ETFE roofs

[georger]

Hi

Please could you let me know if it is possible to model ETFE roofs within IES?

many thanks

[ZapBran]

You can but only very basically.

I asked IES about this a couple of years ago and I'll give you what they told me...

ETFE (Ethylene TetrafluoroEthylene) is a fluorocarbon-based polymer (a fluoropolymer): a kind of plastic. ETFE does not have an exact material within the <VE> however, your best approach would be to model these surfaces as glazing and the best approach is basically the same as for normal glazing: first adjust the cavity resistance to match the U-value, then adjust the transmittances & reflectance’s to match the solar data. Essentially, in the absence of the ETFE material within our database, you are manipulating the values of a normal glazed unit to represent the properties of the transparent plastic.

The assumption in the software is that building surfaces are opaque to long-wave radiation. An ETFE construction would need to be modelled as an approximately equivalent construction subject to this constraint. In outline the approach would be to match the short-wave characteristics and the total solar transmittance, and incorporate the long-wave properties by matching a U-value calculated taking these into account.

The way the VE handles the coatings etc are described in some detail in Section 7.13 of ApacheSimCalculationMethods.pdf: Solar Transmission, Absorption & Reflection by Glazing. You will find this under Help – user guides. The method covers coatings that are wavelength specific but their properties are averaged over the solar spectrum.

I phoned XXX at IES a few months back (no need for you guys to know my mate's name) to find out if any progress had been made but unfortunately no... they seem to have be concentrating on other things over the last few years rather than tightening up the particularly good sim engine and the inputs to it that I would have hoped for.

Zap.

[waleeed1234]

The assumption in the software is that building surfaces are opaque to long-wave radiation. An ETFE construction would need to be modelled as an approximately equivalent construction subject to this constraint. In outline the approach would be to match the short-wave characteristics and the total solar transmittance, and incorporate the long-wave properties by matching a U-value calculated taking these into account.