[BLDG-SIM] Windows Shading Coefficient

[Anil Misra]

One has to be careful about defining the shading factor. The shaded portion of the window in PREBID is treated as the opaque part of the window which may have a very different U-value than that of the glass (glazing). The heat conducted across the window will be affected if a glazing forms significantly large portion of the wall.

Let me explain by the following example (a single glazed window with wooden frame).

If the shading coefficient is 0.5, beam and diffuse radiation will pass through 50% of the area of the glass. The remaining 50% of glass area would be treated as wood.

In reality, heat conduction will take place through the remaining 50% of the glass area (it should not be treated as wood).  (Imagine the difference when the conductivity of glass = 2.88 kJ/m-K and the conductivity of wood = 0.54 kJ/m-K).

A better method to model shading would be to treat the beam and diffuse radiation with the shading coefficients in IISiBat before it is given as input to Type 56.

Caution: The modified radiation to be given separately for windows, it should not affect the radiation incident on the walls. This would require creating a separate surface to contain the windows only. Same caution is required also when Types 34 and 68 are used as suggested by David.

David: pl confirm the above statement.

Anil Misra

  ----- Original Message ----- 
  From: David Bradley 
  To: BLDG-SIM at gard.com 
  Sent: Monday, November 15, 2004 9:38 PM
  Subject: [BLDG-SIM] Windows Shading Coefficient


  Dear Maurizio,


    1) I'm currently modelling in PREBID a residential building for which the montly Shading Coefficients on the windows have been calculated with the software ECOTECT. I insert the SC in the appropriate field ("external shading coefficient") as an input and set the "view factor" to 0,5 (vertical surfaces). It's the exact way? My doubt is that the solar incident radiation is halved (view factor = 0,5) and then reduced of the SC...

  It is correct, provided that the shading coefficient from Ecotect is the opaque fraction of the window (i.e. 1 = completely shaded).
  The view factor to the sky (FSky) is only used for longwave radiation so it will not interfere with shading.

  The one thing to bear in mind about PREBID's external and internal shading coefficient is that the entered fraction effects both beam and diffuse radiation equally. Thus if you enter a value of 0.5 for the external shading factor, half of the incident diffuse radiation and half of the incident beam radiation will enter the space. If you want to treat beam and diffuse radiation separately, you can use one of the external shading models (Type34, or Type68).


    2) It's possible to use old TESS libraries with TRNSYS 16 or are they already comprised in the new version?

  Because of the change in coding standards for components between version 15 and 16, the TESS Libraries v. 1.x are not directly useable with TRNSYS v 16. We have, however, expanded the libraries and released version 2.0, which are not only compatible with TRNSYS 16 but are also backwards compatible with TRNSYS 15. If you are interested in upgrading, you will be credited the full amount that you paid for your version 1.x libraries toward the purchase of version 2.x libraries. If you do not wish to upgrade then you can follow the steps laid out in the TRNSYS 16 documentation that show you how to modify a TRNSYS 15 Type to make it accessible from TRNSYS 16. I will send along a second email containing a document that lists the contents of the 12 version 2.0 libraries as well as an order form that contains the pricing information. I would be happy to answer any questions that you might have about them.

  Kind regards,
    David



  ****************************************************************************************
  Thermal Energy System Specialists (TESS), LLC 
  David BRADLEY                           2916 Marketplace Drive - Suite 104 
  Partner                                        Madison, WI 53719 
  Phone: (608) 274-2577 USA 
  Fax: (608) 278-1475 
  E-mail: bradley at tess-inc.com 
  Web Pages:  http://www.tess-inc.com     and      http://www.trnsys.com

  "Providing software solutions for today's energy engineering projects" 
  ****************************************************************************************



======================================================
You received this e-mail because you are subscribed 
to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe 
from this mailing list send a blank message to 
BLDG-SIM-UNSUBSCRIBE at GARD.COM




======================================================
You received this e-mail because you are subscribed 
to the BLDG-SIM at GARD.COM mailing list.  To unsubscribe 
from this mailing list send a blank message to 
BLDG-SIM-UNSUBSCRIBE at GARD.COM
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20041115/ae039223/attachment-0002.htm>