Chiller Staging

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I have building with 6 chillers (2 different capacities) and I would like to model them with 14 stages of operation. How can I independently control the increment (add chiller) and decrement (stop lag chiller) of an individual chiller stage. I was using equipment control, however, the saw tooth approach does not account for the overlap of plant stages. Thank you for your time.


Janne Kairento LEED AP, EIT

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Joined: 2011-09-30
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Quick thought here. Why not create a custom set of chiller curves which directly models your different stages and associated chiller efficiencies and model as one large chiller.

Timothy Howe, MS, LEED? AP BD+C

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Joined: 2011-09-30
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I don't have a chiller project handy but I quickly, and poorly
created an example boiler load management schedule. The building has
three boilers, each sized at 0.23 MBH.

"Equipment Control 1" = EQUIP-CTRL
LOADS-THRU-1 = 0.23
LOADS-THRU-2 = 0.4
LOADS-THRU-3 = 999
BOILERS-1 = ( "Boiler1", "Boiler2" )
BOILERS-2 = ( "Boiler 3", "Boiler2" )
BOILERS-3 = ( "Boiler2", "Boiler1", "Boiler 3" )
MAX-LOAD-1 = ( 0.15, 0.14 )
MAX-LOAD-2 = ( 0.2, 0.21 )
MAX-LOAD-3 = ( 0.22, 0.22, 0.22 )

As you can see, I have boilers coming on and off with little thought
to over lapping. Boiler 2 is on for all three stages.
The interface allows for five stages with up to 10 pieces of
equipment defined in each stage. I am not sure if that covers your

>> Christopher Jones, P.Eng.

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Joined: 2011-09-30
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I had e-mailed the posters off-list, but here is the reply in case it is useful to anyone else.

I'm not sure that would work for determining when one chiller would be on as the load rises, and two chillers would be on as the load falls. The program still only makes the decision based on load without knowing if the load was increasing or decreasing at any time unless that's been added since I looked.

Also the pumping for one vs. two chillers might be important.

If the purpose of the study is to determine the optimal staging, I do think a spreadsheet might be more flexible for your scenario. Use eQUEST to provide the load and building temperature conditions at each hour, and use your own logic to stage chillers and calculate the energy usage. This will be based on an ideal case of known conditions.

However with six chillers of two different types in the plant, the ability to model the proposed sequence is going to exceed the accuracy of the assumptions used to calculate the loads and system response. For an Appendix G type analysis the eQUEST staging might suffice unless the two chiller types are very different, or unless this is an existing building with monitored chiller plant data that you are trying to match.


(Also testing my new e-mail address ;)...old one will continue to forward though.)

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

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Joined: 2012-05-08
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