Issue 1/2009
01/02/09
Energy Efficiency of Lift Systems - Comparison on basis of VDI 4707
Gerhard Thumm
1. Introduction
When speaking about potential energy savings for lifts, two basically contradictory statements have to be evaluated:
1. Lifts account for only 3 % to 8 % of a building’s total power consumption
Therefore it is often more economical for the building owner firstly to reduce the power consumption, for example by means of better thermal insulation or by using energy-saving lamps, than to invest in increased energy efficiency in lifts.
2. Lift installations possess a high potential for saving energy
Due to the high number of new lift installations installed each year, and high inventory , there is in fact considerable potential.
Category: Issue 1/2009
Posted by: Editor
In 2008, approx. 500,000 new lifts will be installed; in China alone approx. 130,000 new installations will go into operation. The worldwide portfolio is estimated at 8.5 million lifts.
Reducing the current energy costs of these installations by 25 % would mean an annual savings of approx. 5 terawatt hours. This corresponds to the power generated by about 3800 wind turbines.
Thus lifts can contribute considerably to reduce worldwide energy consumption.
2. Standardisation efforts
The prolonged socio-political discussion about energy and the directives that are already in place regarding this subject in Europe have also led to corresponding standardisation efforts for the field of lift technology.
This paper goes into greater detail regarding two of these activities:
- In the area of ISO standardisation, the ISO 25 745 standard entitled “Energy performance of lifts and escalators” is under development. The first part has already been completed and deals with measuring the energy demand of lift systems. Part 2 will deal with the classification of various lift systems, such as the differences between traction and hydraulic lifts, and between various drive systems such as geared and gearless drives.
A point system is proposed for this with the objective of classifying into a four-step energy class system.
- On European level, the improvement of energy efficiency in lifts is being very strongly supported by the ELA (European Lift Association). In 2006, this umbrella organization for all national European lift associations established a working group that addresses primarily the question of energy efficiency. Additional topics are the drafting of recommendations and commenting on existing draft standards on this subject. Initiated by order of the European Commission, a study has been launched in 2007 that will also contribute to promoting more energy-efficient lifts and escalators within the EU. The study , which will be conducted until 2010, aims at creating guidelines for users and providing politicians with recommendations for action.
Completion of the study is planned for the year 2010.
- On national level, activities are going on in Germany on the VDI guideline 4707, which this paper will discuss in greater detail. This guideline was created with the aim of enabling easy calculation of the typical energy demands of a lift installation depending on its use. An essential characteristic is the classification into energy efficiency classes, which closely resemble the familiar classification of household appliances, such as washing machines, refrigerators, etc.
Seven efficiency classes are defined from A to G. This classification also corresponds to the classification of the household appliances listed below as well as to the energy efficiency of buildings as defined in the EU Directive 2002/91/EC, dealing with the energy performance of buildings.
Products that are labelled
Refrigerators & Freezers: directives 94/2/EC and 2003/66/EC
Washing machines: directives 95/12/EC and 96/89/EC
Washer driers: directive 96/60/EC
Dishwashers: directives 97/17/EC and 99/19/EC
Air-conditioners (up to 12 kW of cooling capacity): directive 2002/31/EC
Ovens: directive 2001/40/EC
Household Lamps: directive 98/11/EC
This enables the lift to be evaluated directly as an essential building component in comparison to the energy efficiency of the building itself, although lifts are not mentioned in the directive itself.
3. Objectives of VDI 4707
The following briefly addresses the objective of VDI 4707, which serves as the basis for the subsequent system comparison.
The guideline is to provide a basis that makes it possible to establish a generally comprehensible and transparent comparison of lift systems from various manufacturers without complex calculations.
In order to take similar user parameters as the basis for this comparison, two essential basic requirements are defined:
- The usage category (frequency of use)
- Measurement of the so-called energy demand classes, i.e. power consumption when the lift is running, and when it is stationary.
Lift are extended systems that, in contrast to household appliances, differ largely in parameters such as duty, travel speed, number of trips/time unit, accessory features etc., which have a critical effect on the respective power consumption. In order to make comparisons, therefore , the respective energy demands have to be standardised.
