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PLEH2EREH
12-06-2014, 11:17 AM
ENLIGHTEN ME PLEASE ON DISCHARGE PRESSURE, SUPERHEAT, AND OIL TEMPERATURE. SYSTEM IS A 1K TON CHILLER WITH 134A REFRIGERANT AVERAGING 42 PSIG SUCTION AND 130~ DISCHARGE PRESSURE AND 40~PSID LUBE OIL. I KNOW WHAT DISCHARGE SUPERHEAT IS BUT I'M SORTA CONFUSED ON THE OIL TEMPERATURE VS DISCHARGE TEMPERATURE AND ISSUES THAT COULD HAPPEN. COMPRESSOR IS NOT OIL INJECTED AND USES LIQUID INJECTION (txv's) FOR OIL COOLING. TKS!!

RANGER1
12-06-2014, 11:54 AM
130Psi saturated temperature = 103deg F (40 deg C).
Oil temperature must be above saturated condensing pressure approx 30 deg F (15 deg C)
oil temperature on liquid injection would be about 130 deg F (55 deg C).

This ensures oil is free of liquid refrigerant.

IF oil temp to low, maybe poor lubrication of bearings, oil foaming in oil separator,
higher oil carry over, oil pump cavitation or lower pressure than required.

PLEH2EREH
13-06-2014, 10:37 PM
Ok, I got that. Would it be safe to say then that discharge superheat would need to be at least 30 deg. f ? Or did I miss something?

RANGER1
14-06-2014, 12:38 AM
Ok, I got that. Would it be safe to say then that discharge superheat would need to be at least 30 deg. f ? Or did I miss something?


Yes you are correct, but discharge temp could be set as high 140 degF (60 degC) with liquid injection, you would have to check with Howden rep.

PLEH2EREH
17-06-2014, 11:03 AM
Thanks for the help on that. Another question please: Same unit, as the compressor slide valve increases the oil flow increases... i was told. If that is true, would the oil pressure tend to decrease as well? I don't think it would and that the oil pressure regulator should maintain the set *30 psi* , that is if the oil pump was sized right nor worn out, or plugged oil filter, and there is no leak by-rather it be a valve or wear in the compressor. And the second part is: if that oil flow through the compressor does increase what would happen to the oil temperature without the liquid injection? What I have witnessed is as the slide increases with more load the oil temperature rises, which I thought was butt backerds!

RANGER1
17-06-2014, 11:52 AM
Thanks for the help on that. Another question please: Same unit, as the compressor slide valve increases the oil flow increases... i was told. If that is true, would the oil pressure tend to decrease as well? I don't think it would and that the oil pressure regulator should maintain the set *30 psi* , that is if the oil pump was sized right nor worn out, or plugged oil filter, and there is no leak by-rather it be a valve or wear in the compressor. And the second part is: if that oil flow through the compressor does increase what would happen to the oil temperature without the liquid injection? What I have witnessed is as the slide increases with more load the oil temperature rises, which I thought was butt backerds!

The bigger the differential pressure across compressor (difference between suction & discharge pressure) the more oil flow.
Oil pressure may decrease if oil warms to higher temperature.
Without liquid injection oil temperature will increase until it trips on hi oil or discharge temp.
If the slide loads up more, compressor is doing more work, so oil temp may increase, because same oil flow, more work done, more heat liquid injection opens more to cool oil/discharge temp.
If liquid injection works properly & does not leak, oil temps should be pretty constant after initial start & warm up.

Tycho
17-06-2014, 06:45 PM
You mention an Oil pump, so I'm guessing it is a WRV compressor, not an XRV

I don't think I have had a WRV unit with LRI (Liquid Refrigerant Injection) for oil cooling, all our WRV units have seawater cooled oil coolers. Also no experience with 134a on these compressors, only ammonia.

However :)

On a WRV compressor with an oil pump, the minimum differential oil pressure we set our systems to is 2.4 bar (35psi)(don't have the howden recommended values in my head), there is a by-pass on the oil pump discharge so we can adjust the delivery pressure of the oil pump.
Just yesterday I had a major headache on a ship with oil injected discharge cooling on three WRV163 and the reg valve on the oil injection was over sized so the difference between loosing oil pressure or cutting out on high discharge temp was "looking at the valve sideways"

Anyways, on our ammonia XRV units without an oil pump (OP minus LP = lube pressure) and using a TEAT with a range of 55-95 Celsius (131 - 203F), (I adjust the danfoss TEAT valve so the system is running with a stable oil and discharge temperature when the compressor is at 100% slidevalve with the highest suction pressure I can get.) we regulate it so we end up with a discharge of 55 - 65 Celsius (131 - 149F), the oil temperature would then be around 10 Kelvin lower, at around 45-55C (113 - 131F).
This is with -7C (19F) suction and 30C (86F) discharge (2,2 bar (32psi) and 10 bar (145psi))
Of course, since the XRV is OP minus LP the oil pressure is application is between 7 and 7.8 bar (101-113psi) depending on the suction pressure.

