List the functions of an All-Air System.

• A. Heating/cooling, humidification/dehumidification, ventilation and exhaust, filtration.
• B. Heating, dehumidification, filtration, cooling, energy recovery.
• C. Ventilation only, with no filtration.
• D. Heating/cooling, humidification/dehumidification, ventilation and exhaust, filtration, pressurization.

Answer: (D)

An all-air system is meant to condition and move air through the space to control comfort and air quality, combining several essential functions in one system. It includes heating and cooling to set the room temperature, humidification and dehumidification to keep humidity at appropriate levels, ventilation and exhaust to bring in fresh outdoor air and remove stale air, filtration to remove particulates, and pressurization to maintain the desired pressure relationships between spaces and the outdoors. Energy recovery can be a feature in many designs, but the core set of functions required here is captured by heating/cooling, humidity control, ventilation/exhaust, filtration, and pressurization. The other options miss one or more of these elements—for example, omitting pressurization, or lacking ventilation and humidification while emphasizing energy recovery or restricted to ventilation only with no filtration.