Do you know the use of CO2 as a refrigerant? One of the lesser known uses for carbon dioxide is as a refrigerator gas. CO2 is used more and more in our sector as a alternative that is not harmful to the environment .
To protect the ozone layer, the Montreal Protocol. Among the substances that were agreed to eliminate are HFCs (hydrofluorocarbons), which are part of traditional refrigerants. Therefore, it was necessary to look for an alternative, among which is CO2 or carbon dioxide.
Increasingly, CO2 is gaining importance as a natural refrigerant internationally. It originates through the combustion of coal, hydrocarbons or fossil fuels, the fermentation of liquids and the respiration of both people and animals. It is a gas that is free in the atmosphere and that allows to modify its state by varying its pressure and / or temperature. Unlike HFC refrigerants, CO2 does not damage the ozone layer (ODP = 0) and its impact on global warming is minimal (GWP = 1).
Uses of CO2 as a refrigerant
The use of CO2 as a refrigerant has various applications, among which are:
- Industry: It is often used as a cooling fluid for low temperature applications and as a secondary cooling fluid for medium temperature applications.
- Heat pumps: Used in applications where both heating and cooling are needed.
- Transportation: Its use in this sector is aimed at reducing the carbon footprint.
- Food distribution: CO2 complies with the environmental measures imposed on this sector.
Advantages of CO2 as a refrigerant
ENVIRONMENTAL BEHAVIOR
As just mentioned, the environmental indicators for CO2 are much more favorable than those for HFCs. By using carbon dioxide as a refrigerant, what you are doing is recycling one of the greenhouse gases . To do this, what is done is purifying it, making it reach purity levels of up to 99.99%.
INACTIVE GAS
CO2 is a gas that is chemically inactive . This means that it is neither flammable nor toxic. It is also odorless, so if a leak were to occur, nothing would happen. In addition, CO2 has a good rate of heat exchange of temperature in evaporators, condensers and gas coolers.
LOW COST
It is a gas with a lower cost than most refrigerants since it is inexpensive to produce. This, added to its thermodynamic properties, is one of the reasons why its use is increasing.
ENERGY EFFICIENCY
CO2 cascade systems achieve high levels of efficiency and performance in low-temperature systems. In addition, having a high volumetric refrigeration capacity, allows the use of smaller pipes, components and compressors. This, together with the high efficiency of heat transfer, translates into lower energy consumption. In other words, greater energy savings are achieved than with other refrigerants.
SIDE EFFECTS
Unlike other refrigerant gases, CO2 does not have long-term side effects. Thanks to its low levels of toxicity, CO2 does not pose a risk to users or the environment.
How CO2 works as a refrigerant
CO2 can be used as a refrigerant in its phases known as subcritical and transcritical.
- Subcritical application: These are refrigeration systems in which the working point is below the critical point of the refrigerant gas. In the case of CO2, it works like any other refrigerant, it evaporates by absorbing heat, it is compressed and condensed. It goes from a gaseous state to a liquid when it loses heat.
- Transcritical application: These are refrigeration systems in which the working point is above the critical point of the refrigerant gas. In this case, the CO2 does not condense and therefore the change from gas to liquid is not done in the traditional way. High discharge pressures occur, necessitating special pressure regulation controls and pipes with design pressures of 120 barC.
Cooling systems
CO2 refrigeration systems will depend on various factors such as the climatic zone or the amount of elements that have to be cooled. These systems include:
SINGLE STAGE TRANSCRITICAL CO2 REFRIGERATION
It is a transcritical single-stage refrigeration process. This application has various uses such as, in addition to cooling, heating systems, medium-high evaporation temperatures, heat pumps or heat recovery systems.
As already mentioned, CO2 used transcritically does not function the same as other gases since it does not condense. Special pressure regulating controls are needed as high discharge pressures occur. In these systems, the temperature of the CO2 at the exit of the gas cooler is 31°C and the evaporation temperature is below.
BOOSTER SYSTEMS WITH TWO COMPRESSION STAGES
It is a system with two stages of understanding where subcritical and transcritical cycles are combined. Two coolers are used in these systems.
In the first low temperature stage one or more subcritical CO2 compressors are used and in the second medium temperature stage one or more transcritical CO2 compressors are used.
The liquid refrigerant used is drawn from a intermediate receiver. The refrigerant is pumped to the medium evaporation temperature equipment and subsequently to the low evaporation temperature applications, after having passed a second expansion.
COOLING SYSTEMS WITH CO2 IN CASCADE
In cascade systems, the refrigerant gas is used in two separate refrigeration circuits at high and low evaporation temperatures. In low-temperature circuits, CO2 is used in a subcritical state, which is later combined with a second high-temperature circuit. In high temperature circuits, the heat of condensation is collected through an intermediate exchanger and is subsequently used in medium temperature applications.
Refrigeration is our thing…
Which companies offer this CO2 refrigeration solution that is environmentally friendly?
At Intersam we manufacture CO2 evaporator equipment up to 60 bars and gas coolers up to 130 bars. Because trusting Intersam means achieving maximum efficiency without losing sight of the sustainability of the planet.
For any questions, we are on the other side of the email at comercial@intersam.es . Happy to answer any questions about this and other systems.