U-value calculations for windows and doors

[Studio Partington]

I've been looking at how, if at all, the presence of trickle vents is taken into account in whole unit u-value calculations for windows and doors.
From a quick look through BS EN10077-1 the section for thermal conductivity through frames covers different types of window frames. Does this mean that the impact of air-gaps and cavities due to trickle ventilators, even those incorporated by window manufacturers effectively do not get accounted for in any heat loss calculations?

[Mark Siddall]

Richard,
Have you been looking at a particular section?

Without cracking open the standard my response would be:

1) The Uw is really just about conductivity so certains aspects of convection are excluded.
2) The conductivity through certain air gaps do get some specific consideration – but not of the the trickle vents.
3) From the Uw calculations that I've seen I've not seen any that consider thickle vents.

Not much help I suspect but I'd like to get a better handle on where you are going with that.

Mark

[Anonymous]

I think the right document is http://www.bre.co.uk/filelibrary/pdf/rpts/BR_443_%282006_Edition%29.pdf which says:
Trickle vents are often provided in windows. While their presence affects
heat transfer in practice, ventilation is regarded as a separate issue to
transmission heat losses, so do not include the trickle vents in U-value
determination. Specifically:
● in hot-box tests, the trickle vents should be closed and sealed with tape to
ensure no air transfer;
● perform calculations as if the trickle vents were not present.

[Nick Grant]

Here is an infra red photo of the trickle vents in our house!

[Author]

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