BDL Error

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All,

I get the following BDL error in my model

WALL has no heat capacity. U-Value used.

I am modeling the baseline envelope as prescribed in Appendix G of
90.1-2004. Referring to Appendix A of 90.1-2004 to model the baseline
envelope, I created layers for the wall construction seen in the attached
screenshot. The resulting U-value for the wall is 0.124. Can I not model a
wall in this manner? It seems specifying the U-value alone in the
construction layer would do the same thing.

Thomas Vu, E.I.

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Hello Thomas,
I don't think you can make a construction where all the layers are R-value inputs. For a construction to have layers the program must be able to calculate some mass for the wall. If you want to specify only the thermal resistance of the wall choose "u-value input" when you create a new construction and put in the overall u-value for the wall assembly.

Kelsey Van Tassel

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Thomas/Kelsey:

A little while ago Adam Boyd put forward a very handy resource I'm attaching.

You're right in that the root issue here is that you can't really model a wall with no mass. When you specify a layer by U-value only (simplified method), notice that you cannot enter a mass for that layer. If you read the associated help files you'll learn this method of specifying materials is only intended for things with negligible mass (i.e. air films). Specifying a whole construction with layers and ignoring mass means you have a wall which is going to act really weird when it comes time to figure out heat retention/transfer behavior with the exterior. It works fine in simpler loads/modeling programs that assume information for you, but in eQuest you have to account for mass in your constructions.

That said, Appendix G and Appendix A do not explicitly tell us the thermal mass properties of the intended baseline construction layers, but helpful fellows like Adam have shared the legwork of looking these items up - read the thread below, examine and try to import the attached .inp into your model.

~Nick

NICK CATON, E.I.T.

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Hi

I am using eQuest 3-63 can any one help me out on the below error please find the attachment.

TYPE=PROPERTIES TH=0.0625 COND=0.1330 DENS=45.0 S-H=0.2 ..
Cannot simulate LAYERS Ceilg Cons Layers as given. The wall is too thin or too light. THICKNESS and/or DENSITY*SPECIFIC HEAT is too small. Use U-VALUE CONSTRUCTION.

BDL Error

cannot simulate Layer ceilg cons layers as given. The wall is too thin too light. Thickness and/or Density*specific heat is too small. Use U-Value construction.

Thanks
Ramesh BR

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Ramesh,

For future reference, you need to send out more than your pd2 file for others to be able to view your model. In this case, you should at minimum send the pd2/inp, and you?d want to include the non-library weather file as well if you anticipated others might need to run simulations to troubleshoot. That said, I think I can guess at the source of this error without looking at your model:

When defining a custom construction (or modifying a wizard construction) - you cannot define too many layers using the ?simplified? method with only an R-value. This is how simpler programs like HAP/TRACE operate ? I suppose they assume thermal massing figures, if retained/transferred heat is modeled at all. This input method for construction layers exists in eQuest specifically to define things like air film which have no appreciable thermal mass.

If the total defined thermal mass of the wall is too low or zero, the program giving you an error like this because it is recognizing that the energy model will behave unlike any real construction.

~Nick

NICK CATON, E.I.T.

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Hi Nick

Thanks a lot for your prompt reply, as requested please find the attachment of the complete project file.

The layers
"Ceilg Cons Layers" = LAYERS
MATERIAL = ( "Gypsum LW Agg 3/4in (GP04)" )

"Ceilg Construction" = CONSTRUCTION
TYPE = LAYERS
LAYERS = "Ceilg Cons Layers"

are getting created automatically please let me know where i am wrong. And one more clarification I had created four storey building if you look at the model it has an gap of one floor I do not where i am wrong.

Thanks
Ramesh BR

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Ramesh,

This is an odd problem, but for now, I think you need to either (A) choose a different interior ceiling type (drywall/acoustic), or else (B) go to detailed, change the ?Ceilg Construction? construction to ?U-value Input,? type ? 0.87, and then right-click delete the ?Ceilg Cons Layers? in the component tree ? either route will allow the model to run.

All,

I think this is a bug in the SD wizards?

The SD Wizard-generated layers construction for ?Plaster Ceiling,? for interior ceilings is causing the BDL error as follows:

*ERROR*****Cannot simulate LAYERS Ceilg Cons Layers as given. The wall is too

thin or too light. THICKNESS and/or DENSITY*SPECIFIC HEAT is too

small. Use U-VALUE CONSTRUCTION.

The preceding line is:

COMMON RATIO = 0.0000009191 U-VALUE = 0.8696221113

0.87 isn?t odd, and library gyp board is the only layer defined aside from the final air film layer. The problem goes away if ?drywall? or ?acoustic? ceiling is selected instead.

~Nick

NICK CATON, E.I.T.

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Hi Ramesh,

Regarding your second question of a ?missing floor? ? I haven?t opened your file, but I think I know what the problem is. eQUEST can use a ?floor-multiplier? and simulate only one floor of each type. So on your 4-story building you have 1 ground floor, 2 middle floors, and 1 top floor. eQUEST assumes that the 2 middle floors are identical and will only model one of them. If you want it to explicitly model each floor you can un-tick the box labeled floor multipliers.

If you had a 5 story building it would also only show 3 floors if you use floor multipliers. I hope this helps.

[cid:image001.png at 01CB176A.E10C4100]

Regards,
Alex Krickx

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