How to Effectively Cool 1L Plastic Bottles in a Compact Beverage Production Line

Cooling beverages efficiently is a crucial step in modern bottling and beverage production lines. Maintaining product quality, ensuring food safety, and meeting production targets all depend on an effective cooling system. Recently, a Thai client faced a challenge with cooling 1-liter plastic bottles from 75°C down to 65°C in a high-speed production line with a capacity of 7,000 bottles per hour. The available tunnel for cooling measured 5.8 meters in length, 2.2 meters in width, and 1.7 meters in height, and the production facility space was limited to just 6 by 4 meters. Additionally, the client wanted to use water for spray cooling without adding any antifreeze agents, since the product was a consumable beverage. This blog will summarize the considerations, challenges, and solutions for achieving this goal, including the regulatory context of refrigerants in Thailand.

Understanding the Cooling Challenge

The first step in evaluating the cooling process is calculating the heat that needs to be removed from the beverage. Each 1-liter plastic bottle contains roughly 1 kilogram of liquid, assuming the liquid’s specific heat capacity is similar to water, approximately 4.18 kJ/kg·°C. To cool the liquid from 75°C down to 65°C, the required heat removal can be calculated using the formula:

Q=m⋅c⋅ΔT

Where:

• m is the mass flow rate (kg/s)
• c is the specific heat (kJ/kg°C)𝑇
• ΔT is the temperature change (°C)

Liquid mass per bottle: 1 L ≈ 1 kg

Liquid initial temperature: 75°C → Target temperature: 65°C

Production capacity: 7,000 bottles/hour

Specific heat capacity of water: 𝑐 c = 4.18 kJ/kg\cdotp°C

Time conversion: 7,000 bottles/hour → Bottles per second:

7000/3600 ≈ 1.944 bottles/s ≈ 1.944 kg/s

Q_per second​=1.944⋅4.18⋅10≈81.3 kJ/s=81.3 kW

For a production rate of 7,000 bottles per hour (≈1.944 kg/s), the required cooling capacity is approximately 81 kW. This calculation represents the ideal heat removal needed under perfect conditions.

Constraints: Space and Tunnel Length

In this case, the facility space was limited to 6 × 4 meters, and the cooling tunnel could not be extended beyond its current length of 5.8 meters. The short tunnel length presented a challenge: with a conveyor speed corresponding to 7,000 bottles per hour, the approximate residence time of each bottle inside the tunnel is around 30 seconds.

Given this limited exposure time, the design of the cooling system had to focus on maximizing heat transfer efficiency. Traditional approaches, such as simply increasing tunnel length or slowing down the production line, were not feasible due to space and operational constraints.

The Limitations of Using 25°C Water

A preliminary idea might be to use 25°C tap water as the cooling medium. However, calculations and experience show that using water at this temperature would result in only a partial temperature drop. With a 30-second residence time and a 40% heat transfer efficiency, the liquid temperature might only decrease by 5–7°C. This would lower the 75°C liquid to approximately 68–70°C — insufficient to meet the target of 65°C.

Transition to Low-Temperature Cooling

To achieve the desired 10°C drop within the limited tunnel length, the solution was to use low-temperature water at 3–5°C. By lowering the water temperature significantly, the thermal gradient between the liquid and the cooling water increases, which directly enhances heat transfer rates.

Empirical data and heat transfer calculations suggest that with 3–5°C water, a 30-second residence time in the tunnel is sufficient to reduce the liquid temperature from 75°C down to the target 65°C. This ensures the beverage is safely cooled without extending the tunnel or slowing the production line.

Considerations for Cold Water Circulation

Using water at such low temperatures introduces additional considerations:

1. Avoiding Freezing: Directly using water at 0°C could risk ice formation in the spray system. Since the beverage cannot tolerate antifreeze additives, the water temperature should be maintained at 3–5°C to prevent freezing while still achieving effective cooling.
2. Spray Efficiency: High-efficiency nozzles, such as fine mist or fan-type designs, are critical. These maximize surface coverage and ensure each bottle receives adequate cooling.
3. Sufficient Water Flow: The circulation system should provide a flow rate 3–5 times the liquid flow rate, ensuring that cold water temperature remains stable during operation.
4. Temperature Control: A PLC-based control system with temperature sensors monitors the water temperature and adjusts pump speed or cooling output to maintain a consistent 3–5°C range.

