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74 TRG-TRC016-EN
notes
period three
System Variations
The smaller swing chiller is turned on to handle the low cooling loads either
during the night or during unoccupied periods of time. When the building load
exceeds the capacity of the swing chiller, it is turned off and a larger chiller is
turned on. The larger chiller handles the building cooling load alone until it
becomes fully loaded. Then the swing chiller is turned on again. The swing
chiller is alternated on and off between the larger chillers' operation to serve
as a smaller incremental step of loading. This sequence more favorably
matches the capacity of the chiller plant to the system load. It keeps the large
chillers loaded in their peak efficiency range and operates with the fewest,
and smallest, pieces of ancillary equipment (pumps and cooling towers) at any
system load.
A common concern is to prevent the swing chiller from cycling too frequently,
which could shorten the life of the equipment. In large chilled-water systems,
however, the changes in building load typically occur slowly enough that this
is not a problem.
A final asymmetric design option is to use one high-efficiency chiller and one or
more standard-efficiency chillers. In this type of system, the high-efficiency
chiller should be preferentially loaded to minimize system energy consumption.
Swing Chiller
percent cooling load
percent cooling load
chiller 1
chiller 1
100
100
80
80
60
60
40
40
20
20
0
0
swing chiller
swing chiller
chiller sequence
chiller sequence
chiller 2
chiller 2
swing chiller
swing chiller
swing chiller
swing chiller
Figure 82