Energy efficiency in elevators

Background

Anyone who follows the news will certainly not have missed reports on changes in the world’s climate. In the meantime the cause has been unequivocally identified as the increased output of greenhouse gases, triggering a rise in global temperatures. This doesn’t sound half bad for the average Central European, but global warming will undoubtedly bring about some serious changes:

• The glaciers will melt. This will create problems with the drinking water supply in some regions. The rivers will carry less water particularly in the summer months – a hindrance for inland shipping, industry, agriculture and power plants that use river water for cooling (meaning higher electricity costs).
• The polar ice caps will melt. They are both a stabilizing element for the planet’s climate and the engine driving the Gulf Stream. What’s more, the Arctic and Antarctic are the moving force behind the nutrition cycles in the oceans.
• An enormous amount of water is bound up in the polar ice caps. If the ice melts, then mean sea level will rise. Broad, densely populated land areas will be flooded and in Europe Kassel or Cologne might become seaports. Waves of migration will begin.
• The deserts will spread. Periods of drought will increase and foods will become ever more expensive. Famine will ensue, above all in the poorer countries. Extensive migration will be the result (Africans moving to the EU, southern Europeans moving northward).
• Ocean temperatures will rise, increasing the amount of thermal energy stored there. This will lead to more frequent and much more violent storms.
• Habitats for marine life will change. Species will migrate to more northerly regions or become extinct. Less fish will be available for food and the prices will rise further, bringing about an increase in hunger in the world. This is another cause for migration. Anyone who might be thinking – “That’s great. It will solve the impending demographic imbalance in the industrialized nations and stabilize pension programs.” – has got it all wrong.

There is even more bad news. Energy will become more expensive!

This will affect us in two ways. The first impact is direct, through higher energy costs, and the second is through increased prices for products. Natural gas now costs 21% more than the same time last year. The prices for oil, coal and electricity have risen and will continue to climb. The phase-out of atomic power has already been decided upon and the remaining operating lives for nuclear power stations have been limited. Investments for new coal and natural gas fired power plants are being sold to us as being absolutely necessary.

The first automobiles with pure electric drive are to appear in five years. That will drive up the demand for electricity enormously. Traffic density is continuing to increase not only here in Europe, but above all in the new growth markets in China and India. At present the number of registered automobiles is rising by 15% annually in India. That means growing demand at constant or declining supply levels.

What can be done?

The supply of fossil fuels is limited. New reserves are being explored but extractionis both complex and costly. It is not yet possible to cover total energy demand with renewables. In Germany the share of electricity generated with renewables is about 12% at present (2009). This is far from enough to supply the entire market. The only option is to reduce demand. But how?

Getting along without elevators is hardly an alternative. Quite the contrary, the demand for residential space accessible by elevator will continue to rise as the population ages. Using electrical equipment less frequently or less intensively is not an alternative for elevators. Thus new technologies will have to be developed to lower electricity demand without limiting functionality.

At present, electricity accounts for 5 to 8 per cent of all the energy used in a building. The heat lost through hoistways open to the atmosphere and the energy required for ventilation and any climate control equipment serving the machinery rooms will have to be added to this. Heating consumes the largest share, coming to 60 per cent of demand. Governments and lawmakers have set strict limit values so that this value will fall over the course of time. The first “zero energy” houses were built several years ago. If the demand for thermal energy is eliminated in a building, then the percentage share of energy consumed by elevators will suddenly rise to 20 % of overall energy needs. And with this they move right into the sights of those who are aiming to conserve energy.

The total costs of elevator ownership

Procurement represents only about 25 to 30 per cent of the total costs incurred over an elevator’s service life of about 20 years. Thus operating expenses far exceed the acquisition costs. In addition to the energy drawn directly for lift operation, there are indirect energy costs tucked away in spare parts, in maintenance work, and in the fabrication and disposal of the elevator. Reducing an elevator’s energy requirements has a direct influence on product costs and operating expenses.

Government and legal guidelines

The political sphere has provided a framework for reducing carbon dioxide (CO2) emissions and energy demand. The Kyoto Protocol, adopted in December of 1997, mandated global reduction in the output of greenhouse gases. Most nations have signed and ratified the Kyoto Protocol in the meantime. The share of greenhouse gases in the atmosphere nonetheless continues to rise. There are currently no elevator industry standards relating directly to energy consumption but several committees are working on norms.

