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Open Loop Systems
Closed Loop Systems

A geothermal system includes three principal components:
• Geothermal earth connection
• Geothermal heat pump subsystem
• Geothermal heat distribution system

Earth Connection

Using the Earth as a heat source/sink, a series of pipes, commonly called a "loop," are buried in the ground near the building to be conditioned. The loop can be buried either vertically or horizontally. It circulates a fluid (water or a mixture of water and antifreeze) that absorbs heat from, or relinquishes heat to, the surrounding soil, depending on whether the ambient air is colder or warmer than the soil.

Heat Pump

For heating, a geothermal heat pump removes the heat from the fluid in the earth
connection, concentrates it, and then transfers it to the building. For cooling, the
process is reversed.

Heat Distribution

Conventional ductwork is generally used to distribute heated or cooled air from the
geothermal heat pump throughout the building.

Residential Hot Water

In addition to space conditioning, geothermal heat pumps can be used to provide
domestic hot water when the system is operating. Many residential systems are now equipped with desuperheaters that transfer excess heat from the geothermal heat pump's compressor to the house's hot water tank. A desuperheater provides no hot water during the spring and fall when the geothermal heat pump system is not operating; however, because the geothermal heat pump is so much more efficient than other means of water heating, manufacturers are beginning to offer "full demand" systems that use a separate heat exchanger to meet all of a household's hot water needs. These units cost-effectively provide hot water as quickly as any competing system.

Types of Geothermal Heat Pump Systems

There are four basic types of ground loop systems. Three of these—vertical, horizontal and pond/lake—are closed-loop systems. The fourth type of system is the open-loop option. Which one of these is best depends on the climate, soil conditions, available land, and local installation costs at the site. All of these approaches can be used for residential and commercial building applications.

At DRAGIN Geothermal Well Drilling, Inc., we have extensive experience in all four types of geothermal loops.

Open Loop System

The simplest of geothermal heating systems, open loop systems have been used
successfully for decades. The geology of the New England area lends itself to open loop vertical installations or “standing column well” installation.

Open loop systems are ideal for residential installations where available land area is minimal and/or where disturbance to existing landscaping needs to be minimized.

The open loop system uses well water or in some cases surface body water as the heat exchange fluid that circulates directly through the GHP system. Once it has circulated through the system, the water returns to the ground through the same well, a recharge well or surface discharge.

In New England where depth to bedrock is relatively shallow a single well open loop system, also called a standing column well, can be used. The water is withdrawn from the bottom of the well and returned at the top and allowed to heat or cool as it traverses down the well to where it will be withdrawn again. In most instances the bedrock is fairly impermeable and less than 10% of the water being pumped from the well is “new” or “fresh” groundwater. Hence, this type of system behaves primarily as a closed loop system. And only 4 to 8 gallons per minute is required to heat and cool most homes.

This type of open loop system typically consists of one or more standing column well (the number of wells is related to the BTUs or total tonnage required to heat or cool the building). Each well is six inches in diameter and 1,000 to 1,500 feet deep. A 4-inch induction pipe/tube is placed in each well. The heat pump is then installed inside the induction tube. PVC or HDPE piping connects the well to the heating and cooling system inside the building.

You may ask does an open-loop system cause environmental damage? The answer is no. They are pollution free. The geothermal unit merely removes heat from or adds heat to the water. No pollutants are added whatsoever. The only change in the water returned to the environment is a slight increase or decrease in the temperature. Heat is transferred between the groundwater and the internal circulation water without ever physically coming into contact or mixing with one another.

Closed Loop Systems

Water (or a water and antifreeze solution) is circulated through a continuous buried pipe in the closed loop or u-bend system. The length of loop piping varies depending on ground temperature, thermal conductivity of the ground, soil moisture and system design.

Vertical Loops
Large commercial buildings and schools often use vertical loop systems over horizontal loop systems. Vertical loops are also used in applications where the soil is too shallow for trenching. Vertical closed loop systems involve a series of deep (100- to 500-foot) well drilled about 15 feet apart. Wells (typically 4-to 5.5-inches in diameter) are then fitted with two pipes that are connected at the bottom with a U-bend to form the “loop”. The vertical loops are connected with horizontal pipe (i.e., manifold), placed in trenches and connected to the heat pump in the building. The loop is filled with fluid and the ends of the pipe are joined together forming the closed loop.

Fluid circulates from the well to a heat exchanger and then back into the well. The well water and the water loop are separate so if the quality of the well water is questionable, the heating and cooling equipment is not susceptible to any detrimental effects.

The major draw back to this type of system is that a large number of boreholes are usually required and spacings between boreholes can vary between 10 to 15 feet, thus a large area of land is often required.
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