Efficient simulation of multiple borehole heat exchanger storage sites

Abstract

In this paper, an adapted model is developed for borehole heat exchangers (BHEs) to simulate geothermal applications such as heat storage on a large scale efficiently and with high accuracy. The adapted numerical model represents all BHE components, allowing for a detailed representation of the governing processes. The approach is calibrated and validated for a single U-tube BHE using a high-resolution experimental data set from a laboratory thermal response test. It is found that the computational effort can be reduced by factors of *50, *50 and *25 for single U-tube, double U-tube and coaxial BHEs, respectively, if an absolute deviation of less than 1 % compared to a conventional fully discretised model is allowed. Computation times can be reduced further by accepting higher deviations. The adapted modelling approach allows for a detailed and correct representation of the temporal and spatial temperature distribution under highly transient conditions by applying it to a high-temperature heat storage scenario using multiple BHEs. The model is especially suited to represent coupled flow and heat transport processes, to account for groundwater flow in the BHE region as well as geological heterogeneities and especially interaction between a large number of BHEs.Keywords Borehole thermal energy storage Á Borehole heat exchanger Á Numerical simulation Á Fully discretised models Á OpenGeoSys List of symbols aSolid compressibility (Pa -1 ) bFluid compressibility (Pa -1 ) cq Volumetric heat capacity (J m -3 K -1 ) dThickness (m) D Heat diffusion dispersion tensor g Gravitational acceleration (m s -1 ) k Intrinsic permeability (m) L Length (m) m Side length (m) n Porosity (-) p Pressure (Pa) Q Sources and sinks (kg m -3 s -1 ) Q H Heat sources and sinks (W m -3 ) rRadius (m) R th Thermal resistance (K W -1 )Transport velocity (m s -1 ) z Depth (m) a Dispersivity (m) kThermal conductivity (W m -1 K -1 ) l Fluid dynamic viscosity (N s m -2 ) q Density (kg m -3 )

First Results Of A Numerical Characterization Of A Field Scale Cement Based Thermal Energy Storage System

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Application and Validation of a Dynamic Energy Simulation Tool: A Case Study with Water Flow Glazing Envelope

“…A refrigerant fluid transports the heat. This solution is optimum in cold countries when the systems allow heat injection into the ground in summer [8,9]. At a certain depth, the temperature of the ground remains steady over the year, so borehole heat exchangers are considered an optimum solution when the available area is limited [10].…”

Monitoring the impact of intensive shallow geothermal energy use on groundwater temperatures in a residential neighborhood

“…Hence, knowledge about subsurface temperature distribution and evolution is important for the ecological and economic sustainable intensive thermal use of the shallow subsurface and management of shallow geothermal resources (e.g., Epting et al 2013;Vienken et al 2015). Respective research focuses mainly on the assessment and prediction of local groundwater temperature evolution and resulting impacts in the vicinity of large scale installations (e.g., Bauer et al 2015;Boockmeyer and Bauer 2016) as well as monitoring of groundwater temperature distribution on city scale to detect and quantify the anthropogenic heat impact, i.e., formation of urban groundwater heat islands (e.g., Zhu et al 2010). Investigations on neighborhood scales are scarce because individual system sizes are small and monitoring is hence often not required.…”

“…Numerical models are frequently used to predict and visualize induced groundwater temperature changes and potential system interaction. The constant advancement of simulation tools and computational power allow meanwhile investigations on various scales (Boockmeyer and Bauer 2016;Hein et al 2016). However, the lack of monitoring data (heat pump operation and groundwater temperature data) for model parametrization and calibration as well as the lack of reliable exploration data with resulting oversimplification of the geological and hydrogeological regime lead to resulting simulation uncertainties in practice (e.g., Schelenz et al 2017;Hermans et al 2018)-making exploration and actual groundwater temperature monitoring indispensable.…”