Elevators are always in that uncomfortable space between access regulation and compromises made by engineers. What’s different now is that many green building standards treat vertical transportation as an active part of the building’s energy profile, rather than a compliance item to be checked off. In multi-story buildings, elevator systems can use up to 5% of the building’s total electricity, and standby from 40% to 80% of the lift’s total energy usage in residential and low traffic conditions (ACEEE). The crux of that last statistic should ring alarms for any designer building a low-rise building with a single-shaft lift making perhaps a dozen trips a day.
ISO 25745 – The Energy Classification Framework Every Lift Spec Should Reference
ISO 25745 is the international standard for categorizing lift energy performance into a seven-band scale from Class A (most efficient) to Class G (least efficient). It takes all energy use, running cycles, standby, and start/stop losses, and converts it into an equivalent annual consumption.
If you are building anything vaguely aimed at green, it’s not a choice; you need to reach Class A. It’s the default expectation. Any recent certification will require proof that the specified lift is A or as close as you can get, and the ad-man’s brochure won’t cut it. You’ll need official test reports that use the ISO 25745 method.
What ISO 25745 also does, and this is often missed, is that it makes you talk about how the lift will actually be used. A Class A motor in a lift that’s too big, the wrong capacity for the building or running too fast, that lift will be less efficient in reality than a correctly matched, slightly lower-rated unit. The classification only counts if the lift is in proportion to its real traffic load.
Standby Management, Right-Sizing, and the Space Efficiency of Cabin-Style Lifts
In most cases, standby power is the weak link for residential lifts in the energy efficiency argument. A lift that’s making fifteen journeys per day is dormant for the other twenty-three and a half hours. If the cabin lighting, the ventilation fans, and the control displays are all drawing power constantly, then the standby load overwhelms the annual figure, no matter how efficient the motor. The annual electricity draw of the largest motor on a modern lift, the one that drives the hoisting mechanism, is comfortably below 1000 kilowatt-hours. Retrofitting a lift in a 5-floor building, the likely scenario in the deep retrofit of a 1960s apartment block, would cut annual energy consumption by less than 3000 kilowatt-hours even if the existing lift is an older inefficient model.
But modern standby-management, essentially a form of sleep mode, switches non-essential systems into hibernation once the lift has been unused for a set period of time. Lighting falls to zero or near zero, ventilation ceases or slows, and display screens turn off. The lift can wake in seconds to respond to a call. In a well-specified modern system, the standby draw can fall under 50 watts. In a poorly-specified legacy installation, it can top 300 watts continuously. Over a year, this is a significant chunk of the electricity consumed by the lift, and hence of the building’s total energy use.
‘Right-sizing’ is the other element to this. A lift that is larger than necessary, where the building’s actual lift-use patterns could easily be met with a smaller cabin and motor making fewer or slower journeys, will cost more to run and, crucially in the embodied carbon calculation, have required a heavier lift mechanism in the first place. The purpose of the lift is, of course, to move people and goods quickly and comfortably between floors. But if its capacity is oversized for the building it is in, and its speed over-specified for the number of floors it travels, the extra energy use is not the only problem: every lift-lobby will have needed to have been bigger, which means every floor will have needed to be heavier.
Low-rise residential and small commercial, meanwhile, can often dispense with the passenger lift altogether, opting for cabin lifts instead. These smaller, semi-enclosed units offer an attractive compromise in airtightness terms between the internal and external zone, require less structural alteration, and mesh neatly with the requirements for airtightness mentioned earlier under Passivhaus. Working with experienced cabin lift specialists to identify an enclosed platform lift configuration that satisfies the detailed accessibility requirements (not just the dimensional and operational requirements but also the unit-residential-access requirements, as a lift is a public workspace) can save the structure of the whole residential block. The carbon savings are enormous, and may be the difference between a project calculating at 12 tonnes carbon dioxide per unit-year over a lifecycle, and 10.
BREEAM’s Ene 06 Category and Why Transport Analysis Matters at Design Stage
BREEAM evaluates energy-efficient transportation through its Ene 06 credits. A formal transportation analysis is required at the design stage, meaning that you cannot simply consider the use of stairs instead of a lift to tick the Ene 06 box. You also cannot cheat by claiming the goods lift was specified for wheelie bins, but look, you’ve added a lift for people as well. Lift systems are defined in Ene 06 as a lift, so only those (plus escalators and moving walkways) that are not assessed under MAN 05 are considered.
