The first step is to layout the piping system including connection to the all AC units, then from the units’ specification sheet (cutsheet from the manufacturer) find the required flow (gpm) for each unit and write on the drawing next to the each appropriate unit. Start from the end unit in piping system and add up the units’ flow (gpm) on each section of piping (between the units) and write down the amount of the flow on each piping section, continue all the way to the start point of the piping system. By using the pipe sizing chart for hydronic system from ASHRAE handbook at line 4 psi/100 ft size the supply pipe for each section (the water velocity in each pipe shall not exceed 4 to 5 fps (foot per second)). The return pipe would be the same size of the supply pipe.
For sizing the pump: Measure the longest run (from pump location to the last and farthest AC unit), assume longest length as “L” foot:
DL= L x 2 x 1.3 = 2.6L
(Lp + Cp + BVp + CVp) = Lt
Pump head = 1.10 Lt
Pump flow = Total AC units flow