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About Geoexchange HVAC systems
Introduction *(See geoexchange videos & links at the bottom)
 Geoexchange,
also known as ground source heating and cooling (GSHC) technology. Geoexchange
(GSHC) technology is not new. Geoexchange systems have successfully operated for decades in a variety of
building types. While the basic technology has been around for more than
fifty years, many improvements have recently been made, including types of
materials used, design and installation methods, and the efficiencies of
compressors, pumps and other equipment.
Geoexchange systems are applicable in both
existing and new
buildings. Their benefits are greatest in buildings with similarly sized
annual heating and cooling loads and those desiring independent climate control
of many rooms with the potential for heating and cooling different zones
simultaneously. Geoexchange is an "Energy Reducing System".
Office buildings and schools are particularly good
applications for geoexchange technology. They have relatively high
occupancy, fluctuating usage schedules, and widely varying heating and cooling
requirements within individual zones (offices and classrooms) that are difficult
to meet efficiently with conventional systems. Further, efforts to improve
the efficiency of conventional systems employ control strategies that add
considerable cost and complexity to the systems, increase maintenance
requirements, and often compromise occupant comfort.
Large open spaces, such as gymnasiums and theaters in schools,
can be comfort conditioned with geoexchange systems. Also, the total
energy requirements of these spaces are generally lower because of their only
occasional occupancy. Large warehouse applications that often favor the
low cost rooftop equipment, would most likely not realize the economic benefits
of geoexchange systems.
In some instances, geoexchange systems can be installed for
the same cost as conventional systems, but generally the added investment of
installing the ground heat exchanger can cause initial cost of a geoexchange
system to be higher than that of a conventional system. The lower energy
and operating costs over the life of the system offsets the added
initial investment. Depending on building type, system design, operating
parameters, and energy costs, the simple payback for the marginal cost of a geoexchange system usually falls between 2 and 8 years.
Replacement of a functioning HVAC system in a building with
any type of alternative system requires a substantial capital investment.
Replacing a functioning system that is providing adequate heating and cooling at
a reasonable operating cost is typically not cost effective or one can expect an
extended payback The best
times to consider installing geoexchange technology is when a new building is
being planned, or when considering the replacement of an existing system that no
longer meets the needs of the building or has reached the end of its useful
life.
The environmental benefits of geoexchange are also an
important consideration. Geoexchange systems can help facilities
qualify as Green Buildings. Green Buildings incorporate practices that
significantly reduce or eliminate adverse environmental impacts and increase the
efficient use of energy, environmental and human resources. See the U.S.
Green Building Council @
www.usgbc.org (LEED - Leadership in Energy & Environmental
Design)
This energy and environmental approach becomes clear when you
consider that every million square feet of space conditioned with geoexchange
technology results in a combined savings of more than 7.6 million kWh and 38,207
MMBtu's of fossil fuel. That savings will obviate the need to import
approximately 20,490 barrels of crude oil per year and result in an annual
emissions reduction of about 1,525 metric tons of carbon equivalents. This
is like taking over 1,200 cars off the highway, or planting 764 acres of trees.
Most significantly, utilities will see a 2.5 megawatt demand reduction for each
of the 20 years that the geoexchange system is in operation.
How Geoexchange Systems Work and What Makes Them Efficient
Geoexchange systems couple the building to the local environment; The ground provides a nearly constant temperature source for efficient
heating and cooling; Geoexchange systems are distributed systems rather than a central
system; and Energy is moved around the building efficiently with
water rather than
air.
Basic Geoexchange Concept
Geoexchange technology transfers heat between the steady
temperature of the earth and a building to maintain the building space
conditions. Below the surface of the earth the temperature remains in the
45-65 degrees range, depending on the region, throughout the year.
This stable temperature provides a source for heat in the winter and a
means to
reject excess heat in the summer. In a geoexchange system, a
fluid is
circulated between the building and the ground loop piping buried in the ground.
In the summer, the fluid picks up heat from the building and moves it to the
ground. In the winter, the fluid picks up heat from the ground and moves
it to the building. Heat pumps in the building make this transfer of heat
possible.
