Geothermal heating

[tonyv]

Hello, all. Having lurked here for several months, I've finally joined, and am ready to pose my first question![:)]

I'm in the final stages of purchasing in the Ariège; hope to complete in September. Initially, it will be a maison secondaire, until I retire in 3 years time. The house dates from the 70s, and is in quite good nick; just needs a new bathroom and kitchen. It's of stone/timber construction, 2 stories, well insulated, double glazed on the ground floor, about 130M² living space, at an altitude of 600M.

However, apart from a massive open firepace (no insert), it's equipped with ancient electric convector heaters, which will have to go! So I'm planning on installing some sort of central heating; there is no town gas available; and I don't like the idea of oil, which leaves electricity.

I rather like the idea of geothermal energy, and have been told that the total cost of installation, when starting from scratch is similar to that of oil. Not sure whether to believe that. There's 4000 m² of ground, mostly level, so plenty of space to sink horizontal captors.

Is there anyone here who has taken this route, or has other experience with this type of energy source? I'd be very grateful for any comments, and possibly any pointers re cost of such a system.

The geothermal installers all make a big deal of the availability of a 50% grant from the state for this sort of thing, but I've not been able to find the detail on how this applies. Again, if anyone has experience I'd like to hear from them.

Cheers, Tony

[andyh4]

Can't help with most of this, but the "grants" are usually rebates on your French tax bill - so until you are tax registered you get nothing.  I assume this will be the case for Geothermal as well.

 

Bon Chance.

[Jonzjob]

It is the case and the % goes down when the house is over 5 years old too. Plus it is only for the equipment and not the instalation, which must be done by a regestered tradesman.

Mind you the TVA is only 5.5%.

If you do take the geothermal route and are in the position of fitting wet underfloor heating then that is the most efficient way of using it because the water temp only needs to be about 35 degC as opposed to 60 odd for rads. We looked into it but with not enough horizontal space without nuking our mature garden and 2 vertical holes costed at 16,000€ we got a condensing boiler instead. That is a fantastic bit of kit and has cut our LPG consumption by about 2/3.

[buckdendave]

Tony

As John says, geothermal works best, i.e. most efficiently, with underfloor heating (PEX/PER pipes under the floor screed, etc.) because it yields low grade heat.  You need to bury quite a lot of pipe (standard small bore PE) - it can be horizontal or vertical, but there are standard formulae for calculating how much you need for the required power.  These connect to a heat pump which supplies the heating system.

Dave

[tonyv]

Thanks, everyone for your input.

I have a stone floor which I'm unlikely to rip up, so no underfloor heating, I'm afraid.

Disappointing words, but hardly surprising, I guess, on the grants front. I'm rather hoping to be paying very little tax in France.

As for the system itself, it appears that no-one, so far, has installed one. I suppose I'll just get some quotes once I'm there, and then do the aritmetic...

Thanks again for your help.

Tonyv

[suein56]

[quote user="tonyv"]
Disappointing words, but hardly surprising, I guess, on the grants front. I'm rather hoping to be paying very little tax in France.
[/quote]

If you are in the French tax system and pay little or no tax then a cheque will be sent to you to cover the rebate.

Sue

[Anton Redman]

Have a look at reversible air-conditioning in particular DC invertors which claim to able to function to - 15 degrees C and offer up to three times the amount of heat output for every Kw used.

[Jonzjob]

It may work down to -15 Anton, but doesn't it get less efficient as the temp goes below +5 or so?? Or is that only the 'normal' reversable kit?

[tonyv]

I assume you are referring to aerothermal heat-pump systems, Anton? Do you have personal knowledge of these working at such low temperatures?

Personally, I would not touch these with a barge-pole, if the outside temperature is likely to drop below 10°C. The phisics dictates that the condenser must be at a lower temperature than the surroundings, which means very much sub-zero in winter conditions. If there is any humidity in the air, that will freeze out on the heat exchanger, thereby neatly insulating it. No heat tranfer - no heating.

Thanks for the thought, anyway.

Cheers, Tony

[Anton Redman]

I did say claim. I would have a look at what the bigger local stores and hotels use for heating in winter. If they are noit using it it will not work in your local conditions. They do clearly become less effecient as ambient temperature declines.

[tonyv]

[quote user="spg"]

If you are in the French tax system and pay little or no tax then a cheque will be sent to you to cover the rebate.

[/quote]

That's interesting, Sue. Thanks for the information.

