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58 TRG-TRC016-EN
notes
period two
Chilled-Water System Design
The advent of microprocessor-based controls has led to another method for
determining flow in the bypass pipe. Temperature sensors are placed in the
supply and return pipes of the production and distribution loops, and in the
bypass pipe. With these temperatures, a chiller-plant control system,
programmed with fluid mixing equations, can determine the quantity of excess
or deficit flow that exists at any time. Because a small change in temperature
may indicate a relatively large change in load or flow in the bypass pipe,
it is important to use accurate, calibrated sensors to ensure acceptable system
operation.
The primary advantage of this method is that it does not depend on flow
velocity in the pipe. Also, it is reliable and cost effective because the
temperature sensors are relatively-low-cost devices.
Integrating the chiller controls with a chiller-plant control system, however, is
imperative for efficient system operation. The control of chilled-water systems
will be discussed further in Period Four.
Temperature-Based Calculations
b
y
p
a
s
s
p
i
p
e
b
y
p
a
s
s
p
i
p
e
return
return
tee
tee
supply
supply
tee
tee
system
system
-
-
level
level
controller
controller
Figure 64