craig

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.

I would certainly suggest a window film applied internally to the glass, several suppliers of this film exist and you can get various levels of film from decorative to mirror effect. I would suggest having a look at window film companies such as [commercial link deleted]