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Commercial HVAC Tech question

Old 09-04-2018, 02:42 PM
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Commercial HVAC Tech question

Is anyone out there a commercial hvac tech? Brainstorming an issue on a Carrier 110 ton.

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Old 09-05-2018, 05:27 AM
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I work with engine driven chillers up to 1000 tons, R22, R134A, Also deal with some air cooled to 50 tons, R-22 and R404A. What is you issue?
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Old 09-05-2018, 05:33 PM
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Well, I might have it sorted but essentially it's an R22 Carrier unit feeding a shell and tube exchanger with a glycol buffer and an Alfa Laval plate and frame. We started losing R-22 at a rate that suggested a major leak but we could not find with a sniffer. Next thought is that the bundle is leaking allowing R-22 into the glycol but the storage tank did not show a major hit for refrigerant. We've opened the bundle to fix the leaking tubes and found that on one circuit many are leaking, beyond 10% of the capacity and there is evidence of contamination from burnouts in the past, maybe a burnout filter hadn't been used successively. Now that it's all back together it's worse than before and I'm wondering of when the B circuit went low, could it have pulled glycol into the breached tube and back into the compressor? What are the odds of failure of the compressor if so. Also, it seems as thou an EXV were failing...and we had evidence of low head pressure for no apparent reason on a full charge. Overall, I'm trying to steer this in the right direction.

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Old 09-06-2018, 05:09 AM
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When we have a leak and cant find it or unsure of the source we pull all the refrigerant out and pressurize with N2 to 200 psi or so, take press and temp readings and let it sit for 24 hrs to determine the leak rate and soap the heck out of every thing. I assume that this is air cooled, on occasion we have had to put flourecent dye in the system to locate leaks there.
As far as glycol in the system not sure how that would affect it. If water the water will freeze at the expansion valve once system pressures reach freezing temp and suction pressure will take a nose dive. when exp valve warms system will run again until freeze temp and low suction again. With glycol ???? what is the concentration and freeze point? What was leaking on the tubes? If at the tube sheet near joint and tubes are crushed that is a sign of an operational freeze.
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Old 09-06-2018, 01:40 PM
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We pulled the shell and tube apart to find several leaks. Not really repairable, the unit needs to be replaced or completely rebuilt and pressure tested with a new RIN stamp. Unfortunately it does appear as though glycol had been drawn in to the compressor when it had low head pressure. The glycol pressure overcame the charge pressure and penetrated the breach. Compressors are likely toast too. Oh well, live and learn. I think you may be on to something though with the operational freeze idea, that seems plausible. Note to self, low head pressure and no identifiable leak source = real bad. Glycol was concentrated down to 20F based on refractometer.

Thanks for the input.
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Old 09-07-2018, 04:38 AM
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Assuming this is a 2 pass hx where liquid refrigerant enters the bottom half of the tubes then returns on the top half and chilled water or glycol is in the shell. In an operational freeze the tubes at the tube sheet where liquid refrigerant enters the hx is the coldest point. What happens is ice will build on the back side of the tube sheet and when it freezes hard enough it start to crush the tubes and the seal where the tubes are rolled into the tube sheet will fail. That,s what happens with water anyway. With glycol it may not freeze hard enough to crush the tubes. Freeze protection with a glycol solution is called out at 2 temps, 1 is freeze point where you can no longer pump the fluid the other is burst protection where it will break or crush pipes.
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