Geothermal Heat Pumps / Geoexchange

Wood Pellet BoilersWhat it is:

Geothermal heat pump systems, also known as ground source heat pumps or geoexchange systems, are a proven, oftentimes efficient method of heating and cooling homes, commercial buildings, government buildings, churches and schools around the world. 

Although geothermal heating and cooling is not entirely renewable,  thermal energy "moved" by a geothermal heat pump is renewable.  Electricity is needed to operate the heat pump.  Depending on the system design and the heat load of the building, the amount of electricity used can be significant and expensive. As most electricity today is produced with fossil fuels, from power plants that are only about 30% efficient, the gains made by using renewable, clean geothermal energy can be completely canceled out by the losses at the powerplant. If the electricity used to run the geothermal heat pump is from renewable sources, then the geothermal system clearly benefits the environment.

Geothermal heat pumps operate a little bit like a reversible refrigerator. Rather than take heat (thermal energy) out of food and move it to outside the refrigerator, a heat pump takes thermal energy from the ground and moves it to inside a living space. In the summer, the process is reversed, taking thermal energy from the living space and putting it into the ground.

Advantages:

  • Can be set up for extremely efficient operation.
  • Can be used to heat and cool.
  • Geothermal uses renewable energy.
  • Clean operation. No combustion on site.
  • Long Life (50+ years for a closed loop ground loop)
  • Low maintenance (for a closed loop ground loop).
  • No noisy outdoor units such as you would find with standard AC.

Disadvantages:

  • Very costly to install.
  • Not a good solution for retrofits, which typically require high output temps (lowering efficiency substantially)
  • Units get about 1/3 of energy from electricity which is typically generated by combustion of fossil fuel.
  • High cost of electricity in northeast greatly reduces or eliminates economic incentive
  • Units must run at low output temperatures (100-110°F) for good efficiency.
  • Some ground loop types lower water table and often have high maintenance expense

Ecological Impacts:

The most important impact is related to the electrical energy produced to run the heat pump.  Geothermal heat pumps use electricity to run compressors that raise the temperature of the refrigerant to the desired output level. The higher the output temperature, the more electrical power is consumed.  Much electricity in the northeast is produced non-renewable fuels. There’s also the unfortunate reality that, according to the Dep’t of Energy, electricity power generation and transmission is only about 32.5% efficient. A further 3% being lost in fuel transportation to the power plant. That means that about 71.5% of the energy contained in the fuel for making electricity is wasted.

A second impact, seen with standing column wells, is that water must be pumped out of the ground to raise well temperature so the heat pump doesn't lose efficiency.  This affects the water table (it may lower it).

Special comments

You’ll occasionally hear about another type of heat pump: air source heat pumps. These heat pumps do not have a ground coupling; they use the air for a heat source (heating) and heat sink (cooling). They are actually very much like refrigerators except they reverse for heating and cooling and use outside air for heat source and heat sink. Air-source heat pumps are less expensive to install than geothermal systems because they don’t have a ground coupling. However, they are not as efficient as geothermal systems when the outside temperature is either cold or hot. They work very well for heating when outdoor temps are 45°F and higher, and for cooling when outdoor temps are below 90°F. Outside of these parameters, the efficiency of these systems drops off significantly.

Interested in learning how you can save money and reduce your environmental impact? Simply fill out our short online request form and we can help design an EcoHeat solution that's right for you.

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EcoHeat Quick Fact:

Geothermal energy can be accessed via closed loops, standing column wells, and direct
exchange. Each method has a set of important advantages and disadvantages.