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# Different building standards in idf-file

Hello There,

We wanted to simulate several buildings, which all have different heating demands. At first, we changed the conductivity of the materials, to get a higher heat flow towards the outside. Next, we tested the customization of the wall thickness.

In both cases, we got a different annual heat demand, but is there any better approach or is something suggested from energyplus itself?

In Germany there are several building standards like EnEV02 or EnEV16, which defines, how good the isolation of a building is. Therefore, it is necessary to model different annual heat demands.

Material,
EPS_Roof,                 !- Name
MediumSmooth,             !- Roughness
0.476,                    !- Thickness
0.035,                    !- Conductivity
15,                       !- Density
1000,                     !- Specific Heat
0.9,                      !- Thermal Absorptance
0.7,                      !- Solar Absorptance
0.7;                      !- Visible Absorptance

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Changing both the Conductivity [W/m-k] and Thickness [m] are both ways to change the R-value of the insulation material, which is calculated "by dividing the thickness of a material (in metres) by its thermal conductivity (k-value or lambda value (λ) in W/m-K)."

So the R-value for the EPS_Roof material you defined above is 0.476 m / 0.035 W/m-K = 13.6 [m^2-K/W]. These are the correct units for thickness and conductivity according to the Input-Output Reference.

"Unlike U-values, R-values do not include surface heat transfers at the boundary of the element by convection and radiation."

"U-value = 1 / (the sum of the R-values of the layers of the element + the resistance of the internal and external surfaces of the element)"

These internal and external surface resistances are the inverse of so-called "film coefficients." The internal and external surface resistances must have the same units as the R-value, or [m^2-K/W]. The film coefficients have the inverse units, [W/m^2-K].

https://en.wikipedia.org/wiki/Heat_tr...

The R-value is only a measure of resistance to conductive heat transfer, and does not include film coefficients or the effects of convection and radiation at the solid-fluid interface on either side of a surface element.

Depending on the tool you are using and whether it supports Ruby scripting, you could add measures that change the R-value of certain materials directly, rather than editing Material properties by hand in the IDF. You can find such measures on the Building Component Library. https://bcl.nrel.gov/. Try searching for "R-value" or "insulation" and filter by "envelope measures."

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Thank You very much :)

( 2021-07-29 03:16:13 -0500 )edit