Standardization at ISO

The ISO charged Working Group ISO/ TC178/WG10 with writing the ISO 25 745 standard. The first section, which includes specifications on measurement and calculation, is already available in draft form. The second section will deal with guidelines for classifying elevators based on energy consumption.

Standardization in the EU

The following EC directives on the subject of energy have already gone into effect but they have only an indirect influence on elevators.

EC Directive 2002/91/EC

EC Directive 2002/91/EC considers the overall energy efficiency of buildings (also referred to as “Energy Performance of Buildings”, EPB). About 40% of total energy demand in the European Union is accounted for by buildings that are included in the compass of this European Community directive. This directive was transposed into national law in Germany in the form of the Energy Savings Act (EnEG) which, in turn, is the basis for the Energy Savings Ordinance (EnEV). As prescribed by the EnEV, a so-called “notifi ed body” or an energy supply utility is to issue a Building Energy Certificate. This serves as proof of the status of energy conservation measures in the structure. If the measures described in the EPB are implemented, then energy savings of at least 30 % can be anticipated.

EC Directive 2005/32/EC

A further regulation dealing with energy is Directive 2005/32/EC on energy-using products (EUP), a.k.a. the Eco-Design Directive. Important in conjunction with the EUP Directive is a verification process similar to CE certification. A symbol is used to indicate that the product was developed and manufactured in accordance with environment-friendly and thus energy-saving criteria. Not yet clear is the extent to which these two EC directives will affect elevators and escalators since they are not expressly mentioned in the text or annexes of either of the two directives.

ELA working group on ecology and energy

The European Lift Association (ELA) has established a working group for the socalled “E4 Project” (Energy-Efficient Elevators and Escalators) within the Intelligent Energy Executive Agency (IEEA/EC).

Standardization in Germany

VDI Guideline 4707 was written by the Association of German Engineers last year. It describes the evaluation and labeling for elevator energy use using uniform criteria. Similar to the EnEV for buildings, a uniform energy certificate is to be issued for elevators. VDI Guideline 4707 thus provides an easily understood means for classifying an elevator’s energy consumption.

Elevators are assigned to utilization type categories in order to do justice to differing applications and types of construction. Then two energy measurements are made. Firstly the energy drawn during a defined test journey is measured. A round trip is made with the cab empty – one trip ascending, one descending – across the full height of the hoistway. Then the demand at standstill, 10 minutes after the most recent trip, is determined. Depending on the utilization category to which the lift is assigned, the measured values can be used to quantify energy efficiency during travel and when idling, and the overall efficiency class.

The product of many lively discussions, the so-called “white copy” or final version of this guideline is slated to appear in March of 2009. The guideline’s objective is overall energy saving. It has actually already reached this goal since the simple announcement of the change has prompted many manufacturers of components and lifts to devote attention to the topic and to develop energy-saving products.

Measuring energy needs

By definition, efficiency (from the Latin: efficere, “achieving an effect”) is the ratio of output to the effort needed to achieve that output. If we look at the energy efficiency of an elevator, then we have to determine the ratio of effort and output. Effort is invested in the fabrication and installation of the lift, maintenance, heat generation and waste heat, electrical energy, and ultimately disposal at the end of its service life. This is compared with the output, i.e. conveying a certain mass over a certain vertical distance. But establishing this ratio is not especially practicable.

Consequently, only the absolute amount of electrical energy required to operate the lift is considered.

If you intend to determine the energy drawn by a lift, then there’s no getting around electrical energy measurements. Before beginning with that, however, it is appropriate to give some thought to the physical properties of the current and voltage connected to the elevator and what is actually measured. To that end, a brief overview of the physical fundamentals follows.

First we have to ask ourselves the question: “What is to be established?” The amount of electrical energy required for an elevator is to be determined. When dealing with direct current, the power output is the product of current and voltage.

P = U * I

Elevators, however, use 3-phase power. The following formula applies to currents and voltages that change through time:

The electrical energy results from the determination of power over a period of time.

