geothermal and solar heating for a house

System · February 2011

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!

stephendv · February 2011

Re: geothermal and solar heating for a house

I prefer the passivhaus concept: super insulation, minimize cold bridging, good airtightness and heat recovery ventilation - then you only need a tiny supplementary heating system. Your location sounds ideal for this. Instead of sticking solar thermal panels on the roof, you use the large glass windows and your concrete floor as the solar collector. The thermal mass in the concrete acts as a heat storage medium.

You'll then need to have some form of summer shading for those windows to prevent overheating in summer.

http://www.passivhaus.de/ for the official german standard

and in English: http://www.passivhaus.org.uk/

russ · February 2011

Re: geothermal and solar heating for a house

Passiv Haus - They get a bit carried away with this part, 'the total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120 kWh/m2/yr'.

I like the concept but as usual the organizations get a bit carried away with themselves.

The architects I talked to here including the one we use look at you like you are talking Chinese when you talk about energy conservation.

stephendv · February 2011

Re: geothermal and solar heating for a house

russ wrote: »

Passiv Haus - They get a bit carried away with this part, 'the total primary energy use for all appliances, domestic hot water and space heating and cooling is less than 120 kWh/m2/yr'.

Seems perfectly reasonable to me

Bear in mind that under PH requirements you won't be using more than 15kWh/m2/year for heating and cooling, that leaves 105kWh/m2/year for everything else. In a 100m2 house, that's 28kWh per day - luxury.

LucMan · February 2011

Re: geothermal and solar heating for a house

officialpa wrote: »

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!

Bonjour,
You won't need a geothermal system in the south of France, the climate is extremely well suited to an air to water heat pump. These systems will supply you with all the domestic hot water, heat and A/C that you will require with out the wells.
http://www.daikinac.com/residential/altherma.asp?sec=products&page=53
http://www.raizverde.pt/english/heating/108.html
Sanyo, Fujitsu, Toshiba, and others manufacture these systems for sale in Europe.
The system is setup to use 2 solar thermal panels to assist in HW production.
Also an excellent combination with a solar PV array.

BB. · February 2011

Re: geothermal and solar heating for a house

Remember too that glass windows are poor insulators when compared to an insulated wall...

Shading from summer sun (overhanging roof to block sun) and heavy drapes to insulate glass during winter/nights can help. Some folks here have used large south facing windows in the winter to help with heating.

Using concrete walls to store heat can help moderate temperature swings.

If you are not familiar with the term--Here is some information about heat recovery ventilation systems. Insulated and sealed homes are great for conserving heat/energy--but for some people (like my wife), she can feel very stuffy in such a home without fresh air.

Home Power Magazine has lots of articles about insulating/designing homes for low energy usage.

If you can find homes in your area that have the features you want---Check if you can arrange to visit (possibly with their architect/builder) see if they will meet your needs or not.

Designing the home to set back into the hillside can help insulate and reduce the impact of the home on the property. Making sure the home is protected against ground water/excess humidity from coming in through the walls is important too.

-Bill

russ · February 2011

Re: geothermal and solar heating for a house

The hot water for household use is not free as the suppliers would suggest.

I believe that solar hot water easily beats anything else if you get sun.

The extra pane of glass seems to pay for itself in a few hundred years - looked into that closely and in mild climates I can not see where it can be justified.

Concrete walls normally mean a stucco type finish and external insulation if the French style of construction is similar to here. This type of home can be really well sealed which leads into the next item Bill mentioned - HRV. I have one and love it.

BB. · February 2011

Re: geothermal and solar heating for a house

I am not sure if Russ talking about the "extra pane of glass" is talking about double pane windows or my earlier unclear comment about "extra glass" (I clarified as lots of south facing windows to collect heat in winter).

Anyway--I live in a fairly moderate "Mediteranian" climate (south of San Francisco)--And I really like the double panel low "E" (emissivity--coating to reflect heat and Ultra Violet light) windows I retrofitted into my old homes.

Before, our south and west facing rooms that got full sun would be extremely hot (we would close doors to those rooms to keep the rest of the home cool).

We had moderate ceiling insulation and stucco or wood walls (no wall insulation--50-60+ year old homes) and found that they really got hot (and cold) with the old windows (even if they did not leak air).

