Auxiliary equipment in refrigeration system at seafood plants, food plants and frozen storage warehouses face the pressure of 24/7 operation under severe temperature and pressure conditions. Liquid slugging, oil carried into the evaporator, air entering the system and unstable pressure are the leading causes of unplanned shutdowns, compressor damage and falling COP. Auxiliary equipment in a refrigeration system is everything outside the compressor, condenser and evaporator
An industrial NH3 or Freon refrigeration system typically integrates 9-12 groups of auxiliary equipment across 4 positions in the cycle: the discharge line, the liquid line, the suction line, and the intermediate/operational support group. This article analyses the function, installation position and selection criteria for each item of auxiliary equipment, based on 20 years of design, manufacturing and installation experience at Tan Long on seafood and food projects nationwide.
What is auxiliary equipment in a refrigeration system?
Auxiliary equipment in a refrigeration system is everything outside the 3 main items of the cycle: the compressor, the condenser and the evaporator. Although it does not take part directly in the four processes of compression, condensing, expansion and evaporation, auxiliary equipment keeps the system operating safely, stably and efficiently.
Definition and the boundary with main equipment
Auxiliary equipment is all supporting equipment outside the compressor, condenser and evaporator. The distinction lies in the role within the refrigeration cycle: main equipment directly produces the cooling effect, while auxiliary equipment only supports and optimises operation. “Auxiliary” does not mean “unimportant”; it simply denotes position within the cycle.
| Criteria | Main equipment | Auxiliary equipment |
|---|---|---|
| Role in the cycle | Takes direct part in the 4 processes | Supports, protects, optimises |
| Number of groups | 3 fixed groups | 9-12 groups depending on design |
| Mandatory | Always | Depending on system requirements |
The role of auxiliary equipment in system operation
Auxiliary equipment serves 3 core roles: protecting the main equipment, stabilising the cycle and raising the COP. A liquid separator removes remaining liquid refrigerant droplets to stop liquid slugging destroying the compressor suction valves and pistons. A high-pressure receiver holds pressure steady as the cooling load varies, ensuring the expansion valve receives 100% liquid refrigerant. Filters and filter driers
Classifying refrigeration auxiliary equipment by position in the cycle
Auxiliary equipment in a refrigeration system is divided into 4 groups by position in the cycle: the discharge line, the liquid line, the suction line, and the intermediate/operational support group. Classifying by cycle position helps the design engineer place equipment accurately on the P&ID drawing and select specifications matched to the pressure and temperature at each point.
Auxiliary equipment on the discharge line
The discharge line is the pipe run from the compressor outlet to the condenser, at a high pressure of 0.8-1.8 MPa (8-18 bar) and a temperature of 70-120°C. The oil separator is fitted here, and a non-condensable gas purger branches off the top of the condenser. Compressed vapour leaving the compressor carries lubricating oil at 18-25 m/s, so the oil must be separated
Auxiliary equipment on the liquid line
The liquid line runs from the condenser outlet to the expansion valve, with refrigerant in the high-pressure liquid state. Pressure is held at ≤ 1.8 MPa and temperature at 30-40°C depending on the heat rejection medium. Auxiliary equipment here comprises the high-pressure receiver, mechanical filter, filter drier, sight glass, and a heat recovery vessel on Freon systems. The high-pressure receiver stabilises
Auxiliary equipment on the suction line
The suction line runs from the evaporator outlet to the compressor, at a low pressure of 0.05-0.5 MPa and a temperature of -40 to -10°C. The liquid separator, low-pressure receiver and controlled-level liquid separator are fitted here. Because they work at sub-zero temperatures, these vessels must be insulated with 150-200 mm of polyurethane, with a protective stainless steel outer cladding. The core objective at this position
Intermediate and operational support auxiliary equipment
The intermediate group applies to two-stage compression systems; the operational support group applies across the whole system. The intercooler cools the first-stage discharge vapour and subcools the high-pressure liquid before the expansion valve, and is mandatory on systems with an evaporating temperature below -30°C. Support equipment includes the oil receiver, solenoid valves, safety relief valves, check valves
Function and installation position of each item of auxiliary equipment
Among the 12 common groups of auxiliary equipment, the oil separator, liquid separator and high-pressure receiver play the key roles in industrial NH3 refrigeration systems. The sections below cover each group in descending order of priority, with specifications and operating principles drawn from refrigeration engineering texts and real installation experience.
