For the performance improvement of carbon dioxide heat pump systems, two new systems, a mechanical subcooling heat pump system that auxiliary cycle with ejector and a mechanical subcooling heat pump system that major cycle with ejector are proposed. The new systems combine the advantages of mechanical subcooling and ejectors. Three original carbon dioxide systems including a base system, a base system with ejector and a mechanical subcooling heat pump system are chosen as comparison systems to demonstrate the advantages of new systems. Meanwhile, three kinds of heating terminals and six typical cities in different regions are selected for comprehensive evaluation. Furthermore, the optimal operating conditions for each system with traditionally designed radiator, floor-coil radiator and small temperature difference fan-coil unit as terminals applied in different regions are obtained through multi-objective optimization. Compared with the base system, the coefficient of performance of the new system that auxiliary cycle with ejector and the new system that major cycle with ejector are improved by 17.58–20.90 % and 25.78–26.87 %, respectively, under rated working conditions. More importantly, the above new modified systems can operate at optimal conditions due to the reduction of optimal major discharge pressure. The new system that major cycle with ejector also reduces the minimum evaporating temperature limit to −40 °C, providing better low-temperature adaptability. Compared with the original mechanical subcooling system, the initial investment cost of the new system that major cycle with ejector is increased by only about 1.46–3.41 % under the optimal design conditions. For cities other than Harbin, the life cycle cost of the base system with ejector is lower than that of all remaining systems throughout the entire life cycle, which is the preferred system. In addition, the new system that major cycle with ejector is also a system that could be considered for selection. The life cycle cost of the new system that major cycle with ejector can be below that of the original mechanical subcooling system within 7 years and that's an acceptable amount of time. For Harbin, the life cycle cost of the new system that major cycle with ejector is lower than that of the base system with ejector after 6 years of running time. And the life cycle cost of the new system that major cycle with ejector is 12.7 % lower than that of the base system with ejector when the operating time reaches 15 years. The new system that major cycle with ejector will be more competitive in modifying the carbon dioxide heat pump systems if the equipment quality can be improved to extend operating time. The above analysis will provide a reference for the selection of systems and operating schemes in different regions.

中文翻译：

---

改良二氧化碳热泵系统综合分析及住宅供暖运行方案确定：多目标优化方法

为了提高二氧化碳热泵系统的性能，提出了两种新系统：带喷射器辅助循环的机械过冷热泵系统和带喷射器主循环的机械过冷热泵系统。新系统结合了机械过冷和喷射器的优点。选择三个原始二氧化碳系统，包括基础系统、带喷射器的基础系统和机械过冷热泵系统作为对比系统，以展示新系统的优势。同时选取不同地区的3类供热终端和6个典型城市进行综合评价。进一步，通过多目标优化，得出不同地区应用的以传统设计的散热器、落地盘管散热器和小温差风机盘管为末端的各系统的最佳运行工况。与基础系统相比，在额定工况下，带喷射器辅助循环的新系统和带喷射器主循环的新系统的性能系数分别提高了17.58%~20.90%和25.78%~26.87%。更重要的是，由于最佳主排放压力的降低，上述新改进的系统可以在最佳条件下运行。带喷射器主循环的新系统还将最低蒸发温度限制降低至-40℃，提供更好的低温适应性。与原机械过冷系统相比，在优化设计条件下，带喷射器大循环的新系统初始投资成本仅增加约1.46%~3.41%。对于哈尔滨以外的城市，带有喷射器的基础系统在整个生命周期中的生命周期成本低于所有其余系统，是首选系统。另外，带有喷射器的主循环新系统也是可以考虑选择的系统。新系统的生命周期成本（带喷射器的主循环）可以在 7 年内低于原始机械过冷系统，这是可以接受的时间量。对于哈尔滨来说，运行6年后，带喷射器主循环的新系统的生命周期成本低于带喷射器的基础系统。当运行时间达到15年时，带喷射器主循环的新系统的生命周期成本比带喷射器的基础系统低12.7%。如果能够提高设备质量，延长运行时间，带喷射器主循环的新系统在改造二氧化碳热泵系统时将更具竞争力。上述分析将为不同地区的系统和运营方案的选择提供参考。