CO2跨临界制冷技术
跨临界二氧化碳热泵冷热联供关键技术
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CO2跨临界制冷循环原理及新技术
二氧化碳跨临界循环制冷CO 2作为制冷剂的应用历史•CO 2作为最早的制冷剂之一，在19世纪末到20世纪30年代得到了普遍的应用，到1930年，80%的船舶采用CO 2制冷。
•但由于当时采用的CO 2亚临界循环制冷效率低，特别是当环境温度稍高时，CO 2的制冷能力急剧下降，且功耗增大。
•同时，以R12为代表的CFC 或氟氯烃制冷剂的出现，以其无毒、不可燃、不爆炸、无刺激性、适中的压力和较高的制冷效率等特点，很快取代了CO 2在安全制冷剂方面的位置。
•近年来，制冷剂对臭氧层的破坏和全球温室效应等环保问题日益突出，而CO 2跨临界制冷循环的提出，CO 2作为制冷剂开始重新得到重视•该循环系统的最大特点就是工质的吸、放热过程分别在亚临界区和超临界区进行。
压缩机的吸气压力低于临界压力，蒸发温度也低于临界温度，循环的吸热过程仍在亚临界条件下进行，换热过程主要是依靠潜热来完成。
但是压缩机的排气压力高于临界压力，工质的冷凝过程与在亚临界状态下完全不同，换热过程依靠显热来完成。
CO作为制冷工质的优缺点2优点•良好的安全性和化学稳定性•具有与制冷循环和设备相适应的热物理性质•CO2优良的流动和传热特性•CO2制冷循环的压缩比较常规工质制冷循环低缺点•运行压力高•循环效率低带回热器和不带回热器的CO 2跨临界单级循环进行理论分析和实验性能测试2•典型的CO 2跨临界单级循环主要由压缩机、气体冷却器、节流阀和蒸发器组成．图1和图2分别给出了CO 2跨临界单级循环原理图和细图．图l 中：低压气态制冷剂经压缩机被压缩成高压气态制冷剂(过程l 一2)，经气体冷却器进行定压放热(过程2—3)，然后经节流阀进行节流降压(过程3—4)，低压液态制冷剂在蒸发器内进行定压吸热(过程4一1)，最后回到压缩机，从而完成一个循环．2•制冷循环增设回热器，可以减小节流损失、增大制冷量，从而提高系统性能．图3和图4分别给出了带回热器的CO 2跨临界单级循环原理图和细图．两个循环性能对比分析•图5给出了两个循环COP随蒸发温度的变化．随着蒸发温度的增加，两个循环COP均呈增加趋势，蒸发温度越高，系统性能越优；•在整个蒸发温度变化范围内，带回热器循环平均性能要比不带回热器循环提高4．55％左右；•对于理想压缩机循环，系统性能要比实际循环性能高33．3％以上，但这种理想循环是不存在的．•图6给出了两个循环COP 随气体冷却器出口温度的变化．•随着气体冷却器出门温度的增加，两个循环COP均呈下降趋势，温度越高，系统性能越差；•在气体冷却器出口温度变化范围内，带回热器循环平均性能要比不带回热器循环提高5．23％左右．•两个循环COP 随压缩机排气温度的变化，见图7．•在排气温度变化范围内，相同对比条件下，带回热器CO 2跨临界单级循环系统COP 要高于不带回热器循环，且带回热器单级循环排气温度要稍高些．•无论带回热器还是不带回热器循环，随着压缩机效率提高，系统COP 均变大，压缩机排气温度均有所降低，不带回热器循环降低幅度较大．•由图7还可以看出，两个单级循环都存在一个最优排气温度，使得在此温度下系统COP 最大，带回热器循环对应最优排气温度要高于不带回热器循环最优排气温度．结论•(1)在蒸发温度变化范围内，带回热器循环平均性能要比不带回热器循环提高约4．55％；在气体冷却器出口温度变化范围内，带回热器循环平均性能要比不带回热器循环提高约5．23％；相同对比条件下，带回热器CO跨临界单级循环系统COP高于不2带回热器循环的，且带回热器单级循环最优排气温度稍高些．•(2)两种单级循环的制热量、制冷量、制热COP和制冷COP，均随压缩机排气压力增加存在极值；随冷却水流量、冷冻水流量以及冷冻水进口温度增加而增加，随冷却水进口温度增加而下降．•(3)相同测试工况下，带回热器循环系统具有较高的性能．其中，制热量和制冷量分别比不带回热器的单级循环平均高约3．33％和5．35％，制热COP和制冷COP分别提高约11．36％和14．29％．CO2跨临界循环的应用前景与研究进展•1、汽车空调•2、热泵•3、食品冷藏•4、循环系统关键设备的研究进展•1、汽车空调•过去汽车空调中一般使用CFC12作为制冷工质，这使得汽车空调制冷剂的排放量在所有氟利昂的排放中占有相当大的比例。
CO2跨临界制冷循环原理及新技术
二氧化碳跨临界循环制冷CO 2作为制冷剂的应用历史•CO 2作为最早的制冷剂之一，在19世纪末到20世纪30年代得到了普遍的应用，到1930年，80%的船舶采用CO 2制冷。
•但由于当时采用的CO 2亚临界循环制冷效率低，特别是当环境温度稍高时，CO 2的制冷能力急剧下降，且功耗增大。
•同时，以R12为代表的CFC 或氟氯烃制冷剂的出现，以其无毒、不可燃、不爆炸、无刺激性、适中的压力和较高的制冷效率等特点，很快取代了CO 2在安全制冷剂方面的位置。
•近年来，制冷剂对臭氧层的破坏和全球温室效应等环保问题日益突出，而CO 2跨临界制冷循环的提出，CO 2作为制冷剂开始重新得到重视•该循环系统的最大特点就是工质的吸、放热过程分别在亚临界区和超临界区进行。
压缩机的吸气压力低于临界压力，蒸发温度也低于临界温度，循环的吸热过程仍在亚临界条件下进行，换热过程主要是依靠潜热来完成。
但是压缩机的排气压力高于临界压力，工质的冷凝过程与在亚临界状态下完全不同，换热过程依靠显热来完成。
CO作为制冷工质的优缺点2优点•良好的安全性和化学稳定性•具有与制冷循环和设备相适应的热物理性质•CO2优良的流动和传热特性•CO2制冷循环的压缩比较常规工质制冷循环低缺点•运行压力高•循环效率低带回热器和不带回热器的CO 2跨临界单级循环进行理论分析和实验性能测试2•典型的CO 2跨临界单级循环主要由压缩机、气体冷却器、节流阀和蒸发器组成．图1和图2分别给出了CO 2跨临界单级循环原理图和细图．图l 中：低压气态制冷剂经压缩机被压缩成高压气态制冷剂(过程l 一2)，经气体冷却器进行定压放热(过程2—3)，然后经节流阀进行节流降压(过程3—4)，低压液态制冷剂在蒸发器内进行定压吸热(过程4一1)，最后回到压缩机，从而完成一个循环．2•制冷循环增设回热器，可以减小节流损失、增大制冷量，从而提高系统性能．图3和图4分别给出了带回热器的CO 2跨临界单级循环原理图和细图．两个循环性能对比分析•图5给出了两个循环COP随蒸发温度的变化．随着蒸发温度的增加，两个循环COP均呈增加趋势，蒸发温度越高，系统性能越优；•在整个蒸发温度变化范围内，带回热器循环平均性能要比不带回热器循环提高4．55％左右；•对于理想压缩机循环，系统性能要比实际循环性能高33．3％以上，但这种理想循环是不存在的．•图6给出了两个循环COP 随气体冷却器出口温度的变化．•随着气体冷却器出门温度的增加，两个循环COP均呈下降趋势，温度越高，系统性能越差；•在气体冷却器出口温度变化范围内，带回热器循环平均性能要比不带回热器循环提高5．23％左右．•两个循环COP 随压缩机排气温度的变化，见图7．•在排气温度变化范围内，相同对比条件下，带回热器CO 2跨临界单级循环系统COP 要高于不带回热器循环，且带回热器单级循环排气温度要稍高些．•无论带回热器还是不带回热器循环，随着压缩机效率提高，系统COP 均变大，压缩机排气温度均有所降低，不带回热器循环降低幅度较大．•由图7还可以看出，两个单级循环都存在一个最优排气温度，使得在此温度下系统COP 最大，带回热器循环对应最优排气温度要高于不带回热器循环最优排气温度．结论•(1)在蒸发温度变化范围内，带回热器循环平均性能要比不带回热器循环提高约4．55％；在气体冷却器出口温度变化范围内，带回热器循环平均性能要比不带回热器循环提高约5．23％；相同对比条件下，带回热器CO跨临界单级循环系统COP高于不2带回热器循环的，且带回热器单级循环最优排气温度稍高些．•(2)两种单级循环的制热量、制冷量、制热COP和制冷COP，均随压缩机排气压力增加存在极值；随冷却水流量、冷冻水流量以及冷冻水进口温度增加而增加，随冷却水进口温度增加而下降．•(3)相同测试工况下，带回热器循环系统具有较高的性能．其中，制热量和制冷量分别比不带回热器的单级循环平均高约3．33％和5．35％，制热COP和制冷COP分别提高约11．36％和14．29％．CO2跨临界循环的应用前景与研究进展•1、汽车空调•2、热泵•3、食品冷藏•4、循环系统关键设备的研究进展•1、汽车空调•过去汽车空调中一般使用CFC12作为制冷工质，这使得汽车空调制冷剂的排放量在所有氟利昂的排放中占有相当大的比例。
跨临界二氧化碳制冷技术现状研究
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CO2跨临界制冷技术
单一C02跨临界压缩机运行制冷技术简况技术优势:该循环系统的最大特点就是工质的吸、放热过程分别在亚临界区和超临界区进行。
压缩机的吸气压力低于临界压力,蒸发温度也低于临界温度,循环的吸热过程仍在亚临界条件下进行,换热过程主要是依靠潜热来完成。
但是压缩机的排气压力高于临界压力,工质的冷凝过程与在亚临界状态下完全不同,换热过程依靠显热来完成,此时高压换热器不再称为冷凝器,而称为气体冷却器。
在以空气为热源、热汇的制冷和热泵系统(主要是汽车空调以及家用空调)中,CO2循环在跨临界条件下运行,其工作压力虽然较高,但压比却很低,压缩机的效率相对较高;流体在超临界条件下的特殊热物理性质使它在流动和换热方面都具有无与伦比的优势,超临界流体优良的传热和热力学特性使得换热器的效率也很高,这就使得整个系统的能效较高,完全可与传统的制冷剂(如R12、R22等)及其现有的替代物(如R134a、R410A等)竞争。
加上CO2在气体冷却器中大的温度变化,使得气体冷却器进口空气温度与出口制冷剂温度可能非常接近,这自然可减少高压侧不可逆传热引起的损失。
由于CO2的临界温度低,为31, ℃因此, 制冷循环采用跨临界制冷循环时,其排热过程不是一个冷凝过程,压缩机的排气压力与冷却温度是两个独立的参数,改变高压侧压力将影响制冷量、压缩机耗工量及系统的COP。
研究分析表明,高压侧压力变化时,循环的COP 存在着一个最大值,因此,CO2跨临界制冷循环在对不同工况下,存在对应于最大COP 值的最佳排气压力。
CO2 在气体冷却器中较大的温度变化,正好适合于水的加热,从而使热泵的效率较高。
传统空调系统大多把冷凝热当作废热而直接排向大气,既造成能量的浪费又产生环境的局部热污染。
而对跨临界循环,由于超临界区工质密度在不断增加,循环的放热过程必将有较大的温度滑移,这种温度滑移正好与所需的变温热源相匹配,是一种特殊的劳伦兹循环,其用于热回收时,必将有较高的放热效率,因而用于较高温度和较大温差需要的热回收时具有独特的优势。
二氧化碳跨临界制冷循环
二氧化碳跨临界制冷循环摘要：CO2是一种环保型的自然工质，它对臭氧层不产生任何破坏作用且具有较小的温室效应。
本文概述跨临界C02制冷循环的原理，提出几个影响该循环的技术关键。
介绍跨临界CO2循环的相关应用领域，指出CO2作为性能良好的自然工质有着很好的发展前景。
关键词：二氧化碳；制冷；跨临界循环引言由于制冷剂中氯原子对大气臭氧层有破坏作用，《蒙特利尔协议》规定R12 等CFCS（氯氟碳）在制冷工质中被禁用，危害程度较小的R22 等HCFCS（氢氯氟碳）的禁用日期也一再提前。
