[Equest-users] Underfloor Patchwork

[Dakota Kelley]

Vikram,

 

I’ve had the same question, and I would love to hear other people sound off…

 

I believe eQUEST is trying to account for additional heat loss in perimeter zones, where the slab meets the foundation wall.  I’ve noticed that all the construction layers are the same except for the outer-most layer.  eQUEST usually creates a zone-specific layer like “EL1 UFMat (G.S1.U2.M1)” of type “R-value”.  The resistance of this material is what varies; core zones usually get something like R-100, and perimeter zones get something in the R-1 to R-20 range depending on whether foundation insulation is specified in the wizard.  If you choose the default core/perimeter zoning scheme, what eQUEST is doing becomes a little clearer.  The perimeter zones will all have a unique UF construction, but the layers will have identical properties.  Naturally, it gets more complicated with custom zoning when a perimeter zone extends fairly far into the core of the building.

 

To test my hypothesis I’d have to sit down with the ASHRAE Handbook, determine a specific construction’s F-value based on the location’s heating degree days, and then use design temps and the linear feet of perimeter exposure to backtrack into an equivalent U-value that I can compare to eQUEST.  However, the answer will still be an estimate at best.

 

To answer your question, I usually simplify the post-wizard defaults down to one core zone construction and one perimeter zone construction.  For the perimeter zones, I usually make a perimeter construction with a U-value equal to the average of the perimeter zones’ post-wizard UF constructions.  eQUEST does not account for the fact that the soil’s thermal properties fluctuate as it gains and loses moisture, so I wouldn’t lose too much sleep over it.

 

Thanks,

 

                                

                         DAKOTA KELLEY                                                              

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From: Vikram Sami [mailto:VSami at lasarchitect.com] 
Sent: Tuesday, August 11, 2009 1:38 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Underfloor Patchwork

 

This is a question that I’ve wondered about for a while. When you come out of the wizard, an UF material is created for each zone(like below), with different properties for each zone – with an amazing variation in properties across the board. Does anyone know why? Is it reasonable to assign one material to all of them (assuming they are the same construction and sitting on the same soil), and if so, how do I know which material to pick out of the 20+ construction assemblies created? 

 

 

 

 

 

Vikram Sami, LEED AP 
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