Geoexchange systems exchange thermal energy between a building
and the ground. When the building needs heating the system extracts energy
from the ground and pumps it into the building where it is concentrated by the
heat pump. Conversely, when the building needs cooling the heat from the
building is concentrated by the heat pumps and the system removes heat from the
building and pumps it to the ground. This exchange of thermal energy makes
the system efficient. Rather than creating heat by burning a fuel on site,
the geoexchange system moves thermal energy between the ground and the building
using heat pump technology.
The relatively constant temperature of the ground makes this
energy transfer efficient throughout the year - even during the coldest weather.
When the building needs cooling the system takes advantage of the relatively
constant ground temperature that is often cooler than the outdoor air in the
summer. Alternative systems must move energy from the building to the
hotter outdoor air while the geoexchange system gains efficiency by transferring
the energy to the cooler ground.
Benefits of Geoexchange
Geoexchange technology has several benefits, including:
Low Operating Cost - The efficiency of
the heat pumps operating under moderate loop temperatures provides the basis
for high efficiency and low operating cost. The cost to move energy
around the building is also low as heat pumps are placed at each space.
There is no need to circulate large amounts of air around the building to
transport energy nor is there a need to reheat air to maintain comfort in
certain areas of a building. Simplicity - The distributed
nature of the system makes it easy to understand. A heat pump located at
each space will provide independent heating and cooling. The operation
of one heat pump does not affect any other heat pump. Control simply
requires turning the unit on or off in response to the area that needs
heating or cooling. Low Maintenance - The heat pump
itself is a packaged unit no more complex than typical residential air
conditioning equipment. The components are the same as those used for
outdoor applications that have much wider operating ranges and exposure to
the weather. Diagnosing issues is easier due to the distributed nature of
the system. Any problem is typically closely related to the equipment
serving the particular space. No Supplemental Heat Required -
Heat pumps can meet all of the space loads, including ventilation loads.
Ventilation air can be tempered by separate heat pumps and/or conditioned
with heat recovery equipment. Low Cost Integrated Water Heating -
Heat pumps can be dedicated to meet hot water loads. These heat pumps
become particularly attractive when there is a large cooling load relative
to the heating load. By extracting some of the heat from the ground
loop for water heating, the ground heat exchanger size and cost can be
reduced. No Required Exposed Outdoor Equipment -
The ground heat exchanger is buried and the heat pumps are located inside
the building. Vandalism, noise and visual screen problems are
eliminated. Designers do not have a supply space on the roof for
equipment making options such as standing seam metal roofs or large sloped
roofs possible. Very Low Environmental Impact -
No
fossil fuels need to be consumed on site. Pollution can be best mitigated at
a central power plant where electricity is produced. As the efficiency of
electricity production or renewable power generation increase so does the
environmental efficiency of the heat pump system. Level Seasonal Electric Demand -
With winter heat pump operation displacing fossil fuel use and summer heat
pump operation occurring at moderate more efficient loop temperatures, the
electric demand is more consistent throughout the year so the average price
of electricity is reduced. Longer Life Expectancy - Both the
American Society of Heating Refrigerating and Air-Conditioning Engineers
(ASHRAE) and the Electric Power Research Institute have concluded, based on
independent research studies, that the appropriate service life value for
ground source heat pump technology is 20 years or more. This benchmark
is the current industry standard.
Making the Ground Connection
The availability or lack of land for the ground heat exchanger
can define the design options but need not exclude the use of a geoexchange
system.
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 There are a variety of ground loop options to suit
specific project needs, vertical bores, pond and open well, to name a few.
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The loop consists of long life high density polyethylene
that is fused to provide a leak-tight continuous loop of pipe.
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The loop material may be warranted for 50 years.
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Water with a benign additive to prevent freezing is often
circulated within the loop.
The unique aspect of geoexchange systems is the ground coupling. The
ground loop provides the means of transferring heat to the earth in the
summer and extracting heat from the earth in winter.
Types of Ground Heat Exchangers
Closed Loop vs. Open Loop
Closed loop systems are environmentally benign. They are
sealed so that no fluid is exchanged with the environment. The fluid often
includes an antifreeze solution to protect the heat pump equipment. Some
alcohols or a food grade glycol additive are sometimes used to eliminate any
potential impact due to spills or leaks. Leaks are rare and generally
occurring because of a contractor cutting a buried pipe. The connection
process heats the pieces of tubing and fuses them together - effectively
becoming one continuous pipe. The high density polyethylene piping used in geoexchange systems is the same or higher grade of pipe used in cross country
natural gas piping and often comes with a fifty year warranty.
