Modeling neighborhood-scale shallow geothermal energy utilization: a case study in Berlin

Jakob Randow,Haibing Shao,Anke Bucher,Steve Thiel,Shuang Chen,Tom Reinhardt,Karsten Rink,Katrin Lubashevsky,Rüdiger Grimm,Olaf Kolditz

doi:10.1186/s40517-022-00211-9

Abstract

Nowadays, utilizing shallow geothermal energy for heating and cooling buildings has received increased interest in the building sector. Among different technologies, large borehole heat exchanger arrays are widely employed to supply heat to various types of buildings. Recently, a 16-borehole array was constructed to extract shallow geothermal energy to provide heat to a newly-developed public building in Berlin. To guarantee the quality of the numerical model and reveal its sensitivity to different subsurface conditions, model simulations were conducted for 25 years with two finite element simulators, namely the open-source code OpenGeoSys and the widely applied commercial software FEFLOW. Given proper numerical settings, the simulation results from OpenGeoSys and FEFLOW are in good agreement. However, further analysis reveals differences with respect to borehole inflow temperature calculation implemented in the two software. It is found that FEFLOW intrinsically uses the outflow temperature from the previous time step to determine the current inflow temperature, which makes it capable of much faster simulation by avoiding iterations within a single time step. In comparison, OpenGeoSys always updates the inflow and outflow temperature based on their current time step values. Because the updates are performed after each iteration, it delivers more accurate results with the expense of longer simulation time. Based on this case study, OpenGeoSys is a valid alternative to FEFLOW for modeling ground source heat pump systems. For modellers working in this field, it is thus recommended to adopt small enough time step size, so that potential numerical error can be avoided.

Highlights

The current energy transition in the world demands increasing amount of renewable and sustainable energy sources
Kolditz et al 2012; Shao et al 2016), as well as the commercial software FEFLOW, are utilized to generate simulation results for a 16-Borehole Heat Exchangers (BHE) Ground Source Heat Pump (GSHP) system project located in Berlin
In this study, a neighborhood-scale GSHP system model has been setup based on a building project in Berlin

Summary

Introduction

The current energy transition in the world demands increasing amount of renewable and sustainable energy sources. Borehole Heat Exchangers (BHE), Ground Source Heat Pump (GSHP) systems extract geothermal energy from the shallow subsurface by circulating fluid in the BHEs, and Randow et al Geothermal Energy (2022) 10:1 transfer the heat into the building through a heat pump. It is one of the low-carbon and emission-free technologies that satisfies the energy transition target of the building sector. BHEs can store the surplus thermal energy from building cooling into the subsurface, which can increase the system performance (Hein et al 2016). Ahmadi et al (2017) revealed in their study that using GSHP systems for cooling purposes can be more efficient than traditional air conditioning systems

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Discussion

Conclusion