Geothermal Heating Systems

Technology Snapshot & Benefits:
Geothermal heating systems, also known as geo-exchange, ground source pumps, or earth-coupled pumps, take advantage of the earth's nearly constant temperature (45-75 degrees Fahrenheit, depending on latitude) to heat and cool buildings. They work by pumping water and antifreeze or a refrigerant under the ground to be heated or cooled by the earth and then pumped back through piping in the house. In the winter, the earth is used as a heat source, and in the summer as a heat sink. These systems are effective in any climate. The systems pollute less than traditional fuel-burning systems and are about three times more efficient. They are also more efficient than air-to-air exchange heating/cooling systems because water can transfer a greater amount of heat than air. They also have a longer lifetime than either system because almost all system components are indoors or underground. The average lifetime is 25 years for outdoor components and 50 years for parts that are installed indoors or underground.

Geothermal systems reduce the probability of a fire or carbon monoxide leak in a home because they do not require any combustion. Another huge benefit is the reduction of pollution. According to the Geothermal Heat Pump Consortium, geothermal systems reduce CO2 emissions by about 1.1 million metric tons over 20 years, which is "the equivalent of converting about 58,700 cars to zero-emission vehicles, or planting more than 120,000 acres of trees." Geothermal systems have the EPA ENERGY STAR® label, which not only indicates that using these systems benefits the health of our planet, but also that there may be incentives associated with installing the system, such as tax benefits or lower mortgages. Geothermal systems are also better at controlling relative humidity in buildings compared with other systems.

There are two different types of geothermal heating and cooling systems: open-loop and closed-loop. Open-loops systems require a body of water, and work by pumping water from this source through the house and then back into the body of water. In closed-loop systems, closed-loop piping through which water flows is buried under the ground. The piping for closed-loop systems may be installed vertically or horizontally, with vertical piping requiring a deep but thin trench and horizontal piping requiring a wide but shallow trench.

Geothermal systems are very popular among people who have used them. In fact, the California Energy Commission's Consumer Energy Center reports that 95 percent of people who have installed these systems would recommend them to others.

Estimated Cost Savings:
Geothermal heating systems can save between 30 and 70 percent on heating and cooling costs compared to traditional fuel-burning systems, and are estimated to use an average of 25 to 50 percent less electricity. These systems are often able to generate excess heat in the summer or even the winter, and a device called a desuperheater can use this excess heat from the system's compressor to heat water at no additional cost. These systems are expensive to install, costing about $2,500 per metric ton of unit, which works out to about $7,500 for the average-sized American home. This is nearly double the price of installing a traditional air conditioning unit. Closed-loop systems require an additional cost for drilling the trench in which the piping is laid, which can cost $10,000 to $30,000, although the costs of installation have decreased in recent years and are expected to continue falling. Overall, the long-term monetary benefits of transitioning to a geothermal system outweigh the initial cost. The U.S. Department of Energy estimates that the installation costs will pay for themselves in five to ten years, and then building owners will actually profit from the system for the remainder of the system's life. Schools and businesses, which will probably be using the system for a long time, could take special advantage of this profit to purchase new school or business necessities.

Besides saving money on monthly energy bills, geothermal heating systems are usually more durable and require fewer maintenance and repair costs compared with other units. Having a geothermal system adds value to a property proportional to how much monthly energy bills are reduced. Some states also offer monetary incentives for installing these systems.

Property owners who want some of the benefits of a geothermal system but simply cannot afford installation can consider an air-geothermal hybrid system, called a dual-source system. These systems are less efficient than a pure geothermal heating and cooling system, but more efficient than a pure air-based or fuel-based system. Also, dual-source systems are cheaper to install than pure geothermal ones.

Issues:
It is very important to get a qualified contractor to look at the building and land around the building to determine the best kind of geothermal system to maximize comfort, efficiency, and savings. All systems should be customized to a particular situation. It is very important to make sure the contractor is knowledgeable and qualified.

Open-loop systems are initially cheaper to install because they do not usually require drilling; however, it is important to note that these systems work only where there is a sufficient amount of fresh, relatively clean water available. If this is the case and an open-loop system may be used, you must research local regulations on discharging water and make sure these regulations are met.

Regional Issues:
Geothermal heating systems work in all climates, even extreme ones. Good contractors should be able to give advice on specific regional issues that affect drilling and installation, for example, very hard ground.

