Wood house with high inertia

Heating, insulation, ventilation, VMC, cooling ... short thermal comfort. Insulation, wood energy, heat pumps but also electricity, gas or oil, VMC ... Help in choosing and implementation, problem solving, optimization, tips and tricks ...
airsp
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Wood house with high inertia




by airsp » 23/10/11, 22:04

Hello,

On a MOB, what constructive principle do you recommend to have a strong thermal inertia.

The goal is to protect yourself from the summer heat.

For this case, I'm afraid that a mud brick wall will not be enough for a full house of 120m2.

Do you recommend a lime-hemp mixture on the walls, earth-hemp ...

I admit to being a little lost, to the point of telling me that the MOB may not be suitable for the high temperatures of summer.

Thank you for your advice
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by dedeleco » 24/10/11, 00:17

I admit to being a little lost, to the point of telling me that the MOB may not be suitable for the high temperatures of summer.

I do not understand this fear of the rare heat wave in France!
Where are you ??

A recent wood house is much better insulated than an old house in blocks poorly insulated !!!

So if it is 4 times better insulated for the same inertia, or conservation of cold or heat coming from outside, you need 4 times less thermal mass with high heat capacity to have the same duration of inertia retaining the freshness or the heat in the house !!!
This is calculated, following the conditions for example 38 ° C outside (never in France and current in the USA East coast) and in 28 ° C is 10 ° C to keep which gives a thermal flow half of that in opposite direction in winter for 0 ° C outside and 20 ° C in !!
So you need to know your winter heating power by 0 ° C outside and 20 ° C in, divided by two for these 10 ° C = 20 ° C / 2 and multiply by the desired number of hours of thermal constant !!!
Given the duration of the heat of 8h of day in summer in France (the night is cool in comparison, whereas in the USA the heat wave lasts weeks even the nights) it is enough to multiply by 5 to limit the heating to 2 ° C the 1 / 5 of the 10 ° C at the end of the thermal constant, ie 40h = 5x8h.
The classic breezeblocks have a thermal constant of 24h about a little lower, but with much more thermal losses.
So if this type of old house at 200KWh / m2an asks about 15 to 20KW power for your 120m2 to heat to 20 ° C and 0 ° C outside, with your BBC home to 50KWh / m2an, 4 times better insulated to keep 10 ° C is 2 times less difference of T on 8h, it takes a power of 4x2 = 8 times less 15 to 20KW is 1,8 to 2,5KW.
On the thermal constant of 24 to 40h necessary for 1,8 to 2,5KW of spontaneous clim,taken at 2KW to simplify, it is necessary to store this cold of 2KWx24 to 40 = 48 to 80KWh of 10 ° C of the night in a volume to be determined with the heat capacity of the chosen body indicated on:
http://de.wikipedia.org/wiki/Temperatur ... %A4higkeit
clay (tonboden) 0,88KJ / Kg ° Kx1,45Kg / dm3 = 1,276 KJ / dm3 ° K
either for 10 ° K or 12,76KJ / dm3 to store per liter of clay (concrete 1,66 times more) which gives in KWh on 3600s 12760J / 3600 = 3,54Wh / dm3 or liter of clay or compacted earth !!
So for the thermal constant from 24h to 40h, with 2KW of thermal power coming from outside 10 ° C warmer, 48 to 80KWh stored, ask 48000 / 3,54 = 13,56m3 to 22,6 m3 clay loam (1, 6 times less concrete and tons 1,45 times more) !!!

So if your interior wall is less bulky, your thermal constant will be a little weak !!!
You can add tiled floor tiles for a comparable mass or volume (1,6 times less concrete)!
The walls on the inside must have at least this earth mass incorporated in total, with a good thickness (length of thermal diffusion in the wall to be calculated).
The breeze-block houses with more than 10 tons of breeze blocks ensure this inertia.
BBC ask 4 times less but it is very heavy!

Finally if you take water it will take about 4 times less volume but at least 4 m3 to have a valid inertia of a day!

Finally another solution is to put a heat exchanger underground (Canadian well) that brings the cold of the earth of this volume at least to cool the house, like a free air recovering the free cold of the earth that keeps the memory of the cold of Winter !!
The heat volume of the Canadian well must match the total heat wave duration !!

To store the summer heat for the entire winter of about 120 days, 120 volumes are required to be higher, about 500m3 to 2000m3 between water and earth, and much less if the storage is heated much more than 10 ° C !!.
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by aerialcastor » 24/10/11, 20:44

The management of the summer comfort operates according to 4 parameters:
- inertia
- the phase shift of the envelope
- the reduction of solar gains
- the reduction of internal contributions


For inertia, there are several possible approaches that can be complementary:
- Do not put underfloor heating, and fully use the floor slab as a thermal buffer, with either insulation under slab or vertically outside the basement walls.
- Have a cinderblock wall, concrete bancher or mud brick or cooked without technical doubling that will reduce heat exchange
- Have heavy walls masonry and not placo (the fermacell can be an alternative between the two)



For the phase shift, which is the time that the heat wave will go through the material, dense insulation such as cellulose wadding, wood wool (€€€) or Métis, banish the glass wool of rock and polytruc).
The installation of ventilated attic is a very good solution.

