UA Convergence Error

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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

Paul Diglio's picture
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Joined: 2011-09-30
Reputation: 400

Bill, David, Jeff and Nick:
Thank you for the responses.
I am using 3.65 Build 7175.? I am not using the refrigeration mode, as far as I know.? The only two modes shown under Select Version are 2.2 and 2.3.? I am using 2.3.? Doesn't the refrigeration version have an R after the DOE version?

I am not using a waterside economizer.? I have 2 air handlers per building.? One feeds the north all three floors and one feeds the south all three floors.? They are VAV units with a chilled water loop and an electric reheat coil for each building.? Each building has 2 chillers for the loop and one pump.? The VAV boxes do not have reheat capability.

Perhaps the oddest thing is that this project is in Saudi Arabia and I am using the TMY2/RIYADH83.bin weather file.
The error message I am getting is:
***ERROR***********************************************************************
Heat-Exchanger: EA Sys1 A-1 (VAVS) (G) UA calculation
failed to converge.
The EA Sys A-1 in the above error message changes.? Sometimes I increase the number of ACH/Hr for a few zones in building A and I get an error message for EB System B-2 (building B) or EC System C1 (Building C).? Can't make rhyme or reason of connection.

Many thanks,

Paul Diglio
87 Fairmont Avenue
New Haven, CT 06513

203-415-0082

On Monday, December 9, 2019, 5:27:53 PM EST, Jeff Hirsch wrote:

That message seems to indicate you are using the refrigeration version (2.2R) ... for a conventional building model you should use 2.3 or 2.2 not 2.2R ... in the refrigeration version coils use a heat exchanger model, so you probably have many heat exchangers. But, again, perhaps you should be using 2.3.?Jeff Hirsch
James J. Hirsch & Associates
voice mail: (805) 553-9000
mobile: (805) 532-1045

?From: Paul Diglio via Equest-users Sent: Monday, December 9, 2019 3:13 AMTo: Equest-users 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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Paul Diglio's picture
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Joined: 2011-09-30
Reputation: 400

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= Capacity
UA= product of conductance and cross sectional area.
delta T= Temperature difference between ends.

[image: image.png]

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

[image: image.png]

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.Kumar
Freelancer-Energy Simulation and Day-lighting.

*....................................................................................................................................................*
.

---------- Forwarded message ----------
From: Paul Diglio
To: Equest-users
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

_______________________________________________
Equest-users mailing list
Equest-users at lists.onebuilding.org
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org

Sharad Kumar2's picture
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Joined: 2015-05-21
Reputation: 0

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 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
To:?Equest-users
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?

_______________________________________________
Equest-users mailing list
Equest-users at lists.onebuilding.org
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
_______________________________________________
Equest-users mailing list
http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
To unsubscribe from this mailing list send? a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG

Paul Diglio's picture
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Joined: 2011-09-30
Reputation: 400

I didn?t think of this earlier, but search the *.inp to see if one is in there associated with the AHU that crashes, maybe some relic code is in the file that isn?t shown in the UI.

DSE Mobile
773.490.5038

David Eldridge's picture
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Joined: 2012-05-08
Reputation: 1

Hi David:
No heat exchangers in the .inp file.
Thank you,
Paul Diglio
87 Fairmont Avenue
New Haven, CT 06513

203-415-0082

On Tuesday, December 10, 2019, 10:46:12 AM EST, David Eldridge wrote:

I didn?t think of this earlier, but search the *.inp to see if one is in there associated with the AHU that crashes, maybe some relic code is in the file that isn?t shown in the UI.

DSE Mobile773.490.5038

Paul Diglio's picture
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Joined: 2011-09-30
Reputation: 400

Thanks Brian, glad to hear I'm not having hallucinations.? I don't think the sizing matters because I input the actual airflow, static pressure, cooling capacity and heating capacity.
I seem to be making progress by changing some of the inputs.
Regards,

Paul Diglio
87 Fairmont Avenue
New Haven, CT 06513

203-415-0082

On Tuesday, December 10, 2019, 11:34:06 AM EST, Brian Fountain wrote:

Paul,

?

I have seen this error in 2.3 ? and have had it crop up with small changes to the building/model as you describe.? I am struggling to remember how we got past it.?

?

I believe it has to do with the new sizing routine for air handling units.? I was hoping Doug Maddox would jump into the conversation.? (he has a video at maddoxenergy.com on the sizing routine but it does not address this issue specifically)

?

A couple of questions:

?

1)?????Do you have heating and cooling design days set up?? I would recommend this. (otherwise it runs the whole year for sizing).

2)????? ?

?

I will continue to try and remember which project(s) this came up on and how we resolved it.? Sorry I am not more help but you aren?t alone (which also doesn?t help).

?

Brian

?

?

?

Footprint

Brian Fountain
Associate
d416 572 8501 m416 562 6831

?

Paul Diglio's picture
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Joined: 2011-09-30
Reputation: 400

Hi Paul,

The way to have a heat exchanger in the model is as follows:

The Heat exchanger is made as follows with the project tree right click.

[image: image.png]
By right click on the project we can have heat exchanger which is as
follows:

[image: image.png]

Then by double click on the heat exchanger we can have the heat exchanger
dialogue as follows.

[image: image.png]

So in this way we can have a heat exchanger made in the built.

*Thanks and regards*,
Sharad.Kumar
Freelancer.

Sharad Kumar2's picture
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Joined: 2015-05-21
Reputation: 0

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 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

?

Paul Diglio's picture
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Joined: 2011-09-30
Reputation: 400

Hi Melanie:
I thought everyone would like to know that in addition to helping resolve my convergence issues, by putting in cooling and heating design days my project simulates much faster.
Before, the simulation meter would go up to 185% before it was complete, and with the CDD and HDD defined, the simulation completes at 105%, which takes about half the time.
Thank you,

Paul Diglio
87 Fairmont Avenue
New Haven, CT 06513

203-415-0082

On Wednesday, December 11, 2019, 1:43:45 PM EST, Melanie Stachowiak wrote:

Paul,

Go to project & Site and set up design degree days if they aren't already in there (one for cooling, one for heating). If you've already created them, just adjust the number of degree days. You can also isolate to a single hour if you wish instead of having a high or low. Looks like it was my cooling design degree day that was causing the problem. I still have my heating degree day set up for seven days. This was set up for Buffalo NY (ASHRAE climate 5A), so your values might be different depending on your location. ?

See screen clips below.

~Mel

?

????????????????

?

?

Melanie G. Stachowiak, P.E., LEED AP BD+C, CMVP
Project Manager, Sustainability/Commissioning Services Group

M/E Engineering, P.C.
Suite 320, 60 Lakefront Boulevard
Buffalo, NY 14202
716.845.5092 x1207 | C: 716.830.7038
mgstachowiak at meengineering.com
www.meengineering.com

?

Paul Diglio's picture
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Reputation: 400