目前已获应用的R134a，R410A，R407C 等HFCS （氢氟碳）仍是一类新的化学合成物，它们不仅制造成本昂贵，而且已被证明能产生较为严重的温室效应。
另外，随着研究的深入，有可能证明HFCS 在其它方面也有危害。
因此，在制冷系统中对地球生物圈中原来就有的“自然工质”进行研究，已成为近年来的前沿课题之一。
二氧化碳（R744）目前被称作是一种被遗忘的制冷剂，它在19世纪被广泛地使用，从20世纪30年代后被冷落。
现在，大家认为：已经到了使用现代的高新技术重新利用二氧化碳的时候了。
1.CO2制冷二氧化碳基本上不会引起环境问题，它无毒不燃，具有氨和烃类制冷剂所不可及的一些优点。
另外它价廉，与一般的制冷设备和润滑系统都相容。
它可以高度压缩，因此可以利用先进设备及设计大大减小压缩机的体积和管道直径。
它在高压下良好的传热效果是该制冷剂的另一个优点。
总而言之，在满足制冷要求的情况下，使用二氧化碳制冷剂可以大大降低设备的投资。
2.工作原理跨临界蒸汽压缩式制冷循环是利用气体液化后可吸收蒸发（汽化）潜热的特性以达到制冷的目的。
跨临界系统由压缩机C ，气体冷却器G ，内部热交换器I，节流阀V ，蒸发器E 与储存器A组成封闭回路，以CO2为工作介质，气体工质在压缩机C 中升压至超临界压力P2，在T 一S 图上为过程1一2 ，然后进入气体冷却器G 中，被冷却介质（空气或冷却水）所冷却。
商用制冷应用的二氧化碳跨临界制冷系统开发
商用制冷应用的二氧化碳跨临界制冷系统开发摘要本文探讨了一种商用制冷应用的二氧化碳跨临界制冷系统的开发。
二氧化碳作为环境友好型的自然冷媒已经成功的应用于商用制冷领域,在多种复杂的场合发挥着重要的作用,其应用系统型式多样。
首先，本文对传统制冷系统的不足进行了简要介绍，并提出了采用二氧化碳跨临界制冷系统的优点。
随后，本文详细介绍了该系统的设计原理、工作流程和关键组成部分，包括压缩机、冷凝器、蒸发器和节流阀等。
然后，本文对该系统的性能和效果进行了分析和评估，实验结果表明该系统具有较高的制冷效率和环保性能。
最后，本文讨论了该系统的未来发展方向和展望，并总结出本文的研究结论。
通过本论文的研究，我们可以发现二氧化碳跨临界制冷系统是一种非常优秀的制冷系统，可以提高制冷效率和降低环境污染，具有广阔的应用前景和市场潜力。
本文介绍了CO2跨临界制冷循环系统研究发展过程,针对系统主要部件的研究及问题进行了分析,总结了CO2跨临界制冷循环系统在商用食品冷冻冷藏、汽车空调、热泵系统、人工冰场等领域应用研究现状,并且展望了CO2跨临界制冷循环系统的发展前景。
关键词：二氧化碳，跨临界制冷系统，商用制冷引言随着全球环境问题的日益严重和能源价格的不断攀升，制冷系统的节能和环保已经成为制冷技术发展的主要方向。
二氧化碳跨临界制冷系统是一种新型的高效、环保的制冷系统，其具有较高的热效率和较低的环境污染，已经成为了制冷技术领域的研究热点。
本文基于此，介绍了一种商用制冷应用的二氧化碳跨临界制冷系统，并对其进行了详细的设计、分析和实验研究。
一、基本原理二氧化碳跨临界制冷系统是一种基于二氧化碳的制冷技术，其原理基于二氧化碳在超临界状态下具有较高的压缩性、传热性和流动性能。
超临界状态是指当二氧化碳的压力和温度超过了其临界点（7.38 MPa和31.1℃）时，二氧化碳就处于超临界状态。
二氧化碳跨临界制冷系统的基本组成部分包括压缩机、换热器、膨胀阀和冷凝器等。
国家速滑馆超大冰面二氧化碳跨临界制冷系统关键技术研究和示范应用
国家速滑馆超大冰面二氧化碳跨临界制冷系统关键技术研究和示范应用-概述说明以及解释1.引言1.1 概述在这篇长文中，我们将详细讨论国家速滑馆超大冰面二氧化碳跨临界制冷系统的关键技术研究和示范应用。
本文旨在探究该系统的技术特点、实验结果以及其对相关领域的意义和影响。
超大冰面二氧化碳跨临界制冷系统是一种基于二氧化碳（CO2）的制冷技术。
该系统以国家速滑馆的冰面为应用背景，利用CO2作为制冷剂，通过跨临界制冷技术来实现冰面的保持和控制。
在本文接下来的章节中，我们将详细介绍国家速滑馆超大冰面二氧化碳跨临界制冷系统的技术原理和关键技术要点。
首先，我们将对该系统的整体结构和各个组成部分进行介绍，包括CO2的选择、制冷装置的设计和系统控制策略等。
随后，我们将重点关注该系统的关键技术研究，包括CO2的适应性研究、系统运行参数的优化以及设备的安全性研究等方面。
在示范应用章节中，我们将介绍该系统在国家速滑馆的实际运行情况，并分析其效果和优势。
最后，本文将对研究成果进行总结，并展望该技术在未来的应用前景。
我们还将探讨该系统对相关领域的意义和影响，例如在大型体育场馆的节能与环保方面的推广价值。
此外，我们还将提出一些后续研究方向，以期进一步完善该系统的性能和应用范围。
通过本文的撰写和研究，我们将深入了解国家速滑馆超大冰面二氧化碳跨临界制冷系统的技术特点和应用价值，为相关领域的技术发展和推广提供重要参考。
1.2文章结构1.2 文章结构本文主要通过对国家速滑馆超大冰面二氧化碳跨临界制冷系统的关键技术进行研究和示范应用，以期达到以下几个目的。
首先，引言部分将对文章的背景和意义进行概述，说明本研究的重要性。
其次，正文部分将详细介绍国家速滑馆超大冰面二氧化碳跨临界制冷系统的整体结构、工作原理和关键技术的研究内容。
其后，我们将展示该系统在实际应用中的示范效果，并进行结果和讨论。
最后，结论部分将对本研究的成果进行总结，并展望该技术在未来的应用前景和对相关领域的意义和影响。
跨临界二氧化碳制冷技术 - 世界第一台多功能两阶段二氧化碳(概要
A PROGRESS REPORT ON THE WORLD’S FIRST MULTIFUNCTION TWO STAGETRANSCRITICAL CO2 REFRIGERATION SYSTEMK. VISSER Principal KAV Consulting Pty Ltd, P O Box 1146, Kangaroo Flat, Vic, 3555, Australia Tel: +61 3 5447 9436 Fax: +61 3 5447 9805ABSTRACTThe world’s first multifunction two stage transcritical CO2 refrigeration system will have been operating for about 16 months by the time the 10th IIR Gustav Lorentzen Natural Refrigerants Conference is conducted in June 2012. This paper reports warts and all on the trials and tribulations experienced during the commissioning of the system in early 2011 and its operations since then.The two stage transcritical CO2 refrigeration plant replaces 22 independent cooling and heating systems comprising air cooled single stage HCFC and HFC condensing units for one blast freezer, one cold store, two chillers, one process chilled water chiller and four reverse cycle AC units, six R134a air to water heat pumps, three gas fired water heaters and two sets of electric under floor and door heaters for the existing blast freezer and cold store.Operating conditions are +5°C SST for office AC, –5°C SST for high stage and chilling duties and –35 to –40°C SST for the booster duties serving the new cold store and blast freezer. The AC compressors also serve as economiser compressors for the main chilling and freezing plant, which therefore runs at high COP’s with a virtual gas cooler CO2 exit temperature of +5°C.During commissioning several design faults were discovered, i.e. firstly, great difficulty to control the pressure in the +10 and +5°C vessels with conventional mechanical spring loaded constant pressure regulators; secondly, the high miscibility of CO2 refrigerant in POE oils resulted in a −5°C oil still not performing at all; t hirdly, the lack of suction superheat on the high stage and AC compressors resulted in low compressor discharge temperatures and hence some difficulty in heating water to adequately high temperatures. This was caused by the designer’s desire to achieve the highest possible COPs with low CO2 gas cooler exit temperatures. Fourthly cold store and chiller evaporator designs got mixed during manufacture. In the end it was necessary to change the circuiting of these units in the field, a difficult job requiring great skill. Finally there is still some uncertainty in the designer’s mind about the best way to handle CO2 liquid flow from the gas cooler during subcritical operations. A