Issue 3/2008


05/02/08

Methods for determining and evaluating the energy efficiency of elevators

Werner A. Boehm

The discussion about climate change and energy consumption – both in the political realm and society as a whole – is becoming more intense virtually every day. One nightmarish scenario follows hot on the heels of the next and there are repeated calls for quick and comprehensive action. The expectation here is not only that government respond but also that every individual make his or her own personal contribution to reducing energy demand.
Category: Issue 3/2008
Posted by: Editor

Operating on the basis of the often-cited Kyoto Protocol, which mandates a drastic reduction of CO2 emissions, the EU has adopted several EC directives centered on or associated with energy. Two of the most important are EC Directive 2002/91/ EC, Energy Performance of Buildings (EPB), implemented in Germany as the Energy Conservation Ordinance (EnEV), and EC Directive 2005/32/EC, Energy-Using Products EuP (Eco-Design Guideline).

Elevators are not expressly mentioned in these two EC directives aimed at increasing energy efficiency. Rather, the items mentioned in the EPB include building fittings such as heating, air conditioning and lighting systems and thermal insulation. Once again, elevators are not mentioned by name in the EuP, but motors are mentioned and all traction and hydraulic lifts do have motors.
Operating under the premise that every one of us will have to make a contribution to reducing energy demand and in light of the number of elevators (4 million in the EU, 650 thousand in Germany) and further considering the fact that elevators, on average, make up about 5 % of the energy demand in an office building, the elevator industry has taken a proactive stance and has itself decided to assign high priority to this subject.
Working group WG 10 of the TC 178 technical committee of the ISO is in the process of drafting ISO Standard 25745. This norm will have several parts. Part 1 devotes it attention to the determination and measurement of elevators’ energy demand. Part 2 will focus on evaluations and measures for improvement. But some time will pass before this globally and internationally applicable ISO standard is published.
At the national level, Switzerland may be seen as a pioneer. SIA 380/4, “Electrical Energy in Multi-Story Buildings”, contains the requisite specifications for lifts. Also of great significance is the Swiss study on “Power Consumption and Savings Potentials for Elevators”, prepared by the Swiss Agency for Energy Efficiency (S.A.F.E.) under the aegis of the Swiss research program on electricity.
In Switzerland the energy consumption was measured at more than 30 elevators differing in technical design and built by a variety of manufacturers. A particularly astounding finding was the reduction of relative consumption during travel in modern lifts but, by contrast, a great increase in stand-by consumption.
The results of this series of measurements in Switzerland form the basis for ISO Standard 25745 as well as for various European Lift Association documents and for VDI Guideline 4707 in Germany.
Two norms will apply in Germany in the future. One is the EnEV – Energy Conservation Ordinance (Ordinance on Energy-Saving Thermal Insulation and Energy-Saving Equipment Technology in Buildings). The other is VDI Guideline 4707 E on energy efficiency in elevators, now available in a draft version.
The EnEV ordinance, based upon the Energy Conservation Act (EnEG) adopted in Germany, represents the national implementation of the EPB Directive (Energy Performance of Buildings). Of significance in the EnEV, among other matters regulated there, is the requirement for a building energy certificate which may be issued either on the basis of consumption or connected demand.
The Eco-Design Guideline (EuP) has a major influence on the design of the relevant components. Conformity with the EuP is one of the factors certified when the EC label is applied.
Of major significance in future, daily work in elevator engineering will be VDI Guideline 4707 E on energy efficiency in elevators. The draft version of VDI 4707 E is now available as a so-called “green copy” and can be purchased from the Beuth Publishing Company. It seems that the “white copy”, i. e. the final version of VDI 4707, after the inclusion of comments, will appear in the autumn of 2008 and can then be used in everyday practice.
VDI 4707 E, “Elevators, Energy Efficiency”, defines the relevant parameters, depicts how the specifications and parameters are determined, and explains the requirements for measurement devices and measurement work. Over and above that, VDI 4707 defines energy consumption classes and energy efficiency classes.
VDI 4707 E also shows how the newly defined elevator energy certificate is prepared in compliance with VDI Guideline 4707.
Taking VDI 4707 E as the basis, the present article is to show what methods and procedures are to be used in determining and evaluating the energy efficiency of elevators in practice.
The significance of energy efficiency
As has already been mentioned, the significance of energy efficiency will continue to rise rapidly in the future. This gives rise to a need for methods and procedures that make it possible to determine and evaluate energy demand with minimum effort. They must also enable uniform and easily understood labeling. Finally , they have to be applicable both to new passenger and freight lifts and to existing elevators.
