Geo

Contents:

Geothermal Energy

Geothermal Power

Geo-Exchange (Ground Source) Heating/Cooling

Geothermal Energy

Geothermal energy is associated with taking advantage of the temperature differences found within the earth and those on the earth’s surface. There are two forms of Geothermal Energy of particular interest to us. The first involves the capturing of heat from high temperature pressurized water which has been heated by contact with Earth’s hot magma. This form of geothermal energy requires the use of heavy industrial equipment and a significant capital investment. The second form of geothermal energy involves taking advantage of the Earth’s relatively constant subsurface temperature. This form of geothermal energy requires a relatively inexpensive heat pump/exchanger system to add or remove heat from a dwelling. To avoid confusion we will refer to the first form of geothermal energy as Geothermal Power and the second form of geothermal energy as Geo-Exchange (Ground Source) Heating/Cooling..

Geothermal Power

Like many other renewable forms of energy, Geothermal Energy has been exploited since ancient times. The Romans used it for space heating and bathing. It once was thought that the heat within the core of the earth was mainly the result of the earth’s violent formation - billions of tons of super hot material smashing together, congealing, and trapping the heat inside. However, it is now believed that radioactive decay is the main cause for the earth’s hot molten core. And at 4,000 miles below the earth’s surface the core is very hot, approximately 7,200 degrees F. To put this temperature in perspective, the surface of our Sun has a temperature of 11,000 degrees F. Even just 50 to 60 miles down the earth’s magma can range between 1200 and 2200 degrees F. However, 50 miles down is still a long way. And this is the main reason why Geothermal Plants are nearly always located on the boundaries of tectonic plates, where the earth’s magma comes closer to the surface. To capture this geothermal energy special geothermal wells are drilled to locate underground reservoirs of heated ground water. The ground water which is normally under high pressure is piped to a facility where it is converted to steam. The steam is used for space heating, industrial purposes, and/or conversion into electricity. In concept, geothermal plants are the simplest of all the power generation technologies. It involves the use of common industrial heat exchangers and well known steam management practices. The only downside in establishing a geothermal plant is the cost of locating and installing geothermal wells. Even so, there is much more involved in locating a geothermal plant. To capture the heat of the magma and/or lava, ground water must be present in sufficient quantities. Moreover, the porosity of the rock within these underground reservoirs must be established. In addition, the mineral content of the water must be at acceptable levels to prevent fouling of heat exchanger equipment. Finally, even if all the indicators are present the area may still not be a good candidate for a power plant. Power plants require a significant amount of infrastructure to connect to the grid. Remote areas are not normally good candidates. This all said, the cost of operating a geothermal power plant is comparable to that of a coal fired plant - presently, the least expensive way to generate electricity. Considering that geothermal power plants have practically none of the environmental concerns associated with coal fired plants, it seems incredulous that countries that lie along the edges of tectonic plates do not take more advantage of this dependable renewable resource. Especially considering that of all of the renewable energy technologies, including hydroelectricity, geothermal energy is probably the most dependable resource for generating primary electricity.

Pros

Most geothermal plants operate practically emission free – no carbon dioxide or other combustion by products.

A geothermal plant is about the same size of a thermal hydroelectric plant of equivalent capacity. However, it does not require the extensive support facilities for fuel.

In concept, geothermal plants are the least complex of all power generation technologies.

Geothermal plants can be used as a primary source of electricity the same as thermal hydroelectric plants.

Geothermal energy is the most dependable form of energy. Nearly all plants constructed are still in operation. However, for a small minority of plants, there have been some glitches in not returning sufficient amounts of water to the geothermal well.

The cost of operating a geothermal plant is comparable to that of operating a coal fired plant - but without any of the environmental concerns associated with burning coal.

Cons

Very high cost associated with drilling and installing a geothermal well. However, once installed there are no fuel costs.

By venting steam, geothermal plants appear to be emitting copious amounts of pollution into the air. However, this steam is nearly 100% water vapor. (In fact, geothermal plants may actually reduce the amount of sulfur that normally would have vented through hot water springs.)

Some plants do produce silica and sulfur dioxide. Most however, remove these substances from the waste steam and sale them for industrial purposes or return them to the geothermal well.

Geothermal wells can release green house gases that have been trapped beneath the earth. However the amounts are far less than that associated with burning fossil fuels.

Want to learn more about geothermal power:

Statement of Howard Gruenspecht, Deputy Administrator, Energy Informantion Administration, U.S. Department of Energy

http://www.eia.doe.gov/neic/speeches/howard052405.pdf

Geothermal California

http://www.geothermal.org/articles/California.pdf

Geo-Heat Center

http://geoheat.oit.edu/

Vulcan Power Companyhttp://www.vulcanpower.com/html/properties/saltwellsbasin.htm

Calpine Corporation

http://www.calpine.com/

* Visit our Planning Tools Section for Informaiton on how to choose the right alternative energy system, how to hire contractors, and Do-it-yourselfer tips and instructions.

