{"id":23703,"date":"2020-01-14T12:44:38","date_gmt":"2020-01-14T10:44:38","guid":{"rendered":"https:\/\/www.intarcon.com\/refrigeracion-co2-transcritico\/"},"modified":"2023-01-11T17:03:34","modified_gmt":"2023-01-11T15:03:34","slug":"transcritical-co2-refrigeration","status":"publish","type":"post","link":"https:\/\/www.intarcon.com\/en\/transcritical-co2-refrigeration\/","title":{"rendered":"Transcritical CO2<\/sub> refrigeration"},"content":{"rendered":"\t\t
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Commonly known as R-744 when used as a refrigerant,\u00a0carbon dioxide (CO2<\/sub>) has become one of the most popular natural refrigerants<\/a>\u00a0in recent times.<\/p>

It is a refrigerant classified according to the Safety Regulations for Refrigeration Installations as “Safety Class = A1”, i.e. “non-flammable” and “low toxicity”.<\/p>

It has excellent thermo-physical properties, although it poses difficulties due to its low critical temperature value (30.978\u00b0C) and its high pressures. It has a volumetric capacity that is much higher than that of conventional refrigerants.<\/p>

This gas has a high thermal conductivity and high density in the gaseous phase<\/strong>, which results in good heat transfer in evaporators, condensers and gas coolers<\/strong>; so these characteristics allow smaller units to be selected, compared to those that use CFCs, HCFCs and HFCs. Also, due to the fact that it has a low pressure drop, the diameter of the pipes can be reduced.<\/p>

What is a transcritical cycle?<\/span><\/h2>

Transcritical cycles are those in which the compressor discharge pressure is greater than the critical pressure and, therefore, the refrigerant cannot be condensed<\/strong>, i.e. the compressor discharge pressure is greater than the critical pressure. It consists of only using CO2<\/sub> in the unit and cooling it above the critical point, with no phase change during this cooling process. The transcritical cycle is common for these systems to work with high compressor discharge temperatures, due to the need to reach high pressures (around 95 bar) in the gas cooler to be able to exchange heat with the environment.<\/p>

It consists of only using CO2<\/sub>\u00a0in the unit and cooling it above the critical point, with no phase change during this cooling process. It is common for these systems to work with high compressor discharge temperatures, due to the need to reach high pressures (around 95 bar) in the gas cooler to be able to exchange heat with the environment.<\/p>

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In this type of cycle,\u00a0the gas cooler pressure has an optimal value that the control must try to reach to avoid high energy consumption.<\/strong><\/p>

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The expansion from the gas cooler pressure generates vapour that has no useful cooling effect.\u00a0This vapour must be recompressed to the gas cooler pressure.<\/strong>\u00a0In the most basic assembly, this vapour is compressed by the main compressor.<\/span><\/p>

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This same system can be applied to have positive and negative cold, using a\u00a0booster assembly<\/em><\/strong>. The vapour generated in the pressure regulation valve is compressed by the MT compressors.<\/p>

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Transcritical CO2<\/sub>\u00a0cycle: performance improvements<\/h2>

The downside of a transcritical system is its efficiency<\/strong>,\u00a0as it has to compress the vapour generated at the gas cooler outlet,<\/strong>\u00a0and it must overcome the high compression ratio. This is aggravated by a high outside temperature, as more vapour is generated.<\/p>

In transcritical systems, in order to obtain operating efficiencies similar to conventional fluid systems, it is very common to use more complex cycles that result in improved efficiency, such as:<\/p>