The Basics of Geothermal

How does a Geothermal heating and cooling system work?

Outdoor temperatures fluctuate with the changing seasons but underground temperatures don’t. Four to six feet below the earth’s surface, temperatures remain relatively constant year−round. A geothermal system, which typically consists of an indoor unit and a buried earth loop, capitalizes on these constant temperatures to provide “free” energy. In winter, fluid circulating through the system’s earth loop absorbs stored heat and carries it indoors. The indoor unit compresses the heat to a higher temperature and distributes it throughout the building. In summer, the system reverses, pulling heat from the building, carrying it through the earth loop and depositing it in the cooler earth.
What makes a Geothermal system different from ordinary systems? Unlike ordinary systems, Geothermal systems do not burn fossil fuel to generate heat; they simply transfer heat to and from the earth to provide a more efficient, affordable and environmentally friendly method of heating and cooling. Typically, electric power is used only to operate the unit’s fan, compressor and pump.

What are the components of a water source Geothermal system?

The three main parts consist of the heat−pump unit, the liquid heat−exchange medium (open or closed loop), and the air−delivery system (ductwork).

What are others saying about geothermal?

An EPA study of energy efficiency concluded geothermal energy is the most environmentally friendly heating/cooling system.
The United States National Renewable Energy Laboratory concluded that geothermal energy is more efficient and cost−effective compared with conventional residential systems.
The California−based Consumer Energy Center praises versatile geothermal energy.
The Geothermal Energy Association discusses the benefits of renewable geothermal energy.
Find out what the Union of Concerned Scientists has to say. Even major energy producers (power plants) recognize geothermal energy advantages as a renewable source of power.
Up to 95% of geothermal system owners would recommend installing such a system in the home. That's reflected in a number of online users' and owners' forums, including GeoExchange where you can experience the viewpoints of geothermal system owners.

How efficient is a Geothermal system?

A Geothermal system is three to four times more efficient than the most efficient ordinary system. Because geothermal systems do not burn fossil fuels to make heat, they provide three to four units of energy for every one unit used to power the system.

Is the efficiency rating actual or just a manufacturer’s average?

All heating and cooling systems have a rated efficiency from a U.S. governmental agency. Fossil fuel furnaces have a percentage efficiency rating. Natural gas, propane and fuel oil furnaces have efficiency ratings based on laboratory conditions. To get an accurate installed efficiency rating, factors such as flue gas heat losses and cycling losses caused by oversizing, blower fan electrical usage, etc., must be included.
Geothermal heat pumps, as well as all other types of heat pumps, have efficiencies rated according to their coefficient of performance or COP. It’s a scientific way of determining how much energy the system produces versus how much it uses. Most geothermal heat pump systems have COPs of 3−4.5. That means for every one unit of energy used to power the system, 3−4.5 units are supplied as heat. Where a fossil fuel furnace may be 78−90% efficient, a geothermal heat pump is about 400% efficient. Some geothermal heat pump manufacturers and electric utilities use computers to accurately determine the operating efficiency of a system for your home or building.

Do Geothermal systems require much maintenance?

No. Geothermal systems are practically maintenance free. When installed properly, the buried loop will last for generations. And the other half of the operation − the unit’s fan, compressor and pump − is housed indoors, protected from the harsh weather conditions. Usually, periodic checks and filter changes are the only required maintenance.

What does Geothermal mean for the environment?

Geothermal systems work with nature, not against it. They emit no greenhouse gases, which have been linked to global warming, acid rain and other environmental hazards.

Are all Geothermal heat pumps alike?

No. There are different kinds of geothermal heat pumps designed for specific applications. Many geothermal heat pumps, for example, are intended for use only with higher temperature ground water encountered in open−loop systems. Others will operate at entering water temperatures as low as 25_F, which are possible in closed−loop systems. Most geothermal heat pumps provide summer air conditioning, but a few brands are designed only for winter heating. Geothermal heat pumps also can differ in the way they are designed. Self−contained units combine the blower, compressor, heat exchanger and coil in a single cabinet. Split systems allow the coil to be added to a forced−air furnace and utilize the existing blower.

How does a Geothermal heat pump work?

Anyone with a refrigerator or an air conditioner has witnessed the operation of a heat pump, even though the term heat pump may be unfamiliar. All of these machines, rather than making heat, take existing heat and move it from a lower temperature location to a higher temperature location. Refrigerators and air conditioners are heat pumps that remove heat from colder interior spaces to warmer exterior spaces for cooling purposes. Heat pumps also move heat from a low−temperature source to a high−temperature space for heating.
An air−source heat pump, for example, extracts heat from outdoor air and pumps it indoors. A geothermal heat pump works the same way, except that its heat source is the warmth of the earth. The process of elevating low−temperature heat to over 100_F and transferring it indoors involves a cycle of evaporation, compression, condensation and expansion. A refrigerant is used as the heat−transfer medium which circulates within the heat pump. The cycle starts as the cold, liquid refrigerant passes through a heat exchanger (evaporator) and absorbs heat from the low−temperature source (fluid from the ground loop). The refrigerant evaporates into a gas as heat is absorbed.
The gaseous refrigerant then passes through a compressor where the refrigerant is pressurized, raising its temperature to more than 180_F. The hot gas then circulates through a refrigerant−to−air heat exchanger where heat is removed and pumped into the building at about 100_F. When it loses the heat, the refrigerant changes back to a liquid. The liquid is cooled as it passes through an expansion valve and begins the process again. To work as an air conditioner, the system’s flow is reversed.

Does a Geothermal system heat and cool?

One thing that makes a geothermal heat pump so versatile is its ability to be a heating and cooling system in one. With a simple flick of a switch on your indoor thermostat, you can change from one mode to another. In the cooling mode, a geothermal heat pump takes heat from indoors and transfers it to the cooler earth through either groundwater or an underground earth loop system. In the heating mode, the process is reversed.
Will the minimum entering water temperature affect which Geothermal heat pump I buy?
Yes. If you have an open loop system, your entering water temperatures (EWTs) may range from the 70s in the southern United States to the 40s in Canada. All heat pumps can handle temperatures in the moderate−to−warm range. A closed loop system, on the other hand, may encounter EWTs below freezing. Not all geothermal heat pumps will operate efficiently at those temperatures. It’s important to know what EWTs at which your heat pump will operate most efficiently.

Can a Geothermal system also heat water?

Yes. Some geothermal heat pumps can provide all of your hot water needs on demand at the same high efficiencies as the heating/cooling cycles. An option called a desuperheater can be added to most heat pumps. It will provide significant savings by heating water before it enters your hot water tank.