BER Consultants: Real U-Values For Shuttered Glazed Walls.

BER Consultants: Real U-Values For Shuttered Glazed Walls.

Postby teak » Tue Jan 12, 2010 2:02 pm

Glazed walls on south faces of new houses are becoming common.
As are open plan Kit/Din/Lounge areas.
But no one wants the bill associated with heat losses through large
glass areas in winter nights.
My (hardly original) solution would be insulating shutters.
Placeable outside the glass wall/window if a porch or verandah adjoins.
Otherwise inside.

Does anyone involved in BER work know a source of actual data (not
merely estimates based on material properties) for insulation shuttered
glass wall units and/or guidelines on efficacious design of same ?
teak
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Re: BER Consultants: Real U-Values For Shuttered Glazed Walls.

Postby henno » Tue Jan 12, 2010 9:21 pm

teak wrote:Glazed walls on south faces of new houses are becoming common.
As are open plan Kit/Din/Lounge areas.
But no one wants the bill associated with heat losses through large
glass areas in winter nights.
My (hardly original) solution would be insulating shutters.
Placeable outside the glass wall/window if a porch or verandah adjoins.
Otherwise inside.

Does anyone involved in BER work know a source of actual data (not
merely estimates based on material properties) for insulation shuttered
glass wall units and/or guidelines on efficacious design of same ?


most triple glazed units available on the market would actually have better performance u values than say a cavity wall with 60mm PIR insulation.... the selection of the standard of glazing will have a much greater impact in insulation than another "stick on" technology... and perhaps much more economical as well....

but if you were to go down the shutter route id comment as follows:
1. the shutters, when closed, should provide as sealed a cavity as possible. A draughty shuttering will have little if no insulating affect.
2. the internal face of the shuttering should have a reflective surface to reduce the emissivity of the cavity, thus improving insulation performance.
3. the choice of material should have high thermal resistance. Plastic coated metal is perhaps a strong choice. Wood will not be able to keep the standard of sealed cavity required. Aluminium or steel alone will simply allow trapped heat dissipate quickly.

the main use of shutters originally were two fold, the protection against wind driven precipitation, and the reduction of heat loss due to parallel wind movements. By creating a smoother surface along the buildings facade, the wind heat loss effect is greatly reduced.
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Re: BER Consultants: Real U-Values For Shuttered Glazed Walls.

Postby goneill » Wed Jan 13, 2010 12:07 pm

http://www.historic-scotland.gov.uk/roger_curtis_improving_traditional_building_performance.pdf

This man gave this lecture, or one very like it at Boyle before Christmas.
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Re: BER Consultants: Real U-Values For Shuttered Glazed Walls.

Postby teak » Thu Jan 14, 2010 3:14 pm

This is a new build. To decent semi-passive spec.

So non-glazed parts of the external walls would have U ~ 0.18 W/(m2K).
Having a glazed part with U ~ 2.0 W/(m2K) would create draughts,
especially in any open plan area.
[I think U ~ 2.0 is a realistic figure as the best A-class units have a
U value of 1.40 and one must make allowances for door/windows in
the glazed area.]

Problem is that to bring U down to ~ 0.2 with external shutters is
not very attractive from a purely economic viewpoint.
PIR K-12 insulation is €22 per sq m inc. VAT.
With the ply casing, hinges, seals and flaps, guides+ tracks, fasteners
and skilled labour I'd put the final figure at €1,500.
Expecting to save 90% of 120 day winter heat loss (€120) through the glass,
the payback period is > 10 years.
Certainly not a home improvements loan proposition !
Yet for freedom from draughts and conservation of energy, it is a quite
desirable thing to do.
It is so hard to get good realistic data.
All one can get within the industry is that limited data that helps a particular
vendor's case for selling insulation, frames, glass, etc.
We need a Building Services Research Centre in Ireland.
teak
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Re: BER Consultants: Real U-Values For Shuttered Glazed Walls.

Postby henno » Thu Jan 14, 2010 5:13 pm

teak wrote:This is a new build. To decent semi-passive spec.

So non-glazed parts of the external walls would have U ~ 0.18 W/(m2K).
Having a glazed part with U ~ 2.0 W/(m2K) would create draughts,
especially in any open plan area.
[I think U ~ 2.0 is a realistic figure as the best A-class units have a
U value of 1.40 and one must make allowances for door/windows in
the glazed area.]

