Heating and Cooling Load Analysis

[ben.115043]

I've been using MEP for a few months now and am just realizing that the native analysis tool doesn't seem to be as clever as I thought. I can't find any information on the following things and was wondering if my hunches are right.

-Glass doors are apparently always counted as solid as per their building construction setting. There is no way to indicate glass doors as far as I know. How could I do this other than changing out all of the doors for windows? A lot of our buildings have entire walls of sliding glass doors.

-Does this analysis tool account for overhangs? Shading devices? I can't seem to get these basic devices to register when computing the loads. One solution for the shading devices would be to create a new window type in the building construction dialog, but once again I can't figure out how to do this.

Our office was relying on MEP to be a quick way to fine tune our structures to provide better energy performance. If we can't even get our open area and shade devices to work properly, that makes it pretty useless.

Thanks

Ben Regnier

[kyle.bernhardt]

Glass doors are apparently always counted as solid as per their building construction setting. There is no way to indicate glass doors as far as I know. How could I do this other than changing out all of the doors for windows? A lot of our buildings have entire walls of sliding glass doors.

You are correct, you can only define the pre-existing Door Constructions defined in Revit MEP. There are none available that contain transparent sections at this time. You would have to model them as Windows rather than Doors to accomplish this goal.

Does this analysis tool account for overhangs?

The analysis methodology we use is the ASHRAE Heat Balance Method, which does not take into account overhangs or shading surfaces. While it is a more comprehensive analysis methodology than the Radiant Time Series method used by Trane Trace, it's common for Peak Load analysis applications to not utilize Shading Surfaces. I agree that there is an impact of Shading Surfaces, but that is not a part of the analysis methodology.

Generally things like this are incorporated into full blown energy analysis that quantifies anuual energy usage.

If you are looking to take into consideration the full radiant heat loads of the Sun on your building, then I would recommend that you investigate the full IES <VE>, Green Building Studio, or ecotect, as they provide that ability.

Shading devices? I can't seem to get these basic devices to register when computing the loads. One solution for the shading devices would be to create a new window type in the building construction dialog, but once again I can't figure out how to do this.

As discussed in the White Paper on this subject, we generate Shading Surfaces for any "Volume Bounding" element that is not actually bounding an Analytical Volume. If you want to get creative with bounding elements, you can certainly simulate many shading surfaces.

We are limited in what we can transfer by the gbXML schema, as it is surface based. This makes it pretty difficult to represent the complex forms oftten used for Shading Surfaces. Additionally, we don't really have a mechanism today to "mark" an element as a shading surface. Without that, you'd end up with a complex model that choked the analysis engine. DOE-2 for example, won't accept more than 1024 shading surfaces.

Hope that clears up your questions. If you have additional questions, you can take a look at the PDF in our Help File that documents the analysis methodology.

Cheers,
Kyle B

[steven.rosen]

Yes, you can have shading surfaces. These surfaces are generated when Bounding Elements in the Revit Physical Model do not actually bound any Rooms. NOTE: Within the <VE> Shading Surfaces are known as Obstructions. It is important to understand that only elements that have the Room Bounding parameter checked (except Floors & Ceilings) and no adjacent Rooms will be converted into Shading Surfaces in the Analytical Model.
Yes, you would need to call your glass door a window to use the <VE> glass U values. Alternatively you can export your model to XML (with your glass doors defined as doors) and import that XML file to a loads calculation program that allows you to specify the U value and percenatge of glass that comprises your door.

[ben.115043]

Thanks! I think that additional building construction values (as well as the possibility to make custom construction types) should definitely be a wishlist item.

[jlondenberg]

...You would have to model them as Windows rather than Doors to accomplish this goal....

Is there any way to call your door a window apart from deleting it in the model and placing a window of the same size/location?

[kyle.bernhardt]

Is there any way to call your door a window apart from deleting it in the model and placing a window of the same size/location?

Yes, there is a way. We define the Opening Type in the Analytical Model based upon the Category of the Family in Revit. You want your Door to be a Window for Energy Analysis, change its Category to Window.

You Tags won't work and it will mess up your schedules, but you asked for a way, and there you have it.

Cheers,
Kyle B