Re: [EnergyPlus_Support] Warmest Function Increases Boiler Natural Gas Usage?

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

Rich addressed the fan power, chiller, and tower energy use.

The increase in gas use is not right.  Is there a central heating coil in this 
VAV system?  Is it picking up it's setopint from the air loop outlet node?  If 
so, it may be warming cool mixed air to that some VAV damper somewhere can stay 
fully open at low cooling loads.  

Be sure the heating coil setpoint is not linked in any way to what the warmest 
set point manager is doing for cooling.  No two setpoint managers should be 
setting a temperature setpoint on the same node.

Mike


On 22 May 2007 at 0:22, noelcrrl wrote:

> All-
> 
> I am modeling the warmest function in a Hospital building.  The model 
> is equipped with a VAV system (pre-heat coil, cooling coil, a central 
> heating coil, & reheat coils).  I have the warmest setpoint node set 
> at the supply fan outlet.  The warmest function is set up to deliver 
> supply air between 55F and 60F.  Also, the chilled water is delivered 
> to the cooling coils between 44F and 52F, depending on outside air 
> temperature.  
> 
> When I increase the upper limit of the warmest function from 60F to 
> 65F and the chilled water upper limit from 52F to 54F, the natural 
> gas consumption of the boiler increases by 7%.  In addition, the 
> supply fan energy usage increases by 6%.  The energy saving benefit 
> of the chiller and the cooling tower, 2% and 3%, respectively, is not 
> enough to overcome the boiler and fan energy usage increases.  The 
> overall energy usage (total facility) increases by 2%.
> 
> I am confused to why this is happening?  How can increasing the reset 
> temperatures increase overall energy consumption instead of 
> decreasing it?  Why is the heating energy usage increasing in this 
> manner?
> 
> Thanks in advance for your help.
> 
> Noel
> 
> 
> 
> 
> 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.pdf under the
> Documentation link 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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