Balance Newsletter

Reducing Energy Costs through Elevator Efficiency

By Kellie Lindquist & Mike Lewis

As more and more of the world's population is living in towns and cities, there is an increasing challenge to use energy more efficiently in commercial buildings. Buildings use about 40 percent of all energy consumed in the world. And elevators, in turn, consume up to 10 percent of the total energy in a building. Based on a carbon footprint analysis, the most significant environmental impact for elevators relates to the electricity consumed for their 20- to 25-year life span.

Because of an elevator's energy consumption, buying or installing elevator equipment that promotes low energy consumption and high Power Factor (PF) can help significantly reduce electrical bills. Power Factor (PF) is a measurement of electrical system efficiency in the distribution and consumption of electrical energy. The lower the PF number, the poorer the PF efficiency and the higher the PF number, the greater the PF efficiency. If PF is 0.70, then 70 percent of the electric power being provided is being converted to real work. If PF is 0.90, then 90 percent of the electric power being provided is being converted to real work. Typically, PF is between 0.70 and 0.95 for a commercial or industrial facility.

Electric utility billing is divided into two main components. The Consumed electricity for the billing period (typically one month) and the Demand electricity for either that same billing period or for a previous billing period. The Consumed electricity is the normal, everyday amount of energy a facility might use in its typical course of operation. The Demand electricity is the abnormal, high use of electricity that might occur.

The utility companies establish peak Demand as the highest usage of energy during defined 15-minute periods. Decreasing this peak Demand in a building is one way to significantly reduce utility bills and save energy. In addition, in some areas, utilities also use Power Factor in the computation of the Demand charge. A facility with a low Power Factor could result in a Demand charge penalty that increases the monthly Demand cost. However, a facility with a high Power Factor will avoid these increased cost penalties.

Newer, more innovative elevator control systems can not only decrease a facility's peak Demand, they also can contribute to improving a building's overall Power Factor, which will reduce energy consumption and costs.

A comparison of two elevator motor control technologies demonstrates the advancement
in energy consumption and PF improvement. During a recent modernization of two identical elevators, "before" and "after" energy data was collected. The original, 1st generation SCR (silicon controlled rectifier) DC motor control was measured using a series of fixed run patterns and known loads. After modernization, the new insulated gate bipolar transistor-based AC motor control for a permanent magnet synchronous motor system was measured using the exact same run patterns and known loads. The Power Factor for the SCR-DC system averaged 0.24. Power Factor for the IGBT-based permanent magnet AC control averaged 0.92. In the end, less energy was being consumed to move the exact same load through the exact same distance. More of the energy consumed was being converted into real work with less waste in terms of heat and magnetism.

Furthermore, today's elevator control technology contributes to reducing a building's Demand electricity use first through overall less energy consumption and through improved efficiencies. No longer are highly inductive loads (motors) routinely connected directly to supply lines through mechanical contactors. Generally speaking, today's systems employ solid state rectifier front ends and Pulse Width Modulation (PWM) techniques to capture and convert AC voltage to DC voltage. This DC Buss creation is then applied to the motor as a PWM signal, impacting the AC line as a source to re-charge the DC Buss during the elevators operation.



Additionally, newer elevator technology that promotes higher Power Factor can directly affect the amount of energy used, thus reducing the overall operating expense. As elevator motor control technology advances there is a favorable decline in energy consumption. Using motor-generator sets as the baseline, moving to 1st and 2nd generation SCR-based controls can result in energy use reductions of approximately 10 percent to 15 percent on geared applications and possibly 25 percent to 30 percent on gearless applications. But, Power Factor does not substantially improve, if at all.

Continuing the technology move to IGBT-based DC controls and Permanent Magnet AC motors reductions of 55 percent to 60 percent from the baseline can be anticipated. And at the same time, Power Factors move from the 0.25 range into the 0.90 range. Results vary depending on the exact elevator application and measurement techniques employed.



For building managers to reduce energy consumption and save money, it is crucial for them to be aware of the affects of Power Factor to help reduce the overall Demand electricity. By doing so, the monthly utility bill will decrease and there also may be potential for utility rebates with the local utility company.