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What are some common problems using IES VE for Title 24?

asked 2015-07-10 18:26:27 -0600

updated 2015-07-10 18:29:12 -0600

I'm working on an existing IES VE model that will be used for Title 24 compliance. IES lists the following general guidance for errors:

I am receiving errors with room names. Can you offer any general guidance for the 3D model?

As the Title 24 module in the VE runs the CBECC-Com Ruleset & EnergyPlus simulation engine for compliance, there are a few limitations with regards to naming the rooms. Please note that these issues do not exist elsewhere in the VE:

  1. The &, >, <, and $ symbols cannot be used.
  2. No more than 10 rooms allowed per thermal zone.
  3. Duplicate room names are not allowed. Each room and each zone must have a unique name.
  4. Rooms on different floors cannot be on the same thermal zone.
  5. The analysis will not be successful with any space or surface polygon (PolyLp in CBECC-Com) containing more than 120 vertices due to a limitation in the EnergyPlus simulation.
  6. Self-shading surfaces (from ModelIT) are not accounted for in the Title 24 calculation.

Another common issue we see coming through to our technical support team is a mismatch on ventilation information. Some entries include 15 cfm/person, for example, but then the ventilation source is set as cfm/ft2. The CBECC ruleset will then check for the cfm/ft2 value, which is 0, and gives an error about not enough ventilation.

So my question is whether other IES VE users have encountered additional issues with translating to CBECC-Com and whether the above guidance holds? I'm specifically interested in #3, which I think may have been fixed by appending the room ID to the room name; at least in the translated OSM file I looked at.

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answered 2015-11-16 15:20:50 -0600

IES updated to use CBECC-Com version 3c a few months ago, so I believe the ventilation issue is resolved. The others are definitely true. Another issue to add to your list is interior holes- it's actually a big benefit of IES when using Apache, but can't be translated to the T24 module/CBECC-Com. You can use the "RMHI" (remove holes interior) command in ModelIt to remove them.

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answered 2016-12-20 17:42:26 -0600

yungahhh gravatar image

From my adventure with using IES-VE for Title 24 compliance, most of the guidance hold and I noticed the following usability:

1) I still get the ventilation mismatch issues a lot of times. Usually, it's an easy fix for one or two zones after being exported to CBECC-COM and just scroll through the ventilation exhaust tab and checking if they are equaled.

2) Remove all holes or non-window glazing from IES-VE to CBECC-COM.

3) As for room names, I think the advice is pretty much true and avoid many problems down the line. For instance, rooms with the same name will be mapped into the same zone when you develop the zone in IES.

4) A number of things that typically doesn't translate through CBECC-COM is the Supply segments which cause error. When you name the Supply and Return - you kind of need a naming convention that would allow you to keep track and apply them to the appropriate zones - depending on how many systems you have. Copying systems over and having the same name for some of the flow causes error sometimes.

5) There are several ways to make windows in IES, but I would recommend to NEVER use the free-hand window option (when you're in plan view and just specify window width by dragging). It has more potential to generate surface errors because sometimes it doesn't define the geometry needs to be defined in E+/OS.

6) Use Title 24 materials when building constructions. And just double check your SGHC after exporting to CBECC-COM and run the model from there.

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Asked: 2015-07-10 18:26:27 -0600

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Last updated: Dec 20 '16