Wednesday, February 21, 2007

How Much Energy Does an Elevator Use?

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.

39 comments:

Kevin said...

Thanks for the interesting analysis. I've been wondering about how much energy elevators use ever since my company switched offices to one where I'm able to take the stairs if I choose (before it was emergency use only). I presently am on the 6th floor and always take the stairs. Even if the electricity consumption of elevator use isn't excessive, it's still a good idea for health purposes (plus, every little bit helps in saving energy.. more for our heirs). However, I'm considering switching to elevator use for my trips back down to ground level, as I think walking down stairs is hard on the knees, and an elevator going down shouldn't require very much electricity.

Fat Knowledge said...

Kevin,

I agree with you.

I wonder now whether you actually put energy into the system, as you walk up the stairs, but then your body weight is used to bring the elevator down and that energy can be harnessed. But, I don't think so as the counter balancing I think causes energy to be used which ever direction you go.

MC Spanky McGee said...

You make a simple logical error here: you assume that because one person would only save a small amount of energy in a particular timeframe, it would never add up to a significant amount.

However, if *everyone* were to use the elevator less, that would add up to significant amount of energy, especially when added to the all of the other supposedly insignificant conservation practices.

If I cut out all of my 100s of small wastes, the result can be a big savings.

Fat Knowledge said...

Spanky,

If I cut out all of my 100s of small wastes, the result can be a big savings.

Good point. But, for me I would rather focus on a few big changes and let all the little stuff slide, then try and make hundreds of small changes.

Also, I find that people propose these small changes because they have no desire to make large/significant changes. That people feel that they are a good environmentalist just because they recycle or don't take the elevator even if they use lots of gasoline, eat lots of meat, and live in a large house or otherwise live an environmentally deleterious lifestyle.

For me, I just want to focus on three things:
1) limit the amount of driving/drive a fuel efficient car/use public transportation
2) live in a small apartment with little need for heating or cooling
3) a diet with limited amounts of meat

I think you get the most bang for you buck by focusing on these 3 things rather than lots of the small things.

However, if *everyone* were to use the elevator less, that would add up to significant amount of energy...

I am not a big fan of looking at it this way. Instead, I look at it is if everyone reduced their energy consumption by 1%, than at the national level energy consumption will be cut by 1%. The savings at the country level will be much larger in absolute terms, 300 million times as large in the US, but if we want to make large cuts in emissions at the national level, say 20%, everyone needs to cut their emissions by 20%.

JJ Decay said...

since i have to get bak to my assignment i just wanna say thanks for the great info, evaluation and detail. good stuff ^^

Fat Knowledge said...

JJ Decay,

Glad you liked it. :)

Anonymous said...

Gee, Fat Knowledge, don't be so hard on Spanky!!! What is wrong with making lots of small changes?! You don't know that Spanky IS reluctant to make your 3 big changes. Perhaps you lack the ambitiont to pay attention to details and DO the little things that can add up. I think everyone should do your 3 changes AND Spanky's little things. Do ALL that we can!!!

Anonymous said...

One may wonder whether your single source for data, Otis, is providing accurate power consumption information. Seems to me that the basic physics of lifting several hundred pounds would require more than an insignificant amount of power.

Fat Knowledge said...

Anon,

One may wonder if you came with a preconceived notion of what the answer should be and when this post didn't conform that you chose to blindly attack the source rather than questioning your own preconceived notion.

Do you have any reason to believe that Otis is providing inaccurate information? While that is possible, I don't see how it would be in their interest to do so. If you have another source for information, I will gladly look at it and revise the post.

As for the basic physics requiring more than an insignificant amount of power, I guess it depends on what your definition of significant power is.

As I calculate it, using an elevator for a year uses 70 kWh. In a physics sense, 70 kWh is a significant amount of energy. But, since the average home uses 10,000 kWh a year, compared to that is seems insignificant.

The average American uses the equivalent of 100 energy slaves. So, the amount of energy needed to run an elevator might be large when looked at in terms of human power, but given our additional 100 energy slaves it is not that big. I think a lot of people aren't aware of just how much energy we use.

I just watched A Crude Awakening: The Oil Crash. In it they state that one barrel of oil is the equivalent of 25,000 man hours of physical work. Assuming 42 gallons in a barrel of oil, one gallon is the energy equivalent of 600 man hours of physical work. While 600 man hours of work sounds significant, one gallon doesn't, given that each American uses around 500 of them a year.

