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Re: [EnergyPlus_Support] We having a little trouble interpreting this from the manual...

The field you are referring to occurs in COMPACT HVAC:SYSTEM:UNITARY and 
COMPACT HVAC:SYSTEM:VAV.  The text in the Input Output Reference is misleading, 
sorry.  Here is a revised section (if this is still not crystal clear, please 
let me know and I will try again):

Field: Economizer Type
Enter one of the following options concerning the type of economizer:
o None
o Return air temperature
o Return air enthalpy
o Return air temperature and enthalpy

The default value is None which indicates no economizer operation. If set to  
Return Air Temperature, the economizer will operate whenever the temperature of 
the air entering the mixer on the outside air side is less than the return air 
temperature.  If set to Return Air Enthalpy, the economizer will operate 
whenever the enthalpy of the air entering the mixer on the outside air side is 
less than the return air temperature.  If set to Return Air Temperature and 
Enthalpy, the economizer will operate whenever both the temperature and 
enthalpy of the air entering the mixer on the outside air side is less than the 
return air temperature and enthalpy.  

For systems with continuous fan operation, the economizer will modulate to meet 
the required mixed air temperature setpoint.  For systems with cycling fan 
operation, the economizer will be fully open (maximum outside air flow rate) or 
fully closed (minimum outside air flow rate) for a given time step.  Economizer 
Upper Temperature Limit, Economizer Lower Temperature Limit, and Economizer 
Upper Enthalpy Limit, if specified, will also turn off the economizer when one 
of these limits is exceeded (see these fields below).

Mike


On 13 Feb 2007 at 6:15, aileen_marie_therese wrote:

> "Field: Economizer Type
> Enter one of the following options concerning the type of economizer:
> ? None
> ? Return air temperature
> ? Return air enthalpy
> ? Return air temperature and enthalpy
> The default value is None which indicates no economizer operation. 
> For Return Air
> Temperature, whenever the outside air temperature is greater than 
> the Economizer Upper
> Temperature Limit the outside air flow rate is set to the minimum. 
> If set to Return Air
> Enthalpy, when the outside air enthalpy is greater than the 
> Economizer Upper Enthalpy Limit
> the outside air flow rate is set to the minimum. If set to Return 
> Air Temperature and Enthalpy,
> either limit is used."
> Are we talking about the return air temperature (ie the temperature 
> of the air returning from the conditioned space) or the outside air 
> temperature when we say the type of economiser is "return air 
> temperature"?
> 
> Thanks
> 
> Annie Egan
> 
> 
> 
> 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.
> 
> EnergyPlus Documentation is searchable.  Open EPlusMainMenu.idf and press the "search" button.
>  
> Yahoo! Groups Links
> 
> 
> 
> 
> 


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





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