Ammonia Refrigeration
Ammonia refrigeration compressor lubricants are mineral, synthetic-blend, or polyalphaolefin (PAO) fluids selected for industrial systems that run on ammonia (R717). Ammonia holds low miscibility with mineral and PAO lubricants. Oil separation, carryover control, low-temperature fluidity, and operating viscosity govern lubricant selection.
Ammonia delivers high thermodynamic efficiency and carries zero ozone-depletion and zero global-warming potential. Large industrial refrigeration systems use ammonia for cold storage, food processing, freezing, beverage production, and process cooling.
NEXT Lubricants produces OEM-approved ammonia compressor lubricants for screw and reciprocating compressors. The range covers mineral and synthetic grades for standard refrigeration, low-temperature service, and continuous-duty installations.
For the full chemistry, diluted-viscosity, and low-temperature comparison, see How to Select an Ammonia Compressor Lubricant: HTMO vs PAO
Low miscibility does not mean low solubility. Ammonia dissolves into an ISO VG 68 mineral oil at approximately 5% by mass at 70 °C (158 °F) and 30 bar (435 psi), reducing operating viscosity to roughly 8 cSt.
The working minimum is 10 cSt at the lubrication point—measured on the diluted lubricant at operating temperature, not on the fresh ISO grade defined at 40 °C (104 °F).
Pour point does not predict low-temperature behavior. Two ammonia lubricants can share a −42 °C (−44 °F) pour point yet differ by more than 25% in measured viscosity at −35 °C (−31 °F).
Lubricant reaching the evaporator insulates the heat-transfer surface. Published R717 research shows heat-transfer coefficients falling at oil concentrations between 0.1% and 1%.
Polyol esters (POEs) react chemically with ammonia to form amides, viscous material, and sludge. POE contamination must be excluded from R717 circuits.
Flooded systems separate and drain the lubricant; direct-expansion systems require it to return with the refrigerant. This requires a miscible grade, typically specified one ISO viscosity grade higher.
How Ammonia Refrigeration Works and the Compressor's Role
An ammonia refrigeration system removes heat by evaporating liquid R717 at low pressure and then rejecting that heat after the ammonia vapor has been compressed and condensed at a higher pressure. The refrigerant subsequently passes through an expansion stage and returns to the evaporator to repeat the cycle.
The compressor elevates low-pressure ammonia vapor to the pressure needed for condensation and heat rejection. Industrial installations typically employ rotary screw or reciprocating compressors in single-stage, two-stage, booster, or economized configurations, depending on system capacity and the desired temperature level.
The lubricant safeguards bearings, rotors, cylinder walls, and other moving parts, while also aiding in sealing, cooling, and reliable oil-system operation. Its viscosity and condition influence compressor reliability, and its separation and carryover behavior can impact the broader refrigeration system.
Cold Storage & Distribution
Large-scale cold stores and temperature-controlled distribution centers use ammonia refrigeration to maintain stable low temperatures across high-capacity facilities operating under continuous load.
Food Processing & Freezing
Food processing plants, blast freezing tunnels, and freezing spirals rely on ammonia refrigeration for rapid product freezing and precise temperature control throughout continuous production operations.
Brewery, Dairy & Beverage Production
Ammonia refrigeration supports fermentation temperature control, pasteurization chilling, and cold conditioning in brewery, dairy, and beverage production environments.
Industrial & Process Cooling
Chemical, petrochemical, and industrial manufacturing facilities use ammonia refrigeration where large cooling capacities, low evaporating temperatures, or precise process temperature control are required.
Ice Production and Ice Rinks
Industrial ice plants and ice-rink refrigeration systems use ammonia for efficient centralized cooling and dependable operation across large evaporator loads.
Lubrication Considerations for Ammonia Refrigeration
Ammonia refrigeration places distinct demands on compressor lubricants compared to systems using HFC, HFO, or hydrocarbon refrigerants. Key considerations include low refrigerant–oil miscibility, oil separation, low-temperature behavior, operating viscosity, and resistance to thermal degradation.
Low Miscibility, Oil Separation, and Carryover
Ammonia has very low miscibility with mineral and PAO lubricants, and the lubricant is denser than liquid ammonia. Oil escaping the compressor settles at the bottom of vessels rather than travelling with the refrigerant, which is why ammonia plants are built around separators, oil pots and drain points. Accumulated oil insulates the evaporator surface — published R717 work shows heat transfer falling at oil concentrations between 0.1 % and 1 %.
Low miscibility is not low solubility. Measured data shows ammonia dissolving into an ISO VG 68 mineral oil at around 5 % by mass at 70 °C and 30 bar, cutting operating viscosity to roughly 8 cSt. Selection must therefore be made against the delivered viscosity at the lubrication point — a working minimum of 10 cSt — not against the fresh ISO grade.
