[Equest-users] UA Convergence Error

[Paul Diglio]

Thanks so much Jeff, now it makes sense and I will try to find the dt problem/

Paul Diglio
87 Fairmont Avenue 
New Haven, CT 06513 

203-415-0082 

    On Tuesday, December 10, 2019, 8:22:18 PM EST, Jeff Hirsch <james.j.hirsch at gmail.com> wrote:  
 
 I do not believe that screen exists in 2.3 recent versions and it looks like the version he is showing is from an older refrigeration version. The error you are getting is, I believe, generated during the air handler coil design calculations when it is trying to find the effective heat exchanger UA for the coil. It takes the flows and temperatures on each side of the surface and solves for a UA that results in a capacity within .1% of the specified or calculated required coil capacity. From the starting point “guess” (based on the required capacity divided by the design dT) it tries 100 iterations of the calculation each time altering the UA guess via an extrapolation or interpolation based on the history of guesses. Perhaps it cannot find the UA in 100 iterations due to a mismatch between some specified flow/temperatures values on either side of the HX surface ... check your inputs for a dT too small or a specified flow or capacity that seems incompatible with any specified or defaulted dT. We removed the HX input command (and thus eQUEST dialog) back in 2010 and instead default the creation of each HX during the design calculation phase – thus, unfortunately, the number of iterations and max error are set in code (100 and 0.001%) and not user changeable. Perhaps we need to reconsider that decision, but for now this problem can only be fixed by getting dT’s, flows and capacities to be compatible so a UA can be found within the iteration and tolerance limits. Jeff Hirsch
James J. Hirsch & Associates
voice mail: (805) 553-9000
mobile: (805) 532-1045


 From: Paul Diglio via Equest-users Sent: Tuesday, December 10, 2019 7:29 AMTo: equest-users ; Sharad Kumar Subject: Re: [Equest-users] UA Convergence Error Hi Sharad: I can't find any heat exchangers in my model.  How did you pull up the heat exchanger screen? Thank you,
 Paul Diglio
87 Fairmont Avenue 
New Haven, CT 06513 
  On Tuesday, December 10, 2019, 9:29:01 AM EST, Sharad Kumar via Equest-users <equest-users at lists.onebuilding.org> wrote:   Hi Paul,
I think the problem is being caused due to some heat exchanger kind of thing being modeled in the built.

I am guessing out the problem as follows:
The UA calculations does not converge as there can be might possibility that then UA product and after multiplication with delta T does not converge with the meeting of the capacity as the formula is Q= U* A* delta T.
Q=  CapacityUA= product of conductance and cross sectional area.delta T= Temperature difference between ends.

  Hence try to succumb with the problem in lieu-wise as above.



The other factors to have the UA product calculations to be right are as in above help page super-script which might can also guide as there are other factors based calculations is there as if there the boxed figure are outrun.
Hope this might help. Thanks and regards,Sharad.KumarFreelancer-Energy Simulation and Day-lighting.
..................................................................................................................................................... ---------- Forwarded message ----------
From: Paul Diglio <paul.diglio at sbcglobal.net>
To: Equest-users <equest-users at lists.onebuilding.org>
Cc: 
Bcc: 
Date: Mon, 9 Dec 2019 11:13:13 +0000 (UTC)
Subject: [Equest-users] UA Convergence Error
Hi Folks: I am getting a "heat exchanger XX Sys1 UA calculation failed to converge" error.  The model has three building in it and only two air handlers per building.  I don't have any heat exchangers attached to the air handlers or any heat recovery installed.
 Sometimes the error occurs when I change the glass type via the library and other times I get the error when I adjust the air changes per hour in one or two zones. In the example above, the error was for system B2, but it varies...sometimes systems A or C 1 or 2. Any ideas what the problem could be?  
 Thank you,
 Paul Diglio
87 Fairmont Avenue 
New Haven, CT 06513 


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