geothermal and solar heating/cooling for a house

[officialpa]

Hi,
I have a house in South of France and I am planing to rebuild it totally. The house is about 600 square meters (6 460 sq feet), on a south facing hill, on the hight of 555 meters (1 820 feet). The structural work is concrete and the front elevation will be all glass. There is little flat surface around the house, most of the land is on slope of the hill. I am considering geothermal heating and/or solar panels. Do you think this is a good idea for such a house or should I go with traditional heating/cooling systems? What would you advise? All advise and ideas are much appreciated!

 

[semipro]

Geothermal is great. We use it but it sounds like this location just begs for passive solar, for heating at least. Do you really need air conditioning during the summer or could you get by with ventilation?

 

[officialpa]

There surely is a need for AC! It gets really hot..

 

[benjamin]

Does the area get humid as well as hot? and does it cool off much at night during the hot spells? Since you have the concrete already and you say you're totally rebuilding, it would be a shame not to take advantage of the mass by putting it inside the "envelope" as much as possible. If the climate is right then the mass can provide comfort in summer as well as winter. About all I know about France is your climate is milder than the latitude would suggest to us Americans.

If you have to have AC then I would consider geothermal the first choice for heating and cooling. Passive solar, very efficient construction, and wood backup makes a lot of sense with or without the geothermal. Solar panels for winter heat (as opposed to domestic hot water) don't make much sense over here, but it depends on other factors for you.

Please tell what your price is for electricity, and how much sun you get in the heating season. Also, are there any sites similar to this (alternative energy, home design etc.) for your area, so we can get a different view of things.

 

[semipro]

There surely is a need for AC! It gets really hot..

Check out "ductless" heat pumps. There's been a lot of discussion here lately on them. They offer flexibility, zoned cooling, and high efficiency. One or more of these units combined with passive solar may work well for you. With lots of thermal mass and a southern exposure passive solar should be very effective... and inexpensive.

 

[Jerry_NJ]

My geoghremal uses vertical, not horizontal, buried heat sink/source. I have two vertical loops that go well into the water table which makes them very good for transfer of heat. The unit provides a COP (heating) of nearly 4, i.e., 4 time as much heat per killo-watt as would be delivered by a resistive heating strip. The cooling runs in the range of 20 and both of these are independent of the air temperatures. Here in New Jersey USA the cost of my heat with geothermal electric is about half what one pays with oil heat at $3 a gallon for #2 oil. I also have a wood stove fireplace insert, thus my main interest in "hearth.com". But, as I have to buy most of my firewood, wood and electric cost me about the same. I do enjoy a wood fire heat and do use it, but it doesn't same me a lot of money.

My heat pump is about 16 years old and has have no maintenance cost until the last couple of years when I had to replace the main multi-speed blower (forced air) and later the dual ground loop circulation pumps. Both repairs were expensive and totaled about $2K US. Taken over the 16 year life this is a small amount of maintenance cost. I assume the compressors will go something in the near future, but for now they "sound" and work great.

I made some measures and found the COP and heat output still on factory specifications. The COP came in at about 3.8 in stage II (high) heat position. stage I has higher efficiency as it makes uses the full system resources to deliver less heat.

PS: South of France, near Nice? I have been to Nice many time on business and recall it as subtropical, i.e., not much need for heat, but need for cooling. I recall being there in July and while it was hot during the day, there was a rain shower on many of the afternoons which cooled it down a good bit. Nice is, of course, on the Bay of Angels of the Med, so that must moderate the weather a good bit. I suppose higher elevations get cooler.

 

[Later]

+1 on passive solar

 

[officialpa]

Thanks for the advice. I am also considering possible ways of using the heat produced from air conditioning the house in the summer to heat up the water in the swimming pool instead of just pumpming the heat out of the house? any ideas on how to get round that?

 

[semipro]

Thanks for the advice. I am also considering possible ways of using the heat produced from air conditioning the house in the summer to heat up the water in the swimming pool instead of just pumpming the heat out of the house? any ideas on how to get round that?

Its called a desuperheater. This article has some of the basics. http://www.popularmechanics.com/home/improvement/energy-efficient/1274631

You'd probably be better off having a desuperheater supply your domestic hot water and leave the pool heating to some inexpensive solar heaters. There are some pretty innovative ones out there, some as simple as loops of black poly tubing laid out in the sun and fed by your pool pump.

 

[Jerry_NJ]

Right, I have a desuperheater on my geothermal. In the summer the heat it dumps into the hot water tanks is free, give I would otherwise be throwing it away. There are also standalone units for the hot water heater. Now none of these designed to heat 50 gallons of water (albeit to 150 degrees Fahrenheit) would add much to a pool size "sink". Yes, if you get much sunshine the black tubs in the sun and a circulation pump would work well, the problem is placing the black pipes out of sight. I know from my garden hose that within a hour of summer sun the whole hose is full of hot water, I'm talking 100' of 5/8" hose. Same would be true for a larger diameter black pipel There are solar collectors on the market too that you can just install, no need to construct the loops.

 

[benjamin]

A desuperheater will heat a small amount of water to a higher temperature but most of the heat goes to the water heat exchanger. You can hook a heat exchanger to the water loop to heat the pool water, it would take a couple of valves, another pump for the pool (unless you use an existing pool pump) and a big heat exchanger because you want to keep the temp difference as small as possible. If you didn't have treated pool water, no chlorine etc, you could pump the pool water directly through the heat pump just like lake or well water.