Condensation in Radiant Shop

Kevin Pulver

I have the IR gun, but no psychrometer. The condensate runs into the floor drain, and flue/makeup are OK, just a few feet out through the wall and up a bit. I'll try to attach a couple photos.
(I didn't do the gas line)Thanks, Kevin

Kevin Pulver

New Steel Building

about 3000 square feet. Has the white plastic-covered fiberglass insulation package in walls and ceiling. (Foam under slab)
The Knight gas boiler is doing a great job, but the owner is complaining of a lot of condensation on his windows, doors, and C-purlins in the walls.
Incidentally, the insulation gets squeezed down to about 1/2" thickness between the horizontal C-purlins and the steel sheeting on outside walls.
He parks an ice covered pickup in it at night and doesn't turn the heat up very far.
I told him it was just a matter of warm meeting cold and the condensation was natural. (I didn't say normal)
I told him I would ask the Wallies. Does he just need to heat it up a bit more past the dew-point or???
I've never had anyone ask me about this before.
Kevin

Brad White

I dew want to point out

a few things.

Now, normally when I see condensation, I first say, "Dang! That has to be really cold!", followed by, "Dang! That really has to be humid too!".

If it is reasonably dry and you have condensation where you normally would not, then I go to how cold the surfaces are getting. Basically an insulation issue or an isolated corner without direct heating. If it is not so cold outside and the same problem, I look for moisture.

The truck is a good start- the floor becomes wet as it melts then evaporates, so the ventilation has to be considered too.

Are they using any propane heaters/salamanders? Any propane fork-lifts? Crowds of people? Full immersion baptisms?

I mean, even a bit of insulation does a lot of good toward keeping things above dew-point (the C-Purlins example). The doors and windows are the "naked truth" sentinels. No insulation but what they came with. If they are condensing, then I suspect high RH.

If the condensation is happening under the insulation, then the interior needs more sealing.

Can you get me some readings on RH, surface and air temperatures? Let me know, I can give you an idea by remote.

A few day/night cycles with a data logger can tell you a lot.

Brad

Kevin Pulver

Well...

Thanks Brad, No forklifts or other sources of heat or water other than parking icy vehicles inside.
Sealed Combustion Mod-Con. (Any potential baptisms would have to be sprinkling type I think.)
It seems just like some of the jobs we've done before.
The only thing is he is keeping the building fairly cool inside. (maybe down in the 50s- I haven't been there to measure.) It HAS been down in the teens here lately, and it HAS been pretty wet I guess if unusual snowfall means anything. And it could be possible that he just now started to heat the building which I guess would make some initial-condensation not to be repeated? Kevin

(I missed your pun initially, but I dew appreciate it. You're quick!)

Brad White

I think you are on track, Kevin

By depressing the temperature of the space, naturally the interior surfaces of the envelope are that much cooler. Also, not knowing how "new" this system is, a good "heat soak" can work wonders.

Say he keeps the space at 55 degrees (in the middle of the 50's for argument's sake). If it is 50% RH in the space, the dewpoint will be about 37 degrees, F. Anything that cold or colder will get condensation on it. The inside surfaces of such a building I would expect, once soaked to the setpoint, to be maybe 5 degrees lower or 50 degrees surface temperature. If this is really the dewpoint, then the RH would be about 82%.

You can see how a few readings will make short work of this, telling which may be the problem. Do you have an IR gun to get surface temperatures? And a hygrometer or psychrometer?

If bona-fide humidity control is desired, a dewpoint sensor or controller is needed to calculate RH and Dewpoint and fire the floor until those surfaces are above dewpoint. The downside is, you can over-shoot comfort in a hurry.

hot_rod

Flue system intact?

condensate piping properly handled?

hot rod

Brad White

Tools

Hi Kevin-

Knowing the concurrent humidity level is equally important.
Even if you do not have a psychrometer, a garden-variety hygrometer will do.

If there is a Radio Shack near you or any good mall, you can pick up one of those portable desktop electronic weather stations for between $25 and $40. Oregon Scientific is one brand. An REI or other mountaineering or outdoors place will have these also. No mountains in Oklahoma, ok ok...

The equipment does not have to be super-accurate. A good pocket psychrometer will run you in the range of $80-$120 for anything worth having, up to $300 or more.

I use a NWS type sling psychromter which ran me about $80 or so ten years ago. I will go digital. I can barely see the mercury (yes mercury) hair line on the scale. I cannot see my own hair line but that is another issue

Paul Rohrs_7

Sling Psychrometer

(in my best Billy Bob Thornton voice)

"Some people call it a psychrometer but I call it a Sling Psychrometer".

Whatcha gonna do with it?

Fixin' to measure humidity wit' it.

Love the movie "Sling Blade",what can I say.


Paul

Brad, the voices are calling you to Denver in April.....Come see.

Tim_41

frost

I have a metal building with the std insulation,door and windows. Its been between 0 and 25 degrees for a month now. I am maintaing 55 air temp and 63 slab temp. I'll get frosty windows in the early am but no purlins are getting condensate.
Do you have a vapor barrier under the foam?

Kevin Pulver

I'm gonna buy me

one o'them sling psychrometers to go with my IR gun.
(Good thing I know a guy with an FFL)
No separate vapor barrier under the foam. "Closed cell Low E slab shield" foam to be specific, and all seams well taped. Thanks, Kevin

Unknown

moisture

You mention the building is NEW.

I've had new home in upstate Vermont condensate so bad that the door knobs had icicles... on the inside!! All this due to the new concvrete and all the fresh paint.

So you have 3000 sq ft of concrete and then bring in ice vcovered trucks.... pretty much a combination for high humidity.

have fun with the sling!!!

scott markle_2

press sleeves

Clean work. Are those Viega press sleeves with upanor hepex ?

I don't remember the guidelines regarding pipe diameter and T spacing but those T's seem really close to me, Can they be to close? if to close does some primary recirculate (mix) even if secondary flows are greater?

How new is the pour ? It's my understanding that is can take a month or so for a slab to fully dry. I would ask how harmful this condensation is, and if the cost of keeping the building warmer is justified. I have heard that one downside to radiant heat in green houses is increased dew on glazing, I guess the lack of air movement has something to do with this.

Radiant is obviously great for building like this but having a few unit heaters in the mix for bringing things up from a cold setback is a nice luxury addition. I like these Modine units

Kevin Pulver

Thanks Scott

You have good eyes. Yes, those are Viega sleeves with the Wirsbo HePex. I just liked the looks of it better than the Wirsbo SSC system and more fun to install than the Wirsbo ProPex expansion system, (though I have those also)

As far as I know, the Tees cannot be too close together. Someone please correct me if I'm wrong. The slab is approximately 7 months old. I buried the 1" supply and returns and got home in time for my wife to deliver twin baby boys that night! The Watts flo-meters are there because our own Paul Rohrs turned me on to them. (and sent them to me also) I really like them. Thanks Paul!
Kevin