Improved Ashrae method for BHE field design at 10 tear horizon

tAmong the strategies for borehole heat exchanger (BHE) field design, the Ashrae method is a powerfuland fast procedure for the prediction of the BHE field length required by the building monthly heat loadprofile. The method needs the calculation of the Temperature Penalty, a key parameter that takes intoaccount the error introduced by the infinite cylindrical source (ICS) solution of the conduction problemwith respect to the “true” g-function solution. Recently the Authors proposed a modification of the originalAshrae (Kavanaugh and Rafferty) method which maintains the simplicity of the original Ashrae modelwhile dramatically improving the estimations of the required BHE field length and geometry withoutcalculating any g-function and with no need of special algorithms or computer codes. The new method(Tp8method) is centred on a scheme where eight heat sources are thermally interfering with the currentBHE source: optimum constants and new model validation had been calculated with reference to a setof more than 200 BHE design configurations described by the pertaining temperature response factors(i.e. g-functions). In this paper the validation of the Tp8model is further carried on in order to prove themodel robustness while the design input quantities (BHE depth, ground properties, mutual importance ofAshrae three load sequences) are changed to cover most of practical cases in borefield design. In particulara further simple term is introduced (and discussed) in Tp8Fourier number calculation which enables thepresent model to assure high accuracy also when the BHE depth is significantly different from usualvalues, say from short to very deep BHEs (60-240 meters).