How Wet Curtain Cooling Works

A wet curtain system is a single, continuous air path. Exhaust fans mounted at one end of the building draw outside air through a cellulose pad that is kept wet by a recirculating water circuit. As the air passes through the pad, water evaporates and removes heat from the air stream, so the air entering the house is cooler than the air outside. In dry climates this normally produces a temperature drop of 5–10°C. The cooled air then travels along the house, picks up heat and moisture from the animals, and is discharged by the fans at the far end.

Because the process depends on evaporation, the achievable temperature drop is governed by outside relative humidity. Dry air gives the full benefit; humid air gives less. This is why evaporative cooling is most dependable in arid and semi-arid regions, and why humid climates usually need a ventilation-led strategy for part of the season.

Matching Fan Capacity to Pad Area and Building Volume

Fan capacity is never selected on its own. Three quantities have to be balanced: the required air exchange rate for the building and stock, the total airflow of the fan set, and the face area of the wet pad.

Total fan airflow sets the air exchange rate and therefore the air speed along the house. Pad area sets the velocity at which air passes through the wetted media. If the pad is too small for the fan set, face velocity rises, static pressure rises, and the fan delivers less air than its catalogue figure — so cooling capacity falls short of the design. If the pad is oversized, water distribution across the media becomes uneven and part of the pad dries out, which wastes pad area without adding cooling.

Pressure drop across a wet pad is part of the system static pressure. Fans must therefore be selected at the real operating point, with the pad wet and the building pressurised, not at free air. Pad manufacturers publish a recommended face velocity range for their media; treat that as the starting point and size the fan set from it.

Choosing the Exhaust Fan for Livestock Buildings

Livestock houses combine long continuous summer duty, humid air, dust and ammonia. Ammonia attacks aluminium and corrodes unprotected steel components. SINDFAN SM axial fans are available from Ø250 mm to Ø3150 mm with GRP blades that resist ammonia and corrosion and are built to run continuously through the summer season. Where the duty is less aggressive — general ventilation and dry air handling — aluminium and nylon blade options are available.

Running Cost and Verified Performance

Fans that run day and night for months make efficiency the dominant running cost. SINDFAN SM axial fans achieve up to 80%+ efficiency, which cuts energy bills against lower-efficiency units delivering the same airflow. Mechanical reliability matters as much as airflow: impellers are balanced to ISO 1940 G4.0, and fan performance is verified by AMCA 210 testing, so the airflow and pressure figures used in a design can be compared against measured performance rather than assumed.

Practical Sizing Sequence

  • Establish the required air exchange rate for the stock and building volume.
  • Convert that to total fan airflow, then split it across multiple fans for staged control.
  • Derive pad area from that airflow and the pad maker's recommended face velocity.
  • Check fan selection at the static pressure of the wet pad plus duct and shutter losses.
  • Stage fans so that early stages run ventilation only and later stages bring full pad cooling.

Regional Considerations

SINDFAN exports to the Middle East, Southeast Asia and Africa, where evaporative cooling is widely used in poultry, dairy and greenhouse operations. Dry Middle Eastern conditions give the largest temperature drop from the same pad area. In humid Southeast Asian conditions the achievable drop is smaller, so design margins should be wider and ventilation capacity higher.

If you are sizing a wet curtain system, send SINDFAN your building dimensions, stocking density, target air exchange rate and local summer design conditions. Our engineers will match fan capacity, blade material and pad area to your duty. Contact us on WhatsApp +852 9524 8434 or at info@sind-tech.com.