On a WRV unit with an oil pump, the lubricating pressure is OP minus HP.
When I commission a WRV unit, I usually adjust the by-pass valve on the oil pump so that the lubricating oil pressure is around 3-3.5 bar (43-50psi) when the compressor is running at 100% capacity on the slide, sometimes I see the oil pressure rising by approx 0.3-0.5 bar (4-7psi) when the compressor decreases capacity (just as the slide valve is unlocks from 100% capacity).

one thing I have noticed on our XRV units is that the LRI does not kick in until the condenser pressure is at 6.8 bar (98,6psi) (17C on ammonia). we have a PM valve between the compressor and condenser to maintain 10 bar (145psi) on the compressor (some people call it a waste, I agree, but it gives us a stable system, we are however replacing them with a different kind of valve that will give us a lower discharge pressure and less power consumption, but I forgot what it's called :))


Again, if we disregard the suction and discharge pressure and refrigerant temperatures, on a WRV the differential oil pressure should be between 2-4 bar (29-58psi), the oil temperature should be 45-55C (113 - 131F), the discharge temperature should be between 55 - 65 Celsius (131 - 149F) (max allowable discharge temp from howden is 90C (194F) so there is still lots to go on).


Just make sure to keep the oil temperature above 40C (104F) standstill and 45C (113F) running, cause below that Howden does not guarantee the lifetime of give any guarantee on the compressor shaft seals

and as Ranger1 said, Oil temperature should be pretty stable once the system is running.

On our LRI applications (XRV compressors) the temperatures may not be stable until the compressor reaches 30-40% capacity on the slidevalve, on it's way up and the LRI kicks in, but once it starts regulating, the temperatures are dead set.
We also have a by-pass valve on the TEAT that kicks in at 65C (149F) discharge temperature.
It's a simple EVRA with a reg valve (danfoss Reg 15 I think, with a medium nozzle), However, I try to regulate the TEAT so it never reaches that discharge temp even at full capacity.


On a complete side note...

On all our units, be it XRV or WRV compressors, with or without LRI oil cooling, the regulating valve for oil cooling the discharge gas is always there as a "standard" on the oil manifold, It should be kept closed on applications with LRI, but personally as a quirk, I always open it a 1/4" turn because in my mind I am being nice to the compressor by giving it a few droplets of oil :)
This could also be the cause of a drop in oil pressure on a WRV with an Oil pump, if someone has opened this valve more than 1 turn, the oil pressure would drop drastically when the compressor passes 60-70% on the slidevalve.

I hope that made sense and I didn't jumble it all up too much, have had a week with pretty loooooooong days and doing all the F and PSI conversions for you backward guys in the states almost did my head in ;) *Pokes PLEH2EREH in the ribs*

PLEH2EREH
18-06-2014, 11:00 AM
Using the 134a pt chart and a *f to c converter* this is what I came up with: Lets say on a average 90 deg f day (water cooled condenser/cooling tower water) when the slide is ~ 96% loaded the discharge pressure is 140 psi (107.2 f/ 42.77c saturated condensing pressure) the oil temperature should be 132.7 f (58.44c). The unit I'm working on was running at 56c (132.8f). It just looks odd to see a .1 deg f difference vs 3.44 c. Still trying to get use to that one. The discharge temperature, lube oil temperature, and the seperator oil temperature were the same. The lube oil pressure was at 34 psi, so it looked to me like everything was ok. Or am I missing something?


PSIG
SAT F
SAT C
OIL F

OIL C










125
100.4
38
130.4
54.66


130
102.7
39.27
132.7
55.94


135
105
40.55
135
57.22


140
107.2
41.77
137.2
58.44


145
109.4
43
139.4
59.66


150
111.5
44.16
141.5
60.83


155
113.6
45.33
143.6
62

PLEH2EREH
18-06-2014, 11:09 AM
Should have proof read before I hit the post button! Not 42.77 c but 41.77c and the 132.7 should be 137.2. So the temperature difference was 4.8 f 2.44c. Sorry.

