A classroom is used 6 h/day for 180 warm days. Option F is a 50 W fan. Option H is a 900 W heat pump. External reflective shading would reduce heat-pump electrical energy by an estimated 25% but costs $1200 to install. Grid emissions are 0.40 kg CO₂e/kWh. The fan moves air but does not lower room temperature. (a) Calculate annual electrical energy and operational emissions for F and H. [5] (b) Calculate H energy and emissions with shading. [3] (c) Explain why these totals alone cannot identify the best option. [3] (d) Evaluate comfort, health, cost, emissions, noise, access and building constraints, then give a conditional recommendation and further evidence required. [5]

Question

Accepted Answer

F uses 54 kWh and produces 21.6 kg CO₂e; H uses 972 kWh and 388.8 kg CO₂e; shaded H uses 729 kWh and 291.6 kg CO₂e. These options deliver different thermal outcomes, so a fair decision needs measured comfort and building evidence. (a) Annual operating time is 6 × 180 = 1080 h. Fan energy = 0.050 kW × 1080 h = 54 kWh; emissions = 54 × 0.40 = 21.6 kg CO₂e. (a) Heat-pump energy = 0.900 kW × 1080 h = 972 kWh; emissions = 972 × 0.40 = 388.8 kg CO₂e. (b) A 25% reduction leaves 75%: shaded heat-pump energy = 0.75 × 972 = 729 kWh and emissions = 729 × 0.40 = 291.6 kg CO₂e. (c) The fan increases convective and evaporative cooling of occupants but does not lower air temperature, while the heat pump removes energy from the room. Energy totals compare inputs, not equal comfort or health outcomes. (d) Measure indoor temperature, humidity, radiant heat, occupancy, noise, air quality, heat-pump efficiency under local conditions and student comfort. Include installation, maintenance, electricity affordability, glare, façade permission and the needs of heat-sensitive users. (d) Use passive shading first where it is structurally suitable, combine fans with ventilation during moderate conditions, and reserve efficient heat-pump cooling for unsafe heat. The final operating rule should be triggered by measured conditions, not a single calendar schedule. (d) Consult students, staff, families, facilities workers and building owners; compare whole-life cost and embodied impacts. Reassess the recommendation as the grid mix, climate and occupancy change.

Build a defensible classroom-cooling recommendation

What a complete response should do

How did this one feel?