Geothermal Energy

What is Geothermal

BACORP has been designing and installing Geo-Exchange systems for 35 years. We have more systems installed than all of our competitors that use these systems, combined.

The technology relies primarily on the Earth’s natural thermal energy, a renewable resource, to heat or cool a structure. The only additional energy Geo-Exchange systems require is the small amount of electricity they employ to concentrate the natural energy and then to circulate high-quality heating and cooling throughout the home. Clients that have used Geo-Exchange systems give them superior ratings because of their ability to deliver comfortably warm air, even on the coldest winter days, and because of their extraordinarily low operating costs. As an additional benefit, Geo-Exchange systems can provide inexpensive hot water, either to supplement or replace entirely the output of a conventional, domestic water heater.

Geo-Exchange heating and cooling is cost effective because it uses energy so efficiently. This makes it very environmentally friendly, too. For these reasons, federal agencies like the Environmental Protection Agency and the Department of Energy, as well as state agencies endorse it.

How it Works

Geo-Exchange systems work on a different principle than an ordinary furnace/air conditioning system, and they require little maintenance or attention. Conventional heating systems must create heat by burning a fuel, typically natural gas, propane, or fuel oil. With Geo-Exchange systems, there’s no need to create heat, hence no need for chemical combustion. Instead, the Earth’s natural heat is collected in winter through a series of pipes, called a loop, installed below the surface of the ground or submersed in a pond or lake. Fluid circulating in the loop carries this heat to the structure. An indoor Geo-Exchange system then uses electrically-driven compressors and heat exchangers in a vapor compression cycle–the same principle employed in a refrigerator–to concentrate the Earth’s energy and release it inside the structure at a higher temperature. In typical systems, duct fans distribute the heat to various rooms.

In summer, the process is reversed in order to cool the home. Excess heat is drawn from the structure, expelled to the loop, and absorbed by the Earth. Geo-Exchange systems provide cooling in the same way that a refrigerator keeps its contents cool, by drawing heat from the interior, not by injecting cold air.

Heating and Cooling Combined

Geo-Exchange systems do the work that ordinarily requires two appliances, a furnace and an air conditioner. They can be located indoors because there’s no need to exchange heat with the outdoor air. They’re so quiet occupants don’t even realize they’re on. They are also compact. Typically, they are installed in a basement or attic, and some are small enough to fit atop a closet shelf. The indoor location also means the equipment is protected from mechanical breakdowns that could result from exposure to harsh weather.

Geo-Exchange works differently than conventional heat pumps that use the outdoor air as their heat source or heat sink. Geo-Exchange systems don’t have to work as hard (which means they use less energy) because they draw heat from a source whose temperature is moderate. The temperature of the ground or groundwater a few feet beneath the Earth’s surface remains relatively constant throughout the year, even though the outdoor air temperature may fluctuate greatly with the change of seasons. At a depth of approximately six feet, for example, the temperature of soil in most of the world’s regions remains stable between 45 F and 70 F. This is why well water drawn from below ground feels so cool even on the hottest summer days.

In winter, it’s much easier to capture heat from the soil at a moderate 50 F. than from the atmosphere when the air temperature is below zero. This is also why Geo-Exchange systems encounter no difficulty blowing comfortably warm air through a home’s ventilation system, even when the outdoor air temperature is extremely cold. Conversely, in summer, the relatively cool ground absorbs a home’s waste heat more readily than the warm outdoor air.

Studies show that approximately 70 percent of the energy used in a Geo-Exchange heating and cooling system is renewable energy from the ground. The remainder is clean, electrical energy which is employed to concentrate heat and transport it from one location to another. In winter, the ground soaks up solar energy and provides a barrier to cold air. In summer, the ground heats up more slowly than the outside air.

The Earth Connection

Once installed, the loop in a Geo-Exchange system remains out of sight beneath the Earth’s surface while it works unobtrusively to tap the heating and cooling the Earth provides. The loop is made of a material that is extraordinarily durable but which allows heat to pass through efficiently. This is important so it doesn’t retard the exchange of heat between the Earth and the fluid in the loop. Loop manufacturers typically use high-density polyethylene, a tough plastic. When installers connect sections of pipe, they heat fuse the joints. This makes the connections stronger than the pipe itself. Some loop manufacturers offer up to 50-year warranties. The fluid in the loop is water or an environmentally safe antifreeze solution that circulates through the pipes in a closed system.

Diagram detailing: Vertical, Horizontal, Slinky, and Pond Geothermal Loops.

