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Opportunities for Elevator Energy Efficiency Improvements
American Council for an Energy-Efficient Economy
WASHINGTON,
DC


Opportunities for Elevator Energy Efficiency Improvements

Harvey M. Sachs
April 2005

One of a series of white papers by the
American Council for an Energy-Efficient Economy (ACEEE)

Abstract

Elevator energy consumption in North American office buildings with central air
conditioning systems is generally considered to be about 5% of building electricity use. Although
the amount is relatively small for an individual building, the aggregate is large. In general,
hydraulic elevators used in relatively low-rise buildings are much less efficient than the traction
elevators used in mid- to high-rise buildings. New technologies, including software, promise
efficiency gains of about 3040% within elevator classes. Powell (2004) suggested the potential
for several hundred GWh/yr in savings from adopting high efficiency technologies.
Interestingly, this is unregulated energy usethat is, it is not covered in building codes
based on approaches like ASHARE 90.1, which focus on envelope, HVAC, lighting, and service
water heating. In practice, elevator energy use is additional, unpredicted electricity use that
shows up on demand and energy portions of utility bills.
There are approximately 700,000 elevators in the United States. We estimate fewer than
100,000 new installations and extensive retrofits annually, with major retrofits occurring on a 20-
to 30-year cycle.
Elevators are generally engineered systems rather than simple manufactured products,
tailored to each installation. Adequate energy simulation software packages are only becoming
available now, and we have not found efficiency metrics that are both useful and simple. For this
reason and the relatively small energy savings potential, we recommend against developing an
ENERGY STAR program for elevators. Instead, it may be helpful if, as part of its Commercial
Buildings thrust, EPA posted potential energy savings from elevator options on its Web site. This
would be something like best practices for new installations and recommendations for retrofits
(capturing energy benefits when modernizing for other reasons).

Acknowledgments

We first thank the many experts who shared their experience and insights with us. They
include Lutfi Al-Sharif, Ph.D., Consultant; Robert Caporale, Publisher, Elevator World
magazine; Chris Powell, United Technologies Corp.Otis; and Rory Smith, Thyssen-Krupp. We
thank Glen Campbell, NRCan, for providing access to the Enermodal Engineering report
commissioned by his agency; Mark Shewfelt, Enermodal, for his assistance; and Bob Knight,
Bevilacqua-Knight Inc., for insights on elevator lighting. Steven Nadel, ACEEE, reviewed the
manuscript. Jean Lupinacci, EPA, stimulated this work with her questions about unregulated Elevator Energy Efficiency Improvements, ACEEE
2
energy consumption and also reviewed a previous draft and provided key suggestions and
contacts. This work was funded through a cooperative agreement between EPA and ACEEE.

Introduction

Actual energy cost is a key performance metric for building owners. Before construction,
building energy simulation software may be used to model building designs and thus predict
energy consumption. These programs appropriately focus on the major building loads, which
include lighting, ventilation, people, and the direct losses and gains through the building
envelope (including the solar gains through windows). Incidental loads thought to be smaller
may be ignored by simulations, partly because they are not under the control of the mechanical
designer. However, if these incidental loads cumulatively are more than a few percent of total
building energy use, ignoring them leads to simulation reports that systematically underestimate
actual energy consumption. This leads to unpleasant surprises after the building is in use.
The energy use of elevators is often in this category of unpredicted energy uses. Literature
on this subject includes reports that are not completely consistent, because the area is not well
studied. By one source, elevators typically use 35% of the electricity in modern buildings
1
(Al-
Sharif 2004a). Simulations suggest that a lightly loaded low-rise hydraulic elevator doing
100,000 starts (door openings) per year would use 1,900 kWh/yr. In contrast, a heavily used
(500,000 starts/yr) non-regenerative elevator in a high-rise commercial building would use about
15,000 kWh/yr (Enermodal 2004). For context, a typical 1,900 square foot electrically heated
house in the West North Central Census Division would use about 7,100 kWh/yr for space
heating (RECS 2001,
2
Table CE2-10c, 5200 HDD). On the other hand, standby power can be as
great as 2 kW/lift (Al-Sharif 2004a), which would translate into about 10,000 kWh/yr by itself
for an elevator that was on for 5,000 hr/yr.
Elevator technology choices (hydraulic vs. traction) can yield 3:1 differences in energy
consumption (Al-Sharif 2004b, Figure 1, which cites Doolard 1992). Within a drive class, the
best performers will use about 3040% less electricity than the least efficient (Al-Sharif 2004a).
At least two-thirds of all elevator installations are hydraulic, limited to no more than 7-story lift.
The rest are traction elevators that use wire ropes (or belts) pulled over sheaves driven by a
motor. In general, traction elevators have counterweights, while hydraulics do not. A
counterweight is connected to the cab by a pulley, so it descends when the elevator rises, and
vice versa. Counterweights decrease the weight to be lifted.
Hydraulic elevators dominate the low-rise market, because they cost substantially less to
purchase. Mid-rise markets traditionally use geared traction motors, while gearless (direct motor-
to-sheave) predominates in high-rise buildings. The oldest and least efficient traction elevators
used motor-generators as DC power sources for the drive motor, and electro-mechanical relays
for control. Current, more efficient units use solid-state variable-voltage, variable-frequency
drives, often with permanent magnet motors instead of induction units. The most efficient
equipment uses regenerative braking to feed electric energy back into the building instead of
dissipating it as heat.

1
The dominant electricity uses in modern commercial buildings are lighting and HVAC, specifically air-
conditioning.
2
http://www.eia.doe.gov/emeu/recs/recs2001/detail_tables.html
American Council for an Energy-Efficient Economy, 1001 Connecticut Ave. NW, Suite 801, Washington, DC 20036
Phone: 202-429-8873. Fax: 202-429-2248. http://www.aceee.org. For additional information, email info@aceee.org
Elevator Energy Efficiency Improvements, ACEEE
3
There are about 700,000 to 800,000 elevators in the United States.
3
With reasonable
extrapolation from a recent Canadian study, these would use in the range of 3,000 GWh/yr
(Enermodal 2004). There is also indirect or induced energy use: virtually all the electricity used
by elevators is dissipated as heat within the building.
4
This offsets heating that otherwise would
be required, but adds to the air conditioning load. For a large, cooling-dominated building, this
will add perhaps 2040% to the direct energy use of the elevators: lower for a very efficient
HVAC system and elevator resistors located outside the thermal envelope; more for HVAC with
high parasitics and low system EER.
Industry experts interviewed suggest that the cycle between major renovations is on the order
of 2030 years, which would correspond to 25,00040,000 renovations/yr. We believe that total
new and renovation opportunities are less than 100,000 units/yr.
5
Both activities are
opportunities for market intervention for energy efficiency. Elevator vintage matters, with new or
upgraded traction elevators using 3040% less energy than older units.
6

The U.S. market has four principal manufacturersKone, Otis, Schindler, and
ThyssenKrupp, all internationally active, plus numerous specialist firms. Sales generally seem to
be through manufacturers local sales offices. There are also specialized design consultants who
help architects and engineers develop bid specifications.
If the goal is to recognize energy-efficient building elevators, the most important
consideration is that elevators are not products. They are best considered as engineered systems.
Once installed, the core elements (cabs, hoistways) will be used for the life of the building in
many cases, whether 50 or 100 years. However, during this service life, many components that
affect energy use will be changed out, typically on a 2030 year renovation cycle. Thus, elevator
systems are analogous to chiller-based built-up air condi