Page 186 - HVAC Pump Handbook

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Pump Drivers and Variable-Speed Drives

Pump Drivers and Variable-Speed Drives 183

TABLE 7.5 Wire-to-water Efficiency of Pump-Motor Combinations

System Data Wire-to-water
GPM Head ft. Motor Hp Pump Eff. % Motor Eff. % Eff. %
20 10 1/4 38 50 19
50 10 1/3 50 57 29
60 15 1/2 53 60 32
75 20 3/4 57 63 36
80 25 1 57 82 47
100 40 2 59 84 50
120 50 3 60 86 52
250 60 5 79 87 69
1
300 70 7 / 2 80 88 71
400 70 10 81 89 75
500 80 15 80 91 73
800 80 20 84 91 74
900 90 25 82 92 75
1000 90 30 84 92 77
1000 110 40 86 93 78
1600 100 50 87 93 80
1800 110 60 87 94 81
2000 120 75 89 94 84
NOTE: These are typical wire-to-water efficiencies for small circulators as well as for larger
centrifugal pumps, several pump manufacturers’ data was used for this information.

A study was made to determine such a wire-to-water efficiency for
small and medium size, 1750-rev/min motors. Table 7.5 and Fig. 7.2
describe the results of this evaluation. Motors under 1 hp were single-
phase, capacitor type; motors 1 hp and larger were three phase. It is
evident that small fractional motors and pumps are very inefficient
and that the improvement in efficiency is pronounced between 3- and
5-hp sizes.
There have been attempts to exchange cooling and heating coil con-
trol valves with individual variable-speed pumps. It is obvious from
these data that the resulting efficiency would be questionable to try
this on smaller coils requiring pumps with fractional-size pumps. A
moderately sized system with several large air-handling units might
be economically feasible if the pump motors were 5 hp and larger.
Obviously, small circulators must be used for very small installa-
tions. However, heating and cooling loads requiring a total pumping
energy of 5 hp and above, should not be broken down into a number of
small pumps.

7.2.11 Motor construction
Most horizontally mounted and some vertically mounted electric motors
for HVAC pumps are manufactured in three different enclosures,

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