Ammonia can be condensed at 30°C in an evaporative condenser with entering air wet bulb temperature of 24°C. We show that an evaporative condenser for subcritical CO_2 condensing at 30°C, i.e. 1.1 K below the critical point, can be designed for a wet bulb of 24°C. Average climate conditions in much of Europe, including the warmer climates in Spain, Italy, Greece and Turkey, are suitable for evaporative condensers to condense subcritical CO_2 at 30°C. Canada, large parts of the USA and China, and most of Australia below the tropic of Capricorn also have climates suitable for the application of evaporative condensers to subcritical CO_2 condensing. The thermodynamic and transport properties of subcritical CO_2 at 30°C change significantly with temperature. We show the effect this has on CO_2 temperature profile, heat transfer and pressure loss for a particular design. The benefits of applying evaporative condensing techniques for the condensation of subcritical CO_2 are examined. They are lower design pressures compared to transcritical operations, lower energy consumption, lower running and operating costs. Hot gas defrosting would also become a standard feature of subcritical CO_2 refrigeration plant operations. It is concluded that the use of evaporative condensers for CO_2 in temperate and many subtropical climates would make CO_2 refrigeration as ubiquitous as any chemical refrigerant and would compete successfully with ammonia when it needs to be used in an indirect application such as the heating and cooling of office buildings and hospitals for example.
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