insulation gain formulas

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 ...
Stephen King
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Registration: 26/11/09, 13:28

insulation gain formulas




by Stephen King » 26/04/10, 13:45

Hello to you,

I would like to calculate the daily, monthly and then annual gain after replacing a window to then estimate the return on investment time for this work.

Are there formulas and if so which ones? Or if not what are the elements necessary to evaluate my gains (in kWh)?

After why not I would like to do the same for doors, walls and roof spaces.

Thank you very much!
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dedeleco
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by dedeleco » 26/04/10, 15:15

Depending on the conditions, in particular the characteristics of the old window, with or without significant air leaks, surface.
The most profitable is to seal the leaks with flexible commercial rubber bands.
The method, without air leakage, is to use the losses of the different elements in W / ° Km2 of the house (supplier data or estimated), then multiply by the surface and summed, then multiply by the difference of temperature between indoor and outdoor and multiply by the price of KWh !!!
Almost obvious, to calculate before and after the planned works !!
So the most profitable is to insulate the largest, most poorly insulated areas (especially without insulation), such as the attic and then the walls, often the windows, which are often small (and also air leaks, such as by a chimney not closed or a VMC or a poorly closing window !!).
Finally the insulation must respect the basic advice, such as absence of humidity which destroys the insulation (vapor barrier on the hot side, except breathable insulation).
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Stephen King
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by Stephen King » 26/04/10, 21:32

Good evening deedeleco and thank you for your response.
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aerialcastor
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by aerialcastor » 26/04/10, 21:51

To calculate the losses it is necessary to use the DJU

She
D (kWh) = U (W / m² / K) * S (m²) * DJU (K) * 24 (h).
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by dedeleco » 27/04/10, 01:08

I have to correct my answer a little because I mixed the units of Watts to Kwatts and therefore divide by 1000 to find the dissipated power in KW then multiply by the operating time in hours (24 per day) all winter then multiply by the price of KWh, because I limited to the price of one hour of heating !!
Finally for a more complete calculation showing the real problems, but figures to be evaluated according to your reality:
http://jehhan.ifrance.com/chauffage/p56.html
http://jehhan.ifrance.com/chauffage/index.html#sommaire
A classic house is inhomogeneous and therefore the thermal losses are complex with the thermal bridges of the very serious concrete slabs which pushes to insulate by the outside but with a price which often is paid for only after more than 15 to 30 years currently.
If the price of fuel goes up, it will be different.
See also the passive house:
http://pagesperso-orange.fr/archicaro/accueil%20MP.htm
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by moby25 » 30/11/10, 15:12

We must especially take into account the comfort gain.
Because in my opinion a lot of work is not really profitable in the short or medium term. For example, changing all your windows with quality glazing is generally quite expensive.

I doubt that we save 1000 € of heating per year in the majority of cases.
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