Re: [TRNSYS-users] Trnsys17

[Chiara Colucci via TRNSYS-users <trnsys-users@lists.onebuilding.org>]

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)

(Model B)

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

Web:      www.trnsys.de

 

 

 

Von: TRNSYS-users [mailto:trnsys-users-bounces@lists.onebuilding.org] Im Auftrag von Chiara Colucci
Gesendet: Mittwoch, 6. April 2016 16:49
An: trnsys-users@lists.onebuilding.org
Betreff: [TRNSYS-users] Trnsys17

 

 

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