Light and heat ...

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 ...
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Grelinette
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Re: Light and heat ...




by Grelinette » 02/07/19, 13:33

Christophe wrote:
Ahmed wrote:It is easy to answer the first question, since light and heat are two rather distinct things: there are glazings that stop part of the infra-red radiation and let pass the visible spectrum (it is a matter of wavelength ).


Yes these are low emissivity glazing, except that, generally (in individual housing at least, on skyscrapers it is less safe), they are mounted the other way around: to keep the IR indoors in winter... : Cheesy:

So I do not think the answer is so obvious ... but it all depends on the drop in brightness that we want to support ... today most people want everything for nothing: the benefits without the disadvantages ... It gets pretty painful ...


This is perhaps a possible solution: reversible glazing ... except that it is above all the heat that we want to manage: that it comes in winter but not in summer, while the light must come in summer and winter .

Currently, to stop the heat we close the shutters during the day, which forces us to turn on the lights!

adding: My children often play with toys that change color depending on the ambient temperature. One solution that seems interesting to me would be to construct buildings whose roof and walls change color depending on the temperature.
When it is hot, roofs and walls lighten, and vice versa when it is cold. How about a tile with this property?
Technically, since we make toys that have this property, we should also be able to make construction materials!


Would it be very interesting to test on a small building covered with photosensitive materials, such as a garden shed or garage to see the effect? Are there tarpaulins or glass sheets of this type?
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Grelinette
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Re: Light and heat ...




by Grelinette » 05/08/19, 15:21

I reactivate this subject to ask a question and have your opinions:

I'm going to put a tarp on a veranda to reduce the arrival of the sun's rays that make this veranda a real oven.
The tarp will be placed approximately 10 cm above the canopy, and there will therefore be an air space between the tarp and the canopy.

I read that there was a method consisting in generating an insulating air current between a sun visor and a wall: the air circulation allowing to improve the insulating effect. I seem to remember that this technique is called "Canadian wall", and that this subject was discussed on econology. (What subject has not been discussed on econology? ... : Cheesy: ).

If we admit that a current of air between 2 walls optimizes thermal insulation, we can think that the faster this current, the better the insulation. Thus, it may be preferable to heat the air in an inter-space in order to increase the air flow, and therefore to apply a dark-colored rather than a light-colored sun visor ...

veranda.jpg
veranda.jpg (105.67 KB) Viewed 2168 times


In your opinion, which tarpaulin will be most effective in reducing the interior temperature of the covered veranda:

- the light one on the left, which repels the sun's rays,

- the dark one on the right, which will absorb the sun's rays, heat the air in the space between the tarpaulin and the roof, and generate a larger air current.
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Re: Light and heat ...




by Ahmed » 05/08/19, 16:02

The convective air current tends to evacuate calories and all the more likely that the temperature will be high between the two walls *; however, the caloric transmission is also carried out by infrared radiation: with the dark tarpaulin, it will be maximum and although very difficult to calculate it, I think that this is not the right solution ...

* From a logical point of view, this assertion is uncertain: what is accelerated is the air flow which effectively depends on the delta of T °, ​​but if it causes a drop in T °, ​​the flow decreases. .. On the other hand, the transmission to the internal wall is done by conduction and it is not advisable to raise the temperature ...
Last edited by Ahmed the 05 / 08 / 19, 16: 09, 1 edited once.
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Re: Light and heat ...




by Christophe » 05/08/19, 16:04

And a two-color tarpaulin?

Black above (to promote convection), white below (to limit radiation)?

ps: to my knowledge, all the event marquees (except circus tent) are white or very clear ...

reps: I had confused polarized and chromatic photo in my messages above, it is rectified ... : Oops:
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Re: Light and heat ...




by wirbelwind262 » 05/08/19, 22:50

Ahmed wrote: however, the caloric transmission is also carried out by infrared radiation: with the dark tarpaulin, it will be maximum and although very difficult to calculate it, I think that this is not the right solution ...

Bonsoir
I confirm, a synthetic canvas (even light gray) turns into a radiant panel above a terrace, it's not comfortable at all (and it slaps with the wind ...)
the canvas has been replaced by reed canisse on the pergola, it is much more effective as a "heat shield"

edit:
black above = maximum absorbency and white below = maximum emissivity : roll:
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Grelinette
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Re: Light and heat ...




by Grelinette » 07/08/19, 12:24

wirbelwind262 wrote:the canvas has been replaced by reed canisse on the pergola, it is much more effective as a "heat shield"

Yes but the canisses, certainly more aesthetic and effective, age badly and are quite expensive: to cover an arbor or a veranda of 15 m², the price is around 30 to 50 € with a synthetic canvas, and triple this price with canisses!

(but to make everyone agree, there are canisses in ... PVC! : Cheesy:)
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Re: Light and heat ...




by wirbelwind262 » 09/08/19, 22:27

Bonsoir
have you planned tears and repairs in case of gales?
I live on the seaside, there is always wind and the canvas quickly becomes noisy
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Re: Light and heat ...




by yves35 » 10/08/19, 02:41

Good evening,

the aluminum side of a survival blanket is the most effective at cutting off the effect of the sun

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