Modelling and evaluation of groundwater filled boreholes subjected to natural convection
Artikel i vetenskaplig tidskrift, 2019

One of the challenges of designing ground source heat pumps systems is the calculation of the effective thermal borehole resistance which affects the heat extraction rate and thereby the required length of the borehole. Calculating effective borehole resistance is especially demanding when the boreholes are filled with ground- water. The natural convection in the groundwater affects the heat transport from the borehole heat exchanger to the borehole wall. The objective of this paper is to present the results of the modified Pygfunction software in which recently developed correlations for calculating influence of the natural convection in boreholes has been incorporated. The calculated results were validated by using results of thermal response test (TRT) from four adjacent groundwater filled borehole in the central parts of Sweden. The numerical results reveal that the ori- ginal and unmodified Pygfunction can be used for accurate calculation of fluid temperatures in borehole heat exchangers by using an effective thermal conductivity of the filling material. However, that requires access to thermal response test data. The modified software calculates the effective borehole resistance with a deviation of about 15–30% compared to the effective borehole resistance from TRT. This deviation is an improvement compared with the standard assumption of neglecting natural convection in boreholes. However, for large in- stallations with more than 4000m of borehole heat exchangers a thermal response test is still recommended in order to ensure a more correct sizing of geothermal system.

Natural convection

Borehole

TRT

HHP

Thermal response test

Hydronic Heated Pavements

Författare

Josef Johnsson

Chalmers, Arkitektur och samhällsbyggnadsteknik, Byggnadsteknologi

Bijan Adl-Zarrabi

Chalmers, Arkitektur och samhällsbyggnadsteknik, Byggnadsteknologi

Applied Energy

0306-2619 (ISSN)

Vol. 253 113555

Safe and ice-free bridges using renewable energy sources

Statens vegvesen, 2014-03-17 -- 2018-12-31.

Drivkrafter

Hållbar utveckling

Styrkeområden

Transport

Building Futures (2010-2018)

Ämneskategorier

Energiteknik

Infrastrukturteknik

Energisystem

Miljövetenskap

DOI

10.1016/j.apenergy.2019.113555

Mer information

Skapat

2019-08-13