What is the best way to size chilled water pipes? is it correct to use velocity method for small sizes but the pressure drop for bigger ones?

I’m using chilled water and condensed pipe sizing chart which is available in the following link: https://www.dropbox.com/s/5rogzsmg44i0zaa/PocketCal.pdf?dl=0

This is the common practice check ASHRAE HVAC Fundamentals [2013] F22 SI page 22.5 :

A variety of upper limits of water velocity and/or pressure drop in piping and piping systems is used. One recommendation places a velocity limit of 1.2 m/s for 50 mm pipe and smaller, and a pressure drop limit of 400 Pa/m for piping over 50 mm. Other guidelines are based on the type of service (Table 8) or the annual operating hours (Table 9). These limitations are imposed either to control the levels of pipe and valve noise, erosion, and water hammer pressure or for economic reasons. Carrier (1960) recommends that the velocity not exceed 4.6 m/s in any case.

I don't think you should go from here. The size depends on the number of barrels that you need to transport at a time (that should be given) and the water flow range that you have. then you select a size accordingly and calculate velocity and pressure drop to confirm the adequacy of your selection and that the requirement of the number of barrels is met, or change the size if necessary.

• Sizing pipes have to flow to the extent necessary and appropriate speed.
• The size of the pipe must be such that high speed water flow creates noise and reduce the life of pipesNshvd.kahsh corrosion due to water flow rate in the pipes should be made to the extent that unjustified increase in the cost of plumbing pipe diameter does not increase.
•     In order to reduce the effect of water hammer in the pipeline, should be controlled flow rate.

the best way to size chilled water pipes is of small diameter. and the it should be make up of copper (cu) because it can't get corried and remain cool for a long time and pressure doesn't drop here.

In McQuay pipe sizer:-

4f/s maximum for pipe below/equal to 50mm and 4ft/100ft for pipe greater than 65mm pipe.

 

here is the online link which helps you a lot.

 

https://www.tlv.com/global/TI/calculator/water-pipe-sizing-velocity.html