Some plants have higher humidity needs, so supplemental water needs to be added to the air. Likewise, houses can easily overheat, especially in warm climate during warm months, making it necessary to have a cooling system in place.
Evaporative cooling can do both of these things simultaneously. Evaporative cooling systems in a greenhouse can often be dual purpose. Evaporative cooling can increase humidity, or decrease temperature. If you understand thermodynamics, you know that these things happen simultaneously. The way air is moved around the greenhouse determines the outcome.
There is an inverse relationship between heat and humidity. As the ambient temperature approaches and exceeds 80 degrees, the relative humidity drops below 80%. As air temperatures rise, the holding capacity of the air increases and air will feel more dry.
To evaporate water, heat (energy) is required. As heat is removed from the air, the temperature of that air is decreased but the heat remains in the air, in another form. For every gallon of water that is evaporated, 8,700Btu of sensible heat is taken out of the air (temperature drop; Donald, 2000) and converted to latent heat (air humidity).
Two systems are available for evaporative cooling: PolAIR High Pressure Fogging or the Oasis Pad Cooling System.
The PolAIR Fogging System creates tiny water droplets that evaporate quickly in the air. Due to their size, they are easily stratified into the greenhouse through air movement. The PolAir achieves a droplet size between 1000 microns and 1500 microns, variable depending on the incoming water pressure. The smaller droplets remain intact without bursting when the contact plant or structural surfaces, so these surfaces remain dry. Larger droplet sizes may result in a mild dew on some plants or structures, ideal for tropical plants.
The Oasis Pad Cooling System installs in the greenhouse walls. Ventilation fans move hot air out of the house and pulls external air through the wet pads, decreasing the temperature of the incoming air. Fan and cool pad systems need to be sized appropriately for optimal performance.