separate subcritical liquid receiver may be required.There were also several supplier issues like the inability to supply some high pressure valves, the deletion of essential components from the oil separators and the oil return arrangements from the oil separators to the compressor crank cases, which caused oil carry rates 200 times higher than those specified at maximum values of 5ppm of CO2 mass.Fortunately all difficulties were resolved and now the plant is performing satisfactorily, although not yet at the efficiencies predicted by the designer, who estimated that the new CO2 plant would ultimately reduce the specific electrical energy consumption by 75%, gas consumption by 60%, global warming emissions – including HFC and HCFC fugitive gases – by 40% and cooling water consumption by 62,000 litres/annum, i.e. 40% when the plant achieves the full design capacity of 7,500 kg/day.1. INTRODUCTIONIt was none other than his late dear friend Prof. Dr. Gustav Lorentzen who revived the writer’s interest in CO2 refrigeration in the mid 1980’s when the Ozone Depletion potential of CFCs and HCFCs became evident. This resulted in the unique International Agreement called the Montreal Protocol in 1987 to phase out the use of CFCs and HCFCs and to prohibit the production and use after certain dates.The eminent refrigeration scientist Dr S. Forbes Pearson designed the first applicationof CO2 in the modern era in 1992. The system comprised two flooded CO2 evaporators. The CO2 vapour is condensed in an ammonia cooled plate heat exchanger. A small demonstration unit was installed in a small -23o C cold store at Marks and Spencerp.l.c., Kilmarnock, Scotland. CO2 hot gas for defrost was generated in a CO2 boiler heated by ammonia from the discharge of an ammonia compressor |1|. Gustav Lorentzen called Ref. 1 “A remarkable paper.”10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.2. THE REVIVAL OF CO2Gustav Lorentzen called publicly for the revival of the use of CO2 in 1993. As Professor Risto Ciconkov shows so eloquently in Figure 1 |2|, CO2 and ammonia were commonly used in all manner of cooling and freezing applications from the 1870s to the 1940s, including cooling for human comfort. The cooling in some cinemas in the George Street complex in Sydney was effected by a CO2 refrigeration system until about 1966! But after the advent of CFCs (R12 etc.) in the 1930s, the use of CO2 rapidly declined. Luckily ammonia (NH3) survived as a Natural Refrigerant for industrial applications.3. EVALUATION OF COP’s3.1 Subcritical operationHCsKyoto 1997 HFC (CFC) HCFCNH3CFCNH3 CO2 HCs1987Figure 1: A brief history of refrigerantsReferring to Fig. 2 the COPs for subcritical CO2 operation depend on suction and discharge pressures, and the degree of liquid subcooling, like all subcritical, i.e. conventional refrigeration systems. 3.2 Transcritical operationAs shown in Fig. 3 the COP of transcritical CO2 compressors is dependent on the suction and discharge pressure and – to a much larger extent – on the CO2 exit temperature from the gas cooler. Hence the endeavour to have the high stage compressors run with a liquid CO2 temperature of +5°C, which is the virtual gas cooler exit temperature. This is achieved by using the AC compressors as economiser compressors as well as they effect a degree of parallel compression. 3.3 Seasonally weighted COPsFigure 3. Transcritical CO2 compressor COPvariation with Sat. Suction Temp. at various gas cooler exit temperaturesThe Melbourne climate has a mean temperature of +15°C. Given the need for water heating, the fact that for a short period of the year the plant would need to run in transcritical conditions and the fact that the highest refrigeration loads occur during the five days that production takes place, it is assumed that the plant will run in transcritical mode 20% of the year, i.e. 1752 hours. This is equal to 250 days production at 7 hours/day.10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.The rest of the time the main plant runs purely to complete the blast freezing cycle and maintain operating conditions. The AC system runs partially as an economising compressor. In Figure 4, the ambient dry and wet bulb temperature occurrences have been plotted from more than 30,000 data readings taken at the Melbourne City weather station from midnight to midnight for 10 years |3|. We have selected the Melbourne City design conditions of +35°C dry bulb, +21°C wet bulb, which were exceeded only 0.4% and 0.3% of the time respectively during the period 1997 – 2006.In Table 1, we have evaluated the Seasonally Weighted COP (SWCOP) based on the Melbourne City climate. An advantage of CO2 is its high pressure, which allows close temperature approaches between condensing temperature and cooling air or water. The lower the ambient temperature, the higher the COP