Geothermal heating and cooling systems has become the fastest growing method to harness geothermal energy. How does geothermal heating and cooling work? What is the difference between a geothermal closed, open, horizontal, vertical and slinky loop? These are all complicated questions that you will know the answer to after finishing this article.
Space heating is a major energy consumer in both the residential and commercial sector. This is why geothermal heat pumps have had a tremendous growth lately. In fact, over one million units with a total capacity of 12 GW are currently installed worldwide. These appliances have an annual growth of about 10% in total energy capacity.
What are geothermal heating and cooling systems and how do they actually work? We will get back to these questions in a bit, but first we need to answer the following question:
What is a Conventional Heat Pump?
A heat pump can be defined as a device that uses energy to move heat from a thermal heat source and dissipates it in a thermal heat sink. We can reach the same temperature levels with lower energy costs compared to electrical heating or furnaces using other sources of fuel.
Typically, the thermal heat source is the outside air while the sink is inside the building (air-source heat pump), but the process can be reversed when cooling is needed such as during the winter. Note that this means that heat pumps can transfer energy against the natural direction of heat flow.
Geothermal Heating and Cooling Systems
In many ways, a geothermal heat pump, also known as a ground source heat pump (GSHP), works exactly like a normal heat pump would, only with one key distinction: Instead of moving heat between a building and the outdoor air, the energy transfer takes place between a building and a ground source.
When heating is needed, geothermal heat pumps move thermal energy (heat), from the thermal heat source (the ground). As with normal heat pumps, this process can be reversed when we want cooling. The technically correct term to use is geothermal heating, since in principle when a building is being cooled; the ground is at the same time being heated. Efficiency is, among other things, determined by temperature differences.
By using geothermal heat pumps, we often have access more ideal temperature differences, which means that efficiency rates goes up and costs goes down.
How Geothermal Heat Pumps Work
Geothermal heating are not reliant on high temperatures. Geothermal heat pumps are therefore economical in far more places than geothermal power plants, which need high-temperature water or steam to generate electricity. One could therefore use geothermal heating and cooling systems practically everywhere.
Just 3 meters (10 feet) below the surface, stable temperatures of around 10 °C (50 °F) can be found. The ground acts as energy storage for incoming sunlight and even though weather above the surface is far from stable, the temperature below is. This stability is key in geothermal heating and cooling systems.
Although the same fundamental principles behind geothermal heating and cooling systems are the same, there are several different approaches to exploit geothermal energy for home use, each with their own set of pros and cons. Which approach is best suited for your particular situation depends on the following factors:
- The climate and soil conditions where you live.
- How much land you have available for drilling and installation.
- Local installation costs.
The different approaches are typically divided into closed, open loop and hybrid (geothermal heating and cooling systems), which again has several different subtypes (method of heat exchange) as you can see below:
- Closed loop
- Horizontal ground
- Vertical ground
- Open loop
- Hybrid (a combination of those above)
What are the differences between open and closed loop geothermal systems?
Closed loop geothermal systems are the most common. A series of pipes is laid underground and heat-absorbing carrier fluid, usually with anti-freeze properties, is pumped through. This carrier fluid extracts energy from the thermal heat source and dissipates it in the thermal heat sink. It then returns to the source again, completing the cycle.
In some areas, open loop geothermal systems can be used. An open loop system draws water in from hot aquifers. It can be less expensive than closed loops, but mineral buildups can happen. In an open loop geothermal system, you also have to get rid of the water somehow.
What are the differences between vertical and horizontal geothermal ground heat exchange?
Horizontal applications are often the best choice for residential situations. They do need more land than vertical systems, but they are not as expensive. By laying slinky ground loops, the amount of space required goes down.
A vertical geothermal system, which goes much deeper into the ground, has even more seasonal temperature stability than a horizontal system would have. A deep vertical system is usually between 100–500 feet (33 to 160 meters). Commercial buildings often choose a vertical solution since they have a higher output of energy for less land.
Geothermal heat pumps are amongst the most efficient for providing heating, ventilation and air conditioning (HVAC), as well as water heating.