Open loop systems must deal with the discharge of water.
Water can be re-injected into a well or discharged to surface water. Open
systems may be buffered through a heat exchanger that protects the closed loop
within the building from water quality issues such as dissolved minerals,
acidity, etc. Whisper Energy only installs closed
loop systems.
Closed-Loop Vertical Bore Ground Heat Exchangers
A popular configuration of the ground loop consists of several
lengths of plastic pipe typically buried in vertical holes. This bore
field is then covered with landscaping or a parking lot. The vertical bore
configuration is a popular choice for systems of all sizes because of its
efficient use of space.
Each bore hole is four to six inches in diameter. A pipe
is lowered to the bottom of the bore, makes a U-turn and returns to the top of
the bore. The remaining space is filled with a grout to seal the hole from
potential ground water penetration. The grout provides the means for
thermal contact between the pipe and the surrounding earth.
Historically, the main purpose of grout has been to protect
the ground water from surface run-off so there was no consideration given to the
grout's thermal properties. In fact, standard grout used in the water well
industry acts like an insulating blanket around the pipes in the bore hole
requiring the installation of more bores. Standard grout can have as
little as one-half to one-quarter the ability to transfer heat to the
surrounding soil.
Newer grout mixtures are available that improve the ability of
the grout to exchange heat with the surrounding ground. Thermally enhanced
grout, developed for use in geoexchange systems, can double or nearly triple the
ability to exchange heat with the ground by controlling the sand particle size
used in the grout formation.
Example of a Borehole
4 to 6 inch diameter bore
Grout fill - thermally enhanced bentonite
100 to 300 feet deep, depending on drilling conditions and economics
Typically, 8 to 20 ft spacing between bores.
Six to twelve individual bores are typically connected
together from a circuit. The circuit connects to a header through a
shut-off valve so that a circuit can be isolated. The header combines the
flow through all the circuits before going to the building portion of the loop.
The header can be installed outdoors in a valve pit or all of the circuits can
be brought into the building before being combined.
Example of a Closed-Loop Vertical Bore Ground Heat
Exchanger
System Operation
Water in the building loop piping is pumped through a heat
exchanger in each heat pump. In the summer, the loop fluid absorbs heat
from the refrigerant and carries it to the ground through the ground loop
piping. In winter, it absorbs heat from the earth through the ground loop
and transfers that heat to the refrigerant. Loop temperatures are
generally expected to be around 40 degrees in the winter and reach 90 degrees in
the summer.
The length of the ground loop is determined by the size of the
heating and cooling loads and the ground thermal properties. The loads are
defined by the size of the building, type of construction, use of the building,
duration of the heating and cooling seasons, and climate.
The thermal conductivity of the soil directly impacts to the
size of the bore field needed. The drilling conditions at the site have a
direct impact on the drilling cost. Knowing the drilling conditions allows
drillers to better estimate the cost of vertical loop systems.
Closed-Loop Horizontal Ground Heat Exchangers
On smaller systems the placement of piping in horizontal
trenches can reduce the installation cost of the ground heat exchanger because
trenching is generally less expensive than drilling. Horizontal fields
require more land area since they run near the surface rather than straight down
into the earth. They also require more piping since the temperature of the
ground closer to the surface is subject to larger temperature swings associated
with the weather. Due to the relatively large land requirements,
horizontal loops are usually applied to systems less than 50 tons in capacity
(about a 10,000 to 15,000 sq ft building). Whisper Energy typically uses
vertical drilling due to space availability limitations for most applications.
Example of Closed-Loop Horizontal Ground Heat
Exchanger
Closed-Loop Surface Water Ground Heat Exchangers
An existing pond or a pond created for a project may also be
used as the heat source or sink. Loop fluid flows through pipes anchored
at the bottom of the pond. Individual pipe coils are typically combined
into a single circuit and attached to a frame. The frame can be floated on
the pond to the desired location, filled with fluid and sunk. Concrete
blocks anchor the frame to the bottom. The frame keeps the pipes slightly
elevated above the bottom surface to promote circulation and to avoid sediment
covering the pipes.