RANGER1
18-06-2014, 11:39 AM
[QUOTE=PLEH2EREH;297322]Using the 134a pt chart and a *f to c converter* this is what I came up with: Lets say on a average 90 deg f day (water cooled condenser/cooling tower water) when the slide is ~ 96% loaded the discharge pressure is 140 psi (107.2 f/ 42.77c saturated condensing pressure) the oil temperature should be 132.7 f (58.44c). The unit I'm working on was running at 56c (132.8f). It just looks odd to see a .1 deg f difference vs 3.44 c. Still trying to get use to that one. The discharge temperature, lube oil temperature, and the seperator oil temperature were the same. The lube oil pressure was at 34 psi, so it looked to me like everything was ok. Or am I missing something?


PSIG
SAT F
SAT C
OIL F
OIL C









125
100.4
38
130.4
54.66


130
102.7
39.27
132.7
55.94


135
105
40.55
135
57.22


140
107.2
41.77
137.2
58.44


145
109.4
43
139.4
59.66


150
111.5
44.16
141.5
60.83


155
113.6
45.33
143.6
62


[/QUOTE

Looks Ok to me,Saturated discharge vs oil temp is reasonably consistent.
what type of liquid control valve are you using on liquid injection?

PLEH2EREH
19-06-2014, 10:31 AM
That is the main problem I believe; TXV's. The sensing bulb(s) are of course in the discharge line. For the external equalization two lines are used. One to the suction piping and the other to the discharge piping. There is an adjustable pressure regulator on the discharge line. I never could get it to react correctly following the "manual procedures", so I replaced the regulator with a new one and, still couldn't adjust the regulator to match what the manual indicated to set it at. SO......those two are blocked in and the TXV's are just operating off of discharge temperature. This operation is initiated by discharge temperature settings in the PLC, each having adjustable set-points. I think these are set at #1 On @ 60c Off @ 58c #2 On @ 62c Off @ 59c. During the hotter months the discharge pressure runs in the 135 psi to 147 psi range. During cooler month it runs lower so I readjust those settings accordingly. And to be honest, I don't think it has ever made it to 150 psi.

RANGER1
19-06-2014, 10:52 AM
That is the main problem I believe; TXV's. The sensing bulb(s) are of course in the discharge line. For the external equalization two lines are used. One to the suction piping and the other to the discharge piping. There is an adjustable pressure regulator on the discharge line. I never could get it to react correctly following the "manual procedures", so I replaced the regulator with a new one and, still couldn't adjust the regulator to match what the manual indicated to set it at. SO......those two are blocked in and the TXV's are just operating off of discharge temperature. This operation is initiated by discharge temperature settings in the PLC, each having adjustable set-points. I think these are set at #1 On @ 60c Off @ 58c #2 On @ 62c Off @ 59c. During the hotter months the discharge pressure runs in the 135 psi to 147 psi range. During cooler month it runs lower so I readjust those settings accordingly. And to be honest, I don't think it has ever made it to 150 psi.

I have seen this old type of TX valve on Frick etc pictures, manuals etc.
If it is a problem I could suggest what works & is now the adopted Frick way.

Most common simple type is a Danfoss TEAT thermostatically controlled valve. Set & forget, install a new orifice every so often. Downside is price & only limited capacity. not sure on model or size of your Howden?
Newer method used by Frick & most is a Danfoss ICM electronic modulating valve, deadly accurate & if set up correctly, very reliable.
Hansen have something equivalent to Danfoss ICM if that's easier to purchase.

RANGER1
19-06-2014, 11:01 AM
http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/10_Expansion%20valves.pdfhttp (http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/10_Expansion%20valves.pdf)

RANGER1
19-06-2014, 12:13 PM
http://www.ra.danfoss.com/TechnicalInfo/Literature/Manuals/01/PDHT0B402_ICM_ICAD.pdf

PLEH2EREH
19-06-2014, 08:36 PM
I have mentioned the electronic expansion valves but spending the money isn't up to me.....

RANGER1
19-06-2014, 09:18 PM
As long as existing system is not injecting to much refrigerant in.
Have seen thrust bearings destroyed if to much goes in overloading bearings.
In that case someone used a solenoid & hand expansion valve, not real accurate!