Wall Join Problems In Heating & Cooling Load Analysis

[METTA001]

Hi,

The problem is, when you connect a thicker wall (i.e 40 cm) with a thinner wall (i.e 20 cm) from exterior to exterior (not center to center), it places an air gap at the wall join. (when you check the analytical surfaces in H&C Loads --> Details tab)

If you connect such two walls from center to center, there is no problem. Type of the walls doesn't change anything.

What I ask is how to connect walls properly, without changing the architecture. We shouldn't be moving the walls that are placed exterior to exterior.

Wall join type (mitter etc.) doesn't have any effect as far as I see.

Thanks for advance. Go get your KUDOS! 🙂

[ssafstrom]

For your own good, don't waste your time trying to get accurate building envelope information from RevitMEP.   I have spent perhaps hundreds of hours trying to get decent results from this feature, and I don't have single accurate result.

This feature will NEVER work correctly unless the model you recieve from the Architect is absolutely perfect.  I have never seen such an instance.

The only good use I have gotten from this feature is exporting the space geometry to an xml file.  That is it!

[METTA001]

Thanks for the reply mate.

I'm making a good use of energy analysis tool, only it takes a lot of time to correct everything. My method is:

• Delete all walls that are connected edge to edge
• Build walls from center to center
• Auto-generate spaces from floor plan
• Open the H&C Loads Analysis screen and press "detais" tab
• Check the analytical surfaces list to see if there is an air gap (I click the plus signs near spaces one by one and check if there is an air gap. Time consuming)
• Build zones to specify temperature setpoints
• Define the true north
• Make analysis

Results are, compared to well known energy analysis packages, simply perfect! There is at most 10% deviation from other programs results.

Still I have to speed up the process and also I shouldn't be changing the architecture. Takes time and architectural change shouldn't be done by an engineer.

Thus I still need any suggestions to solve this wall join problems.

Secondly, I can't define ground surface, and REVIT can't understand which wall is underground, which is not. I can only select the zero-level, which is nonsense since a floor may be in contact with soil from one side and open to air from another side.

Waiting for replies & thanks for any advance 😉

[julianjameson8403]

I'm with ssafstrom on this one as there are lots of little quirks about Revit geometry that cause problems with a thermal analysis model. You get a similar issue if the returns on walls are shorter in overall length than the thickness of the walls used to create them.

Our guys here have previously just accepted the issues and exported via gbXML to an external analysis package - as we only use certified/industry recognised packages of which Revit is not (as far as I am aware). Once they import the gbXML they then go through and clean up the geometry. However I understand that this can be quite a tedious process and sometimes it's quicker to just build it in the analysis package - which unfortunately starts to defeat the object of BIM

[METTA001]

Thanks for the reply Julian!

It is really a boring stuff to clean up the geometry in another program. So you say, better start modeling in the good old analysis programs. 

Maybe AutoDesk design team has anything to suggest on this problem. All architects and engineers recently started to use revit in our country, so better find a solution to make a good use of this program.

Briefly, I ask two questions:

• Two different walls having different thickness produce air gaps in energy model when added exterior to exterior. Thus we have to change the center of the wall and change the architecture, which is not acceptable.
   
• If ground is not a "plane" but a sloped surface, we cant define the ground surface so that Revit can not understand which part of the building is underground. Most of the buildings have underground walls at i.e. north side, open to air walls at southern side. (I'm using 2012 and dont have architecture features as site and topography)

[mit011]

Great tips! I am currently going through a similar process and trying to export a Revit file> gbxml> Sketchup. Have you been able to more efficient/effective methods for making a better model? I am encountering an issues: - surfaces are "repeated" and shows up as N-rm1-rm1-I-F-1 instead of N-rm1-rm2-I-F-1 when exporting. This requires tedious gbxml cleanup before importing to Sketchup, otherwise these surfaces are not translated. Have you encountered a similar problem or do you know why this happens?