Geothermal energy has enabled many to heat their homes in winter, cool them in summer and provide abundant hot water throughout the year, while slashing utility bills by up to 80%. The key question is: how can this abundant energy be tapped to perform the heating and cooling function? The answer: installing geothermal heat pumps.
Geothermal heat pumps are technologies that leverage the nearly constant temperature below the earth (regardless of the season) to heat and cool buildings. Just a few feet under the ground, the earth has a constant temperature of between 50 to 60 degrees Fahrenheit. The temperature below the earth is warmer than the air circulating above it during winter and cooler during summer. Geothermal heat pump is sometimes combined with solar heating to develop geosolar, a system with much greater efficiency. Geothermal heat pumps are known by different names such as earth energy systems, ground source heat pumps, geoexchange and earth-coupled. These names depend on the region you stay and field of study. Scientific and engineering communities prefer to call them ground source heat pumps and geoexchange to alleviate confusion with conventional geothermal power, which extracts hot water several feet deep into the earth for the purpose of electricity production.
Geothermal heat pumps harness this energy from beneath the earth and take advantage of this resource for heating and cooling of buildings.
Geothermal Heat pumps (sometimes referred to as Geoexchange, water source heat pumps), have been in use since 1940’s. Geothermal Heat pumps use the heat below the earth’s crust to heat homes and offices during winter rather, than the outdoor air temperature.
During winter, the heat below the earth is used as the medium to heat homes, as heat is removed from the heat exchanger by the heat pump system and it is pumped into the indoor air delivery system.
During summer, the process is reversed as heat pump moves heat into the heat exchanger from the indoor air. Heat extracted by the heat pump can also be used to heat water, providing a source of hot water during summer.
The three main power plant designs which use geothermal as an energy source are: “dry steam”, “flash steam”, and “binary-cycle” power stations.
How Does a Geothermal Heat Pump Work?
Heating and cooling is achieved through a geothermal heat pump system, which is made up of three main parts: the heat pump unit, the ground heat exchanger, and the air delivery system or ductwork. The heat exchanger encompasses a series of pipes known as loop, which is installed a few feet beneath the earth close to the building. A fluid (a combination of water and antifreeze) circulates through the series of pipes to suck up or disseminate heat into the ground. The fluid is usually blended with antifreeze to prevent freezing during winter.
The working of a geothermal heat pump has a lot in common with a refrigerator. A refrigerator makes a cool place (interior of the refrigerator) much cooler by transmitting heat to a significantly warm place (the area surrounding the interior of the refrigerator), allowing it to become warmer.
During winter, the geothermal heat pump extracts heat from the ground heat exchanger and channels it to the building’s air transfer system, which keeps the house warm and comfortable. During summer, the cycle is reversed. The geothermal heat pump extracts heat from the air inside the building and transfers it into the ground heat exchanger. The heat exchanger dumps the heat into the earth. The heat extracted from inside the building in the summer can be utilized to heat water, providing homeowner free hot water throughout summer.
Geothermal heat pumps are far more advantageous than traditional heating and cooling systems because they tap natural, free heat under the ground. They also operate at peak efficiency when cooling your home. Efficient operation is good for the homeowner as it saves energy, money and minimizes environmental degradation through pollution.
Geothermal heat pumps not only save energy and money but also help in reducing air pollution. They are also more efficient in cooling of the house.
Types of Geothermal Heat Pumps
Geothermal heat pump systems come in 4 main types; closed looped systems, open looped systems, pond or lake systems and hybrid systems. Closed looped systems are further subdivided into two: horizontal and vertical. Let’s look at them in detail:
- Closed-loop systems
Closed-loop systems are made of heavy plastic loops that allow the liquid to circulate through. The closed loops are typically buried a few feet below the ground, or submerged in a water body. The closed loop system consists of a heat exchanger, which coordinates the exchange of heat between the refrigerant, fluid and the heat pump in the closed loop. The closed loop system is further subdivided into;
- Horizontal closed loop
These types of closed loop systems are ideal for large area of land. They are cost-effective and are commonly installed in residential areas, more so for new constructions where adequate land is available. Horizontal closed loop systems need trenches at least four feet deep. There are different configurations of horizontal closed loops, but the most predominant utilize two pipes. The first pipe is normally buried about six feet below the ground, while the other at four feet. Another popular configuration utilizes two pipes laid next to each other, 5 feet below the ground, in a two-foot-wide trench. This kind of looping enables installation of more pipes inside a narrow and shorter trench, which greatly minimizes installation costs and allow for horizontal installation in sites that are not suitable for traditional horizontal applications.
- Vertical closed loop
Vertical closed loop systems are popular in offices, schools, and commercial establishments where space is quite limited. Essentially, the size of the land cannot allow for horizontal loop installation. Vertical closed loops are also applied in areas where the soil is not deep enough for trenching, and they are advantageous since they reduce the impact on landscaping. For this kind of geothermal heat pump, two vertical loops that are bent in U-shaped are placed into small holes (four inches in diameter, 100 to 400 feet deep, and 2 feet apart) into the ground. These vertical loops are then connected to each other using horizontal loops.
- Pond or lake system
Most properties have a pond or lake nearby. A closed system can be installed under this water body. Coiled pipes are installed underneath the water body at least eight feet below to mitigate the possibility of freezing. Nevertheless, the pond or lake must meet certain criteria regarding minimum volume, depth, and quality requirements before it can be considered a prime location for geothermal heat pump.
- Open loop systems
This type of geothermal heat pump is ideal for those with sufficient supply of groundwater. It utilizes this ground water as a ground heat exchanger and navigates the whole system. It’s transferred back to the ground by a means called surface recharge or recharge well. When out there looking to buy an open loop geothermal heat pump, ensure you have sufficient and clean groundwater supply since it’s a local code and regulation requirement.
- Hybrid systems
Hybrid system is a blend of geothermal heat pump, and air source heat pumps to offer a cost-effective and highly efficient system. They leverage the fact that setting up heating and cooling loads is not entirely balanced, with cooling dictating proceedings on numerous occasions because of internal gains. Instead of upsizing the heat exchanger to conform to higher cooling load, it is remodeled to conform to the heating load, and a heat rejector is incorporated into the system. Hybrid systems still get rid of boilers and deployment of fossil fuels, while minimizing the land area and the onset costs needed to set up the ground heat exchanger.
The benefits of geothermal heat pump systems are overwhelming. For starters, they utilize a renewable energy source, which is heat occurring naturally underground. This heat is not affected by seasons, which means it will be available until the end of time. The energy is also, green and clean, which means you will not have to worry about air pollution that contributes to deadly respiratory diseases. Above all, the geothermal systems are uniquely long lasting. They can last for more than 50 years, and the loops come with a remarkable 56-year warranty. This long term warranty alone underscores the fact that you can enjoy the benefits of geothermal energy for the rest of your life.