Geothermal HVAC basics
Sep 4, 2014

Have you ever heard of geothermal heating and cooling for your facility? It’s sometimes referred to as a geo-exchange, a ground source heat pump, or a geothermal heat pump. Geothermal heat pumps take advantage of the nearly constant temperature of the Earth to heat and cool buildings. They can also be designed to use in radiant floor heating systems and/or to provide a free source of hot water.

Geothermal heat pump systems are incredibly quiet. They require less maintenance, and have a much lower operating cost than ordinary heating and air conditioning systems. And they’re eco-friendly; according to the U.S. Environmental Protection Agency, geothermal heating and cooling is the most energy efficient, environmentally clean and cost-effective space conditioning method available.

How it works

Think of the Earth as a big renewable storage battery for heat. At a depth of 10 feet underground, the Earth maintains a nearly-constant temperature of about 54 degrees, Fahrenheit. In the winter, this underground temperature is usually warmer than the air above. During the summer, it’s usually cooler.

During heating, the fluid in the heat-exchange loop absorbs the Earth’s heat. The heated solution is transferred to the heat pump. The heat pump extracts the heat from the heat-exchanger and is then circulated through the ductwork throughout the building.

During cooling, the system works in reverse. The heat pump moves the heat from the indoor air to the heat-exchanger and the fluid carries the heat from the indoors to the ground. The indoor air heat can also be used to provide a free source of hot water.

The U.S. Department of energy has released this video demonstrating exactly how a geothermal heat pump operates.

Parts of a geothermal HVAC system

The geothermal system consists of a heat pump, a loop of underground pipes called a heat-exchanger, and an air delivery system (ductwork).

Four types of loop systems
There are four types of heat-exchanger loop systems, and all are buried underground. Three of them are closed-loop systems; horizontal, vertical or pond/lake, which recirculate the same working fluid over and over again.

  • Horizontal closed-loop systems require trenches at least four feet deep. They are considered to be the most cost-effective loop systems for residential installations, especially new construction.
  • Vertical closed-loop systems are often used for large commercial buildings and other facilities such as schools. They are used in instances where the land area is limited.
  • Ponds or lakes are generally the most economical closed-loop configuration, especially for large facilities. If a building is situated near enough to a river, lake, pond or other suitable body of water, the heat-exchange pipes can be submerged underwater at a depth of about 8 ft., where the water temperature remains constant. Even when the lake or pond is frozen on the surface, the underground water temperature stays at around 40 degrees, Fahrenheit.
  • In the open-loop system, water is drawn from a well. The well water is transported to the geothermal heat pump where the heat is either extracted to provide indoor heating, or added to, for cooling. The heat-exchange loop pipes, now filled with water or a water/ozone-safe anti-freeze refrigerant solution, carry the heat energy to where it needs to go. There is no contamination or chemical change to the water. Most geothermal systems require 1.5 to 2 gallons per minute per ton of capacity, and the water is usually returned to the same source from which it was drawn.

Benefits of geothermal over traditional heating and cooling

  • Low maintenance costs. Since the heat-exchange loops are buried underground, they can have a lifespan of up to 65 years, or longer. And since the heat pump is kept indoors, safely sheltered from the outdoor elements, it can last for decades.
  • Low operating costs. A well-designed and properly installed geothermal system can provide a range of about 50% to 80% energy savings. It only takes a single kilowatt-hour of electricity to produce about 12,000 Btu of cooling or heating.
  • Return on purchase and installation costs. The energy savings from geothermal systems can pay for the costs of purchasing and installation within a few years. Federal Tax Credits, rebates, or other incentives may be available to help offset these costs, as well.
  • Environmentally friendly. The superior energy efficiency of geothermal is what makes them the most environmentally clean space conditioning systems available. The U.S. EPA found that geothermal systems can reduce energy consumption by over 40% compared to air source heat pumps, and by over 70% compared to electric resistance heating with standard air-conditioning equipment.  Geothermal is also 48% more efficient than the best gas furnaces on a source fuel basis, and over 75% more efficient than oil furnaces.

Is geothermal right for your facility?

Depending on climate, land-space available for the heat-exchange loop, existing ductwork and other factors, a geothermal system may or may not be the best option for your facility.

Whether you’re planning on incorporating a geothermal system into your facility’s new construction, or are intending on retrofitting or replacing your existing HVAC system, there are several things you should always do before making any changes to your HVAC system.

Be sure to work with an energy consultant from the very beginning. An Alternative Utility Services (AUS) consultant will help to reduce the amount of heating and cooling load your facility actually uses. Having the correct heating and cooling load calculations is crucial in determining the appropriate equipment size and type needed for your facility. An AUS consultant will oversee the project, from planning to completion, to help ensure optimal system performance and an expected rate of return on investment.

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