Ventilation moisture load is calculated based on the difference in humidity between which two air streams?

Ventilation moisture load is calculated based on the difference in humidity between which two air streams?

• A. Indoor air and outdoor air.
• B. Supply air and return air.
• C. Outdoor air and process air.
• D. Inlet air and exhaust air.

Answer: (A)

Ventilation moisture load comes from the water vapor carried by outdoor air as it is brought into the space. The amount of moisture that must be added or removed to maintain the indoor humidity setpoint depends on how humid the outdoor air is compared with the indoor air. We quantify this using the humidity ratio (mass of water per mass of dry air). The load is essentially the outdoor air flow rate multiplied by the difference between the outdoor humidity ratio and the indoor humidity ratio. So the two air streams involved are the indoor space air and the outdoor air that is being ventilated in. The other pairings don’t directly define the moisture the ventilation must handle.

Ventilation moisture load comes from the water vapor carried by outdoor air as it is brought into the space. The amount of moisture that must be added or removed to maintain the indoor humidity setpoint depends on how humid the outdoor air is compared with the indoor air. We quantify this using the humidity ratio (mass of water per mass of dry air). The load is essentially the outdoor air flow rate multiplied by the difference between the outdoor humidity ratio and the indoor humidity ratio. So the two air streams involved are the indoor space air and the outdoor air that is being ventilated in. The other pairings don’t directly define the moisture the ventilation must handle.