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Geothermal Heating and Cooling 101

By Sarah Brophy and Kymberly Taylor

As gasoline prices rise and fossil fuels disappear, more and more Marylanders are looking down—at the ground. Just six feet below your garden, residence, (or favorite football field) is an almost infinite supply of heat, or geothermal energy. When harnessed to a geothermal heat pump, geothermal energy can be used to heat and to cool your home. Your furnace burns a combustible fuel, such as oil or propane, to produce heat. Geothermal heat pump systems transfer heat stored in the earth into your home, using underground pipes filled with water, and equipment that concentrates and distributes the heat. The initial installation cost for a modest home is about $20,000 and it can take about five to fifteen years for the savings to offset those costs, depending on the systems they replace. However, not only will your energy bills drop 30 to 70 percent (depending on what kind of system you use), you’ll also have the satisfaction of tapping into a clean, renewable energy source: the earth.

Also, your wallet will share in your satisfaction—there are federal and state funds available to defray costs. The Federal stimulus package alone provides a 30-percent tax credit for qualified residential geothermal installations. The effective cost of a $20,000 installation is therefore $14,000 even before Maryland grant funds are considered.

First, your contractor digs three to six foot deep trenches.

How Do Geothermal Systems Work?

Ever wonder why rabbits live in burrows deep in the earth? Six feet or more below the ground in Maryland, no matter what the weather is like outside, the temperature is always moderate, about 56 degrees Fahrenheit. A geothermal heat pump system captures heat from the ground, using water as the heat transfer medium. Water transmits heat 200 times better than the air used in conventional air source heat pumps. These pumps actually work against nature—they turn extremely cold air into hot air in the winter and very hot air into cold air in the summer. This is very inefficient compared to geothermal heat pumps, which extract heat and cold from 56 degree water.

Next, pipes or ground loops are laid down. Sometimes, deep wells are drilled, depending on the site.

Geothermal systems need three things to operate: ground loops, a geothermal heat pump, and a way to distribute energy around your home. This is usually takes the form of duct work.

Ground loops are pipes filled with water buried at least six feet deep near your home. They cycle water from the ground to your home and then back into the ground. There are closed loops and open loops. A closed loop circulates the same water continuously. An open loop is simply a pipe that is open at both ends. Vertical closed loop systems are used almost exclusively in the Annapolis area.

Later, all ground loops are buried.

The geothermal heat pump is the system's “brain.” However, instead of right and left hemispheres, the pump has compressors and heat exchangers. About the size of a washing machine, the system is attached to the outdoor ground loops. Usually, the geothermal heat pump is located in a cabinet in your basement or attic. Ground loops carry water to the geothermal heat pump, which, with its compressor, converts 55 degree ground water into an exceptionally hot gas—approximately 175 degrees. A heat exchanger then removes the heat from the gas and channels it to a blower, or fan, that circulates heat through your home’s ducts or vents.

Geothermal Cooling

In the summer, your geothermal heat pump uses the same ground water to cool your home. Do you ever hear your central air conditioner groaning on a 90 degree scorching day? It is working hard to draw in that 90 degree air and to lower its temperature by about 15 degrees so you can remain cool and comfy inside. Your geothermal pump does not need to work as hard so is much quieter. Instead of converting very hot air to cool air, it begins with 56-degree ground water to produce air cold enough to keep your home comfortable.

The thermal “hot” water cycles back underground, where the earth regulates its temperature back to about 56 degrees. But there’s more. Instead of cycling all the heat back to the ground, this heat can be captured to heat your domestic hot water using a device called a desuperheater. Desuperheaters shorten payback periods and are required in order to receive the 30 percent Federal tax credit for residential geothermal installations and retrofits.

This geothermal heat pump has a desuperheater inside. It directs, by a horizontal pipe, residual heat right to your water tank to assist with heating.

Geothermal Heating in Action

Geothermal energy systems are becoming more and more mainstream. You can find them at The Market House in Annapolis (when it finally re-opens,) Easton’s St. Mark’s United Methodist Church, Kent Island’s United Methodist Church, Washington College’s two newest dorms (and soon in its renovated dining hall), Gilliam and Spector Halls at St. John’s College—and in many residences around Annapolis, including John Martin’s home.

Martin considered solar energy for heating his home when he began exploring renewable energy systems. He ultimately chose geothermal, though at some point he may use solar power to heat his pool. Geothermal heating is a “no brainer,” Martin says, because his residence, due to its northern exposure and extensive glass surfaces, is very expensive to heat and cool. With “geoexchange” he and his family are trying to do their part. “We can continue to enjoy the house, be more energy efficient, and have a greener planet. We’re trying to make a little bit of difference,” he says. He has calculated that the money he saves on energy bills will equal his upfront costs to install the system in just six years. And, he notes, it gets shorter every time the price of oil goes up. In other words, eventually his savings on energy bills will equal the upfront costs.

