The cooling pad fan evaporative cooling system is a cooling device widely used in large multi-span greenhouses. Experiments show that under the power of 20W, the cooling efficiency of the device is 69.23% (calculated by the temperature of the wet curtain), and the human body also feels a large temperature difference. Although the effect of this device cannot be compared to mechanical refrigeration, it can be widely used in a variety of places where air conditioning and other equipment cannot be installed due to power supply or regulatory constraints.

The cooling pad fan evaporative cooling system is a kind of evaporative cooling, which is a cooling device widely used in large multi-span greenhouses. Water adheres to the surface of the water-absorbing material and evaporates and absorbs heat when it contacts with the air flowing through the surface of the material. After passing through the wet curtain, the dry and hot air absorbs water and becomes air with higher humidity.

The cooling pad fan evaporative cooling system used in the greenhouse consists of the following parts:

1. Axial flow fan: In a greenhouse with a wet curtain-fan cooling system installed, the fan is generally designed to continuously discharge the air in the greenhouse to the outside. This ventilation system is also called an exhaust ventilation system (negative pressure ventilation). system).

The selection of the fan takes into account the following factors:

1) Type of fan: room ventilation requires a large amount of ventilation and a low pressure, so an axial flow fan is selected. The fan used for computer heat dissipation is not suitable due to the low power and the ventilation resistance of the wet curtain, and the air volume is small.

2). Safety of electricity use: Since the whole system is close to the water source and the ambient humidity is high, in order to avoid dangers such as short circuit or electric shock, the fan must work under the absolutely safe voltage of 12V.

3). The power of the fan: the power of the selected fan should be appropriate. If the power is too large or too small, it will have an adverse effect on the entire system.

Problems that can arise when the power is too high are:

1). The cooling efficiency is reduced: the air leaves the wet pad without fully absorbing water.

2). The noise is too loud.

3). The water directly flies out of the wet curtain and sprays the device from the air outlet, causing pollution or even short circuit accidents.

Problems that may occur when the power is too small are:

1). The speed of the air passing through the wet curtain is too slow, and there is no wind at the air outlet

2). The fan load is too large, resulting in heat generation, shortened life, and extremely low cooling efficiency or even negative value.

For the problem of excessive fan power, we can solve it by using “fan speed reduction line” or “fan speed controller”, or reduce the speed of the fan by adjusting the output power of the power supply.

2. Cooling pad: The wet curtain is installed at the air inlet of the greenhouse, and its materials are generally porous and loose materials such as poplar shavings, brown silk, porous concrete panels, plastics, cotton, linen or chemical fiber textiles, and corrugated paper wet pads are the most commonly used. . Its size depends on the size of the greenhouse. The thickness of the corrugated paper wet pad is 80-200mm, and the height is generally 1-2m.

Cooling pad design

The shape design of the cooling pad refers to the cooling pad used in the greenhouse, both of which are in the shape of “thousand-layer cake”. The main design principles to follow are:

1). The water absorption of the cooling pad is better

The materials with better water absorption in daily life are generally cotton, cloth, paper, etc. Paper is not considered because it is easily damaged and has a short lifespan. Therefore, cotton material with a certain thickness is a better choice.

2). The cooling pad must have a pad thickness

When the thickness of the cooling pad is insufficient, the water cannot fully evaporate due to the small contact area with the air, and the system efficiency is reduced; when the thickness of the cooling pad is too large, the ventilation resistance is large and the fan load is heavy.

3. Water pump: The water pump is used to continuously transport water to the top of the wet pad, and the water flows down by gravity to keep the wet pad moist.