How can calculate AHU or FCU condensate drain Pipe? condensate drain Pipe depend Motor KW or Cooling coil Flow rate?

IPC chapter 8 table 8-2, Minimum condensate pipe size shows the equipment capacity in Tons or KW and the minimum pipe size you can use. 

 

this schedule show you how to calcualte the condensate drain

To find the DESIGN condensate drain, one needs to know the design inlet and outlet air conditions (precisely the moisture content and air flow rate). The difference between inlet and outlet conditions of the moisture content gives the condensate flow rate.

Then based on the standards from ASHRAE /ISHRAE or from Buildings Codes one can easily select the drain pipe sizes per flow requirements as calculated above.

To find the correct U-leg lengths: as a rule the difference in the heights of U-legs should be mm larger than the static pressure of the AHU blower. (Care should be taken here, because it is also dependent on the blower type, draw through or blow through). 

For the second part of the question, flow rate of air across the coil affects the condensate flow rate.

Is is dependent upon the Static pressure at which Fan/blower for FCU or AHU is designed. It is not related to motor power or otherwise.

it depends on the unit internal maximum experienced static pressure of the unit AHU/FCU so not to allow air to flow through the condensate pipe to the unit and introduce unwanted FA and also to allow for condensed water to escape.

Condensate Drain Pipe Sizing kW Connected to the                         Condensate Drain Pipe Condensate Drain Diameter                       (inches) 0-7.0 kW 3/4'' 7-,5 kW 1'' ,5- kW /4'' - kW /2'' - kW 2'' kW 3'' kW 4''