Coolroom insulation

[Goober]

In a general coolroom using 100mm polystyrene panel, is there a formula for working out what would be the dewpoint on the external surface of the coolroom? Very anal hospital engineer insisting that the soon to installed new coolroom external surface will condensate due a gib wall being installed in front of the room. Ther will be a 50mm gap between the room and gib wall. How do I expalin to him this very unlikley?

[Tesla]

Hi Goober
It is not very unlikley that condensate will form. This would depend on the airflow and humidity across the panel. The panel is coated with white titania which is mould resistant, even so it could still form mould. There are extensive calculations on this forum if you want to search for them. to play it safe considering it is a hospital? you could comply with the engineer and build it with thicker panel (at an extra cost). I built over 75 rooms when I was an apprentice in Wgtn, after time the panel - well I'm sure you've seen mouldy old rooms.

[MilosBog]

I will try to find tomorrow a calculator which was used to calculate the dew point for similar stuff...I think that that can be done in most of the software which calculate the U values of walls, of course with slightly modifications

[Goober]

Thanks for the replies.

Telsa, I know where your coming from, although I would expect to see mould/condensation on a really old room. Anyways, things moving forward with discussions with client. And appears happy that the gap should be sufficient, with inspection hatches to be installed to inspect the closed off surfaces, with the option of ventilation fans installed at a later date if required.

[Magoo]

Goober,
generally expressed as watts per square mtre times temp differential. From memory 100mm EPS is 135w/m2 x Delta T'k. If the external temp gets to ambient dew point then condensation will happen. With a 2.0'C chiller and ambient at nominal 20'C I doubt it. A cavity space may require forced ventilation. Check with panel suppliers for actual conductivity factors

[Goober]

Thanks Magoo, I have seen that formula of yours before, but isn't that for working out heat loss/load through the wall?

[smpsmp45]

Interesting situation. With 100mm EPS panels, & for the temp range of -5 to +5 deg, there shall not be any condensation for sure.
As far as surface temperature calculations are concerned, I too am yet to come across any suitable working formula as such.

But there shall be no condensation outside for sure. We have over 200 cold stores & that too in India with high humidity outside working for last 20 years.

[Magoo]

Hi Goober,
basically the formula is the same as for heat loads as posted, you end up with an outer skin temp applying the temp gradient. I am old so will have to refer to Roy Dossett and get back to you.
Perhaps a call to Bondor or what ever they are called these days, they may be able to give you a quicker answer.

But as an example is service enclosures with 100 mm eurothane with a 60'C temp gradient and they dont sweat.
cheers magoo

[tudorice]

try 100mm Poly urethane instead of poly styrene, better results