Owners, architects, planners, assembly and maintenance firms, operators and surveillance organizations thus will be able to take account of elevator energy requirements when evaluating the energy efficiency of structures as per the EnEV.
VDI 4707 E subdivides the various types of elevators into utilization categories. The classification of elevators thus defined – according to frequency and intensity of use, according to average daily travel and stand-by times, and according to the type of building – serves as the basis for assigning a given lift to an energy efficiency class as per VDI 47407 E.
Seven energy efficiency classes are defined. These are identified with capital letters from A to G and with colors from green to red. Energy efficiency class “A”, with the color green, indicates best energy efficiency for a lift.
It is very important to remember here that differentiation is made between energy demand during travel and that required when the system is at a standstill (stand-by demand). Each is assessed separately when determining the energy efficiency class.
The energy requirement for lifts is expressed in a specific energy demand value , registering the amount of energy ESpec required per distance covered, in meters , and per kilogram of rated load.ESpec is expressed in the dimension mWh/ (m·kg).
VDI 4707 E assumes that in the fi rst step the energy demand will be calculated on the basis of standardized specifications. Only if there is doubt will a second step be employed, in which energy consumption is measured.
Utilization category
A lift’s overall energy demand will be contingent not only upon its engineering design but also upon its use. VDI 4707 E establishes four utilization categories, based on the type of building, the use of the elevator and the number of users. The categories differ primarily according to daily travel periods. Differing energy demand values for the four utilization categories and thus differing energy efficiency classes will result, based upon the ratio of stand-by to travel time.
Table 1 lists the average use period for the four utilization categories and typical examples for lifts in these categories.
Problems will certainly arise in applying VDI guideline 4707 E in day-to-day practice when it is necessary to assign an elevator or bank of elevators to one of the utilization categories listed in Table 1. But neither would it make sense to define a larger number of utilization categories with more detailed divisions.
As was previously mentioned, the fundamental objective for VDI 4707 E in practical use is to permit quick and fairly easy determination of energy demand by way of calculation. The specific energy demand value ESpec for the lift will certainly exhibit tolerable deviations from actual consumption. In cases of doubt, verification measurements.
Determining energy demand
The following steps are used to determine the energy demand values:
  • Determining, during the planning phase, the parameters for the elevator for the intended use
  • Determining the utilization category as per VDI 4707 E
  • Determining the daily demand during standstill and evaluation by assignment to the appropriate energy demand class
  • Determining the daily demand during travel and evaluation by assignment to the appropriate energy demand class
  • Determining the specific overall daily energy demand and evaluation by assignment to the appropriate overall energy demand class
  • Determining the annual energy demand
  • Issuing the elevator energy certificate as per VDI 4707 E
  • As required: measurement of energy consumption values
An example is used here to show how the determination and evaluation of the energy demand or energy consumption is to be approached.
The elevator selected here has the follow parameters as per the planning and project documents:
  • Type of building              Mixed: residential/ physicians’ offices
  • Nominal load QN           630 kg
  • Velocity VN                    1 m/s
  • Number of stops             5
  • Ascent height AH           12 m
  • Number of trips per day 180
With this number of trips per day and the assumed average travel distance of hF = 6 m the result (taking the usual acceleration and deceleration values into account) is a daily utilization period of tU = 0.35 h. Thus the elevator is to be assigned to utilization category 1 as per Table 1 in VDI 4707 E.
Stand-by demand
The determination of the stand-by demand is preferably undertaken by totaling the individual demand values for the various electrical components and those units that make a contribution to the elevator’s operational readiness or actual operation.
Let us take the same example to illustrate. The elevator manufacturer or the responsible installation company determines – for the equipment requested by the client and for the electrical equipment and components typical for the type of lift selected – a stand-by demand of PSB = 20 W.
This corresponds to energy demand class
A for stand-by, as is shown in the following Table 2 as per VDI 4707 E.
Travel demand
The determination of electrical demand during travel in the concrete application is done preferably by extrapolating from known energy demand values for a particular type of elevator. These will be found in tables provided by the elevator manufacturer or the assembly company.