Cheers, Tony

[Fridgeman]

Hi Tonyv

Not quite as drastic as you say. The condensers are fitted with ice stats so as soon as they freeze over the unit goes into reverse cycle for a couple of minuets to defrost the coil.

The refrigerant in the condenser (which acts as an evaporator in heating mode) is at a nominal -28 degrees C, so unless the ambient is lower than -10 degrees C you still get a good heat exchange, now do not get me wrong here, they are not perfect but in my opinion give a good background heat, if you went for geothermal the pay back period is about 15 / 20 years depending on the cost of installation and on paper they look very good but still no real evidence as they have not been in use for that long on top of that there is the maintenence and any break downs and as there are not many engineers to do the repairs how long would you have to wait in the middle of winter?

I think it is a case of compromise, use a wood burner, an extra jumper, plus air to air heat-pumps (or better still there are now air to water heat-pumps, expensive but nowhere near geothermal) in the bedrooms and as they have timers on them set it up for an hour before bedtime and the room will be cosy also you have the benefit of cooling in the summer.

 

 

[tonyv]

Thanks for those wise words, 'frige; certainly something to bear in mind.

I know of two seperate people here in the UK who had air to water heat pumps which were used to supplement oil-fired CH systems (maybe it was the other way 'round). Not really comparable, as this was in the 80's, when that sort of thing was the rage then; I'm sure they've improved. However in both cases (a) they iced up - despite the frost stats - and (b) they were fiendishly noisy. In one case the guy worked for an alternative energy company, and the unit was supplied and maintained free of charge as part of an evaluation programme. In the other case, the chap was highly technically competent, and tried everything to make it work. They both gave up and chucked them out after a few years. As I said, there is no way I'd consider them.

However, I must take your caveats on board; and the time to repair is certainly a factor. Avenir [http://www.avenir-energie.com/] make it all sound so simple, but that's life!

Hmm, a wood-burner, with heat recovery to the bedrooms may be an option, but so low-tech[+o(]. Maybe storage heaters, but I've not had very good experience with them.

I dunno, I'll just have to get some quotes, and figure it out. I've undoubtedly missed this winter for heating, whatever I do[:(]

Cheers, Tony

[Jonzjob]

As I said earlier Tony. We are very pleased with our LPG condensing boiler. Not too expensive to install and although we use it for ur underfloor heating it will work just as well with a radiator system.

We are looking forward to getting a tax rebate of 25% of the cost of the boiler, our house was built in 1982. Plus we had a cheque for 800€ from Total gas because we have an efficient boiler. The cheque is an ECC thing and nothing to do with Total so that should be the same whoever you are with for gas. LPG or natural...

[Chancer]

I use modern night storage heaters,  there is not really enough heat stored during really cold periods but I am limited by not wanting to pay for a more than 30 amp supply, in fact I draw around 36 amps when they start charging at the same time as the ballon but this does not trip.

So for this reason I have a 2750 watt reversible air con unit which cost €129 from brico depot, the only time the heating function is used is a few cold non winter evenings before the storage heaters are switched on,  or more frequently really cold winters afternoon/evenings to supplement the insufficient heat.

I can confirm that the heat output appears (I can only go by how it feels) unchanged when the temperature has dropped to around minus 12. There are certainly periods without heat while the outside unit goes through its defrost cycle, which of course does reduce the overall heat output but these are only one or two minutes each hour.

I make no arguments with the physics claimed by others but I am very happy with the output and energy consumption. I did manage to check the electrical loading in a rather heath robinson way, the unit should consume 998 watts (including fan) to give 2750 watts of heating, I can use it while the storage heaters and ballon are charging but either the 1200 or 1800 watt vitroceramic hob elements will trip the 30 amp disjoncteur différential, the heat output certainly feels like close to 3KW and I only need to use it for short periods.

[Fridgeman]

Tonyv and all

Todays units are very quiet and as long as you have units running on R410 (Leave R407c units alone) are very efficient, and you will get the 2.5 or 3 kW output as stated on the box it's what it is costing that really matters, keeping it simple at +10 deg C for every € spent on electricity you get €4 worth of heat as the outside temp drops you get €3 then €2 untill at around -15 it is € for € taking into account electric heaters output is approx €1.20 for every €1 worth of heat (you loose a percentage in changing electricity to heat) a heat-pump is a viable heating method, not perfect but good value for money.

Wood burners may be low tech but the modern ones are more efficient than the old ones, good for the enviroment too.