Mythbusting CO₂ Refrigeration Methods, Half 1

Carbon dioxide (CO₂) has been used as a secure and dependable refrigerant for the reason that Industrial Revolution. Now, trendy meals retailers are adopting CO₂ (R-744) as their most well-liked refrigerant — and for good cause. The checklist of benefits of utilizing CO₂ is complete:

• It’s a pure refrigerant;
• It’s an odorless, non-corrosive, non-toxic, and nonflammable Class A1 refrigerant;
• It has no ODP and with a GWP of 1, it’s the foundation by which all different refrigerants are measured;
• Its excessive heat-reclaim capabilities enhance stored-energy efficiency;
• It presents vital power and operational value financial savings;
• It has low service and upkeep prices since it may be vented to the environment and doesn’t need to be captured or reclaimed; and
• It doesn’t run afoul of regulatory points, so finish customers gained’t be topic to fines or penalties. As such, it’s future-proof.

CO₂ refrigerants began competing with “artificial refrigerants” within the Nineteen Thirties, with the creation of chlorofluorocarbons (CFCs). CFCs ultimately gave solution to hydrofluorocarbon (HFC) refrigerants, which have been thought-about extra secure and extra dependable within the greater ambient temperatures under the so-called “CO₂ Equator.”

Consequently, CO₂ began to be seen as a secondary refrigerant. Nonetheless, a sequence of technological improvements — coupled with the dangerous results HFCs have on the surroundings — helped restore CO₂’s standing as a scalable sustainable refrigerant. Nonetheless, misconceptions proceed to encompass the usage of CO₂ in refrigeration programs, and a few of these myths will likely be debunked right here.

Delusion: Transcritical CO₂ Can’t Be Used Under the CO₂ Equator

As a result of ambient temperatures improve the nearer one will get to the Equator, the argument goes that transcritical CO₂ programs shouldn’t be used under the CO₂ Equator. As a substitute, many consider {that a} subcritical CO₂ system must be used, which is one wherein the refrigerant will be condensed.

Issues across the CO₂ Equator began to vanish about 10 years in the past, resulting from a sequence of technological advances that included:

• Adiabatic fuel coolers, which mix the condensing of the refrigerant with the adiabatic cooling of the air;
• Excessive-pressure subcoolers, which use a small mechanical vapor-compression cycle coupled to the primary cycle on the exit level of the condenser to supply subcooling;
• Parallel compression programs, which compress extra (flash) fuel on the highest stress stage potential to enhance general power effectivity; and
• Gasoline ejector programs, which get well the power of the high-pressure aspect of the system to cut back the work required on the lower-pressure aspect of the system.

Actuality: The CO₂ Equator fable is now not related, because of advances in refrigeration system expertise.

Delusion: CO₂ Requires Considerably Extra Power vs. Conventional Refrigerants

Perceptions typically form beliefs, but a comparability between a system using R-449A, a mix of HFOs and HFCs, and one using CO₂ refrigerant, sheds gentle on these distinctions. Aspect-by-side checks carried out throughout seven U.S. cities (Minneapolis, Sacramento, St. Louis, New York, Seattle, Atlanta, and Miami) confirmed that when improperly put in, a CO₂ system will be 17% (in Seattle) to 22% (Miami) much less environment friendly than an R-449A system.

Nonetheless, when the CO₂ system is correctly designed and consists of elements, corresponding to adiabatic fuel coolers, parallel compressors, parallel compressors with high-pressure ejectors, and digital enlargement valves (EEVs) the CO₂ system will be extra environment friendly than the R-449A system. The issue is that many operators will mistakenly measurement their CO₂ system based on HFC system parameters.

Actuality: There are quite a few energy-saving potentialities when CO₂ refrigerant is utilized in a correctly designed system, and the advantages will be compounded when further elements are employed.

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IMPROPER INSTALL: Aspect-by-side checks carried out throughout seven U.S. cities confirmed that when improperly put in, a CO₂ system will be much less environment friendly than an R-449A system. (Courtesy of Hillphoenix)

Delusion: Power Consumption Will increase Considerably When a CO₂ System Goes Supercritical

Because the subcritical ambient temperature (lower than 87ºF) across the refrigerant system strikes towards the supercritical CO₂ temperature of 87ºF, the idea is that there will likely be a major and instant spike in power utilization when the subcritical/supercritical line is crossed. This made meals retailers nervous, particularly in hotter climates. However when examined, the outcomes present that so-called vital spike doesn’t occur.

Actuality: Whereas kilowatt (kW) utilization does improve because the supercritical temperature threshold is handed, no drastic spike is skilled. Power consumption will increase alongside the identical regular path because it does in subcritical temperatures — identical to another refrigerant.

Click on chart to enlarge

NO SPIKE: Whereas kilowatt utilization does improve because the supercritical temperature threshold is handed, no drastic spike is skilled. (Courtesy of Hillphoenix)

Delusion: CO₂ Refrigeration Methods Are Too Advanced

Schematic drawings of a typical CO₂ system can look advanced, as they function a number of valves (high-pressure, digital enlargement, and flash-gas bypass), transcritical and subcritical compressors, case and rack controllers, coolers, condensers, and warmth reclaim programs. That may sound like loads to maintain observe of; nonetheless, advances in expertise have additionally busted this fable.

The important thing innovation right here is the EEV, which is way simpler to work with than mechanical valves. Additionally, CO₂ refrigerant programs can now be managed and optimized by computer systems, which suggests each system perform is learn by way of transducers, temperature sensors, and analog and digital inputs. Operation is reported/recorded by way of digital software program and {hardware}, so an efficient computer-controlled system is all you could guarantee correct operation. That eliminates the necessity for a technician to always monitor and manually modify the system’s valves and different elements.

Actuality: Whereas the design and elements of CO₂ refrigerant programs are just like these used for a few years, electronically managed elements make them extra dependable and provides them longer service life. This leads to a decidedly much less advanced and extra strong system.

Keep tuned for Half 2 of this text, which can dispel much more myths about CO₂ refrigeration programs.