Ask what a building's lifts cost to run and the answer is usually an estimate, a rule of thumb, or a figure carried across from another project. Lift energy consumption is one of the few building services where the real number is both straightforward to calculate and rarely calculated.
Lifts and escalators typically account for 3 to 10 percent of a commercial building's base building energy use. A lift's total consumption is the sum of its running energy, drawn while it travels, and its standby energy, drawn while it sits idle. ISO 25745 is the international standard that sets out how both are measured, calculated and classified into energy classes A to G.
What makes up lift energy consumption?
Two components, and they behave very differently.
- Running energy is consumed while the car is moving. It scales with how far the lift travels, how often it starts, how heavily it is loaded, and how efficient the drive and its control are.
- Standby energy is consumed while nothing is happening. The controller, car lighting, ventilation fan, displays, door operator and signalling all draw power around the clock, whether anyone rides the lift or not.
Most people assume the first one dominates. In a great many buildings it does not.
Why does standby energy often matter more than travel?
A lift in a low rise office or a residential building might be genuinely busy for two or three hours a day and idle for the other twenty. Standby draw continues through all of it, including nights, weekends and holidays. Across a year, an idle lift in a quiet building can consume more than the same lift spends moving people.
In a busy high rise the balance flips, and running energy becomes the larger share. This is why the single biggest influence on the answer is not the lift specification at all. It is how hard the building works the lift.
What does ISO 25745 actually do?
ISO 25745 is the international standard for the energy performance of lifts, escalators and moving walks. It exists so that two engineers assessing the same equipment arrive at the same number, which is precisely what a rule of thumb cannot promise. It comes in three parts:
| Part | Covers | What it gives you |
|---|---|---|
| ISO 25745-1 | Energy measurement and verification | A repeatable method for measuring real equipment on site, including the reference cycle to measure against |
| ISO 25745-2 | Energy calculation and classification for lifts | Predicted annual consumption from usage and travel data, plus an energy class from A to G |
| ISO 25745-3 | Escalators and moving walks | The equivalent calculation and classification for escalators, where operating mode drives the result |
The classification matters because it converts a raw kWh figure into something a non-engineer can act on. An energy class travels into a report, a business case or a board paper far more usefully than a consumption table.
How usage changes the answer
ISO 25745-2 sorts lifts into usage categories based on how many starts they make per day and how far they travel. A lift in a two storey building making a few dozen trips sits in a very different category from a lift in a busy tower making thousands.
The practical consequence is worth stating plainly. The same lift specification, installed in two different buildings, can land in two different energy classes. Any figure quoted without the usage assumptions behind it is not really a figure at all.
What actually reduces lift energy?
- Drive technology. Gearless permanent magnet drives are materially more efficient than older geared equipment. Hydraulic lifts are generally the least efficient option once travel and usage rise.
- Regenerative drives. These recover energy when the load overhauls the motor, which happens with a full car travelling down or an empty car travelling up. The payback is strongest in tall, busy buildings and much weaker in quiet low rise ones.
- Standby measures. Car lighting and fan shutdown after a set idle period, controller sleep modes and display dimming. In a low traffic building this is frequently the cheapest and largest saving available, and it is often the one left switched off.
- Control and dispatch. Reducing unnecessary stops and empty travel lowers running energy. This overlaps with service quality, so it rarely has to be justified on energy alone.
What about escalators?
In retail, transport and other public buildings, escalators are often the larger consumer of the two, because the default condition is to run continuously whether anyone is standing on them or not. ISO 25745-3 handles them, and the dominant variable is operating mode. Moving from continuous running to an intermittent or automatic start and stop mode, triggered by passenger detection, produces savings that no change of component can match.
Where the number is actually used
Three places, mostly. A NABERS Energy base building rating, where lift and escalator consumption forms part of the assessed load. A Green Starsubmission or an ESD reference building model, where a defensible figure is needed rather than an assumption. And a modernisation business case, where the question is whether energy savings contribute meaningfully to a payback that has to stand up to scrutiny.
The third of those is where most capital works decisions actually get made, so it is worth taking apart properly.
Modernisation: what does each technology step actually save?
In a capital works program the question is rarely whether to modernise. Obsolescence, parts availability and reliability usually settle that on their own. The energy question is which option to take once the work is going ahead, and the answer depends far more on what is being replaced than on what it is being replaced with.
| What is installed now | Typical upgrade | What happens to energy |
|---|---|---|
| Hydraulic | Traction, or a modern valve and variable speed hydraulic package | The largest single step available. A hydraulic lift has no counterweight and sheds a great deal of energy as heat |
| Single or two speed AC geared | Variable voltage variable frequency geared, or gearless | Large reduction in running energy, with smoother control and less mechanical wear |
| Motor generator set driving a DC motor | A modern variable frequency or gearless drive | Large reduction. The set draws power continuously while it runs, so standby losses fall as well as running energy |
| Early variable frequency geared | Gearless permanent magnet | A moderate reduction. Worth taking when the drive is being replaced anyway, harder to justify on its own |
| Any drive without energy recovery | Add a regenerative drive | Recovers energy whenever the load overhauls the motor. The benefit scales with travel and traffic, so it is strong in tall busy buildings and weak in quiet low rise ones |
Scope matters as much as technology. A control and drive replacement carries almost all of the energy benefit. Car interiors, fixtures and door finishes carry none of it, even though they often dominate the visible cost of the works. If energy forms part of the justification, it has to be attached to the right line items rather than to the project as a whole.
The cheap additions are worth naming while the work is open. LED car lighting, automatic lighting and fan shutdown after an idle period, and a controller standby mode all cost very little in the middle of a modernisation, and they attack the standby load that dominates a quiet building.
What is the payback?
EnergyCalc Studio returns a simple payback period alongside annual kWh, running cost and CO2, so each option can be set against its capital cost rather than argued about in the abstract.
Four things move that payback more than anything else. What is being replaced, since a hydraulic or motor generator installation has far more to give back than a drive fitted in the last fifteen years. How hard the building works the lift, because savings only accrue while it runs. The travel and load, which set how much a regenerative drive can actually recover. And the electricity tariff, which converts kWh into dollars and varies between sites more than most people expect.
Honesty serves better than enthusiasm here. A full modernisation justified purely on energy will usually disappoint. A drive and control upgrade, or a package of standby measures, often does pay back on energy alone. And where a replacement is already committed, the energy difference between the shortlisted options is frequently the number that decides which one gets built.
How to get a figure that holds up
Start with the usage data rather than the equipment list. Establish the number of starts per day and the typical travel, since these drive the category and therefore the result. Capture standby draw as well as running draw, because leaving it out understates a quiet building badly. Then calculate against ISO 25745 rather than a benchmark borrowed from another project, and record the assumptions alongside the answer so the number can be defended later.
If the building is still being designed, the lift count and sizing come first, and the energy question follows from them. Our guide on how many lifts a building needs covers that side of the work.
Work it out yourself
You can model all of this in EnergyCalc Studio, which works to ISO 25745-2 for lifts and AS ISO 25745-3 for escalators. Building the project, comparing existing against proposed and reading the results on screen is free, and it sits alongside our other browser based studios.
The formal energy report is A$500 ex GST per building. It covers every lift and escalator group in the project, with existing and proposed kWh per year, the savings in A$, CO2 and payback, and the ISO 25745 class shift for each group. Adding the Traffic Studio report takes the pair to A$750. Both tools produce preliminary estimates on a stated standards basis, and anything you need to rely on is backed by Elevator Project Management's signed advice.
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