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Geothermal heating is being specified by everyone from self-builders to developers to local authorities in increasing frequency across Ireland. As a relatively new technology in Ireland, it is crucial that anyone considering a geothermal system knows what they are getting into, to ensure an efficient, reliable heating source.
With over 20 years experience in this field in Ireland, Dr Paul Sikora, Vice Chairman of the Geothermal Association of Ireland explains what issues to be aware of when considering geothermal, from site suitability, to what to look for from suppliers and installers.
Today
many people involved in the building industry will have heard
some mention of geothermal heating. Sometimes it is referred
to as 'underground' or 'pipes in the ground' heating. Both
descriptions are appropriate, but they do little to help us
understand how it works and even less to help us decide whether
it might be suitable for the project we are involved in –
be it building or extending the family home, or designing
an office block, hotel or housing development.
In Ireland geothermal heating is almost always a type of solar
heating because the earth’s crust beneath us is solid
and serves to insulate us very effectively from the heat deep
down. The only hints we have of true geothermal heat are the
few warm springs scattered around the country.
When people speak of geothermal heat in Ireland, they are
referring to techniques for refining or concentrating the
low grade heat which resides in the ground or water around
us. The techniques used will vary with the possibilities of
the site in question, but they all amount to a way of making
part of the site surroundings do double duty as a solar panel.
When viewed this way, geothermal heating sounds more like
a type of architecture. In fact this is a good way to see
it, since the task of identifying, quantifying and exploiting
the geothermal resource is as individual as is each and every
building site. Just as a house is much more than piles of
concrete, timber, glass and slate, so a geothermal heating
system is much more than coils of pipe and a refrigeration
unit. Just as a building requires a design element or architect
as well as an assembly element or builder, the geothermal
system must be designed as well as installed.
Assessment and Design
If you are looking at the possibility of using geothermal
heating in your project the first step should be to see whether
it is suitable for the application and whether it is feasible
to develop a geothermal source on the site. Suitable applications
are those where a geothermal installation could reduce the
life cycle cost of the project and reduce the life cycle energy
demand of the project. In other words it should have a good
prospect for an economic return. The feasibility of implementing
a geothermal heating system is an architectural/engineering
question, which must be addressed before even attempting to
assign a budget to the project.
Geothermal sources can take quite a variety of forms. Most
common is the shallow horizontal array - looking much like
an underfloor heating layout in your yard or garden. But even
this is only the starting point for a design. Other factors
to be taken into account are the composition and percolation
of the soil, the topography, and even the shape of the intended
ground parcel. Finally, one must consider the effect of trees,
of other buried services and soak-aways, percolation fields
and longer term development plans for the site.
Other sites may have water-based geothermal potential. Here
one could mention streams, ponds or lakes, shallow high-yielding
aquifers or even a steady source of waste water. Again the
design exercise must take into account the amount of heat
sought and the ability of the proposed geothermal source to
meet this need throughout the season. The exercise must be
done taking into account the restrictions imposed by the site,
as well as the expectations of the client.
Finally there are sites with little or no free ground space
and no hydro-geothermal potential. Here the direct approach
is to use bored holes to insert heat exchanger loops vertically
rather than horizontally. This technique is well developed
throughout Scandinavia and North America where severe winter
weather makes horizontal arrays less attractive. Accurate
design and proper installation of vertical heat exchanger
loops is essential because they are for all intents and purposes
inaccessible once put in place.
The one thread common to all the above approaches is the importance
of the geothermal supplier doing a comprehensive design exercise
before presenting a detailed proposal. On the other hand most
geothermal system suppliers are busy and will try to separate
out a casual enquiry from a serious interest before committing
to an on-site assessment.
You can do a number of things to get the best value from a
pre-visit budget quotation. Firstly, submit a full set of
house plans so that the geothermal provider can determine
a heat demand figure. Secondly, include a site map showing
as much detail as possible of buildings, paved areas, contour
lines and any permanent features, which could affect collector
design. Finally give an indication of the type of soil found
down to a depth of about 1 metre.
After sending in the above information plus any details of
water-based resources, you should expect to receive an initial
budget-costed proposal for a geothermal system tailored to
your site. If the budget figure lies within the range you
are able to consider and if the projected fuel savings/payback
is favourable, the supplier should be able to arrange a site
visit to confirm details and formulate a firm quotation.
In current market conditions (mid 2004), a well-designed geothermal
system with a horizontal array collector serving home heating
plus domestic hot water can show simple pay back times as
low as 6-8 years. Vertical array collectors or pumped borehole
sources are more expensive, but should still have indicated
payback periods not much over 10 years. Commercial installations
in heat-intensive applications such as wet leisure facilities
or health care institutions can have even more favourable
economics.
Continued
on Page 2
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