Re: [EnergyPlus_Support] Problems with purchased air reports

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

The purchased air model is very simple, and it can produce confusing results 
when the outside air option is used.  The purchased air model takes return air 
from the zone and mixes it with the specified outside air volume.  Note that if 
the purchased air flow rate is less than the outside air flow rate, the 
purchased air flow rate is used and is 100% outside air.  

It then takes this mixed air condition (dry bulb temperature and humidity 
ratio) and calculates the enthalpy change required to condition this air to the 
specified supply air temperature and humidity ratio.  This is the total cooling 
reported.  It also determines the sensible change required, and this is the 
sensible cooling reported.  If the mixed air is drier than the specified supply 
air humidity ratio, then the total cooling will be less than the sensible 
cooling.  

Purchased air with the outside air option is useful for determining peak loads. 
 If you are using purchased air for an annual load, it is better to introduce 
the outside air directly to the space using ventilation or infiltration.

Mike



On 26 Jun 2004, at 9:01, sdep1017 wrote:

> When using purchased air, the report "Purchased Air Cooling Sensible 
> Cooling Energy" is higher than "Purchased Air Total Cooling Energy". 
> Shouldn't the latter be higher since it consists both sensible and 
> latent loads?
> 
> I am using the Houston weather file, and have uploaded my idf 
> file "Base w occ - Box 4 purch air auto.idf" in the files section.
> 
> Thanks in advance,
> 
> Yi Chun Huang
> Student
> Carnegie Mellon University
> 
> 
> 
> 
> 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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