Re: [EnergyPlus_Support] please help with modeling of roof top unit

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

The warnings indicate that the results may not be accurate, beacause the DX 
cooling coil model is intended for systems with flow rates near the design flow 
rate.  In reality, low flow rates can result in the coil freezing up and would 
require some type of capacity control on the DX coil.  Use the multispeed DX 
coil for VAV systems.  See the 5ZoneAutoDXVAV.idf example file.

Mike


On 22 Jun 2004, at 0:30, zhaicq98 wrote:

> Hi,
> 
> I am trying to simulate a roof top unit, which includes a DX cooling 
> coil, heating coil and variable speed fan. I am always getting a lots 
> of warning messages, which 
> said "COIL:DX:COOLINGBYPASSFACTOREMPIRICAL "MAIN COOLING COIL 1" - 
> Air volume flow rate per watt of rated total cooling capacity is out 
> of range." I checked the input output reference, and understood that 
> there is a range for this factor. The range is from 0.00004699 to 
> 0.00006041 (m3/s)/W. The rated capacity of my DX coil is 20000 W, and 
> the rated air flow rate is 1.1 m3/s, resulting in a factor inside the 
> required range. 
> 
> I am modeling a VAV system, and the design flow rate of the system is 
> 1.1 m3/s. I set the minimum flow fraction of the system to be 0.3. 
> Thus the actual flow rate of the system could go beyond the range 
> required by the DX coil, when the system is operating. If I have to 
> stick to the range, then the actual flow rate of my system can only 
> vary between 0.00004699*1.1 = 0.94 and 0.00006041*1.1 = 1.21 m3/s. I 
> think this is not a real VAV system performs. 
> 
> Can anyone tell me whether these warning messages matter or not? In 
> addition, what is the proper way to deal with the system I am 
> modeling?
> 
> Thanks a lot for your help.
> 
> -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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