Greenhouse Misting System

Overview

A greenhouse misting system maintains humidity critical for plant propagation, leafy greens, and seedling growth. Unlike general irrigation (which wets soil), misting applies a fine spray or fog directly to foliage, increasing air moisture and reducing transpiration stress. The Control Unit reads humidity and temperature from environmental sensors and energizes the Solenoid Valve Assembly during programmed cycles or when humidity drops below a setpoint.

Water flows from the source through the Misting Pump, a greenhouse-misting-system-filter-assembly, and then through the Main Supply Line to the Solenoid Valve Assembly. When the solenoid energizes, water is pushed through overhead Branch Lines to Nozzles to hundreds of fine Misting & Spray Nozzles that blanket the growing area with mist or light spray.

How it works

The Humidity Sensor, typically a capacitive element, continuously measures relative humidity inside the greenhouse. The Temperature Sensor tracks air temperature, which influences humidity setpoints. Both sensor outputs are transmitted by analog voltage or digital signal to the Control PCB, where a Microcontroller compares readings against user-programmed thresholds.

If humidity drops below the setpoint (e.g., 60% RH on a propagation bench), the Relay Module energizes, applying 24 VAC to the Solenoid Coil. The magnetic field pulls the solenoid plunger, lifting the poppet seal and allowing water from the Misting Pump (already pressurized and waiting upstream) to flow into the Main Supply Line.

Pressure is regulated and filtered by the greenhouse-misting-system-filter-assembly before distribution. The Main Supply Line routes overhead, often at roof or overhead-frame height, minimizing water spillage on equipment. Branch Lines to Nozzles drop down at intervals, with Spray Nozzle or Fog Nozzle heads mounted on Nozzle Stake stakes positioned among plants.

Spray nozzles produce a wider pattern (0.5–2 gal/hour), suitable for benches of potted plants. Fog nozzles create ultra-fine mist (0.1–0.5 gal/hour), ideal for bare propagation media and delicate seedlings. The chosen nozzle type and flow rate depend on plant type and target humidity rate-of-rise.

The controller runs the mist for a set duration (often 5–10 minutes), then de-energizes the relay and solenoid. The poppet reseats, stopping flow. The system waits for humidity to fall back below the setpoint before starting the next cycle. In hot, dry conditions, misting may run several times an hour; in cool or humid conditions, once or twice daily may suffice.

Drip or excess water collects on benches and floors, draining out through a sump system or sloped floor toward a central gutter and pump-back return, conserving water in closed-loop greenhouse operations.