Geothermal Energy Systems - An Intro to Geothermal Power

We tend to think of the climate in terms of hot and cold, but a more scientifically accurate way of thinking about it is in terms of hot and less hot. What we perceive as cold is really an uncomfortable drop in the amount of heat in the air. The complete absence of heat is a theoretical concept called absolute zero, which is calculated as being less than minus 450 degrees on the Fahrenheit scale.

Using the "hot" and "less hot" line of thought, an air conditioner or a heater can be described as a heat mover. In the summer months, the air conditioning system moves heat from inside to outside; in the winter, it does one of two things: either it generates heat using fossil fuels or electricity, or it takes the heat from outside and moves it inside.

This may seem counterintuitive - bringing in winter air to heat the house - but remember that our winters are nowhere close to absolute zero. There is still a great deal of heat out there that can be harnessed, and when it is condensed it can keep a home comfortable in the winter.

Ground Heat

However, it does require a great deal of energy to gather this heat during the months when weather is most extreme. This is where the thermal properties of the Earth come in handy. Just below the surface of the Earth, as close as four feet below the ground, the temperature hovers around 55 degrees. This is heat emanating outward from the planet's molten core.

Instead of drawing winter heat from the outside air (which can feel like absolute zero even if it's nowhere close), a geothermal heat pump draws heat from the ground. It requires much less energy to gather heat from a 55-degree environment than a minus-20-degree environment.

Pipes, Fans, and Antifreeze

Antifreeze is a heat-sensitive chemical that evaporates at low temperatures, absorbing the heat around it like a sponge as it expands into its gaseous state. In a geothermal heat pump, cold liquid antifreeze is run into the ground in pipes. When the antifreeze comes into contact with the 55-degree ground temperature, it heats up and evaporates, soaking up the ground's heat and carrying it along the pipeline.

Fifty-five degrees isn't warm enough by most people's standards of winter comfort, so a compressor squeezes the warmed-up antifreeze gas, concentrating its heat into a smaller area. This concentrated hot gas snakes through a serpentine pipe pattern as a fan blows air across it. As the air rushes past, it absorbs the pipes' heat. This air is then transported through air ducts and blown into the house.

The antifreeze, meanwhile, begins to condense back into a liquid, having given up its heat to the passing air. It then comes to an expansion valve. The effort of expanding causes it to lose more of its heat, and it turns completely back into a liquid. It's ready to start the loop over again.

One advantage of the geothermal system is that it is a type of heat pump. A heat pump is versatile, serving as both heater in the winter and air conditioner in the summer. With the flip of a switch, the antifreeze can flow in the opposite direction and the heat-moving cycle is reversed: in the summer, instead of bringing in heat from the outside, it moves the heat out of the inside.

Advantages

While the geothermal heat pump does use electricity to run, it's more environmentally friendly than a traditional heating/air conditioning unit because it moves heat instead of generating it. It doesn't rely on fossil fuels or electricity-generated heat, which means a geothermal user is pouring fewer greenhouse gases into the atmosphere. It also means the person paying the utility bills is paying for fewer resources every month. These savings mean that a geothermal system can pay for itself in as few as five to 10 years.