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Energy efficiency in lifts

update2014/7/5, view

Simon Hirzel, Elisabeth Dütschke (Fraunhofer Systems and Innovations Research Institute)

Until just a few years ago questions of energy efficiency attracted hardly any attention in elevator engineering. Instead , safety, comfort and the footprint were in the limelight. In the meantime, however, energy use is being taken into consideration to an ever increasing extent.
Category: Issue 3/2010
Posted by: Editor

The E4 Project (short for “Energy Efficient Elevators and Escalators”) examines this subject at European level. The three-year research effort was initiated with the support of the European Commission and completed in April 2010. The objective of the undertaking: to improve energy efficiency for lifts and moving stairs in residential buildings and commercial structures. The results in a nutshell: From the technical viewpoint, significant savings are possible with the use of modern technologies. Implementation often falters, however, due to a lack of knowledge and the allocation of the cost burdens.

The situation in Europe
About 4.8 million elevators are currently in service in the twenty-seven countries in the EU [1]. In a comparison of the European nations, Spain and Italy are the front runners in regard to the number of lifts, followed by Germany in third place with its 650,000 elevators. These units are used for a wide variety of purposes: for convenient, barrier-free access between two floors in a building, serving high-rise structures many hundreds of feet tall or to move heavy loads in industry, for instance . The equipment ranges from simple, standard lifts through to individually designed luxury units.
Elevators can be grouped into three categories, based on the drive technology used: traction systems with gearing, traction systems without a gearbox and hydraulic systems. The large majority of all the units in service are geared traction elevators (see table). Hydraulic systems account for about one fourth of the elevators now in place in Europe. Gearless lifts, incorporating fairly new technology, make up less than ten percent of the total number in operation and are most likely to be found in buildings associated with the services and commercial sector.
If one considers the elevators’ locations, it becomes apparent that about twothirds of all elevators are found in residential buildings. That share does, however, vary from country to country. When compared with the European average, for instance, the share of lifts in residential buildings in Germany, at about fifty percent, is below average while the portion in the commercial sector is higher than in average.
The figures change constantly as a result of new construction, replacements and rebuilding. About 115,000 lifts are installed each year. When seen against the number of lifts in place, this is a relatively small figure and that reflects the units’ long service lives.
Energy consumption
Estimates show that the lift or lifts account for between three and five percent of total electricity consumption in a building [2]. Annual power consumption will be determined by three factors:
  • the amount of power drawn at standstill,
  • the amount of power drawn during travel and
  • frequency of use.
Power consumption while in operation and during idling periods will be determined primarily by the technical characteristics of the system’s components and their energy efficiency. This means that these factors will be determined during the engineering and installation phases and will, as a rule, not change significantly over the course of the system’s service life. Deviations might be encountered in the course of ageing and wear (bringing about increased friction, for instance). The consumption values for the two modes are largely independent one of the other; low use during travel does not imply low consumption when idling – and vice versa.
What determines trip frequency, along with the location, is the purpose for which the lift is used (barrier-free access, moving loads etc.) and the nature of the user groups. Seldom-used lifts in residential buildings can exhibit idle periods in excess of ninety-five percent while other elevators – in hospitals, for instance – are used very often. Differences in the frequency of use can mean widely diverse annual energy consumption levels even in units of identical design.
In order to expand the empirical base for measurement data on elevator energy consumption, seventy-four lifts across Europe were examined for energy consumption during the course of the project. Here consumption both at standstill and during travel were measured, using a standardized method [3]. The value for standstill was measured in each case fi ve minutes after the car’s last movement. To determine the amount of power consumed in travel a reference cycle was executed with the car empty, covering the entire ascent height. The cycle started and stopped with the car’s doors closed at the lowermost landing.
An evaluation of the measurement results for consumption while idling revealed a highly heterogeneous picture. The values, in both the residential and commercial sectors, showed widely differing consumption values, ranging from significantly below 100 watts to more than 700 watts. These variances can be explained by components of differing efficiency and by the fact that the lifts were equipped differently. On average, in the commercial sector, consumption of about 230 watts was found for the commercial sector while the corresponding value was about 190 watts in the residential sector.
As regards consumption during travel, observation of the absolute consumption values (one example being a reference trip covering the entire ascent height) does not give us the basis for any solid comparison of divergent elevators in regard to energy consumption. Assuming that the power consumption of the two door movements at the beginning and end of the cycle, as measured in the E4 Project, is negligible in comparison with the consumption during the cycle as a whole, one may use VDI Guideline 4707-1 [4] to calculate specific consumption during travel. The result here is how much energy an elevator uses on average in order to move one kilogram of net load through one meter. The markedly higher specific consumption of the hydraulic systems in comparison to the traction lifts is highly apparent. One factor that explains this is that conventional hydraulic systems do not incorporate a counterweight. This means that – in addition to the payload proper – the car itself will have to be lifted and that calls for greater motor output.
Based on the evaluation of the seventyfour elevators, taken in conjunction with the typical number of trips and the number of elevators in place in Europe, the extrapolated annual overall energy demand for Europe as a whole is about eighteen terawatt hours (TWh) [1]. This corresponds roughly to the amount of power used each year for rail traffic in Germany. The 650,000 elevators in German contribute an estimated two to four terawatt hours to this demand.
