Producing geothermal energy with a deep borehole heat exchanger: Exergy optimization of different applications and preliminary design criteria

Abstract

This paper aims at proposing fast and plain design tools to evaluate the best energy application for deep borehole heat exchangers, exploiting geothermal resources. Exergy efficiency has been chosen as a performance index. Five possible utilization solutions have been analyzed: district heating, adsorption cooling, ORC power production, a thermal cascade system, and combined heat and power configuration. An extensive sensitivity analysis on source characteristics and well geometry has been performed to find the design criteria that ensure the maximum exergy performance.Results show that configurations involving district heating are recommended for exclusive power production. If optimized, district heating exergy efficiency can reach values in the range 40 % -50 % when a geothermal source at the well bottom is lower than 300 °C. For higher values, the combined heat and power production is a preferable choice, reaching an exergy efficiency of up to 60 %. Design charts are also provided to read first-attempt values of the well operative temperatures and flow rate to maximize exergy efficiency for each utilization layouts.

Storing high temperature solar thermal energy in shallow depth artificial reservoir for space heating

“…Deep borehole heat exchanger (DBHE) (Fig. 2) is a closed loop system and is independent of the hydrothermal resources as well as effectively avoids the problems of reinjection, corrosion and scaling, and thus lots of such projects have been implemented around the world especially in China [27][28][29][30][31] . To compare the performance between SDAR and DBHE, a numerical simulation on DBHE is carried out and the calculation results are shown in Figs.…”

Technical Performance Comparison between U-Shaped and Deep Borehole Heat Exchangers

“…The heat transfer between the ground and the DBHE is evaluated using a semianalytical approach based on the thermal resistances of the components of the DBHE [18,19] shown in Figure 1. The analytical solution of the Fourier equation of heat transport, given in the classical line heat source theory by Carslaw and Jaeger, is used to model the heat transfer into the ground source, which is assumed to be a purely conductive medium.…”

“…We used the Geopipe software developed to study DBHEs and written in C [18,19]. In [18], we presented and discussed the developed software essentially.…”

Closed-Loop Systems for Geothermal Energy Exploitation from Hydrocarbon Wells: An Italian Case Study

“…Nu = 0.023Re 0.8 Pr 0.4 (9) with Pr = ρc f µ λ f and Re = ρv f 2r c µ . Finally, thermal resistance to heat conduction through the casings of the well can be determined as follows:…”

“…Additionally, geological and geophysical exploration campaigns into the deepest regions of such geological contexts have ascertained the coexistence of hydrocarbons and low-temperature to medium-temperature geothermal energy resources [5,6]. Recent investigations have attempted to assess geothermal potentials, exploring deep geothermal resources in different regions and reconstructing heat flow maps at different depths [7][8][9].…”