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georgedvf
26-07-2016, 01:33 AM
Hello everyone!
Long time just reading you... now I have an issue.

I have a system with several circuits and multiple compresors on a Parallel system, each liquid line has a subcooler (whose return gets into the Rack's suction manifold) to avoid flashing on a long rise to evaporators, but I noticed that when the subcooler is open the pressure drop on Suction line is very high; when I close the liquid subcooler the suction pressure drop lowers to a reasonable digit.

I calculate this in a Danfoss Cool Selector software, and the theoretically efect should be the opposite, with liquid subcooling there should be lower suction pressure drop.

Any idea why this is happening??

RANGER1
26-07-2016, 09:07 AM
Georgedvf,
If subcooler suction line returns into suction line then theoretically load should be identical with it on or off.
The sub-cooling only helps system run more efficiently in the superheat control of evaporator.
If you turn off & suction pressure lowers, then maybe evaporators working at lower capacity.

What at type of system, pressures temperatures & refrigerant.
How much subcooling do you achieve?
what type of Tx valves?
What type of compressor?

Also clarify what you mean pressure drop or rise in suction line, is it inhibiting performance or just observation

georgedvf
26-07-2016, 01:57 PM
Hello Ranger1.
Suction pressure rises in evaporator when turn on subcooler. It's R134a, 20F liquid subcooling, EEV(pulse electronic expansion valves), reciprocant bitzer compressors.
The suction pressure drop I mean evaporator pressure vs compressor suction pressure, the pressure in compressor doesn't change with subcooler on or off, but when turn on subcooler evaporator pressure goes higher about 5-7psig.

The line rise is in liquid line, it is about 40ft vertical line to evaporators.

RANGER1
26-07-2016, 08:35 PM
Hello Ranger1.Suction pressure rises in evaporator when turn on subcooler. It's R134a, 20F liquid subcooling, EEV(pulse electronic expansion valves), reciprocant bitzer compressors.The suction pressure drop I mean evaporator pressure vs compressor suction pressure, the pressure in compressor doesn't change with subcooler on or off, but when turn on subcooler evaporator pressure goes higher about 5-7psig.Might depend on where or how sub cooler is piped into suction line, or if manifold is big enough.You could size header for evaporator & sub cooler & see what it comes up with.The line rise is in liquid line, it is about 40ft vertical line to evaporators.


Can you size compressor manifold for evaporator load plus sub cooler load & see what you get.
Sound like pipework restriction for whatever reason

georgedvf
26-07-2016, 10:46 PM
The calculated size for suction manifold is 3-5/8" including subcoolers load. The installed manifold is 8" to use it as acumulator as well.

sicisici
28-07-2016, 08:28 PM
Yes have a look in my first question, i put other photos there...