PDA

View Full Version : Compressor too hot in chiller







eligray
19-10-2009, 05:02 AM
I've recently made a chiller with the following:

~6k BTU rotary "Rechi 39r131f"
r507/404a TXV
4x120mm 2000RPM fans on condenser
SLHX
propane as refrigerant
Filter/drier
Homemade receiver

The problem I'm having is that my compressor gets extremely hot. Once the evaporator starts cooling off a bit, meaning that the restriction in the loop rises, the compressor gets quite quickly to very hot temps (80c+) I THINK that this is because there is far less oil flowing through the loop anymore, meaning that the compressor doesn't get the proper oil return. I have tried even putting a 250CFM leafblower-like fan on the compressor, and still it gets very hot, leading me to believe that there is not enough oil in the system. Oil may have escaped quite a bit when I did 10+ leak tests with propane when building my system.

To have my system run safely, I've lowered the TXV restriction quite a bit, so that (in theory) it is getting more oil flow. The downside to this temporary fix is that my temps are very high (7c or so in the PC coolant loop)

One time I left the system with the TXV turned to max restriction, with the 250 CFM fan on there. When I got back, the compressor was at 110c :eek:

Would you guys confirm that too little oil is indeed my problem? Is there any way to just add some via a schrader valve?

Thanks,
Eli

Gary
19-10-2009, 05:37 AM
It's not about the oil.

Start here:

http://www.refrigeration-engineer.com/forums/showthread.php?t=19701

eligray
19-10-2009, 06:29 AM
Any ideas of what it may be about, then?

I didn't see anything in that thread that would relate to this issue here... but I am glad to know that gas can hurt a TXV

eligray
19-10-2009, 06:36 AM
Also, I did notice quite a bit of oil escaping during repeated leak tests... I guess that may or may not be relevant.

nike123
19-10-2009, 06:58 AM
That compressor is for dehumidifier/AC usage which mean high evaporation temperature. It is cooled with suction gases. If your system having low suction temperature and high suction superheat, than it will overheat.
Question is what is saturated suction temperature and what is evaporator and total suction superheat?

Gary
19-10-2009, 07:15 AM
Rotary compressors have the shell on the high side. They are supposed to run hot.

glenn1340
19-10-2009, 08:03 PM
Rotary compressors have the shell on the high side. They are supposed to run hot.

Hmmmm, I didn`t know that. Is that scroll compressors or just rotary ones as that could easily throw me next time I`ve problems on one.

Thanks,
Glenn

Gary
19-10-2009, 08:08 PM
Hmmmm, I didn`t know that. Is that scroll compressors or just rotary ones as that could easily throw me next time I`ve problems on one.

Thanks,
Glenn

Just rotary compressors.

You may have noticed that a rotary compressor always comes with an accumulator mounted on the inlet.

The reason for this is that the suction gas goes directly to the compressor pump section. The pump discharges into the compressor shell, thus the shell is on the high side.

Brian_UK
19-10-2009, 10:49 PM
Any ideas of what it may be about, then?

I didn't see anything in that thread that would relate to this issue here... but I am glad to know that gas can hurt a TXV
The you haven't absorbed the function of a suction cooled compressor yet.

Oil lubricates, refrigerant cools.

eligray
21-10-2009, 05:07 AM
Thank you very much for the info guys. I did realize that compressors would tend to have higher temperatures in a system like this than they would in a normal AC/Dehumidifier, but I didn't realize that they relied so heavily on suction gasses to stay cool.

I'll measure data and post it in this thread next time I get a chance to run the system.

Other than airflow, is there anything else that can be done to help cool the compressor? I'm sure it sounds stupid, but would a little extra oil help things out?

I really appreciate your sharing the knowledge, thanks guys :)

frederik79
28-11-2009, 09:00 AM
oil = lubrication of the inner parts

One time I left the system with the TXV turned to max restriction, with the 250 CFM fan on there. When I got back, the compressor was at 110c :eek:One time I left the system with the TXV turned to max restriction, with the 250 CFM fan on there. When I got back, the compressor was at 110c :eek:


that is because there is to little refrigerant in the evaporator witch gets you high sh.

the task of a txv is measuring the SH.

jim01
16-07-2010, 09:40 AM
your post is really good thanks for your post

Sydneyman
20-12-2010, 03:57 AM
I have the super is too high, it can back to compressor about -2 to 5 degree C so general speaking it can cool down the compressor by system.

I think you refrigerant have air inside, i suggest you to do to ways.
1. open the condensor purge valve to get off the air.
2. reclaim all refrigerant, and put the new refrigerant back to system, and have look the guage read..

thanks