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View Full Version : Minimum run time small close coupled system



kklobas
04-15-2016, 10:11 PM
So I'm finishing the water cooled project I posted about a while ago. A custom Randell line. Two cold pans, two each in sections. The new stuff seems to cool really well. Like almost to quick,about three minutes run time. Cut in at 38 out at 32 ranco 1506 stats. Cold pans using factory stats with fixed five degree diff. What do you think about oil return? They are close coupled and 1/3 hp systems. Almost seem a little to efficient/ oversized but sized off factory air cooled units. ( converted from air to custom water cooled) running 250 head on all three. Sh at 12-15 coil, 30 compressor. Td high at about 23, but cool great?

kklobas
04-15-2016, 10:12 PM
That should be two reach in sections

IRBH
04-16-2016, 01:44 AM
Are these readings & run times obtained with units in service or just test runs?

The 3 minute run is not good- can you lower your settings as 32 off is just air temp.
Pans could be run colder too?

There can't be that much heat transfer in 3 minutes so the off time is probably short also.
This will shorten start capacitor & relay life too.

kklobas
04-16-2016, 09:42 AM
Test runs yes, so boxes were not load d with product. I think I may adjust the cold control to cut in around 41 it does have some degree of adjustment with the altitude screw and cut out screw. The Randell pan stats do not have adjustable differentials though, they are 5 degrees. Air temp does pull from 38 to 32 in 3 minutes. I thought of increasing head to 275 to loose a little capacity? I guess the water cooled are just really efficient. They also don't have 90 degree greasy kitchen air blowing through them, and grease plugged coils like the air cooled did.

IRBH
04-16-2016, 10:25 AM
kk it being a no-load test, I would not worry about the short run times.
Loaded, in kitchen environment & use it should be fine.

Adjust your water outlet temp when loaded.


By your readings it's R404 systems, right?

kklobas
04-16-2016, 11:39 AM
Yes r404

BBeerme
04-16-2016, 12:23 PM
The conditions you described will actually promote oil return, not hinder it.

There are two things going on. First, during the off cycle, the oil will want to absorb refrigerant. Especially in the cooler parts of the system. Then when the system starts up, that oil will be thinner and also want to foam up, both of these things will tend to get the oil back to the compressor quicker.

Secondly, the velocities of the refrigerant are greater when the compressor first starts up. Which greatly aids in moving the oil through the system.

Oil return is at its worst during long run times under little load.

kklobas
04-17-2016, 04:30 PM
I was always told you needed at least 3-5 minutes for adequate oil return?

BBeerme
04-17-2016, 08:43 PM
If you had longer vertical runs, then longer run times might be better, but the title of the thread specified close coupled.



I was always told you needed at least 3-5 minutes for adequate oil return?