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ISO 25745-1:2012 — Energy Performance of Lifts — Part 1: Energy Measurement and Verification
Standardized methodology for measuring and classifying the energy performance of electric and hydraulic lifts
Introduction to ISO 25745-1
ISO 25745-1:2012 is the first part of the ISO 25745 series, establishing a unified methodology for measuring, classifying, and verifying the energy performance of lifts (elevators). Published at a time when buildings accounted for approximately 40% of global energy consumption, the standard addresses the significant contribution of vertical transportation systems to a building’s total energy footprint — typically 2–10% depending on building height and traffic patterns.
The standard applies to both electric traction lifts (with and without machine-room) and hydraulic lifts, covering new installations, existing modernizations, and extensions of service. Importantly, it provides energy classification ratings from A (most efficient) through G (least efficient), enabling building owners, architects, and facility managers to compare products and make informed procurement decisions.
ISO 25745-1 classification is increasingly referenced in green building certification schemes such as LEED v4, BREEAM, and DGNB. Achieving Class A or B under this standard can contribute directly to certification credits, making it a valuable differentiator in the commercial lift market.
Energy Measurement Methodology
The standard defines detailed procedures for measuring lift energy consumption under controlled conditions:
| Measurement Parameter | Description | Unit | Test Conditions |
|---|---|---|---|
| Running energy (E_r) | Energy consumed during a standard round trip | kWh | Full load (rated capacity), reference travel |
| Standby energy (E_s) | Average hourly energy in idle state | Wh/h | 24 h measurement, all systems operational |
| Recovered energy (E_g) | Energy returned to supply (regenerative drives) | kWh | Full load descending, empty car ascending |
| Total annual energy (E_a) | Projected annual consumption | kWh/year | Based on E_r × trips/year + E_s × standby hours |
| Energy classification index | Dimensionless index for rating | — | Calculated per Annex B formula |
Reference travel cycle. Energy measurement is conducted over a defined reference travel — typically a full-stroke round trip from the lowest to the highest landing and back. For lifts serving fewer than six floors, the reference travel is measured as at least three complete round trips. The car is loaded to rated capacity (using calibrated test weights) for the running energy measurement. Acceleration, deceleration, and rated speed must conform to the lift’s design specifications throughout the test cycle.
Standby power measurement. Standby energy consumption — often the largest component of a lift’s total energy use in low-traffic buildings — is measured over a minimum 24-hour period. The measurement includes all energy consumed by the lift controller, door operator, car lighting, ventilation fan, and signalization systems while the lift is not in use. Modern standby management systems can reduce standby consumption by 60-80% by switching off non-essential loads (car lighting, ventilation) after a programmable period of inactivity.
A critical finding from field studies: standby energy consumption accounts for 40-70% of total lift energy use in residential buildings with fewer than 8 floors. Specifying standby management systems — including automatic car lighting shutoff, ventilation standby mode, and controller power-down — can reduce total lift energy consumption by more than 50% in these installations.
Energy Classification and Engineering Insights
ISO 25745-1 defines an energy classification system from A to G based on the calculated energy classification index:
| Class | Energy Index Range | Typical Technology | Energy Saving vs. Class D |
|---|---|---|---|
| A | <0.60 | Regenerative drive, LED lighting, standby mgmt, PM gearless | 60-70% |
| B | 0.60–0.80 | VVVF drive, LED lighting, standby management | 40-55% |
| C | 0.80–1.00 | VVVF drive, fluorescent lighting, basic standby | 20-35% |
| D | 1.00–1.20 | VVVF drive (baseline reference) | — |
| E | 1.20–1.50 | Old VVVF, no standby management | −20 to −40% |
| F | 1.50–2.00 | Hydraulic or old 2-speed AC | −50 to −80% |
| G | >2.00 | Old hydraulic with continuous pump operation | −100% or worse |
Regenerative drive technology. The most impactful technology for achieving Class A classification is the regenerative drive. When a fully loaded descending car or an empty ascending car operates, the potential energy of the counterweight system can be converted back to electrical energy and returned to the building’s power grid. Modern regenerative drives achieve 30-45% energy recovery efficiency, turning a traditional energy consumer into a net energy producer during certain operating phases. The payback period for regenerative drive retrofits in medium-traffic installations is typically 2–4 years.
Permanent magnet gearless machines. The shift from geared to gearless permanent magnet synchronous machines has been one of the most significant efficiency improvements in lift technology. Gearless PM machines eliminate friction losses in the gearbox (typically 5-10% per transmission stage) while reducing motor mass by 40-60%. Combined with VVVF (variable voltage variable frequency) control, these systems achieve motor efficiency exceeding 92% across the full speed range — compared to 75-85% for traditional geared induction motors.
Standby energy management strategies. ISO 25745-1 recognizes multiple levels of standby reduction. Level 1 (basic) switches off car lighting and ventilation after 5 minutes of inactivity. Level 2 (intermediate) additionally powers down the door operator and control electronics after 15 minutes. Level 3 (advanced) achieves near-zero standby consumption (<50 W) after 30 minutes by transitioning the controller to a deep-sleep state while maintaining landing call response capability through a low-power communication interface.
A Class A lift installation typically consumes 6,000–10,000 kWh annually in a 10-floor office building with moderate traffic, compared to 18,000–30,000 kWh for a Class D installation. At $0.12/kWh, the annual savings of $1,440–$2,400 per lift fully justifies the incremental cost of premium efficiency components.
FAQs
Q: Does ISO 25745-1 apply to escalators and moving walks?
A: No. Escalators and moving walks are covered by a separate standard, ISO 25745-3. Part 1 specifically addresses only vertical lift (elevator) installations.
A: No. Escalators and moving walks are covered by a separate standard, ISO 25745-3. Part 1 specifically addresses only vertical lift (elevator) installations.
Q: How is the reference travel distance defined for classification?
A: The reference travel is defined as the full travel distance of the lift installation measured from the lowest to the highest served landing. For lifts with multiple entrances per floor, the main entrance level is used as the reference starting point.
A: The reference travel is defined as the full travel distance of the lift installation measured from the lowest to the highest served landing. For lifts with multiple entrances per floor, the main entrance level is used as the reference starting point.
Q: Can existing lifts be classified under ISO 25745-1?
A: Yes. The standard provides specific provisions for existing installations, including simplified measurement procedures and allowances for unavoidable inefficiencies in older building infrastructure (e.g., machine room ventilation requirements, guide rail condition).
A: Yes. The standard provides specific provisions for existing installations, including simplified measurement procedures and allowances for unavoidable inefficiencies in older building infrastructure (e.g., machine room ventilation requirements, guide rail condition).
Q: Is energy classification mandatory?
A: ISO 25745-1 is an international standard, not a regulation. However, several countries (notably within the EU) have adopted it as a national standard or referenced it in building energy performance regulations. Lift manufacturers increasingly provide ISO 25745-1 classification data voluntarily as a market differentiation tool.
A: ISO 25745-1 is an international standard, not a regulation. However, several countries (notably within the EU) have adopted it as a national standard or referenced it in building energy performance regulations. Lift manufacturers increasingly provide ISO 25745-1 classification data voluntarily as a market differentiation tool.
