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Legacy Center Research
Legacy Project

GEOTHERMAL ENERGY

by Brian A. Puppa, MASc, PEng
Research and Program Director, Legacy Project
Geothermal Energy

The Legacy Center explores what we term "Legacy Living." At its most fundamental level, Legacy Living is about the timely and the timeless over the typical or the trendy. It has several dimensions, one of which is looking at long-term solutions to environmental challenges.

Continuing to burn fossil fuels to heat and cool our homes is not a good long-term solution. It contributes to global warming, and the supply of fossil fuels is limited. Instead, we can look to the earth – to geothermal energy – for one solution that's simple, natural, and efficient. Derived from the Greek "geo" meaning "earth" and "thermal" meaning "heat," it's exactly what it says: heating (and cooling) from the earth, our largest solar energy collector.

The Legacy Center's mandate includes serving as an environmental demonstration and research project. Because it combines an existing building with a new addition, the Legacy Center speaks to the widest possible audience – those looking at a retrofit and those looking at new construction.

The Legacy Center's original building, constructed in
the 1960s, has recently been retrofitted with a geothermal installation for heating and cooling.

Geothermal has been around at least since the 1940s. Recent advances in technology have vastly improved its efficiency, effectiveness, and financial viability. In a 1993 report, the US Environmental Protection Agency (EPA) concluded that geothermal technologies represent a major opportunity for reducing national energy use and pollution, while delivering comfort, reliability, and savings to homeowners.

The sun is the source of all energy in and on the earth. Energy in the ground is stored energy from the sun. At five to six feet below the surface, the earth's temperature is a constant 50-60 degrees F (10-15 degrees C). This latent energy is a steady heat source, even in the coldest winter. In the winter, a geothermal system extracts this heat from the earth. In the summer, the process is reversed – heat is extracted from the building and deposited in the ground (using the earth as a heat sink), with equal efficiency, using the same equipment.

A geothermal ground source heat pump consists of a unit inside a building (roughly the size of a standard house furnace) and a series of pipes buried underground on your property. The plastic pipes are installed in the ground to create a circuit. For closed-loop systems, water or antifreeze solution is circulated through the pipes. During the winter, the fluid collects heat from the earth and carries it through the system into the building. During the summer, the system reverses itself to cool the building by pulling heat from the building, carrying it through the system, and placing it in the ground. This process also creates free hot water in the summer and delivers substantial hot water savings in the winter.

When you're choosing a geothermal system, there are four common loop systems: vertical, horizontal, slinky, and pond. A vertical, closed-loop field is made up of vertical pipes in the ground, in holes usually 150 to 300 feet deep. A vertical system is most appropriate when the land available is limited, as in a suburban housing development. The pipes can run vertically under lawns, landscaped areas, driveways, or even a building. Vertical installations tend to be more expensive because of the higher cost of drilling versus trenching; but since the heat exchanger is buried deeper than with a horizontal system, vertical systems are usually more efficient and can get by with less total pipe.

The Legacy Center is located on a 15-acre arboretum. So, there's enough land available to use a horizontal, closed-loop field. A horizontal field is made up of pipes that run horizontally in the ground and can run as long as 600 feet. Horizontal installations are simpler, requiring lower-cost equipment. However, they require longer lengths of pipe due to seasonal variations in soil temperature and moisture content.

A slinky, closed-loop field has pipes that overlay each other. A closed pond loop is attached to a frame and located in a body of water.

A geothermal ground-source heat pump for heating and cooling has a number of benefits:

  • High efficiencies: One of the most efficient heating and cooling systems available today, with heating efficiencies 40 to 75% higher than other heating systems and cooling efficiencies 40%+ higher than available air conditioners.

  • Lower energy costs and environmental impact: Can reduce energy consumption by up to 70% versus conventional forced air heating and cooling systems. This means less energy is needed from burning fossil fuels that are harmful to the environment. There are no hazardous carbon or gas emissions, or flammable oils.

  • Year-round comfort: Maintains an even temperature and humidity level throughout a building. It keeps the air warmer in the winter and at a more consistent temperature throughout a building, eliminating the hot and cold spots common with other systems.

  • Low maintenance: Because all the piping is underground or underwater, little maintenance is required.

  • Durability: With few moving parts, and parts that are sheltered inside a building, the system is durable and highly reliable. The piping has a life span expectancy of 50 years or more.

  • Free or inexpensive hot water: Unlike any other heating and cooling system, a geothermal heat pump can provide free hot water using a unit called a "desuperheater."

  • Design flexibility: Can be installed in both new and retrofit situations (you can use existing ductwork). Units are about the same size as a traditional furnace.

  • Improved aesthetics: Geothermal systems are easy to conceal, don't require a noisy outdoor unit on top of or beside a building, and have less potential for leaks and ongoing maintenance problems.


