CO₂ is a natural refrigerant used in food retail, commercial refrigeration, and industrial refrigeration applications where energy efficiency, environmental impact, and long-term refrigerant strategy matter. Danfoss supports CO₂ refrigeration with components, controls, monitoring systems, valves, sensors, filter driers, line components, drives, and system management solutions for subcritical, transcritical, cascade, pump-circulated, and hybrid systems.
A suitable CO₂ system can deliver up to 30% energy savings compared with traditional HFC systems, while also helping reduce the environmental impact of refrigeration installations.
Why choose CO₂ as a refrigerant?
CO₂ is one of the most attractive refrigerants for food retail and industrial refrigeration because it combines strong environmental performance with efficient thermophysical properties. CO₂ does not affect the ozone layer and has significantly lower global warming impact than traditional HFC refrigerants.
CO₂ is not a drop-in replacement for every existing refrigerant. Its suitability should be evaluated based on application requirements, Total Equivalent Warming Impact, lifetime cost, system design, and operating conditions.
Key benefits of CO₂ refrigeration
| Benefit | Why it matters |
|---|---|
| Low environmental impact | CO₂ does not affect the ozone layer and has much lower global warming impact than traditional HFC refrigerants. |
| Long-term refrigerant strategy | CO₂ is positioned as a refrigerant that will not be phased out, reducing exposure to HFC phase-down legislation, refrigerant cost increases, and refrigerant taxation. |
| Energy efficiency | CO₂ has strong thermophysical properties, high volumetric efficiency, and high heat transfer efficiency. |
| Smaller system footprint | High volumetric efficiency can translate into smaller pipes, insulation, and compressors. |
| Efficient heat transfer | High heat transfer efficiency can support greater capacity in smaller footprints. |
| Lower pumping power in secondary systems | In secondary systems, CO₂ can save up to 90% on pumping power compared with traditional brines. |
How much energy can CO₂ refrigeration save?
CO₂ refrigeration can reduce energy use depending on the system configuration, climate, and application. The guide states that suitable CO₂ systems can provide up to 30% energy savings compared with traditional HFC systems.
Cascade systems with CO₂ can provide high efficiency in all climates, while transcritical systems can provide an efficient, simple, and cost-effective solution in milder climates.
Where is CO₂ refrigeration used?
CO₂ can be used across several refrigeration and cooling applications. The main application areas highlighted in the guide are food retail, industrial refrigeration, transport refrigeration, heat pumps, server cooling, and electronic cabinet cooling.
| Application | Why CO₂ is relevant |
|---|---|
| Food retail | Food retail installations can have refrigerant leakage from high-GWP refrigerants, making CO₂ a strong option for reducing environmental impact. |
| Industrial refrigeration | CO₂ is efficient as a secondary fluid for medium-temperature applications and as a refrigerant at low temperatures. |
| Transport refrigeration | CO₂ can help reduce carbon footprint in applications where refrigerant leakage rates can create environmental impact. |
| Heat pumps | CO₂ is suited to applications where hot water is needed because transcritical CO₂ cycles reject a large share of heat at high temperatures. |
| Server and electronic cabinet cooling | CO₂ offers non-flammability and high heat transfer efficiency in small footprints. |
Which CO₂ system type should you choose?
CO₂ refrigeration can be applied in several system types. The right choice depends on application, climate, operating temperature, capacity, system complexity, and whether the project is food retail, industrial refrigeration, transport, heat pump, or cooling-focused.
| CO₂ system type | Best fit |
|---|---|
| Transcritical CO₂ booster system | Food retail applications in cold to mild climate areas where heat reclaim and efficient operation are priorities. |
| Cascade HC/HFC-CO₂ system | Applications where high efficiency is needed, including warmer climates, and where CO₂ is used with a separate high-stage refrigerant. |
| CO₂ secondary cooling system | Industrial refrigeration applications where CO₂ is used as a secondary fluid instead of water-based brine or glycol. |
| Pump-circulated CO₂ system | Industrial refrigeration and applications where CO₂ can support efficient heat transfer and smaller component dimensions. |
| Hybrid CO₂ system | Applications where CO₂ is combined with another refrigerant or system architecture to meet performance and application needs. |
Transcritical CO₂ booster systems for food retail
A transcritical CO₂ booster system can enable efficient heat reclaim and is highlighted as one of the most promising system types in cold to mild climate areas. The guide states that energy consumption can be on the same level as, or better than, R404A systems, while the system design remains relatively simple.
