 tons, 0.33 tons, and 0.25 tons) is compared to determine the optimal amount of heating load per pile necessary to meet the total building load over a year in Duluth, MN using PCM. The results indicate that a 0.4 tons load per pile is the most economical option, requiring eight piles to meet the house’s load in Duluth, MN, with an additional heating requirement during 6.30% of the year. The system’s performance is also assessed in other locations in Minnesota, including International Falls and Saint Paul, to compare long-term performance with Duluth for a 0.4 tons building load. The average annual COP using PCM in Duluth, International Falls, and Saint Paul is found to be 4.09, 4.20, and 4.60, respectively, with Saint Paul exhibiting the best performance due to its higher cooling energy demand and low peak heating loads. However, despite having a higher COP than Duluth, International Falls shows the worst performance owing to the high heating loads, thus requiring more auxiliary heating.