Selecting the Appropriate Chiller

We discussed a series of customer requirements with our refrigeration unit supplier and found that a 30HP air-cooled chiller could meet our requirements. The supplier confirmed that their 30 HP air-cooled chiller is rated for a cooling capacity of 83 kW under standard operating conditions. And our system design also counts in several important ways:

• Large Water Buffer: The integrated 10 m³ reservoir acts as a thermal buffer, absorbing heat and smoothing out fluctuations during continuous operation.
• Continuous Circulation: Water is constantly circulated between the chiller, spray system, and tank, ensuring steady thermal exchange.
• Low Inlet Water Temperature: By maintaining water at 3–5°C, the thermal gradient is maximized, boosting effective cooling during the short 30-second residence time.
• Efficient Layout: With a footprint of only 2.4 × 2 m, the chiller fits easily within the facility’s 6 × 4 m available space.

Taken together, these design choices allow the system to deliver the required cooling performance in practice. While the theoretical load estimate provides a safety margin, the supplier’s 83 kW rated capacity combined with thermal buffering and optimized spray efficiency is sufficient for reliably cooling 7,000 one-liter bottles per hour from 75°C down to 65°C.

Regulatory Considerations for Refrigerants in Thailand

Since the client is located in Thailand, it is important to consider local regulations regarding the use of refrigerants such as R-22, R-134a, or other HFCs/HCFCs:

• R-22 Phase-Out:Thailand follows the Montreal Protocol phase-out schedule for ozone-depleting substances like R-22. New equipment using R-22 is restricted, and servicing with R-22 may be limited.
• HFC Alternatives:Most modern chillers now use HFCs such as R-134a, R-410A, or natural refrigerants like R-290 (propane) or R-717 (ammonia) for industrial applications. These are generally allowed, but local registration and certification may be required.
• Compliance:When specifying chillers for Thai production lines, it is important to confirm with the supplier that the refrigerant is legally permitted and environmentally compliant. Using a compliant refrigerant ensures long-term operation, avoids fines, and facilitates maintenance and spare parts availability.

In practice, for beverage production lines, most wind-cooled chillers operating at 3–5°C use HFCs like R-134a, which are generally accepted in Thailand, but confirming with both the supplier and local authorities is essential.

System Design Recommendations

For compact beverage production lines with similar constraints, the following design elements are recommended:

• Low-Temperature Wind-Cooled Chiller: Maintain 3–5°C water temperature to avoid freezing without adding antifreeze agents.
• Large Buffer Water Tank: A 10 m³ tank or similar provides thermal inertia to stabilize water temperature during high-speed operation.
• High-Efficiency Spray Nozzles: Ensure full coverage of bottles to maximize heat transfer within short residence times.
• PLC-Based Temperature Control: Monitor and regulate water temperature, flow rate, and chiller operation automatically.
• Sufficient Circulation Flow: Flow rate of cold water should be at least 3–5 times the liquid flow rate to prevent rapid temperature rise in the tank.
• Regulatory Compliance: Verify that the chiller refrigerant is approved for use in Thailand, meeting local environmental and safety regulations.
• Compact Layout: Ensure the chiller, tank, and tunnel fit within available facility space without compromising workflow.

Conclusion

Cooling beverages in high-speed bottling lines with limited space and tunnel length is challenging but entirely feasible with proper system design. Key takeaways from this project include:

• Using standard 25°C water is insufficient for high-speed cooling; low-temperature water at 3–5°C is necessary.
• Wind-cooled chillers with large buffer tanks can meet high thermal loads without freezing risk, even if the chiller HP seems modest.
• Spray efficiency, water flow, and precise temperature control are as critical as chiller power in achieving desired cooling results.
• Compact, well-designed systems allow high throughput without requiring larger tunnels or extended floor space.
• For clients in Thailand, refrigerant compliance is a crucial consideration; modern HFC-based chillers like R-134a are generally acceptable.

In summary, for beverage producers facing limited floor space and high production speeds, a combination of low-temperature water, efficient spray cooling, a properly sized wind-cooled chiller with a buffer tank, and regulatory-compliant refrigerants is the optimal solution for achieving precise cooling of 1-liter plastic bottles from 75°C to 65°C. This approach ensures product quality, maintains safety, and fits within tight facility constraints while complying with local environmental regulations.