High discharge temps in Mycom 250 VLD

[prj564]

Hi can anyone give advice on how to adjust the compressor to lowr the discharge temp.
I currently have around 85'c discharge and 45'c oil temp.

[RANGER1]

prj564,
Depending on who built package but usually oil injection line which which feeds oil into rotors has a reguating valve & sometimes a solonoid.
If it has a solonoid make sure it is energized & maybe manually jack it open.
If all OK with solonoid regulating valve could be opened a bit at a time to see if discharge temp improves.

Might be worth checking if discharge temp reading is accurate with a touch probe or similar.
Discharge temp should be approx 70-80 deg C If a high stage or second stage machine max dis temp 90deg C
Oil temp at 45 c is good.

[RANGER1]

I'm also assuming its on ammonia with a compressor of this size!
Can yo also advise of pressures/temp & oil pressure of this package?

[prj564]

Hi Ranger 1 thanks for the reply.
Yes the comp is on NH3 Its a new install and the discharge is too high. I have adjusted the oil injection valve 2 turns further open with no discernable change in temps. I am not sure weather to throttle the valve in restricting the flow or to open it more, any advice would be appreciated. My understanding is
1= more flow cooler oil/discharge
2= less flow hotter oil/discharge
Is this right or am I completly wrong

[PaulZ]

Hi prj564
Can you give us the operating conditions of the compressor, pressures and temps as asked for by Ranger, it's a bit hard to advise you with the limited info. If you open the oil injection valve too far your oil pressure may drop too low.
Paul

[RANGER1]

prj564,

Open throttle valve to reduce discharge temp (anti-clockwise).
if throttle valve open to far possible oil compression in compressor (noisy operation, sounds like nuts + bolts going through it).
What size & brand is regulating valve eg Danfoss/Hansen or other?

If its a Danfoss on a 250VLD I would open it approx 2 1/2 to 4 turns max depending on discharge temp etc.Valve would expect to be min 25mm reg valve.

Oil pressure 200-400kpa above discharge pressure.

Also can you tell if any flow of oil is going into compressor oil injection.
ie is it warm , also if you close valve briefly & then open have someone watching oil pressure it should change due to different oil flows through it.

I would expect 50 - 100kpa pressure drop which equals good flow through this valve.
Basically 50% of total oil flow goes into oil injection to control discharge temp & for sealing .

Let us know how you go

[RANGER1]

prj564,
Can you also describe oil circuit, is it like this or other?

-oil pump pre-filter
-oil pump c/w oil relief valve
-oil cooler
-oil filter
-main oil to bearings
-oil injection solonoid
-oil injection regulating valve

Have you set the Vi adjustment to suit operating conditions?

[prj564]

Hi Ranger1 the circuit you decsribed is the same on this package. I have noticed a minor drop in oil pressure since opening the oil injection valve.

[prj564]

Hi Paulz operating conditions are
suction = -45'c
discharge = 1050kpa, ambient temps vary this to some degree (1000 / 1200kpa
oil pressure 350kpa above discharge.

[RANGER1]

prj564,
Did you manually jack open oil injecton valve?
Have you double checked discharge temp with an accurate thermometer?
If all above has been done I would suggest you inspect oil lines,oil injection valve (which we don't know what size yet) & connection point in compressor for blockage.

You are not giving to much information away!

[RANGER1]

Also check oil injection solonoid is installed in correct direction of flow

[Magoo]

I agree with everyting that RANGER 1 has suggested.
Next thought would be increase the oil pressure differential above 3.5 bar/g.
The discharge temp is regulated by oil volume through screw.
Does the oil diff gauge read pressures at oil manifold at screw after the oil cooler etc,.

[RANGER1]

Hope its not someone who works for the same company I work for!

[Josip]

Hi, prj564

Hi can anyone give advice on how to adjust the compressor to lowr the discharge temp.
I currently have around 85'c discharge and 45'c oil temp.

....Hi Paulz operating conditions are
suction = -45'c
discharge = 1050kpa, ambient temps vary this to some degree (1000 / 1200kpa
oil pressure 350kpa above discharge.

For me your discharge temperature is almost Ok, because you are running compressor in vacuum, probably very dry ammonia vapor ... what is your suction superheat? maybe 8-12K if not more try to lower suction superheat to 1-3K...

what is capacity of your compressor when you have 85*C discharge temp? probably not at 100% capacity

we need as much as possible info to be able to give some help...


Best regards

[RANGER1]

Josip,
From Mycom programme if oil temp is 45deg C it would be hard to get over 80deg C theoretical discharge temp.
Even with 20deg C s/heat on suction at 50% load.
If oil temp 50deg C , yes it would be possible to get approx 83deg C.

I doubt we will ever hear what happened on this one.

[Josip]

Hi, RANGER1

Josip,
From Mycom programme if oil temp is 45deg C it would be hard to get over 80deg C theoretical discharge temp.
Even with 20deg C s/heat on suction at 50% load.
If oil temp 50deg C , yes it would be possible to get approx 83deg C.

I doubt we will ever hear what happened on this one.

Agree with you, but it is also possible to have too much open valve for oil recovery - thus direct injection of hot gas into suction chamber - probably connected after suction temp probe avoiding proper measurement-alarm of suction superheat which is still OK for PLC, but not for discharge temp probe...

I can be wrong, too...

Best regards, Josip

[RANGER1]

Josip,
Just a general comment not aimed at anyone.
I'm not trying to be to smart but I can't understand a lot of screw equipment suppliers who talk about efficiency & power savings.
Everyone seems to instal a needle valve or similar from coalescers compartment to suction of compressor.
This seems inefficient to me as you are constantly returning hot gas & oil when present.
Surely it does'nt cost to much to instal a float valve, as it only returns close to 100% oil not hot gas.

[Segei]

Josip,
Just a general comment not aimed at anyone.
I'm not trying to be to smart but I can't understand a lot of screw equipment suppliers who talk about efficiency & power savings.
Everyone seems to instal a needle valve or similar from coalescers compartment to suction of compressor.
This seems inefficient to me as you are constantly returning hot gas & oil when present.
Surely it does'nt cost to much to instal a float valve, as it only returns close to 100% oil not hot gas.

There are many ways to save energy in industrial refrigeration. However, before implementing these measures a few questions should be answered. What are the savings? What are the paybacks to implement these measures?
Needle valve pass very little gas from discharge to the suction. However, float valve will cost more than needle valve.

[prj564]

Thanks guys for the replys and advice Ive been away for a while. The above mentioned problem seens to have been a partially blocked needle valve in the injection line to the comp. You could feel the oil was the same temp either side of the valve but was not passing any more oil when opened further.

[Josip]

Hi, prj564

Thanks guys for the replys and advice Ive been away for a while. The above mentioned problem seens to have been a partially blocked needle valve in the injection line to the comp. You could feel the oil was the same temp either side of the valve but was not passing any more oil when opened further.

... thanks for reply .... problem solved ... good lesson for anyone ....

Best regards, Josip

[Magoo]

Thanks for reply, one question... did the restriction enter the screws. And what was the restriction.

[Jahangir]

Dear Friends,
after all this reply i cant see the oil type and its quality.so please check oil quality first and make sure that is compatible with your system. check system cop and then other parameter.i think that these values are OK !
Regards

[RANGER1]

For everyone's interest we should have asked the basic question of Vi setting at the begining.
Should be "H" portfor duty stated.

Recently heard story of someone having another similar problem with "H" port setting when
should have been "M" port setting , causing high discharge temps.

[Magoo]

Hi Ranger1.
you made a very good comment about VI settings. Been there same problem.