OM 780-2 Page 43
Stage-up with Series-Piped Chillers
Consider the chiller system in Figure 13. A typical sequence order would be to enable chiller 1, then 2, then 3, and finally
4. A problem would occur because chiller 4 would not be enabled by the CSM. Chiller 1 is enabled normally. Chiller 2
will be enabled when chiller 1 reaches full load. On primary-secondary systems, chiller 3 would typically get enabled when
the load requires more flow than the single primary pump supplying chillers 1 and 2 can deliver. After chiller 3 is enabled,
water flow is split between the two sets of series-piped chillers, which also splits the cooling load between the two sets.
Chiller 3 would move to a full load condition but chillers 1 and 2 would both move to partially loaded conditions (roughly
50% load each). Since chillers 1 and 2 never reach full load, the CSM would not stage-up to enable chiller 4, even if the
system required more cooling capacity.
Figure 13. Chiller System with Evaporators Piped in the Series/Parallel Configuration
Chiller #3
Chiller #1 Chiller #2
Chiller #4
Centrifugal
Centrifugal Centrifugal
Centrifugal
When staging-up series-piped chillers, the CSM will automatically enable the second chiller of a series-piped pair 30
seconds after the first was enabled when either of the following conditions already exist in the system.
1. A pair of series-piped chillers are both already enabled
2. Any non-series piped chiller is already enabled
Series-piped chiller pair is already enabled
Condition 1 allows the first and second chillers in Figure 13 to be enabled separately, but once a third chiller is enabled the
forth chiller will automatically be enabled 30 seconds later. A typical chiller system would have a sequence order where
chillers 1 and 2 are the first and second chillers enabled based on run time, and chillers 3 and 4 would be enabled together
when additional flow or additional capacity is required. The table below shows how this typical series-piped system would
be configured and the resulting stage-up sequence.
Table 11. Example of a Typical Sequence Order with Series-Piped Chillers
Chiller # Sequence Number (in Row 1
of the Sequence Order Table on
the Chiller Seq screen)
This Chiller Series-Piped
With Chiller # (variable on
the Chiller Setup screen)
Resulting Sequence Order
1 1 2 First Chiller On = 1 (or 2 based on lowest runtime of 1 or 2)
2 1 1 Second Chiller On = 2 (or 1 based on runtime of 1 or 2)
3 2 4 Third Chiller On = 3 (or 4 based on lowest runtime of 3 or 4)
Forth Chiller is Automatically Enabled 30 seconds after Third
Chiller was Enabled
42 3
Non-series chiller is already enabled
Condition 2 allows for the same type of automatic series-piped pair chiller enabling as condition 1 but allows for systems
with evaporators piped in a combination of the Series/Parallel Configuration and Parallel Configuration. In this case a
single non-series-piped chiller that is already enabled will force both chillers of a series-piped pair to be enabled.
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