[bldg-sim] Chiller Staging

Mike Roberts mroberts20 at kc.rr.com
Fri Apr 18 10:08:11 PDT 2003


Joe,

First, I am not sure which version of the program you are using.  It sounds
like DOE-2.2, but could be JJ Hirsch level 100+ of DOE-2.1E.  Are you using
the eQUEST or PowerDOE interfaces?

The primary/secondary loops routine of DOE actually does consider flow and
will not allow a secondary flow greater than the primary flow, so runs the
chillers run in parallel to provide sufficient flow.  While a real life
primary/secondary system can have higher secondary flow, it is unusual and
not normally what you want.  If you use two way valves on the secondary
loop, you can run a single chiller for some hours.  My experience is that
you can do that less than you would initially expect, but if you think it
through, the DOE model will give you results closer to real life than
earlier programs that just do a BTU calculation on the cooling requirements.

Let me know if you need to go further with this.

Mike Roberts

  -----Original Message-----
  From: postman at gard.com [mailto:postman at gard.com]On Behalf Of Joe Hager
  Sent: Friday, April 18, 2003 10:48 AM
  To: bldg-sim at gard.com
  Subject: [bldg-sim] Chiller Staging


  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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