Page 170 - HVAC Pump Handbook

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HVAC Pump Performance

HVAC Pump Performance 167

of the efficiencies of the motor and the variable-speed drive. It must be
determined by the variable-speed drive manufacturer with recognition
of the manufacturer and the quality of the electric motor.
Steam turbine–driven pumps also will be reviewed in Chap. 7; the
energy required by them is usually based on a water rate in pounds
per pump brake horsepower. Equation 6.12 is used to compute the
maximum water rate at maximum flow and head.

6.6.4 Actual energy consumed
by variable-speed pumps
The energy consumed by variable-speed pumps requires knowledge of
the water system head curve or area on which they are operating.
These curves and areas will be described in Chap. 9. Table 6.2 describes
the variation in pump efficiency, pump brake horsepower, speed,
motor kilowatts, and overall wire-to-water efficiency of the pump,
motor, and variable-speed drive with a system head curve that con-
tains a constant head of 20 ft. The pump fitting losses are accounted for
in these calculations. The pump head-capacity curve in Fig. 6.1a is used
in these calculations.
The computer program for calculating the wire-to-water efficiency
for this pump is available from manufacturers of variable-speed
pumping systems. The data for the wire-to-shaft efficiency included in
this table are secured from the variable-speed drive manufacturer.
The overall wire-to-water efficiency of variable-speed pumping sys-
tems that have two or more pumps operating in parallel is discussed
in detail in Chap. 10.

TABLE 6.2 System and Pump Variables
Pump Pump Wire-to-shaft Wire-to-water
System Pump speed, efficiency, Pump efficiency, Total efficiency,
gal/min head, ft rev/min % bhp % kW %
0100 020.9 0626 41.1 01.3 58.1 01.7 23.8
0200 023.4 0674 63.2 01.9 61.4 02.3 38.4
0300 027.2 0742 74.3 02.8 65.8 03.1 47.9
0400 032.2 0826 79.7 04.1 70.7 04.3 54.7
0500 038.6 0918 82.6 05.9 75.4 05.8 59.9
0600 046.1 1013 84.1 08.3 79.5 07.8 63.8
0700 054.7 1113 85.0 11.4 83.0 10.2 66.8
0800 064.5 1217 85.4 15.3 85.9 13.3 69.1
0900 075.4 1324 85.6 20.0 88.1 17.0 70.6
1000 087.5 1433 85.7 25.8 89.7 21.4 71.7
1100 100.6 1544 85.8 32.6 90.7 26.8 72.2
1200 114.8 1656 85.8 40.5 91.3 33.1 72.5
1300 120.0 1770 85.7 49.8 91.7 40.5 72.6

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