Re: [EnergyPlus_Support] question about autosizing

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

The error message occured because the specified SHR could not possibly be 
achieved for air at the autosized flow rate entering at ARI rated conditions 
and being cooled at the autosized capacity which was determined by the 
specified supply air temperature in the sizing objects. 

The easiest approach in this case is to autosize all three values, capacity, 
air flow rate, and rated SHR.  The last line of the error states this: "If 
autosizing, it is recommended that all three of these values be autosized."

 You are correct that the DX coil is sized to meet the sensible load without 
providing any active humidity control.  However, the coil will do latent 
cooling, and it cannot do less latent cooling than psychrometrics would allow.

Mike


On 26 Oct 2004, at 19:38, zhaicq98 wrote:

> 
> 
> Hi,
> 
> I have a question about the autosizing of the DX cooling coi. I have 
> a one-zone building conditioned by a unitary system with DX cooling 
> coil COIL:COOLING:BYPASSFACTOREMPIRICAL. I input the SHR of the 
> cooling coil as 0.75. I ask the program to do the autosizing of the 
> component whereever possible. But I got a severe error message:
> 
>   ** Severe  ** For object = COIL:DX:COOLINGBYPASSFACTOREMPIRICAL, 
> name = "ROOFTOPUNIT_Z_SINGLE COOLING COIL", the combination of rated 
> air volume flow rate, total cooling capacity and sensible heat ratio 
> yields coil exiting air conditions above the saturation curve. 
> Possible fixes are to reduce the rated total cooling capacity, 
> increase the rated air volume flow rate, or reduce the rated sensible 
> heat ratio for this coil.
> 
> I tried to reduce the coil SHR to 0.74, and it works. 
> 
> I have a thermostat object for this zone but I do not have a 
> humidistat object. My understading is that the program will autosize 
> the cooling coil in order to meet the thermostat setpoint and leave 
> the indoor humidity as whatever it is. But it seems that this is not 
> the case. 
> 
> I am wondering if anyone can give me some explanation on this issue. 
> Thanks a lot.
> 
> -Chaoqin 
> 
> 
> 
> 
> 
> 
> The primary EnergyPlus web site is found at:
> http://www.energyplus.gov
> 
> The group web site is:
> http://groups.yahoo.com/group/EnergyPlus_Support/
> 
> Attachments are not allowed -- please post any files to the appropriate folder
> in the Files area of the Support Web Site.
> 
> Yahoo! Groups Links
> 
> 
> 
> 
> 
> 
> 
> 
> 



========================================================
Michael J. Witte, GARD Analytics, Inc.
EnergyPlus Testing and Support      
EnergyPlus-Support@xxxxxxxx




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