Explanation of the working principle of heat from the earth.

What is a geothermal heat pump ?
A geothermal heat pump is an electrically powered pump which converts natural heat energy into energy usable for heating or cooling your home or swimming pool.
One of the characteristics of a heat pump is that it is a heating and cooling system in one. You can switch from heating mode to cooling mode by simply pressing a button on your thermostat. In cooling mode the heat pump extracts heat from within the building by means of the fluid and transfers it down into the cooler earth.

Do I need separate circulation systems for heating and cooling?
No. The same system is used for both heating and cooling. The entire process of heating and cooling is reversible.

How is energy transferred from the ground to the building ?
The earth is capable of absorbing energy from the sun and storing this energy in the form of heat. To convey this heat from the subsurface a fluid (ground water or environmetally friendly anti freeze mixture) is used which is then pumped to the heat pump (or heat exchanger) by means of a normal water pump. This is where the conveyed heat is converted for use to heat the building. During the summer the process is reversed and heat inside the building is extracted and transferred to the subsurface.

Is it possible to use a heat pump for heating as well as cooling?

Geothermal heat pumps – closed loop system
The term ´closed loop system´ is used to indicate that the system in use is closed, i.e. that no fluid gets in or out of the system once the pipes are full. The closed loop system uses an anti-freeze mixture that is pumped round through the heat pump. An open system uses ground water from the bore hole.

Where can a closed system be installed ?
This depends on the space available. The close dloop system can be placed horizontally as well as vertically. If placed horizontally, a relative large area is needed, with the tubes placed at one to two meters deep below the surface. Total length of the tubes depends on required capacity of the system. Approximately 500m of tubes is needed for a 200m2 home.

What if there is not enough space for a horizontal closed loop system ?
Only high density poly ethylene or poly butilene tubes are used for the closed loop systems. These tubes are resistant to chemicals found in the subsurface and have good heat conducive properties. The life span for these tubes is between 50 and 75 years. PVC tube is not to be used for these systems.

How are tube segments joined together ?
The only acceptable process of joining tubes is the process of thermal fusion. Thermal fusion means that the ends of the tubes are heated and joined creating a bond which is stronger than the original material (as with normal welding). Joining tubes mechanically is not acceptable, also because of the use of glue in this process, which will lead to leakage in the longer run.

Will the system be damaged if temperatures go below zero centigrade ?
No. The anti-freeze mixture ensures that the system will not freeze during temperatures down to minus 30 degrees centigrade. Three types of anti-freeze can be used: propylene glycol, calcium chloride (salt solution) and methyl alcohol.

I have a pond next to my home. Could I place a closed system in this ?
Yes you could. As long as the pond is wide enough and deep enough. A minimum level of 1.5m of water is required at all times. High density poly ethelene, poly butilene or copper tubes can be used in a pond.

Geothermal heat pumps – open system
What is an open water source system ?
The term ´open water source system´ is used to decribe a geothermal heat pump system that used gound water from conventional water wells. Heat from ground water will be extracted by the heat pump and fed back into a so called return or infiltration source. Ground water has a constant temperature from about 10m depth onwards and as such is an excellent heat source.

What is the temperature of the ground water?
Ground water down from a depth of around 10m is not influenced by temperature differences on the surface, like weather influence and season changes. In Spain ground water has a temperature that varies between 15 and 20 degrees centigrade, depending on the location. At greater depths the temperature of the ground water increases according to the geothermal gradient of one degree per 100m.

Geothermal heat pumps – parts

Which are the main parts of a Geothermal System ?
Three main parts are:  
- The heat pump.
- The heat conducting medium (water or anti-freeze mixture) of the heat exchanger (open or closed system)

Are all geothermal heat pumps the same ?
No, they are not. There are different types, designed for different scenarios. Many heat pumps are designed to deal with high temperature ground water in open water well systems. Others are specifically used for low temperature environments, sometimes only just over freezing point. Some are only suited for heating homes, others dedicated to cooling and a third type is suited for both heating AND cooling.

Do I have to insulate my home when using a geothermal system ?
What is a closed loop system?

The use of a geothermal heat pump will dramatically reduce your energy bills, no matter how well insulated your home is. Of course, the better the insulation, the higher the energy savings.

Does a heat pump have parts that are placed outdoors ?

How efficient is a geothermal heat pump ?

A geothermal heat pump is three times more efficient than the most efficient heating system based on fossil fuels. Instead of burning fuel to create heat, the only thing that the heat pump does is transferring heat from ground water or the subsurface. As such a heat pump produces three times as much energy as is needed to run it. 

How much does a heat pump cost ?

A geothermal heat pump system is more expensive than a conventional heating system (for example a high efficiency boiler). But you would not be comparing apples with apples. 

To get a good picture of the actual costs you should consider this: 

The efficiency is quantified in the Co-efficient of Performance, or COP. This is a scientific determination of the amount of energy produced by the system divided by the amount of energy needed to run the system. Most geothermal heat pumps have a COP of 3 to 5.5. This means that for every unit of energy that is needed to run the system, 3 to 5.5 units are produced in the form of heat. A heating system based on fuel oil or gas has 50-90% efficiency whereas a geothermal heat pump has more than 300% efficiency.