Since the elevator is connected to a 3-phase grid and the phases are not uniformly loaded, the energy for all three phases will have to be determined simultaneously and totaled. This capability is offered by relatively expensive network analyzers such as the Fluke 1735 Power Logger or the MRG 510Flex test kit made by the Janitza company. This kit logs values every 200 ms, storing those values in 128 MB of RAM. The data can be read out later using the appropriate software and then evaluated.

To measure the voltage it is necessary only to connect the measurement probes at the three phases and the neutral conductor. There are several methods for measuring the current, however, and this is rather more complex.

Indirect current measurement

The power does not flow through the indirect current measurement system. Here the current is measured indirectly, based on the strength of the magnetic field surrounding a conductor through which electricity is flowing.

To do this, the conductor is placed inside a current transducer or a Rogowski coil, connected in turn to the measurement system. Depending on the type of transducer used, it may not even be necessary to disturb the circuit in order to make the measurement. The coil can be opened and wrapped around a live conductor.

The great disparity between the current used during elevator travel and idling current makes measurement more complicated. If the current drawn during travel is to be measured, then the instrumentation will have to be engineered to measure maximum travel current. If, for example, the current drawn by a lift is to be measured, and if this current can peak briefly at 200 A, then the next larger measurement transducer (300 A) will be used. This determines the potential measurement range. This has two consequences when measuring the currents drawn while the elevator is not being used.

One problem is found in the calculation of error. This is illustrated in a simplified fashion by way of the following example.

When using a class 1B, high-accuracy measurement instrument as per EN 61 000-4-7:2002, measurement accuracy (Irng) is 0.05 % of the measurement range used. To this must be added an additional 1 % measurement inaccuracy for the Rogowski current sensor in cases where the conductor is not perpendicular to and centered on the coil.

Roughly calculated, the measurement inaccuracy of 0.05 % of 300 A would result in measurement error of ± 0.15 A, corresponding to measurement accuracy of PΣ = 104 W.

When dealing with an elevator drawing about 140 W of power in the standby mode, the measurement error would be 104/140 = 74 %.

Consequently, the values thus measured cannot be used.

A second and very general problem results from the physical aspects of current measurement. It is technically impossible to determine current levels at a defined degree of accuracy across the entire measurement range.

The Measuring Instruments Directive, 2004/22/EC, specifies that the error for values below 40 % of the overall measurement range will be too large and may not be used.

The result is that the power drawn in standby mode and during travel cannot be measured in a single measurement. Two separate measurements will have to be made for the two operating modes!

Direct measurement may well be appropriate when measuring the standby current with its lower value. Here it is necessary to ensure, however, that the measurement instrument is not overloaded or damaged.

Occupational safety

As with all other kinds of work, it is necessary to keep occupational safety in mind when measuring electrical energy.

Anyone who has ever carried out a “realworld” measurement knows how closely we work to components carrying voltage. Workers have to be appropriately trained and work on “hot” components should be carried out only by a qualified electrician.

What’s more, special tools and special safety equipment will be required.

The current version of VDI 4707 describes the consuming units that have to be taken into account when measuring energy demand. In the machinery room for elevators there is usually a main disconnect with which the elevator can be switched off. If the measurement is made here, then the great majority – but not quite all – of the elevator’s energy requirements will have been recorded. Often there are separate feeds for the hoistway lighting, power points on the car, emergency call devices and other using units. This energy also has to be measured and will have to be included in the calculations.

The appropriate instruments are connected to the system – observing occupational safety requirements – and the measurements are then conducted.

Depending on the instrument used, it may store the data in internal memory so that they can be evaluated later, back at the office. Alternately, it might have a trigger input with which the exact time period for the measurement can be specified.

The effort required for measured data analysis will vary, depending on the type of instrument used. Some units will read out a value while others use large quantities of data for evaluation in accordance with a variety of features.

In no case should we underestimate the amount of effort required to arrive at an “accurate” determination of energy demand. New procedures will have to be identifi ed in the future. One option might be a calculated determination, provided that the component manufacturers indicate the consumption values for various operating states. This would make it possible to estimate energy needs prior to installation.

