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Is this formula correct enought for suction line :
delta P = 9.81 * Density of the gas * Height
I am wondering becasue i am checking VRF pipe network and i assume that there will be a big difference in density so i would calulate an average.
My evaporator coils are placed above compressor.
Thanks in advance, any help would be apritiated
No!
This formula is for hydrostatic pressure only.
Suction line has mainly vapor with low density so this value may be neglected as it is much less than dynamic (friction) losses.
The pressure in the suction line is basically given by the amount of refrigerant fed to de evaporator, the amount of refrigerant that evaporates and the pumping capacity of the compressor.
No, the biggest dp comes from the velocity of the gas.
Thanks - i will do my calculation according your advices (but i will find some more formulas for calculating DP height)
You only have to take in account the height in case of rising liquid lines
My opinion about this subject is:
1) For liquid lines the rise effect is very important as if there is no sufficient subcooling the refrigerant will start to flash because of the decrease of the pressure as the liquid rises.
2) For wet suction lines (flooded systems) - not dry suction lines - the effect of the hydrostatic is very important specially for low suction pressures. The hydrostatic penalization due of the carry up of the liquid by the vapour. For example: a R717 compressor sucking at -40ºC (at compressor gauge) if the DN pipe is not correctly selected and if you have a huge difference height between the evaporator and the main suction pipe (main suction pipe above the evaporator) then you would evaporate at -37ºC...-35ºC...it depends also of other pressure losses.
Sandro, sorry I missed the "wet suction". So I deleted my previous post and agree with you.
No problem :)