Oil separators and oil recovery vessels
The oil separator is fitted on the compressor discharge line to separate lubricating oil entrained in the gas and return it to the compressor crankcase. It works on 4 combined principles: an abrupt reduction in gas velocity from 18-25 m/s down to 0.5-1.0 m/s, redirection of the refrigerant flow through inclined baffles, a packing block or mesh screen to catch oil droplets, and cooling of the flow
The oil receiver collects oil from all the oil separators across the system to a single central drain point. A standard AC&R oil return arrangement comprises 3 parts: the oil separator, the oil receiver and a low-pressure float valve. When the oil level in the compressor crankcase falls, the float valve opens and oil returns to the compressor. The oil draining procedure requires the oil to be heated first
Liquid separators and controlled-level liquid separators
The liquid separator is fitted on the suction line upstream of the compressor to remove remaining liquid refrigerant droplets and prevent liquid slugging. A baffle-cone liquid separator for NH3 systems comprises a cylindrical shell in CT3 steel, cone baffles inclined 30° from horizontal, a design temperature of 50°C and a material corrosion allowance C = 2-3 mm. The whole vessel is insulated with polyurethane
A controlled-level liquid separator combines 2 functions: supplying flooded liquid feed to the evaporator and separating liquid droplets from the suction vapour returning to the compressor. It is common in freezing cabinets, block ice machines, flake ice machines and air blast freezers. The vessel carries a float valve limiting the maximum liquid level, a safety relief valve, a pressure gauge and inlet/outlet pipework. The liquid baffle plates are set at 30° with
High-pressure, low-pressure and circulation receivers
The three common types of refrigerant vessel are the high-pressure receiver (downstream of the condenser), the low-pressure receiver (suction line) and the circulation receiver (for pumped liquid feed). Under safety regulations, the high-pressure receiver must hold ≥ 30% of the evaporator volume on top-feed systems and ≥ 60% on bottom-feed systems. The maximum permitted operating liquid level is 50% of
| Receiver type | Installation location | Max pressure | Operating temperature |
|---|---|---|---|
| High stage | After the condenser | 1.8 MPa (18 bar) | -15 to +47°C |
| Low pressure | Suction line | 0.5 MPa (5 bar) | -40 to -10°C |
| Circulation | Low-pressure side, pumped liquid feed | 1.5 MPa (15 bar) | -50 to +40°C |
The high-pressure receiver is fitted with liquid level alarms at a maximum of 80% and a minimum of 20% of capacity, plus a non-condensable gas purging section. The low-pressure receiver is insulated with 150-200 mm of polyurethane and carries 3 protective float switches at maximum, medium and minimum levels.
Intercoolers and heat recovery vessels
The intercooler is used on two-stage compression refrigeration systems to cool the first-stage discharge vapour and subcool the high-pressure liquid before the expansion valve. The three common intercooler types are: the vertical type with a helical coil for NH3 and Freon, the horizontal type for small-capacity Freon systems, and the plate type for semi-hermetic compressors. The coil-type intercooler has the advantage that the oil
Heat recovery vessels are common on Freon systems to raise the COP, and are little used on NH3 systems because mineral oil decomposes easily at high temperature. Heat recovery equipment is normally sized to the system's liquid line and suction vapour line. To avoid condensation on the heat recovery vessel body and frosting on the suction line, engineers usually choose one size larger than the pipework.
Non-condensable gas purgers, filters and filter driers
The non-condensable gas purger vents gases that have entered the system, the filter retains mechanical debris, and the filter drier absorbs moisture in the refrigerant. Non-condensable gases accumulate at the top of the condenser, raising thermal resistance, so condensing pressure rises and efficiency
A filter drier is mandatory on Freon systems because the refrigerant is moisture-sensitive; water reacts to form acids that corrode the compressor and copper tubing. Filter drier cores typically use 3A or 4A molecular sieve, which adsorbs water molecules by molecular size. The mechanical filter retains iron and copper filings and solid debris from installation, protecting the expansion valve and compressor from
How to choose the right auxiliary equipment for an industrial refrigeration system
Auxiliary equipment is selected on 5 core criteria and must comply with Vietnam's pressure equipment safety regulations. The selection process starts from the system design brief, then cross-checks against refrigerant properties and conformity regulations.
Five core criteria when choosing auxiliary equipment
The five criteria are cooling capacity, refrigerant, maximum working pressure, operating temperature range, and material of construction. Each criterion answers a specific technical question, and together they form the complete specification for the auxiliary equipment.
| Criteria | Question to answer | Technical reference |
|---|---|---|
| Cooling capacity Q_0 | What is the peak cooling load in kW? | System design brief |
| Medium | NH3, R22, R404a, R134a hay R717? | Refrigerant properties, compatible materials |
| Maximum pressure | P_max ≥ 1.8 MPa for the high side? | QCVN 21:2015/BLDTBXH |
| Temperature range | Operating from -50°C to +47°C? | PU insulation of 50-200 mm required |
| Material | CT3 steel, 304 stainless or copper? | Refrigerant compatibility |
Important note: NH3 corrodes copper and copper alloys, so NH3 systems must use CT3 steel or stainless steel for all pressure equipment and pipework. Freon systems (R22, R404a, R134a) are compatible with both copper and steel.