And if you look at all the energy that hits the Earth in the form of solar energy that we aren't capturing, the amount needed to run an elevator looks even more insignificant.

leslie said...

thanks for posting this, answered my google perfectly!

Anonymous said...

the update is incorrect. the askpablo site said it would take 1.5 Wh to travel TWO floors, not one. so your conclusion is also incorrect.

it may be that the difference lies in the size of the cab you have chosen. a 20 person cab is pretty big--and heavy. also, the elevator type plays a big role in energy consumption. a hydraulic elevator can consume as much as 3 times more energy than a traction elevator. (see this white paper for a detailed discussion:
http://www.aceee.org/buildings/coml_equp/elevators.pdf
i used an otis elevator website calculator for a six person cab and came pretty close to the askpablo calculation.

but the main point here is: please be more careful before publishing (mis)information! it would have been pretty simple to double check what askpablo said before adding your update. fortunately, the link was still valid, so i could double check. this demonstrates why one has to be very careful when obtaining information from the internet. there are very few fact checkers and sloppiness goes unpunished...

Fat Knowledge said...

anon,

the update is incorrect. the askpablo site said it would take 1.5 Wh to travel TWO floors, not one.

Actually that is not true. This is what askpablo writes:
So, 90.7 kg x 9.8 m/s^2 x 6 m = 5,333.16 J. And 5,333.16 J = 0.0015 kWh. If you assume that the entire system is about 50% efficient you use about 0.003 kWh of electricity to go up two floors (or 0.0015 kWh per person per floor).

1.5 Wh per person per floor (not TWO floors).

so your conclusion is also incorrect.

My main conclusion was that using an elevator doesn't use a lot of energy. Had you been correct (which you weren't) then it would have been .75 Wh per floor, which would have been even less energy and made my conclusion even stronger.

but the main point here is: please be more careful before publishing (mis)information! it would have been pretty simple to double check what askpablo said before adding your update. fortunately, the link was still valid, so i could double check. this demonstrates why one has to be very careful when obtaining information from the internet. there are very few fact checkers and sloppiness goes unpunished...

Kettle. Pot. Black.

Anonymous said...

Goodness - Is that.. 4 muppets put in their place?
Mr "You make a simple logical error"
Mr "You lack the ambition to pay attention to details"
Mr "Seems to me that..."
Mr "The update is incorrect. Your conclusion is also incorrect"

And you weren't hard on Spanky at all. Your patience is remarkable, your answers correct and after this first visit to Fat Knowledge I'm leaving with total confidence in your answers.

Thanks for your analysis and effort :)

Jety said...

Hi Fat Knowledge, thanks for your calculations. I think your estimations are correct.

I created elevator calculator, which shows electricity consumed based on meters traveled. It also showst total coal and CO2 saved (if electricity comes from coal powerplant), car travel distance to produce equivalent CO2 and equivalent 40W bulb switched on time (days).

You can download the calculator and freely use as you like, it is excel sheet - http://jetensky.net/blog/2009/02/21/elevator-electricity-consumption-and-co2-calculator/

Calculator is part of Lunoschod project, where I measured and calculated how much electricity can be saved by using stairs instead of elevators. It has started in 27th April 2008 and two people joined it. Over 10 months 12227 m were travelled up by stairs (and down), with 35 kW saved.

Fat Knowledge said...

Thanks for the link Jety.

I found that the values computed in your spreadsheet were about 3.6 times as high as my estimates. But then I timed my elevator and found that it went 1 meter in .36 sec rather than the 1.29 that you have in your spreadsheet. When I made that adjustment, the values were very close.

I have to say that I have no idea what the kW values of consumption for my elevator are. Maybe the increased speed comes from a greater consumption of power.

Best of luck with your Lunoschod project.

Anonymous said...

is it better to send the elevator back to the first floor after every usage??

Fat Knowledge said...

No, I don't think you should send it back to the first floor. What if the next person who needed it was at the top floor? I would bet someone has done some analysis as to what the best floor to leave it on would be though.

I also think that some of the newer elevators have software that automatically puts the elevator in the spot it determines is the best place to be.

Anonymous said...

question?? is it more efficient to leave the elevator on the floor you get off on, or returning it to the first floor for the next rider in the evening hours(1pm to 12am). leaving it on the upper floor you get out in the morning hours(5am to 12pm)???????don

Fat Knowledge said...

Don,

Actually, now that I think about it more, it is clear to me that if you want to minimize energy usage, you should always leave it on the floor you are on.