Types of Loops

Most loops for Geo-Exchange systems are installed either horizontally or vertically in the ground, or submersed in water in a pond or lake. In most cases, the fluid runs through the loop in a closed system, but open-loop systems may be used where local codes permit. Each type of loop configuration has its own, unique advantages and disadvantages, as explained below:

Horizontal Ground Closed Loops

This configuration is usually the most cost effective when adequate lot space is available and trenches are easy to dig. Trenches are excavated three to six feet below the ground, and a series of parallel plastic pipes are laid. The trench is back filled, taking care not to allow sharp rocks or debris to damage the pipes. Fluid runs through the pipe in a closed system. A typical horizontal loop will be 400 to 600 feet long per ton of heating and cooling capacity. The pipe may be curled into a slinky shape in order to fit more of it into shorter trenches, but while this reduces the amount of land space needed it may require more pipe. Horizontal ground loops are easiest to install while a project is under construction. However, new types of digging equipment that allow horizontal boring are making it possible to retrofit Geo-Exchange systems into existing homes with minimal site disturbance. Horizontal boring machines can even allow loops to be installed under existing buildings or driveways.

Vertical Ground Closed Loops

This type of loop configuration is ideal for structures where space is insufficient to permit horizontal buildings with large heating and cooling loads, when the Earth is rocky close to the surface, or for retrofit applications where minimum disruption of the landscaping is desired. Vertical holes are bored in the ground 150 to 450 feet deep. Each hole contains a single loop of pipe with a U-bend at the bottom. After the pipe is inserted, the hole is back filled or grouted. Each vertical pipe is then connected to a horizontal pipe, which is also concealed underground. The horizontal pipe then carries fluid in a closed system to and from the Geo-Exchange system. Vertical loops are generally more expensive to install, but require less piping than horizontal loops because the Earth deeper down is cooler in summer and warmer in winter.

Pond Closed Loops

If a project is near a body of surface water, such as a pond or lake, this type of loop design may be the most economical. The fluid circulates through polyethylene piping in a closed system, just as it does in the ground loops. Typically, the pipe is run to the water, where long sections are submerged under water. The pipe may be coiled in a slinky shape to fit more of it into a given amount of space. Geo-Exchange experts recommend using a pond loop only if the water level never drops below six to eight feet at its lowest level to assure sufficient heat-transfer capability. Pond loops used in a closed system result in no adverse impacts on the aquatic system.

Diagram of an Open Geothermal Loop.

Open Loop System

Open loop systems are the simplest to install and have been used successfully for decades in areas where local codes permit. In this type of system, ground water from an aquifer is piped directly from the well to the building, where it transfers its heat to a heat pump. After it leaves the building, the water is pumped back into the same aquifer via a second well,called a discharge well, located at a suitable distance from the first.

Standing Column Well System

Standing column wells, also called turbulent wells or Energy Wells, have become an established technology in some regions, especially the northeastern United States. Standing wells are typically six inches in diameter and may be as deep as 1500 feet. Temperate water from the bottom of the well is withdrawn, circulated through the heat pump’s heat exchanger, and returned to the top of the water column in the same well. Usually, the well also serves to provide potable water. However, ground water must be plentiful for a standing well system to operate effectively. If the standing well is installed where the water table is too deep, pumping would be prohibitively costly. Under normal circumstances, the water diverted for building (potable) use is replaced by constant-temperature ground water, which makes the system act like a true open-loop system. If the well-water temperature climbs too high or drops too low, water can be “bled” from the system to allow ground water to restore the well-water temperature to the normal operating range. Permitting conditions for discharging the bleed water vary from locality to locality, but are eased by the fact that the quantities are small and the water is never treated with chemicals.

Other loop designs are also being used. In a few places, for example, developers have installed large community loops, which are shared by all of the homes in a housing development.

Sound Investment

Geo-Exchange is becoming the system of choice in many parts of the United States as consumers learn more about its aesthetic advantages and long-term value, and as it becomes more widely available.

Cost Effective

The extraordinarily low operating costs of Geo-Exchange systems more than make up for any higher installation costs within a few years. According to the U.S. Environmental Protection Agency, Geo-Exchange systems save homeowners 30-70 percent in heating costs, and 20-50 percent in cooling costs, compared to conventional systems. Geo-Exchange systems also save money in other ways. They are highly reliable, require little maintenance, and are built to last for decades. They add considerably to the value of a business or home.

A Wise Choice

Geo-Exchange is a smart investment for consumers who want a system that provides a high level of comfort and low monthly energy bills for as long as they own their businesses or homes.