[TRNSYS-users] Trnsys17

[Chiara Colucci via TRNSYS-users]

Hi Jacob,
I don't know if you remember me. I am analyzing the energy needs of a
building in an urban setting. I modeled in TRNSYS a canyon through virtual
windows adopting the "solution 1" proposed by you. Now I want to analyze
the difference between the model with canyon like thermal zone (including
multiple reflections) (model A) and the model without canyon (model B) (see
figures). The solar radiation absorbed by facades overlooking canyon should
be the same in the two models. This does not happen: the solar radiation
absorbed in the model A is less than in the model B. Why?
Thank you
Best regard
Chiara Colucci

(Model A)
[image: Immagine incorporata 2]

(Model B)
[image: Immagine incorporata 1]

2016-04-22 13:12 GMT+02:00 hotline <hotline at transsolar.com>:

> Dear Chiara,
>
>
>
> A virtual surface isn’t the appropriate approach.
>
> Virtual surfaces should be used  as adjacent surfaces between zones in
> SketchUp which are merged into one zone with multiple airnodes.
>
>
>
> A virtual surface isn’t a heat transfer surface, it doesn’t exist in the
> thermal model. Thus, the error
>
> message is correct. The volume of the canyon zone  isn’t closed and
> therefore no view factor matrix
>
> could be calculated.
>
>
>
> Modelling outdoor space isn’t  a straightforward task.
>
>
>
> Solution 1
>
> In order to generate a closed volume of the canyon and allow solar
> radiation to penetrate into the zone
>
> you need a window. To do the shortwave solar correct you may use a
> so-called “no window” which has a transparency of 100 %.
>
>
>
> However, this surface has a temperature and thereby influences the zone
> air temperature by its inside convections
>
> heat transfer coefficient (HTC) and the longwave exchange by its
> temperature.
>
>
>
> For reducing the influence on the air temperature you may define the
>  inside HTC to be small (like 0.01 kJ/k m²).
>
> For longwave radiation exchange the window temperature should be
> approximately the sky temperature.
>
> However, you can’t fix a temperature of window. You have to try to
> calculate a surface gain such that the
>
> Temperature is close and the model is still converging.
>
>
>
> Solution 2
>
> You use solution 1 for calculating the incident radiation (total and
> direct) on the window and use this radiation
>
> as input to a model which doesn’t contain a “canyon zone”.  For longwave
> radiation exchange you have to
>
> estimate the “effective ground temperature”.
>
>
>
>
>
> All the best
>
> The Transsolar Software Team
>
>
>
> ____________________________________________________________
> _____________________________________
>
>
>
> *Jakob Merk*
>
> TRNSYS Software Team
>
>
> *Transsolar Energietechnik GmbH*
>
> Curiestraße 2
>
> 70563 Stuttgart
>
> Fax:        +49 711 67976-11
> Email:    hotline at transsolar.com
>
> Web:      www.trnsys.de
>
>
>
>
>
>
>
> *Von:* TRNSYS-users [mailto:trnsys-users-bounces at lists.onebuilding.org] *Im
> Auftrag von *Chiara Colucci
> *Gesendet:* Mittwoch, 6. April 2016 16:49
> *An:* trnsys-users at lists.onebuilding.org
> *Betreff:* [TRNSYS-users] Trnsys17
>
>
>
>
>
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at lists.onebuilding.org
> http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org
>
>
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