With the recent rise in interest in “all things eco”, especially amongst many Self Builders, Ground and Air Source Heating is becoming increasingly more popular.

The governments “Renewable Heat incentive” makes the idea even more attractive (see later for details).

Both systems are actually very simple concepts to grasp:

There is heat in the ground. The temperature of the ground stays fairly constant below a depth of around 1m – 1.5m (the actual temperature being dependent upon where you are in the world).

There is also heat in the air (even if it’s only 1 or 2 degrees).

Modern “heat pumps” are able to extract the heat out of the ground or air (like a fridge does), and transfer it into your home for you to use.

In Ground Source Heating, the way it does it is by using electricity to power a pump which pumps water (which contains antifreeze) around a length of tubing laid in a trench, in a borehole or even in a lake or pond. – As it travels through the pipes, the water absorbs heat from the surrounding ground (or water) and carries it back to the “heat transfer” equipment, which takes the heat an uses it for space or water heating in your home. – One advantage of ground source heating over traditional heating methods is that the system can be reversed to provide cooling in the summer months if it is required. The equation used as an approximate guide for the efficiency of ground source heating in the UK is that for every 1 unit of energy you use to pump the water round the system, you should gain 3 – 4 units of energy from the system.

With Air Source Heating, the warm air is drawn into the “air handling unit” which passes it through a system which again works in a similar way to a fridge. The heat is taken from the air into the system, from where it is circulated to wherever it is needed.

This system is possibly more practical to install in a new build than in a renovation or conversion project, simply because with a new build, you can sometimes design the system with more flexibility (if your main garden area is at the rear of your house, with no, or limited access, it is going to be more difficult to get equipment round there to excavate the trenches and to temporarily store the excavated materials than it would be if you had an open space before you start to excavate the foundations for the house). If you are thinking of installing ground source in a renovation project, think through the practicalities as well as the costs and efficiency aspects before you make any decision.

The first thing to do is to choose three or four suitable companies to talk to about your project. – The more people you talk to, the more knowledge you tend to gain on a subject, and the better equipped you become to make the right decision. These people will need to have a reasonable knowledge about the ground conditions in your local area in order to be able to advise you on the best system for you (if you are intending to build on ground which becomes rock at 1.0m down you may have problems)

A survey of your land or garden will be needed to ascertain the best location for th e system to be installed, and to make sure the whole thing is going to be practically possible. – You will need either a significant area of trenching to be dug, or you will have to be able to drill vertically downwards to a significant depth, or you will need to have a suitable area of water (which has an inlet and an outlet), for the system to be able to work.

Assuming everything is ok, you can then start to decide who will be the best company to give the work to. – Get references, ask how long they have been installing these systems, and get them to work give you (preferably) a fixed price quote for the work. – To do this they will need to design the system, prepare drawings and calculations etc. – If they won’t give you a definite price or design a system without some form of “up front” payment, you may be advised to look elsewhere. – You need to be able to choose between prices and proposals from at least 2 or 3 companies before you make a decision on what is going to be a fairly major financial outlay.

The cost of installing a ground source system in the UK for an average domestic dwelling will be between £7,000 and £13,000. – Which end of that scale you end up at will have a major effect on the system’s ability to pay for itself over its lifespan.

You will now be at the stage where you need to decide which system (if any) is going to be best for your project. Your choices will generally be between:

You will need to have access to enough land to be able to excavate (usually) significantly in excess of 100sq m of trench to lay the pipe work in. This can be in any configuration as long as gives the total required area. You will need to be able to temporarily store the excavated materials on site for laying back over the pipe after it has been laid.

The coils of pipe can be laid horizontally or can stand vertically. Horizontal has advantages if the ground is hard to dig, as it allows the system to be laid at a shallower depth. The downside to that is that the temperature may be a little lower than it is deeper down into the ground.

(Hint: The earth should be compacted as it is used to re fill  the trench otherwise after a period of time you will notice a hollow developing in your garden – this can be not only annoying and unsightly, but also expensive to correct, especially if you have landscaped the area).

If you don’t have the area of land to be able to excavate the required length of trenching, another option is to install a borehole system. – Instead of the pipe being laid in horizontal coils, it is inserted into a predrilled borehole where it does exactly the same job. This system is normally significantly more expensive to install, but you may find it to be more efficient because of the increase in ground temperature as the depth increases.

