PERFORMANCE ANALYSIS FO A RESIDENTIAL GROUND SOURCE HEAT PUMP WITH ANTIFREEZE SOLUTION
M. H. Khan, J. D. Spitler
If the minimum anticipated fluid temperature in a ground source heat pump system falls near or below 0oC, an antifreeze mixture must be used to prevent freezing in the heat pump. The antifreeze mixture type and concentration has a number of implications for the design and performance of the system. These include the required ground loop heat exchanger length, the capacity and energy consumption of the heat pump, the circulating pump selection, pumping energy, and the first cost of the system. For example, the required ground loop heat exchanger length and first cost will decrease, due to lower permissible operating temperatures, with increasing antifreeze concentration in heating-dominated climates. On the other hand, the antifreeze also degrades the heat pump performance; operating costs can be expected to increase with increasing antifreeze concentration, and a larger capacity heat pump may be needed. The complex interaction between all of the design variables makes it difficult to choose an optimal design, and it is desirable to have a simulation and life cycle cost analysis that can be used to evaluate all of the variable interactions, to be used as the basis for an optimal design procedure. This paper reports on a simulation procedure implemented in HVACSIM+ and a life cycle cost analysis and gives example result for a typical Canadian residential building. Four different antifreeze mixtures are considered; methyl alcohol, ethyl alcohol, propylene glycol and ethylene glycol. The life cycle cost analysis was based on the electricity costs for the heat pump and circulating pump and first costs forthe heat pump, circulating pump, grout, borehole drilling, U-tube, and antifreeze.
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