Theoretical Study on CO_2 Transcritical Cycle Combined Ejector Cycle Refrigeration System

Chlorofluorocarbons(CFCs) or hydrochlorofluorocarbons(HCFCs) are as main refrigerants used in traditional refrigeration systems driven by electricity from burning fossil fuels, which is regarded as one of the major reasons for ozone depletion (man-made refrigerants emission) and global warming (CO 2 emission). So people pay more and more attention to natural refrigerants and energy saving technologies. An innovative system combining CO 2 transcritical cycle with ejector cycle is proposed in this paper. The CO 2 compression sub-cycle is powered by electricity with the characteristics of relatively high temperature in the gas cooler (defined as an intercooler by the proposed system). In order to recover the waste heat, an ejector sub-cycle operating with the natural refrigerants (NH 3, H 2O) is employed. The two sub-cycles are connected by an intercooler. This combined cycle joins the advantages of the two cycles together and eliminates the disadvantages. The influences of the evaporation temperature in CO 2 compression sub-cycle, the evaporation temperature in the ejector sub-cycle, the temperature in the intercooler and the condensation temperature in the proposed system performance are discussed theoretically in this study. In addition, some unique features of the system are presented.

Energy savings and CO_2 emission reduction by using geothermal heat pumps

The renewable energy will play significant role in the world primary energy consumption in the future. Geothermal energy is immense with 5 000 EJ/a of technical potential, and geothermal heat pumps (GHPs) are one of the fastest growing applications of renewable energy in the world with annual increases of 10 % and much faster in China. With high coefficient of performance (COP) up to 6, GHPs make efficiency of primary energy more than 240 % with assumed a 40 % of electricity generation efficiency, which means energy savings and CO2 emission reduction. In this paper,the geothermal resources and its utilization are talked about, and GHPs technology was introduced. Due to its high efficiency, there will be energy savings by using GHPs. There is also CO2 emission reduction because of using geothermal heat pumps, which is analyzed in the end.

Experimental Performance of Moderate and High Temperature Heat Pump Charged with Refrigerant Mixture BY-3

Theoretical and experimental analysis of a new refrigerant mixture BY-3 was conducted based on a single-stage vapor compression refrigeration system. The water-water heat pump system used BY-3 to produce hot water when the low temperature was 20 ℃. The following results were obtained: the highest temperature at the condenser outlet reached about 85 ℃; when the difference between the water temperatures at the condenser outlet and the evaporator inlet was less than 40 ℃, the coefficient of performance (COP) was larger than 4; when the difference reached 55 ℃, the COP still kept 3; the discharge temperature of BY-3 was lower than 100 ℃, and the refrigerant vapor pressure kept lower than 1.8 MPa. When the water temperature at the condenser outlet reached over 85 ℃, nearly a 5 ℃ superheating temperature was maintained.

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO₂Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.

Reaction Rate Characteristics of SrBr2 Hydration System for Chemical Heat Pump Cooling Mode

Here, we propose a chemical heat pump chiller with a SrBr2 hydration reaction system for utilization of waste heat. The SrBr2 hydration reaction could recover waste heat in low temperatures ranging from 373 K to 353 K, and the system showed good potential in terms of the high cooling thermal-storage density. Previous studies have given little information on the reaction characteristics of the SrBr2 hydration reaction. In this paper, we developed a measuring method for the hydration reaction equilibrium and reaction rate based on the volumetric method. We analyzed the hydration reaction rate with an unreacted-core shell model. In the experiments, the SrBr2 equilibrium temperature observed was equal to the theoretical equilibrium temperature obtained from thermodynamic databases. In addition, the hysteresis gap between the hydration and dehydration values was 2.0 K. Thus, the hysteresis effect was negligible for the chemical heat pump cooling operation. The reaction fraction of the SrBr2 hydration reached 0.7 within 20 s. By analyzing the hydration reaction rate with the unreacted-core shell model, the activation energy value was calculated to be56.6 kJ/mol. The calculation results showed good agreement with those of the experiment as the reaction fraction reached 0.7.

Simulation of Air Source Heat Pump with Refrigerant Injection for Heating Operation

An air source heat pump(ASHP)with refrigerant injection is proposed for the air conditioning system of electric vehicles(EVs),especially for efficient heating in cold winter,when there is no wasted heat of engines.The simulation model is built with the framework of two-phase fluid network,where the compressor is separated as two compressors and the economizer is treated as two heat exchangers in the injection path and the main refrigerant path.With the validated simulation model,the heating performance is analyzed,and the results show that the coefficient of performance(COP)of ASHP with refrigerant injection is higher than 1.4 and the discharge temperature is less than 100℃ when the outdoor temperature is-20℃.The above performance ensures that the air conditioning system and EVs can operate normally with high efficiency even in the cold winter,which is much helpful for the practicability of EVs.

