R-123 centrifugal chiller with climbing purge run-time
An office tower in Ottawa is cooled by a 1,400 kW low-pressure centrifugal chiller using R-123, with a water-cooled condenser, a purge unit and an evaporator that runs in a vacuum at about 40 kPa absolute (5 °C). The purge run-time log, normally about 3 minutes a day, now shows 35 minutes a day and is still climbing. The building is at design load, leaving chilled water is 9.5 °C against a 7 °C set point, and condenser water is 29 °C in and 35 °C out, as designed. The machine has not surged. There is a faint oil film at the evaporator gasket line and around a recently serviced pressure-transducer fitting; the charging valve was last used in April. Refrigerant records show about 40 kg added since May, and the moisture indicator is yellow. The service contractor's written recommendation is: 'Increase purge rate, keep topping up charge, schedule overhaul next spring.'
1. Is the contractor's recommendation acceptable? Explain what the purge run-time trend and the other symptoms indicate.
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No. A purge unit is best read as a leak meter. Run-time rising from about 3 to 35 minutes a day says the quantity of non-condensible gas entering the machine has increased roughly tenfold - and the evaporator is below atmospheric, so every imperfect joint is an inward leak. The oil film at the gasket line and the transducer fitting are candidate entry points.
Air is not a harmless diluent. It does not condense at condenser conditions, it blankets tubes, and it adds its partial pressure to the R-123. The compressor must therefore pull a lower evaporator pressure for the same chilled-water temperature and discharge against a higher condenser pressure - exactly the observed pattern of capacity shortfall at design load, larger lift and shrinking surge margin.
The yellow moisture indicator is a second, separate red flag: moisture is being drawn in with the air, and R-123 plus water plus POE oil forms acids that attack motor windings and bearings. 'Top up and overhaul in spring' treats refrigerant as a consumable and leaves a known leak running for months, contrary to refrigerant-management and leak-repair obligations, and it is expensive. Find and repair the leak first.
2. How would you distinguish air ingress from a water-side (tube) leak, and what tests would you ask for?
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Distinguish by where the water would come from. Tube leak: chilled water is at roughly 350–400 kPa, so a tube failure pushes water into the refrigerant. Symptoms are a wet system - yellow-to-green moisture indicator, high purge activity with water in the purge exhaust, refrigerant analysis showing water and chloride ions, and chilled-water make-up demand or a falling loop pressure. Air ingress: atmospheric moisture only, with the leak at mechanical joints; the oil film at the gasket line and the serviced transducer fitting fits this better.
Tests to request:
- Electronic leak detection around joints while running.
- A standing vacuum (vacuum-decay) test with the machine pumped down and isolated - a rising pressure shows both the leak and its rate.
- If inconclusive, a dry-nitrogen positive-pressure test with soap solution, or ultrasonic/helium tracer.
- A refrigerant sample for water content and chloride ions.
- Chilled-water pressure test or eddy-current/tube inspection only if water-side contamination is confirmed.
Fix the fittings and gaskets first because they are the cheap, likely suspects; then re-log purge time to see whether it stays down.
3. What regulatory and record-keeping obligations follow, and how should the 40 kg addition be handled?
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R-123 is an HCFC, an ozone-depleting substance. Service work, recovery and handling must be done by a certified person, refrigerant must be recovered and not vented, and leak repair plus refrigerant-management records must be kept under Ontario's ODS/halocarbon regulation (O. Reg. 463/10) and the federal Halocarbon Regulations, with records available for inspection.
Practically:
- Log the 40 kg as a leak, not as routine top-up - that is the whole point of the record.
- Repair the leak before returning to normal operation; do not keep feeding a leaking machine.
- Recharge after repair only with recovered or reclaimed R-123 of verified purity, since moisture and acid contamination are already suspected.
- Keep the leak-check dates, amounts added and repaired components on file.
Report the situation in writing to the building owner so the decision and its cost are documented. Given the long-term phase-out of HCFCs, the owner also needs a plan for the machine - but that does not justify operating a known leaker in the meantime.