Heat Load Problems

[Anonymous]

We're experimenting with Revit to see if it can replace Trace. So far, its not looking good for the software. So far we are having these issues:

- No ability to get detail on the load calcs, we can't find anywhere with the heat gain through each wall, the floor, the roof, windows, infiltration losses, or any other source.
- No ability to define exterior or interior walls

I have a room currently sitting in the middle of a three story test building. I didn't like the numbers, so I turned off all the lighting, people, etc. There was still over 500 CFM going to a room that is bordered by rooms on every side, as well as above and below. I'd accept 13 CFM or something low for a room like that, but 500 makes no sense.

Is there anyway we can get enough detail out of the load calcs to be able to trust the numbers? Is there some data file, some place where we can figure out how the components of the overall load?

[Anonymous]

I've been down this very path...comparing results to Trane Trace. Right off the bat, Revit MEP is limited to peak loads calcs only. And you don't get much of a break down of those loads.

The summary only shows the lighting, equipment, and misc load for each space. You don't see any sort of envelope/solar load or any mass heat transfer.

Also, the calculated cfm is based on a delta T of 20, which is fine. But the ApacheLoads Calculations user manual says a delta T of 14.4 is being used.

I also found that some of the room type information doesn't match up with what's listed in Appendix C of the user's guide.

I sent a lengthy summary of these questions to the Autodesk folks. Their reply basically said to read the ApacheLoad Calculations manual (I already did.) and went on to say that the calculation methodology is very complicated and full of math, so it'd be pretty hard to explain to me. We pesky engineers, always getting confused by math...hmmm. Listen, I'm not saying i want to do the math, that's why i have this software. But I have to be able to confirm the numbers. The methodology and the results are all but hidden. Not the case with Trane Trace (and any other load software)

My conclusion was that this feature is pretty useless for an engineer. And imo, a misleading tool in the hands of architects who think they can do load calcs now.

We're pursuing the full version of IES now. I'm finding that it's a fairly easy platform to pick up as a Trace user. Now, getting a good model exported from Revit without a lot of cleanup...that's a whole other discussion.

[Anonymous]

Oh yeah. The Revit->IES import feature is very broken. Also, compared to Trace, IES likes to hide all the data you need in multiple places. I think its the better calculation software, but its really hard to convince it that you want to change the defaults sometimes (or sometimes, hard to convince it to even show you the defaults). Regardless, a straight Revit import and then running Apache produces different load results than Revit. Not hugely different, but its enough to make me worried.

Anyway, thanks for verifying this feature is completely worthless. Its great that its the touted feature of Revit MEP for designing ductwork (that and auto duct sizing, which also has... issues).

[Anonymous]

So the comparisons here are using Revit MEP 2008 - Correct? I know MEP 2008 didn't handle loads well. Has anyone been able to compare using Revit MEP 2009? From Kyles blog (inside the system) he seems to indicate the new features of MEP 2009 directly address the load calc problems. Can anyone besides Autodesk confirm this is now working?

[Anonymous]

I'm talking about 2008. I don't have 2009. This is so frustrating. It seems like "switch to 2009" is the answer to everything these days. And then I'll switch to 2009 and then the answer to everything will be "just wait til 2010 comes out..."

What about all of us that drank the 2008 kool aid and still need to get together a set of construction documents in 3 months? The "better luck next edition" mentality isn't helping any one.

[Anonymous]

Phil I have been using Revit since the first release. Guess what we reviewed it for what we needed and said - no way not ready yet. So I created a list of functions that were mandatory. This varies for Mech, Plumbing, Elec, and FP. And by design phase Schematic, Design Development and CD. TO take Revit, a young product, and expect it do everything required for all phases of design is a pipe dream. The reality is Revit will first be useful in Mech, then in Elec, then for Plumbing and then for FP. From what I read it might be ready for Mech this year for SD, DD, then in 2010 ready for mech from SD to CD. My prediction is that it will be a complete package by release 2015. It will probably workable around release 2011.

[Anonymous]

I know this is an old thread.

I have compared a simple buildng in TRACE vs. REVIT MEP 2009 today and am noticing massive discrepancies.

Cooling loads were low by anywhere from 9 to 45% in different spaces, and heating loads were high by 11 to 47%.

I am a fan of the IES interface, and have not compared the most current version of IES with TRACE, but 2 years ago we were experiencing significant differences is peak loads of IES vs. TRACE as well.

Has anyone seen IES or REVIT stack up to TRACE/HAP/Camel/EnergyPRO/Equest/TAS......from a load comparison perspective?

[Anonymous]

I also tried to compare IES to Trane Trac 6.2
I found out that IES uses the ASHRAE heat balance Method Trace you can use several methods.
Make sure you are using the same method it both pieces of software.
With the same method you can come within 10-15% but you have no way of know how IES came up with there numbers.
I also know that if you export the gbxml file into the new trane trac 6.2 there is a problem with the glass loads.
Trace is way off.
I have come to the following conculsions.
Until Trane trace comes out with a patch for the gbxml problem we will enter it in by hand.
Until IES opens up there reports and allows us to see how things are calculated, we will not be using it unfortunely.