Investigation on the Effects of Different Time Resolutions in the Design and Simulation of Bhe Fields

Abstract

The correct design of a field of Borehole Heat Exchangers (BHE) requires the knowledge of ground thermal properties, heat pump performance and building heating and cooling demand. The sequence of heat pulses from (to) the ground by the heat pump can be described according to different time steps, from hours to months and even years. The monthly time step approach is often the preferred design choice which involves recursive calculations (temporal superposition techniques) and the availability of precalculated temperature response factors (or g-functions) for given BHE field geometries. Such a complex computing task is usually performed thanks to commercial codes in order to fulfil a carrier fluid temperature at the end of a given time horizon, typically 10 or 25 years. In this paper the monthly design approach (EED code and TecGeo proprietary code) is compared with the three thermal pulse approach (modified ASHRAE Method Tp8) and it is demonstrated that for a representative series of case studies the three pulse calculation, easy to be performed at engineering level, is able to provide the correct BHE field overall length with 8% accuracy with respect to the reference monthly calculations.

Extending the Ashrae Tp8 method for vertical borefield design to uniform BHE temperature boundary conditions

“…A different approach has been proposed by Fossa andRolando (2014, 2015) who kept the temperature penalty parameter and proposed a method based on the original Ashrae implementation. Comparisons with EED software results showed the reliability of the improved Tp8 method, which maintains with respect to other formulations a great simplicity and the possibility to be implemented in calculation spreadsheets and employed in Standard method (Fossa et al 2017).…”

Impact of Employing Hybrid Nanofluids as Heat Carrier Fluid on the Thermal Performance of a Borehole Heat Exchanger

“…According to the results, it was shown that the ASHRAE method overestimates the borehole size by 28% compared to that when using GLHEPRO. Fossa et al [10] carried out a comparative analysis between different techniques such as the improved ASHRAE method, earth energy design (EED) code, and TecGeo proprietary code for predicting the total length of the BHE field over 10 years. It was indicated that the developed approach could estimate the BHE overall length with a percent error of 8% compared to the EED code as a reference.…”