Low-Temperature Fluidity
Industrial R717 systems may operate below −40 °C evaporating. The lubricant does not see that temperature inside the compressor, but oil reaching low-side vessels must stay fluid enough to drain — and oil that will not drain accumulates exactly where it does the most damage to heat transfer.
Scanning Brookfield viscosity under ASTM D5133 predicts this; pour point does not. Pour point records where flow stops in a test jar, and two ammonia lubricants can share a published pour point while differing by more than 25 % in measured viscosity at −35 °C. Evaluate the coldest temperature the lubricant encounters, including shutdown and start-up, against measured low-temperature viscosity.
Thermal and Oxidation Stability
High compression ratios, low evaporating temperatures, and demanding continuous duty can expose the lubricant to elevated discharge and oil temperatures. Thermal and oxidation stability impact oil life, viscosity retention, and resistance to sludge, varnish, and deposit formation.
Synthetic-blend and PAO lubricants are particularly beneficial where very low temperatures, elevated oil temperatures, or extended service intervals exceed the practical operating range of conventional mineral oil.
Operating Conditions Affecting Ammonia Lubricant Selection
- Compressor Type and OEM Requirements Screw or reciprocating, and the manufacturer's minimum viscosity at the lubrication point together with the temperature it applies at.
- Evaporating and Condensing Conditions Evaporating temperature sets the low-temperature requirement; condensing pressure sets how much ammonia dissolves into the lubricant.
- Oil-Supply, Injection and Separator Temperature Where delivered viscosity is actually assessed. Usually the lowest of the operating temperatures, and the one most often omitted from an enquiry.
- Lowest Temperature Encountered by the Oil Normally in a low-side vessel rather than in the compressor, and it decides whether accumulated oil will drain.
- Duty Cycle and Maintenance Objectives Continuous duty, target drain interval and the interval between site visits, which together decide whether oxidation life is worth paying for.
Operational Benefits of Correct Ammonia Lubricant Selection
- Reduced Oil Carryover and Lubricant Consumption Helps reduce oil losses and the need for frequent lubricant top-ups.
- Reduced Unplanned Downtime Helps prevent lubrication-related wear, overheating and unexpected compressor shutdowns.
- Extended Component Life Maintains protective film strength to reduce wear on bearings, rotors, cylinders and seals.
- More Consistent Compressor Efficiency Supports effective lubrication and sealing without creating excessive viscous resistance.
- Longer and More Predictable Service Intervals Improves resistance to dilution, oxidation and contamination for more controlled maintenance planning.
Recommended NEXT Ammonia Refrigeration Compressor Lubricants
The following products cover standard industrial R717 refrigeration, low-temperature operation, and demanding continuous-duty installations. Final selection should be confirmed against the compressor requirements and actual operating conditions.
NEXT 717-68
Hydrocracked Mineral Ammonia Refrigeration Lubricant
Base Oil: Mineral
ISO Range: 68
View Product →NEXT 717-68-XLT
Synthetic Blend Ammonia Refrigeration Lubricant
Base Oil: PAO/Mineral
ISO Range: 68
NEXT 717-68-SYN
Synthetic PAO Ammonia Refrigeration Lubricant
Base Oil: PAO
ISO Range: 46 & 68
NEXT 717-100-XLT
Semi-Synthetic Ammonia Heat Pump Lubricant
Base Oil: PAO/Mineral
ISO Range: 100
Find Equivalent Ammonia Compressor Lubricants
Use the NEXT cross-reference database to identify alternatives to commonly used ammonia refrigeration compressor oils. Cross-reference recommendations consider lubricant chemistry, viscosity, compressor type, and application rather than product name alone.
Our technical team can help identify the right product.
Lubricant Selection, Technical Support and Compatibility Documentation
NEXT combines application knowledge, laboratory data and an extensive internal cross-reference database to support lubricant selection, conversions and compressor troubleshooting.
Depending on the application, we can provide:
- Application-Specific Product Recommendations Lubricant recommendations based on gas or refrigerant composition, compressor design, operating conditions and current performance issues.
- Lubricant Cross-Referencing Identifies suitable NEXT alternatives by comparing base-oil chemistry, viscosity, application, specifications and operating requirements.
- Compatibility and Conversion Documentation Provides chemistry comparisons, mixture-test data, material compatibility, flushing requirements and top-off or changeover guidance.
- Dilution Data and PVT Graphs Shows how gas or refrigerant concentration, pressure and temperature affect lubricant dilution, density and operating viscosity.
- Troubleshooting and Root-Cause Support Supports investigations into foaming, oil carryover, dilution, deposits, corrosion, high lubricant consumption and reduced oil life.
What type of oil is used in ammonia refrigeration compressors?
Industrial ammonia systems run on hydrotreated mineral oil, polyalphaolefin (PAO), or blends of the two. Mineral grades cover conventional flooded refrigeration at evaporating temperatures above roughly −35 °C. PAO grades cover low evaporating temperatures, high discharge temperatures and extended drain intervals. Blends sit between the two where full PAO is not justified.
