[Equest-users] wall composition and U value

[Nick Caton]

Interesting case:  I've modeled exactly as you've described for a very unique existing case where the windows were spray-painted opaque from the inside...  

(PS: spray-paint does *not* hold up well over time on exposed glass - file that away as a pretty bad idea)!

Vikram is right:  your approximation including windows would correctly approximate the non-solar heat transfer loads but will fall short when it comes to solar loads, which are usually a big enough deal to warrant actually specifying the windows.  Averaging the non-window constructions is often a very acceptable time-saving measure, especially when the constructions are largely similar.  I would think twice before averaging together constructions with very different properties.

A tip:  if you are going to go through the effort of defining your uvalues separately for each wall construction, it may be worth noting eQuest will tally the net u-value for each construction automatically if you use the layers approach, much like other load calculation software.  I find that as easy as any other method, and you get a weighted construction as icing on the cake ;).


NICK CATON, P.E.
SENIOR ENGINEER

Smith & Boucher Engineers
25501 west valley parkway, suite 200
olathe, ks 66061
direct 913.344.0036
fax 913.345.0617
www.smithboucher.com 


-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Sami, Vikram
Sent: Wednesday, February 29, 2012 1:25 PM
To: tanyer at metu.edu.tr; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] wall composition and U value

You need to separate out the windows - only model opaque elements as walls. Model the windows as windows.

Otherwise - it should be fine to model the wall as a homogenous average of the multiple layers - you should be able to do a weighted average calc.

Do you have insulation? Does it run continuous over everything?


Vikram Sami, LEED AP BD+C
Sustainable Design Analyst
1315 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462    f: 404.892.5823       e: vikram.sami at perkinswill.com   www.perkinswill.com
Perkins+Will.  Ideas + buildings that honor the broader goals of society


-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of tanyer at metu.edu.tr
Sent: Wednesday, February 29, 2012 8:57 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] wall composition and U value

Dear all,

I am trying to find the U value of a wall which is composed of concrete beams and colums (20%) masonry (60%) and glazing (20%).

I know the U values of the components and I would like to calculate the average U value for this wall since it is a single entity in eQuest.

Do I need to include the area of the glazing when calculating the total U value?
0.2 x Ucnct + 0.6 x Umsry + 0.2 x Uglzg

OR, do I have to extrapolate the concrete and the masonry parts as if covering the glazing part?
0.25 x Ucnct + 0.75 x Umsry

As you know we also define the glazing U value later seperately.

Thanks

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