Kooltronic Design Guide - Fan & Blower Selection

Fan and Blower Selection

DETERMINE THE COOLING CAPACITY REQUIRED:

STEP 1: Determine the amount of heat to be removed (in watts)

This step is the same procedure as used for the selection of heat exchangers. The heat exchanger example identifies 922 watts for the total cooling capacity required, which equals the total heat needed to be dissipated (removed).

STEP 2: Determine the Delta T

This value is described by the formula:
Delta T = MAXIMUM ALLOWABLE INTERNAL ENCLOSURE TEMPERATURE - MAXIMUM OUTSIDE AMBIENT (DT = MAIET - MOA). These numbers have already been identified on page 12 in step 2.
The example used there was 120ºF - 110ºF = 10ºF Delta T.

STEP 3: Plot the values for your applications

On the graph below, locate the watts to be dissipated (922W). Draw a horizontal line over to the diagonal line that represents your Delta T (10ºF). Draw a vertical line down. This is the airflow (CFM) needed for your application. In our example the CFM is 365.

Based on standard air density (.075 lbs. per cubic foot), the graph provides quick solutions for the following equations:

Temperature rise in degrees Fahrenheit: CFM = (3.17 x P x 1.25) / Delta T
Example: (3.17 x 922 x 1.25) / 10 = 365.34 CFM

Temperature rise in degrees Celsius (Centigrade): CFM = (1.76 x P x 1.25) / Delta T

CFM = Cubic Feet per Minute

P = Power to be dissipated in watts

Delta T = (see step 2 above)

These formulas include a “safety factor” of 25 percent more air than is strictly required by theory. This is expressed by the constant 1.25 in the formulas above.

STEP 4: Select the System.

On the flow chart below, select the type of air moving product that you need.