Garald Posted May 17 Share Posted May 17 As you know, I have two identical double windows now. (Double glazing on the inside, 18cm space (which I have lined with 2cm cork on all sides, for sound absorption), thick single glazing on the outside.) One has condensation on the outer pane, the other one not. This is obviously a problem I need to solve. What could be the reason? I imagine that the two windows must not be really identical. I can think of two possibilities: (a) in the "bad" window, there is a ventilation exit (from the space between the windows to the outside world) that is blocked or never existed in the first place, or (b) in the "good" window, there is a ventilation exit from the room to the space between the windows that is blocked. Any other possibilities? (For what it is worth, I have PIV - positive-input ventilation: that is, air is drawn in by a fan, and expelled by ventilation exits that are discretely tucked into window frames and the like.. Or so the builder tells me - I can never find them. Not sure the folks who installed the outer windows really understood this (though I've been asking them, to no avail). I do not know whether this is the issue or a red herring.) Link to comment Share on other sites More sharing options...
Alan Ambrose Posted May 17 Share Posted May 17 This the inside of the outer single pane? Maybe just trapped humity when it was installed? Suggest putting some silica gel sachets between the two units - assuming you can get to the space between them. Link to comment Share on other sites More sharing options...
Garald Posted May 17 Author Share Posted May 17 4 hours ago, Alan Ambrose said: This the inside of the outer single pane? Yes. >Maybe just trapped humity when it was installed? No; we opened the windows wide when the parquet specialist came to do a sanding, the condensation naturally disappeared (it was noticeable - the parquet guy was also concerned), we closed the windows back last Friday or so, and it's already the way you see. >Suggest putting some silica gel sachets between the two units - assuming you can get to the space between them. Sure, I'll do that - but that's putting a Band-Aid on a wound. I'd like to get to the reason of the problem. (Besides, I'd have to change the silica sachets constantly.) Link to comment Share on other sites More sharing options...
Temp Posted May 17 Share Posted May 17 I believe the problem is the single glazing on the outside. You can't avoid water vapour getting into the 18cm void and the single glazed outer will be cold. I think it would be better to have a sealed DG unit on the outside, an 18cm gap and SG on the inside. That way the outer unit would be warmer. Probably too expensive to change now. Try putting dehumidifier crystals in the 18cm void? Link to comment Share on other sites More sharing options...
Garald Posted May 17 Author Share Posted May 17 1 hour ago, Temp said: I believe the problem is the single glazing on the outside. You can't avoid water vapour getting into the 18cm void and the single glazed outer will be cold. I think it would be better to have a sealed DG unit on the outside, an 18cm gap and SG on the inside. That way the outer unit would be warmer. Probably too expensive to change now. Try putting dehumidifier crystals in the 18cm void? The single glazed outer layer is heavy security glass, with a decent R. Notice the complete lack of condensation in one of the windows. Notice also that it's not cold in Paris in this time of the year! So clearly there must be another explanation. Link to comment Share on other sites More sharing options...
Alan Ambrose Posted May 17 Share Posted May 17 How airtight do you think the single pane seal is compared between the two windows? Maybe there’s a little cheap battery temp/humidity meter you can put in each one? Link to comment Share on other sites More sharing options...
Garald Posted May 17 Author Share Posted May 17 1 hour ago, Alan Ambrose said: How airtight do you think the single pane seal is compared between the two windows? Right - I suspect that the single pane seal is *not* airtight in the "good" window and that it *is* airtight in the "bad" window, and that it is (deliberately) non-airtight in the inner, double-pane frame - thus humidity is trapped inside the single pane of the bad window. Does that make sense? Or is this much too naïve? I do have a couple of hygrometers/thermometers - let me put them in the two cavities overnight and report back. Link to comment Share on other sites More sharing options...
Temp Posted May 17 Share Posted May 17 Water gets into regular sealed units through the smallest of holes because the gas inside expands and contracts with changes in temperature. That pumps air in and out taking water vapour with it. So unless the whole thing is one triple glazed sealed unit it will be near impossible to keep it out. If the humidity is high small reduction in temperature is all it takes to start condensation. Perhaps the other window gets slightly more sun. Link to comment Share on other sites More sharing options...
