Page 144 - HVAC Pump Handbook

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HVAC Pump Performance

HVAC Pump Performance 141

The pump engineer works at reducing all of these losses to achieve
the highest possible efficiency at all allowable flows through the
pump. Obviously, large-capacity pumps have much higher efficiencies
than small-capacity pumps. Again the high-quality pump has better
efficiencies than the poorly designed and constructed pump.

6.2.3 Effect of specific speed
on pump curves
Specific speed of centrifugal pumps was discussed in the previous
chapters. Its effect upon centrifugal pump performance is described in
Fig. 6.5. The shape of the head-flow and horsepower curves vary
greatly, as the specific speed increases. Most HVAC pumps have a
specific speed of less than 2600 rev/min; large cooling tower pumps
may have higher specific speeds.

Figure 6.5 Head-flow and horsepower curves compared to specific speed and
impeller profiles. (From Turton, Rotodynamic Pump Design, Cambridge Press, used
with permission.)

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