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Sized for home or loop demand
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Additional maintenance / repair cost
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Pump operation = energy loss
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Ground water contamination
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Antifreeze / rust & scale inhibitors
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Depletion of ground water
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DX systems do not remove water from
the aquifers
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"Direct exchange" eliminates the need
for a secondary heat exchanger
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DX copper loops transfer energy faster
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Less excavation/drilling is required
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ESES DX is 20-25% more efficient
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ESES DX averages $1000 less
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ESES Geo Direct DX vs. Water-source
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You know the old saying about opinions, “everybody has one”. While this is true, it is hard to discard facts. This
examination of facts should help others to determine which geothermal system is better: Geo Direct DX Geothermal
or water-source heat pumps. We will closely consider all phases of these systems. While they are very similar in
ways, they are worlds apart in others.
System Design
The first step in any HVAC design is the load calculation. This is one of the most important steps as it is the
foundation for the system. Some contractors rely on “rules of thumb” or “experience” instead of performing an
accurate load calculation. This is wrong and an unacceptable practice. If the contractor does not perform the load
calculation, do not do business with them! After the load calculation has been performed, then the system can be
sized to meet the loads of the structure and the duct system can be designed. The designs must be in accordance
with Air Conditioning Contractors of America [ACCA] standards. Choose the system that meets the load
requirements. Slight overages are ok, but the system should be sized as close as possible to the loads.
Air Distribution System
Both types of systems need an air distribution system. Air has to move across a heat exchanger [called the
evaporator coil] to transfer heat energy. Depending on the mode of operation, heat energy is transferred into or
removed from the air stream through the refrigeration process. The more heat energy that is transferred, the
higher the system capacity. The evaporator coils are generally constructed of highly conductive copper refrigerant
tubes with bonded aluminum fins. The aluminum fins are thinner, have a high conductive capacity and increase the
heat transfer area. Once the heat energy is transferred, it is distributed by the duct system throughout the
structure.
There are two types of heat energy transferred by the heat pump: sensible and latent heat.
Sensible heat is heat energy you can feel and is easily read by a thermometer. The warm air you feel in the winter
is all sensible heat and the cool air you feel in the summer is the absence of sensible heat.
Latent heat is a little different. Latent heat is the moisture related heat in the air. The moisture in the air is in a
vapor form and contains a lot of heat. By reducing moisture in the structure during the cooling mode, you reduce
heat. I’ll explain. A British Thermal Unit [Btu] is a measurement of heat energy. It is defined as the amount of heat
required to raise one pound of water one degree Fahrenheit. Water becomes a liquid at 32° F and boils at 212° F
[at sea level]. To raise that pound of water from 32°F to 212°F takes 180 Btu’s of heat energy. To change that
same pound of water from 212° F water to 212° F steam, it takes another 970 Btu’s of heat energy. This is known
as the “latent heat of vaporization”. Changing the water to steam [vapor] requires a phase change, which requires
more energy. So by removing moisture from the air, you in fact are removing heat. By removing one gallon of
moisture, you remove more than 7,700 Btu’s of heat energy. The cooling system must be sized to meet this load or
a host of other issues will arise.
Refrigeration System
The heart of both types of systems is the compressor. The compressor pumps the refrigerant through the
refrigerant circuit carrying heat energy. A compressor’s heat transfer capacity is rated in a measurement called a
ton. There are 12,000 Btu’s in a ton of refrigeration capacity. Therefore, a 3.0-ton compressor is able to produce
36,000 Btu’s of heat transfer capacity. The system design determines how efficiently heat energy is transferred.
This is where the Geo Direct DX system and water-source systems part company.
In a water-source system, the refrigerant is circulated through a “water to refrigerant” heat exchanger. The heat
exchanger is typically a cupronickle design. This heat exchanger transfers heat energy into the water during the
cooling cycle and removes heat energy during the heating cycle. The 4-way valve or “reversing” valve determines
which mode of operation occurs. Typically, when the valve is energized, the system is in the cooling mode. When it
is de-energized, it is in the heating mode. This valve directs the refrigerant in opposite circulation patterns to
transfer heat energy.
