Pumping Calculations - Basic Mathematics for Water and Wastewater Operators - page 213

Solution:

bhp
Motorefficiency

18 hp

mhp = = = 20.9 hp

086 .

Cost ($/hr) =× × mhp 0.746 kW/hpCost($/kWh)

= 20 .. 9hp × 0.746 kW/hp × $0.014/kWh

= $0.22/hr

Total cost = $0.22/hr × 24 hr/day = $528

■ Example 14.47
Problem: A pump is discharging 1300 gpm against a head of 70 ft. The wire-to-
water (overall) efficiency is 66%. If the cost of power is $0.033/kWh, what is the cost
of the power consumed during a week in which the pump runs 80 hr?

Solution:

Flow (gpm)Head (ft)
3960

× 130 0 gpm × 70 ft

mhp = = = 34.8 hp

× Efficiency 3960 × 0.66

Cost ($/hr) =× × mhp 0.746 kW/hpCost($/kWh)

= 34 .. 8hp × 0.746 kW/hp × $0.033/kWh

= $0.86/hr

Total cost = $0.86/hr × 80 hr = $. 68 80

■ Example 14.48
Problem: What would be the horsepower on a motor that is rated at 35 amperes and
440 volts?

Solution:

Volts Amperes
746 watts/hp

× 440 volts × 35 ampe res

= = 20.64 hp

746 watts/hp

■ Example 14.49
Problem: What would be the horsepower on a motor that is rated at 10 amperes and
440 volts?

Solution:

Volts Amperes
746 watts/hp

× 440 volts × 10 ampe res

= = 5.9 hp

746 watts/hp