RMEP2012 HVAC Loads Analysis

[dennis howell]

Is anyone actually using the built-in HVAC Loads Analysis in RMEP2012? If so, how are you using it? Are you following the conventional wisdom of the model setup or something different? If you are not using the built-in, what are you using and "why"?

[TJP1979]

Anyone?

I am curious about this as well. The mechanical department at my company is way behind electrical in terms of how much they use Revit to do actual design.

[Jrobker]

This is a great question. This question has been ongoing since MEP 2008 and has received very little attention. Many unanswered questions and very little help.

We have tested Revits internal loads and are not comfortable with them yet. On my first 2012 project I finished the loads and noticed one room had 32 walls. I threw up my hands and finished it the old fashioned way.
I have done a little research on this myself and as a company and here are some of the findings.

"Loss coefficients for some fittings. Many post on this."

Negative/empty space between spaces and actual exterior walls.

"No overhangs or shading surfaces. old post (ongoing)"

Architect HAS to create room bounding walls where there should be room bounding walls.

Hottest point of the day discrepancies.

"Ashrae RTS method for SHGC through windows VS Revit discrepancies."

"Only heating losses are accounted for, not heat gains. Steps to solve this will show heat gains in your cooling loads."

"Doesn't recognize dome roofs for cooling loads"

"Workflow of exporting gbXML from Revit, importing into trace to run loads, then exporting the results back to the gbXML file, and finally importing this into Revit. This seemed to work alright, although I had hoped that the gbXML walls would have been defined a little cleaner".

Arduous steps and workarounds/embedded schedules for creating schedules for design purposes.

...and many, many more.

The issue is, everyone is this business has been doing their loads the same way for years. They are comfortable, efficient and know how to use the program of their choice. Revit has too many discrepancies and when somebody needs help there are too few answers, especially from "Revit experts". Everybody I know that provides support from our reseller are from the Architectural side, chances are you know more than they do about Revit MEP. If we turn to the forums we get little feedback. I'm waiting for the program to get it right.

[daniel.morrison]

We tested this out in 2011 and when we noticed it kept telling us that supply air would have a wet bulb temp higher than the dry bulb we knew something was wrong.

We sent the error on to Autodesk and they said they wouild get back to us - we are still waiting.

[dennis howell]

Great comments and findings y'all. Please, anyone else, feel free to pile on. I will be compiling this data to present to my management, and hopefully then to be passed on to Adesk.

[TJP1979]

Thanks, JR. That is a great breakdown of Revit's limitations. I will pass this on to the mechanical department here.

[gabecottam]

We found one fantastic little nugget in 2010. When you cut a curtain wall into a solid wall - depending on the direction you cut the curtain wall (left to right vs. right to left) defines which side is exterior. After it's placed there is a little flip icon that allows you to change the orientation. However - the glass orientation doesn't change. So running a load gave us south facing glass in a north wall.

Problem persisted in 2011.

I mentioned (and demonstrated) this to 4 different autodesk Revit MEP employees last year at AU and none of them had ever been made aware of this problem before.

This seems to have been fixed in 2012 however. So I'm hopeful that if enough of us explain what's broken enough times, we may see results... some day.

[Bvogt]

We are a full service A/E firm with in house architects and we are still having problems getting valid models to use for a gbxml export. Our normal workflow is a gbxml export to Trace. Some spaces still end up with a lot wall slivers. We check and double check the input, perform the load calculation and reimport back to Revit. At some point the model gets to unruly and we just maintain the Trace loads manually and revise the specified cfm.

One methed we are attempting is to have the architects perform a gbxml export for Green Building Studio. We may or may not use it, but it gets the architectural model cleaned up before we perform a gbxml export for Trace.

Can anyone define what the Sliver Space Tolerance does. What is 1' ? Maybe if we use 25', it would cleanup a lot of erroneous chases, columns, etc.

Bob

[dariopetric24823364]

Has anyone figured this out yet? I have just compleated an example of a simple space with Revit supplied default loads. I have created a report in Revit MEP 2012 and exported the file as gbXML to Carrier's HAP. HUGE difference in load analysis. we have used HAP before and none of the engineers are happy with the Revit loads. any thoughts?

[chrisb.80133]

Our firm has been trying to utilize the Revit tools to their extents and our next step was to take advantage of the Load Calcs. After much effort, time and research we found it to be more work than it is worth.

We are looking for a way to at least export the Room Names, Numbers and Space Areas. Has anyone tried this with any success?

Thanks,