A typical CO₂ transcritical booster system is divided into three pressure sections: high pressure, intermediate pressure, and low pressure. Controls for a transcritical system can be grouped into gas cooler controls, receiver controls, injection controls, and compressor capacity controls.
| Pressure section | Pressure range shown in guide |
|---|---|
| High pressure section | 120–140 bar |
| Receiver pressure | 60–90 bar |
| Medium-temperature suction pressure | 35–55 bar |
| Low-temperature suction pressure | 25–30 bar |
CO₂ cascade systems for food retail
CO₂ cascade systems can provide high efficiency, including in hot climates. The guide highlights that only a small amount of refrigerant is needed for the high-temperature stage and that the temperature difference for the cascade heat exchanger is relatively low.
A CO₂ cascade system can use different refrigerants on the high side, including hydrocarbons, HFCs, or ammonia. Control of cascade systems can include condenser capacity control, compressor capacity control, cascade injection control, medium-temperature evaporator CO₂ flow control, and low-temperature evaporator injection control.
CO₂ secondary cooling systems for industrial refrigeration
CO₂ can be used as a secondary fluid in industrial refrigeration systems. The guide states that a CO₂-based secondary cooling system can provide energy savings of up to 20% compared with a water-based brine or glycol system.
The guide also states that, for an experienced installation company, a 500 kW cold-storage refrigeration installation using CO₂ can be cheaper to install than a water-based secondary cooling system, with examples showing installation savings of up to 12%.
The main difference compared with water-based brine or glycol systems is that CO₂ systems can use considerably smaller piping and component sizes for the same capacity.
CO₂ refrigeration and carbon footprint reduction
CO₂ refrigeration can help reduce both direct and indirect carbon footprint in refrigeration systems. The guide states that supermarkets report carbon footprint reductions of more than 30% when switching to CO₂ refrigeration, taking sources such as administration, distribution, and lighting into account.
The guide also states that if all supermarkets worldwide switched to CO₂, more than 50 million tons of CO₂-equivalent emissions could be saved annually.
Case studies
CO₂ refrigeration case examples
REMA 1000: CO₂-based green supermarket in Norway
The REMA 1000 supermarket in Trondheim, Norway, uses an integrated CO₂ and heat recovery solution from Danfoss. The store includes features such as grass on the roof, air curtains, four 170-meter-deep energy wells, and special exterior panels designed to improve use of natural light.
The Danfoss solution is designed to help the store obtain 30% energy savings. The refrigeration system also serves as a heat pump in winter and provides cooling for the air handling unit in summer. Surplus heat from the refrigeration system is used for floor heating, ventilation air heating, and snow and ice melting on pavements.
The AK-SM 850 smart front-end controller from Danfoss secures full energy control of the total store.
Alcampo: R134a/CO₂ cascade refrigeration in Spain
Alcampo, a Spanish supermarket chain, installed an R134a/CO₂ food retail cascade refrigeration system in a hypermarket in Toledo to reduce the environmental impact of refrigeration installations. Danfoss supported the solution design, and the cascade R134a/CO₂ system was selected as the best fit.
In the system, R134a cools the refrigerated services such as refrigerator cabinets and cold storage rooms, while CO₂ cools the freezer services such as freezer units and walk-in freezers. Both use AKV electronic valves for direct expansion, while ETS electronic valves are used in the exchanger where R134a condenses the CO₂.
The guide states that the R134a/CO₂ installation reduced CO₂ emissions by 65% compared with an R404A system.
Flanagan Foodservice: dual-temperature ammonia/CO₂ system in Canada
Flanagan Foodservice in Kitchener, Ontario, Canada, added a new 6,000 m² facility using CO₂ refrigeration technology. The system refrigerates 4,200 m² of freezer space at 360 kW and -15°C, plus 450 m² of ice cream freezer space at 120 kW and -28°C.
The installation uses a dual-temperature ammonia/CO₂ fluid refrigeration package system. Danfoss supplied ICF valve stations feeding CO₂ to the evaporators, flooded shell-and-tube NH₃/CO₂ exchangers, variable frequency drives, and pressure transmitters for NH₃ screw compressors and CO₂ pumps.
The guide states that the system uses only natural refrigerants: ammonia and carbon dioxide, with minimal global warming potential values of 0 and 1 respectively.
Related products
Danfoss CO₂ products and system components
Danfoss offers CO₂ system components for commercial refrigeration, food retail, and industrial refrigeration. The guide lists products across controls, valves, sensors, filter driers, safety valves, pressure transmitters, system managers, service tools, and variable frequency drives.
