2. Daniel A. Rehbein, P.E., LEED™ AP
exp U.S. Services, Inc.
Department Manager of the mechanical
group and a Principal in the Milwaukee
office
25 years of mechanical engineering
consulting experience in Wisconsin
Experience with healthcare, corporate,
commercial, industrial and institutional
projects of all sizes
Graduate of the Milwaukee School of
Engineering
3. • Fundamentals of Geothermal Systems
• Design Considerations
• Geothermal System
Installation/Construction
Epic Geothermal System
• Bore Fields and Pond
• Distribution System
• Central Plant Equipment
Epic Deep Space Auditorium
Geothermal System Basics
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What is a
Geothermal
HVAC System?
Geothermal
System
Basics
5. ##
Geothermal HVAC is the use of the natural
temperature of the earth as a heat source or heat
sink for heating and cooling.
Requires the use of a heat pump to
move energy between different relative
temperatures
Really a GeoExchange
system. Energy is
transferred between the
earth as the source and
the load; which is either
air or water.
6. Not to be confused
with Geothermal
energy.
Geothermal
energy is thermal
energy generated
and stored in the
Earth.
7. Wisconsin has a mean
“undisturbed” ground temperature
between 45-50 deg. F, depending
on the location in the state. This is
the soil temp found well below
ground level (20+ feet deep).
• A geoexchange heat pump system uses the
natural temperature of the earth near the surface
as a heat source or sink, depending on the time
of year
• “Surface” as defined as the top 400-500 feet
below grade
• Deeper can actually mean warmer temperatures.
Also the cost of drilling deep vertical bores can
be expensive.
8. ##
Graph of a test location in Indiana
The ground temperature fluctuates more
the closer you are to grade level
9. ##
Why use a geothermal heat
pump system?
Geothermal systems have a Coefficient of
Performance (COP) greater than 1. More usable
heating energy is obtained than the energy input
to the system
Heating System Type Typical Efficiency COP
Oil Burning Furnace 70-80% 0.7 - 0.8
High Efficiency Gas Furnace 90% 0.9
Electric Resistance Heat 100% 1.0
Ground Source Heat Pump 300 – 400% 3.0 – 4.0
Examples of heating system efficiencies:
10. Types of geothermal systems
Open loop
systems - ground
water with
reinjection well
Open loop
systems -
surface water
system
11. Types of geothermal systems
Closed Loop Systems
Horizontal Loops
Closed Loop Systems
Vertical Wells (Bores)
Closed Loop Systems
Pond Systems
12. What are the basic
components of a
geothermal
system?
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Geothermal
Design
Considerations
Geothermal
System
Basics
18. ##
Geothermal Piping
High Density Polyethylene Piping (HDPE)
Continuous looped pipe with U-bend
for vertical bores or coiled pipe for
horizontal fields or ponds
19. ##
Geothermal Loop Piping Material
• Piping is connected using butt fusion welding
• Provides a strong, seamless pipe joint
• Loop and bore piping typically ranges from ¾”
up to 1 1/4” OD.
• Coil lengths up to 1000 feet available in
smaller diameter piping, coils up to 4” OD
available.
• Straight HDPE sticks available in 48” OD
and larger.
20. ##
HDPE piping wall thickness measured
using SDR = Standard Dimension Ratio
SDR is the ratio of the pipe diameter to wall thickness
SDR = D / s
where
D = pipe outside diameter (mm)
s = pipe wall thickness (mm)
• An SDR of 11 means that the outside diameter of the pipe is eleven times the
thickness of the wall of the pipe.
• The lower the number, the thicker the wall and the higher the pressure rating
• The higher the number, the thinner the wall and the lower the pressure rating
• Most geothermal loop piping is SDR-11.
• Headers and distribution piping from the building to the loop field can be higher
SDR pipe
21. Vertical Heat Exchanger (VHE) Design
• Size of the borefield is based on a
combination of peak building cooling and
heating loads and annual energy usage for
both heating and cooling
• Commercial buildings generally are cooling
dominated. This means the bore field sized is
based primarily on the amount of heat that
needs to be rejected to the earth due to the
building’s cooling needs.
