Geothermal Heat
Exchange Systems
March 10, 2011
Trinity Glen Rose Groundwater
Conservation District
Monty McGuffin, Santos Tovar and Jim O’Connor
Resource Compliance and Protection Department
Page 2
Geothermal Heat Exchange
Known by a variety of other names;
– Geothermal Heat Pump,
– Ground Source Heat Pump,
– Ground Heat Pump,
– Geoexchange,
– Earth-Coupled,
– Earth Energy,
– Water-Source Heat Pumps,
March 10, 2011
Geothermal Heat Exchange
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What is Geothermal Heat Exchange?
Instead of having outside coils exchange heat with the air
(like standard heat pump units), the geothermal heat exchanger
is a central heating and/or cooling system that pumps heat to or
from the ground. It uses the earth as a heat source (in the
winter) or a heat sink (in the summer). This design takes
advantage of the moderate temperatures in the ground to boost
efficiency and reduce the operational costs of heating and
cooling systems.
March 10, 2011
Geothermal Heat Exchange
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Geothermal Heat
Exchange System
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Geothermal Heat Exchange
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How Geothermal Heat Exchange Works
•
These systems have a heat exchanger that facilitates heat transfer between the outside coil
and a liquid. In the case of Kinder Ranch Elementary School, this will be Edwards Water. A
pump circulates the water through buried pipes, where it is heated (winter) or cooled
(summer) by the earth.
•
Ground loop piping is typically made of high-density polyethylene (HDPE) which is the
industries preferred material. Closed loops use relatively small pipe sizes for the portion of
the loop that exchanges heat with the ground, typically ranging from 3/4 to 2 inches. They
can be buried in the earth in either of two ways:
– vertical bore holes or horizontal trenches. When using the hole method, one or
more 6-inch diameter holes are drilled to a depth of 200 - 300 feet. In each hole, a
pipe leads down and then loops back up to the surface, providing as much area
as possible for heat transfer to take place. Typically, one borehole is needed for
each ton of air conditioning/heating capacity.
•
Both methods require good contact between the pipe and the ground, so the holes or
trenches are generally back filled with material like grout or fine soil. If multiple holes or
trenches are dug, they are kept at least 15 feet apart.
.
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Geothermal Heat Exchange
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Geothermal Heat Exchange
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Vertical Closed Loop Installation
• The drilling equipment for vertical borehole excavation
for the Kinder Ranch Elementary School was an air
rotary rig, this type of rig uses air that is pumped down
the rotating drill stem to remove the cutting from the
borehole.
• A thermally-enhanced grout formulation with a higher
ratio of sand to bentonite in the grout mixture (typically
100 to 300 pounds of sand per 50 pounds of bentonite)
is used to seal the looped piping.
• Drilling cost for ground loop installation are typically not
as high as for water well drilling, since logging and
completion procedures are not usually required.
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Geothermal Heat Exchange
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Optional Steel
Casing
Air in
Cuttings out
•Roller Cone Bit
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Geothermal Heat Exchange
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Geothermal Heat Exchange
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Geothermal Heat Exchange
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Vertical Loop Piping
The most common configuration for the vertical loop
piping element in the drilled bore is a U-tube, where a
180-bend fitting has been factory fused to join two
lengths of HDPE pipe, and this inserted into the
borehole
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Geothermal Heat Exchange
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U-tube
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Geothermal Heat Exchange
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Arrangement in Series or Parallel
• Multiple closed ground loops can be arranged in series,
parallel, or a combination of both.
– In series systems, the working fluid can take only one path through the
loop,
– In parallel systems the fluid can take two or more paths through the
circuit.
• Note that parallel arrangements use a reverse rather than direct return to the
building so that all parallel flow paths are of equal length, helping to ensure a
balanced flow distribution.
• Large commercial and institutional buildings such as schools
usually employ parallel loops
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Geothermal Heat Exchange
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Closed Loops Arrangement
Series arrangement of
multiple closed loops
Parallel arrangement of
multiple closed loops
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Geothermal Heat Exchange
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Kinder Ranch Elementary
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Geothermal Heat Exchange
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Kinder Ranch Elementary
Construction of Geothermal Vault
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Geothermal Heat Exchange
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Different Types of Geothermal Systems
Closed Looped
Vertical System
Closed Looped
Horizontal (trench)
System
Open Looped
Vertical Water Well
System
Closed Looped
Pond System
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Geothermal Heat Exchange
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Permitting
1997 revisions to City Code to address Geothermal wells
•Sec. 34-567. Permit for drilling new well required.
•(a) It shall be unlawful for anyone to drill, maintain, or otherwise construct or have constructed, any new water well,
or any other artificial excavation to explore for or produce groundwater, or injection wells for the purpose of a earthcoupled heat exchange system, within the City of San Antonio or SAWS Water Quality Division. This section shall not
apply to: (1) monitoring wells and test wells with a depth of less than fifty (50) feet; (2) blast holes in quarries and
mines; and (3) wells or excavations for the exploration or production of oil, gas, or minerals, unless, without regard to
the original purpose, the well is used as a source of water.
•(b) All drilling or construction of water wells, and injection wells for the purpose of an earth-coupled heat exchange
system, shall be done in strict compliance with the terms of the well drilling permit, the SAWS Water Well Permitting
Procedures, and 30 TAC, Chapter 238.
•(c) In addition to the requirements of paragraphs (a) and (b) of this section, any water well which will penetrate the
Edwards Aquifer shall be drilled and maintained in strict compliance with 30 TAC, Sections 213 et seq., as amended.
This paragraph does not apply to injection wells for the purpose of an earth-coupled heat exchange system.
•(d) To preserve the water quality of the aquifer, the construction of any bore hole, injection well for the purpose of an
earth-coupled heat exchange system, or water well for the purpose of an earth-coupled heat exchange system located
over the Edwards Aquifer Recharge Zone and Transition Zone shall be prohibited.
•(e) An open system, geothermal well that draws water from an aquifer and is circulated through the heat exchange
system or geothermal wells which inject water into an aquifer will not be permitted within the limits of the City of San
Antonio and within SAWS Water Quality Division.
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Geothermal Heat Exchange
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Permitting
•
SAWS – Permit fee covers the Geothermal System in whole
($200)
•
TGR – Permit fee is $350 per bore-hole
•
EAA – Permit fee is collected on each bore-hole ($25 per hole
drilled) typically a pass-through permit is required
March 10, 2011
Geothermal Heat Exchange
Geothermal Heat
Exchange Systems
March 10, 2011
Trinity Glen Rose Groundwater
Conservation District
Monty McGuffin, Santos Tovar and Jim O’Connor
Resource Compliance and Protection Department