Experimental and Numerical Investigation of Thermal Storage Medium for Ground Source Heat Pump Applications

The thesis begins with a literature review of the current status of ground source heat pump (GSHP) systems. The limitations of these systems are discussed and the potential to couple phase change material (PCM) with a GSHP system is explored and presented. The research focuses on a paraffin- based PCM for the experimental studies in this thesis due to its low-cost/non-toxic properties.

The development of a bentonite-sand tank experiment is presented in Chapter 2. A steel casing, which emulates a single borehole positioned at the centre of a 1 m diameter tank was used to study the energy transfer rate from the borehole to the surrounding material in the tank. Using the obtained experimental results, the numerical model for this experiment was developed and validated in Chapter 4. A series of studies were performed in order to determine the temperature distribution profile of the tank for different bentonite thermal conductivity values. Due to a lack of drilling space, a bentonite-based thermal storage medium (TSM) is not a viable solution for many building owners and developers in urban settings. As such, the findings from this study were used towards the design of the concrete tank for testing in Chapter 3 in regards to the placement of the boreholes and PCM tubes.

The development of a concrete tank experiment is presented in Chapter 3. Four boreholes and eight PCM tubes were installed in order to characterize the heat transfer performance and the potential for energy storage with PCM for concrete-based applications. Due to the high thermal conductivity value of concrete, the temperature distribution at various depths and angular positions of the tank were relatively uniform.

In Chapter 5 a numerical model of the concrete tank experiment was developed and validated. The performance of a concrete-based heat exchanger tank with and without PCM were investigated. The findings from these results were essential to inform the design and installation of a full-scale system that is now being used for heating and cooling a residential dwelling.