Timber brise soleil?

[Ferdinand]

3 hours ago, ragg987 said:

We have this. Stainless L-channel and plate knocked up by a local fabricator and off-the-shelf Canadian Western Red Cedar slats cut to size. I kept the downward angle of the slats small - about 10 deg - to permit water run-off without blocking the view and light.

 

In our case it has a practical purpose but is also an architectural feature.

 

 

WAs that wood expensive?

 

I am currently after a 50mm x 250mm x 1.5m chunk for a bench?

 

I am being quoted £25 for that in newly cut Green Oak, which seems OK, but I really want something self-maintaining, so I am waiting for a job lot if I can find one.

Edited June 8, 2017 by Ferdinand

[ragg987]

Don't know, this was one of the few materials I asked my builder to supply and I did not ask for a breakdown. I suspect it might be.

[ToughButterCup]

@Ferdinand, T Knipe, Flookburgh: old school timber merchant. No website, phone is almost never answered; magnificent wood stock. Prices as low as you can find anywhere.  If I need serious wood thats where I go.

 

If you're up this way, go and see the yard. Bring a camera. 1950s writ large.

Ian

[Ferdinand]

Cheers.

[craig]

21 hours ago, JSHarris said:

 

Not possible, as we have triple glazing, with two low e coated internal surfaces.  Fitting an internal IR reflective film would cause the glazing unit to overheat and fail.  The only IR reflective film solution that will work with high performance 3G is an external film, like that which we've already fitted to the larger glazed areas.  This film works very well, and lowers the overall glazing unit temperature quite substantially, with the inner pane staying close to room temperature, even in strong sunshine.

 

I'm curious to know what makes you think the triple glazed unit will fail? I'm presuming you have or have built to PassivHaus standard? I'm presuming the centre pane value is 0.5Ug (probably 0.53Ug or thereabouts). The the coating will be on the outside of the inner pane and the inside of the outer pane & the unit will probably be made up of 4mm Planiclear glazing x3 and Planitherm XNII coatings. With a G value of around 0.54 and shading coefficient of about 0.6 and light transmittance at around 74%.

 

I've used films on the inside on many a project and and I've really only had take to take into account the shading aspect, I've never had a glazing unit fail as a result.

[Jeremy Harris]

The glazing manufacturer, the window manufacturer and the reflective film manufacturers (we have two different types already installed) all say the same thing, that the glazing unit will fail if a reflective film is fitted inside 3g that has two internal low e coatings.  All stated clearly that the warranty on the glazing, windows and internal film would not be valid if internal IR reflective film was installed.  All were quite happy with external IR reflective film, although the film installer insisted on doing a heat build up analysis for our type of glazing before agreeing to install it.  This was required as a part of the warranty, and makes a lot of sense.

 

From a pure physics standpoint, this is pretty obvious, as a reflective layer fitted on the inside will try to reflect back a fairly large percentage of long wave IR, out through the glazing.  In turn, a fairly large percentage of that long wavelength IR will be reflected back inwards, by the two coated internal panes.  The result is that the temperature of the middle and inner pane may rise to an unacceptably high temperature. 

 

Before we had the external film fitted, the inner pane was getting to 35 to 40 deg C, and that itself was contributing a great deal to the heat build up in the house, as there is a large area of South facing glazing acting like a large radiator.  Any internal film would actually increase the temperature of the inner pane, as it is the glass itself that is absorbing a fair proportion of the incident long wavelength IR, before it reaches any film on the inner face.   After the external film was fitted I've found that the inner pane barely gets above room temperature, even on a bright spring or autumn day (the worst case, due to the angle of incidence of the sunlight on the glazing).

 

This is not just something related to our installation or supplier, either, as I had quotes from three suppliers, and they all said exactly the same thing, that they would not recommend or install an internal reflective film.  Even one of the suppliers of DIY kits said the same, not that I was seriously thinking of a DIY install.

 

In addition, we discussed it here, in this thread:

and further down in this thread:

At least one other forum member also has external film fitted, and I believe their experience was very similar to ours, with suppliers/installers insisting that an external film be used.

 

[craig]

Sorry I'm not meaning to be condescening or rude. It just interests me as to why they are saying this, what reasons are they given and what do they actually mean by failure. It would also depend on the type of film that is being used, I'll have a look at what they are saying.

Edited June 9, 2017 by craig

[Jeremy Harris]

In the simplest terms I can think of, imagine a glazing unit that has an internal IR reflective coating, that is largely selective, in that it reflects long wavelength IR back into the house.  It doesn't really matter what the actual numbers are, all that matters is that there is greater long wavelength IR reflectivity inwards than there is outwards, which is the case for all low e coated glazing units.

 

With no internal IR reflective film, the long wavelength IR that is incident on the window from the sun will largely pass through and heat both the inner pane of the glazing (which isn't coated, and so does absorb a fair amount of long wavelength IR) and the inside of the house.  Some of the long wavelength IR radiated from heated surfaces inside the house, and its occupants, gets reflected back inside by the internal coating, and both reduces the overall heat loss through the glazing and adds to the heating of the inner pane.

 

If an IR reflective coating is now added to the room-facing surface of the inner pane, then that will reflect back out a percentage of the incident long wavelength IR.  Some of that will be absorbed by the glass layer that the film is applied to, some will hit the internal IR reflective coating and be reflected back and some will pass through the outer pane to the outside.

 

The problem is the part that is reflected back from the internal coating.  This gets partially absorbed by the inner glass pane, then part of the remainder gets reflected back out again.  Part of this, in turn, gets reflected back, partially absorbed by the inner pane, and partially reflected out again.  This process goes on in parallel with the incident radiation on the glazing, so the effect is to cumulatively increase the temperature of the inner pane of the glazing.

 

The problem is made worse because normal glazing glass absorbs long wavelength IR, something that all glass does to a significant degree, as glass has a high long wavelength IR emissivity, unless it has an IR reflective coating on the face that is exposed to the radiation source to lower its emissivity.  The usual arrangement of low emissivity coatings is to put them on the room-facing internal face of the panes in the glazing unit, as this is the most effective arrangement to both maximise the ratio of long wavelength IR that is reflected back into the house, and protect the coating from damage.

 

If a glazing unit doesn't have any internal low emissivity coating, then the problem would be significantly reduced.   A better solution now would be to use some of the newer glazing systems that have a tough external low emissivity coating, as that avoids the need to use any film.  If I'd known when specifying the glazing that there was an overheating problem (it didn't show up in PHPP, as that uses a rather high 25 deg C default overheating temperature, I later found) and neither did it show up in the SAP worksheet, partly because our house is more sheltered than either model allows for, and we have a microclimate effect around the house that means the outside temperature tends to be at least 1 to 2 deg C warmer than the met data predicts, all year around.

Edited June 9, 2017 by JSHarris