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At the ahu there are inlet and outlets pipe in this chill water flow from chiller to ahu and ahu to chiller near the ahu there typical pressure gauge in this what are the standard pressure required or there are any standard pressure value. Please explain This question asked in interview of hvac engineer post
chilled water pump is calculated based on pressure drop in the last equipment if the last equipment is AHU then u have to calculate pressure loss for 0.25 to 0.35 bar usually in AHU coil
the maximum pressure rating for the pump is 25 PN that equal to 25 bar head maximum,but the system head is usually less about 20 or so .
in order to maintain the flow rate till the last point the pressure drop is calculate ,
the exact pressure in pressure gauge depends on type of system employed.
1) if its district cooling then maximum running pressure is 8 bar in pump room situted al basement level suppose ahu or fahu if on the roof its maximum pressure would be 7 bar .so the pressure gauge should show 7 bar maximum convert it to psi that around 100 psi
2) if there is building with chiller and of height maximum 25 floors then running pressure is 5 bar maximum in pump room situted al basement level suppose and ahu or fahu on the roof its maximum pressure would be 4 bar .so the pressure gauge should show 4 to 4.5 bar maximum convert it to psi that around 60 to 65 psi
That is why we have DPCV (differential pressure control valve) valve situated at the roof level of district cooling type building which maintains the pressure .Its reduces unwanted pressure to built up in the system of chilled water .
pressure from the chiller is pumped and circulated in the system of the Chilled Water system by a Primary Pump or chiller pump to a HX Heat Exchanger where this cooled water is absorbed and reciculated to the loads AHU's, FCU's by the secondary pump. This method is employed to minimize pressure drops and ensure sufficient pressure and flow across the chiller first to avoid chiller coil freezing, and to AHU's and loads for cooling the spaces. There is no determined pressure drop or reading as it depends on the TDH of the pump selected. AHU's are typically rated at5 to Kpa minimum.
We can ask OEM for such pressure drops across the Cooling Coils.