MIL-HDBK-1133
2.7
Water and Sewer Energy. Water and sewer energy
includes the energy associated with potable water and sewage
waste pumping, processing, and distribution. These services are
usually installation-wide and either supplied under contract with
others, operated by the installation facilities organization, or
performed by some combination of these. Where the services are
supplied under contract, there is no energy consumption to deal
with in this process: the cost of the contract includes the
energy component. Where these services are operated on the
installation, an energy consumption value may need to be
identified for energy accounting and allocation purposes.
2.7.1
Water Supply System. Typical water supply system may
consist of well or reservoir pumps and booster or supply pumps.
These pumps account for the vast majority of energy consumed by
most water systems. The calculation of water supply energy
generally involves calculating the energy use for multiple
motors. Two primary calculation methods can be used, depending
on the type of data available at the installation.
2.7.2
Calculation of Water Supply Energy. The first method
applies when motor characteristics data and pump run hours are
available. This information is often kept by the water supply
department for water balancing and motor replacement purposes.
In this case, a straightforward multiplication of motor energy
consumption in kilowatts (kW) by time in hours provides a
kilowatt-hours (kWh) value. Motor energy consumption depends
primarily on motor horsepower (hp) capacity, efficiency, and
loading. The motor capacity and efficiency can often be found on
nameplates or from manufacturers' literature. National
Electrical Manufacturers Association (NEMA) MG1, Motors and
Generators, Table 12-10 provides typical motor efficiency values
if actual efficiencies cannot be found. The efficiency will
affect actual consumption beyond standard capacity ratings.
Motor loading is also known to affect actual motor
energy consumption. However, this effect is usually noticeable
only at loading below 50 percent and can be ignored for most
water and sewer system motors. Equation 7 provides a calculation
method when run hours are available:
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