Control and optimization of central chilling systems - Intelligent Buildings and Building Automation - page 205

Switch off one pump

System curve

Switch on one pump

Pump curve

(3 pumps)

(1 pump) (2 pumps)

Water flow rate

Figure 9.23 Settings of sequence control of constant-speed secondary chilled water
pumps based on differential pressure.

Pump pressure

Throttling

Reducing speed

C

Differential pressure
set-point

A

B

Pump curve

System Curve

m2 m1

Flow rate

Figure 9.24 Control of variable-speed pump with pre-set differential pressure across
the critical load branch.

In the strategy illustrated in Figure 9.23, a lag is specified to avoid the cycling
on/off of pumps and the flow rates at switching on points are slightly higher
that that of relevant switching off points.