Geothermal Energy

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Geothermal Energy The Geothermal Heat Pump
Frederick A. Kundell, Ph.D. Department of
Chemistry Henson School of Science and
Technology Salisbury University
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Geothermal Energy Geothermal energy is thermal
energy emitted from the earth.
Generally, when one considers geothermal energy
one thinks of high temperature deposits.
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Renner, Joel NREL Pix 05424
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J. Ruhle and Assoc.
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Deposits at Geyser, California
Pacific Gas Electric NREL Pix 00060
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High temperature geothermal deposits are easily
converted to electricity.
Gretz, Warren NREL Pix 00426
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On the east coast geothermal investigations have
centered on trapped bodies of water heated by
nuclear decay in granite rock formations. The
Atlantic Coastal Plane has been examined for
blocks of granite and wells drilled to check the
temperature of overlaying bodies of water.
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The highest temperature found to date is 180oF at
Crisfield, MD. Unfortunately, this temperature
is too low for economical use.
Nevertheless, geothermal does have great economic
potential on the Delmarva Peninsula.
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The Delmarva Peninsula is formed from overlain
sand clay strata which can be easily and
inexpensively drilled. This thermal mass is
ideal for use as a heat source or heat sink for a
groundwater-to-air or geothermal heat pump. This
process is referred to as geo-exchange.
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Older systems (open systems) used well water
along with an injection well to flow groundwater
through the heat pump. During the winter heat
was extracted from the groundwater prior to
injection and during the summer heat is added to
the ground water.
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The problem with open systems is that well water
may be acidic or contain suspended or dissolved
contaminates which can damage the unit. Do not
use open systems on the Delmarva Peninsula!
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Newer systems are, for the most part, closed loop
systems. The fluid is pumped through plastic
pipes which are inserted in wells or buried in
trenches. The geothermal fluid exchanges heat
with the surrounding earth. Either trenches or
well can be used.
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Jones, Robert R. NREL Pix 07093
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Jones, Robert R. NREL Pix 07099
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Barlean, John NREL
Pix 07252
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Geo-exchange well system.
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For maximum thermodynamic efficiency the heat
exchange pipes should not be influenced by
atmospheric temperature. Thus, the well
configuration is more effective and less prone to
damage.
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Why the Higher Efficiency? Geothermal fluid,
either from an open or closed loop system, will
be warmer than the outside air during times when
heat is required or colder than the outside air
when cooling is needed. This makes the
geothermal heat pump much more efficient than a
conventional air-to-air heat pump.
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1st Law Type of Heat
COP Efficiency Electric Resistance 1
100 Air-to-air Heat Pump 2
200 Geothermal Heat Pump 4.5 450 COP
Coefficient of Performance
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Geothermal heat pumps are available for
individual homes.
Lundy, Ann S. NREL Pix 07408
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or large buildings
Tundy, Ann NREL Pix 06569
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In a real sense the use of the well configuration
geothermal heat pumps recycles heat. Heat is
pumped into the ground during the summer to be
extracted during the winter.
Clip Art
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Approximate Energy Costs Information
Fuel 2 Fuel Oil Electricity
BTU Equivalence 140,000 BTU/gal 3,413 BTU/KWH
Usable 90 100
Effective Equivalence 126,000 BTU/gal 3,413 BTU/KWH
Cost 2.90 /gal 0.13 /KWH
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Energy Costs per 1 million BTUs
2 Fuel Oil 23.02
Electric Resistant 38.09
Geothermal Heat Pump 8.46
Installation Costs much higher with about a
seven year payback.
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The End