FEATURE |
INCORPORATING COLD CHAIN |
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performance improvements while maintaining |
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the same refrigeration loads( 990kW at-10 ° C |
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and 450kW at-35 ° C). The low-temperature |
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compressor requirement remained five units |
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with 85kW installed power. However, due to |
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the lower discharge pressure achieved by |
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condensing at 28 ° C, the medium-temperature |
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compressor requirement dropped from seven |
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units to just six. This reduction, combined with |
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the compressors operating at a more efficient |
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point on their performance curves due to the |
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lower pressure ratio, resulted in the mediumtemperature |
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installed power falling to 594kW. |
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The total installed compressor power for the |
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subcritical system with the hybrid condenser |
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was therefore reduced to 679kW. |
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Van der Merwe presented a summary |
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comparison highlighting the significant |
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advantages of operating subcritically with |
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the hybrid condenser:
• Total installed compressor power reduced from 1 009kW to 679kW, representing a 33 % decrease
• Average operating pressure( discharge) reduced from 91 bar to 68 bar, a 23 % decrease
• Mass flow rate reduced by 17 %, potentially impacting the size of components and piping
• Total system COP improvement of a significant 57 %, moving from a COP of approximately 1.65( transcritical) to 2.59( subcritical)
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CO2 Rack 5.
that even with this improvement, the COP of a CO2 system( at ~ 2.59) still generally trails that of typical ammonia or traditional Freon( HFC / HFO blend) systems. He clarified that the primary driver for adopting CO2 is not necessarily achieving the absolute highest COP, but rather its compelling environmental
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previous HFC systems to CO2, often driven by corporate head office environmental initiatives. This indicates where CO2 is currently finding its most viable niche in the local context.“ CO₂ offers compelling safety and environmental advantages: it is non-toxic, non-flammable, non-explosive and non-acidic, |
in ammonia-driven systems, functioning without phase change. This evolved into cascade systems, where CO2 ' s evaporator cools a higher-temperature refrigerant like ammonia. The latest evolution, transcritical CO2 systems, are vital in warmer climates, operating above CO2 ' s
Image supplied by SCM Ref Africa
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“ So we think we might be on to something here.”
“ By switching to a hybrid condenser and operating subcritically, the system achieved a 33 % reduction in compressor power and a 57 % improvement in COP.”
While highlighting the significant COP improvement for CO2 itself, he acknowledged
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( GWP = 1, ODP = 0) and safety( non-toxic, nonflammable) attributes.
Regarding the South African market, Van der Merwe observed that while large industrial applications, such as major distribution warehouses, still predominantly utilise large full ammonia systems, CO2 is increasingly gaining traction in the retail sector. Supermarket chains and similar businesses are transitioning from
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with an Ozone Depletion Potential( ODP) of 0 and a Global Warming Potential( GWP) of just 1. These attributes make it one of the safest and most sustainable refrigerant options available. However, its lack of odour means leaks can go undetected, requiring stringent safety protocols in sensitive environments.”
“ Historically, CO2 ' s refrigeration journey began as a secondary refrigerant
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critical point. The potential of subcritical CO2 systems, which condense below the critical point, is also being re-explored. A major historical hurdle for CO2 – the scarcity of high-pressure components – is now being overcome as manufacturers prioritise their development, making CO2-specific systems increasingly viable,” added Van der Merwe. |