MIL-HDBK-1133
motor capacity ( kW )
* run hours = energy use ( kWh )
motor efficiency
(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.
ave. motor capacity ( kW )
gallons
*
= energy use ( kWh )
60 gpm
ave. motor efficiency
(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
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