Give three ventilation strategies to improve IAQ without compromising energy efficiency.

• A. Demand-controlled ventilation, high-efficiency filtration, and heat-recovery ventilation
• B. Mechanical exhaust alone
• C. Opening windows during peak heat
• D. Use of portable air purifiers only

Answer: (A)

Balancing indoor air quality with energy efficiency comes from bringing in fresh air in a controlled way, filtering it effectively, and recovering energy from exhausted air. Demand-controlled ventilation uses sensors to match outdoor-air delivery to actual needs, so ventilation increases when spaces are occupied and air quality demands rise, and decreases when they don’t, cutting energy waste while keeping IAQ adequate. High-efficiency filtration improves the cleanliness of the air inside by capturing more particles, which helps IAQ without necessarily increasing outdoor air intake; just be sure the system can handle the added filter resistance without sacrificing comfort. Heat-recovery ventilation transfers heat (and moisture, in energy recovery ventilation) between the outgoing and incoming air, preconditioning the fresh supply and cutting the heating or cooling energy required to bring outdoor air up to indoor conditions.

These approaches work together to maintain good IAQ while minimizing energy use. Mechanical exhaust alone can undermine IAQ control and pressure balance and tends to pull in unfiltered outdoor air. Opening windows during peak heat can dramatically raise cooling loads and humidity, defeating energy savings and reducing control over IAQ. Relying on portable air purifiers alone addresses air cleaning in a single space but doesn’t introduce or condition outdoor air, nor does it scale to whole-building ventilation or energy-efficient heat exchange.