Abstract ：

With global warming and rising energy consumption, energy conservation, emission reduction, and the development of renewable energy have become critical global priorities. In this context, phase-change refrigeration technology has emerged as a promising solution for energy savings. This paper explores the integration of phasechange cold storage technology and mini-electrical storage technology in direct current(DC) refrigerators. Firstly, household refrigerators were converted to DC operation, and a test bench for phase-change cold storage DC refrigerators was constructed. Subsequently, experimental research was carried out on the temperature maintenance time of the refrigerator after power-off and the energy-saving effect of phase-change cold storage refrigerator in the process. The results demonstrated that the temperature retention time of in the refrigerator's compartments increased by 30 h, 20 h, and 5 h, respectively, after power failure compared to the refrigerator without phase change materials. The 18-h-on/6-h-off mode is the most energy-efficient and cost-effective approach, while the 12-h-on/12-h-off mode offers significant advantages in grid load balancing and system reliability, despite causing minor temperature fluctuations. Moreover, integrating phase-change cold storage with mini-electrical storage not only enhances energy efficiency but also helps reduce carbon emissions.

Keyword ：

Direct current refrigerator Temperature stability Cold storage Performance of system Phase change materials

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Abstract ：

In recent years, the ultra-low-temperature district heating (ULTDH) systems has been developed to further reduce the heat loss in the district heating network. In this paper, on the basis of the ULTDH system, a double- loop booster heat pump (DLBHP) system used for terminal heating is proposed to improve the uniformity of temperature difference and heat transfer efficiency. The building heat load in Beijing was simulated using DEST software, and then the heating simulation model of the DLBHP was established through the TRNSYS software simulation platform. By changing the various control strategies on the heat source side and the heat sink side, the optimization of the operation and control strategies and the system performance were analyzed. The simulation results indicate that compared with the traditional operation modes, the system average COP with optimized control strategy can be increased by up to 9.24 %, and the power saving during the heating season can be up to 1389 kW & sdot;h. It can satisfy the real-time heat load demand of users, and has a large energy-saving potential as well as a broad market application prospect.

Keyword ：

Operational strategy control TRNSYS model building Ultra-low-temperature district heating System performance Double-loop booster heat pump

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Abstract ：

To improve the efficiency of air source heat pumps and eliminate the performance degradation caused by frost in winter, a hot gas bypass defrosting experimental platform was built and the hot gas bypass defrosting experiment under different outdoor temperature and different opening degree of hot gas bypass valve were carried out. The results showed that the defrosting of the heat pump evaporator can be completed well by adopting the hot gas bypass defrosting method without interrupting the heat pump heating. At outdoor temperatures of -10 degrees C, -5 degrees C and 0 degrees C, the most appropriate time for heat pump to activate hot gas bypass defrosting were 30 min, 40 min and 50 min, respectively. The corresponding peak value of average heating capacity were 7.96 kW, 10.16 kW, and 12.08 kW, and the heating COPC values were 3.03, 3.56, and 4.19, respectively. The increase of bypass exhaust volume would shorten the defrosting time but also reduce the heating capacity of the heat pump during the defrosting process. Hence the optimum defrosting start time of the system is different with different bypass valve opening. For the system built by this paper, the 20 % bypass valve opening had the best performance in defrosting, and the optimal defrosting start time was 40 min, during which the average heating capacity and COPC achieved peak values of 10.16 kW and 3.56, respectively. These results provide a reference for the defrosting design of air source heat pumps.

Keyword ：

Hot gas bypass defrosting Optimal defrosting start time Heating performance Air source heat pump

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Abstract ：

In this paper, an air source heat pump water heater based on a dual cylinder compressor (DCWH) with constant speed is proposed, a mathematical model is established and a test bench for the new heat pump water heater is built. Three different operating modes: DSP (Double stage parallel mode), SS (Single stage compression mode), and DSS (Double stage series mode) are developed, and the working performance of it is compared with the conventional variable frequency compressor water heater (VFWH). The results show that the optimal volumetric ratio of the dual cylinder compressor is 0.6, 0.56, and 0.5, respectively. The DCWH system can effectively reduce the discharge temperature and pressure. Compared with the VFWH system, the heating time of hot water can be reduced by 20.27 %, and the water heater system can run under ambient temperature lower than -18 degrees C. The hot water production capacity increase 26 %, energy efficiency ratio is about 6.7-8.4 % higher than that of the VFWH system.

Keyword ：

Dual cylinder compressor Heating capacity Air source heat pump water heater Heating COP

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Abstract ：

Recovering and reusing this waste heat for district heating is an effective strategy to enhance energy efficiency in data centers. To align data center waste heat recovery with heat consumer demand and improve energy utilization, a transient mathematical model of a data center-integrated heat pump district heating system was developed and validated. A case study involving a small data center with 300 standard racks in Beijing was conducted to analyze the system's operational and dynamic behavior. The results show that hot water and heating account for 35.70 % and 64.30 % of the total heat consumption, respectively. During the heating season, the heating heat pump unit exhibits a high heating coefficient of performance (COP), with a maximum heating COP of 5.27. Under year-round operation, the COP of the hot water heat pump unit exhibited periodic 24-h variations. Peak water consumption occurred from 6:00 to 9:00 and 21:00 to 24:00, with corresponding heating COP values of 3.87 and 4.24, respectively. The proposed system in addressing the cooling demand of the data center and the heating and hot water demands of the heat consumers, providing a feasible solution for improving the energy utilization efficiency of data centers.

