Optimization of ground heat exchanger parameters of ground source heat pump system for space heating applications

In this paper Taguchi and utility methods have been employed to optimize eight important parameters (i.e. radius of U tube, borehole radius, heating load, grout conductivity, entering water temperature, distance between U tubes, U tube thermal conductivity and mass flow rate) of GHX (ground heat exchanger) used for space heating applications. Length of GHX, COP (coefficient of performance) and thermal resistance of GHX are considered as the objective functions. In Taguchi method lower the better concept is applied to obtain optimum values for the length of the GHX and its thermal resistance and for COP higher the better concept is used. In utility concept higher the better method has been employed. Based on the results obtained using Taguchi optimization, the optimum parameters and levels for GHX length, COP and GHX thermal resistances are found to be, A2B1C1D1E3F3G1I3, A2B2C1D3E3F3G1I2 and A1B2C1D2E1F1G3I1 respectively. Results obtained using the above optimized set of parameters show 15.17% reduction in the length of GHX, 2.5% increase in COP and 17.1% reduction in thermal resistance of GHX. The implementation of utility concept to obtain a single set of optimum parameters and levels resulted in 3.2% increase in GHX length, about 1.2% decrease in COP and 13.23% decrease in thermal resistance.