Inputs- Building Materials

[ChrisBriley-ID]

I’d like to control some of the inputs of some of the materials so I’d like to understand the inputs.  In my walls for example I chose an Autodesk Material ‘Cellulose Fill’ it seems to yield the correct R-value (or very close to it anyway) when I’m in the ‘Edit Assembly’ window.  But when I check the ‘Thermal tab’ on the material properties.  Things get a bit confusing.  Thermal conductivity for this material is 0.0243 btu/(hr·ft·°F) I’m assuming this is U-value? When I calculate its reciprocal to get an R-value, I get 41.152. Am I correct in thinking that’s R per foot of thickness?  That sounds about right because then that’s R-3.43 per inch.  I'd love to verify this assumption.

If I increase its density, I notice that it does not affect its thermal conductivity or its specific heat?  Then how does Revit or GBS view “Density” of material?  Does Revit and GBS actually consider thermal mass?  that would be very cool.

Permeability:  this is awesome, but leads me to wonder again what revit does with this information or is it for future hygrothermic analysis that Revit plans to perform?  

It would be great if there were a paper or video that described how to work with these inputs accurately.

Glass:  Here’s a really tricky one.  Here, I chose another Autodesk material to begin with (within a window family).  I was expecting to input typical glazing values (U, SHGC, and VT.)  However the input catagories are the same for other materials.  Thermal conductivity is now metric however.  I can handle that conversion, but again, I don’t know it that’s per inch or per foot? 

And what about solar heat gain coefficient.  Here in climate zone 6 it’s a big deal.  Is this emissivity?  If so, is this just a straight conversion?  So if my glazing has a SHGC of 0.61, my emissivity would be 0.61?  Is that right?

[Lance.Coffey]

The material thermal properties relate to the single material. Since there can be multiple materials check the Analytical Properties category of the family type properties to find the Heat Transfer Coefficient (U), Thermal Resistance (R) and Thermal Mass values of the element.

For Window elements, the Analytic Construction parameter pick list (in the Analytical Properties category of the type properties) allows you to select the type of Window, and the selected window will then fill out the glazing values.

[ChrisBriley-ID]

Thanks Lance.

That really doesn't answer my questions. What are Revit's units for U value? Revit uses 'btu/(hr·ft·°F)'  I'm assuming they mean btu/(hr·ft2·°F) per inch?  (and that '2' denotes squared) I'm hoping somone who knows how revit calculates U value would verify this so that I can input non-prescriptive values and have some control over inputs. 

Likewise with galss, I'm trying NOT to use Revit's pre-determined values for glazing.  That's the whole point.  My values do not exist in your list.  I would like to use correct values, thank you.  How do I CORRECTLY input glazing values to my window family materials and get Revit to use those values?

Chris

[ChrisBriley-ID]

Attached is the help topic and my energy settings side by side.  Step 3 says to "Under Detailed Model, select Include Model Properties".  I do not see where I can make this selection.

THings are very vague to me about what Revit is really using from my model and what its assuming.

Chris 

[ChrisBriley-ID]

oops forgot to attach the image.

Chris

[Lance.Coffey]

I believe that Mohammad answered this question (at least tangentially) in the thread:

Inputs- Building Materials (Similar name but different thread)

For those that have not seen the thread above, or changed the Export Category, if you change the Export Category from Spaces to Rooms, then you should see the Include Thermal Properties checkbox.