Replaced with double pane vinyl windows and found that the rooms instantly were no longer hotter than the rest of the house and reduced outside noise a lot. We also had a friend install double pane windows in a much newer home with more insulation, they did not notice the reduction in heat gain/loss as much--but did comment that the home was much quieter.

You may not have aluminum double pane windows in Europe (and your class of home would probably not use them anyway)--but I would stay away from metal framed windows and doors--Even in our climate, the aluminum frame double pane windows sweat (condensed water) like crazy in even our not too cold winters. People thought their windows were leaking rain water.

-Bill

techntrek · February 2011

Re: geothermal and solar heating for a house

With such a large house I doubt that passive heating will be able to supply all of the heating needs - rooms in the rear, especially if they are surrounded by earth, will need another source. In that case solar thermal would work well, using under-floor heating.

Ground-sourced heat pumps would be a fairly close second choice and have the benefit of providing cooling (if needed). However, the very latest mini-split air-sourced heat pump systems have nearly the same efficiency and don't require wells.

russ · February 2011

Re: geothermal and solar heating for a house

The extra pane of glass I was referring to is for triple pane.

In the frozen north they may be great but not in the climate being discussed.

The low E coatings are wonderful - there are several coatings available for limiting the amount of solar gain and maximizing visual clarity. Same with argon or krypton fill. If aluminum frames are used the thermal break is super important.

The sweating on aluminum framed windows probably means they don't have a thermal break in the frame.

For windows, insulation, equipment - They have everything in Europe that is available in the states. We are a bit more limited in Turkey due to a smaller market and less money spent on high end stuff. The same companies supply it across the world.

Insulation in the roof and on the exterior walls - quite important. I used 150mm of Dow XPS foam on top of the roof sheathing. Even on the hottest days there is adequate sea breeze to keep the house reasonably comfortable.

We have a complete AC system (air to water heat pump) but have yet to use it in two summers.

Russ

System2 · February 2011

Re: geothermal and solar heating for a house

Thanks a lot!
I am also considering using the heat produced from air conditioning the house in the summer to heat up water in the swimming pool instead of just pumping the hot air out of the house and waisting it. Do you know anything about such a solution?

BB. · February 2011

Re: geothermal and solar heating for a house

Do you have a place you can install solar thermal collectors for the pool? Roughly, you would need around 1/4 to 1/1 of the area of the pool as solar panels for heating (depending on your location, how many months of swimming per year, screened or not, etc.).

They work very well and are not usually too costly (although, with the price of oil peaking right now--I do wonder what the black plastic type thermal collectors cost these days).

Using the waste heat from your heat pump certainly can help heat the pool and make your air conditioning more efficient...

Perhaps Solar Guppy will be by to talk about his experience and thoughts.

-Bill

stephendv · February 2011

Re: geothermal and solar heating for a house

Air conditioning - in the south of France? Generally only necessary in a badly designed house. Since yours is a new build you have a golden opportunity to get the design right from the start so that you consume less energy overall.
I lived in a riad in Marrakech for a year - the ground floor was mostly a pleasant temperate in summer while the in-the-sun temp was 40C+. Walls were 50cm thick earth which did the trick.
Since you're on a mountain side you can make good use of earth sheltering, and the French love their concrete almost as much as the spanish which will give you good thermal mass indoors.
It will help a lot if you put the insulation layer outside of the thermal mass. Some good ideas here: http://www.viking-house.ie/quinnlite-passive-house.html

and some more interesting info about insulating for summer temps:
http://www.viking-house.ie/decrement-delay.html

techntrek · February 2011

Re: geothermal and solar heating for a house

officialpa - there are ground-sourced heat pumps which have an option to dump waste heat into a water heater. I'm betting the heat produced isn't nearly enough to affect the mass of water in a pool - too little heat and not enough temperature difference. I would go with Bill's suggestion to use solar thermal for that.

GreenPowerManiac · September 2011

Re: geothermal and solar heating for a house

Would suggest a bit of thought in the design first. Design a home (with future options) to go green. When and able to afford such things, it's pretty easy to convert and add on one at a time. A good balance of all renewable energies would be a well rounded system, ultimately. I have 4 of them so far: Solar,Solar water heating, Radiant floor heating and wind power and enjoy them all. Add one at a time is what I'm getting at.

My next big idea is geothermal cooling to replace my power eating AC compressor, and it's as simple as converting the "A" coil in the furnace, running lines through a circulator pump and to a 500 gallon tank buried in the yard.

geothermal and solar heating for a house

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