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

["noelcrrl" <noelcrrl@xxxxxxxxx>]

Mike-

To answer your question...yes I do have a central heating coil.  I 
paid special attention to the setpoint managers as you suggested.  I 
have three set point managers, as follows:  

1)I have a mixed air set point manager that controls the mixed air 
outlet and the cooling coil outlet.  

2)I have set point manager at the heating coil setting it 55F.

3)I have the warmest setpoint manager controlling the supply fan 
outlet between 55F and 65F.  

It seems that the heating coil continues to ignore the 55F setpoint 
and heats the air to a higher temperature.

Please advise?  Thanks in advance for your help.  

Noel





--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Michael J. Witte" 
<mjwitte@...> wrote:
>
> 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@...
>




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