Development of energy demand

There isn’t much reliable data that could be used for a statistical evaluation. Many manufacturers are just now starting to evaluate their elevators but they do not make the fi ndings readily available.

In the course of a research project commissioned by the Swiss Federal Energy Office, measurements were made and analyzed for 33 elevators differing by age, utilization, technologies and manufacturer. Those measurements revealed the following.

The energy drawn during travel in traction elevators has declined thanks to the use of frequency inverters and gearless drives.

The incorporation of frequency inverters, counterweights and pressure accumulators in hydraulic elevators shows that here, too, there is a great deal of potential for saving energy during travel.

In the last 30 years the energy drawn in standby mode has risen significantly, however. It currently accounts for about 60 per cent of overall energy requirements. If this figure is extrapolated to cover the 650,000 elevators in Germany, then total standby consumption comes to about 755 GWh!

The measurements also showed, for example, that energy recuperation equipment is used to return energy to the grid only within a very small segment of the travel path. The requisite energy recovery devices have standby loads that are by no means negligible. Their use thus makes sense only for elevators that are in nearly continuous service – in hospitals, for instance.

If we analyze the energy requirements of an elevator when it is standing still, then car illumination consumes about onethird, provided that the lighting is not switched off in standby. This is regrettably still the case in the large majority of lifts in Germany.

A further third is devoted to automatic door activation whenever power has to be applied continuously to keep the doors in their extreme positions.

The final third is consumed by all the other using units that draw power when idling. These include the controls, frequency inverter, control panels with digital indicators, light curtains, emergency call devices etc.

What can we learn from these figures? How can we reduce the amount of energy drawn by elevators?

Traction elevators incorporating a modern, gearless drive concept and a frequency inverter operate very efficiently in the travel mode.

There is much to be said for installing a frequency-inverter drive at any hydraulic lift that is used fairly often. This will result in a far better energy use situation and the heat which occurs can be dissipated through a braking resistor. This will make a noticeable contribution to extending the service life of the hydraulic fluid.

Energy-saving lamps should always be used in elevators. The car lighting and the displays in the car should always be switched off in the standby phase. If the car light is switched off frequently, then using low-energy fluorescent lamps makes little sense. Modern LED lamps should be used here since their service life will not be influenced by how often they are switched on and off; they reach full brightness immediately after being switched on.

Modern indicators and displays also offer reduced energy requirements if they incorporate LED background illumination, for instance, or are self-illuminating, which is the case for OLED indicators.

If one takes into account not only the electrical energy required but also the energy used when a technician has to make a service call, then all the components have to exhibit long service lives. This virtually precludes using any type of incandescent lamps.

The second major demand for electricity results from holding the doors in their extreme positions. Here it is necessary to select door actuators that keep the doors in position by mechanical means, without or with only a very small amount of electrical energy.

There are further potentials for energy savings at many seemingly minor points. In total, however, they are significant.

One example involves banks of elevators. The intermediate circuits for the inverters can be joined. When an elevator is decelerating, it can make energy available to the other units in the group without triggering any increase in consumption during the standby phases.

In general the elevators should be equipped with highly effective switchedmode power supplies, offering efficiency better than 80 % in all operating modes.

Having noted that the energy demand rises with the elevator’s payload, it follows that an elevator should be engineered so that it only as large as actual demand requires.

If the car for a traction lift is only occasionally used at full rated load, then energy can be saved by selecting a counterweight that is smaller than 50 % of nominal load. If a building’s utilization has changed and an elevator is now overdimensioned, one might consider reducing the size of the counterweight. This will have to be decided by an expert specifically for the individual elevator.

Special anti-creep devices can keep the car in hydraulic lifts from descending to the lowermost landing and eliminate the need for re-leveling phases that require a great deal of energy.

A very effective way to reduce the amount of power drawn during standby is partial or complete shutdown of individual component groups or entire lifts during lowtraffic periods.

In a hotel, for example, it would be feasible to switch off three of a group of four elevators at night. As traffic increases in the morning, the one remaining elevator can gradually “wake” the others. In office buildings not used on the weekends the elevators can be put into a type of deep sleep on the weekends by switching off components. Since the system will first have to “boot” when a call request is entered at a landing button, there will be a delay of about 20 seconds before this call is responded to. This is a compromise that is certainly acceptable in most cases.

