Freon Chiller Cleaning & Water Treatment

1. Scaling Mechanism and Hazards of Freon Chillers

Freon chillers are the core cooling source of central air-conditioning systems, classified by compressor type into centrifugal, screw and reciprocating. Their heat-exchange components are the evaporator and condenser: chilled water (7°C/12°C) exchanges heat with refrigerant in the evaporator, while cooling water (32°C/37°C) carries away condensing heat in the condenser. Because both operate on the water side, poor water quality inevitably leads to scale on the inner tube walls.

The condenser (cooling-water side) is the most prone to scaling. Cooling water is an open loop in direct contact with the atmosphere; airborne dust and microorganisms enter continuously, while evaporation concentrates dissolved salts. When calcium carbonate and magnesium carbonate exceed their saturation solubility, scale precipitates on the tube walls. Algae and bacteria also form bio-slime, further reducing heat-transfer efficiency.

The evaporator (chilled-water side) is a closed loop with lighter scaling, but long-term operation still accumulates rust, silt and microbial by-products. Carbonate scale can also deposit when make-up water volume is large or water is hard.

The hazards of scaling are systematic:

• Higher condensing temperature: scale thermal conductivity is only 0.5~1.0 W/(m·K), far below copper tube (~384 W/(m·K)); 0.5 mm of scale can raise condensing temperature by 2~3°C, increasing compressor discharge pressure.
• Reduced cooling capacity: lower heat-exchange efficiency directly cuts chiller capacity and weakens terminal cooling.
• Higher energy consumption: every 1°C rise in condensing temperature lowers COP by about 3%.
• Shorter equipment life: under-deposit corrosion thins copper tubes, potentially causing tube perforation and refrigerant leakage.

2. Key Cooling-Water Management Indicators

Preventing chiller scaling fundamentally relies on water management. Open-loop cooling water systems should control the following indicators:

Daily management should pair corrosion/scale inhibitors (e.g., HEDP and Sodium Molybdate blends) with biocides, along with regular blowdown and make-up water. Water treatment only slows scaling and cannot eliminate it, so periodic cleaning remains essential maintenance.

3. Chemical Cleaning Solution

3.1 Cleaning Agent Selection

Chiller condensers are mostly copper-tube. The cleaning agent must balance descaling efficiency and copper protection. Sulfamic Acid is recommended as the primary agent — it dissolves carbonate scale effectively with low corrosion on copper. Combined with BTA (benzotriazole) copper inhibitor, it protects the tubes well. For evaporators (copper or steel tubes), Sulfamic Acid or Citric Acid formulas with a suitable inhibitor are used.

3.2 Cleaning Process

Circulation cleaning is applied — the cleaning solution is pumped into the heat exchanger through temporary piping and circulated within the tube side:

1. Pre-inspection and isolation: close relevant valves and confirm the condenser/evaporator is isolated from the refrigeration system.
2. Prepare cleaning solution: Sulfamic Acid 5%~10%, with inhibitor and penetrant, at 40~50°C.
3. Circulate: circulate the solution for 4~8 hours, monitoring pH and iron ion concentration to judge the endpoint.
4. Drain and rinse: drain the spent solution and rinse with clean water to neutral.
5. Passivation: apply passivator to form a protective film on metal surfaces.
6. Acceptance: inspect inner tube cleanliness and hydro-test for leaks.

For sites that cannot shut down, online (no-shutdown) cleaning is available: install a bypass connection on the condenser inlet/outlet pipes and connect a temporary cleaning pump set, cleaning while the chiller keeps running to minimize cooling disruption.

4. Engineering Case

Equipment: A 1,200-ton centrifugal Freon chiller in the central plant of a commercial complex, with a shell-and-tube copper condenser, running 6 years without deep cleaning. The cooling-water side was heavily scaled, condensing pressure was high, and the unit triggered high-pressure alarms.

Inspection: Scale thickness about 1.5 mm on the inner tube walls, mainly calcium carbonate and bio-slime; cooling-water cycles of concentration had long exceeded the limit (about 6).

Solution: Sulfamic Acid circulation cleaning with BTA copper inhibitor, 6 hours, followed by passivation.

Results:

After cleaning, the high-pressure alarms disappeared and capacity recovered, with estimated annual electricity savings of about RMB 120,000. The case shows that regular chemical cleaning combined with water management is the most economical way to keep Freon chillers efficient.

5. Summary and Recommendations

Freon chiller scaling results from the combined effect of water quality and operating conditions. Daily water management (controlling cycles of concentration, dosing corrosion/scale inhibitors and biocides) slows scaling but cannot replace periodic cleaning. Recommendations:

• Clean open cooling-water systems chemically at least once a year, or every 8~10 months in severe-scaling areas.
• Clean closed chilled-water systems every 2~3 years.
• Use Sulfamic Acid with BTA inhibitor to balance descaling and copper protection.
• Passivate promptly after cleaning to extend the cleaning-free interval.

6. FAQ

Q1：How often should a Freon chiller be cleaned?

Open cooling-water chillers should be chemically cleaned at least once a year, or every 8~10 months in severe-scaling areas; closed chilled-water systems every 2~3 years. The interval depends on water hardness, cycles of concentration and operating conditions.

Q2：What agents are used for chiller cleaning? Will copper tubes corrode?

Sulfamic Acid is recommended as the primary agent, combined with BTA (benzotriazole) copper inhibitor. Sulfamic Acid dissolves carbonate scale effectively with low copper corrosion, and BTA protects the tubes — balancing descaling and copper protection.

Q3：Can a chiller be cleaned without shutdown?

Yes. Online (no-shutdown) cleaning adds a bypass connection on the condenser inlet/outlet pipes and a temporary cleaning pump set, cleaning while the chiller keeps running to minimize cooling disruption.

Q4：How much cooling capacity can be recovered after cleaning?

In a 1,200-ton centrifugal chiller case, condensing temperature dropped from 42.5°C to 37.8°C, capacity recovered from 78% to 95% of rated, COP rose from 4.2 to 5.3, saving about RMB 120,000 per year.

Q5：Which water-quality indicators should be controlled?

Control pH (7.0~9.0), cycles of concentration (3~5), total hardness (≤300 mg/L), chloride (≤250 mg/L), turbidity (≤10 NTU) and total bacteria (≤10⁵ CFU/mL), with corrosion/scale inhibitors and biocides plus regular blowdown.

All acceptance criteria follow GB/T 25146-2010 Quality acceptance specifications of chemical cleaning for industrial equipment.

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