Safety regulations applying to pressure vessels
High-pressure receivers, oil separators, liquid separators and intercoolers fall under the list of equipment with strict occupational safety requirements, per Circular 36/2019/TT-BLDTBXH. Regulation QCVN 01:2008/BLDTBXH on pressure vessel safety requires every pressure vessel to be inspected before first use and re-inspected every 3 years
Applying the right criteria and safety regulations keeps a project running stably for 10-15 years — which is why many contractors in the seafood and food sectors choose Tan Long as their primary manufacturer of auxiliary equipment.
Tan Long manufactures auxiliary equipment for industrial refrigeration systems
Tan Long Production pressure vessel, PLC control cabinet and SCADA control cabinet for industrial refrigeration systems, alongside main equipment such as evaporative condenser, refrigeration compressor and turnkey frozen cold storage. The company was founded in 2005, became a joint stock company in 2021, and has a manufacturing plant in Tay Ninh (formerly Long An) plus 20 years of combined engineering experience in industrial refrigeration. Tan Long successfully manufactured its first ultra-fast IQF freezing conveyor in 2011 and is now among Vietnam's top 5 companies in this field.
Notable projects Tan Long has designed and installed include: Frescol Tuna Vietnam in Nghe An (12,000 MT cold store, 6 blast freezing tunnels, 2 screw compressors, 2 condensers for the NH3 system), Lotte F&G Vietnam at Long Hau Industrial Park in Tay Ninh, Kyokuyo Vina Foods, CP Vietnam at Tan Phu Trung Industrial Park in Cu Chi, and Vietnam Clean Seafood at An Nghiep Industrial Park in Soc Trang. All pressure vessels
Frequently asked questions about refrigeration auxiliary equipment
Do small refrigeration systems need a full set of auxiliary equipment?
Small refrigeration systems do not need a full set of auxiliary equipment. Domestic refrigerators and split air conditioners usually omit a dedicated oil separator because so little oil circulates. Industrial systems from 50 kW upwards need the full 9-12 groups of auxiliary equipment to operate safely and durably.
How does auxiliary equipment differ between NH3 and Freon systems?
NH3 does not dissolve mineral oil, so NH3 systems need an oil separator, an oil receiver and a non-condensable gas purger. Freon systems (HFCs such as R134a and R404a) dissolve POE oil, so they need less dedicated oil separation equipment but must have a filter drier. NH3 corrodes copper, so all pressure equipment uses CT3 steel.
What is a liquid separator and how does it differ from an oil separator?
The liquid separator removes remaining liquid refrigerant droplets from the suction vapour; it is fitted on the compressor suction line, works at 0.05-0.5 MPa and is insulated with polyurethane. The oil separator removes lubricating oil from the discharge gas; it is fitted on the discharge line, works at a high pressure of 0.8-1.8 MPa and needs no insulation because its operating temperature is high at 70-120°C.
What types of refrigerant vessel are there in a refrigeration system?
Industrial refrigeration systems have 4 main types of refrigerant vessel: the high-pressure receiver downstream of the condenser, the low-pressure receiver on the suction line, the circulation receiver feeding liquid to the evaporator pump, and the recovery receiver that holds refrigerant during defrost or system repairs.
How main equipment differs from auxiliary equipment in a refrigeration system
Main equipment takes direct part in the 4 processes of the refrigeration cycle, while auxiliary equipment supports and optimises operation without directly producing the cooling effect. The compressor raises vapour from low to high pressure; the condenser turns high-pressure vapour into high-pressure liquid by rejecting heat to the environment; the expansion valve drops the pressure abruptly; the evaporator absorbs heat from the cold chamber to produce the cooling effect.
| Factor | Main equipment | Auxiliary equipment |
|---|---|---|
| Part in the cycle | Direct | Supporting |
| Mandatory for operation | Have | Depends on the system |
| Number of groups | 3 fixed | 9-12 depending on design |
| Typical examples | Compressor, condenser, evaporator | Oil separator, liquid separator, high-pressure receiver |
Contact Tan Long on hotline (+84) 933357058 (Mr. Thinh) or visit the contact page for advice on designing an industrial refrigeration system with all the main and auxiliary equipment matched to your project's capacity.
See also:
- Refrigeration system diagram, structure and detailed operating principle
- How does the refrigeration system leak test process work?
- Water Chiller Schematic Diagram: Detailed & Technically Accurate
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