This could be an option where there is a lot of ground water present. You have two vertical boreholes (usually between 25m and 125m deep). Rather than a closed tube, this system draws the ground water itself through the system, and extracts its heat in the normal way. – The cooler water is then pumped back into the second hole. – the holes need to be a reasonable distance from each other for this system to be efficient.

If you have a pond or lake within your property which has a water inlet and outlet, you could have the option of laying pipe work in the water in the same way as you would lay it in a trench. – The heat will then be taken from the water (and replenished as the water flows through the pond or lake).

Your ground source heating system can be linked to either you hot water system, your heating system, or both.

Manufacturers tend to recommend that if you are pairing it up with heating, that it is better suited to underfloor heating rather than radiators. The main reason for this is that an underfloor heating system runs at a lower temperature than radiators and the system will struggle to get the water temperature up to a point where a standard radiator can emit enough heat to satisfactorily heat a room. – You would probably need to use oversized radiators to serve the rooms.

The equipment needs to be located somewhere. The average size of a domestic heat pump for a ground source system is about the same size as a standard fridge, so a garage or larger sized utility room is a possibility. – Most of the manifolds (the joints between the outside system and the inside) can be positioned in a “catch pit” or some other store outside the property.

One thing to bear in mind if you are planning on using one of these systems is that manufacturers recommend that you have a well insulated property. – Ground source heating works in a completely different way to the sort of heating we are used to. The process of getting the heat from the soil is not a fast one! – you can’t turn up the thermostat and heat the room quickly (especially with underfloor heating), so making sure you keep the heat you generate for as long as possible is important. – This may make the system less efficient or even impractical in some older buildings where it is more difficult to raise the insulation values throughout the property than it is in a new build.

You can use a domestic single phase electricity supply for the smaller systems, but when you get to the larger ones, you will need a 3 phase supply (check with your installer what you have and what you need if you are not sure).

It is not really possibly to give you accurate quotes for how much you will save by using one of these systems. – There are too many variable:

How much the system costs / which system you use / the insulation values of the house / the type of heating in the house / how you power the system (you could use solar power to power the pumps, which brings in a whole new set of figures to consider) / what fuel it is replacing / how hot you like your house,

As a very rough guide, assuming an average family sized detached house which uses the system to provide 100% of its heating and 50% of its hot water, you could save around £200 a year when compared to gas, £850 when compared to electricity, £150 when compared to oil (depending on the price fluctuations at any particular time) and around £150 compared to solid fuel.

(Do not take those figures and make any decisions based on them, they are very approximate and meant as a guide only. Your property will almost certainly be different from these figures).

The government has targets which it must reach in respect of creating energy from renewable sources. By 2020 in the UK our target is for 15% of our energy to be generated by renewable sources.

At the moment, all the options for renewable energy are uncompetitive in the “short term” compared to the most popular existing energy products, so in order to be able to meet the targets it has been set, the government has got to give some pretty decent incentives to get us all to start to consider the alternative energies.

In Feb 2010, the government published a “consultation” which it plans to introduce in April 2011 which will offer financial support to anyone thinking about using any type of renewable energy.

The idea is to make the whole renewable energy industry as competitive as the rest of the energy producing industry. – There are various ways they plan to help, which can all be read via the Department of Energy and Climate Change’s web site at:  http://www.decc.gov.uk/en/content/cms/consultations/rhi/rhi.aspx.
 

We all need to think seriously about “doing our bit” with regards to conserving energy, and all of the renewable options are things we should now start to consider.

All I would personally say at this time is:  “Don’t get carried away in a “Renewable Frenzy”! – Where, “If it says “renewable” I buy it!”

The reason you are reading this guide is usually because you are intelligent people who are looking to improve your quality of life by taking on a project of one sort or another. So, use that intelligence to “weed out the chaff”, and get down to the “good stuff”! – It’s like I say in the “Insulation” section: There comes a point where adding more and more insulation to a building starts to create “diminishing returns”. – In other words, do your homework, find the system(s) that best fulfil the equation of “cost against benefit”. – If you would have to spend another £10,000 on solar power, just to generate the energy to run your air source units fan, then it’s probably time to say “Well that’s probably not a particularly good idea”.