Deep Borehole Heat Exchangers — A Conceptual and Comparative Review

Abstract

Borehole heat exchangers (BHEs) are used for transforming a rock mass into an underground heat storage. Usually, their depth does not exceed 200[Formula: see text]m, but some extend to a depth of almost 3000[Formula: see text]m. Underground heat storages can operate as part of heating and cooling systems, often economically. In winter they extract heat from the rock mass for space heating, while in summer the cooled rock mass is used for air conditioning. The heat extracted from buildings via air conditioning is transferred into the rock mass, thereby regenerating its condition for winter time. Deep borehole exchangers also may operate only in the heating mode. Then, the rock resource conditions are regenerated via heat transfer through neighboring rocks. If a groundwater flow is present, the heat can also be removed and the source conditions regenerated through convection. Here, an overview of the use and operation of deep BHEs around the world is provided. Special emphasis is placed on the Carpathians, where numerous analyses of geothermal heat use have been performed since 1999. Examples of calculations for old oil and gas wells as well as negative exploration boreholes are given. Such analyses have been performed for boreholes in Poland and the Ukraine. However, little research has been published on this subject to date, for reasons described herein.

The application of Vacuum Insulated Tubing in Deep Borehole Heat Exchangers

“…For wells with irregular axis or directional wells adopted for BHE, additional stresses in inner column are caused by inclination [28].…”

Natural and Artificial Methods for Regeneration of Heat Resources for Borehole Heat Exchangers to Enhance the Sustainability of Underground Thermal Storages: A Review

“…For BHEs in former oil wells (Sliwa et al, 2014) [23] or other deep BHEs (Sapinska-Sliwa et al, 2015) [2], including directional wells (Knez, 2014) [24], it can be assumed for modeling that ground surface temperature is constant at the average annual ambient air temperature. The relation between heat extraction rate and temperature of the heat carrier fluid, under various conditions, is described by Eskilson (1987) [25].…”

“…Shallow holes (to depths of about 200 m) are used for heat/cool storage and extraction. Deeper BHEs are generally only used for heating (Sapinska- [2], also with use old oil and gas wells (Sliwa and Gonet, 2004) [3]. Typical constructions for BHEs are presented in Figure 1.…”

Comparative analysis of using borehole heat exchangers in Macedonia and in Poland

“…-single U-tube, -multi U-tube, -coaxial [1,10], -deep BHE [5,6], -helical [12,13], -BHE in piles [4], -BHE with direct evaporation system [7].…”