[EnergyPlus_Support] Warmest Function Increases Boiler Natural Gas Usage?

["noelcrrl" <noelcrrl@xxxxxxxxx>]

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




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