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Multiple-Chiller-System Design and Control

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SYS-APM001-EN
Design Considerations
50
Bypass-line sizing
Bypass lines are required in both primary­secondary and variable-primary-flow
systems. In a decoupled system, the bypass line should be sized for 110 to 115
percent of the largest chiller's design flow rate. In a VPF system, the bypass line
should be sized for the largest chiller's minimum flow rate.
While minimal pressure loss is desirable, substantial water velocity can be
accommodated without significant pressure loss in the relatively short length of
bypass piping. The bypass line must be of sufficient length to prevent random
mixing of the supply and return water streams; a minimum length of five to ten
pipe diameters is recommended.
Amount of fluid in the loop
Two questions must be answered when determining how much fluid is
necessary to maintain proper chilled-water-system control.
n
How fast can the specific chiller respond to changing conditions?
n
How fast can the system respond to changing conditions?
The amount of fluid the loop requires to operate properly is related to the larger
of these two answers. Note that both answers describe an amount of time.
Required Volume = Flow Rate × Loop Time
Where:
n
Required Volume = the amount of fluid in the coil, pipes, evaporator barrel,
storage tank, etc., in gallons [liters]
n
Flow Rate = the system flow rate, in gpm [lps]
n
Loop Time = the time it takes for fluid to leave the chiller, move through the
system and return to the chiller, and allow for stable system operation, in
minutes [seconds]

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Summary :

Required Volume = Flow Rate × Loop Time Where: n Required Volume = the amount of fluid in the coil, pipes, evaporator barrel, storage tank, etc., in gallons [liters] n Flow Rate = the system flow rate, in gpm [lps] n Loop Time = the time it takes for fluid to leave the chiller, move through the system and return to the chiller, and allow for stable system operation, in minutes [seconds]

Tags : system,flow,bypass,fluid,rate,time,loop,amount,chiller,required,length,line,respond
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