3.1 Power consumption during the run
Based on ISO 25 745 part 1, a reference run is carried out on a typical lift installation with an empty lift car in both UP and DOWN directions.
The power consumption during these two trips is measured and standardised by taking the following formula as its basis :
Erun = specificenergy demandreference run/distance travelled * carrying force
VDI 4707 specifies the following classification of the energy demand classes for the travel:
During the public inquiry phase of the guideline, one point that should be considered in greater depth, is the fact that the specific power consumption for the lift system is determined by running non-stop through the entire travel height.
Due to higher power consumption during the acceleration and deceleration phases, this results in a higher power consumption for lift systems having less travel height than it is the case for installations having a more travel height. Here we would need to consider whether the travel height to be travelled during the reference run should be limited to a maximum of 10 metres. This would ensure that the component from the acceleration and deceleration phases is weighted appropriately. In section 6, example 1, this point is underlined using measurements that have been carried out.
3.2 Standby consumption
Measurement of the standby consumption is relatively easy and carried out 10 minutes after completing the last run. The guideline makes no clear statements as to which power consumers have to be operating during the measurement. This enables the manufacturer of the lift installation to let energy-reducing measures take effect during the 10-minute period.
According to EN 81 9.17.3, the lift car light can be switched off when the car stops with doors closed. This is certainly one of the most effective measures for reducing the standby energy demand, thereby achieving a lower energy demand class.
Nevertheless, it must be considered that switching off certain types of lighting too frequently, such as neon lamps, the life time of the lights is considerably reduced. Here we must find a compromise between the demand for a minimum power consumption and a continued adequate life time for the lighting elements.
Additional effective measures include shutting down forced ventilation in the lift car and for the drive.
The standby energy demand classes are defined as follows:
4. Usage categories
VDI 4707 specifies four different usage categories as shown in Table 1.
It is obvious that this classification has been kept relatively general and leaves a certain amount of freedom for interpretation.
This enables identical building configurations with comparable use patterns to be classified into different usage categories, since the travel speed plays no direct role in the evaluation.
In general it can be stated that a lift with a higher travel speed and the same number of floors and trips always tends to fall into the smaller usage category.
The following example demonstrates this for a lift installation that differs only in the travel speed, but which has comparable use patterns.
For the comparison, the same number of trips per day is taken as the basis for both installations.
The same applies when a lift carries out many trips with a small floor-to-floor distance in comparison to an installation with larger floor-to-floor distances and fewer trips. Both installations yield a comparable average travel time in hours/day.
Due to the more frequent acceleration and braking actions, however, the lift with the higher number of trips will consume significantly more energy, and this is only partly taken into consideration by the specific consumption data as shown later in this paper.
5. Total specific energy demand
This is a further standardization step over the period of a day. The target is to have an overall value based on the classifications into the energy demand classes for travel and standby that have been already determined. Dependent on the 4 usage categories presented above, various classifications are defined in accordance with Table 4, VDI 4707.
To come to this overall value, the following figures are calculated:
Erun = specific energy demandrun * distance travelled/day * duty
Estandby = energy demandstandby * standby time (acc. usage table, not real values)
To measure the specific (daily) energy demand, the following standard is used:
Espec = Erun + Estandby / distance travelled/ day * duty
Measurement of this Espec value in particular is connected with considerable simplifications in practice. As already noted in the draft of VDI 4707, the acceleration and deceleration times are not taken into consideration when measuring the distance travelled, for example. Instead, only the rated speed and consequently the simple relation s = v * t is taken as the basis.
Another, certainly not unimportant, simplification applies as well for the standby power consumption, provided that energy- reducing measures were effective for measuring the value in accordance with 3.2. In practice, these measures for reducing energy are generally not effective during standby times of less than 10 minutes.
This means that installations with a medium/ high number of trips (usage category 2, 3 or 4) tend to receive too good evaluations, since the measures of switching off the car light, the fan, etc. will most likely not become effective in real operation during the day.
