Lift Report

Within the guideline VDI 4707 „Lifts energy efficiency (Part1) there is an effort to compare energy efficiency of complete lift facilities because the consideration of just the connected load will not give the appropriate results.

Hence, lifts are divided into energy efficiency classes from A to G similar to fridges or light bulbs. Usually, a lift facility is a complex system and a rating is therefore more complicated. In this case, different travel heights or diverse nominal loads to the point of varied nominal speeds of the single lift facility have to be included. Very useful assistance to assign the energy efficiency class is given by specialized Software-Tools like Energy Label published by the VFA.

In contrast to a light bulb that is either turned on or off; on lift facilities a clear distinction is made between standby and travel demands.

The standby demand is determined 5 minutes after the last trip has ended and includes all relevant components for readiness for operation and maintaining it in standby.

Travel demand is typically determined with a reference trip with an empty cabin and covers a complete trip cycle. The measurement starts at open door at first level. The lift doors close and the lift travels to the top level when the doors open and close once. The cabin travels down and the measurement cycle ends when the doors open. This action should reflect typical use of a lift.

Converting the standby and travel demand into an energy efficiency class, the lift – depending on the frequency of usage – is classified in one of the five usage categories. The average travel time determines the usage category; that is how often a lift is used the higher the usage category is.

Table 1 makes it obvious that a lift in usage category 1 for 99 % of the time is not in operation and consequently stays in standby. Hence, standby demand has a high impact on the energy efficiency class. Demand during travel is negligible under this condition.

The following example shows how strong the impact of the usage category is on the energy efficiency class. In this case, a typical hydraulic passenger lift (630 kg nominal load and a nominal speed of 0.633 m/s over a travel height of 12 m) is evaluated with a low standby demand and a slightly higher travel demand. The difference between these two lifts is the average travel time.

Different studies have shown that approximately 80 % of all lifts are allocated in the usage categories 1 to 3. For this segment, cost optimized solutions in acquisition, installation and operation are absolutely necessary to fulfil market demand. By intelligent design and the selection of accurate components a minimal standby demand can be achieved without difficult. Following are some examples:

Improvements in travel demand are typically considerably more complex and also costly and there is no significant benefit in energy efficiency in lower usage categories as shown in the example. Hence, in most cases a cost-effective and also energy efficient lift (Energy efficiency class: B) can be designed with a hydraulic drive system without difficulties.

Finally, for best cost-value ratio of a lift with low usage intensity the optimization in standby demand is most effective.

With following rule you will design with reasonable effort energy efficient lifts:

If the lift is used seldom focus should be laid on low standby demand;

If the lift is used frequently a low travel demand is important.