The loosely coiled piping allows water to flow across the
bundle as a result of the buoyancy forces created by the temperature difference
of the pond water and the pipe fluid. Pond systems work in heating because
the water is at its highest density at 39 degrees, so in a properly sized system
the water around the pipes at the bottom of the pond is sufficiently above
freezing for heat to be extracted easily.
Example of Closed-Loop Surface Water Ground Heat
Exchanger
Inside the Building
The distributed nature of the geoexchange system contributes
to its overall efficiency. Thermal energy is primarily transported
throughout the building with a water loop. A heat pump in each space
(zone) rejects or extracts heat from the loop to maintain the desired
temperature.
Other systems circulate large volumes of air to provide space
conditioning. A central system may supply cooled air to all spaces with
individual spaces reheating the air to maintain the desired temperature.
Geoexchange systems often save on fan energy as they use many smaller fans to
blow air through short ducts at low pressure. Other systems use extensive
duct systems that transport air greater distances at a higher pressure.
Heat pumps located at each room or zone simply heat or cool
the space as needed by conditioning the air circulated between the heat pump and
the space. A fluid loop connected to the ground heat exchanger circulates
throughout the building providing the heat pumps with a source or sink for heat.
Stopping flow through heat pumps that are off, and reducing the speed of the
pump, minimizes pumping energy on the ground loop.
Fresh air is often introduced through a dedicated outdoor air
system. This system preconditions the outdoor air by recovering energy
from the exhaust air stream through a heat exchanger. A heat pump tempers
the ventilation air to neutral conditions before it is distributed to the heat
pumps serving each room. Providing ventilation air, via a separate
system, ensures that the proper amount of fresh air is delivered to each space.
There is no mixing of fresh air with re-circulated air until it reaches the room
heat pump.
This air distribution system is smaller than the air system in a conventional
system because it contains no re-circulated air. Only the required outdoor
air is delivered to each space as opposed to a central system that often
over-ventilates many zones. The fan energy is minimized because the air
can be delivered at lower pressure and there is no damper or coil to pass
through at each room.
For the most part, the space conditioning of each room is independent of other
rooms. The only common reliance is on the ground loop. Any problem
with a heat pump only affects the room it serves and cannot impact the
performance or energy use of the entire system.
Large Spaces
Large open spaces often require more heating and cooling capacity than a single
heat pump can provide. In moderately sized spaces, multiple heat pumps can
meet the space needs. In larger spaces, systems often employ standard
two-speed air handler units with heating and cooling supplied by water-to-water
heat pumps. These heat pumps condition water rather than air like those
used within a space. The water-to-water heat pumps come in larger sizes
and can be ganged together to achieve larger capacities.
Water Heating
A geoexchange system moves heat from the ground to heat the building. It is also
possible for the geoexchange system to move heat from the ground to heat hot
water to 125 degrees F. Integrating water heating with a geoexchange system is
particularly effective when the cooling load dominates the sizing of the ground
loop. The need to reject heat to the ground can be reduced by using some of that
energy to heat hot water. These systems require additional engineering and
design planning.
Heat Pumps - It's Not Magic, It's Thermodynamics
Heat pumps:
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Use the principal that heat always
flows from a hot area to a cold area;
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Use a refrigeration cycle to move
heat from a colder to a hotter temperature, concentrating it; and
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Create a cold zone in the area where
heat is to be extracted and a hot zone in an area where heat is to be dumped.
The pumping or exchange of energy is done by heat pumps - a refrigeration device
that works by the same concept as a refrigerator. Refrigerators, air
conditioners and heat pumps all operate by pumping refrigerant through a closed
loop in a way that creates two distinct temperature zones - a cold zone and a
hot zone.
When a heat pump heats, fluid from the ground loop flows next to the heat
exchanger tubes containing refrigerant and it is colder than the loop fluid.
Since a primary principle of heat transfer is that heat always flows from the
higher to a low temperature, the refrigerant absorbs heat and evaporates within
the tubing.
The cool refrigerant gas is then compressed and pumped to the high temperature
section which is often configured as a refrigerant coil with air blowing across
it. Because the refrigerant becomes hotter than the air when it is
compressed, it gives up the heat to the relatively cooler air from the space. As
the refrigerant gives up heat to the airstream, it condenses back to the liquid.
