Free-cooling air-cooled screw chiller

The free‑cooling air‑cooled screw chiller is an integrated outdoor‑mounted unit. Compared with conventional air‑cooled screw chillers, it is equipped with built‑in free‑cooling heat‑exchange coils. It uses ambient air as cold source and water/glycol solution as heat transfer medium. No cooling tower is required. Its intelligent control system automatically switches among three operating modes. It is widely applied in projects requiring year‑round continuous cooling, especially data centers and process cooling applications.

1. Working Principle (Three Auto‑switchable Operating Modes)

1. Compressor‑cooling Mode (High‑ambient‑temperature in summer)When outdoor temperature is high and the free‑cooling coil provides insufficient heat dissipation, the screw compressor starts up. The unit follows conventional air‑cooled chiller cycle: compression‑condensation‑throttling‑evaporation to produce chilled water at 7 °C. The compressor undertakes the full cooling load.
2. Mixed Cooling Mode (Transition seasons: spring & autumn)As outdoor temperature drops, both free‑cooling coil and compression system work simultaneously. The free‑cooling coil bears partial cooling load while the compressor supplements residual capacity. The compressor runs at reduced load for lower power consumption.
3. Full Free‑cooling Mode (Low‑temperature in winter)When outdoor ambient temperature is sufficiently low, the compressor is completely shut down. Outdoor cold air flows over free‑cooling coils driven by fans. Heat of chilled water is removed directly via glycol circulating loop with almost zero compressor power consumption, realizing “free cooling”.

Key point: The PLC controller triggers mode switching automatically based on outdoor temperature and chilled‑water temperature difference.Significant power saving can be achieved in cold seasons, especially for projects in northern regions.

2. General Technical Parameters (Industry Standard)

3. Advantages

1. High annual comprehensive energy efficiency: Compressor operation time is greatly reduced when free‑cooling is enabled in winter and transition seasons. Annual power‑saving rate can reach 30%‑60% in northern areas, ideal for non‑stop cooling applications.
2. Simplified system with zero cooling‑water consumption: Cooling towers and cooling‑water pumps are eliminated. Only antifreeze glycol is needed for chilled‑water loop, resulting in easy installation and construction.
3. Outdoor integral layout: Units can be placed directly on rooftops or outdoor platforms, saving civil‑engineering investment for mechanical rooms. Single‑/dual‑compressor configurations are available for operational redundancy.
4. Intelligent automatic mode switching: PLC automatically switches between compressor / mixed / full free‑cooling modes. Remote monitoring and fault alarm functions are supported for stable 7×24‑hour continuous operation, well‑suited for data‑center projects.
5. Wide operating‑condition adaptability: Stable operation down to ‑25 ℃ ambient temperature to satisfy continuous winter cooling demand in northern China.

4. Disadvantages

1. Larger overall footprint: Additional free‑cooling coils increase unit dimension and weight compared with standard air‑cooled screw chillers. Sufficient rooftop load‑bearing capacity and maintenance space are mandatory.
2. Glycol antifreeze required: Antifreeze solution must be filled into hydraulic circuit, raising initial investment. Regular inspection and replacement of glycol will increase maintenance cost.
3. Limited energy‑saving benefit in hot‑humid southern regions: In South China, outdoor temperature remains high in winter; annual full free‑cooling operating hours are limited, leading to longer pay‑back period.
4. Relatively high noise level: Multiple axial fans operate outdoors. Noise‑reduction measures are necessary for sites adjacent to residential areas.
5. Dust accumulation risk on coils: Outdoor fin‑and‑tube coils tend to collect dust. Regular cleaning is required to prevent degradation of free‑cooling heat‑exchange performance.

5. Applicable and Non‑applicable Scenarios

✅ Applicable scenarios‑ IDC data centers & computing rooms requiring 7×24‑hour year‑round cooling;‑ Continuous‑process cooling for electronics, pharmaceutical and chemical industries;‑ Northern and high‑altitude regions with cold winters targeting lower annual operating power cost;‑ Projects without mechanical room and forbidden to install cooling towers.