As the heat energy is being transferred in the heat exchanger, a pump is required to pump the water through the
loop field [closed loop system] to reject or replenish the heat energy. The water in the loop circuit must have an
“antifreeze” additive for corrosion and freeze protection. Most pumps used in this circuit have water lubricated
bearings. The water has to be circulated at a rate of 1.5 to 3.0 gallons per minute [GPM] per ton as specified by
the manufacturer.
Simply, the water-source system uses three heat exchangers in its design: the evaporator coil, the water to
refrigerant heat exchanger and the loop field. No heat exchanger is able to transfer all of the heat energy, resulting
in a “transfer loss”. With three heat exchangers, there are three areas where energy is lost.
Through innovative design, the Geo Direct DX geothermal system has eliminated the need for a water to
refrigerant heat exchanger. The system still uses a compressor and reversing valve to circulate and direct the
refrigerant flow, but the refrigerant is circulated directly through the ground loop system. Heat energy is transferred
directly into or from the refrigerant circuit, a much more efficient method.
Loop system
The loop system differs greatly between the two. Water-source systems use a high density polyethylene plastic
pipe that is buried approximately 5’ below the earth’s surface or in wells that can extend 400 or more feet into the
earth. The polyethylene pipe is an insulator and a poor conductor of heat energy. For example, you can buy the
best stainless cookware set on the market. What is placed on the handle to protect you from getting burned? An
insulator, typically plastic or wood. So why would you want to try and transfer heat energy through an insulator?
The amount of polyethylene loops depend on the soils conductivity in the area and loops can range from 250 to
over 2000 feet per Ton. In a worst case senario, more than 6000 feet of loop could be needed for a 3.0-Ton
system. This equates to a lot of excavation and labor cost. According to data on the high density polyethylene
pipe, it has a thermal conductance or K value [the ability to transfer heat energy] of .42-.51. This requires long
loops to be installed to be able to handle the energy transfer that is required. Longer loops have more resistance
and require the water pump to work harder to push the required amount of water through the circuit, which in turn
increases the water pumps energy consumption. One common problem with water source systems is “short
looping”. This is where there is a lack of loop installed and the system can not transfer the required amount of heat
energy. The amount of loop installed is basically determined by the HVAC system designer or the HVAC
contractor.
The copper loop field of the Geo Direct DX system carries refrigerant through the circuit allowing heat energy to be
transferred “directly” into the refrigerant. The system compressor is pumping the refrigerant through the circuit, so
no additional pumps are required. The water to refrigerant heat exchanger has been eliminated, which increases
efficiency. Unlike polyethylene pipe, copper is highly conductive and has a conductance K value of 400. That is a
conductive rate increase of 769-975%! That means that the heat energy can be transferred faster through a much
smaller loop field reducing the amount of excavation, thus reducing installation costs.
Service and Maintenance
Geothermal systems require periodic maintenance like any other mechanical system and they do malfunction from
time to time. The Geo Direct DX system has a big advantage over water source in this area. Water source systems
have a large number of components that require frequent servicing. Water pumps do not last forever and their
replacement cost can run upwards of $1,500.00 or more. Water source systems use control boards that are made
for their system that monitor a host of information. They have relays to control the pump/s and sensors to monitor
system temperatures. They have a contactor to start the compressor operation and various other controls. Water
to refrigerant heat exchangers can develop “scaling” that has to be removed as this reduces system efficiency and
capacity. Most of these components are proprietary parts or parts that are specifically made for that system. This
means that an Original Equipment Manufacturer [OEM] part must be used to repair the system. Typically, OEM
parts are much more expensive than a generic part that performs the same function.
There is one OEM part on the Geo Direct system unlike their competitors that contain many. Generic parts are
readily available to repair these units should the need ever arise. Since generic parts can be used, repair and
maintenance costs are greatly reduced. There are no water pumps to replace, no water to refrigerant heat
exchangers to clean.
Geothermal Heat Pump Facts:
ESES Geo Direct DX vs. Water-source
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