What’s more, the control algorithms could be modified so that the calls outside peak periods would be optimized in accordance with energy aspects.

Many small measures can be implemented in the electronics themselves. The microprocessors used in the system could be put into hibernation during low-traffic periods, for instance.

Retrofitting example

The amount of energy drawn was determined for an elevator located in the town of Bergisch Gladbach was determined. This is a freight lift that was fitted with a new drive and frequency inverter some years ago. Since this is a test lift used by an elevator manufacturer, a second inverter and many additional sensors were installed here. The following consumption values were determined in initial measurements:

Technical data:

• Elevator manufacturer: Hopman Köln
• Location: Industrieweg 13, 51429 Bergisch Gladbach, Germany
• Elevator model: Freight elevator, serial No. 10063
• Type of elevator: Roped traction elevator
• Rated load: 4400 kg
• Nominal velocity: 0.5 m/s
• Number of trips per day: < 100
• Travel time per day: < 0.5 h
• ETravel: 21 Wh
• PStandby: 485 W
• Energy costs per year: € 929.00

In the absence of any optimization efforts, this elevator would have to be assigned to Energy Efficiency Class C.

An analysis of these values reveals that optimizing the travel phase doesn’t make much sense. At 21 Wh the value for ETravel is ideal; using recuperation circuitry for a lift of this design, executing only 100 trips per day, promises no significant returns.

The amount of power drawn during the idling phase, PStandby = 485 W, is disastrous. This is the place to make some changes. The major using units in the standby phase are car illumination, an information display inside the car, the inverters and the additional test sensors.

The standard functions, “car light off when idling” and “signals off when idling” are not enough to significantly reduce the amount of power drawn in the standby mode. That prompted the decision to install an energy-miser relay. This deenergizes all the using units not required during idling phases.

The BlueModus energy-saving relay was installed in the first retrofitting phase. It switches off the inverters, the electronics in the car and the information display. A call received from a landing, or opening the hinged door at the landing, will cause the control software to “wake up” the elevator. This takes about 10 seconds.

Following the upgrade, a standby load of PStandby = 65 W was ascertained. This value permits classification in Energy Efficiency Class A.

If we compare expenditure and benefit, then the following is found:

• Materials for retrofitting: € 326
• Labor: € 295
• Savings after retrofitting: € 640 per annum
• The costs for upgrade will be amortized in just 354 days!

In addition, we achieve a beneficial effect for the environment, an improvement in the building’s overall energy balance and thus a reduction in building operating costs. The value of the property is increased and the owner’s image is improved.

But that’s not all. Additional economy measures are being planned. Car illumination will be converted to LED technology, the standby circuit will be further perfected, and the control software will be optimized using a new energy conservation function implemented in CANopen. These improvements will make it possible to achieve standby load of 10 W or less.

Practical use

Now the knowledge acquired will have to be put into practice. The examples show that efficiency and profitability can be achieved by adopting energy-saving technology. Retrofitting is also worthwhile since the standby load, in particular, was not exactly the focus of development over the past 15 years.

There are, however, no pat answers here. Every situation is different and it will be necessary to discuss an effective solution with the owner or operator. This means that consulting support will be required.

What can you now do in preparation for employing energy-saving technologies in the future?

First – Learn as much as you can about the subject. This article is a first step. Work your way into the topic. Learn which technologies are suitable for which applications.

Secondly – Advise your customers. Show them that you have the required expertise.

Thirdly – Measure the energy requirements at a specific elevator and demonstrate the savings potential that can be achieved with retrofitting or modernization.

We should not view the new guidelines and standards now in the offing as an additional burden but rather as an opportunity. We will all reap benefits from them – in terms of new business on the one hand and, on the other hand, by helping to preserve the climate.

Links

You will fi nd additional information at:

VDI 4707 E www.VDI.de
International Energy Agency www.iea.org
The Swiss Study www.electricity-research.ch
Calculation Energy certificat www.liftwiki.net/wiki/Portal:Energieeffizienz
The Eco-Design Directive www.umweltbundesamt.de/produkte/oekodesign/
BlueModus® www.boehnkepartner.de