❌ Non‑applicable scenarios‑ Projects only requiring cooling in summer, no winter cooling demand;‑ Sites with insufficient rooftop load‑bearing capacity or no outdoor installation space;‑ Tropical / coastal South China where winter temperature stays high; low free‑cooling utilization hours result in poor economic return;‑ Noise‑sensitive locations without feasible noise‑reduction solutions.

6. Comparison with Similar Chiller Types

Precautions for Unit Use

Installation precautions

1. When lifting, positioning, and installing the unit, safety must be taken into account to prevent collisions and ensure the integrity of the equipment.

2. If the unit is installed outdoors, efforts should be made to avoid exposure to wind and rain (except for rainproof types), direct sunlight, or other heat sources that directly radiate; The computer room environment must be kept dry, clean, and ensure good ventilation, leaving space for unit maintenance and upkeep.

3. For air-cooled units, please ensure that there are no obstructions around the unit and reserve 1 meter of space; There is no obstruction within 2 meters of the top of the unit to ensure good ventilation.

4. It is recommended to install the unit on a strong and level ground, and install shock-absorbing rubber pads under the unit chassis to correct the level of the unit. If there are anchor bolts, they must be installed and fixed.

5. The circulating water pump used in conjunction with the unit should be selected and installed according to the data requirements such as water flow rate and water resistance required by the unit.

6. The water pump must be installed in front of the inlet of the unit, and it is recommended to install a filter at the inlet of the water pump to prevent foreign objects from entering the heat exchanger of the unit; If the unit is installed in areas with poor water quality, water treatment must be carried out first to avoid damage to the heat exchanger.  

7. It is recommended to install valves, water pressure gauges, thermometers, water flow switches, and other equipment for the water pipeline system connecting the unit, in order to facilitate the inspection and maintenance of the unit's daily operation.

8. To prevent air from being trapped in the water system, the air must be completely discharged before starting the compressor.

9. The chilled water pipeline must be insulated properly to avoid loss of cooling capacity, condensation, and freezing.

10. The weight of the system connection pipeline shall not be borne by the machine body. Rubber shock-absorbing flexible joints and gate valves shall be installed at the inlet and outlet of the unit to avoid vibration and facilitate maintenance.

11.When configuring wires for the unit, wires with slightly larger cross-sections (with margin) should be selected according to the power consumption, and reliable electronic control components and grounding power sources should be installed to prevent accidents such as overload and leakage.

12. As the unit is equipped with reverse phase and phase loss protection, attention must be paid to whether the line phase is correct during wiring installation. The unit cannot operate normally when the phase is misconnected or missing.    

13. The operator of the unit must observe the operation status of the unit at all times. Once any abnormal situation is found, please promptly troubleshoot. Forced operation will inevitably cause damage to the unit.

Precautions for operation:

1. Before starting up, check whether all water outlets and pipelines of the unit have been correctly installed and connected.

2. Before starting up, check if the power supply of the unit is connected and if the phase sequence is correct.

3. Before starting up, ensure the safety of the power and water sources. Please carefully refer to the equipment operation manual and strictly follow the instructions for use and operation.

Maintenance precautions:

1. Regularly replace the water in the water tank (it is recommended to replace it every 2 months).

2. Regularly clean the radiator of the unit. For air-cooled units, it is recommended to clean the radiator every 3 months; It is recommended to clean the shell and tube condenser and cooling tower of water-cooled units every 6 months (if the usage environment or water quality is poor, it is recommended to shorten the cleaning cycle).

3. If the unit is not used for a long time, please turn off the main power supply; When the ambient temperature is below 0 ℃ and the unit is shut down for more than 6 hours, the unit and pipelines may freeze, and the damage caused by this is not covered by the warranty. The best way to avoid pipeline freezing is to completely drain all the water in the unit system!

4. Regularly check the water quality on site to ensure that the water source is qualified (pH ≈ 7). If it contains corrosive substances and causes damage to the unit, it is not covered by the warranty.

5. When the unit encounters unavoidable faults during use, please inform our company of the unit model, component name, and other information so that we can provide you with services more quickly.

6. During the warranty period, our company promises to provide free maintenance services for the unit (excluding human damage, improper use, natural disasters, and uncontrollable factors).

Warning: This unit is a high-voltage, highly specialized mechanical equipment, and should be operated correctly by professional technicians strictly in accordance with the "User and Installation Manual".