MCQ Answers
1. A — Energy (kWh) = Power (kW) × Time (hours).
2. B — 2,000 W = 2 kW. E = 2 × 3 = 6 kWh.
3. A — Star rating indicates relative efficiency within a product category.
4. C — Controlled variables are kept constant (e.g., room temperature).
5. B — Saving = 150 × $0.30 = $45/year. Payback = $300/$45 = 6.7 years.
SAQ 1 — Energy Audit Steps (3 marks)
Marking Criteria: 1 mark — describes systematic data collection (inventory, measurement, recording). 1 mark — explains accuracy/reliability measures. 1 mark — identifies how to find biggest savings opportunities.
Model answer: To conduct a valid and reliable energy audit of the science laboratories, I would follow these steps:
First, I would create an inventory of all electrical devices in each lab: lights, fume cupboards, fridges, hot plates, computers, projectors, and chargers. For each device, I would record its power rating from the nameplate or measure it with a plug-in power meter (wattmeter).
Second, I would measure usage time by observation or by asking staff — how many hours per day is each device actually used? Some devices like fridges run 24/7, while others like hot plates run only during classes.
To ensure accuracy, I would take multiple power readings at different times (e.g., startup vs steady state), use the same power meter for all measurements, and record all data in a structured table. I would also note the room temperature and time of day to identify if heating/cooling loads vary.
Third, I would calculate annual energy consumption (kWh) and cost ($) for each device using E = P × t and Cost = E × rate. I would then rank devices from highest to lowest consumption. The top 20% of devices typically account for 80% of energy use — these are the "energy hogs" to target first.
Finally, I would identify savings opportunities: replacing old fridges with efficient models, switching to LED lights, installing timers or motion sensors, eliminating standby power with smart powerboards, and improving insulation. Each recommendation would include a cost-benefit analysis showing payback period.
SAQ 2 — Lighting Calculation (4 marks)
Marking Criteria: 1 mark — correct total power and annual energy for fluorescent. 1 mark — correct annual cost for fluorescent. 1 mark — correct LED energy and cost. 1 mark — correct savings in kWh and dollars.
Model answer:
Fluorescent lighting:
Total power = 50 fittings × 2 tubes × 36 W = 3,600 W = 3.6 kW
Annual hours = 8 h/day × 200 days = 1,600 h
Annual energy = 3.6 kW × 1,600 h = 5,760 kWh
Annual cost = 5,760 kWh × $0.30/kWh = $1,728
LED lighting:
Total power = 50 fittings × 2 tubes × 18 W = 1,800 W = 1.8 kW
Annual energy = 1.8 kW × 1,600 h = 2,880 kWh
Annual cost = 2,880 kWh × $0.30/kWh = $864
Savings:
Energy saved = 5,760 − 2,880 = 2,880 kWh/year
Cost saved = $1,728 − $864 = $864/year
Replacing fluorescent tubes with LEDs would halve the school's lighting energy consumption and save $864 annually in this building alone.
SAQ 3 — Motion Sensor Depth Study Design (5 marks)
Marking Criteria: 1 mark — clear aim and testable hypothesis. 1 mark — correct identification of all three variable types. 1 mark — detailed method with before/after or control/experimental comparison. 1 mark — describes data analysis (calculations, comparisons). 1 mark — describes presentation (tables, graphs, cost analysis).
Model answer:
Aim: To investigate whether installing motion sensors in classrooms reduces lighting energy consumption compared to manual switching.
Hypothesis: If motion sensors are installed, then lighting energy consumption will decrease by at least 25% because lights will automatically turn off when classrooms are unoccupied during breaks, lunch, and after school.
Variables:
• Independent: Presence or absence of motion sensors (sensor classrooms vs control classrooms)
• Dependent: Lighting energy consumed (kWh) measured over a 4-week period
• Controlled: Same number and type of lights, same room size, same school term, same timetable/occupancy patterns, same power meter used
Method:
1. Select 4 matched pairs of classrooms (same size, orientation, number of lights).
2. Install motion sensors in one classroom of each pair; leave the other as manual control.
3. Attach data-logging power meters to the lighting circuits in all 8 classrooms.
4. Record lighting energy consumption continuously for 4 school weeks.
5. Also record occupancy using simple observation logs to verify sensors are working correctly.
6. At the end, remove sensors and repeat for another 4 weeks with roles reversed (crossover design) to control for room-specific effects.
Analysis: Calculate mean daily lighting energy for sensor and control rooms. Calculate percentage reduction: ((control − sensor) / control) × 100. Perform the calculation for each matched pair and average the results. Calculate cost savings at $0.30/kWh and extrapolate to all classrooms in the school.
Presentation: Present data in a table showing each classroom's energy use. Create a bar graph comparing sensor vs control rooms. Include a cost-benefit analysis: sensor cost ($80 each) vs annual savings. Conclude whether the hypothesis was supported and discuss limitations (e.g., sensors may trigger falsely if set too sensitively, holiday periods not tested).