22. Vertical Heat Exchanger (VHE) Design
• Vertical bores are generally spaced at 20 foot on
center, but can also be 15 or 25 foot OC.
• Vertical bore depth is typically in the range of
400 feet, and can be deeper or shallower
depending on design factors
• Bore diameter is generally in the 4”- 6” range.
• Basic rule of thumb for geothermal field sizing is
150 feet of bore per ton of building cooling load
23. The vertical bore
hole is created
just like drilling a
water well,
without the well
casing and pump
Drill rig bores a
vertical hole and
then the U-bend
loop is dropped
down the bore
shaft
24. ##
The vertical bore
hole is then filled
with thermally
enhanced grout.
• Grout is a mixture of Bentonite and sand
mixed with water
• Conducts heat at a high rate
• The grout does not become hard like
concrete, but sets firm and dense
25. ##
Soil Heat Transfer Characteristics
Thermal conductivity (k) is measured in
BTU/(hr⋅ft⋅°F) and is the ability of the soil to
conduct heat
Thermal diffusivity (α) is the ratio of the soil
to conduct thermal energy relative to its ability
to store thermal energy
Geothermal heat exchange effectiveness is
dependent on 2 main factors:
• Thermal Conductivity
• Thermal Diffusivity
26. ##
The size of the VHE is dependent on the
thermal conductivity of the soil where
the borefield will be located, therefore;
Understanding the actual thermal
conductivity of the surrounding soil is
critical!
Designer must arrange for a soil
thermal conductivity test to
understand local conditions
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Geothermal System
Geothermal
System
Basics
Installation/Construction
28. Borefield Configuration
The individual bores are constructed by dropping a looped
pipe down the borehole
The bores are then interconnected to form individual circuits.
Circuits are generally piped in a reverse return arrangement
to balance flow between the individual bores.
29. ##
On larger systems, each
circuit is brought back to
a distribution manifold.
This allows for individual
loop isolation and
balancing
Multiple manifolds can then
be interconnected to the
piping main and brought
back to the geothermal
system pumps
30. ##
HDPE Pipe Joining Methods
Fusion joint types
•Butt Weld (most typical)
•Socket Joints
•Saddle Joints
Electrofusion fittings are typically
used for the 2 latter joints
33. Amount of rock encountered
during drilling
Fissures and voids in the
substructure
Potential Geo installation issues and
considerations
Initial pressure testing of vertical loops
Pressurization of loops during grouting
Final loop pressure testing before
interconnection
Sub-surface conditions
during drilling
Vertical loop installation
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Facts and Figures
Epic’s
Geothermal
System
36. Currently has 3500 vertical bores installed with 2500
more under construction
Shortest bores are 300 feet with deepest at 500 feet.
System includes a 10 acre geothermal pond that can
reject approximately 1300 tons of heat during cooling
operation in summer
The geo pond has 1,296 loops that are 600 feet long
of 1” OD piping.
Main system pumphouse has 12 pumps, totalling
5,400 HP and can accommodate 4 more pumps
37. Geothermal flow capacity to provide close to 80,000
GPM of pumping capacity in a primary/secondary
configuration (160,000 GPM total circulation rate)
System can expand to provide over 30,000 tons of
cooling, enough for 10,000,000 GSF of building
Geothermal mains to the borefields and distribution
piping to the buildings is mostly 36” pipe
All buildings on the campus are served with
geothermal water, including the new Deep Space
Auditorium and the City of Verona’s
well/pumphouse building
38. Total length of HDPE piping installed on the campus
will exceed 1000 miles of piping (5.3 million feet).
This is the distance between Madison, WI and
Gainesville, FL or Galveston, TX.
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Borefield
Installation and
Construction
Epic’s
Geothermal
System
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Distribution
System
Construction
Epic’s
Geothermal
System
