Re: [TRNSYS-users] Internal and external shading factors in Type 56

["Kersken, Matthias" <Matthias.Kersken@ibp.fraunhofer.de>]

Dear Knut!

 

When modelling a internal shading together with a large glazing in a TRNSYS-versions below 17 You have to consider the following!

 

Once the solar radiation as crossed one of Your two zones and (a part of it) has enters the second zone all the radiation will be threaded as diffuse radiation.

If You don't use geosurf-factors all the beam-radiation entering entering the second zone directly will also be handled as diffuse (so set a geosurf at least in the lower zone !)

and at least You also have the diffuse radiation entering the second zone directly.

This means in a two-zone-green-house-model You have a very high amount of diffuse radiation in the zones (of course this effect exists in both directions between the two zones).

 

Now the (high) diffuse radiation in the zone is distributed equal to every m² of zone-wall and windows, this means much more radiation is distributed back to the glazing (where it came from) as it would be in reality and so more energy leafs through the glazing as it would in reality.

If the internal shading is active it keeps this high amount of radiation inside the room and so You may have effects like the room temperature as a light drop for a moment, when You deactivate Your int. shading.

This may explain Your steep temperature changes (?).

A solution for this problem I don not have at hand (except TRNSYS 17) but You my try using a low inside reflection of Your shading, this might reduce this effect.

 

I think Your assumption concerning the heat transmission in the night being influenced by the thermal resistance of the shading is correct.

This effect is' expectable and in already worked with it in TRNSYS (16).

 

With kind regards,

    Matthias Kersken

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Dipl.-Ing. Matthias Kersken Wissenschaftlicher Mitarbeiter / Abteilung Energiesysteme Fraunhofer-Institut für Bauphysik Institutsteil Holzkirchen Fraunhoferstraße 10 83626 Valley eMail: Matthias.Kersken@ibp.fraunhofer.de Telefon 08024 / 643-204 Telefax 08024 / 643-366 www.ibp.fraunhofer.de

Dipl.-Ing. Matthias Kersken Research Associate / Department Energy Systems Fraunhofer Institute for Building Physics Branch Holzkirchen Fraunhoferstraße 10 D-83626 Valley eMail: Matthias.Kersken@ibp.fraunhofer.de Phone +49 8024 / 643-204 Fax +49 8024 / 643-366 www.ibp.fraunhofer.de

 

 

 

 

 

 

 

 

 

 

 

 

 

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Von: knut.erik.enerstvedt@niva.no [mailto:knut.erik.enerstvedt@niva.no]
Gesendet: Dienstag, 10. November 2009 10:11
An: trnsys-users@engr.wisc.edu
Betreff: [TRNSYS-users] Internal and external shading factors in Type 56

Hello all,

 

I'm using Type 56 to develop a model of a greenhouse which has controllable inside screens to reduce incoming and outgoing radiation. I have used the "internal shading factor" of the windows with an input variable to achieve this, since the screens are actually on the inside of the greenhouse. However, the internal shading device does not have quite the effect I expected. It does not seem to reduce solar radiation hitting the zone, so that temperatures rise very high on warm and sunny days. It does however seem to reduce temperature loss at night, but this could be due to the additional thermal resistance. By testing the "external shading factor" instead, I found that this device has the effect I want, blocking out radiation and keeping temperatures down on hot days. Can someone please tell me if I have misunderstood the concept of internal shading? Does it not prevent outside solar radiation from hitting the zone after passing through the windows?

 

Best regards,

Knut Erik Enerstvedt

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