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Chun Kwong,<br>
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).<br>
In any case, I am not sure that the model is wrong and I certainly
don't see anything incorrect in your implementation.<br>
Best,<br>
David<br>
<br>
<br>
<div class="moz-cite-prefix">On 7/10/2013 02:30,
<a class="moz-txt-link-abbreviated" href="mailto:a8304506@graduate.hku.hk">a8304506@graduate.hku.hk</a> wrote:<br>
</div>
<blockquote cite="mid:1373441455.51dd0daff3778@imp3.webmail.hku.hk"
type="cite">
<pre wrap="">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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<pre class="moz-signature" cols="72">--
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI 53703 USA
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F:+1.608.278.1475
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