Local shading has no effect

Advanced 3D solar analysis for a building and its site.
Daithi
VE Student
VE Student
Posts: 25
Joined: Thu Apr 22, 2010 11:40 am
Location: Dublin

Local shading has no effect

Postby Daithi » Mon Sep 19, 2011 2:34 pm

Hi all,

I'm having trouble with modeling trees as local shade. I'm hoping someone might be able to help.

I'm modeling a 6 storey office building in Dublin, facing SE with extensive glazing, with deciduous trees in front of it. I modeled them as simple polygons, which are opaque in the model viewer, and are on the Local Shade layer. In order to take account of the seasonal shading effect of the trees I created the following shading files:

Jan-Apr.shd - Shading file from January to Arpil with trees turned off.
May-Oct.shd - Shading file from May to October with trees turned on.
Nov-Dec.shd - Shading file from November to December with trees turned off.

In addition, as a check, I created a shading file with trees turned off for the whole year:

Jan-Dec.shd - Shading file from January to December with trees turned off.

When carrying out thermal simulations I renamed the appropriate shading file to <project file name>.shd so that ISE VE uses the correct one.

I compared an annual simulation using the first 3 shading files with an annual simulation using the fourth shading file which should quantify the effect of the shading of the trees over a year. As the trees aren't very extensive I didn't expect a huge difference, but as it turns out I got none at all!

I looked at both the solar gain and incident solar power to rooms and surface which would definitely receive shading but there was no difference.

Does anyone have any idea where I might be going wrong? Is my methodology incorrect? Am I missing an ISE VE trick?

Many thanks in advance for any help you may be able to give.

Regards,

Daithi.

User avatar
PCully
Site Admin
Site Admin
Posts: 1414
Joined: Tue Sep 09, 2008 9:52 am

Re: Local shading has no effect

Postby PCully » Tue Sep 20, 2011 8:48 am

I'm surprised you see no difference even when comparing the case when the shading file takes account of the trees all year round.

I did a quick test using large shading surfaces that obscure my windows entirely. I generated two shading files (one with the shading surfaces and one without) and ran sims using each, when I compared Solar Gain in a room from the two runs it was massively different (as you'd expect).

I'd suggest you start by checking for a simple case that you're doing everything correctly and see if you can get reasonable results. Some thoughts:
1. when you add in the shading surfaces are you defining them with "type = Local Shade" (set this on shape settings while drawing or by right clicking the bodies in the rooms browser after it is drawn)
2. make sure you have recalculated the SunCast shading file and not accidentally overwritten one of the existing files (check the auto backup function as well). You can load the shading files into SunCast to check the results here before it goes into Apache as well.
3. Are you running the simulations with the SunCast link checked and have you got the correct shading file in the SunCast folder prior to simulating?

It sounds like you know what you are doing here but it's worth checking over the basics before you start digging deeper.

Phil
IES Worldwide Technical Support

Daithi
VE Student
VE Student
Posts: 25
Joined: Thu Apr 22, 2010 11:40 am
Location: Dublin

Re: Local shading has no effect

Postby Daithi » Tue Sep 20, 2011 3:09 pm

Hi Phil,

Thanks for the reply. I've been investigating further on a quickly constructed one-room model and have made it work by defining the first shading file when only the room exists in the model (ie shading device not modeled), and defining the second after the shading device is modeled. I had assumed incorrectly that turning off the shading devices (unticking in model browser) would mean they were not taken into account in shading calculations.

However, I'm assuming there is a way of 'turning off' shading devices rather than deleting them? Section 3.3 of Suncast User Guide 6.0 mentions making them 'transparent' but doesn't specify how this is done. Sorry for the question, I'm sure the answer is fairly straightforward, but I just haven't found it.

Regards,

Daithi.

User avatar
PCully
Site Admin
Site Admin
Posts: 1414
Joined: Tue Sep 09, 2008 9:52 am

Re: Local shading has no effect

Postby PCully » Wed Sep 21, 2011 9:23 am

ah ok, that's what went wrong. If you untick rooms in the browser you are just hiding them from your view, they are still picked up by the analyses. If you want to run SunCast without the shading surfaces then you could delete them (that's what I did when testing this previously) or switch off the local shade layer (open Layer Properties dialog in ModelIt and you'll find Local Shades on Layer 64, select this and click the off button and you'll see they are greyed out). I tried both methods and they both have the same affect when calculating the SunCast shading file.

The Visibility options you referred to in the SunCast user guide I believe only display surface visibility in the SunCast images, it allows you to generate images with surfaces hidden to see better what's going on inside rooms etc.

Phil
IES Worldwide Technical Support

Daithi
VE Student
VE Student
Posts: 25
Joined: Thu Apr 22, 2010 11:40 am
Location: Dublin

Re: Local shading has no effect

Postby Daithi » Wed Sep 21, 2011 2:42 pm

Hi Phil,

Thanks for the clarification, I've tried deleting and turning off the local shade and have been successful in defining a shading file for Nov-Dec. When I use it in thermal simulations the results are as I had hoped, so happy days there!

Unfortunately, I've developed a second, probably unrelated problem. I'm having difficulty running the Suncast calculations to define shading files which include the month of February (Jan-Apr and Jan-Dec). When I try, 'Checking surfaces' completes, as does the 'Diffuse shading analysis'. However, when the calculations get to 15/Feb 08:00 it just hangs and becomes unresponsive.

I've run a geometry check on intersections and surfaces. All complete without further comments except for 'slivers' and 'unmatched adjacencies' both of which appear to highlight a number of areas. Are these relevant/significant? Any ideas? I've rebuilt adjacencies but to no effect.

Again, thanks for your help to date, I'd appreciate any further guidance you can give me.

Regards,

Daithi.

Daithi
VE Student
VE Student
Posts: 25
Joined: Thu Apr 22, 2010 11:40 am
Location: Dublin

Re: Local shading has no effect

Postby Daithi » Thu Sep 29, 2011 11:44 am

Hi,

I've managed to get it working.

I didn't concentrate on correcting the 'slivers' which would probably require rebuilding the model from scratch, with no guarantee that this would fix the problem. Instead I changed the design day on which the solar shading calculations were carried out. My hunch was that the problem lay in the alignment of the geometry with the sun's position. Changing the design day would change this alignment.

The default design day is the 15th day of the month. I found that in my case the 22nd day worked. So as long as all shading files were calculated on this day there should be no problem.

Shading files completed successfully as did apache simulations using the appropriate shading file. And the results show that the model is working as I expected, ie, more solar gain when trees are turned off.

Thanks again for your help,

Regards,

Daithi.

User avatar
PCully
Site Admin
Site Admin
Posts: 1414
Joined: Tue Sep 09, 2008 9:52 am

Re: Local shading has no effect

Postby PCully » Thu Sep 29, 2011 1:45 pm

Thanks for the update there,

I'm not sure why I didn't respond to your previous note even if only to say you should try correct these errors ;) (it was posted on my birthday last week but that's no excuse!)

Anyway interesting solution to see if SunCast could calculate the shading for another day with slightly different solar angles, I don't expect this would always work but I'm pleased your results look sensible this time

Phil
IES Worldwide Technical Support


Return to “SunCast”

Who is online

Users browsing this forum: No registered users and 1 guest