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.
Curriculum connection
D1.1
describe the negative effects of computer use on the environment (e.g., creation of e-waste, excessive use of paper resulting from unnecessary printing of files and emails, heavy power consumption) and on human health (e.g., exposure to radiation, musculoskeletal disorders, eye strain, mental health problems resulting from social isolation, various health consequences of reduced activity levels);
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D1.2
identify measures that help reduce the impact of computers on the environment (e.g., lab regulations, school policies, corporate and government policies promoting paperless workplaces and computer recycling and reuse) and on human health (e.g., ergonomic standards);
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B1.1
use various problem-solving strategies (e.g., stepwise refinement, divide and conquer, working backwards, examples, extreme cases, tables and charts, trial and error) when solving different types of problems;
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