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Oil management with multiple compressors

PicoHydro on Wed October 03, 2012 11:56 AM User is offline

I'm planning a system that uses two Sanden TRSA12 scroll compressors. What concern should I have about oil flow to each compressor? In some operating conditions only one compressor would be running.

HECAT on Thu October 04, 2012 10:00 AM User is offline

Quote
Originally posted by: PicoHydro
I'm planning a system that uses two Sanden TRSA12 scroll compressors. What concern should I have about oil flow to each compressor? In some operating conditions only one compressor would be running.

Imediate concern would be oil pooling and lack of proper lubrication to operating compressor(s).

I think you should put up much more detail regarding your proposed set up; if you want to get some system design advice from many here that are much smarter than me.

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FLUSHING TECHNICAL PAPER vs2.pdf 

PicoHydro on Fri October 05, 2012 1:11 PM User is offline

Thanks HECAT!

System design advice is definitely what I need. What other technical details would help? The compressors both pump for a single AC system, so the question then is:

• How do I avoid oil pooling and provide proper lubrication to the operating compressor(s)?

Edited: Fri October 05, 2012 at 1:12 PM by PicoHydro

HECAT on Fri October 05, 2012 3:14 PM User is offline

Why two? Just use one bigger compressor.

You may have to use oil separators on the hot gas outflow of each compressor to try and maintain a lubricating oil loop to each compressor.

Where the compressors are located, how they are plumbed, pictures; I am sure would help garner more assistance.

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FLUSHING TECHNICAL PAPER vs2.pdf 

iceman2555 on Fri October 05, 2012 5:15 PM User is offlineView users profile

Total agreement with HECAT. Why double the trouble (possible) with two scrolls. Select a Sanden or Zexel compressor of sufficient displacement, have less headaches for possible lubricant flow issues, hose/plumbing issues, charge issues....heck...it simply makes more sense.....what to use two compressors....go with a dual Sanden SD7H or Zexel TM16 set up.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

PicoHydro on Sat October 06, 2012 4:53 AM User is offline

Thanks, guys, for the reply. The application is a heat pump driven by hydro power. The compressor(s) will be driven by a turgo runner mounted to a shaft driving a pulley. (I need help locating a 6" pulley with automotive grooves.) The power available is limited. More jets of water spinning the turgo runner provide more power. The system spins at the RPM where the torque of the compressor(s) matches the torque of the runner. By using two compressors I can accommodate a greater power range, by engaging the second compressor when I turn on a second jet of water. A single larger compressor won't utilize a range of power levels. Thus the question about oil flow.

It sounds like there is a way to do this. Are oil separators available in automotive?

Do the Sanden TRSA12 have a check valve built in so refrigerant doesn't leak back to the suction side thru the inoperative compressor?

I think I would have to feed oil to the suction port on each compressor. There is a plug on the back side bottom of the TRSA 12. Could it be for oil return?

ice-n-tropics on Sun October 07, 2012 9:17 AM User is offline

Pico,
FYI; The Chrysler electric van had a semi hermetic scroll heat pump with Ranco switching valve and was protected w/ a comprenhensive, very lengthly, patent by Sanden, Valeo and Chrysler.
6 " clutch; A few years ago, (don't remember when) I posted here a thorough procedure to make a sleeve for clutch diameter change via machining and shrink fit per a forum question from overseas.
You are prudent to be concerned about adequate oil return.
The OCR (oil circulation ratio) should not drop below about 5%, weight of oil / (by weight of oil + refrigerant), for a heat pump scroll application with signifigant liquid slugging.
I built a dual TRSA12 (in parallel) A/C system for a mobil R-134a application and am working on a oil balance system for dual or single compressor (one compressor off) operation. Sorry, but I can't comprimise the intelectual property potential. Gravity and flow dynamics as well as refrigerant gas velocity determinate the vaporized/oil droplets and cling oil return path.
Temp-rite make excellent oil seperators and the seperated oil return should be injected into the suction gas to properly lube the front bearings with cool (optimum viscosity) oil.
Seperators should not bypass very much hot discharge gas with the oil, otherwise the temp protection switch (TPS) will sense overheating.
The TRSA12 has a single discharge flapper valve which functions as a check valve (with slow leakage).
[email protected]


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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Sun October 07, 2012 at 12:44 PM by ice-n-tropics

PicoHydro on Sun October 07, 2012 1:06 PM User is offline

Thanks for the reply, Ice-n-tropics. You know, when I first began researching this heat pump project, I spent many days reading thermodynamic textbooks to understand Isentropic Efficiency. Your tag line often sparked my thinking on the subject.

I hope to build the heat pump this fall. The 6" pulley is the drive pulley on the shaft with the turgo runner. I'll use the stock 4" TRSA12 clutch driven pulley.

I've been reading about oil separators at http://www.carly-sa.com/-Oil-management-in-a-refrigeration-.html
Is there a temprite separator that is the right size for single and dual compressor operation? My refrigant mass flow rate will range from 180 to 350 lb/hr, or 3 to 5.5 DCFM.

Please tell me about the (TPS) switch. Is it integral to the clutch circuit? What is the cut-out temperature?

ice-n-tropics on Sun October 07, 2012 6:36 PM User is offline

Pico,
I'll leave the separator research up to you, but I was thinking of a separate oil separator for each TRSA12, otherwise each oil return may need a solenoid shut off valve.
Think the TPS is about 115 or 117 C.
If you had a variable vane turbine or other input control method, then one TRSA12 could easily pump your refrigerant mass flow estimate. But maybe your hydraulic motor or drive ratio limits the rpm.
[email protected]

-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Sun October 07, 2012 at 6:44 PM by ice-n-tropics

PicoHydro on Sun October 07, 2012 7:40 PM User is offline

Wow, Ice, your input control method comment has got me thinking about other ways to harvest peak efficiency from the turgo runner at different RPMs. I could mount two different pitch diameter turgo runners, one on each end of the shaft. Hmm...

Edited: Sun October 07, 2012 at 7:41 PM by PicoHydro

PicoHydro on Mon October 08, 2012 11:05 PM User is offline

What is the plug on the back side bottom of the TRSA 12 for?

ice-n-tropics on Tue October 09, 2012 10:30 AM User is offline

Pico,
If you peal the dust cover silver decal off the plug, the silver hex device can be seen to be a mini pressure relief valve (PRV).
[email protected]

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Tue October 09, 2012 at 10:31 AM by ice-n-tropics

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