A CO2 chiller is a water cooling system that represents a highly attractive ecological alternative. Nowadays, it can be used in virtually any part of the world.
How Does a CO2 Chiller Work?
CO2 Chiller in Subcritical Operation
The CO2 cycle is employed within a cascade installation that integrates two systems. The CO2 circuit operates at low temperatures to cool the liquid, while another cycle is used to condense the CO2. In this configuration, the CO2 in the chiller remains below its critical point.
CO2 Chiller in Transcritical Operation
The main idea of this system is to exclusively use CO2 throughout the installation, eliminating issues related to environmental regulations.
Key Features of CO2 Chillers
- High-Pressure Operation: CO2 chillers operate at very high pressures while maintaining temperatures comparable to other refrigerants.
- Environmental Benefits: These chillers have a promising future as they contribute significantly to environmental sustainability.
- Energy Efficiency:
- Transcritical CO2 chillers for glycol offer high efficiency and reliability for low-temperature cooling.
- Heat recovery is available, allowing temperatures up to 75°C for parallel processes.
- Wide Application Range: They support glycol supply temperatures from -30°C to +12°C and are commonly used with flooded evaporators for cooling industrial brines like CaCl2 and ammonia-water solutions.
- Cascade Systems:
- Cascade setups combine two independent refrigeration systems with a shared heat exchanger.
- Using CO2 in combination reduces ammonia usage by up to 90% compared to ammonia-only systems.
- Specialized Design:
- CO2 chillers use steel or stainless steel pipes designed to withstand high pressures.
- Wall thickness in tubes and exchangers is increased to manage these pressures effectively.
- Advanced Components:
- Compressors are specially designed to handle CO2’s greater cooling capacity.
- Electronic expansion valves and variable-speed fans enhance efficiency at partial loads.
- Refrigerant Advantages:
- CO2 (R744) offers greater cooling capacity and lower pressure drops in pipes and heat exchangers, boosting the COP.
- Non-corrosive, low-toxicity, non-flammable, and cost-effective.
- High heat transfer efficiency due to the refrigerant’s density and pressure properties.
- Compact and Quiet:
- These modern systems occupy less space in machinery rooms and produce minimal noise.
- Many are oil-free, maximizing operational efficiency.
- ASHRAE Classification:
- CO2 is classified as an A1 refrigerant, meaning it is non-toxic and non-flammable.
- However, in confined spaces, large leaks can displace breathable oxygen.
Additional Considerations
- CO2 chillers require a refrigerant purity of approximately 99.99%.
- Systems with high discharge temperatures necessitate interstage cooling, especially for very low-temperature applications.
- Proper safety measures are crucial since CO2 can form a solid phase under certain conditions, such as during overpressure valve release.