When I answered before, I was thinking about how to minimize the amount of time it took to get an elevator. This is a tricky problem.

But, to minimize energy use it is simple. Just leave it where it is. If the next person is on the 1st floor, the elevator will go down there when the button is hit by the next person (and use just as much energy as if you had returned it down there). But, if the next person is on the 50th floor, then the elevator doesn't have to use extra energy to come from the 1st floor.

Anonymous said...

Fat knowledge, thanx for your thoughts!!!!have there been studies or research done on this issue about the use of the elevator???don

Anonymous said...

Your analysis assumes that the information provided by Otis Elevator is correct. I believe their estimate is unreasonably low. Using the Kone website or doing a hand calculation from any of the various textbooks on elevators will estimate a consumption of 8,000kWh/yr to 30,000kWh/yr per hydraulic elevator in a residence with 4-6 landings. (As the capacity per elevator increases from 2,000lb to 5,000lb, the energy consumption increases dramatically.)

Gearless elevators only consume 2,000kWh/yr to 9,000kWh/yr. This is a huge savings, especially now that electricity is over 10c/kWh in much of the country.

While the energy consumption of an elevator per person is less than a refrigerator per apartment, a lot of energy can be saved by taking the stairs.

By the way, you should look into getting an Energy Star refrigerator when yours kicks the bucket. None of them consume more than 30kWh/month.

Fat Knowledge said...

Hi Anon,

Thanks for the information.

I would be happy to add additional numbers to the analysis from the Kone site if if I knew how much energy a Kone elevator used per trip. I don't know how to convert from kWh/yr to kWh a floor. If you know how to convert the numbers, or if Kone lists a value per floor/meter traveled please let me know.

Anonymous said...

Thanks for your thought provoking blog.
Here are some additional sources to check out.

http://www.kone.com/media/en_US/green/index.html

Mechanical and Electrical Equipment for Buildings, 7th Ed by Stein/Reynolds/McGuiness.

Anonymous said...

Hey FK-
I don't know exactly how Kone does their calculation. I'm not sure what their assumptions are. I had been in touch with a Kone rep who was supposed to send me a spreadsheet that they developed. I should try to track him down to find out how they are getting their numbers.
I'll let you know.
~RD

Fat Knowledge said...

Thanks RD,

Looking quickly at my numbers above, I assume 8888 kWh/month for a 20 story building. If I were to divide by 4 to make it a 5 story building (not sure if that is the way to convert or not) then I get 2222 kWh/month. For a year it would be 26,664 kWh, which would be in the high end of your range of 8,000kWh/yr to 30,000kWh/yr per hydraulic elevator in a residence with 4-6 landings.

Looks like my link to the Otis calculator is broken, so I can't see if I could calculate numbers for a 4-6 story building.

Anonymous said...

If anyone thinks elevator usage is a selfish indulgence; I'll make a deal with you. If you allow me to replace the electric motor in your fridge with a recumbent bicycle, I will take the stairs for a year if you cycle several times a day to keep your ice cream from melting. :o)

Anonymous said...

Thanks for the info!it helped me so mch. :)

-Dominic

Anonymous said...

I just don't find the Otis numbers very credible. Does anyone seriously think that moving thousands of pounds worth of elevator plus occupants even one floor requires less energy than a cel-phone battery? Pull the other one. I'd *love* to see a battery that small that could store that much energy, but they don't exist. Instead of getting numbers from Otis, who have a very strong incentive to under-report energy usage, it might be better to get them from people who actually run buildings and pay the power bills. They'll know the real numbers.

Also, the point about multiplying by the number of users is an important one. I work in a small building, but we still have a couple of hundred employees plus visitors. When you multiply out the savings by even that modest number of users, it really does start to look like real savings.

Anonymous said...

Elevator motors are actually motor/generators. An empty cab moving up will put energy back on the grid due to the counterweight supplying the energy to move the cab and the motor/generator sending its' generated energy back to the grid. Now, go recaluculate.

abhishek said...

how much power it can conserve if its roter is coupled with a dynamo which is further coupled with a battary

Anonymous said...

As an Otis elevator technician I can say you are all wrong. You are reading the wrong Otis energy calculator. Every building has different types of controls, motors, generators, pumps, etc. The biggest mistake is to think people only ride twice a day, most office workers ride many, many times a day. Talk to a property manager of a few different buildings and you will find out that they spend a lot of money on electricity for climate control and elevators. Both of which are conveniences, but tenants biggest complaints when they don't work for even a few minutes. I'm not trying to sell anything but our latest systems do reduce energy consumption by a very significant margin. Especially when you factor in the construction materials.

reo said...

