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Geothermal Heating and Cooling Systems

Geothermal Heating and Cooling Systems

Geothermal energy is an eco-friendly source of energy used to power many applications, especially for heating and cooling systems. Its use over the years has proved to be extremely reliable and highly cost-efficient.
HelpSaveNature Staff
Good News
According to Bob Donley, who is a customer support manager at GeoSystems LLC, roughly 100,000 geothermal heat pumps are set up every year in the US. He further says, "In 2008 alone, the industry saw a 40 percent increase in homeowner interest." This clearly goes to say that the interest in geothermal systems is actually increasing.
Geothermal heating and cooling systems are globally used in many industrial and domestic applications. The source of this energy lies in the interior of our planet, the solar energy received at the surface, and also because of the decomposition of the mineral wealth in the depths of the planet. There have been several ancient remains and proofs of the use of geothermal heating systems. These can be traced to the ancient Indus valley civilization, the Roman empire, and the subsequent periods in human history when civilizations flourished. Presently, its main use is in the generation of electricity.

Globally, most of the applications running on the power generated by these systems are used in space heating, for desalination works, farming and heating services, spas, rejuvenation centers, etc. This requires an installation of the system, which can be achieved in different ways. The ground beneath our feet is an excellent source of geothermal energy. The same can be drawn by means of certain equipment. The installation requirements for these systems is provided in detail as follows.
Geothermal Heat Pumps
The entire process of heating and cooling is controlled by the geothermal heat pump, which in itself is a very complex system. The pumping machinery mainly consists of piping tubes, compressor units, air handler units, heat exchanger equipment, connector bends, refrigerant mix, etc. The pumping system mainly works on the cyclic nature of the refrigerant, and the absorption and release of heat undertaken by it. More than one million units of geothermal heat pumps have been installed worldwide. It was first made by an Austrian inventor called Peter von Rittenger, in 1855, and based it on the descriptions provided by Lord Kelvin in 1853. The geothermal heating and cooling systems are broadly classified into two categories: closed loop and open loop.
Closed-loop System
These systems work on the basis of a continuous loop of piping or tubing, which runs under the ground surface. In this type, the pipe carrying refrigerant liquid extends from the ground to the cabinet housing or compressor unit. A second loop is mainly placed below the groundwater level, or submerged inside a water body if possible. The reason being that heat can be absorbed or released in a water body more efficiently than a solid ground surface. Such a piping can be made from polyethylene or related synthetic materials. The refrigerant may consist of a mixture of water and propylene alcohol and methanol.

The exchange of heat between both the loops is possible with the help of a heat exchanger unit, along with expansion tanks and pumping relief valves. The looping size basically depends on the content of moisture in the rocks, and also on the type of soil present in the area, where the system is being set up. The efficiency of a closed-loop system is less than that of the open ones, and hence, longer piping is needed for the entire process, in order to increase the quality of hot or cold air that is provided.

Disadvantage: This system includes high expenses needed to excavate the ground for laying off the entire unit.

Three main subtypes of the closed system exist. They are:
  1. Horizontal Installation
  2. Vertical Installation
  3. Pond Installation
Closed loop horizontal installation
If a large area is available in the vicinity of the house, horizontal looping can be used. An extensive network of pipe loops can be placed just below the surface of the ground, below the frost cover. As long as there is sufficient space available for digging, a complex network of horizontal looped pipes can be used. Coiled loops are another variation of this type, in which the pipes are spread in a coiled manner instead of straight lines. This technique is very popular among non-commercial construction sites, and costs quite less than the vertical method of drilling. The slinky method involves placing of the pipes in such a way that they are coiled in layers on top of each other, thus, saving space and increasing efficiency of heat absorption. It is recommended to place the piping units at a shallow depth, in order for better absorption of heat by the rock layers, which is received from the Sun. In winter, the stored heat is very helpful for providing instant warm air in the house.
Closed loop vertical installation
In case there is a limitation of the land under possession, vertical loops can solve the problem. In this type, the pipes run deep into the depths of the land in a vertical manner. The pipes are connected by a U-bend at the bottom, thus, completing the loop. They are attached by horizontal pipe sections at the upper portions, which are further connected to air handlers and compressor units. The wells or boreholes are filled with a material called grout. It helps in efficient transfer of heat from the rocks to the pipes, and also prevents the aquifers from getting spoiled due to contamination by polluting sources. Another advantage of this material includes the decrease in effects of flooding of the well, which takes place mainly during the monsoon season. The cost of installation of these pipes is more than the horizontal loops, as it requires a lot of effort for setting up. However, even a small area is sufficient for this purpose, and the heating efficiency is the same as in case of horizontal loops.
Closed loop pond installation
If the area near your house has a natural pond or a sufficiently large pit, it may prove to be a big advantage regarding the installation of these systems. In this method, the loops are let into the pond and filled with liquid to sink the pipes further below. This is possible by attaching them to a frame and sinking it below the pond water level. A setup designed in this manner can be possible only when the pond or the source of water satisfies the conditions needed for adequate water depth, quality, and volume. Mostly, the pipe loops are set up about 10 feet below the water level, as they might get frozen during winter.
Open-loop System
Open loop system
The working mechanism of these systems is exactly opposite to that of the closed-system type. It is also known as a groundwater heat pump, and uses two separate water bodies for each pipe loop. Water is pumped from a water body like a well into a heat pump, and it gets circulated through the cabinet unit. Depending on the season, when hot or cold air is provided inside the building or house, the primary loop carries the water into another water body like a well, pond, aquifer, etc. Installing an open-loop system is advisable only in those areas that have a large number of water bodies, which mainly consist of clean water.