Geo-Exchange (Ground Source) Heating/Cooling

Geo-exchange systems have been well established over the last few decades and if designed properly can be very efficient. They can be easily retrofitted into an existing building provided there is sufficient outside space for the ground source loop. In addition, geo-exchange systems are useful in a wide variety of building types including: churches, schools, office buildings, and homes.

Just a few feet below the surface, the Earth maintains a relatively constant temperature between roughly 50 degrees F (10C) and 60 degrees F (15.5 C). Yet in many areas, the ambient air temperature on the Earth’s surface is subject to rather large seasonal swings. Temperatures in the winter can go below O degrees F and in summer exceed 100 degrees F. In fact, the Midwest of the United States undergoes this swing in temperature from season to season routinely. By excavating trenches or thermal wells, installing piping and using heat pumps to pump heat transfer fluid or water through the piping; this ground source temperature can be captured. The heat transfer fluid or water can then be used in a heat exchanger to step up or step down the temperature of the air being used in a centralized space heating/cooling system. In this manner, the fuel or electrical costs for heating and/or cooling can be greatly reduced.

There are essentially two basic types of geo-exchange cooling/heating systems: closed loop and open loop. In a closed loop system either a borehole or trench is made into the earth. A series of pipes are installed and connected to a pump and heat exchanger. The piping is arranged in such a manner as to form a closed loop circulatory system. Heat transfer fluid is then placed within the piping. When in operation, the heat transfer fluid transfers the temperature from the ground to the heat exchanger, where it is used to heat or cool ambient air coming into a centralized space heating system. In an open loop system the ground water itself is pumped from a well into a heat exchanger. It functions in the same manner as a closed loop system except that the ground water is returned to the aquifer or released into a body of water at the surface.

Depending on project requirements and the contractor selected, four different types of loop arrangements are normally employed.

Closed Horizontal Ground Loops

Trenches are dug and the exchange piping is coiled and placed within the trench. The depth and length of the trench is dependent on the heating and cooling requirements of the dwelling, climate, and soil conditions. Trenches normally are dug 3 to 6 feet deep.

Closed Vertical Ground Loops

Boreholes are drilled and the piping is placed within. The number and depth of boreholes is dependent upon heating and cooling requirements of the dwelling, climate, and soil conditions. Boreholes can be drilled from 150 to 400 feet or more. Special considerations in locating boreholes are very similar to locating domestic water wells.

Closed Pond Loops

Piping is coiled and placed within a pond. The length of pipe is dependent upon heating and cooling requirements of the dwelling and temperature of the water. Special consideration should be made regarding the size and depth of the pond as it relates to dependable water temperatures.

Open Loops

A source of ground water is tapped and pumped through a heat exchanger and then returned to a well or pond. Special consideration needs to be made regarding filtration to prevent fouling of equipment and possible contamination of the aquifer.

Pros:

A geo-exchange system uses 25-50% less electricity than conventional forced air heating or cooling systems.

Because less electricity is used with a geo-exchange system there is less power taken from the grid which in turn reduces the need to burn fossil fuels for the production of electricity.

A geo-exchange system heat pump can use a "desuperheater" device to provide free hot water - saving gas and electricity.

A geo-exchange system maintains an even temperature and humidity 24/7.

A geo-exchange system produces less noise than a normal air conditioning system.

A geo-exchange system can be installed in both new and retrofit projects.

A geo-exchange system does not require roof top units or other unsightly outside equipment such as cooling towers. This can be especially important when there is view of the facility from above.

Because roof mounted equipment and penetrations are not required a geo-exchange system may also decrease the cost of roof warrantees.

Nearly all of the piping is underground or underwater and requires no maintenance. Life expectancy of underground piping can exceed 40 years.

Cons:

The initial cost is the primary concern for any geo-exchange system. Payback can be up to 10 years and beyond depending on current energy expenses. Government and Utility Company incentives can however help in reducing the cost.

Open loop systems require filtration to protect the system components from fouling .

Special consideration for the aquifer must be made to prevent contamination from any underground loop system.

Want to learn more about Geo-Exchange (Ground Source) Heating/Cooling:

GeoExchange, Geothermal Exchange Organization http://www.geoexchange.org/

The Geoexchange http://www.thegeoexchange.org/what-is-it.html

* Visit our Planning Tools Section for Informaiton on how to choose the right alternative energy system, how to hire contractors, and Do-it-yourselfer tips and instructions.