Experts in Geothermal Systems
Potential electricity savings above 60% in air conditioning mode.
Heating costs comparable to gas heaters, but without the carbon pollution.
Air conditioning and space heating with the same building system, saving space.
Geothermal systems can deliver space heating and cooling with very low operating costs, achieving significant savings compared with conventional HVAC systems. The underground is an effective heat source during winter and an effective heat sink during summer, and geothermal systems take advantage of this. MEP engineers can analyze the heating and cooling needs of your building, as well as underground conditions, to design a suitable geothermal system for your property.
Geothermal systems are also known as ground-source heat pumps (GSHP), since they effectively pump heat between a building interior and the underground. Heat is extracted from the building and released underground during summer, and the opposite process is carried out during winter.
In spite of their name, geothermal heat pumps are completely different from geothermal power plants, and the two concepts should not be confused. A geothermal heat pump exchanges heat with the ground at relatively low depth to achieve a very high HVAC efficiency, while a geothermal power plant uses heat from deep underground to drive a steam turbine and produce electricity. Geothermal power plants are also significantly larger than ground-source heat pump systems.
Geothermal systems have a higher upfront cost than other HVAC configurations, but they compensate this with the highest energy efficiency in the industry, achieving significant savings throughout the service life of a building.
Compared with conventional air conditioning systems, geothermal heat pumps labeled by ENERGY STAR can easily achieve electricity savings above 60 percent. They can also match the operating cost of gas-fired heating systems, but without the associated air pollution.
Types of Geothermal Systems
Geothermal systems can be classified into three main types, based on how they exchange heat with the underground: direct exchange (DX), closed loop and open loop systems.
Direct exchange (DX) geothermal systems exchange heat with refrigerant lines that are buried in direct contact with the ground or groundwater, as implied by their name. This is the oldest type of geothermal system.
- Since heat is exchanged directly with the ground as refrigerant travels through buried piping, these systems have a higher efficiency and a lower installation cost than other geothermal heat pumps.
- Direct exchange heat exchangers are susceptible to refrigerant leakage and pipe corrosion, and they must be designed to withstand both conditions. Even a slight opening in refrigerant lines can cause a massive refrigerant leak in a short time.
- The risk of groundwater contamination due to leaks is eliminated in direct exchange systems, since refrigerant tends to evaporate when exposed to the atmosphere.
Closed loop geothermal systems use water to exchange heat between the refrigerant the and underground, and refrigerant never travels underground as a result. Water circulates through a series of buried loops before returning to the heat pump, releasing or gathering heat depending on the operating mode. Closed loop geothermal systems use a mixture of water and antifreeze in the underground piping loop, and leaks prevention is very important to avoid groundwater contamination.
The underground piping of geothermal systems can have a horizontal or vertical configuration. The horizontal configuration is easier to install because piping is buried at a relatively low depth, but this option is only viable for properties with a large extension of land. Vertical piping configurations are more suitable in crowded cities with limited space for each building.
Open loop geothermal systems also use water to exchange heat with the underground, but groundwater is pumped directly to the heat pump. The main drawback of open loop systems is that groundwater cannot be treated easily before circulating through the heat pump, exposing the system to corrosive substances or abrasive particles. However, open loop geothermal systems are a viable option when groundwater conditions are suitable.
When a geothermal system is installed closed to a large body of water such as a lake, the piping that normally travels underwater can simply be submerged. This provides a simpler and less expensive installation, but it is only possible if the property has access to a large body of water.
How Geothermal Systems Deliver Indoor Heating and Cooling
Heat pumps can also be described based on how they heat and cool building interiors. The classification above describes how they exchange heat with the underground, but not how the heating or cooling effect reaches indoor spaces:
Liquid-to-air heat pumps heat or cool indoor air directly, just like packaged rooftop air conditioners. After being cooled or warmed, the air is circulated through indoor spaces using air-handling units and ductwork.
Liquid-to-water heat pumps are similar to chilled water systems, since the heat pump is used to heat or cool water, which is then circulated through the building. The water then heats or cools indoor air as it circulates through fan-coils. If this configuration is used with a closed-loop or open-loop geothermal system, keep in mind that the water circulating underground is completely isolated from the water circulating through the building.
Benefits of Geothermal Systems in the Building Sector
Geothermal systems can achieve significant power bill savings with energy-efficient air conditioning. In heating mode, their operating costs can be equal to or less than those of gas-fired heaters, but without the greenhouse gas emissions.
Ground-source heat pumps are a viable option to develop buildings that are fully powered with electricity. Although this is also possible with conventional resistance heaters, their operating cost is prohibitive because they are much less efficient than heat pumps. By displacing space heating and domestic hot water systems that run with fossil fuel combustion, geothermal systems can greatly reduce the greenhouse gas emissions of modern buildings.
Like with any other HVAC installation, having equipment of the right capacity is very important. Undersized heat pumps cannot meet the heating and cooling loads of a building, while oversized equipment is more expensive to own - this applies for both upfront costs and maintenance.
Since geothermal systems are so efficient, they are often eligible for local incentive programs, especially if you use equipment with a solid certification such as ENERGY STAR. By working with qualified MEP engineers, you can get a geothermal system design that meets local codes while earning rebates and other similar incentives.
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