Low-E, Double Glazing, uPVC, Aluminium, U-values, SHGC

Hi Everyone,
If you have any quesions about your energy rating, or Low-E, Double Glazing, uPVC, Aluminium, U-values, SHGC, acoustics (noise), or anything to do with windows and doors, I will answer all questions, technical, aesthetic or practical.

In addition, if you have problems with windows and doors, ask away.

Thanks
Ed

Hi Ed,

Following on our correspondence from a different thread, would you please be able to clarify the difference between thermally broken and standard frame?

I will check with my builder what he has opted for, but good to be equipped.

So the ballpark quote you provided of 18k was for the single glazing standard frame yeah?
and 28k upgrade cost was for the double glazed but not sure if standard frame or thermally broken or upgraded frame??

Appreciate your response.

Regards,
Kurshid.

Hi Kurshid
Thermally broken frame design separates the inside and outside of an aluminium frame by using a polyamide (nylon) connector.


However, the real litmus test is the performance of windows. Thermally broken, is only as good as the performance of the window, there may be excessive radiation which overcomes the value of thermally broken frames. Our standard window outperforms most thermally broken aluminium frames where energy is concerned because we control the radiant heat movement by restricting the exposure of aluminium internally.

I can't give you a quote as I don't have the details, my comment is a guide only.

Thanks

Does it make sense to pay 2x-2.5x premium in order to move from U=1.8-2.0 double glazed to U<0.7 tripple glazed windows (+obviously better quality hardware and frame)?

There are quite a few asumptions here which I do not agree nothing is said about the frames and insulation around the windows when installed most carpeters ignore proper insulation.
the difference in proce quoted above is very wide in some cases extreme glass costs is not so high for the manufacturer but his intent is to make a very expensive comparison

Thanks for the thread!

We've just new windows and external doors (10 openings in total) installed as part of an extensive home renovation to a single skin brick home with timber frame (1940's bungalow, with brick veneer added in 1980s).

All doors and windows are framed in solid Vic Ash and double glazed glass. We didn't explore all of the various options at the time, but I know these are double glazed with an argon vacuum. I'll assume it's not low-E glass, as that wasn't specified.

I'm happy with that, as we're working with an older building, and these will definitely outperform what was previously there (single plain glass), and these windows were also quite inexpensive.

The only concern is the three big apertures that face West and cop some pretty harsh sunlight for at least half the year. I realise that low-e might've been a better option here, to reduce the heat transfer.

I suppose my question is how much better would it be? Two of the three apertures will be hard to fit blinds (2 sets of double doors), so perhaps the only other options would be to fit an external eave to provide some block.

Keen to hear your thoughts!

Cheers, -Jonny

Sorry I missed your post Jonny,
You are right. Extend the eave over the doors, it beats low-E.

Ed

Hi Ed,
I've been inspecting a number of newly built homes with double glazed windows. From what I've seen, so far all double glazed windows have an aluminum spacer bar between glass panes. I've been reading how aluminum spacer bar are commonly used, but can also contribute to further heat loss.

If an aluminum frame is thermally broken with decent U-Value, SHGC etc. ratings, how much impact would an aluminum spacer bar play in the overall efficiency of a double glazed window?

Regards.

The spacers are included in the WERS Uw rating, so I would only look at the Uw rating.

It is true that a "warm edge spacer" is more efficient that the standard aluminium spacer, but taking into account the impact of the spacer in the overall Uw, the window design is far more important.

The recoorded difference between these would be U 0.1 Watts/m2/oK. But as I say it's built into the Uw that is published in WERS.

Thanks Ed.

Just to clarify my understanding. So regardless the spacer material (to a slight degree), by looking at UW of window, that will determine if the overall window performance will meet my specific requirement. For example, a window with an aluminum spacer can have a better UW rating, verses a window with a insulated spacer, but lower UW rating.

Yes, exactly... Just make sure you compare like with like as far as the glazing is concerned. e.g. 4/12/4 clear.

So with comparison for like with like, so I understand, for example -

4(pane)/ 12 (alum spacer)/ 4 (pane) clear
verse
4 (pane) / 12 (plastic spacer)/ 4 (pane) clear

I am sure if you interrogate the data in WERS you will find an example showing a warm edge spacer versus a standard spacer, for the same window. This should lead you to the conclusion that the difference with warm edge is around U -0.1. Spacers are isolated from the glass and the air by the seal.

If you check the EcoEco, EcoTech windows out, we don't have the warm edge spacer and the window is not thermally broken. but as an aluminium window it beats every other aluminium window in WERS which is not themally broken regardless of air/argon, warm edge/standard and it also beats many thermally broken windows, e.g AWS Thermalheart. We are moving to warm edge as we speak.

Very insightful, thanks Ed.

It is not only spacer, but overall profile itself. For example, this is how one of the best thermally performing profiles in the world look like - you can see that is not only warm edge spacers, but also the number, location, shape and material of the seals, the quantity and shape of the chambers and many others smaller tricks make it perform the way it performs both thermally and acoustically (roughly comparable to moderately insulated brick veneer wall).

And of course, it should be coming with respective glazing (e.g. the glazing itself on this profile performs to U value of 0.5). Profile itself is responsible only for around 33% of the U value performance in Australia, the rest is glazing.