Introduction: ISO VG 100 is the viscosity grade most industrial ammonia screw packages are built around, and matching it to actual load, discharge heat, and evaporating temperature is what keeps rotor bearings alive.
A water-cooled ammonia screw chiller rarely runs at one steady point. Discharge temperature climbs on hot afternoons, evaporating temperature falls when load drops, and the oil must hold a film on the rotor bearings through both swings. Before a scheduled change, the practical question is not whether ISO VG 100 refrigeration oil is good oil. It is whether this grade in a mineral base oil still matches the load, discharge temperature, and evaporating temperature your machine actually runs at.
ISO viscosity grades climb from 32 through 46, 68, and 100, and screw compressors with large rotors sit at the top of that ladder. A 100 cSt viscosity at 40°C builds a thicker hydrodynamic film than a 46 or 68 grade at the same shaft speed. That film keeps rotor lobes, journal bearings, and thrust faces separated under load. Ammonia screw packages commonly run rotor diameters of 100 to 300 mm with bearing clearances above 0.05 mm. A film that thin needs viscosity to stay intact when the machine is working hard, not just idling. The oil does more than lubricate in a screw compressor. It seals the gaps between the rotor lobes, carries heat out of the bearing zones, and damps the pressure pulses that travel down the rotor. Dropping to a lighter grade to cut churn losses usually trades film thickness for wear on the parts that are expensive to replace. QISHANR Lubricants, a naphthenic refrigeration oil manufacturer, builds 5GS around that requirement: 100 cSt at 40°C for film strength, plus 8.4 mm²/s at 100°C so the oil still has body once it reaches running temperature inside a loaded compressor. That second number matters more than it looks. Oil that thins too far at operating temperature stops protecting the discharge-end bearing, which is exactly where an ammonia screw compressor works hardest.
Ammonia does not dissolve mineral oil. That single fact reshapes the whole selection. In an HFC system, oil leaves the compressor with the refrigerant, travels the circuit, and returns through the suction line with the gas. In an R717 system, the oil largely stays in the compressor and crankcase. Whatever escapes is pushed back by oil separators, drop legs, and gas velocity rather than by miscibility. The practical result is that the oil spends more of its life hot, inside the machine, doing bearing work. Ammonia also runs at pressures and discharge temperatures that punish a weak oil. R717 pressure and temperature are tightly linked, so a fouled condenser or a hot day can push discharge temperature up quickly, and normal screw operation already sits in the 80°C to 120°C band. Oil that oxidizes or carbonizes in that environment leaves deposits on the rotors and fouls the separator. A stable naphthenic mineral oil holds up here, and a wax-free base keeps the oil flowing back from evaporators running as cold as -35°C to -10°C. If your plant also runs R134a, R410A, R404A, or R32 equipment, treat it separately. Those HFC and HFO systems need POE or PVE oil, so they call for wholesale POE refrigeration oil from a POE refrigeration oil manufacturer, not an ISO VG 100 mineral grade. ISO VG 100 mineral oil belongs to the ammonia, R22, R290, and R600a side of the plant. The ammonia machine on mineral oil and the R410A chiller next door are two different lubrication problems, even when they sit in the same room.
Flash point and pour point mark the two ends of the window your oil has to survive. Flash point tells you how the oil behaves when the compressor is hot; pour point tells you how it behaves when the evaporator is cold. Between them they cover most of what an ammonia screw compressor goes through in a season.
ISO VG 100 earns its place in large ammonia screw compressors because thick-film lubrication, sealing, and heat removal all depend on viscosity. A wax-free naphthenic mineral base also handles ammonia's immiscibility and cold evaporators without drama. What decides whether it suits your machine is the combination of rotor size, discharge temperature, evaporating temperature, and how clean the system is. If your R717 screw compressor runs 100 to 300 mm rotors with normal discharge heat and evaporating temperatures between -35°C and -10°C, this is the right grade family. If the circuit is heavily contaminated or acidified, plan a proper drain and clean rather than a straight top-up. If you buy wholesale refrigeration oil for plant inventory, match the grade to those operating conditions and confirm the compressor model with a refrigeration oil manufacturer before ordering.
A: Yes. ISO VG 100 is the standard grade for large ammonia screw compressors, and QISHANR 5GS covers R717 systems with rotor diameters of 100 to 300 mm and evaporating temperatures from -35°C to -10°C. The heavy viscosity holds the bearing film, the wax-free naphthenic base keeps oil returning from cold evaporators, and the mineral chemistry is a natural match for ammonia, which does not dissolve mineral oil.
A: They bracket the working window. A 190°C COC flash point gives real headroom above the 80°C to 120°C discharge temperatures of a water-cooled screw machine and the peaks created by hot weather or a fouled condenser. A -30°C pour point keeps the oil fluid through the -35°C to -10°C evaporating range, so it returns from the evaporator instead of thickening or forming wax.
A: No. HFC and HFO refrigerants such as R134a, R410A, R404A, and R32 need POE or PVE oil, which mixes and returns with those refrigerants. Mineral oil is not recommended for those circuits. Keep ISO VG 100 mineral oil for mineral-compatible systems like R717, R22, R290, and R600a, and confirm the refrigerant and compressor model before ordering.
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