Evaporative Air Cooler Project Design - Fuzhou Green Mechanical and Electrical Technology Co., Ltd.

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Installed Cooler Project Design Guide

1. Selection of install air cooler

The choice model of evaporative air cooler depends on the size of area to be cooled and the cooling method (whether it is overall cooling or localized cooling). Generally the larger the area and the farther the air delivery distance, the larger the air volume of the evaporative air cooler should be choice.

2. Using psychrometric chart to confirm air supply temperature

The choice model of evaporative air cooler depends on the size of area to be cooled and the cooling method (whether it is overall cooling or localized cooling). Generally the larger the area and the farther the air delivery distance, the larger the air volume of the evaporative air cooler should be choice.

3. Selection of air cooler quantity

Entire ventilation valculation in theory

Calculate the cooling load, moisture load and airflow of the using room according to conventional air conditioning load calculation formula, and then calculate the whole cooling capacity that air cooler can provide. And then you may decide the quantity and model no. that you want. The total cooling capacity of air cooler should be larger than that required by the using room, the margin can be 10%. Total cooling capacity of evaporative air cooler can be calculated in theory as follows:

Total cooling capacity: S=L X ρ X Cp{e•（tg－ts）+(tn－tg) }/3600 in which:

L--actual air supply capacity of air cooler (m3/h)

ρ--air density of air outlet(kg/m3)

Cp--air specific heat (kJ/kg•K)

e--saturation efficiency of air cooler, normally in 85%

(tg－ts)--wet-bulb depression(℃)

(tn－tg)--temperature difference between indoor and outdoor (℃)

Set △t1=(tg－ts), △t2=(tn－tg), △t1 should be positive value, △t2 can be both positive or negative value. Total cooling capacity S=L XρXCp(e•△t1+△t2), ρ、Cp、e are constant, we can see that total cooling capacity relates to actual air output, wet-bulb depression and temperature difference between indoor and outdoor. △t1 and △t2 are uncertain values and change according to outside environment conditions, so the formula of total cooling capacity is only use for qualitative analysis.

Calculate in experience

Calculate the quantity of air cooler needed in a space according to air changes, which is a commonly used method in actual engineering design.
Definition of air changes: air changes (times/hour)=total air output L/ (room area S ×the height of air supply outlet or exhaust outlet(take the large one H))
Usually, air change is 25～30 times/ hour
In some crowd public areas, air change is 30～40 times/ hour
In some workshop with heat appliance, air change is 40～50/hour
Air change can increase properly in some wet areas, and decrease in hot and dry areas.

Calculate as follows:

Calculate the areas that needs to be cooled, confirm the height of air supply outlet and exhaust outlet and take the large one

Confirm air change according to actual condition

The volume of cooling space V× air change N, and get the total air supply
capacity that the space needs

Total air supply capacity divide actual airflow of independent unit and get the quantity of air cooler that you need

4. Design of ventilating duct

Basic terms air flow

Calculating air flow method of round duct
L=900лd²v （m3/h）
d------inner diameter of the duct （m）
v------speed    （m/s）
Calculating air flow method of rectangle duct
L=3600abv   （m3/h）
a、b------the net width and height of cross section of the duct(m)

Resistance of duct system

The resistance include the friction and local resistance, the formula is as follows:
△P=△Pm+△Pj
△P-----total resistance of the system (Pa)
△Pm----- friction resistance (Pa)
△Pj-----local resistance (Pa)

The calculation of friction resistance

△Pm=△pm•L
△pm----- on-way resistance (Pa/m)
L-----length of the duct section (m)

Loss of local resistance

△Pj=ξ•v2ρ/2
ξ------local resistance coefficient
v------air velocity of the space where local resistance loss occurs （m/s）
ρ------air density（kg/m3）

Important points for designing air cooler duct

The material of ducts should be galvanized sheets, or glass steel, plastic, aluminum foil sheets, etc.
Grilles or diffusers should be installed at the places where cooling is needed. The specification can be decided according to airflow and air speed. The material could be aluminum, plastic etc., and the type could be selected according to actual situations. We recommend double deflection air grille with 3-6m/s airflows speed, and an airflow adjusting valve is recommended.
The dimension of the duct is usually assumed as follows: the wind velocity is 6-8m/s in the main duct, 4-5 m/s in the branches, and 3-4 m/s at the end.
The design of the duct system is supposed to be economical, low resistance and low noise to get maximum airflow of “Green” air cooler. In order to reduce the resistance, the curvature radius of the elbow should not be less than 1.5 times of the width of the elbow.
It is much better to make the duct go straight, avoiding corners and branches, to reduce resistance.
According to different airflows, the duct should be designed with sections of different specifications to be connected together. The reducing ducts should not be too many, usually no more than 4 steps class ducts in a whole system.