Error - Wall is too thick or too dense

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Dear All,

I am modelling a multilayer wall consisting of materials - Cement Plaster,
Medium weight concrete and Air.

The total wall thickness is ~ 1.2 ft. However, a simulation error is
obtained - "Wall is too thick or too dense".

Error persisted even when total wall thickness was increased by increasing
air gap thickness.

However, error did not occur when air gap thickness was reduced.

It appears that reducing air gap reduces density of the wall (density varies
directly with air gap).

Kindly inform whether there is a method in eQUEST by which such simulation
error (Wall is too thick or too dense) can be nullified.

Thanks in advance.



Prasad S Wani's picture
Joined: 2014-04-14
Reputation: 0

Hi Prasad,

Reducing your air gap would make the overall wall construction more dense... so if that eliminates the error message, then the error must be rooted in your wall construction exceeding some maximum thickness. I have run into this on much thicker constructions before involving large amounts of concrete, but 1.2 ft seems within a range of constructions I've successfully modeled without such errors as well.

Are you leveraging custom (not library) wall materials and/or have you modified any of the library material density entries, specifically? If so, I'd double check your inputs/units, but if that's not the issue, I would suggest reducing thickness of your concrete layer to a point that the "maximum construction thickness error" does not occur, and increasing its material density per unit depth (thickness) in turn to achieve the same net mass for that construction layer.

[cid:489575314 at 22072009-0ABB]


Smith & Boucher Engineers
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Nick-Caton's picture
Joined: 2011-09-30
Reputation: 805

Prasad, others,

When DOE-2 (the base program under eQUEST) reports a wall as too thick or too dense, what
it's really saying is that it failed to find a Common Ratio between the three response
factors at the end of 100 time steps (hours). Response Factors are what DOE-2 uses to
model heat flows, where the three response factors (X,Y,Z) give the fraction of the heat
flow occurring each hour after the initial pulse. For the residual heat flows beyond 100
hours, DOE-2 uses the Common Ratio since all three response factors are decaying (so to
speak) at the same rate.

When the Common Ratio is still changing, then DOE-2 says that the wall is "too thick or
too dense". Such situations are caused not just by the thickness or density of the wall,
but also when there are anomalies in the thermal characteristics of the layers. For
example, I've found that for a foundation layer (which is where I've most often
encountered this problem), DOE-2 will accept a single layer of dirt 5.25 ft thick, but
once a layer of insulation is added, the dirt layer can only be 2 ft thick or less.

In the case cited below, what is the order of the 3 layers? Is it as written - plaster,
concrete, then air ? - or is it plaster, air, and then concrete?
In the latter case, it's the air layer that's probably limiting the allowable thickness of
the concrete. How are you modeling the air gap? If it's as a mass layer and not a
resistance layer, you might want to play around with its thermal characteristics to reduce
the discontinuity, and see if that helps. What I mean is that as long as the resistance
of the air layer is correct, adding some thermal mass to it (or "transferring it" from the
concrete :-)) might help. Although this might sound wrong, but it's probably better than
limiting the thickness or mass of the concrete just to avoid the dreadful "too dense or
too thick" error.


Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at for simulation-ready weather data
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"

Joe Huang's picture
Joined: 2011-09-30
Reputation: 406


I used Nick's technique when I encountered the same error a few years ago, except I didn't bother adjusting the density of the insulation. I was evaluating insulation thicknesses on an underground wall. If I remember right, the maximum thickness of a wall in eQUEST is 20 inches, and for an underground wall eQUEST uses 12 of those inches for soil, so I had 8 inches left to play with. Since I was comparing insulation thicknesses of 2" and 3" I made the concrete 5" thick in the model, even though the actual concrete thickness was more.

The results from that model were kind of interesting. The additional insulation was beneficial for rooms that were heated only, but not for rooms that were cooled. The relatively cool wall must help with cooling more than it hurts with heating. Adding insulation reduces that free cooling.

Keith Swartz, PE, BEMP, LEED AP
Senior Energy Engineer | Energy Center of Wisconsin | Madison.Chicago.Minneapolis
608.210.7123 |

Keith Swartz's picture
Joined: 2011-09-30
Reputation: 0