Geoenergetics analysis - correct design of the lower heat source

Introduction

The correct design of a bottom source of heat in the form of borehole heat exchangers depends on a range of information related to the borehole itself and the future heat/cooling consumer (Śliwa and Gonet, 2011). Using advanced numerical simulators and acquired knowledge, GeoTec Energy Sp. z o.o. produces a study entitled “Geoenergetic Analysis”.

What is a geoenergetics analysis?

The geoenergetic analysis allows the determination of a bottom source concept operating on borehole heat exchangers (BTES - Borehole Thermal Energy Storage) based on the thermal properties of the rock (rock mass parameters), the design parameters of the borehole heat exchanger and information about the future heat/cooling consumer.

The study occludes:

• the potential energy performance of the downstream heat source with borehole heat exchangers (i.e. heating/cooling capacities and amount of heat exchanged),
• possible seasonal load variants for borehole heat exchangers,
• selection of supplementary sources in the event of heat/cooling shortages for momentary loads or for storing energy in the rock mass (heat/cooling),
• thermal properties of the rock or the parameters of the test hole (effective thermal conductivity in the borehole and thermal resistance of the borehole heat exchanger on the basis of the performed thermal response tests or provided results of the thermal response tests)
• number of boreholes, required depth, distance between boreholes, design, trajectory of the borehole axes and their arrangement,
• performance of the single borehole heat exchanger or the entire field of boreholes.

What data are needed for the study?

The most accurate form of determining the energy efficiency of borehole heat exchangers, the thermal resistance of the borehole heat exchanger and the effective thermal conductivity of the rock is the Thermal Response Test. The quality of the geoenergetics analysis will be higher if data from a previously conducted TRT are used (Gonet et al., 2011).

Data needed for the study:

• location:
  • map of land available for borehole exchangers with dimensions,
  • suggested area for drilling,
• lithological profile,
• TRT data:
  • effective thermal conductivity value of the profile rocks,
  • thermal resistance of the borehole heat exchanger,
  • average rock temperature,
• design data of the borehole heat exchanger:
  • design (single U-tube, double U-tube, etc.),
  • borehole diameter,
  • borehole depth,
  • depth of casing of exchanger tubes,
  • distance between exchanger pipe axes,
  • type of material used for sealing of exchanger tubes,
  • outer diameter of the exchanger tubes
  • thickness of the exchanger tubes wall,
  • exchanger tube material,
• data on the heat transfer medium (type, concentration),
• data on heating/cooling demand,
• data on system operation (heating, heating+cooling, cooling).

Literature

• Gonet, A. i inni, 2011. Metodyka identyfikacji potencjału cieplnego górotworu wraz z technologią wykonywania i eksploatacji otworowych wymienników ciepła. Kraków: Wydawnictwa AGH.
• Śliwa, T. i Gonet, A., 2011. Otworowe wymienniki ciepła jako źródła ciepła lub chłodu na przykładzie Geoenergetics Laboratory WWNiG AGH (Borehole heat exchangers heat or cool source on the basis of Laboratory of Geothermics of Drilling, Oil and Gas Faculty in AGH University of Krakow). Wiertnictwo, Nafta, Gaz, 28(1-2), pp. 419-430.