MIL-HDBK-1133

(7)

where motor capacity is in kW or horsepower multiplied by a

conversion factor of 0.746.

If run hour data is not readily available, a less exact

approach can be used. This approach involves applying data for

total delivered gallons of water and gallon-per-minute (gpm) pump

ratings to estimate run hours. At its roughest level, the total

gallons of delivered water can be divided by the total gpm rating

for all pumps to obtain average operating hours based on an

average pump rating. Multiplying the operating hours value by

the average pump motor capacity (kW) will provide an estimated

water energy consumption. This process should be completed for

as small a set of motors as possible where water use data exists.

Using the smallest possible motor set will make the average pump

motor capacity value as accurate as possible.

Care should be taken if booster pumps are in use.

Because these pumps typically pump the same water again, their

inclusion in the calculation of average operating hours will

produce lower than actual pumping hour values. The energy use of

these pumps should be calculated separately. Discussions with

water supply personnel may also provide information on which

pumps are used the most. Equation 8 provides a calculation

method when run hours must be estimated.

60 *gpm*

(8)

where

ave. motor capacity (kW) = average capacity of target

set of motors

ave. motor efficiency

= average capacity of target

set of motors

gallons

= total delivered gallons

for target set of motors

gpm

= average gpm rating for

target set of pumps

27

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