and the higher the heating load will be in addition to hot water requirements, but the lower the cooling load will be. Ithas been assumed that on average 20% of the plant Figure 4. Ambient Dry & Wet Bulb Temperature capacity would run in transcritical mode to provide heat Profile –Melbourne City, 10 year period for all purposes and when the ambient cooling air 1997 – 2006, 24 hrs/day |3|. temperature is too high to reduce the discharge pressure below 7.38 MPa, the critical pressure.Table 1. Evaluation of Weighted COP with ambient temperature conditions for 12 monthsrunning of CO2 cooling in the City of Melbourne in: a. DX CO2 with +5°C evaporating temperature for factory cooling and office ACb. DXCO2 with –5°C evaporating temperature for high stage, chiller, chilled water and packing room4. SYSTEM FUNCTIONS AND CAPACITIES, AND OPERATING METHOD4.1 BackgroundIn September 2009 Exquisine Pty Ltd decided to install a two stage transcritical CO2 refrigeration plant to replace 22 independent systems providing heating and cooling at their Thornbury, Victoria, food processing facility where they manufacture high end frozen dairy desserts. The project was supported by a 50% grant from AusIndustry under the Re-Tooling for Climate Change program. A CO2/ammonia cascade plant was briefly considered but with residential properties bordering the site, it was judged best not to use ammonia. Plant operating noise was also a potential problem.10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.4.2 Definition of plant functions |4|A complete range of high end desserts are manufactured at the Exquisine factory where the two stage transcritical CO2 plant has been installed..1 Refrigeration duties and capacities.1 Carton blast freezing of 1,500 kg of product per day growing to 7,500 kg per day at an average airtemperature of –33°C. Q = 70kW@To = –40°C.2 Cold storage with the same plant of about 50 tons of frozen products mostly in shipper cartons, butsome unpacked. Q = 20kW@To = –40°C..3 Chill storage for ingredients at 0°C. Q = 10kW@To = –5°C..4 Packing area cooling to a temperature of +10°C maximum. Q = 25kW @ To = –5°C. .5 Generate 5,000 litres of 4°C process chilled water per day from a mains water temperature of +20°C.10kW@To = 0.5°C, back pressure controlled..6 Factory cooling and AC. Q = 25kW@To = +5°C..7 Office cooling and heating. Q = 10kW@To = +5°C..2 Heating duties.1 Under floor, and door facia and threshold heating of cold store and blast freezer, about 4kW. Processhot water to glycol via PHX..2 Factory AC reheat. Max. 15kW direct from process water. This is also required for air reheat duringcleaning with full fresh air exhaust cycle..3 Office AC reheat and heating in winter 10kW direct from process hot water..4 Potable 65°C hot water for daily cleaning, 5,000 litres, 30-60kW. 12 to 6 hours. Depends onavailability of suitable heat..5 Potable domestic hot water..6 Process hot water for several production processes like chocolate melting..7 Heating of glycol for blast freezer evaporator defrosting..3 Refrigeration capacity summary.1 90kWR@To = –40°C for blast freezer and cold store..2 170kWR@To = –5°C for high stage, packing room, water chilling and chill store..3 35kWR@To = +5°C for factory cooling and office AC.4.3 Description of system. See Fig. 5 |4|Two Bitzer CO2 booster compressors (18), plus one standby unit (19) serve the DX evaporators in the blast freezer (16) and cold store (17). The boosters discharge to a –5°C intercooler (14), which also serves a suction trap for the evaporators in the ingredient holding chiller, the packing area and the process water chiller. Four Bitzer high stage compressors including one standby (3 & 2) discharge either to a two stage gas cooler (4a & 4b) or two PHX water heaters (5) as required by hot water demand. The PHX water heaters will heat a maximum of 10,000 litres of water per day from mains water temperature to 65 to 80°C depending on demand and requirements. Switching from the gas cooler to the PHX water heaters is effected by automatic three way valves.Transcritical or subcritical CO2 is expanded via automatic ICMT valves into an expansion vessel (7) which is maintained at a pressure of 45 bar (+10°C SST). Flash gas is relieved via a back pressure regulator into the +5°C AC suction accumulator (8). From the 45 bar vessel liquid is fed to the +5°C DX evaporators for factory cooling (9) and office AC (10) with the suction returning to the +5°C suction accumulator (8).The level in the 45 bar vessel is maintained by allowing excess CO2 to flow to the +5°C suction accumulator by a Differential Pressure (DP) sensor operated modulating valve. Two Bitzer AC compressors (1) maintain the pressure in the +5°C vessel at 38.7 bar on demand. In addition to the AC load these compressors also act as flash gas i.e. economizer compressors for the