Year 9 Science · Unit 3 · Lesson 23
Apply Worksheet
Learning Goals
1. Why is a reading from a plug-in power meter better evidence in an audit than the age of the building or the number of students?
2. Apart from mains power, name two kinds of fuel or energy that a full audit of the school should include.
Scenario: one classroom
A classroom at Riverside Secondary College, NSW, has 30 LED lights (10 W each), one air conditioner (2,400 W), five computers (150 W each) and one interactive projector (300 W). All of them run for 6 hours per school day, on 200 school days a year. Electricity costs 30 cents per kWh.
| Appliance | Power (W) | Energy per year (kWh) | Cost per year (dollars) |
|---|---|---|---|
| 30 LED lights | |||
| Air conditioner | 2,400 | ||
| 5 computers | |||
| Interactive projector | 300 | ||
| Total |
Source: sample values for this worksheet.
3. Complete Table 1, starting with the yearly operating time of each item.
Operating time h
4. Which appliance dominates the classroom’s energy use? What percentage of the total does it use?
Percentage %
5. The school could replace the air conditioner with a new model that gives the same cooling but draws only 1,600 W. The new model costs 1,800 dollars. Using the same hours of use, find the energy and money it would save each year, and its payback time.
Less energy kWh
Less cost dollars
Payback years
Investigation: computers on standby
The computer lab has 25 computers. They are shut down at the end of each day but stay plugged in and switched on at the wall. Your class wants to find out whether switching them off at the wall saves a useful amount of energy. The lab’s power points can be measured with a plug-in energy meter.
6. Plan the investigation by completing each part below.
Hypothesis
Write an if… then… because… prediction.
Variables
Method
Results table
| Night | Left on at wall (kWh) | Off at wall (kWh) |
|---|---|---|
Safety
7. Write a short recommendation to the principal on how to cut this classroom’s electricity bill. Use your Table 1 results and your payback time, and say what else you would measure before the school spends money.