Numerical methodology for feasibility analysis of ground source heat pumps

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2014-8
Gamage, Kumudu Janani
Ground source heat pump (GSHP) systems provide an alternative energy source for residential and commercial space heating and cooling applications by utilizing the favorable temperature profile at a certain depth under the ground surface. GSHP’s aftereffects on the ground temperature profile need to be considered for estimating the economical breakeven point. The present study develops a new semi-analytical model to analyze the short term response of the ground heat exchangers by accounting the depth dependencies in the heat transfer rates along the borehole. The model utilizes the solution of Kelvin’s infinite-length line source theory to predict the borehole wall temperature but incorporates working fluid’s inlet temperature to modify the heat transfer rate with time and depth to capture the borehole wall temperature variations in short time periods. The developed model is validated against other widely used short-term response models based on g-functions as well as three dimensional finite volume (FV) simulations, which can address the short-term transient behavior of the ground temperature response accurately but at high computational costs. The novelty of the model is that it is able to predict fluid’s exit temperature for both short- and long-term periods without a need to explicitly consider load aggregation at a modest computational cost. The developed model is implemented on a case study for a dormitory building at METU NCC campus to investigate the economic feasibility of the proposed GSHP system by carrying out the breakeven point calculations against a conventional boiler for space heating applications. The study reveals that full sized GSHP system with a supplementary backup unit can economically break-even the GSHP installation cost after 4 years of GSHP installation with 470 ton CO2 emission reduction.

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Citation Formats
K. J. Gamage, “Numerical methodology for feasibility analysis of ground source heat pumps,” M.S. - Master of Science, Middle East Technical University, 2014.