| Product group | Examples from the guide |
|---|---|
| Transcritical expansion valves | ICMTS, CCMT |
| Pressure regulating and gas-bypass valves | ICS with CVP-HP/XP, CCM/CCMT |
| Electronic expansion valves | AKVH, AKV, AKVA, ICM, CCM/CCMT |
| Valve stations | ICF |
| Solenoid valves | EVR, EVRH, EVRS, EVRST, EVUL, ICLX, ICS + EVM |
| Shut-off valves | SVA-S, SVA-L, GBC |
| Check valves | SCA-X, CHV-X, NRV |
| Gauge valves | SNV-ST, SNV-SS |
| Sight glasses | SGP |
| Filter driers and filters | DCRH, DML, DMT, FIA |
| Regulating valves | REG-SA, REG-SB |
| Liquid level controls | AKS 4100, EKC 347 |
| Safety valves | SFA 15, DSV |
| Pressure switches | RT, KP 6 |
| Pressure sensors | AKS 2050, AKS 32, AKS 32R, AKS 33 |
| Temperature sensors | AKS 11, AKS 21A |
| Gas detectors | GD/DGS |
| Case controllers | AK-CC 550A |
| Pack controllers | AK-PC 772, AK-PC 781, AK-PC 783 |
| System managers | AK-SC 255/355, AK-SM 850 |
| Service tools | AK-ST500 |
| Variable frequency drives | FC 103 |
Why use Danfoss for CO₂ refrigeration?
Danfoss supports CO₂ refrigeration with complete system solutions, including ADAP-KOOL® control and monitoring systems, regulating and injection valves, temperature sensors, pressure sensors, gas detectors, filter driers, and line components.
Danfoss has experience from thousands of transcritical and cascade installations, more than 2,500 CO₂ transcritical systems installed globally, more than a decade of CO₂ valves in the field, and more than 10 years of experience with CO₂ system design across controls, valves, and compressors.
All Danfoss components released for CO₂ have been tested to withstand the impact of CO₂.
FAQ
Why is CO₂ used in refrigeration?
- CO₂ is used in refrigeration because it has strong environmental performance, does not affect the ozone layer, has much lower global warming impact than traditional HFC refrigerants, and offers efficient thermophysical properties for several refrigeration applications.
CO₂ vs HFC systems for supermarket cold rooms — cost comparison?
- CO₂ has higher initial cost but lower long-term refrigerant cost; HFC is cheaper upfront but faces phase-down.
Is CO₂ a drop-in replacement for HFC refrigerants?
- CO₂ is not a drop-in replacement for all existing refrigerants. Its suitability should be evaluated based on application, Total Equivalent Warming Impact, lifetime cost, system design, and operating conditions.
Which applications are suitable for CO₂ refrigeration?
- CO₂ can be used in food retail, industrial refrigeration, transport refrigeration, heat pumps, server cooling, and electronic cabinet cooling.
What are the main types of CO₂ refrigeration systems?
- The guide covers transcritical booster systems, cascade systems, secondary cooling systems, pump-circulated systems, and hybrid systems.
What is a transcritical CO₂ booster system?
- A transcritical CO₂ booster system is a CO₂ refrigeration system highlighted for food retail applications in cold to mild climate areas. It can enable efficient heat reclaim and can operate at energy consumption levels comparable to, or better than, R404A systems.
What are the main pressure sections in a transcritical CO₂ booster system?
- A typical CO₂ transcritical booster system has a high-pressure section, an intermediate receiver pressure section, and low-pressure suction sections. The guide shows high pressure at 120–140 bar, receiver pressure at 60–90 bar, medium-temperature suction pressure at 35–55 bar, and low-temperature suction pressure at 25–30 bar.
Why use CO₂ in industrial refrigeration?
- CO₂ can be efficient as a secondary fluid in medium-temperature industrial refrigeration applications and as a refrigerant at low temperatures. The guide states that CO₂ systems can use smaller piping and component sizes than water-based brine or glycol systems for the same capacity.
How much can CO₂ reduce supermarket carbon footprint?
- The guide states that supermarkets report carbon footprint reductions of more than 30% when switching to CO₂ refrigeration, taking all sources into account.
Energy-efficient refrigeration for grocery store walk-in coolers?
- Use high-efficiency compressors, EC fans, LED lighting, and demand-based defrost cycles. Utilize floating head pressure if condensers are outside.
What refrigerant strategy should a supermarket chain adopt as R404A is phased out?
- Transition to low-GWP refrigerants like CO₂ or A2L blends, considering retrofit feasibility.
How do CO₂ transcritical systems compare to A2L systems for commercial walk-in coolers in the US?
- CO₂ offers zero GWP but higher complexity; A2L blends are simpler retrofits with lower GWP.
Which Danfoss products support CO₂ refrigeration?
- Danfoss CO₂ solutions include ADAP-KOOL® control and monitoring systems, pack controllers, system managers, expansion valves, pressure regulating valves, gas-bypass valves, solenoid valves, shut-off valves, check valves, filter driers, pressure sensors, temperature sensors, gas detectors, and variable frequency drives.
Downloads
This page summarizes the key decision points from the Danfoss CO₂ refrigeration guide. Download the full PDF for the original guide, application diagrams, product range, case examples, and supporting details.