Installation:
Installation and installation costs of geothermal systems vary, depending on the type of system installed and the availability of a water source. All installations, however, involve installing some type of piping and units for converting and distributing heat. The ductwork used in these systems is the same as that used for traditional systems, so no change is required during installation. The most important thing about installation is finding a good contractor.

More Information On This Topic:

"Geothermal Heating/Cooling Systems" - Residential Environmental Design

"Geothermal Heat Pumps" - U.S. Department of Energy, Energy Efficiency and Renewable Energy

Geothermal Heat Pump Consortium

"Geothermal or Ground Source Heat Pumps" - California Energy Commission, Consumer Energy Center

Reflective Roof Coating

Technology Snapshot & Benefits:
According to ENERGY STAR®, Americans spend about $40 billion annually to air condition buildings - one-sixth of all electricity generated in this country. In areas that are sunny and warm for most of the year, or have a very hot summer, the costs to individuals are particularly devastating. Reflective roof coating is protective coating that can be applied to roofs to keep a home cool without having to use as much air conditioning. Reflective roof coating is also called albedo coating, since the materials used have high albedo, or ability to reflect the sunlight. Reflective roof coatings have other benefits as well: they can increase efficiency in some air conditioning and ventilation units on the roof and because UV radiation expedites roof ageing, they also slow roof decay. These special coatings work by reflecting the sun's light and releasing absorbed heat.

Reflective roof coating is most effective for flat roofs because flat roofs usually absorb more energy than slanted roofs. The effectiveness also varies with the thickness and color of the coating, with lighter colors and thicker coatings being significantly more effective. In fact, bright white reflective coatings can have a solar reflectance of 85 percent and cut a roof's cooling load up to 70 percent.

Reflective roof coatings can be made from various materials. Paint-on coatings include acrylic paints, polyurethane, and elastomeric. These types of coatings do not require professional installation. Single-ply reflective sheets made from plastic, PVC, or rubber are effective, as are reflective roof tiles made from concrete, clay, or metal. In terms of total cost (raw price, installation fees, and maintenance fees), white titanium dioxide paint and aluminum sheets are the best choice. However, elastomeric and acrylic coatings reflect a higher fraction of solar energy. Longevity of the material used should also be considered.

No matter which materials are used, most homeowners who employ reflective roof coating experience cooler indoor temperatures and lower cooling costs.

Estimated Cost Savings:
Reflective roof coating can cut cooling costs from 10 to 70 percent depending on the coating used, climate, and the degree of sunlight to which the roof is exposed. Hot areas that are sunny for a majority of the year benefit the most from reflective roof coatings. The decrease in monthly energy bills far outweighs the costs of installation. Coatings that are painted on typically cost $15 to $25 per gallon and can be applied by the homeowner. Professional installation of single-ply roof sheets or tiles typically costs the same as installing any other type of shingle or tile; so, if installed at the initial building of a home or rebuilding of a roof, there will be little to no extra cost for the homeowner. Cost for single-ply PVC membranes averages $3 per square foot.

Issues:
Reflective roof coatings are a simple way to cut costs and help the environment. Virtually all roofs can be made to absorb less heat and reflect more sunlight using some type of reflective roof product. However, if the roof membrane is decaying, the coating will not be as effective and it is recommended that the membrane be replaced before the coating is applied. It is best to consult a professional or product manufacturer about the ideal type of coating for a specific roof.

Regional Issues:
Reflective roof coatings are not recommended for areas that are cool or cold for much of the year and/or experience high cloud coverage. They most benefit people in areas that are warm and sunny for most of the year. In warm and/or sunny cities, this coating can help fight the "urban heat island" effect, or increased temperatures due to greater reflectance and absorbance of sunlight by a conglomeration of dark, metal buildings. Decreased indoor temperatures in areas that can become extremely hot can increase comfort and reduce the likelihood of heat-related illness or death.

Installation:
Paint-on coatings are applied using a roller, a brush, or airless spray equipment, and require minimal skill to apply. The roof should be properly cleaned before applying the coating. It is important to consult with the coating manufacturer for tips and advice on how to apply a specific coating to a specific roof. Single-ply reflective shingles and roof tiles must be installed by a professional roofer.


For more information on this topic:

Reflective Roof Coating Institute

ENERGY STAR® Reflective Roof Products

U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy: Cool Roof Calculator