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SYS-APM001-EN Chiller System Design and Control 9
Figure 6. Two-way valve
Variable-speed pump load control
By using a pump for each coil (Figure 7), the flow may be controlled by
varying the pump speed. In such systems, there may be no control valves at
the coil. This can reduce both the valve and the valve installation costs, but
increases coil pump and maintenance costs.
Figure 7. Variable-speed pump load control
Face-and-bypass dampers
Figure 8 shows a control variation using an uncontrolled or “wild” coil. In
this system, control of the conditioned air supply is executed by face-and-
bypass dampers that permit a portion of the air to bypass the coil surface.
Advantages of this strategy are the elimination of control valves and
improved part-load dehumidification. A disadvantage is that all the water is
Two-Way
Modulating
Valve
Airflow
Airflow
Variable
Speed Pump