The categorization is made in accordance with VDI 4707 using the following figures:
6. Dimensions
The following shows the measurements made on different installations and draws attention to some particularities in this connection.
The measurements on the lift installations were made using the measuring instruments shown below in Figures 3 and 4:
Power measuring device: LMG500 ZES
Clamp-on ammeter: CHB3 Unitest
Evaluation unit: DIADEM National Instruments
The first example will illustrate the measurement of the specific energy demand for the travel depending on various travel heights:
The lift installations concerned are machine room-less lift system, type: synergy, using a synchronous gearless drive.
Three lift installations are taken into consideration.
Example 1:
This example underlines the statement that a lower travel height leads to a higher value of the specific energy consumption and thus to a worse efficiency class for travel.
The second example selected is an installation with different rated speeds, which has already been addressed in Chapter 4.
It highlights an installation with a frequency converter, type CPI, in the test tower at ThyssenKrupp Aufzugswerke. The installation was operated at 1.0 m/s and at 1.6 m/s. The following readings were taken, and the corresponding standardizations were carried out in accordance with VDI 4707.
Example 2:
This example shows that for the same number of trips, a lift with higher travel speed in the various classifications scores comparably and that for the value of the specific (daily) energy demand, it scores even better than the installation with 1 m/s.
In additional measurements, lift installations with different drive systems were compared and also classified into the energy efficiency classes in accordance with VDI 4707.
Parameters of 4 different elevator systems to be evaluated:
Results and classification of the measurements
7. Evaluation of the results
The results show in general that it is not easy to reach the categories A in the energy demand classes as defined in VDI 4707. In all examples shown in this paper the main component for the standby consumption, the car light, has already been switched off before the standby value has been taken.
To reach the desired classes A, more measures as the application of regenerative drives as well as control systems that apply sleep modes must be considered.
If the market however will accept all measures that are considered and proposed, like switching off the position indicators in the landings, has to be discussed with the customers.
The above examples show that some times the achieved results do not look quite logical. In the first example an elevator system with the same speed and the same duty, but different travel heights result in different energy demand classes. There are arguments that this might be even correct due to the acceleration and deceleration phase. But in the calculation method exactly this fact is neglected and the formulae are only based on the distance of travel according the usage categories .
In the second example the same number of starts but differentspeeds lead to a result, that the specific energy demand for the faster elevator is category B though the energy demand for the travel was B and for the standby D. The same elevator with a lower speed resulted in the overall category C what seems more logical.
In this comparison of different elevator drives exactly the opposite can be seen: The hydraulic elevator with a very low usage (class C for travel) and a very good (low) consumption for standby (class B) suddenly dropped to class D for the overall specific energy demand.
Such kind of non logical outcomes should be considered in the running revision of the draft.
note: This has been accomplished in the meantime and the non logical results do no longer exist to such an extend.
8. Additional elements of the VDI 4707
In addition to the various definitions for classifying the lift systems into efficiency classes, the draft standard provides notes in Chapters 6 and 7 for calculating the annual energy demand and the effect of various lift parameters with respect to the energy efficiency that could already be taken into consideration in the planning phase.
Appendixes A and D contain practical notes, examples and recommendations for manufacturers and highlight optimization options for reducing the power consumption.
9. Summary
With VDI 4707 we have a draft standard that is oriented closely to the European directives on the subject of energy efficiency.
The way in which the various energy efficiency classes are presented is comparable with the familiar classification for household appliances and for building technology. This helps manufacturers, consultants and building owners to make a corresponding comparison for lift installations.
Of course, there are also other ways the classification could be presented, e.g. a point system, as the ISO draft proposes. Ultimately, however, the statement is meant to give guidance to our customers and to provide the ability to attain a comprehensible comparison in addition to other statements already known to the users.
Unfortunately it appears that the opinions of the experts in the committees of ISO and VDI are quite different and there seems no agreement possible at present. Certainly, however, the goal of achieving an internationally uniform classification in the field of lifts (and escalators) remains.
1/2009