The transportation analysis itself is a constructive way to ensure you are fitting the right product for your mobility solution. It’s simply a freight model extended to occupants and will diagnose the cost-performance of competitors in a mixed market. Lift configurations will usually end up competing against the use of stairs, but also through-floor lifts, wheelchair-platform lifts, external hoists, steplifts, and good old reasonable adjustment to the thresholds.
Passivhaus and the Problem With Lift Shafts in Airtight Envelopes
Passivhaus certification sets the bar for airtightness far higher than most buildings ever reach. The standard demands an air change rate of 0.6 per hour at 50 Pascals pressure difference or less. A conventional lift shaft punches a thermal and air infiltration hole right through that envelope.
Traditional lift shaft construction creates two separate problems. Firstly, thermal bridging: the shaft structure conducts heat right across the building’s insulation layer, degrading the thermal performance of the whole wall assembly. Secondly, the shaft itself functions as a stack, drawing warm air out of the building in winter and pulling cold air in at the base. Both effects are unacceptable on a Passivhaus project.
Self-contained shaft systems deal with both problems. A purpose-designed cabin lift, with a factory-built, insulated shaft enclosure, can form part of a Passivhaus envelope without the need for a site-built concrete or masonry shaft. The lift shaft becomes a sealed unit in its own right, with controlled interfaces at each landing. This makes it easier to achieve the required airtightness, as the shaft system has infiltration rates that are low and predictable and can be taken into the design and construction calculations.
The Passivhaus challenge is also why lift shaft placement in the design plan matters. Internally placed shafts, surrounded by conditioned space on all sides, eliminate the thermal bridging problem completely. External shafts demand far more careful detailing and are harder to certify.
Mechanical Drive Selection: Why Gearless Traction is the Right Answer For Low-Energy Buildings
Hydraulic, geared traction, and gearless traction are the three drive types used in the lifts and their energy profiles are quite distinct.
Hydraulic lifts work by using an electric pump to drive fluid through a small hole and raise a piston. Mechanically, they’re about as simple as it gets, which is why they’re frequently used in low-rise buildings. Installation costs are quite low as well, but you pay for that initial cheapness in long-term energy bills. The pump has to work harder to lift the cab with every trip, so hydraulic is the least energy-efficient drive type.
Geared traction lifts are the most common. An electric motor drives a gearbox, which moves the counterweighted cab along a track. The motor carries the weight of the cab and the passengers, while the counterweight offsets the weight of the cab. They’re a good all-around choice for medium to high buildings where the benefits of counterweighted cabs begin to significantly offset the friction losses introduced by the gearbox. However, they aren’t competitive with gearless traction systems in terms of energy use.
Gearless traction lifts are driven by a permanent magnet synchronous motor, similar to the motor type used in modern electric vehicles. Since motor and cab are directly linked, there is no gearbox or oil used in the drive system. This reduces losses and simplifies long-term maintenance. Combine that with the counterweighted cab loading cutting the overall energy the motor uses to move the cab and the gearless traction system is the lowest-power option for an elevator in a relatively low building.
Leveraging EPDs for LEED Materials Credits
LEED’s Materials and Resources category allows you to earn credits by documenting the environmental impact of specific products. An EPD (Environmental Product Declaration) is the document that enables this for a lift.
An EPD is a standardized, independently verified report that shows the lifecycle environmental impact of a product: raw material extraction, manufacturing, transport, installation, use-phase, and end-of-life. Not all lift manufacturers produce EPDs. If you’re going after LEED, check the EPD box first. Then, shortlist products.
The EPD also factors into the newly intensified conversation about embodied carbon. If a lift arrives with known-in-advance carbon data, that product is not creating a gap in your project’s whole-life carbon model, without data, there’s a gap, and during third-party verification, that gap is your problem.
If you’re serious about reducing carbon in your projects and meeting your company’s science-based targets, you can’t afford to create gaps. The EPDs need to be acquired, checked, and declared right at the beginning of the project.
Making the Specification Decision Stick
Green building certification is achieved through design decisions and not when the construction is practically finished. The lift specification is one such decision that has implications for energy performance, structural load, embodied carbon, airtightness, and accessibility, all at the same time.
Well, the solution is simple: assess the transport requirements early on, select the drive technology according to the real needs of the building, make sure that standby management is specified by default, and demand ISO 25745 classification data and environmental product declarations from the manufacturers before deciding. An appropriate lift, properly incorporated into the building design, will not only consume less energy but will also contribute to the energy performance of the whole building.