[TRNSYS-users] abnormal fluctuation of cooling

[David Bradley]

Yujun,
  I am not sure that there is anything wrong with the simulation; you 
have 18 airchanges per hour of ambient air that is somewhere between 16 
and 21C going into the space and that is keeping the zone temperature 
below 26C when the cooling would turn on. If you switch off your natural 
ventilation by multiplying the equation by zero, you'll see that the 
space gets up to the cooling temperature every day.

 You should probably multiply the zone capacitance by 5 or 10. The value 
that you have for the zone accounts only for the thermal capacitance of 
the zone air (it ignores the capacitance of all the other things in the 
zone like shelving, products, furniture, etc.). You should also set the 
humidity capacitance multiplier to a value of about 5 to account for the 
furniture's capacity to absorb moisture. Lastly, I think that a 1 hour 
timestep might be too long. Bear in mind that the decision to activate 
or deactivate the natural ventilation system can only be made once per 
timestep. The fact that the natural ventilation is on for one time step, 
then off for one time step, then back on for a time step suggests to me 
that the system isn't very stable.

Best,
 David


Yujun TAO wrote:
> Hello,
> I simulated a cooling commercial with a natural ventilation, the 
> natural ventilation is modeled in a equation.
> I don't understand why there is abnormal fluctuation of Qcool curve 
> and the temperature doesn't reach 26 degrees.
> I feel it maybe concern the equation.
> Could someone help me?
>
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Thermal Energy System Specialists (TESS), LLC 
David BRADLEY                      22 N. Carroll Street - Suite 370 
Partner                            Madison, WI 53703 
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E-mail: bradley at tess-inc.com 
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