Pipe Test

The pressure is not the same everywhere in the system. At lower points, the pressure is higher on account of vertical head. In a flowing system, upstream pressure is higher than downstream pressure on account of "friction" losses. The designer is correct in principle, but the relevant pressures may differ from 4 bar, depending on the system design.

If the chilled water pipe system is to be tested before commissioning it should be tested as per the relevant professional codes. Generally it is recommended to pressurize the piping network app 1.5 times the design pressure and allow it for certain time. Observe for any reduction in pressure. Log the details. To calculate the system pressure you need to use proper formulas and HVAC handbooks .

I'm neither a piping nor an HVAC guy, so let me ask:

• (Incidental: I guess the water we're talking about is what's known as chilled water?)
• I'm assuming the 40 meters of static head is because the building (or the part of it served by this system) is 40 meters tall (or extends 40 meters above the location of the pump for the system)? (This then represents a static head of 4 bar, because 1 meter of water ~= 0.1 bar.)
  
• The system is closed (as you say). When the pump is running, is it intended (or designed) so that the chilled water at the top of the building is 4 bar?

If so, then the total pressure (static + dynamic from the pump) at the top of the pipe system is 4 bar, and at the bottom of the (40 meter tall) pipe system is 8 bar, and thus, if you are required to test at 1.5 x the system design pressure, you need to test at 12 bar (as measured at the bottom of the system).

If you're testing with water, when you measure 12 bar at the bottom of the system, you'll measure 8 bar at the top of the system. If you're testing with air, when you measure 12 bar at the bottom of the system, you'll also measure 12 bar at the top of the system.