Garald Posted May 18 Author Share Posted May 18 (edited) Huh. Left hygrometers/thermometers inside each inter-window space, and the results are not at all what I expected! "Good" window (no condensation): 29.2 C, 74% humidity "Bad" window (condensation) 34.8 C, 52% Temperature indoors: 22.5C Temperature outdoors: 18C Small basil plant in the "bad" window, a pelargonium and a sad geranium in the "good" window. Edited May 18 by Garald Link to comment Share on other sites More sharing options...
Garald Posted May 18 Author Share Posted May 18 90 minutes later: "Good" window: 39.5 C, 57% "Bad" window: 43.3 C, 42% Temperature indoors: 23 C Temperature outdoors: 19 C Link to comment Share on other sites More sharing options...
Alan Ambrose Posted May 18 Share Posted May 18 Hmmm interesting - if I understand correctly that means the good window's dew point is ~30C and the bad window ~25C. That is, with outdoors temps at 19C (and the inside of the outside pane approximately the same) you should have condensation in both. But that's assuming that the RH doesn't change inside each window as air moves in and out through heat expansion/contraction. I guess the numbers at say 3-4am (when it's coldest) would be most indicative. When DGUs fail the condensation gathers and generally stays once the seal is broken. Maybe that's what's happening here. In any case, I think the easily available options are either silica gel (and maybe a better seal) or maybe venting the void better. I should say that this isn't my subject though More knowledge people will be along shortly... Link to comment Share on other sites More sharing options...
Garald Posted May 19 Author Share Posted May 19 (edited) I am now (on a cloudy day, 17C outside) getting almost identical readings on both windows: "Bad" window: 22.8C, 79% humidity "Good" window: 23.5C, 78% humidity - and yet: fresh condensation has set on the inside of the "bad" outer window, and not on the good window! I can try switching the basil and the pelargonium. Waiting for the more knowledgeable people to chip in Edited May 19 by Garald Link to comment Share on other sites More sharing options...
Gone West Posted May 19 Share Posted May 19 1 hour ago, Garald said: I can try switching the basil and the pelargonium. I would remove the plants altogether, which may make it easier to see what other effects may be at play. Link to comment Share on other sites More sharing options...
Garald Posted May 20 Author Share Posted May 20 Wow. I left the plants switched overnight, and now the "good" window (which now has the basil plant between the two panes) has condensation, and the "bad" window does not! "Good" window with basil plant and condensation: 27.2C, 83% "Bad" window with pelargonium and no condensation: 32.2C, 51% Link to comment Share on other sites More sharing options...
Alan Ambrose Posted May 20 Share Posted May 20 Well that's wacky, but congrats on the scientific method. >>> basil plant between the two panes Ah, the plants are *between* the DGU and the single glazing? Well they do do the transpiration thing of course. Link to comment Share on other sites More sharing options...
Garald Posted May 20 Author Share Posted May 20 (edited) Update: the window that now has the pelargonium has some condensation... and the one that now has the basil (and before had no basil and no condensation) now has a stunning amount of condensation (and a stunning 91% humidity at 21.9C). Basil plants are apparently transpiration monsters. Edited May 20 by Garald Link to comment Share on other sites More sharing options...
Alan Ambrose Posted May 21 Share Posted May 21 Maybe you can find some commercial use for that hard won knowledge Link to comment Share on other sites More sharing options...
Garald Posted May 21 Author Share Posted May 21 50 minutes ago, Alan Ambrose said: Maybe you can find some commercial use for that hard won knowledge Hah. If I remember correctly, one of the clauses of my job as a French civil servant is that I should not have another career at the same time, with a single exception: writer. More seriously - I've now put the basil plant outside the kitchen window. An alternative would have been to pair it with a plant that thrives in humid conditions - an orchid perhaps? Link to comment Share on other sites More sharing options...
SteamyTea Posted May 21 Share Posted May 21 The Calvin Cycle. Just yesterday I was chatting to someone about it. Link to comment Share on other sites More sharing options...
Garald Posted May 21 Author Share Posted May 21 Wait, no, the other direction, no? Photosynthesis consumes water, breathing releases it? Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now