[Retric]

Physics:

dmd said on December 4th, 2008 at 3:47 pm

Ok, check my math here:

The owners estimate that the door will generate approximately 4600 KWH per year.

Let’s say they’re open 14 hours a day (say, 7am-9pm) for 360 days a year. That’s about 5000 hours.

Now, divide 4600 kilowatt hours per year by 5000 hours - that gives 920 watts.

920 watts - or 1.2 horsepower - from opening to closing, all year. I know Dutch people are (a) generally healthy and (b) like cafes, but somehow I doubt those figures.

[kqr2]

I did a quick check on powered automatic revolving doors. The one in the example brochure is probably bigger than the Dutch one but it requires 230V @ 10Amps or 2300 Watts. So, 920 watts to turn a smaller revolving door doesn't seem too outrageous.

http://www.dorma-usa.com/prod/entrance_systems/crane_revolvi...(code)/product_overview/(parent)/29532

Also, it appears that they have hooked a power gauge to the door so patrons can measure the amount of power they generate. So, their power estimates do have some basis.

http://www.expatica.com/nl/articles/news/Revolving-cafe-door...

[Retric]

People are not using it all the time and starting the electric motor to move the revolving door uses more power than it takes to move the door.

Edit: They could have their units mixed up or just measuring the peak output which is not the same as average output.

. Each time you pass through the door you generate enough power to make a cup of coffee.

Ben said on December 4th, 2008 at 4:46 pm

I call bullshit on this - there is no way one person generates the energy to heat a cup of coffee.

Energy needed = mass * temp raise * specific heat capacity = ~0.25kg * ~70C * 4.187 kJ/kgK = ~73kj

If it takes you a generous 10s to walk though the door you would need to be producing 73kj/10secs = 7.3kWatts!!!

According to http://www.ncbi.nlm.nih.gov/pubmed/10090637 the maximum a normal person can produce is ~500W so they are way off.