Keyword ：

Waste heat recovery Integrated heat pump district heating system Dynamic performance analysis Data center

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Abstract ：

为了转移建筑峰值负荷,提出一种CO2水合物蓄冷空调系统,该系统以CO2为循环工质,以CO2水合物为蓄冷介质,采用直接接触式蓄冷方式,可有效减少传热热阻,提高系统性能.基于热力学循环分析方法,对CO2水合物蓄冷系统循环建立数学模型,进行理论分析,结果表明:当CO2消耗量增加到制冷剂质量流量的20％时,系统的性能系数增加到原来的1.25倍.根据温度降低C02水合物更容易生成的特性,随着蒸发温度的升高,潜热蓄冷量减少,总瞬时蓄冷量和压缩机功耗降低,系统性能系数增大.升高蒸发温度和降低气冷器出口温度有助于提升蓄冷系统的性能.气冷器出口温度对系统的最优排气压力影响较大,而蒸发温度的变化对系统最优排气压力影响较小.当蒸发温度从2℃升高到8℃时,系统的最优排气压力值均维持在8.6 MPa左右.当气冷器出口温度从35℃升高到45℃时,最优排气压力的平均上升幅度约为0.24 MPa/℃.

Keyword ：

最优排气压力 蓄冷空调 直接接触 蓄冷介质 CO2水合物 性能系数

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Abstract ：

数据中心低碳转型减排对实现碳达峰、碳中和目标具有重要意义.对全国数据中心总体情况进行对比分析,基于中国关键年份CO2排放和强度目标,引入能效提高率、非化石能源消费占比、负排放技术强度3个变量,采用情景分析法分析数据中心CO2排放总量.研究结果表明:数据中心的耗电量逐渐增加,而碳排放量呈先增加后降低的趋势,数据中心的电能利用效率(PUE)呈逐渐下降的趋势,3种情景的碳达峰时间均为2030年,碳中和的时间分别为2059、2057、2055年.展望2060年碳中和目标,数据中心行业应进一步提高能效利用率、提高非化石能源占比、加强碳捕集与封存技术创新和提升碳汇水平.

Keyword ：

碳中和 减排路径 情景分析 数据中心

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Abstract ：

随着人们环境保护意识的加强，天然工质制冷剂重新受到研究人员的关注。空气是一种安全且对环境绝对友好的天然制冷剂，未来，压缩空气制冷循环有望成为传统蒸气压缩制冷循环的潜在替代品。压缩膨胀机作为压缩空气制冷的核心部件，其工作效率对机组性能有直接影响。为了设计出能够配合膨胀机高效工作的离心压缩机，需要对传统的设计方法进行一些修正。本文将质量、动量、能量守恒与射流尾迹区理论相结合，并将传统的离心压缩机相关参数推广到较低压力的范围中，提出了一种与现有的涡轮膨胀机相匹配的离心压缩机几何参数的设计方法。使用该方法为现有的膨胀机设计了对应的离心压缩机，并利用其他学者分析过的离心压缩机模型对该方法进行验证，利用计算流体力学方法(CFD)对压缩膨胀机变工况下的工作性能及对膨胀功的利用率进行模拟分析。按本方法设计的离心压缩机在设计工况下能够以高于92%的效率利用膨胀机的输出功。在变工况条件下能够以高于88%的效率利用膨胀机的输出功，并且在设计质量流量附近能够顺利运行。

Keyword ：

离心压缩机设计 空气压缩制冷 膨胀功利用率 压缩膨胀机

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空气源热泵的高效除霜是技术难题，准确测量霜层厚度可为除霜控制提供最可靠依据。总结和分析了现有基于霜层测量的除霜技术手段，包括数字千分尺、游标尺、扫描探针显微镜、激光测厚、中子射线、光电转换、传感器、图像处理、声学信号和人工智能等，对其各自优势及局限性进行了比较分析，为今后空气源热泵基于霜层测量的除霜控制研究提供参考。

Keyword ：

空气源热泵 霜层 除霜控制

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Abstract ：

为提升家用空气源热泵热水器水箱外微通道冷凝器的性能,建立了家用空气源热泵热水器水箱外微通道冷凝器的准稳态模型,实验验证结果显示模型误差能控制在±9%以内。依据模型对微通道冷凝器的换热量、换热系数、压降等性能进行仿真研究。结果发现,微通道冷凝器为四流程时能够减小压降并保证换热量满足需要;关键参数微通道截面的最佳尺寸在1.6～2.6 mm~2系统性能最优,同时扁管内微通道数应控制在16～24根。研究结果为家用空气源热泵热水器微通道冷凝器的设计提供借鉴。

Keyword ：

数学模型 热泵热水器 仿真 微通道冷凝器 优化 制热量

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