Which of the following is a complete list of functions of an All-Air System?

• A. Heating/cooling, humidification/dehumidification, ventilation and exhaust
• B. Ventilation and exhaust, filtration
• C. Heating/cooling, humidification/dehumidification, ventilation and exhaust, filtration
• D. Heating/cooling, humidification/dehumidification, ventilation and exhaust, filtration, pressurization.

Answer: (D)

The essential idea is that an all-air system conditions a space using only air as the conditioning medium, so it must handle both temperature and moisture, bring in outdoor air for ventilation, remove contaminants through filtration, exhaust stale air, and manage space pressurization as needed for containment and protection of adjacent areas. All five functions are necessary to meet typical indoor air quality, comfort, and safety requirements.

That’s why the complete list includes heating or cooling, humidification or dehumidification, ventilation and exhaust, filtration, and pressurization. Any list that omits one of these functions isn’t complete.