[bldg-sim] Chiller Staging

[Joe Hager]

Hello,

In DOE-2 I am having trouble with chiller staging.  

System Description
I have a simplified model that has four zones, two cooled by DX units and two with chilled water coils.   I have a primary chiller water loop with two 500 ton (6 MBtu/h) chillers and two constant speed primary chilled water pumps.  On the secondary chilled water loop I have a variable speed secondary chilled water pump and the two zone cooling coils (with two way valves).  I have created an Equipment Control sequence that has the first chiller running to loads through 4.5 MBtu/h and then both chillers running to loads through 999 MBtu/h.

When I run the model I am getting this warning:
 **WARNING**********************************************************************

             An EQUIP-CTRL sequence will be overridden because

             the selected equipment cannot meet the resulting

             flow requirements.

             Loop: prim chw loop                    First occurrence:  6/21/ 4 
 

and the chillers always run in parallel.  My question comes because I have been adjusting the capacity of the two RTUs with the chilled water coils and if the cooling capacity of those units is well below the capacity of the chillers then they stage properly or if I increase the capacity of the chillers well beyond the capacity of the RTUs then they stage properly, but when the capacity of the RTU's is close to the capacity of the chillers then I get that error above and the chillers don't stage.  



Any help would be greatly appreciated.



Joe Hager

DMI

(617) 527-1525 


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