Just below the frost line, the temperature remains steady at around 10 degrees Celsius (50 degrees Fahrenheit) no matter what time of the year it is. Geothermal energy utilizes this constant temperature to heat homes in the winter and cool them in the summer. With access to an unlimited supply of 10 degrees, you are able to heat or cool your home on demand. The efficiency of the geothermal system stems from the fact that you are not making heat, but moving it around.
How it works
From the ground up: A closed loop system of 1-inch high-density polyethylene (HDPE) pipe is filled with water. This transfers heat between the ground and the house with a pump. Vertical wells are drilled with a 4- to 6-inch-diameter vertical wall (the number and depth depend on the location of the site and the size of the home). The pipes join together in a header and bring lukewarm water in through the basement walls. Each hole is backfilled with bentonite grout (enhanced grouts, engineered with fly ash are also available) to maximize thermal conductivity between the ground and the pipes.
Above ground: Once the now 10-degree water reaches the house, it is pumped to the geothermal unit. Here a heat pump, (similar to a standard air-conditioner, only allowing for the flow of refrigerant to be run in opposite directions) allows for air to be passed over a coil which is either very cold or very hot, depending on the set direction. This treated air is then sent through standard ductwork to heat or cool your home.
Benefits of geothermal energy
- Geothermal systems provide efficient, renewable heating, cooling and hot water.
- Through energy savings, geothermal pays for itself in a couple of years.
- Geothermal energy requires little maintenance once installed and has few moving parts to break down.
- The systems are safe and there is no risk of carbon monoxide in the home.
- Aesthetically pleasing as most of the system is inside the house which increases curb appeal and the system is smaller than most HVAC systems on the inside too.
- Reduced reliance on fossil fuels and reduced pollution.
Kinds of piping systems
Open loop systems: These systems are less common than their closed loop compatriots. These rely on a water source to provide the cooling and heating effect. Just like the underground systems, water temperature remains constant at 10 degrees Celsius if your pond or lake is deep enough. Here water is pumped into the heat pump inside the building and is used for heating and cooling. When installing these systems, it is essential to conduct a thorough environmental impact study to ensure that there is sufficient water to power the system and that the system will not negatively affect your neighbour’s water supply.
Closed loop systems: A closed loop system is comprised of a series of pipes filled with water containing antifreeze to avoid the risk of bursting. The pipes can run vertically or horizontally depending on your property size. Vertical loops are more common and here a well driller will drill 5 inch diameter wells. Horizontal systems can be cheaper as a ditch rather than a well is utilized when burying the pipes.
Return on Investment
This rate depends on many factors including location, size of the home and the system utilized. According to the International Ground Source Heat Pump Association, geothermal systems are 50 to 70 percent more energy efficient than other heating systems and offer cooling at a rate 20 to 40 percent more efficient than air conditioners. Estimates are that a 2,000 square foot home with a well-sealed envelope will cost only about $1-$2 to heat or cool a day. The average system costs between $20 000 and $40 000, which means that initial investments can be recovered in 4-5 years with 20% ROI annually. If you are considering a new building or a retrofit involving geothermal energy, use the calculator here for more accurate ROIs. Keep in mind however, that geothermal systems operate with electricity (to run the compressor, pumps and fans), which needs to be available in order for the system to function.