Green Elevators

Energy is like hard drive space - how ever much is available will be used, and the cheaper it is the less time is spent thinking about more efficient ways of using it.

No matter how clean or renewable and energy source is, there is always still an environmental cost. In simplistic terms: wind turbines make a noise and don't exactly blend into the environment, solar panels require energy hungry manufacturing processes, tidal and wave energy generators go in the sea and therefore disrupt the underwater eco-system, bio diesel requires land that could be used to grow food...

So, my take on it s that the only real way to minimise our impact on the environment is to become super efficient in our use of energy to the point where true clean and renewable sources can provide no more and no less than what is needed - this brings me to some thoughts on a 'Green Elevator'.

Ever wondered how much energy is used daily by elevators around the world? Lifting a 100Kg person 50 metres (about 10 floors up) requires 50,000 joules (1,000 newtons * 50 metres). If we now consider all the people in the world who go up an elevator to their office every day we soon get to an enormous number - anyone out there want to try come up with a reasonable estimate?

A couple of things one has to consider to keep it realistic:
1. Lifts generally have some kind of counter balance so the motor doesn't necessarily have to lift 100Kg just because there is a 100Kg person in the lift - however, the lift is generally either heavier or lighter than the counter balance and energy is required to move it up and down.
2. If the lift is heavier than the counter balance while going down, the lift speed is controlled using brakes which use very little energy.

Here's a scenario: We have a 6 level building where 2 people work on each level (1 to 5 excluding the ground) and each person weighs 100Kg. When the lift is on the ground floor, its counter balance is on the 5Th floor, when the lift is on the first floor, the counter balance is on the 4Th and so on. The basic counter balance weighs the same as the empty lift. When people climb into the lift, it weighs itself and adds equal weight to the counter balance.

Now let's put 1000Kg of weight on the 5Th floor.

At 8 am, all 10 people climb into the lift on the ground floor - the 1000Kg on the 5Th floor is added to the counter balance so the balance and full lift are the same weight and the only energy required for the lift to go up is the little bit required to overcome inertia. On the first floor, 2 people climb out - the lift now carries 800Kg and the counterbalance drops off 200Kg on the 4Th floor. Two people climb out on each of floors 2, 3, 4 and 5 and 200Kg are left on each opposite floor (4, 3, 2, 1, ground).
At 5 pm everyone goes home so the lift picks up 2 people on the 5Th floor (and the counter balance picks up 200kg on the ground floor), two people climb in on the 4Th floor (and the counter balance picks up 200kg on the 1st floor) etc. When everyone gets out on the ground floor, the counter balance drops off the 1000Kg on the 5Th floor and we are back where we started.

Because we can safely assume everyone who goes up, must come down, one simply has to start the work day with the total mass of people who work in the building stored on the top floor.

To cater for a margin of variation, store some extra weight on the top floor and each intermediate floor, and of course the building has to be designed to be able to hold the extra weight on each floor. Combined with regenerative breaking during deceleration to reclaim some of the energy used to accelerate and you have a lift that can run on a fraction of the energy of a conventional lift.

It could probably work using e.g. 25Kg weights with some mechanism to attach and detach and store them on each floor or perhaps water in tanks that simply pump across the required amount between the tank and counterweight.

So that's the idea, I'll leave it to the engineers to come up with the design.