rest of the system. This means the rest of the system with the bulk of the capacity is fed with +5°C liquid, i.e. the bulk of the10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.system runs with a virtual gas cooler exit temperature of +5°C. As can be seen from Fig.2 the COP in transcritical operation is highly sensitive to the gas cooler exit temperature. The two AC compressors may discharge to the water heaters or two stage gas cooler as required.From the +5°C suction accumulator liquid CO2 is fed to the evaporators in the ingredient chiller (11), the packing area (12) and the water chiller (13). The suction from these is going to the –5°C suction trap/low pressure receiver (LPR) (14). This vessel is now fed with liquid CO2 from the +5°C AC suction accumulator/economizerflash off vessel in which a constant level is maintained by a DP sensor operated modulating valve maintaining a level with excess CO2 flowing to the –5°C LPR. Liquid CO2 from the –5°C LPR is fed to the blast freezer evaporator (16) and one cold store TX valves (17). Three feeds to the BF coil are needed because of the wide fluctuation in refrigeration heat loads from the start of operation (1,500 kg per day) to ultimate capacity (7,500 kg per day).The pressure in the +5°C vessel will be maintained by capacity controlling the lead AC compressor down to 60% speed. As the load in the +5°C vessel from AC and flash gas reduces further, the AC/economizer compressor will be stopped and the pressure maintained by a back pressure regulator feeding flash gas to the –5°C suction trap (LPR) via (24). The LPR is also used as a de-superheater for the CO2 booster discharge. The amount of de-superheating in this vessel depends on how much booster discharge gas is admitted directly into the high stage compressor suction to regulate the amount of superheat with respect to the final compressor discharge temperature to generate a sufficiently high water temperature in water heating mode.Legend Figure 5Figure 5. Schematic of two stage transcriticalCO2 refrigeration system with heat recovery and AC/economizer compressorsApart from transcritical running for water heating, the system will run mostly in subcritical mode given the prevailing ambient temperature conditions in Melbourne through any year. See Figure 4.A strong emphasis has been placed on overall total system efficiency. The oversized two stage gas cooler is adiabatically assisted on the second stage only in the chase for a low gas cooler exit temperature – in10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.transcritical mode – or a high degree of liquid subcooling. It is estimated that the system will run in transcritical mode a maximum of 20% of the total time, whilst the remainder of the time it will run in subcritical mode.5. DESIGN PROBLEMS EXPERIENCED AND LESSONS LEARNEDDuring commissioning it became evident that some of the problems were related to the design of parts of the system..1 Pressure regulation in +10 and +5°C vesselsIt soon became evident that the standard CVP type constant pressure regulators to regulate the pressure in the +10°C vessel was not capable of maintaining 45 bar in the vessel. The pressure fluctuated significantly. The same problem was experienced with the pressure regulator between the +5 and −5 vessels. The two regulators were replaced with ICM type electronic regulators. These still hunt at low loads, but they react much quicker and provide a satisfactory level of control. It is expected that the stability of the control will improve as the system refrigeration load increases over time..2 Oil still from the −5°C low pressure receiver/desuperheater/high stage suction tra p All the oil leaving the AC, high stage and booster compressors will at some time end up in the −5°C vessel. It therefore seemed logical to install a thermodynamically neutral refrigerant heated oil still under the −5°C vessel. Because of the low TD of 10 K maximum a large heating coil was required to deliver the desired capacity of 4 kW. The coil installed was much too small and in the end leaked CO2 into the oil distilling space. This rendered the oil distilling function unserviceable.The oil is removed by a −5°C liquid heating coil evaporating any refrigerant in oil carried over from the DX blast freezer and cold store evaporators into the −40°C booster suction trap. This oil still function was installed as a back up as it was realised that not all the oil would be removed in the −5°C suction trap and because some 60% of the CO2 refrigerant flow through the system is evaporated at −40°C for the heavy blast freezing and cold storage load. This system works well and there is no oil accumulation in the system. .3 Lack of suction superheat on the high stage compressorsThe use of the AC compressors as parallel or economiser compressors for the rest of