WHAT IS GEOTHERMAL?

Geothermal systems heat and cool your home, school, or office by utilizing the near-constant ground temperature in the earth. In Wisconsin, below about six feet the ground is about 50° throughout the entire year. Geothermal systems (also called GeoExchange, Ground Source Heat Pumps, or just ‘Geo’ Systems) use heat pumps to absorb heat from this 50° earth during the winter and then expel heat to this earth in the summer.

The design of your geothermal system will depend on the particular site of your building. But there are many other important factors affecting the cost and performance as well – the thermal conductivity of the ground and the heating and cooling requirements of your building have a large impact on the system design. Contact a WGA member today to learn about a design for your specific application.

HOW IT WORKS

A heat pump operates no differently than your refrigerator. A compressor in the heat pump unit absorbs heat from the ground loop in the winter (when the ground is much warmer than the outside air) and transfers it into the air in your building at a much higher temperature. A fan then circulates this hot air just like a typical heating system. Or, if a radiant floor is installed, the heat pump transfers this energy to the fluid that is running in the floor.

In the summer, this compressor operates in the other direction and absorbs heat from your building’s air, transferring it to the ground loop (when the ground is much cooler than the hot summer air). Conventional air conditioners operate similarly, but must reject the heat to the hot summer air, lowering their efficiency considerably.

COMPONENTS

The key piece of the geothermal system is the ground loop. This is made of conventional polyethylene pipe, with thermally fused joints for reliability – most carry 50-year warranties! A fluid, often including a non-toxic antifreeze (propylene glycol), is pumped through this ground loop by a small circulating pump. It is this fluid that transfers the heat to/from the ground and your building. The heat pump unit is connected to the loop and operates as explained above. Heat pumps have become a common piece of mechanical equipment, and are made and sold by many of the heating and cooling companies that supply conventional equipment. (Interested in even more technical detail? Click here.)

The ground loop can come in several different configurations.

CLOSED LOOP SYSTEMS

Closed loop systems are more common than open loop systems because they can be installed at almost any site. Closed loop systems have a continuous ground loop; the fluid inside never comes in contact with the environment.

Vertical loop

A vertical loop system uses wells drilled one to three hundred feet into the ground as the ground loop. A u-shaped pipe is placed in each trench so that fluid can go down the well, transfer heat, and come back to the surface without ever contacting the rock or soil. These wells take up significantly less room than other configurations, but will cost more. The depth of vertical systems can also lead to consistent performance.

Horizontal loop

It is also possible to place the ground loop in a horizontal configuration, in which the piping is simply laid in one or many trenches in the ground. This is an inexpensive method of installation, and is often used in residential or light commercial applications. There are many different layouts for horizontal systems. In some cases 2-6 pipes are distributed in each trench; in some cases a ‘slinky’ formation is used. If a large amount of earth can be moved to create one very wide trench, rows of pipe can all be laid in this trench in a ‘racetrack’ formation. All have been successful heat transfer devices.

Pond loop

If a pond (or lake) is available on the building site, it is often convenient to simply sink the loop into the pond and transfer heat to and from the water of the pond. This can be just as efficient as a ground loop if care is taken in choosing a large enough body of water.

Open Loop Systems

An alternative option involves using groundwater itself as the heat transfer fluid, and drawing this groundwater into the fluid loop for use by the heat pump. This is called an open loop system. These systems are often more efficient than closed loop systems, but do use a substantial amount of groundwater. In Wisconsin, there are regulatory constraints on open loop systems. The main constraint is that the groundwater cannot be reinjected into the earth, but instead must be dumped out onto the surface and allowed to seep back in slowly (to avoid contamination of groundwater supplies). These systems are therefore only possible in some sites.

Applications

For your home

Geothermal can be an excellent way to bring comfort to your home in both winter and summer. Many Wisconsin homeowners have installed a standard vertical ground loop; those with more land area or ponds have been able to install a horizontal or pond loop. All have enjoyed a large change in their monthly utility bills, which are lower throughout the entire year. And they’ve enjoyed other advantages as well:

• Equipment is reliable, lasting longer than a typical furnace; the ground loop lasts many decades.

• With installation of a desuperheater, the geo loop will yield free hot water during much of the year.
• Safer operation with no combustion or potential for carbon monoxide.
• Can avoid increases in gas costs, and even go fossil-fuel free with renewable electricity purchasing!
• No noisy outdoor unit operating in the summer. 

Learn about a family saving big on their utility bills with geothermal; read the testimonial.

For your school

Geothermal heat pump systems have seen more success in schools than in most sectors. A school is an excellent fit for a geothermal system because the administration is generally interested in long-term operating savings, the heating and cooling needs of Wisconsin schools are well balanced, and the buildings generally have a large site for convenient layout of the ground loop. Many Wisconsin schools from the north woods to the southeast corner of the State have already gone geothermal. Some additional reasons for this choice are:

• Significantly lower life-cycle cost than any other system over the life of the school.
• Lower maintenance requirements for the school’s staff, both with indoor equipment (heat pumps) and the complete lack of outdoor equipment to service.
• Individualized temperature controls in each classroom.
• Quiet operation.
• No boiler room is required.
• Construction savings due to less indoor equipment and ductwork.
• An excellent educational example for the students of sustainability in action! 

Learn about a large school that made the choice to save energy with geothermal; read the testimonial.

For your business

Geothermal heat pump systems not only save energy and protect the environment, they are also good for business. Many Wisconsin businesses have already made the switch to take advantage of many of the excellent benefits of geothermal heating and cooling:

• Lower monthly costs, in many cases from the first day of use if the first cost is rolled into a business loan.
• Less space taken up by mechanical equipment. Geothermal provides both heating and cooling in one package.
• Quieter, less visible equipment than rooftop or other outdoor condensing units.
• In many cases the floor-to-floor height can be reduced.
• Minimal maintenance for staff.
• Reliable equipment.
• Good corporate citizenship for choosing a more sustainable heating and cooling alternative. 

Learn about a business having great success with geothermal; read the testimonial.

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