Problem to export building model with tilt façade to IDF

xwang_neiep · Posts: 4

I have the problem to export building model with tilt façade developed by Designbuilder 1.7 to Enegyplus 2.2 IDF. There is always of warning for floor data setting, the angle of floor should be 0 or 180 instead of 135 for my case, the geometry setting for windows is also not correct. As a result, the heating/cooling load generated from Energyplus is also wrong. The west and east façade of the building have 45 degree of tilt angle against the ground. See the attached for DB model, generated IDF file directly from DB.

By the way, I am using the evaluation version of desingbuilder 1.7. Does the licensed version of Designbuilder have the same problem? Or is it just because of the function limitation for evaluation program.

Xichun

AJ Lester · Posts: 90 Location: Auckland

Hi Xichun,

Firstly, there are no limitations on the evaluation version of DesignBuilder. The only difference between the evaluation and licensed version is that when using the evaluation version, the license reminder screen will pop up each time you go to run a simulation or visualise the model. Apart from that, the two are the same.

With respect to your problem: what you are running into is a problem which relates to how DesignBuilder decides what is a wall and what is a roof/floor construction. The standard orientations for roofs, floors and walls in DesignBuilder / EnergyPlus are as follows:

Roof: 0 degree tilt
Floor: 180 degree tilt
Vertical walls: 90 degree tilt

DesignBuilder has an option that allows it to interpret when you have intended to model a floor/roof and when you have intended to model a sloping wall. At the moment yours is set such that it thinks you are modelling floors/roofs when you are actually modelling sloping walls.

In order to avoid this problem, you should select the block or blocks that have sloping façades and then go to Building Model Options (the yellow spanner button). From the Building Model Options dialog, select the Block tab. Under this you will see the option Allow Pitched Roof Construction. You should uncheck the box so that pitched roofs are disallowed. In this way, DesignBuilder will expect all roofs to be at 0 degrees, all floors at 180 degrees and all other surfaces will be taken to be walls.

If you need to allow pitched roofs, but still have sloping walls, leave the Allow Pitched Roof Construction option active, and just change the angle to something which is less than the angle of your walls, but greater than the angle of your roof. I.e. if your walls are sloping at 45 degrees, and your roof at 30 degrees, then set this limit value to 35 degrees. In this way, all surfaces with a tilt of less than 35 degrees will be taken as pitched roofs, all surfaces with tilt greater than 35 degrees will be taken as walls.

Hopefully this helps you to sort out the problem!

Best regards and good luck with the modelling,

Andrew Lester

xwang_neiep · Posts: 4

Hi Andrew,

Thank you very much for your reply.

I followed the procedure as you described, and for the Northern Block, there is no problem when trasfering directly from DB to IDF. However, for the southern block, i have the same problem. The floor angle showen in IDF is still 135 instead of 180 or 0. Is there some other skills to solve this prolem?

Kind regards,

Xichun

AJ Lester · Posts: 90 Location: Auckland

Hi Xichun,

I have taken another look at your file, and I can see the problem. It appears that the program cannot deal with the sloping surface going in that direction.

Perhaps someone from the DB team can weigh in at this point and advise if my interpretation of the situation is correct: The transition angle seems to work fine for walls with a slope greater than 0 degrees but less than 90 degrees (i.e. wall sloping and 'facing' the sky), but I believe that for wall slopes which are greater than 90 degrees but less than 180 degrees (i.e. wall sloping and 'facing' the ground) the program interprets them as a floor. Can this be confirmed?

Returning to your issue Xichun, when I inspected the exported .idf file, the parameters assigned to that wall in the .idf showed that although the surface type was "floor" the construction type was nonetheless the correct type for the wall (i.e. it matched all the other walls) and the adjacency was exterior environment (as per all the other walls), the view factor to ground was reasonable etc. In essence, it is a wall labelled as a floor.

So, to rectify the situation, I believe all you need to do is change the surface type from 'floor' to 'wall' in the raw .idf file and the warning will stop appearing. Since all the other parameters seem to match the required wall parameters, it seems logical that the only issue EnergyPlus is having is that it is seeing the wall labelled as a floor and throwing up a warning result. As always, I advise you to double-check that the relevant parameters in each .idf file you edit in this way do match the parameters for all other walls of similar construction in the .idf file. Like most people, I often make little mistakes, and I'd hate for one of them to upset your work!

Since you are exporting .idf files, I am assuming that you are using EnergyPlus itself to add functionality, and as such, you're probably fine to usee the idf editor or simply replace the text 'floor' with 'wall' in the appropriate place.

One thing you may want to check out, however is the warning relating to the interblock surface: it is coming up with 8 vertices and EnergyPlus cannot triangulate the surface (perhaps because it is split down the middle and no amount of triangles can resolve the surface). Check it out and make sure it is working fine.

Hopefully, that all helps you somewhat.

Best regards,

Andrew Lester

xwang_neiep · Posts: 4

Hi Andrew,

Thank you very much for your help.

Yes, it seems that the program can not deal with the sloping surface. But the area of the sloping surface in the EnergyPlus is same as that showed in the Designbuilder. By changing the properties of sloping floor into wall can solve the problem.

Xichun

Andy Tindale · Posts: 1235 Location: Stroud

Hi Xichun and Andrew,

Andrews comments seem right, i.e. that the idf generation is OK but that the surface facing down towards the ground is being labelled as a floor rather than a wall. This shouldn't affect results but I have made a change to the DB code for v.1.9.0.002 and later so it flags the surface as a wall instead and this gets rid of the E+ warning message.

Thanks for bringing this to our attention.

Andy

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