A geothermal heat pump operates by extracting heat from the ground, and redistributing it in your home. It does this by circulating refrigerant through underground pipes, which very efficiently carries out a heat exchange process. This heat is then used to provide heating, or for hot water. It operates in the same way as a boiler in a home central heating system, but instead of using oil or gas to produce the heat, it extracts ambient heat from the ground.
Looped pipes are buried underground, in a horizontal or vertical array. In a process similar to that of a refrigerator, a mixture of water and antifreeze (or environmentally friendly R410A) is pumped through the pipe array. A condenser then transfers this heat into the domestic heating system, which can be distributed in radiators or an underfloor heating system, or it can be applied to the domestic hot water supply.
Click on this link to see a pop-up graphic of how a geothermal heat pump works, provided by the Energy Saving Trust of the UK (Note: you must have pop-up enabled in your browser).
Advantages of Geothermal Heat Pumps
- Ground source heat pumps produce significantly less CO2 than conventional heating systems, and contribute to you being able to completely lower your carbon footprint. By using renewable energy sources to power your heat pump, your system can become carbon neutral.
- Even though you still use electricity to power the heat pump, this is much less than you would for a normal heating system, and you can eliminate the use of oil or gas.
- For every unit of electricity you use for running the pump, you gain between 3 and 4 units of heat.
- There is a Federal Tax credit for installing a geothermal heat pump, as well as several state incentives.
- The cost of a geothermal installation can be recovered within 6-10 years.
- An average installation can save you approximately $200 per month in heating costs.
- A geothermal heat pump requires very little maintenance, and can last up to 30 years. It is called a ‘fit and forget’ system. This means 20-25 years of almost free heating, after paying back the initial investment.
- The power demand of a heat pump is low enough to justify installing a solar panel power source, or wind turbine (in suitably windy areas) so that no power is drawn from the grid. In fact, with a large enough solar power installation, and a solar water heater, you could end up selling power back to the grid, if that possibility exists in your area.
- You will no longer require fuel deliveries.
Disadvantages of Geothermal Heat Pumps
- Expense – it is expensive to install a ground source heat pump. Costs can range from $12,000 to $20,000, depending on the size and type of installation. This is reduced significantly by the various tax incentives available, but you must often pay up front first. With savings on energy bills, you can recover this amount in 6-10 years.
- Heat pumps do not achieve the same temperatures as central heating boilers. This means that they are better suited for under floor heating, although you can increase their effectiveness by increasing the size of your radiators. It also means that you need to start the heating earlier in the winter or fall, and that the pump will run longer each day than a normal central heating system. Nevertheless, you will still save on costs.
- The ground works required to dig the trench for the underground loops can be expensive and disruptive. You will need to dig at least 3 feet (and preferably 6 feet) down, and hopefully not disrupt any other pipes or lines buried in the same area. You are almost certain to require planning permission in urban areas. If you chose to install a vertical loop, you will need a drilling rig to park on your lawn, to dig three or four holes.
- Ground source heat pumps can be retro-fitted, but they are best suited to new building projects, where the costs, planning permission and ground disruption can be included in the overall building project.
- Geothermal heating is generally only recommended for homes with good insulation and air tightness. This is because the heating levels are not so high that you can afford to lose or waste any heat, like you would with a conventional (more expensive) system.
- Heat pumps require electricity to run, so you cannot claim to be energy neutral, unless you go to the added expense of installing a solar panel array, and wind turbine and a solar water heater to help with domestic hot water needs. The whole package is very expensive up front, but the energy savings are significant, and you could benefit by being able to sell power to the grid.
How Green is Geothermal heat energy?
A heat pump uses about one third of the energy to produce heat that a conventional oil or gas heater will use. However, it still uses some electricity, so it is not totally carbon neutral. It does use a natural, renewable heat source, and it can be hooked up to solar panels and a wind turbine to totally remove the carbon footprint. Overall, it is the most green domestic heating system available, but can only reach its full ‘green’ potential when harnessed with other renewable energy sources in a domestic home.