the system results in a virtual gas cooler exit temperature of +5°C at transcritical conditions or a virtual subcooled liquid temperature of +5°C at subcritical conditions. This makes for high COPs for the high stage compressors which carry the bulk of the load. Furthermore, the liquid feed from the +5°C to the −5°C vessel is mixed with the booster discharge and superheated −5°C saturated suction vapour from the water chiller, PHX and the coolroom and packing area evaporators.The consequence of the above two features is that there is virtually no superheat in the suction vapour to the compressors which limits their discharge temperature to the extent that it is difficult to reach a final water temperature of 80°C at the exit of the two water heater PHXs operating in series..4 Cold store and chiller evaporator size and circuitingIt became evident that there had been a mix up with the design of the cold store and chiller evaporator. This was discovered when the cold store evaporator was struggling to reduce the cold store temperature. It was discovered that the cold store evaporator was circuited for chiller duty with only one circuit for the entire load. The effect of much higher capacity requirement in the cold store coupled with the higher vapour volume at −40°C evaporating temperature (ET) compared to the erroneous design ET of −5°C meant that the CO2 pressure drop in the single circuit was so great that the CO2 boiling point was so deeply depressed, that the evaporator struggled to handle even a relatively small load. Changing the circuiting to three circuits in situ was a difficult job requiring a great deal of skill. Luckily we found a very skilful tradesman who increased the cold store evaporator circuits from one to three and the circuiting in the original mis-designed cold store evaporator from two to one circuit.6. ENERGY EFFICIENCY ANALYSIS AND FUTURE PROJECTIONSFigure 6 shows the daily electrical energy consumption in kWh and the specific energy consumption per unit of production.In Table 2 the specific energy consumption has been compared over two periods i.e. the last five months and the last three months of the financial year 2010/2011 are compared with the two corresponding periods in the financial year 2009/2010.10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.Figure 6. Daily electrical energy consumption in kWh and specific energy consumption per unit production.Table 2. Comparison of specific electrical energy consumptionN.B. No figures available yet on gas consumption reduction and attendant GWE Although the reductions in Specific Energy Consumption (SEC) are well short of the forecast targets wehave identified a number of reasons why the reductions in SEC were not as great as we had hoped.1. The blast freezer fans have been running @ 100% speed rather than 80% for low freezing capacity,lower than design blast freezing air temperatures because of unfounded fear of large ice crystal growth during slow freezing. Attempts to operate at one third blast freezer evaporator capacity proved unwise and were energy intensive. Warm glycol defrost was not as efficient as expected. 2. Compressor discharge pressures are higher than they should be due to algorithm for subcriticaloperations not being fully developed due to a shortage of funds and initially water heating at 80 bar rather than 90-100 bar. 3. Old refrigeration systems were running during commissioning of new system and other old systems likeelectrical underfloor heating in the old cold store and blast freezer continued to operate.4. Some extra process equipment and pumps not taken into account during design.5. People object to working in the new refrigerated packing room. It is too cold and doors are left openand there is significant infiltration into the cold store. The general air tightness of the panel construction of the -23°C cold store and -30°C to -35°C blast freezer is suspect. 6. Efforts to reduce the energy consumption are continuing by tuning the systems as more is learned aboutits peculiarities. The reduction in gas consumption for water heating has not yet been evaluated.10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.7. CONCLUSIONS AND THE FUTURENow that we have nearly 12 months operating experience it is fair to conclude that two stage transcritical systems are viable even in relatively warm climates like Melbourne. From the previous sections it is fair to conclude that the project reviewed above has experienced a degree of difficulty ranging from minor to significant. The overall positive conclusion is that all systems have been made to perform their intended function, but not always at the promised efficiencies and at significant expenditure of time and money. Notwithstanding the preceding litany of woes in not achieving planned energy efficiency, a 31.7% reduction in