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Hello,
Have any minimum limit for cooling water temperature for water cooled condensing unit piston compressor ?
For water chiller this often 22o C( 13 o C for less 2 minutes) when start-up the chiller.
The standard condition for condenser often 40oC. But i do not know could the compessor can start-up, turn-off many times with constant cooling water temperature 8o C ?
Any people worked in similar case ?
Thanks
hi WTA, well I guess your ambiant temp, is higher than the UK ,? but has it ever run ? have you inspected the con /water strainer ? do you have any water treatment is the condencer tubes blocked ? are they clean ? have you rodded them out ? how old is the unit ? we need many answers to see what is going on , regards sedgy ,
Hello Sedgy
40 oc is not ambient temperature. I got them from manufacturer condensing unit catalog ( like Bitzer) - its standard refrigerant condensing temperature.It an new cold storage application. we use them on basement so we want to use chilled water 8oC from chiller (already have). we use closed circuit so water is pretty clean and have not much concern about concentration. Our chilled water system working very well and reliable. The only concern is water-cooled condensing unit's working range limit for condenser.
Thank for your reply
Yes there is a lower limit of water cooled condensing units but you won’t find it mentioned explicitly neither in the compressor nor condenser manufacturer’s literature.Quote:
Have any minimum limit for cooling water temperature for water cooled condensing unit piston compressor ?
For water chiller this often 22o C( 13 o C for less 2 minutes) when start-up the chiller.
The standard condition for condenser often 40oC. But i do not know could the compessor can start-up, turn-off many times with constant cooling water temperature 8o C ?
Any people worked in similar case ?
The compressor literature will give you only a minimum condensing temperature and this is because in reciprocating compressors you need two things for the valve plate to operate:
- Pressure above the valve plate to close the valves efficiently
- Use as much of the volume swept by the piston as you can for volumetric efficiency
With low condensing you lose these mechanisms and the capacity of the compressor collapses.
If you read the compressor manufacturer's literature you’ll see that you need a minimum condensing temperature.
If you try to play with the condenser differential, increasing it to try to reduce the media temperature you also reduce flow in the condenser and if you don’t respect minimum flows it may bring the condenser’s capacity down. This minimum flow is not mentioned explicitly but you usually have limits you have to respect (operational envelope).
So it is the operational envelopes of the devices you select that give you the minimum conditions.
The compressor has a limit of star/stops but it doesn’t depend on condensing pressure. Usually the main problem is that you stress the motor coils, overheat to motor and loose oil to the system which doesn’t come back because the compressor doesn’t work long enough to recover it
Why do you thing the start/stops relate to t water temperature? It may be but my first guess would be low thermal load!
The cool water decreases condensing temperature which increases compressor capacity and you have an oversized compressor.
Thanks for detail explanation.
I want use constant chilled water (8oC) for cooling (condenser entering) cause we need them for basement cold storage while have chilled water pipe nearly :D. I think for start/stop because it pretty standard for start-up/reset water limit condition of water cooled chiller whatever type. i will check with compressor catalog for operational envelope. But anyone have worked with low condensing condition ? Please share with me a little experience.
Regards
I would have thought it would effect TX valve operation due to smaller than designed pressure difference across valve.
This coul cause possible low suction pressures.
I don't think it would cause any damage as long as compressor oil is not diluted with refrigerant, sump heater working etc.
You could install a water pressure regulator in condensor cooling water outlet, which opens on set discharge pressure ie Danfoss, Penn etc
Thank for the advices. You showed many concerns :((.Quote:
Originally Posted by RANGER1
1/
Most of water cooled condensing unit (nearly all reciprocating compressor ) were standardize with 20 oC suction gas temp. ever with minimum 10oC condensing temperature (bitzer reciprocating compressor with R407 C). While my inlet water temperature is only 8 oC, i don't know how to check the compatibility of compressor and condenser coil especially when start-up. Please give me some advice ?
2/ Sorry for the terminology unfamiliar : sump heater is oil sump heater is crankcase heater. Are they one ?
3/ Could i know the intent for pressure water regulator , variable condenser water flow ?
Regards