After listening to the author of the Long Emergency speak of how we are running out of oil and that buildings over 7 stories were going to go away because we wouldn't have the energy to run elevators, I wondered how much energy it took to run an elevator. I think this guy is a quack and history will prove him wrong, but I still wanted to know if there was anything to what he said.



When I found this Otis Elevator Energy Use Calculator, I decided to investigate.



1) How much electricity does a typical high rise apartment dweller use in elevator trips in a month?



Assuming you are traveling 20 floors, making 2 round trips a day you would use 5.8 kWh a month (calculations below). At $.07 a kWh this would be $.40 worth of electricity. To put that in perspective, my refrigerator uses approximately 52 kWh a month and the average home uses 888 kWh a month or 153 times as much. So it is not very much.



2) How much electricity is used per round trip, per floor and per km?



Per round trip (20 floors): 100 Wh. This is about how much a desktop computer and monitor use running for 30 minutes.



Per floor (one direction, 3 meters): 2.5 Wh. That is approximately 1/2 the amount of energy it takes to recharge a cellphone battery.



Per km: 800 Wh. To put this in perspective, the Tesla Roadster electric uses 110 Wh per km. A counter weighted elevator is therefore about 1/7 as efficient as the Tesla Roadster per km. Then again the elevator goes up and down while the Roadster travels on flat land.



3) Does reducing your use of elevator trips make sense?



For health reasons, probably. Walking up a couple of flights of stairs a day is good excerise and your heart will be happy with you. But in terms of reducing energy usage for environmental reasons, not really. There are many other things that are much easier to do that would have bigger impacts. Changing 3 100 W light bulbs to CFLs would save more electricity than the typical apartment dweller going cold turkey on elevators.



If you were to walk up and down 3 flights of stairs instead of an elevator, that would save 15 Wh a day or 450 Wh a month. That would be enough to power a 37" Plasma TV for 3 hours. It is something, but not much. If you wanted to save energy, you would be better off trying to walk or take public transportation to work.



If living in a high rise in a dense urban environment allows you to save more than 1 gallon of gasoline due to decreased driving, the elevator usage more than pays for itself in energy savings.



After all this analysis, I am left with the same thought that I had when I started this, elevators don't use much energy and that Long Emergency guy is seriously bonkers.





Calculations



Data was gathered from the Otis Elevator Energy Use Calculator. They use the following assumptions:

1) Residential Building:

- Each user performs 2 runs per day (up and down);

- Each run, as a rule, corresponds to half of the elevator's total rise;

- Each floor, as a rule, is 3 m. high;

- In part of the runs, the elevator does not spend energy As I understand it, each run is an up and down so this means there are 4 single leg journeys a day. I believe this assumes that you are the only person in the elevator each time you take it. This might over estimate the total as sometimes you share a ride. On the other hand, sometimes you are on the ground floor and the elevator has to travel many floors to get to you, so this would under-estimate the total. Hopefully they more or less cancel each other out.



I entered the following values:

Car capacity: 20 people

Number of stops (including main entrance and basements): 41

Total population of the building: 1000 people

Number of elevators that serves this population: 1 There are many types of elevators that it calculates for: Variable frequency type controller - Gearless machine (Current technology): 5777 kWh/month

AC type controller - Geared machine and Hydrolic (Old technology): 8888 kWh/month

Gen2™ elevator system - Machineroomless (Latest technology): 4493 kWh/month I chose to go with the current technology, but numbers can be adjusted accordingly.



As 1/1000 of the people, one persons total comes to 5.777 kWh a month. Since the run corresponds to 1/2 the total rise, 41 stops means that you travel 20 floors (from the 1st to the 21st), which is 60 meters. 5.8 kWh /60 trips (2 trips a day * 30 days a month) = .1 kWh /120 meters (double for up and down)= .8 Wh a meter = 800 Wh a km.



Update: I found this post on AskPablo about energy use of elevators. He puts the energy needed to travel one floor at 1.5 Wh. This is a bit lower than my 2.5 Wh estimate, but in the same ballpark.