Before anybody says anything about computers and the environment, we are going to find out what this room actually uses. Guessing first, measuring second — and the gap between the two is the interesting part.
Step one: guess, in writing
Each group writes down, before measuring anything:
- How many watts a laptop draws while somebody types on it.
- How many while it is asleep with the lid shut.
- How many the projector draws.
- Which of the three uses the most over a school year.
Commit to numbers. Vague guesses cannot be wrong, which makes them useless.
Step two: measure
With a plug-in power meter, take a reading for each device in three states: working hard, idle, and asleep. Record what you actually see, including the readings that surprise you.
| Device | Working | Idle | Asleep |
|---|---|---|---|
| Laptop | |||
| Desktop | |||
| Monitor | |||
| Projector |
Step three: multiply
Watts are per moment; the year is what matters. For each device work out the energy for a school year — how many hours a day, times how many days, times the watts, divided by a thousand for kilowatt-hours.
Do one by hand first. Then notice how much you would not want to do the rest by hand: that is the argument for Formulas as Algorithms, arriving on its own.
What to argue about
- Whose guess was furthest out, and in which direction? Groups usually overestimate the laptop and underestimate the things left on.
- Idle time is often the biggest number in the table. Why is that surprising, and what does it suggest to do?
- The projector is used for two hours a day. Does it belong in the same conversation as the laptops at all?
- What is not in this room but is still your energy use — the servers answering every search you make?
Afterwards
Your numbers become the input file for The Green Audit, so record them somewhere you will find again — with units. A table of numbers whose units nobody wrote down is a table of nothing.