[TRNSYS-users] Types 68 and 34 (shading)

[Enertech]

Dear Fernando and TRNSYS Users,

(b) If the upstream component is type68,

   Sky diffuse on window = Shaded sky diffuse on window without overhang
* (1-Fws)

In both cases (a) and (b) I suppose that the sky diffuse radiation input
is always the input number 4 of type34. The label in the proforma is
somewhat error prone (it says “sky diffuse on the horizontal”).

I think you’re right !! There’s an error in the TYPE 34 proforma : input(4) 
has to be the diffuse radiation on surface and not the horizontal diffuse 
radiation. You can check it in the TYPE34 source code.

I’m a little bit angry to discover more and more errors in proforma 
definitions. How can we trust in TRNSYS simulation results if there is 
these kinds of error in models ?

I’m working on complex building projects with a lot of far-away masks 
(TYPE68) and a lot of overhangs, with very short notice (of course!!). I’ve 
no time to check that all inputs defined in proforma are the ones needed by 
source codes


I’m sorry to be so hard on this subject but modelling a building is not an 
easy job and I need to trust in models I’m using otherwise it only remains 
for me to say to my boss that I can’t do this job anymore, there’s too much 
errors in the software.

Salutation,
C. Plantier

,At 11:38 16/08/2005, Fernando Domínguez Muñoz wrote:
>Dear TRNSYS users,
>
>I have some doubts about TYPES 34 (overhang and wingwall shading) and 68
>(shading by external object) that I would like to discuss with you.
>These problems are related to the diffuse radiation calculations.
>
>In order to model a vertical window with an overhang and a wall in front
>(of the window), I tried to use types 16, 68 and 34 connected in
>cascade. The first parameter of type34 changes the way in which the view
>factors are calculated, being offered the following two choices:
>
>(a) If the upstream component is type16, there is no problem:
>
>     Sky diffuse on window = Sky diffuse on horizontal * (0.5 ­ Fws)
>
>Where Fws = view factor between window and sky (takes account of the
>overhang and the windwalls)
>
>(b) If the upstream component is type68,
>
>   Sky diffuse on window = Shaded sky diffuse on window without overhang
>* (1-Fws)
>
>In both cases (a) and (b) I suppose that the sky diffuse radiation input
>is always the input number 4 of type34. The label in the proforma is
>somewhat error prone (it says “sky diffuse on the horizontal”).
>
>In case (b), locations behind the window were already excluded (by
>type16), so the first term is 1. I do not understand the second term,
>because the overhang is obstructing part of the sky over the window, so
>the involved radiation should be that coming from the vault of heaven,
>
>(b*)  Sky diffuse on window = 1*Shaded sky diffuse on window without
>overhang - Sky diffuse on horizontal*Fws
>
>In fact, suppose that type68 is used without obstacles defined (all
>obstruction height angles equal to zero). In this case
>shaded_view/full_view = 1, so
>
>   Shaded sky diffuse on window without overhang=0.5* Sky diffuse on
>horizontal
>
>The results of expressions (a) and (b) are inconsistent:
>
>(a) Sky diffuse on window = 0.5* Sky diffuse on horizontal ­ Fws* Sky
>diffuse on horizontal
>
>(b) Sky diffuse on window = 0.5* Sky diffuse on horizontal ­ 0.5*Fws*
>Sky diffuse on horizontal
>
>A different and more difficult situation is when the overhang or a
>wingwall (or part of it) sees the external obstacle (that is, there are
>two obstacles in series). In this case, part of the shaded radiation is
>obstructed. So as to solve this problem, I would try to compose the
>geometry of the problem by combining several masks.
>
>Other questions are:
>
>Q1) The geometrical dimensions of the window can be comparable to those
>of the obstacle in some cases. In this situation strict view factor
>algebra should be used, but if we use type68 it is not clear where to
>place the measurement reference for the obstruction angles, because
>these angles are different for different points on the window. The best
>place seems to be the centre of the window.
>
>Q2) When type68 is used in conjunction with type1 (flat solar
>collector), I think that the description given in the proforma is error
>prone, because the total radiation given by type68 does not include the
>ground reflected radiation, so it should not be directly connected with
>the total radiation input of the solar collector type. This term can be
>difficult to calculate when the obstacle is close to the collector (in
>this case the radiation reflected by the obstacle can be significant),
>but shall be included anyway.
>
>I hope this helps.
>
>Fernando Domínguez Muñoz
>University of Málaga (Spain)
>_______________________________________________
>TRNSYS-users mailing list
>TRNSYS-users at engr.wisc.edu
>https://www.cae.wisc.edu/mailman/listinfo/trnsys-users

===========================
ENERTECH
F-26160 FELINES SUR RIMANDOULE
tel-fax : 04 75 90 18 54
Email : sidler at club-internet.fr
Web  : http://perso.club-internet.fr/sidler
================================ 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/trnsys-users-onebuilding.org/attachments/20050819/165ce848/attachment-0005.htm>