对二氧化碳或CO的兴趣2，作为食品零售应用程序中的制冷剂，从来没有比今天更强烈，因此，关于这些系统的能源效率有很多讨论。能源讨论的重点是两个因素：气候变化绩效和财务上的理由。
生命周期气候表现或LCCP是一种标准方法，是将技术与它们对气候变化的影响进行比较，这是通过大约等效释放的CO衡量的标准方法2。传统的HFC制冷系统具有两个强大的LCCP组成部分：直接和间接贡献。直接贡献是制冷剂向大气中释放到大气中的结果，并且基于制冷剂的全球变暖电位或GWP（与LCCP一样，GWP是基于制冷剂与CO相比的制冷剂对气候变化的影响。2）。制冷剂的释放绝不应该是故意的（目前在大多数司法管辖区都是非法的），但是它通常在食品零售冷藏系统的生活中发生，主要是通过泄漏。虽然可以最大程度地减少这些泄漏，但使用低的全球变暖电位制冷剂（例如CO）2可以使这种效果微不足道（CO2has a GWP of 1, compared to ~4000 for a refrigerant like R404A). It is important to note with regards to leaks, there are rules and regulations being proposed (particularly in California) which may add financial penalties to the environmental penalties associated with leaked refrigerants.
The indirect component is due to the effect of the energy used in operating the refrigeration equipment. The less energy that is needed to operate the equipment, the lower its contribution to the climate effects will be. Since both of these components in a traditional HFC system, direct and indirect, are of approximately the same magnitude, even a relatively inefficient low GWP systems can still provide climate change benefits.
财务理由可能对CO的广泛改编更为重要2系统，因为合作2systems in North America are substantially more expensive than traditional refrigeration systems. This is due to the facts that CO2系统以高压力运行（增加了组件的成本），它们比传统的HFC系统更为复杂（带有带有阀门的旁路线，在气体冷却器出口处的高压跨性别阀和额外控件）和CO2systems do not yet have the purchasing volume in North America to drive down component and installation costs. In order to be financially justified, these systems need to overcome this initial capital outlay by providing ongoing operating cost reductions.
显然，CO还有其他财务考虑2系统，例如长期监管和社会影响，但是这些系统难以量化。但是，如果我们使用更简化的财务模型，那就容易得多betway1188 证明额外的资本支出是合理的。
严格由于其作为制冷剂的物理特性，CO2has some inherent challenges compared to HFC refrigerants with regards to energy. These challenges stem from the high working pressure (over 1000 psi vs. around 200 psi for R22) and the relative performance through the heat rejection and expansion process. While these disadvantages seem to be significant, as much as a 20% penalty, they can be mitigated through the system's design.
On the other hand, there are properties of CO2这也有助于该系统在食品零售应用中的效率，包括出色的容量效率（AS R22的冷却效果的6倍以上），低压缩比（压缩机的入口和出口压力之间的比率）和低粘度（使粘度低（使其产生）（泵浦更容易）。此外，已经开发了利用CO的独特属性的新技术2to improve efficiency.
使讨论复杂化的是通常在CO上使用的技术2systems that can also be applied with great effect in traditional HFC systems. These items can make the initial cost of a CO2system seem even higher versus a basic HFC system, but can be considered separately and be financially justified in any system. Many retailers have found that implementing advanced energy saving technology on their HFC systems to be well worth the cost.
There are three key technologies that fall into this category. The first is electronic expansion valves with case controllers, which allow the suction pressure to be optimized to minimize the load on compressors as conditions change. The second is the use of variable speed drives to allow the compressor and condenser capacity to more closely match changes in load. The third is heat reclamation to use waste heat of the refrigeration cycle.
由于废热的质量低（即低温），热填充，特别是在HFC系统中，主要用于补充热水需求。在CO2systems, the temperature of this waste heat is much higher, allowing it to be used for hot water, comfort heating, dehumidification reheat, or regeneration of desiccant, etc.
co2specific technologies take into account the system's design. Booster systems arrange the compressor piping to allow the low temperature compressor to boost the suction pressure for the medium temperature compressors, saving work and energy. Parallel compression deploys a portion of the medium temperature compressor capacity to recover and re-compress, at a lower compression ratio, the flash gas formed when the compressed vapor exiting the gas cooler is expanded to allow it to condense into liquid. A large portion of the flash gas in the receiver can be considered lost capacity for the system, though reclaiming it with a minimum amount of work can increase system efficiency by as much as 20% during trans-critical operation.
The most recent development is a device called an ejector. An ejector can use high pressure compressed vapor from the gas cooler and utilize the energy lost during expansion to increase the pressure of the flash gas, allowing it be introduced into the suction side of the parallel compressors, reducing the work needed to compress the gas. This technology is very effective in dealing with one of the most inefficient aspects of CO2冷藏并可能克服CO的固有缺点2温暖气候中的反式关键系统。
Let's sum it all up with representative numbers for warm climate applications
(note: the following are full year estimates):
| Transcritical CO2 | HFC Systems | |
| 基本制冷剂效率 | -20％ | 基线 |
| 带有案例控制器的电子扩展阀 | +10% | +10% |
| 可变速度驱动器在压缩机和冷凝器上 | +5% | +5% |
| 热收回 | +10% | +5% |
| co2Booster system technology | +5% | |
| 平行压缩 | +10% | |
| 喷射器技术（气体和液体） | +10% | |
| 总机会与基本HFC系统 | +30％ | [+20％] |
| 总机会与高级HFC系统 | +10% |
It should be noted that while the energy improvements in cooler climates may be lower, the overall efficiency of transcritical CO2systems increase with cooler ambient temperatures (i.e., less time operating in transcritical mode).
本摘要中未包括的是使用绝热或蒸发冷凝器/气体冷却器，这可以为这两个系统提供效率的5％。实际上，随着对系统设计的额外关注2与HFC蒸发器相比，气相冷却器的使用量少得多，最多要少80％。这些设备的性能在当地气候下大大差异，并且是其系统的特定性。也就是说，这是另一个有趣的技术。
尽管该分析对于所有应用程序都远非严格，但本文的目的是总结可用的情况和技术，以更清楚地了解当今的可能性。显然，跨批评二氧化碳技术已经准备好在几乎任何气候中部署，并可以提供可观的环境和财务利益。