|
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@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 -- *************************** 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 |