Cooling and Heating Load Analysis

[nubrun.188780]

My firm has recently begun trying to use the Revit MEP heating and cooling load analysis instead of using Trace. But we've ran across a few problems. First, is there a way to add a new wall definition, so that we can customize the U-value, or other properties? I would imagine that there is some sort of database that it pulls from.

Also in the load report under results for space, under the heating column it lists infiltration and I was wondering if anyone can offer a definition on how the infilitration value is calculated because it seems excessive.

Thank you,
Nick

[nubrun.188780]

Another thing we noticed is that when we change values for our spaces, if we make the changes in the heating and cooling load menu, we have to run the calculation twice for these changes to take effect. On the other hand if we change the properties in the element properties for the space or zone then it takes only one calculation for the changes to integrated into the calculation.

Has anyone else had any issues or experience with this?

[jlondenberg]

We've found an issue in our office with the built in RevitMEP load calc's. It seems that when you make changes to the occupancy and fresh air settings, the cooling/heating load from the outside air does not change. Use with caution!

[steven.rosen]

"if we make the changes in the heating and cooling load menu, we have to run the calculation twice for these changes to take effect."
That's bad - needless to say. I can't reproduce that. When I change the Space Type, Construction Type, People & Electrical Data - in the heating and cooling load menu, that new information matches the Properties in the Space. Could you please specify what exactly was not updating and if you are using the web update 1 version of 2009?

[steven.rosen]

"how the infilitration value is calculated"
If you can please go to Help, under the title, Preparing for Heating and Cooling Loads Analysis, select the link "Appendix C - Energy Analysis Building & Space Type Imperial Data". In this IES document you will see the values used for Space & Building Types.

[steven.rosen]

"changes to the occupancy and fresh air settings, the cooling/heating load from the outside air does not change"
This does appear to be occuring when placing inputs using the Outdoor Air Information dialog, it will be reported, thanks for finding this issue.

[steven.rosen]

If I have not answered all concerns, there is a document that can be accessed from the Help menu - in the Heating and Cooling Loads Analysis Calculation page, scroll down & select the link: Revit MEP Apache Loads Calculation Methods.
This will take you to the IES document "ApacheLoads Calculation Methodology as used in Revit MEP 2008 <Virtual Environment> 5.7"