Geothermal Systems

Geothermal systems

A Geothermal system is a  central heating system that can harness heat available in the environment to provide space heating and hot water. Low grade  heat is collected from the ground, water or air and compressed by a heatpump to higher temperature heat, suitable for space heating and domestic hot water pre-heating.   The  temperature below the surface of the earth remains relatively constant  throughout the year such that the ground acts as a good heat source in winter.  If connected to wind generated electricity (such as that from airtricity) geothermal technology can offer an offer an emissions free way of heating your home.

Heat Pumps can be economical because some 70% of your heat can come from the ground. For every unit of electricity used to drive the heat pump, 3 to 5 units of useful heat can be generated. Manufacturers generally refer to the ratio between the useful heat produced and the electricity used as the coefficient of performance (COP). With an overall energy efficiency in excess of 400%, compared to 70%-85% efficiency for a conventional oil or gas boilers, this can make  heat pumps very economical.

In Tipperary there are over 200 installations of geothermal systems since the introduction of the Greener Homes Scheme, the most popular system being the horizontal ground collector heat pump.

Description of the System for Ground source and Water Geothermal Systems

schematic of Ground Source Geothermal sytem

• The heat source will be either the  ground or water depending on the system chosen.

• A system for capturing the heat. This will include a network of pipes buried in the groumd to collect and deliver the heat to a heat pump which will transform  low grade  into medium grade heat.
• A distribution system. This will transfer the heat collected  to the house using an underfloor heating system,  fan coil radiators or low temperature radiators.  Traditional radiators are not recommended for this technology as they require temperatures much higher than the ones generated by the heatpump.
• A set of heating controls usually taking the form of a heating programmer and thermostats in zones.

Types of collectors

Ground source Horizontal collectors are currently the most common collectors . Pipes are buried at a depth of 1 - 2m

Ground Source vertical collectprs are used when land is limited. Pipes are buried at 15-20m deep

Open Aquiler Collectors would be used when the heat source is water

Lake/Pond Collectors are used when a well is able to deliver 6L of fresh water per minute per kW installed

Air Source systems

Air source heatpumps recover heat from the outside air.  They work alongside heat recovery systems. While air source heatpumps are cheaper and more straightforward to install your home has its highest heating demand when the air is coolest outside. This raises the cost and lowers the efficiency of these air source heat pumps As the term “pump” implies, a heat pump moves heat from one place to another. In the winter, it moves heat from outside to inside to heat your home. In the summer, it can move heat in the other direction to cool your home. However homes with heat pumps should have a medium to high thermal mass and in that case cooling will not be needed in the summer day time as purging at night enables large thermal absorption in the daytime.

If you decide to proceed with a heat pump it is a good idea to lower the heat demand of your home by insulating efficiently and sealing your home well. Furthermore it is essential to increase the thermal mass well above standard build types. 

Other factors to consider when installing a Geothermal System

• Collector types, area and suitability Horizontal collectors will obviously require a large area approximately 30 m2 per kW installed. The soil type is also important , a free draining clay soil is recommended. Vetical collectors will require one or more bore holes local to your home. 
• Quotations for geothermal systems. Quotations should be reviewed thoroughly . As a lot of ground preparation work may be involved it is worth checking what is included in the quote.
• Geothermal as a retrofit option. It is possible to install a geothermal system only if the  existing heat distribution system is suited.

For more information on Geothermal systems and the grants available

SEAI administers the grant scheme. For more information

Their website also offer additional information on Geothermal systems