The contractor who installed the Martins’ system notes that geothermal systems may have huge financial and environmental benefits; however, the homeowner should understand that initial capital costs are relatively high. Retrofits for modestly sized homes start at about $20,000 for a 3-ton geothermal system. He points out that the U.S. Environmental Protection Agency reports that geothermal systems are “the most energy-efficient, environmentally clean, and cost-effective space-conditioning systems available.” The U.S. General Accounting Office predicts that if geothermal systems were installed nationwide they could save several billion dollars annually in energy costs and substantially reduce pollution.

Keep in mind that, especially if you are retrofitting an existing building, the drilling process can surprise you and your neighbors. Inevitably water, dirt, and sand combine to create a mucky mess. The Martins needed four 300-foot wells. Though Martin prepared the yard by removing the sod and covering the driveway with tarps, he says the whole process still generated “a hefty mess.”

Institutions confront the same concern as homeowners over rising utility bills. Containing energy costs at Washington College in Chestertown is critical, especially with 30,000 square feet of new dorm space. Briggs Cunningham, climate action coordinator at the college’s Center for Environment and Society, says that by installing geothermal, “the college can keep its budget at a fairly consistent level.” There was some student concern about building “new” (not typically considered a sustainable practice), but the dorms will allow more students to live on campus and provide student housing as older dorms are retrofitted or used for other purposes.

When it comes to accessing geothermal heat, the Eastern Shore and Annapolis have a geological advantage over many other parts of the country: soil composed of sand, clay, and not much rock. Pliable earth makes drilling wells for geothermal exchange much easier than it is in other areas, even if the hole is just six inches across. At St. Mark’s United Methodist Church in Easton, twelve wells were needed, each 404 feet. These were dug during the first phase of expansion. And there is room for 28 more wells for future phases. The Kent Island United Methodist Church drilled 50 wells and has room for another 50 if the church expands.

Though geothermal systems seem unwieldy, one professional in charge of the Easton and Kent Island church expansions reminds us that the systems are versatile: they can be modified to work with existing radiators or to direct hot and cold air into different zones. And they can be controlled automatically, much like a conventional central heating and air conditioning. If a loop in a well fails, the well can be closed off and sealed and a new well drilled and connected. “The new technology is finding its ground. It’s not a fast recovery system, but it’s very constant and saves energy and lowers operating costs,” he says.

Ground loops are buried and completely concealed, so this formidable mess disappears when the job is done.

Paying for Renewable Energy

Your contractor should be able to help you sort out grants and tax credits that may help reduce your costs. There is the 30 percent Federal tax credit for residential systems and the Maryland grant program has benefited from 2009 government stimulus money though, at this writing, applicants may face a waiting period in 2010. Even if you don’t receive a grant, you may be eligible for a reduction in property taxes, especially in Howard, Montgomery, and Prince Georges Counties. You can learn about state grants and rebates on the Maryland Energy Administration’s Web site: www.energy.state.md.us. Remember to hold on to your receipts and purchase documents so you can prove that you qualify.

Some alternative energy systems just may not be feasible. When you consider the cost of a system and whether it will suit your needs, take into account three factors:

• Installation cost

• Appropriateness to your site

• Available rebates, grants, and tax credits as well as the energy savings that offset the initial cost

• Maintenance costs. Geothermal systems, because they work with so little effort, have a long lifetime and minimal maintenance costs.

We must add “planet” to the list. It’s not all about economics, but also about something priceless: a healthier environment for future generations.

Sarah S. Brophy’s new initials after her name are LEED-AP: Leadership in Energy and Environmental Design-Accredited Professional. With green building and living becoming mainstream, LEED is no longer just for businesses, architects, and engineers—it’s for homebuilders and homeowners, too.

The simplest and easiest practices continue to make a difference in your energy use. Here are ways to conserve energy in two important areas:

Heating your house

Ask your utility company, or find an experienced contractor, to conduct an energy audit to identify inefficiencies in your home. Infrared technology may be used to spot air leaks. An auditor will also examine your insulation and look for gaps from animal holes or missing building fabric around light fixtures and piping that let heat escape.

Put up those darned storm windows; use insulating blinds or curtains and those funny draft “snakes.” Examine your sliders, if you have them, and ensure that they are sealed properly. One expert notes “even the best slider made is a poor excuse for a window or door.”

Check weather stripping on doors and caulking on windows. Eliminate gaps where heat can leak out.

Keep furnace filters clean to improve airflow.

Keep blankets and throws on your most-used chairs and couches. While watching television or reading, wrap up rather than turning the heat up.

Warm cold floors with seasonal throw rugs.

Heating water

Turn down the temperature on your water heater. Find the tank, locate the thermostat, and drop it to 120 degrees or so. If you are turning on cold water in the bath or shower to adjust the temperature of your hot water, your hot water is too hot.

Water loses a lot of heat traveling through pipes. Make sure the tank and the pipes are well insulated.

Tags: Geothermal Heating Renewable Energy Geothermal Cooling Green Home Improvements

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