These selection tables are prepared using the measured values determined during reference trips defined in VDI 4707 E. These measurements are made for specimen systems or for pre-existing elevators of the type involved. They serve as standard values for calculating demand during travel.
In the example selected, the fictitious elevator manufacturer DeLidon Lift GmbH is offering its newly engineered “HEUD System 1.0”. Specific power demand during travel is determined using the selection table for “Typical energy demand values for the HEUD System 1.0 elevator design”. That value is found to be ETravel/Spec = 0.68 mWh/(m·kg).
This corresponds to energy demand class A for travel as shown in the following Table 3, taken from VDI 4707 E.
Specific overall energy demand value
Using the daily travel time of 21 minutes (tU = 0.35 h) previously determined and taking 180 trips per day, the distance covered sNom = 1080 m per day.
This results in daily energy demand of ETravel/Ref for travel each day of
At daily stand-by time for the lift of (24 h – tU) = 23.67 h the energy demand ESB for the daily stand-by period comes to
Consequently, overall daily energy demand comes to
If this value is again divided by the distance covered sNom per day and the rated load QN, the result is the specific energy demand for the elevator at
Thus the elevator can be assigned overall to Energy efficiency class A as per the following Table 4, taken from VDI 4707 E.
Determining annual energy demand
The energy demand values determined can be used to estimate the demand for electrical energy to be expected in a building for the operation of the left within a certain time frame. This is done by multiplying the specific energy demand value for the elevator installed there with the number of trips to be expected during this period, the average distance per trip, an average loading factor (payload and balancing) and rated load.
Where the daily use times for elevators deviate significantly from the travel times assumed in Table 1, annual energy demand can also be extrapolated on the basis of the energy demand values for travel and stand-by with the estimated times for travel and stand-by. The times for travel are derived from the expected number of trips and the average distance covered per trip
Probable annual energy demand EYear is calculated by extrapolating with the values already determined for energy demand per day. When determining the ETravel energy demand the loading factor k is taken into account (k = 0.8 for traction lifts, k = 1.2 for hydraulic lifts).
Overall energy demand per day EDay thus results from
In this way the annual energy demand can be determined. One further factor to be considered is the determination of N = number of operating days. In the case of the elevator selected for this calculation example 280 days in operation each year are assumed for its utilization. This results in annual energy demand of
Elevator energy certificate
The parameters determined for energy demand can be communicated to the owner or operator by the elevator manufacturer or by the assembly company in conjunction with the bid for an elevator. The parameters can be entered on the elevator energy certificate as shown below. This certificate can form the basis for the energy evaluation of elevators in the context of the EnEV (building energy certificate) .
The above example of an elevator energy certificate is described in VDI 4707 E only in regard to its content but not in regard to how it is to be depicted. This should preferably be oriented on the depiction used in the building energy certificate.
Measuring energy consumption values
Energy consumption values are measured for two reasons:
  • To determine standard energy demand values in selection tables used by the elevator manufacturer or installer to calculate the demand values in specific applications.
  • To verify the energy demand values specified by the elevator manufacturer and/or to determine whether there have been changes in the energy demand values resulting from changes in the elevator technology as a result of aging, maintenance or rebuilding. Here, however, one should allow for permissible tolerances of ± 20 % in the values.
Stand-by consumption is determined by measuring the individual consumption values. Stand-by consumption is determined ten minutes after the end of the last trip.
Consumption while traveling is measured during a reference trip. One reference trip comprises ascending and descending through the entire length of the hoistway with an empty car. Door motion is included.
The energy consumption measured in watt-hours (Wh) during the reference trip is set in relationship to the total distance covered (twice the ascent height) and the rated load at the car. The reference trip can be executed several times in sequence to ensure measurement accuracy.
Since the amount of energy consumed by the drives in traction and hydraulic elevators may, for instance, vary according to the temperature and thus the viscosity of the oils, measurements should be made at average operating temperatures.
The reference trip with an empty car is used for standard elevators with a traction drive and 40 % to 50 % counterweight balancing or with a hydraulic or drum drive and only a small counterweight or none at all. Where elevators have a different weight balancing system, the energy demand during travel will have to be determined using a loading spectrum. This comprises multiple trips:
