[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [TRNSYS-users] Type 60c outlet temperature



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@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@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


_______________________________________________
TRNSYS-users mailing list
TRNSYS-users@cae.wisc.edu
https://mailman.cae.wisc.edu/listinfo/trnsys-users

-- 
***************************
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@tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com

_______________________________________________
TRNSYS-users mailing list
TRNSYS-users@cae.wisc.edu
https://mailman.cae.wisc.edu/listinfo/trnsys-users




_______________________________________________
TRNSYS-users mailing list
TRNSYS-users@cae.wisc.edu
https://mailman.cae.wisc.edu/listinfo/trnsys-users

-- 
***************************
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@tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com