Although the number of elevators in residential structures is almost twice that in the commercial sector, their cumulative consumption is less. Among the contributing factors are the size of the lifts and differing use frequency. Considering all the lifts in residential and industrial situations, about seventy percent of the energy consumed is during idling periods. In the commercial sector, by comparison, the larger number of trips means that the standstill periods make up only about forty percent of annual energy consumption.
Savings potentials and their implementation
If one observes the energy saving potentials throughout the European “fleet” of elevators, then it is determined that with the consistent utilization of the best available technologies (including high-efficiency drives and components, components that can be switched off when not needed) an estimated sixty percent of the energy now used could be saved [1].
In practice, however, energy-efficient solutions are not universally employed. In Germany awareness of energy efficiency in elevators is on the increase. A market survey [5] on this subject did show, however, that familiarity with the question of energy efficiency in elevators declines the further one moves along the chain from the manufacturer to the final user – and that smaller end users are less aware, too. What we see is that – on the part of operators in particular – there is a deficiency in both awareness and information on this subject. To create broader consciousness of the subject of energy efficiency, for example, information from independent sources could be made available. Information campaigns could be carried out and the identification of elevators’ energy efficiency levels could be forced. At this point it would also be sensible to include elevators in the European Energy Performance of Buildings Directive (EPBD). This would, on the one hand, further increase attention to the subject. Additionally, the elevators would also become a part of the associated guidelines and grant programs.
A further obstacle for the implementation of energy-efficient solutions is that elevators are often installed by a developer who, after completion of construction, sells or rents the building, including the elevator , to the final user. Here, from the developer’ s viewpoint, cost-favorable procurement is in the foreground. For the end user, however, the total costs of ownership across the entire life cycle would be of significance. At the same time, the energy consumption for the elevators, in comparison with the building’s overall demand, is relatively low and thus often does not overcome the operator’s perception threshold. Especially in buildings with multiple tenants and/or owners, the energy costs for elevators are shared by the individual parties and thus seldom attract much attention.
The study demonstrates that there are hardly any relevant technical considerations that might oppose the use of efficient technologies. User comfort and safety continue to be ensured following the adoption of efficiency measures. The energy-efficient technologies are generally considered to be fully mature.
If, measures to increase energy efficiency are targeted in spite of all these obstacles, then two questions arise: Which energy efficiency measures will bring about relevant savings? What is the cost benefit ratio for each of these measures? Arriving at answers that are generally valid proves to be difficult. There is general consensus that switching off the car’s illumination can be effected profitably with little effort. In the case of more extensive measures and particularly when rebuilding, the question of effort and returns can be answered only for the individual case. Finding those answers can certainly be rewarding.
A holistic energy study should take proper account of consumption during both travel and idle periods and consider the elevator’s use patterns. When undertaking a rebuild it is often possible to draw upon logs showing the number of trips. Otherwise estimates or values drawn from experience may be helpful. When dealing with a seldom-used elevator in a residential building, for instance, reducing stand-by consumption will generally lead to greater savings at more favorable costs than would be the case for adopting energy recuperation measures during travel.
All the considerations for energy efficiency in lifts should take the entire life cycle into account. This would start with the planning and engineering of the lift, including the selection of energy-efficient components and using an intelligent control concept. Considerations then go further, embracing energy efficiency aspects during elevator installation, operation and maintenance. Over and above this, a harmonized larger system embracing a number of elevators can result in additional savings – by shutting down individual lifts during off-peak periods, for instance [6].
It has been demonstrated in the course of the E4 Project that there are clear differences between individual lifts in regard to energy consumption. All in all, however, significant savings are possible and reducing consumption during idle periods assumes an important role. At the same time it is necessary to launch measures to sharpen awareness of the subject and to make available on a broader basis information on energy saving potentials and the costs for exploiting them. Given elevators’ long service lives, a decision in favor of the one solution or the other will “cast energy consumption in stone” for a long period of time.
Additional information
More extensive information on the subject of energy efficiency in elevators and escalators will be found on the E4 Project Web site at www.e4project.eu. The E4 Project was supported by the European Commission within the framework of the Intelligent Energy Europe Program (Grant Agreement – EIE/07/111/ SI2.466703). It was carried out in cooperation with the European Lift Association (ELA), the University of Coimbra (Portugal), the energy agencies in Italy (Italian National Agency for New Technologies, Energy and Sustainable Economic Development – ENEA) and Poland (Polish National Energy Conservation Agency – KAPE) along with the Fraunhofer Systems and Innovations Research Institute (Fraunhofer ISI) in Karlsruhe. The authors are responsible for the content of this article.
Supported by
[1] Almeida, A. T. D. et al.: E4 – Energy efficient elevators & escalators: Estimation of savings. [Report elaborated for EC] 2010; Available from: www. e4project.eu.
[2] Sachs, H. M.: Opportunities for Elevator Energy Efficiency Improvements. 2005; Available from:www.aceee.org/buildings/coml_equp/elevators.pdf.
[3] Brzoza-Brzezina, K.: Methodology of energy measurement and estimation of annual energy consumption of lifts (elevators), escalators and moving walks. [Report elaborated for the EC] 2008; Available from: http://www.e4project.eu/Documenti/ WP3/E4_WP3_D3.1_Meth_Descr_FINAL. pdf.
[4] VDI: Aufzüge Energieeffizienz - 4707 Blatt 1. 2009, Beuth: Berlin.
[5] Dütschke, E. and S. Hirzel: Barriers to and strategies for promoting energy-efficient lift and escalator technologies. [Report elaborated for the EC] 2010; Available from:http://www.e4project.eu/ Documenti/WP5/E4-WP5%20-%20D5_1_Barriers% 20Final%2020100225.pdf.
[6] Hirzel, S. and E. Dütschke: Guidelines for new lift installations and retrofitting. [Report elaborated for the EC] 2010; Available from:http://www. e4project.eu/Documenti/WP5/E4-WP5%20 -%20D5_2_Features%20Final%2020100224.pdf.
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