Theoretical and Experimental Cost–Benefit Assessment of Borehole Heat Exchangers (BHEs) According to Working Fluid Flow Rate

Abstract

In ground-source heat-pump systems, the heat exchange rate is influenced by various design and operational parameters that condition the thermal performance of the heat pump and the running costs during exploitation. One less-studied area is the relationship between the pumping costs in a given system and the heat exchange rate. This work analyzes the investment and operating costs of representative borehole heat-exchanger configurations with varying circulating flow rate by means of a combination of analytical formulas and case study simulations to allow a precise quantification of the capital and operational costs in typical scenario. As a conclusion, an optimal flow rate minimizing either of both costs can be determined. Furthermore, it is concluded that in terms of operating costs, there is an operational pumping rate above which performance of geothermal systems is energetically strongly penalized.

Application and Design Aspects of Ground Heat Exchangers

“…As for the heat flux, it is advisable to express the value per heat exchange surface [59] or even simpler per unit length [15,103,109]. Care must be taken, as unit length can be expressed as the pipe, vertical borehole, or horizontal trench length.…”

“…Hydraulic assessment will find a balance between thermal efficiency and operating costs that both increase with increasing flow. Greater thermal efficiency means lower initial costs [109].…”

How a sensitive analysis on the coupling geology and borehole heat exchanger characteristics can improve the efficiency and production of shallow geothermal plants

“…In contrast, the ground is not an isotropic and homogeneous medium but is instead characterised by specific and variable thermophysical characteristics due to geothermal heat flux, lithology, porosity and presence of water ( Chicco et al., 2019 ; Giordano et al., 2019 ), so that the ground behaves as fixed variable that cannot be changed to improve heat power extraction. Additionally, pipes can be coaxial, single, or double U shaped and made of steel or polyethylene so that variables increase, and thermal performances are not easy to forecast ( Badenes et al., 2020a , Badenes et al., 2020b ).…”

Determination of the Selected Wells Operational Power with Borehole Heat Exchangers Operating in Real Conditions, Based on Experimental Tests

“…Real measurement results are required for calculations and simulations. A number of studies [25][26][27][28][29][30][31][32][33][34] have been conducted to evaluate the performance of BHE in heat pump systems. All of these studies described the impact of BHE based on the evaluation of COP improvement in these systems.…”