Also, I think something people forget in calculations like these is how much energy your body uses; say, for example, that by walking up X number of floors instead of taking the elevator, you save y amount of energy because the elevator is not used. That may well be true, but your body also uses up energy in walking up those steps, energy that you will presumably need to replace by eating. And if you eat food that is grown inefficiently, shipped in to the supermarket from far away, kept cool on the supermarket shelves for however long, wrapped using lots of needless packaging, etc. -- all of those costs would have to be offset against the amount of energy that the elevator would be using. And who knows, maybe the elevator would wind up being more efficient than a human body that replenishes its energy using inefficiently grown/shipped/marketed/packaged food.

Anonymous said...

Oh my gosh! What an uproar! How many ways shall we dissect this? And then to compare elevator energy usage to the human body’s energy use, and the energy usage of packaging and shipping and cooling and…ENOUGH ALREADY!

Your basic conclusions are correct:
• The overall energy used by an elevator is relatively small
• We can all benefit by using the stairs more often

Elevator manufacturers DO have an incentive to “fudge” the numbers. It’s called marketing! If you inflate energy usage, you inflate potential energy savings. (IMHO Kone’s claims tend to be exaggerated. Otis’s calculations are more realistic.) The reality is, all elevator manufacturers are developing and installing more energy efficient systems. That is what people want. That is what they buy! Elevator systems that are 20-30 years old or older are inherently less energy efficient (and typically last a lot longer too, but that’s another subject.)

Physics is physics. Mass times distance times speed = energy consumed. You can slice it and dice it in dozens of different ways and come up with nearly the same answer. These are all theoretical values because there’s no way to finitely predict usage and demand. Eventually, the manufacturers all come up with comparable products to their competitors.

We need elevators. Hydraulic elevators are less energy efficient than counterweighted traction elevators, but are economically more attractive in low rise buildings. As the installation cost of traction elevators approaches the installation cost of hydraulic elevators, presently in the 3-4 stops range, then the logical choice is the better performance and energy efficiency of a traction elevator. It’s a no brainer!

So use the stairs if you can, whenever you can. And don’t feel guilty about using technology to get you to the 10th floor in 30 seconds instead of the 10 minutes it will take you to climb the stairs. In the big picture, the energy savings is insignificant. The benefits to your health are 100 times greater.

Tom said...

If you doubt Kunstler in "Long Emergency", spend some time here: http://www.theoildrum.com/.

Anonymous said...

Interesting article. Thanks for putting it together.

Keep in mind that elevators also use energy whether or not they're moving. Apparently, in many elevators the grease in the motors at the bottom needs to be heated constantly to enable smooth operation. So, while you can save a very small amount of energy from taking the stairs, you could save more by closing elevator banks altogether.

Anonymous said...

reo said... "Also, I think something people forget in calculations like these is how much energy your body uses; say, for example, that by walking up X number of floors instead of taking the elevator, you save y amount of energy because the elevator is not used. That may well be true, but your body also uses up energy in walking up those steps, energy that you will presumably need to replace by eating. And if you eat food that is grown inefficiently, shipped in to the supermarket from far away, kept cool on the supermarket shelves for however long, wrapped using lots of needless packaging, etc. -- all of those costs would have to be offset against the amount of energy that the elevator would be using. And who knows, maybe the elevator would wind up being more efficient than a human body that replenishes its energy using inefficiently grown/shipped/marketed/packaged food."

HAHA, America is fat, remember? I think we'll do just fine without the, maybe, 100 calories burned while going up the stairs. Are you any type of scientist?

Luca said...

I thanks very much for the post, that gives interesting information. I agree with FatKnowledge that, in absolute terms, the energy spent is not so much.

But if we compare the 100 Wh an elevator spend for 20 floor with some 0.05 Wh the human body (132 lbs) spend to do the same, it's impressive!

Anonymous said...

thanks for the information.
Q: How much power/current does the heater in the elevator takes?

jaison said...

i'm really thankful to you for this information. i was never known that the power consumption of lifts are this much lower. this makes me to think that why can't we depend on solar cells at least for the lifts . in the example you have mentioned above requires only 361 square meter of solar cells to operate the lift with solar energy..:)

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