Lift Energy Efficiency Standards and Motor Efficiency

The ISO25745-2 standard provides a systematic frame work for evaluating and ranking the energy consumption of various lift systems. The standard approximately models the drive system (motor and inverter) with a constant efficiency where the power lost is directly proportional to the shaft power out. The efficiency of the real system is, of course, dependent on the operating speed and the load in the car. This paper explores the effect of the constant efficiency assumption by comparing the calculated energy consumption of the ISO model to a more complete model that includes the dependence on speed and load. The magnitude of the deviation depends partially on the type of equipment used; permanent magnet motors can be reasonably approximated as constant efficiency, but efficiency of induction motors is highly dependent on the torque required for a given application. The paper also quantifies the customer value by relating the energy consumption calculations to operating cost.