How to design a pad & fan evaporative system to cool a greenhouse?

The pad & fan cooling greenhouse system cools down temperature, using evaporative cooling. On hot summer days, this is an efficient way to cool small greenhouses, keeping the plants in the best climatic conditions. In addition, this system uses exhaust fans to absorb air from outside into the greenhouse.

Firstly, the air is blown through the pad, which constantly evaporates water, creating a cooling effect. Then, the fans blow the cool air into the greenhouse, resulting in an overall decrease in temperature.
Some greenhouses need to be cooled at night, mainly in tropical regions. However, the wet pad and fan system may not provide the desired results in tropical regions, where absolute humidity is often high at night.

When outside conditions are humid, pad and fan system will lose its efficiency and provides less cooling capacity. This is because evaporative cooling is based on the difference between outdoor and indoor conditions.

Some of the pad & fan cooling greenhouse system’s benefits include:

-it keeps the inner temperature of the greenhouse cool at all times, ensuring a lower temperature even during hot periods of the year

-it decreases the temperature and increases the humidity, thereby reducing transpiration of the plants

However, it has also disadvantages:

-the distance between the pad and the fan reflects unequal cooling

-if the system runs constantly, crop growing will be probably uneven

-it is not effective in areas with high humidity (ex: coastal areas)

Pad and fan systems are manufactured by companies such as Munters. For small greenhouse, the cooling box is a good alternative. They are manufactured by companies such as Metmann.

Like the pad & fan cooling greenhouse system, it uses evaporative cooling method to cool down the greenhouse temperature.

Clear water is pushed through a stainless steel nozzle. Then, the water particles are evaporated before reaching the crops. This system works with a pumping unit equiped with a high pressure pump. Nevertheless, it must be installed at the right height, depending on the climate conditions. Lastly, nozzles must be assembled in alternation for a homogeneous coverage.

Advantages:

-natural cooling (it regulates temperature to a very large measure in situations where ventilation is not enough, thereby decreasing the inner temperature when needed + less C02 will be lost and more will be available for crop growth).

-minimal water use (due to temperature control and humidification)

-optimal humidity

-small droplets (micron) lead to a higher droplet density

Disadvantages:

-this technology is very dependent on the climate. Indeed, if it is too humid, the system will not work efficiently.

Fog systems are manufactured by firms such as MJTech

Conclusion:

Evaporative cooling systems such as pad & fan or fog are efficient for cooling down greenhouse temperatures. They are well suited for hot & dry areas but not for humid & hot areas.

Pad & fan cooling systems are suitable for greenhouse with a small distance between pad and fan. Fog systems are suitable for any greehouse size but hard water must be treated.

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