specific energy consumption has been achieved when increasing production 113.5%, which increased energy consumption 45.8%. This was much more than predicted. The total integration of all refrigeration, AC and heating duties into one two stage transcritical CO2 system holds a lot of promise to very substantially reduce the total energy consumption and attendant emissions, plus the entire elimination of direct emissions caused by the escaped fugitive HFC refrigerant gases. There is no doubt in the author’s mind that transcritical CO2 systems offer a great opportunity to reduce the cooling and heating costs in existing buildings as they are eminently suited to being retrofitted. Purpose designed and built CO2 systems for the built environment coupled with other strategies have an even greater potential for energy consumption reductions |5|.CO2 as a refrigerant is suitable for use in very small to very large systems in all manner of applications. However, the large scale application so desirable awaits the development of larger, new high pressure two stage compressors or the adaptation of existing high pressure two stage compressors with high crank case pressure capability, such as Compressed Natural Gas compressors.8. ACKNOWLEDGEMENTSMr David Rose, the Managing Director of Exquisine, has the author’s undying gratitude for his courage to try this unproven application of CO2 refrigeration and heating into one working prototype. He has done society at large a great favour, somewhat at hisown expense. AusIndustry’s financial support is gratefully acknowledged. It is unlikely the project would have been able to proceed without the substantial support. The help of and assistance from the following people are also gratefully acknowledged.Dr Petter Neksa, Senior Research Scientist, SINTEF, Trondheim, Norway, for supporting the idea of the first fully integrated CO2 plant in the world; Mr Sergio Girotto, Managing Director of Enex srl, out of Treviso, Italy, for checking our design and suggesting modifications; Dr Andy Pearson, Managing Director of Star Refrigeration out of Glasgow, Scotland, for reviewing the installation and suggesting modifications; Mr Ruediger Rudischhauser, Managing Director of Bitzer Australia (BA) for breaking BA’s policy by selling the two compressor racks to the end user direct to assist getting this project off the ground; Mr Glen Wiles, General Manager, Guenter Australia, also for selling the evaporators and gas cooler to the end user, direct to facilitate this unique demonstration project getting off the ground; Mr Murray Carter, Project Manager, who took firm control of the project when it was necessary to create some order out of the chaos which developed during the installation phase; Mr Kristian Sorensen out of Denmark for assisting the local refrigeration contractors with the commissioning between the end of November and mid December last year; Mr Jim Nonnie, VP Engineering, Temprite Inc. for his quick, decisive and positive assistance with the high oil consumption problems; and Mr Mark Kristensen, Sales and Marketing Director of HB Product for his quick, decisive and positive assistance in providing HB oil level sensors for fitting to the Temprite oil separators.9. REFERENCES|1| Pearson, S. Forbes – Star Refrigeration Ltd. Development of Improved Secondary Refrigerants. Proc.Inst.R. 1992-93.7-1|2| Professor Risto Ciconkov – University of Saints Cyril and Methodius, Skopje, Republic of Macedonia.Figure 2.|3| Australian Bureau of Meteorology, Melbourne, Vic (208) “Dry and Wet Bulb Temperature DataAustralian Capital Cities except Darwin”. 1997 – 2006.|4| Visser, K. An HFC/HCFC Free Food Processing Plant: The Energy and Environmental Benefits of aTwo Stage Transcritical CO2 plant. 9th IIR Gustav Lorentzen Conference: Natural Working Fluids, Sydney, 12-14 April 2010.|5| Visser, K. The possible reductions in energy and water consumption, and CO2 emissions when usingCO2 refrigeration for building heating and cooling. Forum – Ecolibrium, April 2010, Volume 9.3, pp.42-54.10th IIR Gustav Lorentzen Conference: Natural Working Fluids, Delft, 25-27 June 2012.。
CO2跨临界直冷冰场在2022年北京冬奥会首都体育馆的运用
CO2跨临界直冷冰场在2022年北京冬奥会首都体育馆的运用CO2跨临界直冷冰场在2022年北京冬奥会首都体育馆的运用2022年的北京冬奥会是中国继2008年夏季奥运会之后再次承办的一项盛大体育盛会。
作为冰上项目的重要场馆之一，首都体育馆早已成为备受全世界瞩目的焦点。
为了提供更好的冰面质量和环境保护，北京冬奥组委决定引进CO2跨临界直冷冰场技术，这将是国内首次在大型体育场馆中应用这一先进技术。
CO2跨临界直冷冰场，简称CO2冰场，是一种利用超临界二氧化碳制冷的技术。
相较于传统的冰场制冷方式，CO2冰场具有更高的能效和更低的环境影响。
CO2冰场是利用二氧化碳的特殊性质，在超临界状态下，将二氧化碳作为制冷介质通过传热设备输送到冰面，实现对冰面温度的控制。
同时，CO2冰场还可以利用废热回收系统，将制冷过程中产生的热能回收利用，提高能源利用效率，降低能源消耗。
CO2冰场在能源利用效率和环境保护方面的优势是显而易见的。
首先，CO2冰场的制冷效率比传统冰场更高。
相比常规冰场制冷中使用的制冷剂，CO2具有更高的导热系数，能更快速地将冷量输送到冰面，提供更好的冰面质量。
其次，CO2冰场不使用任何对臭氧层有害的物质，不会对环境造成污染。
同时，CO2作为一种无毒、无味、无色的天然气体，其在大气中停留时间较短，对气候变化的影响很小。
在首都体育馆的应用实践中，CO2冰场的效果也是令人惊叹的。
一方面，CO2冰场在提供高质量冰面方面表现出色。
由于CO2具有较高的导热系数，冷量传输速度更快，使得冰面的温度均匀分布，避免了传统冰场中出现的温度差异问题。
