Nelson Mechanical Design, Inc. Mechanical Systems Design & Contractor Martha's Vineyard, Nantucket, Cape Cod

The Geothermal concept has been commercially available since around the 1940s. Greater manufacturing and training improvements have made geothermal systems reliable and energy efficient. With system efficiencies approaching 400%, geothermal systems can supplement or replace your heating and hot water systems and reduce annual operating costs by 50% or more.

Geothermal systems use several approaches to connect to the stored solar energy in the Earth - via copper or plastic pipe (direct exchange or water source) in the ground or via plate heat exchangers in the ocean or a pond.

Direct Exchange uses copper refrigerant lines in the ground and water source uses a plastic line in the ground that is filled with a propylene glycol / water mix. Both are reliable, can be installed many ways, and are Energy Star rated systems.

We are dealers for Earthlinked Technologies, the world leader in direct exchange geothermal systems. These systems use copper refrigerant lines to couple to the earth and extract or dispose of heat (depending on heating or cooling mode). Many of our customers are curious about the durability of the copper underground. The Copper Council of America has deemed that these lines should last virtually indefinitely in non-aggressive soil. For problem areas, anode protection (similar to a zinc bar on a boat hull) systems ensure that the copper experiences no corrosion. The refrigerant in the lines in non toxic and will not hurt the aquifer or the ozone.
With Direct Exchange, there are three ways that we can couple to the earth - horizontally, vertically, or diagonally. In all installations, the copper lines are installed into manifolds that must be six feet below finish grade. These manifolds are then connected to two main refrigerant lines that extend into the building and are connected to an EarthLinked heat pump. This heat pump is then connected to a new or existing heating, cooling, or hot water system.

In a direct exchange horizontal installation, we install our refrigerant lines at six feet below finish grade. You will need approximately one square foot of usable yard per one square foot of conditioned space. The copper lines must be installed level within twelve inches across the entire yard and must be placed in clean sand. These lines are then connected to manifolds and these manifolds are brought into the building via two main refrigerant lines. These lines are then connected to a heat pump, and the heat pump to your heating, cooling, or hot water system.

In a direct exchange vertical installation, our drilling crew will bore a four inch diameter hole one hundred foot deep. We shall then install a refrigerant line in this hole and grout the hole with a MA approved bentonite grout. The copper refrigerant line installed in this single hole will produce one ton or 12,000 BTUs of heating/cooling capacity. Additional holes are installed for every additional ton of heating/cooling required. These lines are then installed together into a manifold six feet below finish grade. The diameter of this manifold pit is anywhere from the ten to twelve feet. These manifolds are brought into the building via two main refrigerant lines. These lines are connected to a heat pump, and the heat pump is connected to your heating, cooling, or hot water system.

DX DIAGONAL: In a direct exchange diagonal installation, we perform the same installation as the vertical type, but the surface pit is smaller (about six feet). Each of the boreholes is typically drilled at a 15 degree angle from the vertical. The lines extend to the same hundred foot depth and are approximately 55 feet apart at this depth. This installation is great for tight spaces or a retrofit where the excavation of the pit is less intrusive.

WATER SOURCE: We offer Climate Master, Bosch (Florida Heat Pump), and Water Furnace geothermal heat pumps. Water source heat pumps use a black plastic high density polyethylene (HDPE) pipe filled with a liquid such as water or propylene glycol to couple to the ground and extract or reject heat (depending on heating or cooling mode). There are many different ways to couple to the earth with water source systems, such as open loop, closed loop, and Ocean and lake plate type heat exchanger systems.

Water source open loop systems remove or extract heat from the earth by drawing water out of the local aquifer, running this water through a heat pump, and delivering it back to the aquifer. The heat pump is then connected to your heating, cooling, or hot water system. This is done with a draw and injection well, or a standing column well.

This type of system has two cased wells that are strategically placed to draw aquifer water into the heat pump and then re-inject that same water back into the aquifer.

This type of installation uses a single well. The water is drawn from the bottom, sent through the heat pump, and returned to the top of the well casing. These types of systems need to be very deep so that the returned water has time to replenish the heat that has been gained or lost.

These types of systems are more common than the open loop systems. Closed loop systems use HDPE lines to couple to the earth and remove or add heat. These lines can be installed vertically or horizontally. These lines are connected to a manifold and then connected to the heat pump. The heat pump is then connected to your heating, cooling, or hot water system.

CLOSED LOOP HORIZONTAL: There are many arrangements for the installation of closed loop horizontal installations. However, they all consist of HDPE pipe and they are all installed below six feet. They can be installed in trenches or fields. The most common type of installation is the “Slinky” patter. Coils of HDPE pipe are arranged in a “Slinky” pattern and are buried six feet down. This creates the ground couple heat exchanger that is then connected to the heat pump. We can assume approximately 2 -4 square feet of yard to one square foot of conditioned space.

CLOSED LOOP VERTICAL: This installation uses large diameter bore holes (about 6 – 10 inches) cored into the earth. We can assume approximately 250 to 400 feet per ton (12,000 BTUs). An HDPE loop is installed into each hole, and then the hole is filled with a bentonite grout as required by the MA Ground Water Association and the DEP. These lines are then connected together into a manifold and the manifold is then connected to the heat pump. The heat pump is then connected to your heating, cooling, or domestic hot water systems

OCEAN / LAKE PLATE TYPE HEAT EXCHANGER SYSTEMS: Plate type heat exchangers can be installed in fresh water ponds, brackish water ways, or in the ocean. Plate type heat exchangers eliminate the ground coupling installations described with horizontal and bore hole type systems. This is a very cost effective way to install a geothermal plant. Instead of hundreds of feet of refrigerant or HDPE lines connected to the earth, plate type systems use the solar energy stored in a waterway. The plate is installed in the water with two lines connected the plate with the heat pump. This system is filled with a food grade propylene glycol that is completely non toxic.

Slim Jim

LAKE-FRONT STAINLESS STEEL PLATE EXCHANGERS: Stainless steel plate type heat exchangers are used for strictly fresh water installations. A plate or multiple plates are suspended from a dock or mounted on skids. The key to fresh water installations is making sure that the pond is large enough to be replenished by the sun faster than the heat is extracted.

OCEAN-FRONT TITANIUM PLATE EXCHANGERS: Titanium plate type heat exchangers are used in brackish water or the ocean. Just like stainless steel plates, they are suspended from a dock or mounted on skids. The great thing about ocean plate heat exchangers is that the ocean is a giant solar battery. Unlike fresh water installations, we do not have to worry about removing more heat that we can use.