Online Condensation Analysis

[willbish]

Any recommendations for a good online condensation analysis?

Ive been playing around with this one https://www.ubakus.de/u-wert-rechner/?

Its spot on but a lot of the materials are German and its proving difficult matching them to equivalents.

 

 

 

[Ed Davies]

You asked for a good one so I'll go off-topic and mention one I wrote: https://edavies.me.uk/2014/05/cra/

 

It is, as the rubric says, a toy. It doesn't know any materials, you just have to input the physical characteristics you know (though it's reasonably flexible in how you do that but think carefully if the number you have is the resistance or the resistivity, etc) so at least you aren't limited to the ones it knows. There's a “Plot” button at the bottom to get the results. I never actually got round to doing the plotting, it just gives you loads of numbers (which aren't even rounded to sensible numbers of digits).

[willbish]

Thanks @Ed Davies,

 

Looks like green slime heading my way! ?

 

I hadn't acknowledged the differing units of vapour permanence /permeability/ resistance/ resistivity, I'm not pretending I understand these differences yet.

 

For me the Ubakus model is difficult to use because I want to experiment with different roofing membranes; my ecologist has specified a traditional bitumen felt membrane for the bat roost however this conflicts with using full fill insulation in the rafters.

My current thinking/aspiration is to use a vapour permeable membrane for the eaves sections along with full fill insulation, then where the loft space starts transition to bitumen to keep the batman happy. There will be no insulation in the loft space rafters.

 

If anyone has any other bright ideas /suggestions that would be great.

[A_L]

1 hour ago, willbish said:

I hadn't acknowledged the differing units of vapour permanence /permeability/ resistance/ resistivity, I'm not pretending I understand these differences yet.

 

You may find the attached PDF helpful

 

There is a 30-day free trial with a CRA (similar to the one you have referenced) available here http://www.builddesk.co.uk/software/builddesk-u/

Vapour_Resistances includes perm conversions.pdf

[willbish]

Thanks @A_L

 

Would help if I spell it correctly, permeance

 

 

 

[willbish]

As part of a quote for spray foam insulation I got some condensation analysis done.

 

Should I take issue with the following from attached analysis

 

-Outside temp 5*, wouldn't 0 or -5 be better to show larger gradient

-Similarly inside temp 15*, as above, also plainly not accurate

-Missing layer, I will be using an 18mm chipboard on between layers 2 & 3

-Condensation rate of 0.2g/m2h & Condensation rate 60days 284.2g/m2h.

That seems significant but is it?

 

 

[A_L]

@willbish , 15/5°C is the CIBSE defaults for this calculation. I am not entirely sure why they have a positive condensation rate at the interface in layer 2. The vapour pressure is lower than the saturation vapour pressure and the structural temperature higher than the dew-point temperature.

Certainly my own CRA software (operating to the same BS5250 standard) does not indicate a problem, even with chipboard added and a 20/-5°C temperature scenario.

[willbish]

That's reassuring and much appreciated, thank you @A_L