Re: www.refrigerationengineers.co.uk

[Samarjit Sen]

What would be the effect on the system when the air cooled condensing unit has been installed at a vertical height of more than 40 ft. from the freezer. On the head pressure is going up as high as 500 psi and the suction pressure at 25 psi. The system is with R 22. In my opinion the pipe lines have not been designed properly and excessive refrigerant with impurities and extra oil has been charged. The entire
liquid line is full of oil inspite of there being an Oil
Separator. Could some one advice me if I am wrong or right and what could the remedy be. As against the evaporative temperature required being -25 Deg. C the contractor has selected the capacity at -38 Deg. C Evaporation presuming there would loss due to the length. The total length of the pipe line is more than 70 ft for the suction line and same for the liquid line.

[sihombing]

Dear Samarjit,
please check your condenser, it may be dirty, partially blocked or the condensing air is not sufficient.

i agree with you,
there is an air or other noncondensable gasses in refrigeration cycle.

how about the running current?

rgds,

[Peter_1]

If designed properly, there will be no problem if the condensor is installed at a height of 40 ft.
You gave too less information to figure this out.

Where is the receiver located?
Capacity?
What discharge lines are installed?
Double risers?
Can the compressor run in a part-load condition?
Are there U-bends in the discharge line?
How's the discharge done just after the compressor?
Is there a U-bend just after the compressor discharge?
Is there an NRV in the discharge?
What maks you think that the suction is influenced by a high installed condensor?
What er the actual measured working conditions, LP, HP, discharge and liquid temperature, liquid pressure on the receiver, ..?
Can you measure HP on the condensor?

This information is needed to give you the right answers.

[AMARNATH JHA]

Hi Samarjit
Really this much height is not adviceable.However pls check the condenser for clenliness.You are complaining about moisture in the system.Pls let me know what types of filter is used.
Thanks
AMARNATH JHA

[Peter_1]

I haven't read that there was moisture in the system.

Re-read you post regarding complaints about suction temperature/pressure.
Same questions regarding temperatures and pressures.

How do you know there's too much oil in the system?

To remove oil (if there's too much oil in it):
Pump all the R22 in cylinders and gently heat them with a heatgun.
Blow the system with OFN, vacuum it completely, install new filter dryers.
Recharge the R22 in gas form so that only pure R22 is charged and the oil remains in the recovery cylinder.
Pour the oil out of the cylinders and measure the amount of oil you recovered.

Too much oil in the system will drastically reduce evaporator capacity.

[old gas bottle]

R22 at that temp will give all sorts of problems,oil being one,it needs to be on R404a or if only 22 available, check the evaporator is matched to the unit,as you know the evaporating temp needs to go up to about -25/28, oil traps in the suction line,oil sep,and i would use somthing like a semi synthetic oil to get it returning better,it would mean cutting the suction pipe of the evap and also the liquid line and draining all the oil out of the system and starting again. happy days.

[S.M.Gokhale]

Dear Samarjit,
Oil throw can occur due to various reasons.

Is the compressor new or a used compressor with worn out piston rings installed? Is the oil separator selected correctly? which make of oil separator is installed - a local one may not be efficient at all. As liquid line is also flooded, it appears that oil is escaping the separator.

Oil return - especially at low temperatures depends on refrigerant gas velocities - these need to be sufficiently high to return the oil. Arbitarily oversizing of pipelines can cause a problem of oil return.

Circuiting of the condenser and cooling coil also should be checked to ensure efficient system performance and to maintain proper refrigerant velocities.

Sometimes if the evaporator is undersized and liquid refrigerant is returning to the compressor, it will lift the
oil from the crankcase.
Regards

[Samarjit Sen]

Thank you freinds for your expert opinion. The plant has been installed by a reputable refrigeration firm and we had provided the condensing unit with Bock compressor. The system has been installed and designed by the firm who has taken up the contract. Due to the problems they are facing they had contacted us saying that the compressor is defective. The suction line laid is 7/8" OD and the liquid line laid is 3/8" OD. They are unable to state as to the number of bends. As per our pipe sizing the dimensions should have been 7/8" OD Suction Line and 1/2" OD Liquid Line. The Drier installed is of Danfoss and the same was found blocked on opening. The complete line was full of oil and the Expansion Valve was fully chocked. The firm who had taken up the job had opened the compressor head and could not find any defects. They had intimated that they ran the unit at 500 psi head pressure which heated up the headdue to which the colour of the same had changed. I had advised them to first change the liquid line, flush the system and charge refrigerant slowly over a period of time. Now it is upto them to decide. I thank you all for your valued opinion which will be of great help.