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Wet Curtain Cooling System - Fan and Pad for Greenhouse
Wet curtain cooling system for greenhouses: pads on one wall, fans on the opposite wall, cutting indoor temperature by 4 to 12 degrees Celsius. .
TEL：+86 191 5068 3942
  • Features
Wet curtain cooling pad mounted on the side wall of a greenhouse

How the Wet Curtain Cools a Greenhouse:

The wet curtain is fixed along one wall of the house and the fans are set in the opposite wall. When the fans run they pull air out of the house, and the pressure inside drops. Air then has to come in through the only open path it has - the wet curtain. Because that outside air is normally not saturated, it picks up moisture as it passes through the pad, and evaporating water takes heat out of the air stream. Depending on the outside temperature and the humidity on the day, the temperature inside the house drops by 4 to 12 degrees Celsius as the fan keeps drawing air through.
 

The Pad, the Water Circuit and the Fans:

The pad itself is a corrugated cellulose sheet with a large wetted surface, held in a frame along the wall. A pump lifts water to a distribution pipe above the pad; the water runs down the sheet, and the part that is not evaporated is collected in a trough and returned to the tank, so the same water circulates all day with only the evaporated share topped up. The fans are axial units set in the opposite wall, sized so that the whole air volume of the house is exchanged often enough to hold the temperature down on the hottest afternoon. Pad area, water flow and fan capacity have to be matched to the house volume, which is why the three are specified together rather than bought separately.
 

Layout Points That Decide the Result:

A cooling system only performs as well as the air path allows. The curtain wall is kept free of obstruction so air enters evenly along its full length, and the fan wall is kept clear so the outgoing air is not pushed straight back in through an open door or a broken vent. Roof and side vents are closed while the system runs, otherwise the fans simply pull outside air in through them and the pad does nothing. Leaks at door frames and end walls cost as much performance as undersized fans, which is why airtightness is checked before any pad is specified.
 

Where a Wet Curtain Pays Off:

Evaporative cooling is most useful where the summer is hot and the air is dry, which covers most of the greenhouse markets we supply in Africa, South Asia and the Middle East. It is normally specified for vegetable and seedling houses that have to keep producing through the hot months, and for flower houses where a short heat spike would spoil the crop. It also works alongside the rest of the greenhouse equipment range we build - shading to cut the load before the pad has to deal with it, and circulation fans to even out the air once it has been cooled.
 

Sizing a Cooling System for Your House:

Tell us the span and length of the house and the crop you plan to grow, together with your summer temperature and humidity - a dry 40 degrees is easy work for a wet curtain, a humid 35 degrees is not. With that we will size the pad area, the pump and the greenhouse accessories around it, and quote the system as a set. The same house can be built with a polycarbonate or a film cover, and the cooling load is worked out for whichever cover you choose. Ventilation, shading and greenhouse irrigation can all be quoted with it. For the full picture of what we build, read more about our greenhouse factory, call +86 191 5068 3942 or send an E-mail to sales@cngreenhouses.com.
 
Guidance on protected cropping and greenhouse climate control is published by organisations such as the USDA, and international greenhouse trade news is reported by HortiDaily.
 

Frequently Asked Questions:

Q: How much can a wet curtain cool a greenhouse?
A: It depends on the outside temperature and how dry the air is. In the conditions we normally size for, the temperature inside the house drops by 4 to 12 degrees Celsius once the fans and the pad are working together.
Q: Which side does the curtain go on and which side the fans?
A: The curtain goes on one wall and the fans on the opposite wall, so the air has to travel the length of the house. The fans pull air out and create the pressure drop; the only way fresh air can come back in is through the wet pad.
Q: Does the system waste water?
A: No. The pump lifts water to the top of the pad, it runs down the sheet, and whatever is not evaporated is collected in a trough and returned to the tank. The same water circulates through the day; only the evaporated share has to be topped up.
Q: Can the curtain be used in a humid climate?
A: It works, but the cooling effect is smaller, because evaporative cooling depends on the air being able to take up moisture. In a humid region the load is better cut first with shading, and the pad sized for the realistic drop rather than the ideal one.
Q: Should the vents be open while the cooling system runs?
A: No. Roof and side vents are closed while the fans run. If they are left open the fans pull outside air straight in through them and the curtain does almost nothing - this is the most common reason a system underperforms on site.
Q: Can a cooling system be added to a house later?
A: Yes, but it is cheaper to plan it with the structure, because the frame is drilled and the pad, pump and fan positions are set out at the design stage. Send us the span, the length and your summer conditions and we will size it either way.

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