[TRNSYS-users] Strange results from Type52

[David BRADLEY]

Chun Kwong,
   I suspect that when the water flowrate drops below a certain point, 
the heat transfer rate between the air and the water begins to decrease. 
I modified your simulation so that there is an equation that sets the 
pump control signal starting at a value of 1 and ending at 0 after 12 
hours. That way, you can see the progression of the outlet water 
temperature (I also used a shorter timestep). As you say, the water 
outlet temperature starts out increasing but when the flow rate through 
your coils gets to about 4000 kg/h (1.1 L/s) the outlet temperature 
starts to go back down. At that point, the face velocity of water 
through a single tube in the coil is only about 0.2 m/s, which seems a 
bit slow. I don't think that you have reached a laminar/turbulent flow 
point because there is not a sharp break in the water outlet 
temperatures (which you usually see because the Reynolds number drops 
very suddenly).
   In any case, I am not sure that the model is wrong and I certainly 
don't see anything incorrect in your implementation.
Best,
  David


On 7/10/2013 02:30, a8304506 at graduate.hku.hk wrote:
> Hello.
>
> I try to investigate the performance of a cooling coil at different chilled
> water flow rates (see attached .tpf file).  When I adjust the control signal of
> the water pump from 1 down to around 0.4, the chilled water leaving
> temperatures increase as expected.  However, when I further reduce the control
> signal, it appears that the leaving chilled water temperatures begin to
> decrease.  Is it the problem from the cooling coil model or any other issue?
> Please advise.  I am using TRNSYS16.1.  Thank you!
>
> Best Regards
> Chun Kwong LEE
> City University of Hong Kong
>
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>
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> TRNSYS-users at cae.wisc.edu
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-- 
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David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
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d.bradley at tess-inc.com

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