Thus, in this system, two separate sources are used for both the tasks: (i) addition/subtraction of heat from the supplied water and subsequent transfer of air; and (ii) disposition of the used water supply.

Disadvantages:
  1. This system is more efficient than the closed-loop type, but has a disadvantage that the groundwater sources, or any surficial recharge well might get polluted; this harms the flow of water, and hence, the mechanism of the heat pump that consists of exchanging heat with the groundwater does not work in a proper manner.
  2. Also, both the water sources or wells should be situated far away from each other for better conductivity. Many regions do not recommend these systems, and it can be set up when the various criteria, regulations, and conditions that are present in the local regions are satisfied.
Hybrid Systems (Standing Column Well)
In these systems, two or more water sources are needed, like two adjacent wells. This technique utilizes the combination of heat sources; hence, the name hybrid systems. If they are not present close to each other, the temperature equilibrium won't be maintained, as both the wells need to recharge and discharge their heat levels according to the seasons. Water is drawn from the portion near the bedrock of one of the wells, and used for transfer to heat pumps. Depending on the season, heat is subtracted or added, and the remaining water is transferred back to the upper portions of the well. This water then travels back down to the bedrock and gets recharged with heat from the solid rocks and minerals. This system can be said to be a variant of the open-loop type.

Now, especially during the summer season, the extra heat from the water is not required by the building and can be stored in the well. The temperature of the water column increases, and at this time, the adjacent well can act as a coolant. By drilling an opening between both wells, cold water from the second one can mix with the already-heated water column, thus, forming a way to supply cooler air during the summer season. Alternatively, the extra heat stored can be used during winters.
Working
Geothermal heating process
▶ The boundary just beneath the house or building is known as the heat line, beyond which geothermal energy goes on increasing according to the geothermal gradient. The pipes are placed under this line accordingly depending on the type of system (open or closed). Inside the house, the entire geothermal pumping unit is installed along with the compressor cabinet and air handlers. Through the primary pipe loop, hot refrigerant is pumped into the ground, which comes in contact with the underground rocks.

In summer, the temperature of underground rocks is less than that of the atmosphere; i.e., it is cooler. The refrigerant's heat gets dispersed and absorbed by the ground surface, leading to a drop in its temperature. This cooler liquid is brought up to the geothermal units inside the house. The warm normal air from the house comes in contact with this liquid and cools down. This cold air is then supplied to the interior of the house. The warm refrigerant is again pumped through the compressor unit into the ground, and the process repeats till an optimum temperature is achieved.

In winter, the reverse scenario occurs. The underground temperature is higher than that of the atmosphere, as the ground has stored heat from the previous summer. The refrigerant is pumped through the primary coil under the heat line, and gets heated due to the surrounding high temperature. This warm refrigerant is transferred from the surface to the geothermal units set up inside the building. This liquid heats up the air inflow of the house, which is received from the home interior through a separate vent, resulting in the formation of warmer air. This air is then provided inside the house to keep it warm during the cold winter months.
Benefits
▶ The geothermal energy source is one of the most important ones in case of renewable sources of energy. It is not just used for heating and cooling purposes, but is also used for generation of electricity.

▶ In case of providing warm and cool air flow to homes and buildings, these systems are a great option to reduce your ecological footprint, against the dependency on fossil fuels for running of air conditioners and central heating units.

▶ Being a foolproof system, it is not affected by any major obstacle that would spoil the working mechanism.

▶ The output is better in quality and quantity than the machinery that runs on conventional sources.

▶ It is a single-time investment, and timely maintenance can make the geothermal heat pumps run for decades.

▶ The temperature that is desired inside the house can be simply changed by controlling the amount of refrigerant used.

▶ Extra heat can be stored in case of open-loop systems.

▶ As the major source of heat is present due to the Earth's own inherent heat and the resultant geothermal gradient, this source will not get exhausted ever, as long as our planet exists.
Drawbacks
This technology is pretty expensive than the conventional methods described above. It is not useful for a short-term investment regarding keeping your home interior at an optimum temperature.

The refrigerant types that are used are toxic in nature, and may pollute the underground rock lithology and groundwater sources like aquifers and wells.

One of the biggest disadvantages of this technology exists in regions where high seismic activity has been recorded. Due to major ground upheavals, the equipment placed under the heat line may get damaged in a permanent manner, and replacements are pretty expensive.

Soil pollution might also be caused if vast areas are used for installing geothermal heat pumps; hence, the land may become unfit for any productive use like agriculture.
These systems are recommended to be built only in those regions that meet the following criteria:
  • Large areas of land that are not used for any other purposes
  • Sources of clean water that can be successively recycled
  • Permission from the local government body for machinery setup
  • Banning of certain system types in some places, etc.
Geothermal energy is a popular source of alternative energy, and its use for heating and cooling purposes have made it possible for construction of smart and environmentally-friendly homes.