Geothermal and Ground Source Energy

Is there a difference between Geothermal and Ground Source Energy?

Not to put too fine a point on it, YES.  Ground Source energy is latent thermal energy stored within the top 100m or so of the Earth's surface.  Geothermal energy is thermal energy emitted from the Earth's core, and can only be accessed at significant depths, i.e. greater than 150m.  The two terms are often used in place of each other, but generally speaking in the UK renewable energy systems of this type use Ground Source energy rather than true deep Geothermal energy.

Well in that case, where does Ground Source Energy come from? 

Ground Source energy is latent thermal energy stored in the ground which is generated and replenished by the Sun.  Every single day the Sun provides enough heat energy to the surface of the Earth to fulfill mankinds energy needs by over 500 times.  Over time, this heat energy penetrates the ground where it is stored at depth like a giant battery.  At an average depth of 6 metres below the surface of the UK and Ireland the ground temperature is constantly 10oC-12oC, regardless of the outside air temperature.  This is continuously replenished by thermal energy radiated from the Sun, regardless of season.  Once you drill down past 100m, Geothermal energy accessed at these greater depths can cause the temperature of the ground to increase up to roughly 1oc for every further 50m of depth. 

So how do you get Ground Source Energy out of the ground?

The basic principal of the most common Ground Source renewable energy systems is to extract this thermal energy from the ground using pipes in dedicated vertical boreholes or horizontal trenches under the footprint or in the grounds of a development.  This is referred to as the ground loop, or geo-exchange.  Water, or more often a water and glycol solution, is circulated through these pipes, entering the system at a lower temperature to the surrounding ground and gently warming as it progresses through.  This principal may also be reversed to dissipate heat into the ground, and thus provide renewable cooling to the building if required.

And then what?

Ground Source Heat Pump systems comprise three basic elements; ground loop or geo-exchange, Heat Pump and heat distribution system.  The low grade heat captured during the circulation process is transferred to a Heat Pump where it is used to heat a refrigerant, which is then compressed, generating further heat.  This heat, in the form of hot water, is then trasferred via the appropriate systems into a usable energy resource providing space haeting and hot water.  The temperature of the water output from the heat pump is typically 35oC-40oC, ideally suited to the requirements of modern commercial heating systems.  As all the components of the system are contained either in the ground or the structure of the building, GSHP's represent an innovative method of utilising a renewable energy source within a building without compromising it's design aesthetic or functionality.

 Resized HP Diagram

 

 

 

 

  

 

 

So what's so great about Ground Source Heat Pumps then?

One of the key features of a Ground Source Heat Pump system is that it represents a  renewable energy technology that is not weather dependent. Fluctuating and unpredictable temperatures and levels of wind and sunshine hours can have a huge effect on the output of turbines, photovoltaic panels and Air Source Heat Pumps and their subsequent efficiency, however seasonal variation and fluctuation have little to no effect on the output of a GSHP or Geothermal system, if designed correctly.  In fact, via software modelling, it is possible to see exactly how a Ground Source system will perform over a 25year lifespan.

Other beneftits of Ground Source Heat Pump systems include a low dependence on conventional power.  A system will, typically, create four units of heat for every unit of electricity used. The source of this electricity used is not important, and thus GSHP systems can be combined with other renewable technologies that generate electricity to create a totally renewable and sustainable package. 

GSHP's have a long service life. In a traditional ground coupled system, the Heat Pump itself will have an average life span of in excess of twenty years and the ground loop in excess of fifty years. The system is incredibly low maintenance, and as it produces no local toxic emissions like a conventional boiler system there is no requirement for annual safety checks.

Via a GSHP, renewable heating can be provided to a building without compromising the design or functionality of the project. As all elements of the system are contained either beneath the structure or within a plant room configuration of comparable size to existing systems, no additional structures, panels or collectors are required.

GSHP technology can be retrofitted to existing systems or structures to provide renewable heating and cooling.

All components of the system are either below ground level or within a plant room setup there are no unsightly additions to the façade of a development, and the technology is not seasonally affected or weather dependent, like many other renewable options.