Guide to Transcritical CO2 Refrigeration
Transcritical CO2 refrigeration systems are gaining acceptance in the supermarket refrigeration industry. National and international policies that originally targeted the reduction of CFCs are being expanded to include HCFCs and HFCs. Technology advancements in CO2 systems are making these systems more economically viable, in terms of both equipment and installation cost but also energy and operating costs.
CO2 as a refrigerant has emerged as one of the frontrunners to be the refrigerant of the future. It has the advantages of being environmentally friendly, has good heat transfer properties with a high latent heat of vaporization. CO2 is also non-flammable and non-toxic. The primary disadvantage of CO2 as a refrigerant is relatively high operating pressures.
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There are a few important differences to note between subcritical and TC systems. First, there’s no condensing function in TC systems. Instead, TC systems include a gas cooler to dissipate heat. Another difference involves the use of a high-pressure expansion valve to controls the introduction into the evaporator.
Benefits of transcritical CO2 systems
- Cost
There are a few notable benefits associated with opting for transcritical CO2. First, when compared to other refrigerants, carbon dioxide is much cheaper on a per-pound basis. For example, R-410A, a popular HFC refrigerant, averages between $6 and $8 per pound. On the other hand, we regularly buy CO2 for less than a dollar a pound.
Changing HFC or HFO systems over to CO2 isn’t practical, and it will take time for the return on investment to be realized, but the cost savings of CO2 compared to traditional refrigerants are real and significant. These cost savings come in the form of cheaper fluids as well as higher attainable efficiency for the system as a whole.
- Sustainability
- Heat Reclaim
Design and material considerations
Given the high pressure of transcritical CO2 systems, more rugged materials are required. At Super Radiator Coils, we design and manufacture three products for TC applications: gas coolers, hot gas reheat coils, and evaporators.
To do so, we rely on tube materials like stainless steel and copper alloy strengthened with nickel and tin along with copper alloy headers and connections. While stainless steel is typically seen more often, copper alloy is an excellent option for TC CO2 applications for a couple reasons. First, it can be brazed, allowing for easy integration into systems with copper connections. It’s also far less costly than stainless steel. The tube material we use is UL listed up to 1740 PSIG (120 bar).
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