Comment by KingOfCoders
2 days ago
I find things like this interesting, I guess everyone finds this normal but,
"Power consumption is down 45% - 50% annually."
Well is it 45 or 50? Is this a measurement or prediction or a random number? From an engineer or marketing? If prediction, why not saying so? Is this a range for several years depending on elevator usage?
Things like this irk me a lot.
Perhaps it ranges (if a measurement).
But my best guess is they simply _cannot know_ because the usage patterns of the new elevators will be different from the old elevators based on dispatching and sequencing and call systems. In other words, even if they know the exact consumption of the old system, and even if they expect precisely the same number of passengers per day, the _actual operating cost_ will depend on who arrives in the lobby, at what time, destined for which floors, and all other traffic patterns throughout the year.
I think the error bars are too high to say more than that. I doubt they did a measure of the power the original consumed, just an analysis of the system. They likely only have whole building power consumption, where HVAC is the majority of the costs: 1 degree difference in the weather or a couple tenants taking a vacation will make a much larger difference than the elevator.
I wouldn't be surprised if most of the savings was the new lights are LED while the old only incandescent was available - this is just speculation though, I have no idea. Every gear and every stretch of the ropes cost a little bit of efficiency and the modern system has less of those.
The reduction in cable weight probably was a big part of the savings, next to the vfd. Normally counterweights hang from the same sheave as the elevator. Its not clear to me from the sketch, but with the counterweight in different shaft the cable may have run three times the height of the building (the excessive length was noted) and that's a lot of mass to accelerate and brake.
> I wouldn't be surprised if most of the savings was the new lights are LED while the old only incandescent was available
It’s definitely not the lighting, you only need a few thousand lumens to have bright elevator lighting. If you need 4000 lumens, that is (5) 60W incandescent lamps, switching to LEDs that do 100 lumens per watt (8W lamp) saves you 260 watts/hr.
The new elevator uses a VFD (they call it a VVVF) to control the motor which is where virtually all of the gains come from. Lowering the speed of the motor lowers the power usage, it’s a non-linear relationship but a motor spinning at 75% speed uses 1/4 to 1/3rd of the power that it would use at full speed.
> They likely only have whole building power consumption
You can easily measure the power of a single circuit or single panelboard using a submeter: https://www.shopemondirect.com/catalog/shop/Shop-E-Mon-Direc...
> saves you 260 watts/hr.
It saves you 260 watts, continuously.
You can easially measure power by many different means - but I would expect they didn't.
The lights may be running 24x7, while the elevator motor is only running when it is moving, which is why I wouldn't be surprised if they used more power than the motors. Of course I have no information on how this building is used.
1 reply →
it also might be a regenerative VFD, unless the fault current contribution was too high and they chose not to
they probably haven't had the new elevator in operation for a whole year yet, so they're likely extrapolating. also, they won't really know the true usage of the elevator over the whole year so they're kind of guessing. they know per trip or per pound carried, but they don't know what that translates into actual real world on the power bill