Page 311 - HVAC Pump Handbook

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Basics of Pump Application for HVAC Systems

308 The HVAC World

Figure 10.17 Best efficiency control.

at design condition, and the pump would operate noisily. With best
efficiency control, the second pump would be added at 125 percent
capacity of one pump, and the two pumps would operate at a much
higher efficiency if they are variable-speed pumps. Best efficiency con-
trol does require a system flowmeter if flow is used as the means for
sequencing. Unfortunately, many systems do not have accurate
flowmeters that can be used for pump sequencing.
If the pumps are variable speed on systems without flow meters,
pump speed can be used to start or stop the second pump. The wire-
to-water efficiency calculation, or kW input control, is used to compute
the speeds at which the second pump should be added or subtracted.
These computed speeds can be checked under actual operation to
ensure that the pumps are being sequenced properly, particularly if a
watt transmitter is available to indicate the energy consumption by
the pumps.

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