  • 40 % with an empty car
  • 30 % with one-third load
  • 30 % with two-thirds load
A special loading spectrum can be defined for special types of applications. This deviation from the norm will have to be documented.
Measurements are made downline from the main switch for the drive power circuit and downline from the switch for the elevator’s illumination circuits. The hoistway and machine room lighting are not taken into account when measuring energy consumption.
In addition, there may be power circuits present that serve the controls for a bank of elevators. A measurement in the standby status will be made for these power circuits, too, and the energy consumption value thus determined can be prorated to the stand-by consumption for the individual elevators. This is also done for any other equipment required for the operation of the elevator.
Low stand-by power levels and high acceleration power levels with currents that deviate from the ideal sine curve impose considerable demands on measurement technology.
Requirements for the measurement instruments
  • For the measurement of the drive power circuit
  • Determining 3-phase effective power with a minimum of three values per second
  • Taking account of harmonics generated by frequency inverters
  • Sufficient measurement range for maximum acceleration and stand-by status
  • Power is determined by the measurement instrument, based on the effective values for voltage and current.
  • The effective values must be determined continuously between two scan points.
  • Recording the power values during the reference trip (chart: power as a function of time).
  • For the measurement of the illumination circuit
  • Determining single-phase effective power with a minimum of three values per second
  • Taking account of harmonics
  • The power is determined by the measurement instrument based on the effective values for voltage and current.
  • The effective values must be determined continuously between two scan points.
  • Power values can be read when the car is stationary.
Measurement shall be carried out by trained and competent persons who are familiar with the measurement equipment and its use. The appropriate elevator personnel will have to be on hand, as well, in order to ensure safety.
Measures to increase energy efficiency
Measures to increase energy efficiency can, of course, be implemented both in new systems and when updating existing equipment. Offering the so-called “modernization packages” is recommended. They could include measures to increase safety as per BSV/SNEL/EN 81-80, measures to boost energy efficiency as per EnEV and VDI 4707, and measures to increase performance capacity and quality (service life).
The following measures to increase the energy efficiency are recommended. They are applied during the development process and during the service life of a lift:
  • During the planning phase, consider optimizing the basic engineering design – in regard to the required counterweight and the relation of payload to displacement load, for example. Energy- optimized solutions could also be selected when designing the project phase.
  • Analysis by individual functions in order to minimize stand-by consumption, above all at the controls.
  • With limited availability e. g. during return trip or trip to parking position or adapted group functions.
  • In component selection: Here differentiation should also be made according to the effect at a standstill (e. g. using LEDs for car illumination) and during travel (e. g. using an inverter with energy recovery or by employing hydraulic pressure accumulators). A tour of the Interlift ’07 revealed a wide variety of offerings for energy-efficient components.
  • Assembly quality is, of course, also of great significance. Ultimately, when observed more exactly, an elevator’s energy demand will depend only upon its efficiency since the potential and kinetic energy applied to the elevator system will, at 100 % efficiency level, also be returned completely. To the same extent, maintenance quality is also of significance for energy consumption.
Summary
Publication of the final version of the new VDI Guideline 4707 E, “Elevators, Energy Efficiency”, will make available an aid for the evaluation and labeling of energy efficiency for elevators. An example was used to show how the guideline is to be applied. The methods used to determine and evaluate energy demand values and the procedure used when measuring energy consumption values were explained. VDI 4707 E thus forms a uniform basis for the evaluation of energy use in elevators in conjunction with overall energy efficiency for buildings. One result of all this work is the issuing of an energy certificate that is submitted to the elevator’s operator in conjunction with operating documentation.
The author
Werner A. Boehm carried out several executive functions for the elevator and escalator company ThyssenKrupp Elevator AG with its global scale of operations. In recent years he has devoted his attention to the interests of the elevator technology association, VFA-Interlift e.V. He is a member of German and European committees that turn devote their efforts to measures for improving energy efficiency in lifts.

 

3/2008

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