hi every one
what is the most important parameter to test and verify when commisioning chilled water system
what is the most pratical way measuring the flow in each loop?

Most important, at least for me, is all safety interlocks and devices are in place, properly sized, and operating as intended.

Most practical way of cintinuously measuring loop flow is with a flow meter. Measuring differential pressure drop would be as important, or even more so, as it would go along with factory equipment safety interlock. If commissioning, the easiest way is to ask the TAB subcontractor.

thank you urgross
what type of flow meter(s) has to be installed?
is it common pracice to measure the flow to each fan coil unit?

Absolutely, you need to balance flow at each fan coil unit. Typically, all you'll need is a differential pressure gauge, and the knowledge that multiple trips around the loop will be required to get things set up correctly.

Pumpmann, the chiller should maintain a consistent CHW system supply temperature, at set point, across varying loads and flows required by the system. That is its purpose in life. Staging means/methods also needs to be verified and adjusted if necessary if there are two or more chillers.

For flow measurement, the balancer should set flow to design values at each balancing valve. For commissioning, you should spot check flow by running pumps at full speed (forcing open some loads), recording DP across pumps, and verifying flow approximates what is shown on the pump curves.

You need also to verify if there is leakage in the chilled water pipes.