PowerPointPrsentation

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Geothermal Site Investigation Present
Developments of the Geothermal Response
Test Geothermal Resources Council Annual
Meeting 2007 September 30 - October 3, 2007
Reno, Nevada
Prof. Dr.-Ing. Rolf Katzenbach, Dipl.-Ing.
Frithjof Clauss, Dipl.-Ing. Thomas Waberseck
Institute and Laboratory of GeotechnicsTechnische
Universität DarmstadtPetersenstrasse 13D-64287
DarmstadtGermanyPhone 49 61 51 16 21
49Fax [phone]Email katzenbach_at_geo
technik.tu-darmstadt.deInternet www.geotechnik.t
u-darmstadt.de
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Energy can be extracted from or stored in the
subsoil by e.g.
Geothermal Use of the Subsoil

• Borehole heat exchangers
• Ground loops
• Earth-contacting massive absorbing elements
• Groundwater wells

shallow
deep
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Geothermal Use of the Subsoil

• A geothermal facility is only efficient if it is
  dimensioned, built and operated properly.
• Fundamental basis for the dimensioning are the
  assessment of the governing influencing
  quantities and the application of scientifically
  based design procedures.

Energy demand kW
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Influencing Factors

• Subsoil Conditions

• Soil layers
• Natural temperature of the soil
• Thermal properties (heat capacity, thermal
  conductivity)

c mainly dependent on - Temperature t- Water
volume w
l mainly dependent on - Pore volume n- Pore and
crack contents (air, water) - Temperature t -
Dry density of soil rd - Water volume parameters
w und Sr
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Influencing Factors

• Subsoil Conditions

• Soil layers
• Natural temperature of the soil
• Thermal properties (heat capacity, thermal
  conductivity)

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Influencing Factors

• Subsoil Conditions

• Soil layers
• Natural temperature of the soil
• Thermal properties (heat capacity, thermal
  conductivity)
• Ground water (level, flow velocity and direction)

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Influencing Factors

• Subsoil Conditions
• Constructional and Thermal Factors

• Geometry of the borehole heat exchangers
  (distance, size )
• Diameter, wall thickness and material of the heat
  exchanger tubes
• Quality and thermal properties of the borehole
  grouting
• Hydro-mechanical and thermal properties of the
  heat exchanger fluid
• Mass transport of the heat exchanger fluid
  (velocity, amount)

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Influencing Factors

• Subsoil Conditions
• Constructional and Thermal Factors
• Usage-specific Factors

• Usage mode- only cooling, only heating, both
  heating and cooling- direct use with heat
  exchanger or use with heat pump
• Heating and cooling demands

Assessment of the energy demand
Assessment of the energy potential of the subsoil
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Geothermal Site Investigation
Laboratory Tests

• Darmstadt thermal conductivity test apparatus
  (porous media)

• Thermoscanner - thermal conductivity (solid media)

• Calorimeter - heat capacity

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Geothermal Site Investigation

• Laboratory tests only give information on the
  local properties
• Not all influencing factors are considered

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Geothermal Response Test (GRT)

• First idea Mogensen (Sweden, 1983)
• He suggested circulating a chilled fluid as
  energy carrier medium in a borehole heat
  exchanger in the subsoil.
• The thermal reaction of the subsoil is quantified
  measuring the flow and return temperature.
• Assuming a constant energy withdrawal rate along
  the length of the heat exchanger, the parameter
  effective thermal conductivity can be
  determined from the thermal reaction of the
  subsoil (thermal response) after achieving a
  quasi-steady state.

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Geothermal Response Test (GRT)
The fluid temperature in the borehole heat
exchanger Tf can be determined by calculating the
line source temperature in the borehole margin (r
rb) by
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Geothermal Response Test (GRT)
For a constant specific energy transfer rate q
the time function of the fluid temperature from
has the form
The effective thermal conductivity of the
thermally influenced subsoil is given by the
gradient k of the determined test straight line
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Geothermal Response Test (GRT)
The first mobile pilot Geothermal Response Test
facilities based on the idea of Mogensen were
developed in Sweden (Lulea University of
Technology) and in the USA (Oklahoma State
University) in the mid 90s.
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Enhanced Developments of the GRT
After the first positive experiences with the
GRT, worldwide numerous further equipments were
put into operation during the following years.
Beside an increase of mobility by the application
of smaller equipments the aim of the developments
of the recent years was the further improvement
of the test realization and the analysis of the
GRT. Furthermore, emphasis was placed on the
essentials of three aspects
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Automated Control and Feedback Systems

• Constant energy input is regulated permanently by
  controlling the variables pumping rate and flow
  temperature
• Flow and return temperature are measured inside
  the borehole heat exchanger

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Fiber Optical Temperature Measurement
Fiber optical measurement facilities are useful
for the depth depending determination of the
thermal conductivity.

• Installation of a glass fiber cable in the
  borehole heat exchanger
• By measuring the backscattered light and
  determining time depending amplitude of Stokes
  and Anti-Stokes-components temperature over the
  depth can be measured with a spatial resolution
  range of 25 cm to 50 cm

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GRT with Hybrid Cable

• Installation of a hybrid cable in the borehole
  heat exchanger functioning as measuring and
  heating cable at the same time
• By electrically heating-up the cable, an over the
  entire length defined energy input is injected
  into the subsoil
• Temperature changes along the glass fiber are
  recorded by the fiber optical measurement
  technique

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GRT with Hybrid Cable
temperature C
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Wireless Probe - Micro Fish

• Probe consists of pressure and temperature
  sensors and a mini-datalogger including a
  microprocessor in a closed metal tube (length
  235 mm, Ø 23 mm, weight 99.8 g)
• Probe sinks under its own weight down a completed
  borehole and records pressure and temperature at
  selected intervals
• Measurement run for a 300 m borehole could be
  completed in less than one hour
• Readout of the measurement data the geothermal
  gradient can be determined for each layer

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Conclusions

• The Geothermal Response Test is an efficient and
  reliable testing procedure for a Geothermal Site
  Investigation.
• Especially for larger facilities with a number of
  heat exchanger elements, the conduction of a
  Geothermal Response Test is economically
  efficient, since the dimensioning can be based on
  the obtained data. Hence, the risk of over- or
  under- dimensioning can be reduced substantially.
  This can lead to a significant reduction of the
  financial investment in the facility.
• The described improvements of the Geothermal
  Response Test increase its accuracy and deliver
  much more detailed information on the subsoil
  conditions.
• Further improvements will make the test more
  efficient by itself. The attractiveness of the
  GRT will rise even for small facilities and as a
  standard final inspection procedure.

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Thank you very much for your attention!