Comparison of the applicable scenarios, advantages and disadvantages of closed-circuit cooling towers and open-circuit cooling towers
I am an HVAC expert. This issue is critical in air-conditioning system design because the choice of cooling tower type directly affects the energy efficiency of chillers, initial system investment, operation and maintenance costs, and long-term reliability. According to Section 8.6 of the Code for Design of Heating Ventilation and Air Conditioning of Civil Buildings (GB50736-2012), the selection of cooling towers should comprehensively consider factors such as building characteristics, climatic conditions, water quality, and noise requirements. Below I will compare closed-circuit and open-circuit cooling towers in detail from the two aspects of applicable scenarios and advantages and disadvantages.
**I. Comparison of Applicable Scenarios**
- **Open-circuit cooling towers**: Suitable for large central air-conditioning systems (such as commercial complexes and industrial plants), especially projects where the cooling water quality is good or has undergone chemical treatment and where sensitivity to initial system investment is high. For example, in a large shopping mall project in South China in which I participated, open-circuit cooling towers were used together with screw chillers. Because local water resources were abundant and water quality met standards, the operation was stable. However, it should be noted that open systems are susceptible to contamination and therefore are not suitable for precision air conditioning or data centers with high water quality requirements (according to the Code for Design of Data Centers, GB50174-2017, closed systems are recommended).
- **Closed-circuit cooling towers**: Suitable for scenarios with strict water quality requirements or environmental sensitivity, such as data centers, hospital operating rooms, precision instrument plants, and cold regions (to avoid winter freezing problems). For example, in a data center project in a northern region, we selected closed-circuit cooling towers with ethylene glycol solution for freeze protection, which effectively avoided the risk of winter shutdown and maintained the cleanliness of the cooling water.
**II. Comparison of Advantages and Disadvantages**
| **Characteristic** | **Open-circuit cooling tower** | **Closed-circuit cooling tower** |
|----------|----------------|----------------|
| **Initial investment** | Relatively low (simple structure, no coils) | Relatively high (includes coils and a closed circulation system) |
| **Operating energy consumption** | Relatively low (low pump head) | Relatively high (must overcome coil resistance; fan energy consumption increases slightly) |
| **Water quality maintenance** | Susceptible to contamination (drift, scaling, algae); regular chemical dosing required | Clean water quality, less contamination, low maintenance frequency |
| **Energy efficiency** | Approaches the wet-bulb temperature; better cooling effect | Approaches the dry-bulb temperature; slightly poorer cooling effect (especially at high temperature and high humidity) |
| **Winter operation** | Requires freeze protection measures (such as electric heat tracing or drainage) | Antifreeze can be added; suitable for severe cold regions |
| **Maintenance cost** | Relatively high (requires cleaning fill and treating scale) | Relatively low (coils are easy to clean, but seals require regular inspection) |
| **Noise** | Relatively high (fan and water flow noise) | Relatively low (sound attenuation measures can be added) |
**III. Actual Engineering Cases**
- **Case 1 (open-circuit)**: A hotel project in the south used open-circuit cooling towers + centrifugal chillers. Initial investment was saved by about RMB 150,000, but after 3 years of operation, water quality scaling caused the condenser heat exchange efficiency to drop by 20%, requiring shutdown for cleaning. Recommendation: If open-circuit is selected, an automatic chemical dosing and blowdown system must be provided (refer to Article 6.7.6 of GB50019-2015).
- **Case 2 (closed-circuit)**: A data center in the north used closed-circuit cooling towers + plate heat exchangers. Although initial investment increased by 30%, it avoided the risk of pipe freezing and cracking in winter, and the cooling water cleanliness was high, resulting in stable server operation. Experience shows that closed-circuit systems have better cost-effectiveness in cold regions.
**Summary**: Open-circuit cooling towers are suitable for large systems in non-severe cold regions where initial investment sensitivity is high and water quality is controllable; closed-circuit cooling towers are suitable for applications with high water quality and reliability requirements or in cold environments. When selecting, it is necessary to comprehensively weigh the project location's climate, water quality, system type, and maintenance capability.
The above are reference opinions. The actual project situation still needs further comprehensive evaluation and implementation in combination with specific operating conditions, site conditions, and other factors.