How Do You Calculate Interstitial Condensation Correctly?

[Biggidybo]

Hi all,

I would like to confirm the following calculations as I have had to get each from various sources.


a) Condensation occurs when Vapour Flow is below the Dew Point?

b) Dew point = Temp (DegC) - (100 - Relative Humidity) / 5

c) Vapour Pressure = Relative Humidity (%) x SVP (kPa)

d) Vapour Flow = Vapour pressure / Vapour Resistance

d) I am confused by the next stage in working out the vapour flow for each material, what's the best way this is done?
Is the calculation:

Temperature at material = Temp inside - (Temp inside - Temp outside) x Humidity x U value

what U value do I use for my calculation, the one for the individual material or the one for all the materials added together?


Also in what units would the Vapour Pressure and Vapour Flow be measured?


Thanks for your time


Biggidy

 

[Navin A S]

Yes, condensation occurs when the vapour flow is below the dew point. The calculation for dew point is correct.Vapour pressure is usually measured in kilopascals (kPa), and vapour flow is usually measured in grams per hour (g/h). The calculation for vapour pressure is correct. For vapour flow, the calculation is:Vapour Flow = Vapour Pressure / Vapour ResistanceThe vapour resistance is dependent on the material and should be determined by consulting the manufacturer's data sheets or other sources. The U-value is the thermal transmittance of a material, which is a measure of how well it insulates. You should use the U-value of the individual materials or all the materials added together, depending on what you are trying to calculate.