Design Guide

How to Choose the Evaporative Air Coolers
 
. Selection of Air Cooler
 
Aolan evaporative air cooler has various products series, including Miracle Mobile Series, Demeanor Mobile Series, Wind Marshal Series, Wind Charisma Series, Wind Supremo Series, Wind Domination Series, Wind Superior Series and Wind Emperor Series (details in catalogue). The case of Miracle Mobile Series and Demeanor Mobile Series is made of plastic, with beautiful design, small airflow and suitable for residential applications. The case of Wind Marshal Series, Wind Charisma Series, Wind Supremo Series and Wind Domination Series is also made of plastic, with beautiful design, compact structure, large airflow and high cost efficiency. Wind Superior Series and Wind Emperor Series use centrifugal fan, with larger airflow and long drive distance than axial one, suitable for large areas and commercial applications. Correct selection of air cooler should take several points into consideration, including application area, people density, heat productivity and place of installation.
 
. Using psychrometric chart to confirm air supply temperature
 
First, confirm the outdoor state point W according to local meteorologic conditions, outdoor state from W points along the line in such enthalpy 85% (air cooler saturated efficiency. 

. Selection of air cooler quantity
 
Entire Ventilation
 
  •  Calculation 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=LρCp{e•tgts+tntg}/3600

in which: L------actual air supply capacity of air cooler
m3/h

         ρ------
air density of air outletkg/m3
         Cp------ air specific heat
kJ/kg•K
         e------saturation efficiency of air cooler, normally in 85%

      
tgts)------wet-bulb depression
      
tntg------temperature difference between indoor and outdoor
Set
t1=tgts, t2=tntg, t1 should be positive value, t2 can be both positive or negative value.
 
Total cooling capacity S=LρCpe•t1+t2, ρCpe 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.
 
(1) 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))

(2)Usually, air change is 25
30 times/ hour

(3) In some crowd public areas, air change is 3040 times/ hour

(4) In some workshop with heat appliance, air change is 4050/hour

(5) air change can increase properly in some wet areas, and decrease in hot and dry areas.
Calculate as follows:

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

(2) Confirm air change according to actual condition


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

(4) Total air supply capacity divide actual airflow of independent unit L1, and get the quantity of air cooler that you need.

.Design of ventilating duct 

  1. Basic terms
     air flow
    calculating method of round duct
            L=900лd2v 
m3/h
               d------inner diameter of the duct 
m
                    v------speed   
m/s

 calculating 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 densitykg/m3 
  2. Points for designing Aolan air cooler duct
 
 
1The material of ducts should be galvanized sheets, or glass steel, plastic, aluminum foil sheets, etc.
 
2Grilles 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, wood 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.
 
 
3The 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.
 
4The design of the duct system is supposed to be economical, low resistance and low noise to make the maximum airflow of “Aolan” 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.
 
5It is much better to make the duct go straight, avoiding corners and branches, to reduce resistance.
 
6Both auto swing air grilles and duct can be used for side discharge air coolers.
 
7According 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 ducts in a whole system, and the length is≥2D-d.
 
8The connection between duct and air cooler should be hose, with no temperature preservation design.