Humidification Load Calculator

This calculator sizes a humidifier by computing the moisture that needs to be added to dry ventilation and infiltration air to reach a target indoor humidity. It converts Outside Relative Humidity and Target Indoor Humidity into humidity ratios using a saturation-pressure approximation at Outside Temperature and Inside Temperature, then multiplies the difference by Ventilation Airflow (plus an infiltration allowance scaled by Infiltration Rate) to get Moisture Load. Inside Temperature has an outsized effect on every output -- more than twice as strong as Target Indoor Humidity or Ventilation Airflow at default values -- because it feeds into the saturation-pressure formula that determines how much moisture warm indoor air can hold at the target humidity; raising Inside Temperature from 72°F to 79°F (about 10%) raises Moisture Load from 9.7 to 12.47 lbs/hr, while the same percentage increase in Ventilation Airflow only raises it to 10.67 lbs/hr.

Humidifier Capacity is picked from a stepped list of standard sizes (5, 10, 15, 20, 25, 30, 50, 75, 100, 150, 200 lbs/hr), so it only changes when Moisture Load crosses one of those thresholds -- both scenarios above cross the 10 lbs/hr boundary and bump the recommended capacity to 15. Water Consumption and Energy Cost scale directly off Moisture Load. This is a design-condition estimate, not a full psychrometric load calculation -- it doesn't account for latent loads from occupants or process moisture sources inside the space.