[TRNSYS-users] Type 60c outlet temperature

[Igor Seso]

Hi David,

I don't use any equations for the flow rate just a pump with fixed flow rate and simple controller Type 2. When I put for example a tank Type 60c - 0,3 m3, with internal heat exchanger having area of 1,45 m2 and length 16m I set up flow of 260kg/h with 4 m2 collectors and there are no problems, but if I increase the boiler to 1 m3 exchanger area to 3,5 m2 and length 20m leaving the same flow rate I have convergence problem ( message "1 non -convergences for Hx 1.Final UAHx value = 169.181"), then increasing the flow to 400 kg/h there is no problem, the simulation reaches it end of 8760h. Any idea why this happens? (I assume that there is something influenced by the total volume of the system collector-heat exchanger...)

Regards
Igor    
On Wednesday, April 9, 2014 5:49 PM, David BRADLEY <d.bradley at tess-inc.com> wrote:
 
Igor,
  It is a little worrisome that you get convergence problems at low
    flow rates. If you have used equations to set a minimum turndown
    ratio on a pump (essentially a minimum flow rate) then you can
    certainly run into some situations where your setpoints are not met.
    When doing this, however, it is important that you use similar
    equations in conjunction with your controller model so that the
    controller doesn't try to make the pump do something that it is
    unable to do (and thereby lead to convergence problems).
Kind regards,
 David



On 4/8/2014 13:37, Igor Seso wrote:

Thank you David, exactly that was the problem,  I was recording temperatures above 60 C when there was no flow through the valve - I put a trigger printer recording only temp. when there is flow and the temperatures values were exactly as the set mixing temp.    
>
>
>I tried to put pipes between the collector the tank and the pump  to get more realistic results regard outlet temperaturesas a result of the increased thermal mass and it was ok - but the only disadvantage is that the pump flow can not go under certain value (total volume of fluid in pipes) it gives convergence problems...so it means that it is not possible to test the influence of low flow on system efficiency etc..
>
>
>Regards,
>Barto
>
>
>
>
>
>
>On Tuesday, April 8, 2014 7:34 PM, David BRADLEY <d.bradley at tess-inc.com> wrote:
> 
>Barto,
>  It is not really possible to
                                    diagnose the problem without looking
                                    at the project. I would recommend
                                    using an online plotter to look at
                                    all of the temperatures and flow
                                    rates of all the flows going into
                                    and coming out of the tank. If for
                                    some reason all of the temperatures
                                    in the system are over 60C
                                    (including the temperature of the
                                    tempering water) then Type953 would
                                    not be able to temper the outlet
                                    flow. It could also be that you are
                                    seeing higher than 60C temperature
                                    at the mixing valve when there is no
                                    flow through the valve.
>  If you are not able to sort out
                                    the problem using Type65 as a
                                    debugging tool then you should send
                                    your project to your distributor so
                                    that they can have a look at it.
>Kind regards,
> David
>
>
>
>
>On 4/7/2014 08:16, Barto Pene wrote:
>
>Hi , 
>>
>>
>>I get some strange result i.e I can not find logic in it: I use tank Type 60c only heated by standard solar collector installation. I use the differential controller(monitoring temp.) to limit the tank top temperature to 60C and I'm also using tempering valve Type 953 with diverting and three-wat valves for controling the outlet temp. In the simulation I get temperatures at the outlet of the three-way valve (after mixing) higher than 60C (even 80-90C) how is it possible?
>>
>>
>>When I model the HX in Type60c with glycol solution I get convergence problems and with water there is no problem...?
>>
>>
>>Thank you
>>
>>
>>Regards
>>Barto
>>
>>
>>_______________________________________________
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>
>-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA P:+1.608.274.2577
F:+1.608.278.1475 d.bradley at tess-inc.com http://www.tess-inc.com http://www.trnsys.com
>
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>_______________________________________________
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA P:+1.608.274.2577
F:+1.608.278.1475 d.bradley at tess-inc.com http://www.tess-inc.com http://www.trnsys.com
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