Condensation Analysis - Vapor Resistance?

[Marc Jensen]

Hello All,

My name is Marc, I am new to these forums and pretty new to IES. Right now I am working on a factory roof, where we would like to see if there would be any condensate forming on the fibre-glass skylights (This construction is not shown in the image, I just used a standard one to show the issue).

Now when I enter into the Project Constructions (Opaque) and select the Condensation Analysis button, I am greeted with:




Now what is the Vapor Resistance of a material. All I found from my research is this:

The vapour resistance of a material is a measure of the material’s reluctance to let water
vapour pass through. The vapour resistance takes into account the material’s thickness, so can
only be quoted for a particular thickness of material. It is usually measured in MNs/g (“MegaNewton seconds per gram”).

Is this what is asked? And why are the defaults 50? Also It would help to have the following:
1) Ability to resize that window so that we can see what is written under vapor.
2) The units, if any or a link to the help page regarding this feature.


When the simulation was run with 50 as defaults for the materials, no condensate formed apart from at -40 celcius and with a delta T of around 50....

Any help would be appreciated.

Marc

[Marc Jensen]

Actually I realise I think I posted this in the wrong section! Can this be moved

[PCully]

Hi,

The Constructions Database User Guide gives some more guidance on this http://www.iesve.com/downloads/help/ve2 ... tabase.pdf

The column is Vapour Resistivity and these values should be set on the material layers in the Construction prior to opening the Condensation Analysis, otherwise you are presented with defaults of 50 for all layers and given the option to override this in the Vapour Resistance dialog.

From CDB User Guide:

Vapour Resistivity: the vapour resistivity of the material or air gap. This field is blank for many materials, but a value must be supplied before condensation analysis is carried out. Values for commonly used building materials are listed in Table 16 in the Apache Tables document.

The unit is GNs/kg.m

You can access Apache Tables from the VE Help menu >> User Guides and there are some standard data on Engineering Toolbox (as well as I'm sure other web resources) http://www.engineeringtoolbox.com/vapou ... _1807.html

Phil

[Marc Jensen]

Thanks Phil!

That helps:) Ok, I will track down some data and tweak my settings to see if condensate will form

Thank you