Extended version at 25 years of the ASHRAE-Tp8 method for the design of BHE fields operating with geothermal heat pumps

The correct design of Borehole Heat Exchangers (BHE) fields serving ground-coupled heat pumps (GCHP) is essential for assuring the desired performance of the system over time. The ASHRAE method for BHE field design applies the temporal superposition of three aggregated thermal pulses to quantitatively account for the annual building heating and cooling demand and it introduces the temperature penalty correction term T p . This method, as originally conceived, refers to a 10-year time horizon. In this paper, the T p8 version of the ASHRAE method is extended to a reference period of 25 years, as sometimes required in GCHP applications. New T p8 constants have been calculated for square, rectangular, in-line, O, U, and L borefield configurations, by applying reference gfunction solutions. The robustness and accuracy of the present method have been assessed by comparisons with EED and GLHEPRO results for different European buildings and a series of BHE field configurations. In terms of overall borefield length prediction, the present method revealed to be accurate within 10% with respect to the reference software that work on a monthly basis and use a full set of g-functions.