A Web Application for Geothermal Borefield Design

The correct design of a borehole heat exchanger (BHE) system implies the accurate knowledge of borehole and ground thermal properties, the correct evaluation of building heating or cooling demands and the correct procedure to assess the final overall BHE length related to BHE configuration shape. A careful design is required to make profitable payback plans and provide expected long time performance. In this paper the principle and description of a web-based suite of tools for BHE design is presented. The web application intends to implement some of the main procedures universally adopted in BHE system design. A section of the present paper describes the implementation of an improved ASHRAE method which allows the BHE system to be designed by considering three representative building heat loads, their respective thermal resistances based on ICS model and a temperature penalty variable which takes into account the long term BHE interaction effect. A new hybrid implementation of the Ashrae method based on g-function calculation is also described for arbitrary borehole field configuration design. This arbitrary shaped borefield design allows the designer to fit the peculiar needs of each application project. Current free or commercial programs allow the user to design BHE systems according to a priori determined set of available configurations in terms of borefield shape and borehole to borehole distances while real applications often require the borehole field geometry not to respect a regular matrix configuration. A further section describes a toolkit for Thermal Response Test (TRT) analysis which allows the estimation of BHE and ground thermal properties. This toolkit provides also a method for the evaluation of the error related to TRT analysis results. Furthermore, a section for analytical estimation of borehole thermal resistance based on literature review is also presented.