The biggest disadvantage of geothermal is the relatively high installation cost compared to a conventional furnace and air conditioner. And there are additional costs for electrical work, ductwork, water hook-up, and other provisions or adaptations. Government grants are often available to help offset initial installation costs. The energy savings over several years usually pay for the system.

Note that all geothermal systems require an emergency back-up. The Legacy Center has an electric heat back-up system, which can be triggered manually or automatically if the temperature outside is extremely cold and the interior temperature increase called upon is too great for the heat pump to handle in a reasonable time period. The Legacy Center also has a generator in the case of a total hydro failure.

The Legacy Center's ClimateMaster Tranquility geothermal heat pump units, distributed by NextEnergy, were installed by Quest Geothermal.

The first step in the Legacy Center retrofit was digging the trenches. This digging should
be done by a professional firm familiar with geothermal installations and soil conditions in your area.

When planning
the location of a trench, be aware of hydro, water, and phone lines, as well as tree roots. The trenches at the Legacy Center start at the building and then curve around the building 300 feet toward the pond, running carefully between several trees in the arboretum (we
did not want to damage any root systems).

We had initially considered doing
a pond loop, but the Legacy Center pond wasn't deep enough for the installation.

The Legacy Center trench is about 5 feet deep by 5 feet wide. The soil is very sandy, so even though we were digging in winter, during temperatures below freezing, it was fairly easy to excavate. You could see steam rising from inside the trench, reflecting the much warmer soil temperature 5 feet below the surface.

Installations can be done in the winter, as long as equipment can dig through the frozen soil. The biggest negative of a winter installation is that frozen boulders of soil don't fall back into place very well and the filled-in trench is rougher in the Spring.

Three trenches were required for the Legacy Center retrofit. Trenches were about five feet apart. The first two trenches were dug, and then the third was excavated as the middle trench was refilled.

Each level of the two-story building is controlled separately. The upper level required two trenches and
the lower level required one trench.

The geothermal heat pump unit for the upper level (2,400 sq ft) is a 4 ton, while the unit for the lower level (2,200 sq ft) is a 2 ton. The lower level is built partially into the side of a hill, so
it generally stays at a constant, comfortable temperature in both winter and summer and doesn't require as much heating or cooling.

Each trench has two pipes running down and back. The black geothermal pipe was laid along the bottom of one wall of the trench, runs down the entire length of the trench, and then loops back toward the header by running up the center area of the trench.

Geothermal earth loops are made from high density polyethylene pipe. A series of pipes, commonly called a loop, carry a fluid used to connect the geothermal system's heat pump to the earth. These loops are either 3/4" or 1 1/4" diameter and the headers are either 1 1/4" or 2" diameter. Geothermal pipe has the same characteristics as the piping used for natural gas lines and are joined by heat fusion.

After a long,
cold winter day of excavation and laying pipes, the Legacy Center trenches were refilled. Large boulders of frozen earth were still visible. The area would have to be regraded in the Spring.

In the existing Legacy Center building, the two original forced air electric furnaces from the 1960s were in a small enclosed furnace room. The building also had a
15-year-old air source heat pump for summer air conditioning and some winter heating.

There were separate furnaces for the upper and lower levels of the building. Both furnaces hung from the ceiling with a maze of ductwork under-neath. All the exposed ducts were replaced.

A big challenge during the retrofit was utilizing the limited furnace room space more effectively to allow adequate room for servicing and storage.

The new geothermal heat pump units are about the same size as a regular furnace. A walk-out from the lower level of the Legacy Center building gave easy access for taking out the old furnaces and bringing in the new equipment.

It took nearly a week to complete the tricky installa-tion and get all the new ductwork to fit in the small space available.

Ductwork in
the newly-reconfigured furnace room runs along the walls and the ceiling. Ductwork for the building runs underground as well as through open-cavity brick and concrete walls.

The new heat pump units are tucked to each side of the furnace room, opening up more space for walking and storage.

The unit straight through the doorway is the
2 ton unit for the lower level. The unit to the left of the doorway is the 4 ton for the upper level.

Each unit can
be operated independently using separate thermostats on each level. You can switch to either heating or cooling at the thermostat.

When they're operating, the new units are quite quiet. They were installed on special mats to minimize vibration. Front panels can be removed for maintenance, and to clean the coil and condensate pan.

When Spring arrived, the trenches had to be regraded, since the ground was quite rough. After grading, the trenches were reseeded. We
call the area Geothermal Walk; visitors can walk the length of the trenches to get an idea of the extent of the installation. When installing geothermal, one expense installers don't usually mention is cleaning up and replanting/reseeding after excavation. Especially for a horizontal installation, it can be a significant additional cost.

Initial experimentation and analysis of the geothermal system at the Legacy Center has already yielded some interesting results. Check back on this webpage for update reports. For more information or to arrange a site visit, contact Brian Puppa, the Legacy Project's Research and Program Director, by e-mail or at 1-800-772-7765.

© BA Puppa, www.legacyproject.org

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