In India in most of the states, temperatures can easily exceed beyond unbearable circumstances. Such high temperatures reduce crop quality and worker productivity. Evaporative cooling is the most common method for reducing the temperature inside a premise. Air conditioning or refrigeration systems can be used, but their installation and operating costs are usually prohibitive. Evaporative cooling is an economical & environment friendly process that reduces air temperature by evaporation of water into the airstream. As water evaporates, energy is lost from the air causing its temperature to drop.FAN & PAD EVAPORATIVE COOLING SYSTEMS
Fan and pad systems consist of exhaust fans at one end of the greenhouse and a pump circulating water through and over a porous pad installed at the opposite end of the greenhouse..FACTORS THAT INFLUENCE FAN AND PAD EVAPORATIVE COOLING SYSTEM:
- Operational considerations:
It is very important to keep the building as tight as possible so entering air will be forced through the pads. Make sure that all doors and other openings are kept closed except when in use and that any gaps in the greenhouse coverings are sealed. If not, air will be pulled through these openings rather than through the cooling pad. The efficiency of a fan and pad cooling system depends on air moving through the cooling pads.
- House Location and Orientation:
Orientation of the greenhouse relative to other buildings or structures and in relation to prevailing summer winds influences the efficiency of operation. Fan arrangements and locations of the fans and pads should be determined by greenhouse location and orientation.
The most widely used type of pad material is corrugated cellulose that has been impregnated with wetting agents and insoluble salts to help resist rot. When properly maintained these pads do an excellent job of cooling air. With proper maintenance, corrugated pads should have a lifetime of ten years.
Aspen pads were commonly used in the past. However, under hot conditions the life of an aspen pad is usually short. Aspen pads are very susceptible to algae infestation that leads to rotting and compaction.
The amount of pad area needed depends upon several factors including the type of pad material used. The pads should be continuous along the entire length of the wall. Cellulose pads can be used with airflows of up to 230 cubic feet per minute per square foot of pad.
To maximize operating efficiency, you must have adequate pad surface area and an adequate water supply and distribution system. Complete pad surface wetting occurs when about 1/3 gallon of water per foot of pad length is recirculated. A valve should be placed in the line from the pump so the water flow through the distribution pipe can be adjusted.
- Airflow Through Cooling Pads:
The required face velocity of the air will depend upon the pad material. This velocity will determine the number of square feet of pad area needed for a house of a given configuration. Locate the pad so that all air entering the house will have to pass through the pad.
Regardless of the type of pad material used, the fans should have the capacity to provide a minimum of one air change per minute in the greenhouse. Equip the fans with automatic shutters to eliminate back drafts when a fan is not operating