The liquid passes through a restriction that maintains the pressure difference
between the hot and cold zones. As the pressure of the liquid drops, it
vaporizes and its temperature drops to the cold zone temperature where it begins
the refrigerant process again.
In order to provide cooling, a heat pump has a reversing capability so the hot
zone and the cold zone can be swapped. With the zones reversed, heat is
extracted from the indoor air and transferred to the ground loop.
Maintenance
Routine maintenance involves keeping the coil clean which requires changing the
filter in each heat pump. Heat pump maintenance requires no more specialized
skills than servicing the equivalent of a residential air conditioner. Research
has shown that with proper water and airflow along with regular filter
replacement, the heat pumps should perform well for 20 to 25 years.
Placement of the heat pumps, in or near the space they are conditioning, calls
for consideration regarding ease of maintenance and noise level.
Summary
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Geoexchange systems couple a
building to the surrounding environment. The movement of heat from the ground to
the building for heating or from the building to the ground for cooling is the
basis for the high efficiency offered by the systems. The ground provides
a very stable temperature source, or sink, for exchanging energy between the
building and the environment.
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Numerous configurations of the
ground heat exchanger are possible to meet the needs of many different project
characteristics. Systems can use ground water directly to minimize land
use, or incorporate a network of sealed piping to transfer heat with the ground.
Lakes, ponds and rivers can also provide a means of geoexchange.
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The distributed nature of the geoexchange system provides simplicity in operation and maintenance as well as
contributing to the lower energy use of the system. Moving heat around the
building with a water loop adds to the efficiency of the system compared with
moving heat around the building with an air distribution system.
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Energy saving for heating and cooling is
generally in the 40 to 60% range depending on the
insulation or "R" factors within the building and other factors. The typical
overall savings is generally in to 25 to 35% range
for all systems when geoexchange is installed. Well fields (loop fields)
have a typical life of 50+ years and can be installed
under asphalt or concrete parking lots, recreational facilities,
etc., except for treed areas or under the structure itself.
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All equipment is located inside with the exception of some
retrofit systems which are available for certain applications. The well
fields are all underground which extends the useful by many years. New
geoexchange installations have no outside condensing units, no rooftop
units, no roof penetrations, and no gas lines. Retrofit systems my be
rooftop or wall mounted. Geoexchange systems typically need one third the
space of conventional systems.
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Geoexchange HVAC systems can be
installed in both new and existing structures. Listed are just a few
applications where geoexchange systems will work: schools and universities,
commercial and residential developments, correctional facilities, strip centers,
government facilities and military bases, grocery and convenience stores,
libraries and churches, office building and more.
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Geoexchange systems are very cost
competitive, however, the life of a geoexchange system will far exceed
conventional systems and the energy saving and efficiency will save clients
thousands of dollars in utility cost over the life of the system. The
environmental advantages of geoexchange systems are tremendous and every system
makes a major impact.
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With all of the advantages, geoexchange is becoming the space conditioning system of choice for commercial,
schools, residential and governmental installations whose owners, managers,
instructors, etc. desire maximum comfort for the customers, students or
employees.
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Whisper Energy LLC has a dedicated
team of professional engineers, designers and professional installers to provide
the most effective and efficient geoexchange systems. Geoexchange is
renewable energy at its core and serves as a great example of how we can use
technology as a benefit for all.
Additional Links & Videos
*(Videos will take time to load & some will require
persistence to view)
Geothermal Heat Pump Consortium
http://www.geoexchange.org
Residential Geoexchange Heating & Cooling Video
http://geoexchange.us/residential/videos.htm
Commercial Geoexchange HVAC Video
http://geoexchange.us/commercial/videos.htm
Schools Geoexchange HVAC Video
http://geoexchange.us/schools/videos.htm
Government Facilities HVAC Video
http://geoexchange.us/federal/videos.htm
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Military Housing Video
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Federal Facilities Video
IGSHPA - International Ground Source Heat Pump Association
http://www.igshpa.okstate.edu/geothermal/residential.htm
Note: Information on the proceeding pages was gathered from the Geothermal Heat
Pump Consortium and the International Ground Source Heat Pump Association.
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