For the reduction of the solar gains, it is necessary to provide a cap or sun breezes on the windows oriented South. You have to put BSO on the West windows. The caps do not work on the West glass because the Sun is too low on the horizon for the cap to shade the glazing.
It is absolutely necessary to avoid the velux to the south unless having shutters.

For the reduction of the internal contributions there is no 30solutions, it is necessary to use devices with low consumptions of energy (class A +). Similarly for lighting, it is better to use low conso lamps see LEDs rather than halogens.
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by bernardd » 24/10/11, 21:54

And put solar panels (photovoltaic or thermal) on the roof with a real ventilation between roof and panels?

We see again that the integration advocated in France is not the best solution ...

The external surface of the roof passes from 60 ° at least if it is in direct sunlight, at the air temperature in the shade of the panels: the heat flow by conduction through the roof depends on the difference in temperature, the heat flow decreases drastically.
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by aerialcastor » 25/10/11, 20:14

Yes it worked too but not so well. It may be enough, and at some point you have to do a thermal study to see if the solution is valid.

We can also ventilate the cover over its entire surface by putting a large counter-litter, but the volume of wood increases quickly so the price too. 9a also places pb on the edge boards that become so high that they are no longer made of solid wood.

The integration of the panels still benefits, it serves as a cover, it is still less tiles to pay.
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by dedeleco » 26/10/11, 01:27

For the question of phase shift with attenuation
Do you recommend a lime-hemp mixture on the walls, earth-hemp ...

the quantitative answer is in paragraph 3
http://www.grasp.ulg.ac.be/nvdw/NVdw/Do ... hermo9.pdf
the values ​​in
http://de.wikipedia.org/wiki/Temperatur ... %A4higkeit
for one oscillation per day (period T of 24h = 86400s) with wood or alternate layers of good insulator and earth or plaster of effective overall diffusion coefficient D = 0,1mm2 / s, gives for attenuation by e ^ 2 = 2,7x2,7 = 7,39 with an external T amplitude of 10 ° C (ie 20 ° C max between day and night), which allows only the amplitude 10 / 7,39 = 1.35 ° C inside the house to penetrate, a thickness of 2xRoot root (TxD / Pi) = 2xRac (86400x0,1 / 3,1416) =104mm thick solid wood or alternate layers of equal thicknesses of clay and very good insulation.
The phase shift is given by the same formula, but the main thing is the attenuation of the canicular oscillations of the day compared to the night by 7,39, to take the average value over a day and to go from 20 ° C outside between day and night to 1,35x2 = 2,7 ° C in !!
Straw, rammed earth or hemp should work about the same, with a little more thickness.
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airsp
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by airsp » 31/10/11, 17:38

Thank you for all these clarifications

Subsidiary question :
- is a lime / hemp concrete wall 30cm (r = 2,3) sufficiently insulated?
- if not, how to increase the insulation without having to add a vapor barrier?
- is the wall lime cuvée cold?

Thank you
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by dedeleco » 31/10/11, 18:53

It all depends on the desired insulation, R = 3 is about 10cm very good insulator but soft without inertia.
Read this site:
http://www.construction-chanvre.asso.fr ... 25_20.html
everything depends on the proportion of concrete and cement.
and the thermal resistance for 30cm increases from R = 3 to 5 by decreasing this proportion.
It all depends on the strength of the wood frame ???
Also see:
http://www.chanvribloc.com/Isolation%20 ... n-ext.html
http://www.chanvribloc.com/wiki/index.p ... e_en_30_cm

Hemp alone leads about twice as cold as the best air-bubble insulators, all soft and non-inertia, so it takes double the thickness for the same insulation and gain inertia.
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by Napo dwarf » 31/10/11, 19:16

some double flow VMCs allow nighttime over-ventilation

otherwise a Provencal well it can help
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by Did67 » 01/11/11, 16:07

What walls are we talking about ???

As said by Arialcastor, a house will be even more comfortable in summer that the heat does not enter (so good insulation, so wood frame without thermal bridges = +++) and that inside have inertial masses that can easily exchange large amounts of heat.

So, even if a few calories come in, because you have to open it well, because we live and give off heat, they will be quickly absorbed and it will continue to be perfectly cool. Otherwise, "thermos flask" effect: super-insulation and a few calories which enter make the temperature rise excessively.

So indoors, especially do not use insulating materials, hemp or whatever: stone (I caricature), agglo filled with sand, stabilized raw earth banchée left bare, bricks of mud left with a wash ... in short, especially do nothing that would upset the exchanges ...

And plan an over-ventilation at night; it must refresh this mass every night, so that the day, the calories can be absorbed without it raises the temperature ...

The ideal MOB would be an old barn with thick walls of stone locked in a MOB at the end!

Finally, in fact, Provençal wells are a way of "deporting" inertia: we use the inertia of the external ground in depth and we bring the cool in summer and lukewarm in winter ...

dedéléco: the Americans would not they be a little kings of the air conditioning ???
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