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  Reply # 357748 28-Jul-2010 15:04
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mentalinc: http://researcharchive.vuw.ac.nz/bitstream/handle/10063/1248/thesis.pdf

Much nicer link. 238 pages - care to give a summary?

"Of the tested products, the low-E secondary glazing produces the largest cost-benefits. At current energy and material costs, secondary glazing was found to not be a financially viable solution in warmer climates such as Auckland. In cooler climates such as Christchurch and Dunedin, secondary glazing was found to be a cost effective retrofit alternative for existing single glazed homes."

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  Reply # 357753 28-Jul-2010 15:08
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i thought dehumidifiers save power, bc dry air takes a lot less energy to heat up dry air compared to damp air.

Also evapouration is an endothermic and condensation is an exothermic reaction.

So Steam -> Water gives out energy/heat.




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  Reply # 358046 29-Jul-2010 00:28
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Very interesting... Page 39 of the PDF (p. 21 as printed at the bottom) has a good chart from Godfrey (1972) showing the R-value change as a function of the cavity width - looks like the optimal width is 20mm, but 10mm is probably also very good - you wouldn't want less than that. I was thinking 5mm would be ok but I think now I'll aim for 20mm.

Also found this: "...the danger of condensation within the air gap can only be reduced by ensuring that both the original windows and the secondary double glazing are efficiently sealed, and providing a desiccant within the air gap to reduce the humidity and hence dew point of the trapped air (Richardson, 2001)" (p.48/30)

Hmm, I actually don't mind a tiny bit of condensation from trapped moisture - it will be virtually nothing compared to what I have now, certainly not enough to create pools of water on the sill!

In essence, the investigation said that any retrofitted double glazing is *far* better than none (if done properly), but in warmer areas (namely Auckland) the cost is too high to justify the savings in heating - though I think they were mostly concerned with market prices of more or less off the shelf products (talking about $70-80 per square metre iirc) rather than true DIY from scratch (Probably closer to $10-$50 depending on material)

I'm actually now considering doing an acrylic sheet that fits within the window sill, sitting slightly back from the window, snugly sitting inside in a strip of closed cell foam around the outside to seal it and protect the paint - very quick, no adhesive or other fixings, dead easy to install and remove.

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  Reply # 358149 29-Jul-2010 10:16
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pih:  

Also found this: "...the danger of condensation within the air gap can only be reduced by ensuring that both the original windows and the secondary double glazing are efficiently sealed, and providing a desiccant within the air gap to reduce the humidity and hence dew point of the trapped air (Richardson, 2001)" (p.48/30)

Hmm, I actually don't mind a tiny bit of condensation from trapped moisture - it will be virtually nothing compared to what I have now, certainly not enough to create pools of water on the sill!



 

That is why double glazing has a vacuum between the two pieces of glass, it is also how yu can tell when your double glazing has broken, there is condensation inside the two pieces of glass

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  Reply # 358446 29-Jul-2010 15:07
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They dont have a vacuum in them, since that would make the class curve inward and look ugly.

They use some argon and something gas which is low at transfering heat.




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  Reply # 358625 29-Jul-2010 18:03
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richms: They dont have a vacuum in them, since that would make the class curve inward and look ugly.

They use some argon and something gas which is low at transfering heat.


Thanks for that, the point is it is sealed, no air transfer



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  Reply # 362301 3-Aug-2010 12:49
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Quick report back.
Have done the double glazing on one childs bedroom and have had zero condensation thus far, however it hasn't been that cold recently so it's not a full report back/pass yet.

To achieve the 20mm target air gap I had to put the secondary glazing on the outside of the aluminium frame.

It cost me $9.95 for some 50mm wide builders tape from the wharehouse, which was white and suitable for outdoors use. We have white frames so that's fine.

The plastic sheeting turned out to be bubble wrap, as I found a big role of it in the shed. It looks rangi as but I don't mind losing the view from this room if it works over winter.  Still lets the light through fine too actually.

What I've learnt so far / I think this is a major:
Double glazing only seems to work (in reducing window condensation) if you are trying to heat a room

If you heat a room with single glazing the hot humid air hits the cold window pane and condenses to water on the cold window surface.

If you heat a room with double glazing, over time the hot air heats the window pane and the air trapped beyond it in the air gap.  This heated trapped air ensures the inside window pane is warm enough not to condense the water out of the air.  This is great and problem solved.

If you don't heat the room, there will be no heating of the trapped internal air, and no heating of the internal pane, and no significant reduction of window condensation.  This was the case for the test window in my room which we don't heat at night, only the childrens rooms.

(The last point above is possibly a reason why some people complain that double glazing doesn't work for them.)

Haven't done the shower yet, have been sick as this last week.  Having trouble finding clear/transparent corflute in Palmerston North.



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  Reply # 362312 3-Aug-2010 12:59
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itxtme:
richms: They dont have a vacuum in them, since that would make the class curve inward and look ugly.

They use some argon and something gas which is low at transfering heat.


Thanks for that, the point is it is sealed, no air transfer

Yeah they don't use a vacuum, could easily break the glass panes over a large window.
There are many types of double glazing, including some that actually are not sealed completely and have small vents at the bottom.
Then there are different types of glass, thicknesses, spacings and with 'e' treatments on some panes etc.  It's all pretty involved and expensive too, but now part of the minimum build standards in NZ.

