Soup of the Day

This week I’ll mostly be…

… not using the lift. As part of my commitment to the CATE project, set up by Mark Watson, I have become one of several ministers for CATE projects and one of this weeks many tasks is not to use the lift. But why? Firstly the lift is just plain lazy if you’re only travelling between one and four floors (accept if your unwell or disabled). That is a lot of potential energy going to waste and a lot of calories that won’t get burnt. Instead a power-station has to pump a few grammes of carbon into the atmosphere to get you to the third floor.

I figured out that if Siân and I stopped using the lift in our building for a year, we would save a lot of energy. To figure out how much energy saved, I had to predict (educated guess) some values and the margin of error would make most physicist’s cry, but it does give an good idea of exactly how much power can be saved. So get a cup of tea, and prepare to be amazed.

To work all this out I am using a typical person living in a flat on our floor (fifth floor) in our building because that provides a good average for City population, plus I know the values for most of the variables. Before we start, we need to ascertain all the variables and constants.

• Modern buildings have a vertical floor spacing of 4 metres, we live on the 5th floor which equates to a height of 20 metres.
• Almost all lifts in buildings use a counterweight system, meaning the mass they are lifting is less than the weight of the lift because as the passenger car raises, the counterweight falls. The counter weight is usually equal to the weight of the lift plus the weight of half the passenger capacity. In The Green Building, the lift is designed for 15 people maximum, or 800kg. So if we half that to 400kg plus the weight of the person raising in the lift ( 76.2kg in this case) we get 476.2kg (on average). This means the lift motor is having to lift/lower 476.2kg.
• We need to know that gravity effects us at 9.8 metres per second squared (9.8m/s²). This translates easily. If you were free falling, for every second you would travel 9.8 metres further than you did in the last second.
• Now we need to know a little about energy. The metric measurement of energy is in Joules, but that means nothing to most people. The imperial measurement of energy over time is the kWh (Kilowatt-Hour) which is used to measure power consumption in the UK, so 1kWh translates to 1kW of energy sustained over 1 hour. 1 kWh is equal to 3,600,000 Joules. (Source: Wikipedia)
• 1kWh in the UK produces on average about 0.51Kg of Carbon Dioxide. (Source: Defra)

Finally there is another important factor we should consider, the dreaded Calorie. Not so important to the environment, but very important to us. A single Calorie is the the amount of energy it takes to raise the temperature of 1 gram of water by 1 degree Celsius; a single Kilo-Calorie is the same, except it is the amount of energy to raise 1 kg of water by 1 degree Celsius

• Recommended intake for women per day 1940 k/calories
• Recommended intake for men per day 2550 k/calories

In the UK, they never bother with the ‘k’ part for some reason, but it is there.

Obviously expelling energy burns any calories you have taken that day. 1 Calorie is equal to 4.1868 Joules.

Now we have all we need to see how much energy we’re saving and how much energy you’re burning by walking up / down the stairs rather than taking the lift in an average building. I’ll use our flat as the example.

Our person uses the lift 5 times a day on average in a single week. They live on the fifth floor 20m above ground level.
The average distance in a week they travel in the lift is 0.7km (5 trips x 20 m x 7 days = 700m, 0.7km).

We have already established the average mass the lift is lifting, even if it is going down (it still has to lift the counterweight), the mass is 476.2kg with our person on board. (We’re not going to bother with the energy to get the lift to where our person is for now as it is not a constant we can work out, plus it is prudent to mention that the weight of our person and the lift is not a constant. There could be someone else in the lift already when our person gets in)

Now lets look at the results, split into convenient sections for you.

Kilo-Watt Hours (standard measurement of power used)

To figure out how much potential energy our person is using in the lift in one week, we need to convert the total mass and the distance into Joules. The equation is simply Mass x Gravity x Distance (height), or mgh.

m x g x h = 476.2kg x 9.8m/s x 700m = 3,266,732 Joules

3,266,732 Joules is equal to 0.91kWh , or in another words, 1 kilowatt of energy sustained for 1 hour.

Fiscal Cost

1kWh in Manchester costs £7.30, so 0.91kWh is worth £6.64. That’s £6.64 a week our person is saving (or £345.28 per year).

Carbon Cost

0.91kWh is also worth 0.46kg in Carbon, so our person is saving an extra 0.5kg of carbon raising into the atmosphere a week (24kg of carbon a year)

Sustained Power

0.9kWh is equivalent to a 960.1 Watt sustained power source for one hour; or one Philips Cineos 42″ flat panel television (48 Watts), 15 energy saving light bulbs (15 x 7 = 105 Watts), the washing machine (165 Watts), two powerful stereos (2 x 85 = 170 Watts), and a standard bread-maker (500 Watts) all ON simultaneously for one hour.

Effect on Health and Fitness

When it comes to fitness, we’re only really interested in the trips up stairs [see footnote]. So we’ll half the average number of trips to 2.5.

This means that the total distance is now 350 metres, which is an expenditure of 1,633,366 Joules per week, or 233,338 Joules per day.

233,338 Joules per day is equal to 58.34 k/calories, which is 3% of a woman’s daily allowance regained. Each trip upstairs in our building is worth 23.3 k/calories.

Footnote : Going down stairs expels less than one thousandth of the amount of energy required to go up stairs, so we’ll ignore it.

After all that, if Siân and I both stop using the lift in our building for one week, we’ll save about £13 per week, 1 kilogram less carbon will rise into the atmosphere, and we’ll be able to watch a lot of television whilst making bread.

Now before you all start commenting saying that this is all wrong, please believe me I know. There are lots of figures here that can be improved on generally, but think of this as an introduction and something to get you all talking (and walking). If you do have more accurate figures for anything, please do add them as a comment and we’ll get this as correct as possible. I’m particularly interested in a dietician to give me accurate calorie information.

So what can be done to help? Well firstly regenitive elevators should be installed everywhere. These lifts generate power if the heaviest load is descending. Currently this power goes to a large resistor bank to produce wasted heat, but it could be re-used. Secondly elevators should use renewable energy sources as the lift in The Green Building does, which receives a large portion of it’s power from the wind turbine on the roof of the building.

Finally, please go and visit Mark Watson’s CATE web site and please try doing at least one CATE challenge this week.