When using the Autodesk Revit + Insight workflow for early architectural energy modeling, and using the Detailed Items option which uses the Thermal Assets associated with each Revit material, it is often necessary to create a custom asset for a specific product.
In this workflow, the custom thermal resistance and mass values are what get feed into the DOE 2.2. energy modeling engine, for walls, floors roofs, etc.
That is the topic of today's post...
In this example, per the image above, a specific open cell spray foam insulation is being considered; click here to open this PDF. This document lists the thermal resistance [75˚F, (h-ft 2-˚F)/Btu]. And, the aged r-value for several thicknesses.
If we want to represent this material in Revit we must do a little math, as Revit multiplies the thermal asset properties X the thickness of the "layer" in the wall type, which is great... as it offers the most flexibility.
The conductivity listed above, for 1 inch, notice its units show -in so you do need to divide that by 12 to get the ‘normal’ conductivity (0.02246 btu/(hr·ft·°F)) which gives an r-value of 3.71.
Next, enter various thicknesses and compare to the second image above, from the manufacturer's cut sheet. Then, if needed, adjust the Thermal Conductivity up/down slightly until Revit's wall type (in this example) r-value matches.
FYI: In this example I deleted the thermal properties for the other layers within the wall to focus only on the insulation.
Before pushing the Energy Analysis Model (EAM) out to Insight, you can double check the wall/roof/floor assembly has the correct information by selecting an analytical surface and reviewing the properties as shown below.
When this information is pushed to Insight, be sure to select the BIM Setting for the inputs, now that things are more refined for the given project. In the image below, notice how the wall construction (@ 20.7 r-value) is lands below R38 and above R13 on the graph.
FYI: the triangle, see image below, represents the BIM Setting within Insight.
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