For every cost comparison a baseline case has to be defined. In countries with MEPS (Minimum Energy Performance Standards) this is the motor with the respective efficiency level, in countries with no mandatory requirements it is the most often used standard motor in a given market. Then a project case has to be defined with higher efficiency motors up to IE3.
The cost of variable speed drives has to be added to the project cost if they are considered to be feasible for the given type of machines and operation.
In case of replacement upon failure no cost for the existing motor has to be taken into account. In case of premature replacement a residual value for the lost operation time can be included with the purchase price calculation.
The operating cost consists of electricity, maintenance and repair.
The anticipated electricity consumption is calculated based on the following three elements:
Average annual load factor (for example see figure 12),
Motor efficiency for this average load factor,
Annual operating hours.
For fixed speed motors these elements can be estimated easily with fair accuracy. For the calculation of motor systems with variable load and the eventual use of variable speed drives the calculation of the average load factor, the respective hours of operation and the efficiencies of the motor plus the variable speed drive have to be based on a typical load profile. If a relevant measured load profile of existing systems is not available an average profile has to be assumed (example):
Percentage of Loading (%)
1.000 1.200 1.400 Hours per Year