Re: [EnergyPlus_Support] DX cooling coil runtime fraction?

["Michael J. Witte" <mjwitte@xxxxxxxx>]

The HVAC time step is shortened if the system loads or space temperatures
change too much within a single HVAC time step.  The HVAC simulation iterates
to convergence within each time step, but the "detailed" reporting only reports
the final result for each time step.  I would not expect to see this type of
behavior in most cases.  What type of system do you have which is using the DX
coil?

Mike


On 16 Sep 2004, at 7:48, Rahul Chillar wrote:

>
> Because the performance of the DX coil is frequently non-linear, the air
> conditioner model must call the DX coil model several times (iterate) to
> determine the proper run time fraction to meet the zone load. The cooling
> convergence tolerance is the error tolerance used to terminate the iteration
> procedure when the following equation is satisfied:
>
> (QZoneLoad- Q Window AC out )/(Qzone Load) < CoolingConvergenceTolerance
>
> The maximum number of iterations is currently limited to 15, with a warning
> message generated if the above equation is not satisfied within the maximum
> number of iterations.
>
> Also while iteration say the first guess value may be 1 then the next will be
> zero to get the bounds in which the answer exists then it reaches upper bound of
> say 0.8 then the next lower bound is 0.2 so the anwer is between 0.8 and 0.2.
> this continues till convergence is reached. Thanks Rahul Chillar
>
> zhaicq98 <chaoqinz@xxxxxxxxxxxxxx> wrote:
> Hi,
>
> I have a question about the output object: DX cooling coil runtime
> fraction. I output the data using detailed output mode. I specify the
> timestep is 10 minutes in my simulation. When I look at the results,
> sometimes the output is for each minute. To my understanding, this is
> related to the convergence of the simulation. Am I right?
>
> What surprises me is that during the short timestep (1 or 2 minutes),
> the runtime fraction of the DX coil varies a lot. For example, for
> the previous minute, it could be 0.9. Then next minute, it becomes 0.
> Then next minute it is 0.5. I have no idea how to interpret these
> data.
>
> Thanks!
>
>
>
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> Thanks
> Rahul Chillar
> Grad Student
> Building Systems lab
> Univ Of Illinois Urbana Champaign
>
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========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support
EnergyPlus-Support@xxxxxxxx




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