Insulated window frames

Prodigalson

Trying to decide on the windows for our direct labour build and wanted to put this up for discussion.

The build has minimal North facing windows and fairly high amount of glazing on South/West aspects.
Everything will be put through the PHPP prior to final decisions but just in the mean time I trying to get my head around the various options.

From experience or anyone's opinion's which of the following would be considered to most suitable.

[A]Triple glazed window where the frame is not insulated but has an overall frame/window value of U=0.80

Or

A double glazed window with an insulated frame,I waiting on the over all U value for this but lets say it's U=1.0 for discussion but it may be slightly higher.

The wall U-value will be between 0.15-0.17 all going well so is it a waste of cash opting for [A] or would people still feel the triple glazing comfort level is the way to go?

How important is the insulated frame when not attempting to go fully passive?
Would insulated frame lessen the chances of condensation in double glazing?

Thanks in advance.

atech

Prodigalson,

Would you be able to PM me with the name of the manufacturer/suppliers of these please.

To get values like those you are probably looking at something like:

Triple glazed window- Ug= 0.6 Uf= 1.1
Double glazed window- Ug= 1.1 Uf= 0.7

In this case the the double glazed window has more of a chance of condensation on the glazing, the triple glazed has more of a chance on the frame.
However, If your windows become larger than 1.3x1.5m in size the triple glazed becomes better because there is a better proportion of glass to frame. And as you said the comfort level standing next to them would probably feel better.

In terms of cost I think you will have to put both into the PHPP and see what difference that makes to your heating and energy demand and see what the payback period would be.

I just did this with one i've been messing around with and it didn't actually make a huge difference (maybe €150 saving a year if i calculated correctly).
Every house is different though so it may be worth it in your case.

sinnerboy

Thermal comfort is a key factor. During the heating season the glass surface temperature of a double glazed window will drop to about 16 degrees - triple glazed will drop to about 18 degrees .

Now you may think 2 degrees difference - so what ? The thing is you will feel the difference . The ambient internal air at 20 degrees , the surface temp of double glazing at 16 degrees will be sensible i.e. your body will sense it - and won't like it .

You may say - heavy curtains then - and thereby drop the surface temp of the glazing lower and increase the incidences of condensation .

To eliminate this discomfort you will need rads next to the window
- therefore , distribution pipework , zone controls ( valves + stats ), and of course a space heating unit (boiler / heat pump ) . If you follow the PHPP process to its logical conclusion you can instead provide space heating by pre heating the supply air from your HRV .

PHPP will show you that
- if keeping to the same overall energy demand
- you will spend more on insulation for walls/roof to compensate if you lower the window U Value
- than you spend on the extra over for triple glazing .

Prodigalson

Thanks
atec/sinnerboy

atec here's the triple glaze value I was given from the quote

Total U value of glass = 0.6W/m2K
Total U value of frame and glass combined = 0.80 W/m2K

Double glaze
Ug = 1,1 as you suggested,

I can't see an overall U value on the manufactures web site and I only request a quote on the triple glaze as comfort is key to my wife she'll definitely feel the 2 degree drop that sinnerboy is suggesting.


Will PM the manufacture web site.I can't find any reference on them having been used here before,the Irish distributor is only placing the first orders at the moment so still untested in this country but the product looks good in the show room(for our taste),fairly chunky with solid hinges/handles which was my issue with some of the triple glazed units we viewed.
I have no involvement with the product so any opinion on what you see web site would also be appreciated.

Sinnerboy we're going underfloor and HRV so has you say the PHPP is the real answer to my concerns,all the research is only sending me in circles sotime to get some real figure to make the decisions.

Appreciated you thoughts it great to have a resource like the boards when your starting to build,it might just keep me sane.

sinnerboy

Ug of 1.1 will result typically give a whole window U Value of about 1.4 ( size approx 1.2x x 1.4m with 1 vertical divider - 1 fixed ope 1 opening) .

More frame %, less glass % will increase the U Value 1,5 ~ 1.6 ~ 1.8 etc

atech

Prodigalson,

Thanks for the PM.
From what you said I think you are refering to the Alu Therm Windows (Timber with Aluminium Clad with Insulation Between).

I seen on the manufacturers website that a solid timber frame double glazed window, Ug 1.1 also, had a Uw of 1.2.
On the suppliers website a similar Alu Therm double glazed window, Ug 1.1, had a Uw of 1.1. There was cert's to back up that one.

So I think their is a good chance the double glazed option would come out at an overall u-value of around 1.1 alright. Make sure you get a cert though.

In any case though your probably better off going for the one with the better glazing u-value as percentage wise your probably going to have 60-80% glass and only 20-40% frame so as sinnerboy said you'll feel the difference in comfort and save on heating.
And probably more importantly keep the other half happy

sinnerboy

atech wrote: »

a similar Alu Therm double glazed window, Ug 1.1, had a Uw of 1.1. There was cert's to back up that one.

With respect Atech this is very suspect . Granted I have not seen what you have but Uw = Ug is impossible . The Uf ( U factor of the frame ) will always devalue the Uw to below the Ug .

For PH one must also factor in Si spacer ( linear thermal transmittance of the glazing unit spacer ) and Si install (linear thermal transmittance of the installation detail i.e. fixing method frame to wall .

Uw = Area g * Ug + Areaf * Uf + Si spacer * spacer perimeter length + Si install x frame perimeter

Any evidence of this on the cert you saw ?

atech

No disrespect taken. I'm wary of alot of manufacturers/suppliers claims too.

In this particular case I think the cert looks fairly valid. It doesn't show the SI values but clearly shows the Uw. It was done by ift Rosenheim which is approved to carry out testing/certification. I'll PM you the cert to see what you think yourself.
Note the frame manufacturer has also got 4 passive house frames in the PHPP with Uf values between 0.73-0.95.

sinnerboy wrote: »

but Uw = Ug is impossible . The Uf ( U factor of the frame ) will always devalue the Uw to below the Ug

I think in the majority of cases you are correct but if they are using a frame with a Uf of 0.95 and the SI values are 0.04 then it would come out equal to the Ug.
I got a window u-value calculator which I downloaded from somewhere, it's fairly good at working out the Uw. I'll send ya that too, might be handy sometime.

Prodigalson

A final post to say thanks again,very informative posts......
The Irish supplier has spent a lot of time checking out this company prior to getting involved and was also happy with the certs provided so decision made from my side,that's one thing off the list.....

sinnerboy

atech wrote: »

sinnerboy wrote: »

but Uw = Ug is impossible . The Uf ( U factor of the frame ) will always devalue the Uw to below the Ug

I think in the majority of cases you are correct but if they are using a frame with a Uf of 0.95 and the SI values are 0.04 then it would come out equal to the Ug.

atech - you are right of course I should not have stated "impossible"

Uw = Ug can be achieved if the Uf is better than Ug .

I would caution anyone reading that the moral of the story is to look for a detailed breakdown of the thermal performance of components making up the whole window . Certain suppliers will push details of the performance of the glazing only . If they are not keen to talk about the frame as well - be suspicious .