Problem is that to bring U down to ~ 0.2 with external shutters is
not very attractive from a purely economic viewpoint.
PIR K-12 insulation is €22 per sq m inc. VAT.
With the ply casing, hinges, seals and flaps, guides+ tracks, fasteners
and skilled labour I'd put the final figure at €1,500.
Expecting to save 90% of 120 day winter heat loss (€120) through the glass,
the payback period is > 10 years.
Certainly not a home improvements loan proposition !
Yet for freedom from draughts and conservation of energy, it is a quite
desirable thing to do.
It is so hard to get good realistic data.
All one can get within the industry is that limited data that helps a particular
vendor's case for selling insulation, frames, glass, etc.
We need a Building Services Research Centre in Ireland.


any decent double glazed unit should be no more than 1.6 u value. A good double glazed unit would be 1.2 - 1.4. If any supplier is still doing 2.0 windows id expect them to be out of business soon.

as far as draughts are concerned, the u value of the window has no relationship to its air tightness. Windows should be rated in accordance with the BFRC http://www.bfrc.org/ . Airtightness is specifically dealt with in this classification (The effective heat loss due to air penetration is measured) and an A rated window should be selected.

If checking how good or bad a window is from manufacturers data, look for the results of an air permeability test EN 1026. The resultant classification is in accordance with EN 12207. As far as im aware the higher the class the better. I havent seen a result greater than class 4.

It doesnt make sense to try to add on another element when the issue can be resolved by the selection of a better quality window in the first place. If the dwelling is really aiming at low energy performance, triple glazed A rated windows should be selected. In my experience you are looking at, at most, 15% over the cost of a similar double glazed unit.
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Re: BER Consultants: Real U-Values For Shuttered Glazed Walls.

Postby teak » Thu Jan 14, 2010 5:48 pm

Thanks for link.

Yes -- if those passive house rated glass units were affordable it would be preferable.
Drawing elaborate home-made shutters is not on for many people, e.g. elderly, sick,
pregnant, handicapped, etc.
And people get a bit lazy on winter evenings.

I've found one passive-standard glazing supplier.
I'm told that there may soon be others supplying into Ireland.
So there we leave this problem.
Thanks to all.
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Re: BER Consultants: Real U-Values For Shuttered Glazed Walls.

Postby Monty G » Sun Jan 31, 2010 10:54 pm

[quote="henno"]as far as draughts are concerned, the u value of the window has no relationship to its air tightness. Windows should be rated in accordance with the BFRC http://www.bfrc.org/ . Airtightness is specifically dealt with in this classification (The effective heat loss due to air penetration is measured) and an A rated window should be selected.
/QUOTE]

The BFRC (and our NSAI celtic clone) should be treated with caution. Bear in mind that the scheme was only ever designed for replacement windows and the ratings are about as useful as a NAMA valuation ie there is a value but its relative to put things mildly. I’d put it on a par with the ‘dynamic u-values’ of supply air windows, or the ‘effective u-values’ beloved of Rationel, or…. go-faster stripes on a Nissan Micra.

http://www.bfrc.org/pdf/GGF%20the%20limits%20leaflet.pdf
“The actual energy consumption for a specific application will depend on the location of the window in the building, the building parameters such as insulation and occupancy, the building geometry and orientation, the local climate and the indoor temperature set by the occupants. The BFRC Rating allows accurate comparison of window performance under identical conditions.”

The BFRC u-value data is accurate – but only for the stated size and construction of window. The airtightness figure is useless for an assessment of the windows actual performance sitting in a wall. It’s derived from the result of a test conducted at 50Pa and dividing the result by a factor of 20 - making just about any window appear to be ‘airtight’. (Real world testing is undertaken to 600Pa). The solar factor (g value) is for the whole window construction whilst DEAP specifically requests g factor of the glazing only. The ‘Energy Index’ is a nonstarter for trying to simulate the actual performance of a building – as its not designed to do that. Obviously a north facing ‘A’ rated window is going to have a completely different energy balance then the same window in a south facing elevation.
There are BFRC ‘A’ rated windows with a u-value of 1.6W/m2K. Not exactly what I would be looking at if I was building a low energy building.

OP. Forget the A rated nonsense and pursue the triple-glazed option. Without going to any great trouble you can get glazing with a u-value down to 0.5 and a g value in the region of 0.35 or lower (which would be a pretty good double-glazed solar-control specification). This will keep your internal glass temp at a comfortable temperature during cold winter nights and most summer days. You don’t need ‘Passiv Haus’ windows to achieve this. Download a copy of Calumen (St Gobain) or Spectrum (Pilkington) and you can easily play around with glazing specifications. Give the window supplier a specification that is specific to the building and break it down to individual windows.

Monty

PS. The u-value of a window is certainly affected by its air-tightness. Hot-box testing shows this up unlike software modelling which assumes the thing is built as per the CAD dwg.
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