Dear All,
Can anybody please tell how to model multilayer wall (thick concrete+ air
gap +thick concrete + other materials ) in eQUEST ?
I tried eQUEST option of layered construction, but error occurs "Wall is too
thick".
Is there any other method to model it ?
Thank you in advance.
Regards
Prasad
I haven't run into this error myself, but I have the loose understanding that eQuest begins having trouble when constructions are in excess of ~3feet.
Very thick concrete constructions have come up on the lists before - I would put forward that if you have many feet of heavy-weight concrete (thermally massive), under many circumstances your construction is approaching the performance of an adiabatic construction, moreso if this envelope is underground. Another way of putting this is net heat transfer may be negligible. Additional details/context regarding what's happening thermally on both sides of the envelope might help others in the list chime in with support/disagreement on this front.
That said, if you just want to get around the thickness limitation, you might be able to define a layer for your thick concrete using a custom (theoretical/impossible) material to represent say 6ft of concrete pressed into a 1ft thickness (applying a 6x factor to all the per-foot material properties). Haven't tried this myself but it's a thought.
~Nick
[cid:489575314 at 22072009-0ABB]
NICK CATON, P.E.
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Smith & Boucher Engineers
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The easiest way to do this I think is in the DD wizard. I have a big wall buildup also - similar at least.
First of all, remember if you have multiple kinds of exterior wall buildup you want to draw separate shells for those areas. For example, my current project has a part of the building that is 2X6 exterior walls because it was added later on to a 8" cmu exterior wall building.
The shells just get drawn separately and you can specify the layup in the design development wizard for each.
The easiest way to do this, from what I've seen, is to first calculate the R-value of the system and any EIFS layers you may have added.
When you specify the exterior walls in the design development wizard show your construction (CMU, 2x6, whatever it is) and get as close as the wizard will let you to the actual wall system.
Then you need to make sure the R-rating of the final wall system in equest is the same or similar to the R-rating of the wall you have at your building. This will make sure that the energy simulations are at least in the ballpark- based on overall construction type and R-value.
The same will work for Roof construction too. Get as close as you can to the actual roof layup in the wizard. Then get close to what the R-value is for the foam.
If the R-value of the system is more than what you can see in the insulation dropdown menus, just add "additional insulation" and use that dropdown menu to add more.
This is all done on Sheet 3 of the design development wizard.
On sheet 4 is Your vertical wall construction type/ insulation and ceiling finish & insulation so don't forget about that either. Remember to show any insulation here that you may have at ceiling level.
Chris Baker
CCI CAD Drafter
Fort Wainwright, Alaska
Prasad,
I don't think modeling the wall in another way will overcome the problem of "Wall too
thick", which indicates that DOE-2 is not able to derive a common ratio for the wall
response factors after 100 time steps. Please check your inputs to make sure that they're
correct, and if so, then your wall construction is simply too massive or has too much
thermal discontinuity (?) across the layers, like concrete, insulation, concrete,
insulation, etc. for DOE-2 to handle. You can model the wall as a pure resistance layer,
but then it would have no thermal mass at all. Better to play around with the material
properties, esp. the specific-heat, until the error goes away.
Joe
Joe Huang
White Box Technologies, Inc.
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