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  Reply # 362318 3-Aug-2010 13:10
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Thanks for posting back your findings - very interesting.  Let's hope for the sake of DIY-anecdotal-unscientific discovery that we have some cold nights in the next couple of weeks and you can post back with some comparative data :)

Jaxson:
If you don't heat the room, there will be no heating of the trapped internal air, and no heating of the internal pane, and no significant reduction of window condensation.  This was the case for the test window in my room which we don't heat at night, only the childrens rooms.

(The last point above is possibly a reason why some people complain that double glazing doesn't work for them.)


And this is the very reason that I'm going to try acrylic inside the glass window frame - I just can't see acrylic attracting that much condesation, whether the room is heated or not.  In extreme humidity and/or extreme cold perhaps, but not nearly as much as unheated glass.  Acrylic is just not a good enough conductor of heat - but I have yet to test this.



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  Reply # 362336 3-Aug-2010 13:36
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Yeah it is very early days now.

I wanted to be able to still use the windows for daytime ventilation (ie open/close them easily) so mounting on the outside was optimum for my cheap/quick tests.   Acrylic does seem to be the weapon of choice for secondary glazing. 

What I did find that confirmed the importance of heating the air gap, was that in the room that wasn't heated, the bubble wrapped window pane was much warmer to touch during the afternoon sun than the single glass panel.  This was the first sign that the bubble wrap was actually doing something.



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  Reply # 365396 9-Aug-2010 13:56
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Thought I'd post up some pics of the results I've had:

This shows what the window looks like now, and the only tiny strip of condensation down by the lower window frame.  It's ugly as such, but I didn't need that view anyway.  Essentially we have had zero condensation since I taped this to the outside of the window two weeks ago.



This close up shows how the bubble wrap sheeting has been applied to the outside of the window, so I do get the close to 20mm air gap.  (Which seems much bigger than you get with 'real' double glazing?).  Being on the outside means I can still open the window fine.



Anyhow, this photo was from this morning, in a room that is heated by an oil column heater.
Next door is our room, where we do not heat the room at night, and have single glazing.  I cleaned the carpets yesterday throughout the whole house, so the environment was excessively humid for this test.

In contrast to the room above, this morning our room looked like this:
 








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  Reply # 453133 29-Mar-2011 13:44
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Hi all,

Crack up, bringing up a thread from a year ago.  It's getting cold now so I've started to look at the DIY double glazing again. 

The bubble wrap has gone, was ripped down over summer, and the wife found some quite thick clear plastic sheet at spotlight for like $8 a meter.  It's 1.36m wide so 1 meter does a few smaller windows.  Only needed 3 or 4 meters for both the kids rooms.

Looking at maybe some blanket insulation for upstairs to cover these rooms too as I have that blown insulation in the ceiling that shifts and clumps over time.  Not the best really.  Have moved it around a bit though to try and redistribute it properly/evenly so it will be better than last year anyway.

Will post some pics when the windows are done again this year if anyone is interested.

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  Reply # 453138 29-Mar-2011 13:56
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Jaxson: Hi all,

Will post some pics when the windows are done again this year if anyone is interested.


Yup, I am keen.  I am wanting to explore options to make our place a bit warmer.  Have installed insulation in the roof (on top of the 30year old blown insulation) and moisture proofed under the house by laying thick polothene sheeting on the damp dirt.

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  Reply # 453161 29-Mar-2011 14:52
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I had 3M window insulation that I got from bunnings, basically big sheets of glad wrap. It worked to reduce condensation, but it was ugly. I changed it out for acrylic panels, fitted by a specialist company. These work a lot better, and look a lot better too.

With aluminum windows you'll still get a lot of condensation on the metal, no matter what you do. Putting one panel across the whole window space would help, but you couldn't open your windows then. You'd really want the aluminum windows with a plastic spacer in them so prevent condensation, or proper double glazing.

I have blown wool in my ceiling. I decided it wasn't great and got pink batts put in over the top, and it definitely helped a lot. Cost about $1200 for a reasonably large house, and I fitted it myself.




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  Reply # 453177 29-Mar-2011 15:38
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Thanks.

Yeah I just got a quote of $1300 to do our house (100m2 roughly) and that's installed and includes the 1/3 covered by the energy grant thing.  ($650 grant contribution and $1,300 by me so price to company is actually $2,000). 

To be fair that's actually fairly close to buying the raw material myself so that's probably not bad to get the installation fairly cheap or for free. 

I like the idea of raking the blown rockwool and pink batt stuff to one side, laying new stuff and then throwing it all back over the top. 

Or leave it there, level it all out and then lay stuff over the top of the existing stuff.  This approach seems to give a higher system R value by covering the roof 'studs' as well.  eg http://www.nrl.co.nz/main.php?page=202

Yeah I'm going for this thicker sheet plastic over the windows, on the outside.  Intent is to still be able to open the windows, and to produce a 20mm air gap distance as discussed last year here on this same thread.  This is just for my situation, others specifics may vary.

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