Direct-expansion systems are the exception and require an ammonia-miscible polyalkylene glycol (PAG) instead, because they depend on the lubricant returning with the refrigerant.
The deciding inputs are the compressor type and OEM viscosity requirement, the evaporating temperature, the measured discharge temperature, and the lowest temperature the lubricant reaches anywhere in the system — which is usually not inside the compressor.
Is ammonia really insoluble in refrigeration oil?
Incorrect, and this is one of the most persistent errors in the field.
Measured pressure-volume-temperature work puts ammonia solubility in an ISO VG 68 Group II mineral oil at approximately 5.2 % by mass at 70 °C and 30 bar, with viscosity falling to about 8.09 cSt. A PAO at the same conditions carries about 4.1 % and delivers 9.66 cSt.
Both sit at or below the 10 cSt working minimum. The practical consequence: an ISO VG 68 lubricant in an ammonia compressor is not delivering ISO VG 68 performance, and the higher the condensing pressure, the further it falls. This is why ammonia heat pumps commonly move to ISO VG 100.
Why is pour point a poor way to compare ammonia lubricants?
Because pour point records the temperature at which a sample stops flowing in a test jar. It says nothing about how viscous the fluid became on the way down, and the test has known repeatability limits.
Two ISO VG 68 ammonia lubricants can carry identical published pour points of −42 °C and differ by more than 25 % in measured viscosity at −35 °C. Across a group of commonly used products, the ranking by pour point does not match the ranking by measured low-temperature viscosity.
The comparable measurement is scanning Brookfield viscosity under ASTM D5133, which reports actual centipoise as the sample cools. It matters because a lubricant that thickens in a low-temperature vessel drains slowly or not at all, so it accumulates exactly where it does the most damage to heat transfer.
NEXT publishes measured Brookfield data rather than pour point alone when comparing ammonia grades.
What actually happens when lubricant accumulates in an ammonia evaporator?
It insulates the heat transfer surface, and the cost appears as compressor run hours rather than as an oil problem.
Because ammonia has very low miscibility with mineral and PAO lubricants — and because the lubricant is denser than liquid ammonia — anything escaping the separator settles as a separate layer at the bottom of vessels and evaporators rather than circulating back.
Published work on R717 in an 8 mm tube shows tube-side heat transfer coefficients falling at oil concentrations between 0.1 % and 1 %, with the effect strongest in annular flow. Earlier work recorded a 30 % reduction in heat transfer coefficient from an oil film. It does not take much accumulation before a plant is either losing capacity or running colder suction temperatures to compensate.
The controls are separator performance, reliable draining of oil pots and low points, and a lubricant fluid enough at low temperature to actually drain when the valve is opened.
Can polyol ester (POE) be used with ammonia?
No. This is one of the few absolutes in compressor lubrication.
Ammonia attacks the ester bond and depolymerizes POE, producing solids, viscous residues and sludge that foul heat transfer surfaces and can block orifices and expansion devices.
It matters beyond product selection in one specific case: in an ammonia/CO₂ cascade the CO₂ side commonly runs POE, and the CO₂ circuit normally sits at the higher pressure — so a cascade heat exchanger leak carries ester contamination toward the ammonia circuit rather than away from it. That belongs on the design review checklist, not only on the lubricant order.
What changes when converting from a naphthenic oil?
The seals, and it catches people out because it has nothing to do with chemical compatibility.
Naphthenic oils swell elastomers. A plant that has run one for years has a seal population that has been swollen for that entire time. Moving directly to a highly refined hydrotreated mineral or PAO can shrink those seals and produce leaks on a system that was tight the week before.
The answer is a seal-conditioned grade for the transition rather than a different chemistry. NEXT 717-68-SC carries seal conditioners for exactly this case, and it is the grade NEXT routes every naphthenic replacement to.
Expect a second effect at the same time: modern hydrotreated base stocks will lift deposits the naphthenic oil left behind. That is desirable over the life of the system and a filter problem in the first weeks, so monitor oil and suction filters closely after the change.
Can another brand's ammonia compressor oil be replaced without flushing?
In most cases within the same chemistry family, yes — and NEXT holds documentation rather than an opinion on it.
NEXT tests its ammonia grades against widely used competitor products at 80/20, 50/50 and 20/80 mixture ratios, covering chemical compatibility, physical properties and foaming tendency. Products that pass receive a formal substitution statement, which confirms that the NEXT product can be used for top-up without draining the system, that performance will be equivalent or better, and that no equipment or operating condition changes are required.
Statements currently exist for ten commonly used ammonia lubricants across hydrotreated mineral, naphthenic and PAO chemistries.
Two limits apply. Naphthenic products route to the seal-conditioned grade for the reason above. And an ammonia-miscible PAG for direct-expansion duty is not compatible with hydrocarbon lubricants in either direction — that conversion requires a full drain, flush and filter change.
Ask for the statement covering the product currently in the machine before planning the changeover.