Mass transfer deck slab edge calculation

[Pavlo Serdechnyi]

Hello everyone!

I faced some difficulties trying to define the U-value of the mass transfer deck slab edge.

According to the definition from the 2015 Seattle Energy Code (based on International Energy Conservation Code): "Mass transfer deck slab edge is that portion of the above-grade wall made up of the concrete slab where it extends past the footprint of the floor above. The area of the slab edge shall be defined as the thickness of the slab multiplied by the perimeter of the edge condition." Please see the picture attached to this message for better visualization of such a thing. 

The code requires defining and calculate this area separately, so I think that I can not add the Psi-value to the general thermal resistance of the wall above this thermal bridge.

It would be great if someone could help me with this question of calculating the exact U-value of the mass transfer deck slab edge area. And I will be glad to hear any ideas of what informational sources can bring me closer to my goal.

Thank you!

Paul Serdechnyi

[yal...@gmail.com]

Hi Paul,

Seattle code requires compliance through U-value for what is really a psi-value problem which makes no sense and would be better to use psi values for something like this. However given you need to comply and have no other choice I would find the psi value which is a heat loss per linear distance and divide it by the slab thickness to get a u-value which is a heat loss per unit area. For walls and opaque assemblies you need to use material properties and boundary conditions per ASHRAE 90.1 Appendix A which is outside the scope of NFRC.

Yalin