Low temp R-507 oil return issues
Just installed a R-507 Low temp Beacon II system and am having a oil return issue. The condenser unit is mounted about 3-4 feet above the evaporator on the roof and I have a u-trap on the outlet of the evaporator. After running the system for a day the sight glass on the semi-hermetic was at about 1/8-1/4 oil level running so I added about 5-7 oz of oil and it came back up to half full sight glass.
Now fast forward a week and the sight glass is down in the 1/4 full level again. I'm running about 6 degrees of evap superheat with a total superheat at the compressor of about 35-40 degrees. The sub-cooling hangs around 5-7 degrees and for the most part everything looks good except the oil level. I don't want to keep putting oil in and have the system burp it up later on and cause a serious problem but worry about long term damage to the compressor.
Being its a 2HP semi-hermetic it just uses the splasher system so have no way of checking oil pressure aside from just the sight glass.
The system is a Heatcraft Beacon II (climate control label). The evaporator is a LSF090 and the condenser CSS-021L6 with a EAVA-021E Copleland semi-hermetic.
I've tried running extra defrosts going from the preset four to six and it still hasn't made the oil "burp" back into the compressor. Its been pretty mild weather here with highs in the high 70s and lows in the 50s and 60s. I tried blocking off the condenser to bring up the head pressure for a bit to see if that would get the oil back but I didn't want to do it too long being its a air-cooled semi-hermetic.
So my questions are, first I know Copeland specs 1/2 a sight glass and up to a 3/4 sight glass but is 1/4 going to hurt it? I've gotten answers from yes it will to 1/4 to 3/4 is good.
Being my suction riser is only 3-4 feet at best should I reduce it from the 7/8" to maybe a 5/8"? As a random thought would switching to R-404A help oil return because of its R-134a content?
I've never had a oil return issue with such a small system so kinda at a loss for ideas and appreciate any you guys can offer.
Your riser is a oversized, but should work fine, try adding a little more oil and monitor it. If you have a trap and an accumulator it should be fine. I would have gone with 5/8 riser. Set your defrosts back to 4.
Looking at the Heatcraft performance info for this condensing unit, the capacity at -20ºF SST/90ºF Ambient with R404A/R507 is 9420 Btuh. According to Andy Schoen's Line Sizing Calculator, the 7/8" riser would result in a velocity of 1638 ft/min at that condition. The recommended minimum velocity is 1500 ft/min, so the 7/8" riser should be OK for oil return.
As for the oil level, the Heatcraft Installation Manual recommends the level be just above 1/4 of the sightglass (See p.32). I suspect adding too much will tend to cause excessive oil in circulation...especially with a splash type oil system.
I haven't had any experience with R507, but I've never read anything negative about its oil returning ability.
As long as it shows in the glass I wouldn't worry about it. Even small k body compressors these days have an oil pump.
Ok never thought they put oil pumps in anything under 3 or 4 horsepower semi herma.
Even though the guides say 7/8" is ok, would it be better to go with 5/8" ?
I'm going to be shutting it down after Christmas for a week to paint the floor and finish up with installing the lights (health inspector wants more lighting) and can swap out that riser with 5/8" easily and put a inverted trap at the top if it will help.
Just kinda worried when summer comes the higher head pressure will make the oil burp back up.
Don't Poke The BEARS.......
In my opinion. Keep on running with 507, it's "softer" for the compressor and more efficient to pick upp energy than 404A. Circuits on 404A with heat problems is running "cooler"/better on 507. Why?
We think that's the 134a in combination with a little different mixture between the two other ref's that's making it. In 507 there's no 134a, and the mix is 50/50.
Instead. I recommend to put a oil separator on the hot gas line
Should I go with a impingement, helical, or coalescent type oil separator?
Seriously. I haven't thinked 'bout different types. I'm just ordering from my dealer. Normally, It's "henry" brand for the separators, I think they're the helical type.
What kind of oil are you adding?
And just so you know
If you do in fact have an oil return issue...
Adding an oil separator doesn't fix it.
No oil separator is 100% efficient.
Soon enough, your oil will collect back at the point of no return.
Emkarate POE ISO 32 (150 SUS)
I understand and that's why I didn't go that route with the separator from the start. I just wish I knew what was causing the problem in the system.
Heatcraft doesn't offer a oil separator on such small systems so it should be a problem and there must be something with my piping. The only thing I can think of is putting in a 5/8" riser with inverted trap at the top and also add a oil separator to keep as little circulating as possible.