这使得运动员在比赛中能够更好地掌握冰面的性质，发挥出更好的竞技水平。
另一方面，CO2冰场在能源利用方面也取得了显著的成就。
CO2冰场利用废热回收系统将制冷过程中产生的热能回收利用，为冰场供暖，减少了能源消耗，实现了绿色低碳的运行。
除了具有明显的技术优势外，CO2冰场的引入还为中国冰雪运动的发展带来了新的机遇和挑战。
跨临界循环二氧化碳制冷系统研究
跨临界循环二氧化碳制冷系统研究摘要：本文对CO2跨临界制冷循环的典型流程与特点进行了阐述；并从超临界CO2特性的研究、CO2制冷设备的研究和开发以及CO2跨临界循环系统安全和可靠性方面展开论述，分析了二氧化碳跨临界循环制冷的发展趋势。
关键词：二氧化碳；跨临界循环；制冷前言：作为最早的制冷剂之一，CO2在19世纪得到了广泛的应用。
到19世纪30年代，世界上约80%的船舶采用了CO2制冷，但是当时的CO2制冷效率不够高，功耗极大，并逐渐被同期出现的以R12为代表的氟氯烃制冷剂代替。
近年来，制冷剂对臭氧层破坏加剧，且造成了全球温室效应等诸多环保问题，CO2作为制冷剂重新出现在公众视野中。
本文将对CO2跨临界循环制冷的研究现状和进展进行介绍。
一、CO2跨临界制冷循环流程及其特点CO2跨临界制冷循环基本流程CO2跨临界制冷系统流程图如图1所示，压缩机对气体工质进行压缩，使其压力升至超临界压力之上，（f—a过程），进而在气体冷却器内由冷却介质对其进行冷却（a—b过程）；为使制冷压缩机的性能系数（COP）有所提高，在内部回热器中，压缩机将进一步对从气体冷却器中释放的气体进行回气冷却（b—c,e—f过程）；最后进行节流降压（c—d过程），部分液体发生液化，在进入蒸发器后，湿蒸气发生汽化（d—e过程）进而对附近的介质热量进行吸收，最终达到了制冷目的。
储液器的作用是进行液气分离并负责制冷剂的补充。
图1 CO2跨临界制冷系统流程图本系统的最显著特点是工质的吸热和放热过程在相对应的亚临界区和超临界区分别进行，压缩机的吸气压力要比临界压力低，临界温度高于蒸发温度，循环吸热过程依然在亚临界状态下发生，通过潜热完成换热过程。
但是临界压力低于压缩机的排气压力，所以工质的冷凝过程不同于其在亚临界状态下的过程，而是通过显热实现换热过程。
CO2跨临界制冷循环特点CO2跨临界的优点CO2具有无毒、来源丰富、制冷量大等优点。
这是唯一一种天然的、兼备热力特性、环保特性、安全特性的制冷工质。
二氧化碳跨临界制冷研究
凝器，而称为气体冷却器（简称气冷器）【８ｊ。 跨临界制冷循环是当前Ｃ０２制冷循环研 究中最为活跃的领域；
图１为典型的跨临界二氧化碳制冷系 统流程图，图１为相对应的制冷循环压一 焓图。气体工质在压缩机中压缩后压力升 至超临界压力以上。在ｐ—ｈ图上为过程 ｆ—ａ；然后进入气体冷却器，被冷却介质 冷却（ａ—ｂ过程）；为提高ＣＯＰ，从气体 冷却器出来的气体在内部回热器中进一步 被压缩机回汽冷却（ｂ—ｃ和ｅ—ｆ过程）； 再经过节流降压（ｃ—ｄ过程）．部分气体 液化，湿蒸汽进入蒸发器汽化（ｄ—ｅ过 程），吸收周围介质热量而制冷。储液器
起汽液分离（蒸发器出口不过热）、补充 制冷剂等作用删。
２二氧化碳压缩机研究关键点 压缩机的安全可靠性与性能价格比。 是Ｃ０２循环压缩机推广应用的关键问题 也是众多研究机构的研究的重点。 Ｃ０２压缩机的进排气压力差为 ５．ＯＭＰａ一８ ＯＭＰａ。在大压差下运行．要
求在压缩腔设计和压缩机尺寸的确定的 影响。较高的运行工作压力，并不会成为 Ｃ０２作为制冷工质推广应用障碍。
三、二氧化碳压缩机的若干关键技 术问题
１润滑油问题 二氧化碳跨临界循环系统选择润滑油 面临许多困难；超临界状态的二氧化碳容
２器ｌ＿｜’℃液讣凼嚣 ；， 图１ 二氧化碳跨临界回热循环流程图
易溶解于润滑油中，稀释后的润滑油粘度 会大大降低；压缩机承受压力负荷较高。 润滑油膜可能会被流动的超临界状态的二 氧化碳破坏；润滑油膜可能会被溶解在润 滑油中的二氧化碳汽化所破坏；超临界状 态的二氧化碳可能会与润滑油发生化学反 应及腐蚀。
浅谈二氧化碳制冷技术
浅谈二氧化碳（2CO ）制冷技术 摘 要:由于CFC 类制冷剂对臭氧层的破坏作用，大部分CFC 与HCFC 类工质将被逼退出使用。
制冷工质的替代和环保问题自然成为制冷空调行业的关注焦点。
自然制冷工质如CO 2受到越来越多的关注。
文中简述了2CO 作为制冷剂的发展历史和它退出历史舞台的原因； 根据2CO 作为制冷剂的相关热物理和化学性质以及三种可能的2CO 制冷循环，说明了采用2CO 为替代CFC 与HCFC 类工质、采用跨临界循环的优越性和必要性； 对各国采用2CO 为制冷剂的制冷、空调、热泵系统的应用及其研究情况进行了综述，浅谈研究发展的方向。
关键词：2CO 跨临界循环 工质 制冷前言:自从人类发明利用制冷设备制冷来为生活、生产和科研等服务以来,制冷剂就伴随着制冷系统和制冷技术的改进而发展。
从最初采用的O H 2、3NH 、2CO 等自然工质到上世纪30年代,CFC 与HCFC 类物质就开始大量作为制冷工质，以其优越的循环性能，很快就取代了过去的自然工质.但随着大气臭氧层空洞的出现和全球气候的变暖，人们终于认识到制冷空调行业所使用的CFC 与HCFC 类制冷剂对大气具有破坏臭氧层负作用和产生温室效应。
更在上世纪80年代发现南极上空的臭氧空洞后，世界上引发了环境问题新高潮,保护臭氧层的蒙特利尔议定书的签署正式生效，一系列CFC 与HCFC 类工质被列入受控表。
这使到全世界的制冷空调行业面临严重的挑战，CFC 与HCFC 类工质的替代早已成为当前国际性的热门话题。
今年已到2010年，根据的蒙特利尔议定,一系列受控的CFC 与HCFC 类工质在今年必须淘汰使用，制冷工质的替代问题更是破在眉睫。
面对以上问题，国内外制冷空调行业均在探索总结历史经验，寻求正确、科学、环保的制冷工质。
在环境保护与替代制冷工质的研究进程中,有学者认为选用自然工质是解决环境温度最终方案。
一批具有特定的物理性质的自然物质又开始得到了重视和研究。
二氧化碳的跨临界包涵的化学知识
二氧化碳跨临界相关化学知识二氧化碳跨临界是以二氧化碳为制冷剂的一种制冷技术，根据二氧化碳制冷剂的性质可超临界制冷和亚临界制冷。
其中，二氧化碳跨临界直冷制冰系统，是在国家速滑馆制冰工作中采用的系统，有着绿色环保的优点，最大的优点就是能让冰的温度保持均匀。
此外，直冷制冰技术，是制冰领域一种制冰方式，和传统的盐水式制冰方式有着很大的不同。
用二氧化碳作为制冷剂提供冷源，结合直冷式制冰方式组合而成。
技术优点
和传统的制冰技术相比，最明显的区别是“此次冬奥会上采用二氧化碳跨临界直冷制冰系统制出来的约5500平方米的冰面，冰温很均匀，温度差基本上能够控制在0.5摄氏度以内，这是用氟利昂制冷剂或乙二醇载冷剂制冰的冰场很难达到的效果。
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单一C02跨临界压缩机运行制冷技术简况
技术优势：
该循环系统的最大特点就是工质的吸、放热过程分别在亚临界区和超临界区进行。
压缩机的吸气压力低于临界压力，蒸发温度也低于临界温度，循环的吸热过程仍在亚临界条件下进行，换热过程主要是依靠潜热来完成。
但是压缩机的排气压力高于临界压力，工质的冷凝过程与在亚临界状态下完全不同，换热过程依靠显热来完成，此时高压换热器不再称为冷凝器，而称为气体冷却器。
在以空气为热源、热汇的制冷和热泵系统（主要是汽车空调以及家用空调）中，CO2循环在跨临界条件下运行，其工作压力虽然较高，但压比却很低，压缩机的效率相对较高；流体在超临界条件下的特殊热物理性质使它在流动和换热方面都具有无与伦比的优势，超临界流体优良的传热和热力学特性使得换热器的效率也很高，这就使得整个系统的能效较高，完全可与传统的制冷剂（如R12、R22等）及其现有的替代物（如R134a、R410A等）竞争。
加上CO2在气体冷却器中大的温度变化，使得气体冷却器进口空气温度与出口制冷剂温度可能非常接近，这自然可减少高压侧不可逆传热引起的损失。
由于CO2的临界温度低，为31, ℃因此, 制冷循环采用跨临界制冷循环时，其排热过程不是一个冷凝过程，压缩机的排气压力与冷却温度是两个独立的参数，改变高压侧压力将影响制冷量、压缩机耗工量及系统的COP。
研究分析表明，高压侧压力变化时，循环的COP 存在着一个最大值，因此，CO2跨临界制冷循环在对不同工况下，存在对应于最大COP 值的最佳排气压力。
CO2 在气体冷却器中较大的温度变化，正好适合于水的加热，从而使热泵的效率较高。
传统空调系统大多把冷凝热当作废热而直接排向大气，既造成能量的浪费又产生环境的局部热污染。
而对跨临界循环,由于超临界区工质密度在不断增加，循环的放热过程必将有较大的温度滑移，这种温度滑移正好与所需的变温热源相匹配，是一种特殊的劳伦兹循环，其用于热回收时，必将有较高的放热效率，因而用于较高温度和较大温差需要的热回收时具有独特的优势。
优点：
（1）安全、环保、无污染； CO2 作为制冷剂其优点在于，无毒，没有可燃性，价格便宜、来源丰富、无须回收，与普通润滑油相溶，容积制冷量约是R22 的5 倍，CO2 是唯一同时具有优良的热力特性、安全特性和环境特性的自然工质。
制冷系统蒸发器采用顶排管，冷凝方式采用植入式地源冷凝技术。
（2）节能（以每立方米容积年耗电量计算）：我国年平均耗电量为130度左右，先进发达国家年耗电量为60多度，而该冷库年耗电量仅6度左右。
（3）库温稳定：该冷库温差波动在±0.5度波动，将大大提升冻品的储藏品质，延长食品的实质质保期。
（4）机房占地面积小。
应用：
经过调查，北京市京科伦工程技术有限公司、北京市京科伦冷冻设备有限公司近年来多次承办智能立体库、速冻隧道等项目，工程项目遍布全国的22个省份的40个多城市，项目合作企业包括双汇、金锣、雨润、思念、三全、惠发等中国知名企业，所承担的项目均达到或超过了设计要求。
此次中冷联盟论坛中，各会员单位参观了由北京京科伦承建的武汉山绿物流公司冷库，显示了其技术的成熟性。
以下为冷库参观情况：
本次参观的冷库，是国内第一座单一C02制冷的低温自动化立体冷库，冷库容积15万立方米，设计1.2*1米的托盘位数26236个，自动化出入库设备可满足每日出入货量达到总储藏量的20%。
库体尺寸：83.6m(长)×59m(宽)×30m （高），装卸货间面积：17.5m(长)×59m(宽)×24.6m（高），共三层，一层装卸货间，设计温度10℃；夹层是设备间和参观走廊，制冷机房，配电间等；二层自动化分拣车间，设计温度-18℃；三层保鲜库，设计温度-4℃~4℃。
此二氧化碳跨临界制冷系统是此库的亮点之一。
亮点之二是建筑形式采用国际最先进的库架一体式，库内无结构立柱，能够最大程度地利用库内空间；采用独立筏板基础设计，受力均匀，冷库整体无冷桥，具有最好的抗震能力，安装施工便利，速度快。
亮点之三是围护结构应用注塑式整体发泡技术。
采用双面不锈钢现场焊接，形成全封闭外壳，消除了连接缝隙，提高了使用寿命的同时，大大降低了能耗。
亮点之四是链条式输送机全部采用伺服控制，运行速度最快达到30米/分钟。
亮点之五是发货月台与库内连接通道设备为环形双道互锁门，开、关门响应速度快，不超过2秒，货物通过门时无等待时间。
亮点之六是结合客户需求及经营情况，配备了冷链物流行业第一个零担货物的机器人自动分拣系统，大大提高货物的分拣速度和效率，为客户提供更多的服务，为冷链物流行业的发展模式带来新的变革。