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Mushroom Fruiting Room Humidifier Sizing
Estimate how much moisture your fruiting room loses when exhaust fans draw in fresh air. Use a worked example to turn airflow, temperature and relative humidity into a capacity in pounds or kilograms of water per hour.
Start with the air that leaves the building
Size a mushroom fruiting room humidifier from the amount of water vapor needed per hour. Room dimensions help establish volume. The steady ventilation load comes from the actual fresh air entering that volume and the difference between its moisture content and the room target. An air handler moving 3,000 CFM might bring in only 300 CFM of outside air. Count the measured outdoor portion for this calculation.
For a room that exhausts directly outdoors, identify where replacement air comes from. A conditioned corridor can deliver a different moisture load from an outdoor louver. Record both airflow and the temperature and RH of that incoming stream during the operating condition you plan to size.
A worked fruiting-room sizing example
Consider a 25 × 40 × 10 ft room with an illustrative target of 60°F and 90% RH. Incoming air is 40°F and 50% RH at sea level. Compare two fresh-air settings at the entering air condition. Neither setting is a recommended ventilation rate for a particular crop.
| Measured makeup air | Water evaporated for ventilation alone |
|---|---|
| 300 actual CFM | 10.4 lb/h · about 4.7 kg/h |
| 600 actual CFM | 20.8 lb/h · about 9.4 kg/h |
The incoming humidity ratio is approximately 0.0026 lb water/lb dry air, and the target is about 0.0099. Each pound of incoming dry air needs roughly 0.0073 lb of added water. At 300 actual CFM, the dry-air mass flow is about 1,423 lb/h. Multiplying these values gives the first estimate. At otherwise identical conditions, the extra 300 CFM adds another 10.4 lb/h of demand.
To reproduce it: Use facility/outdoor-air mode, sea-level pressure, actual CFM, 40°F and 50% RH entering, 60°F and 90% RH target, and zero adjustments. Run the commercial humidifier sizing calculator.
What changes the installed capacity?
Loads and moisture gains
Door openings and unmeasured infiltration can add dry air. A cooling coil can remove water when it runs below dew point. Conversely, wet floors after washdown and evaporation from the crop can add moisture. Keep measured gains and losses separate so a ventilation-only estimate does not become an oversized equipment order.
Delivery and turndown
The room can need high output during a winter exhaust cycle and very little after washdown. Review minimum controllable output as well as peak capacity. Establish the sensing points and evaporation distance before selecting nozzle count or duct placement.
What information should a grower bring to a sizing review?
- Room and crop. Dimensions, rack layout, crop stages, number of zones and the temperature/RH schedule for each.
- Ventilation. Measured outdoor or makeup airflow at normal and peak demand, source of that air, and an indication of whether the fan runs continuously.
- Weather and HVAC. Coincident incoming temperature and RH, site elevation, heating and cooling schedules, and whether a coil removes moisture.
- Utilities. Water-quality analysis, available compressed air, washdown access and the preferred equipment location.
Confirm ventilation requirements for the species and farm’s operating plan independently of humidifier sizing. Cornell’s specialty mushroom guide explains how incoming fresh air changes both the humidity and temperature that the equipment must control.
Choose how to deliver the calculated load
Compare direct-space ES100 and in-duct TS100 options, or send your room conditions for review.
Request a room sizing review → Mushroom humidification systems