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Composite Materials/Materials, K-values, Energos/Uvalues for assemblies in VW

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Currently I am in the process of recomputing many of the k-values for the materials that come shipped with VW there are quite a few things missing when regarding the calculation of K-values and R values - namely - Thermal Bridging.


In Ashrae Fundamentals and ASHRAE 90.1 / International energy conservation code - there are values that are calculated separately for :

1. Wood Stud wall assemblies (Cavity Filled insulation batt)

2. Steel stud wall assemblies (cavity filled insulations)

3. CMU Assemblies (i.e. weight/cores grouted, ungrouted, filled or partially filled)

4. ASHRAE Fundamentals (Chapter 26 and chapter 33 respectively)


There happens to be a predicament that is caused by composite materials vs traditional material types in VW

1. True R values cannot be determined from composite material k-values due to bridging calculated as noted in ASHRAE 90.1 and/or steel/wood reduction coefficients with insulated cavity walls, and / or concrete / masonry conditions with integrated insulation types. I.e. Masonry with grouted cores, or partially grouted insulated, partially grouted uninsulated, etc...

2. Do worksheets have the ability to subdivide composite materials in worksheets to show their respective counter parts? i.e. wood stud wall 16" o.c. w/ batt fiber insulation (is composed of two materials) - can worksheets show the composite material and their respective integral materials (i.e. batt fiber separate from wood stud wall partition)

3. Calculation of interior and exterior air film - is this automatically integrated into Energos? or should those components be added to each wall type?

4. Given that composite materials calculate composite k-value - based on the percentage of the respective components, an automated method's purpose of calculating UA values would be defeated (I think). Any ideas regarding this?


As a result, my question is this :

1. What are the benefits of composite materials? What is their purpose, and how are they helpful to Energos or Energy conservation code compliance - other than finding the percentage value of components in their respective assemblies and multiplying them by their respective k / r values?


This will certainly guide the material / composite material process - where i needed to decide to create CMU / grouted / insulated materials as a single material, or as a composite one?


I know this post is long winded, hopefully we can have a productive discussion!

Thanks in advance!

Edited by Samuel Derenboim
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  • Vectorworks, Inc Employee

Hi @Samuel Derenboim let me try and answer this question:


There are several prescribed methods to accurately determine a compound material R-value taking thermal bridging into account. One of those is called Isothermal Planes method, and uses lambda values of individual materials within the compound and applies percentages to obtain the lambda value of the compound material. This method is described by ASHRAE and is what Vectorworks uses to calculate compound material lambda values and it works well for timber studwork and masonry, bit less so for metal studwork which needs a complex modelling assessment to get accurate lambdas or R-values. If that's what you need and the Isothermal planes method is not precise enough, you have the option of doing manual calculations separately for those wall assemblies and inputing that R-value in the Insertion tab of the Wall settings instead of using the automatic calculation. 


Interior and exterior surface resistance (air film layer) is automatically taken into account - you can actually see those if you go to Edit List under Object Boundary Type in Energos section of Walls, Slabs and Roofs. These are constants depending on building element position and whether the thermal flow is upward, downward or horizontal so you just need to choose a correct option for each element. 


As a general comment on compound Materials, they provide you with a solution for multiple distinct materials within a single thickness component. Without them, there is no real way of handling something like insulated studwork. Using compound Materials allow accurate quantity take-offs for example, and embodied carbon assessments to include correct areas/volumes of each of these materials.


Hopefully I've answered some of the queries, but as you said - it starts a productive discussion. 


Thanks for asking these great questions!

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