Experimental Evaluation of the Heat Output/Input and Coefficient of Performance Characteristics of a Chemical Heat Pump in the Periodic Operation of CaCl₂Hydration

We herein evaluate the use of a chemical heat pump (CHP) for upgrading waste heat. CaCl2 was used in the system of CHP. We evaluated the heat storage and heat releasing of CHP, and confirmed the practicality from the experimental results. The reactor module employed was an aluminum plate-tube heat exchanger with corrugated fins, and the CaCl2 powder was in the form of a packed bed. Heat storage operation and heat dissipation operation are performed at the same time and supplied to the heat demand destination. At this time, an environmental heat source can be used during the heat radiation operation, and the heat output can release more heat than the heat input during heat storage. The heat discharging and charging characteristics of the reactor module were evaluated experimentally. The coefficient of performance (COP) was calculated for the heat upgrading cycle, and the heat output in the system was determined. A COP of 1.42 and output of 650 W/L, based on the heat exchanger volume, were obtained using a 600 s change time for the heat pump.

Case Studies of Energy Saving and CO₂Reduction by Cogeneration and Heat Pump Systems

This paper describes two case studies: 1) a cogeneration system of a hospital and 2) a heat pump system installed in an aquarium that uses seawater for latent heat storage. The cogeneration system is an autonomous system that combines the generation of electrical, heating, and cooling energies in a hospital. Cogeneration systems can provide simultaneous heating and cooling. No technical obstacles were identified for implementing the cogeneration system. The average ratio between electric and thermal loads in the hospital was suitable for the cogeneration system operation. An analysis performed for a non-optimized cogeneration system predicted large potential for energy savings and CO2 reduction. The heat pump system using a low-temperature unutilized heat source is introduced on a heat source load responsive heat pump system, which combines a load variation responsive heat pump utilizing seawater with a latent heat-storage system (ice and water slurry), using nighttime electric power to level the electric power load. The experimental coefficient of performance (COP) of the proposed heat exchanger from the heat pump system, assisted by using seawater as latent heat storage for cooling, is discussed in detail.

CO_2车用热泵空调系统技术研发及性能提升

本文研发了一套CO_2跨临界车用热泵空调系统,该系统采用CO_2车用电动压缩机、微通道换热器、电子膨胀阀等关键部件,克服了CO_2车用热泵空调系统高压和高排气温度的技术挑战。实验研究了系统充注量对CO_2车用热泵空调系统性能、循环特征及膨胀阀开度的影响。提出在热泵模式下将室内换热器串联来提高高压侧的换热能力,并实验验证了该方法对车用热泵空调系统性能的提升作用。结果表明:相比于单一气冷器,采用串联气冷器的车用热泵空调系统的制热量和COP_h分别提升了17%～31%和20%～33%;该系统在-20℃全新风环境下,出风温度可达40.4℃,COP_h为1.8。因此该系统能够满足电动汽车在低温环境下的乘客舒适性和整车负荷需求,且在制热能效方面优势显著。

CO_2应用于我国工商制冷行业的适用性研究

CO2是我国工商制冷行业HCFCs淘汰管理计划中明确的替代品之一,本文从技术标准、性能测试、替代成本、市场前景等方面对天然制冷剂CO2应用于工商制冷行业的适用性进行分析,结果表明：国内外相关标准认为CO2理论上可以适用于所有类型的制冷系统应用,但在充注量方面需规避泄漏窒息的风险;CO2热泵热水器在超低温工况和GB/T 21362—2008名义工况下的COP比R410A热泵热水器分别高7.9%和10.7%,CO2冷风机蒸发器比传统产品在性能上具有一定的优势;CO2热泵系统替代R22系统的成本会增加1～2倍,CO2冷冻冷藏系统替代R22系统的成本会增加20%～30%;CO2在工商制冷行业的热泵热水机和冷冻冷藏设备领域具有较好的应用潜力,但还需在制冷循环效率提升、高效部件开发、高压运行安全性保障等方面开展深入的工作。

适用于-20℃环境的CO_2汽车热泵系统的开发及性能测试

开发CO_2跨临界汽车热泵,是解决R134a汽车热泵在低温环境下制热量不足、无法正常工作问题的有效措施。本文理论分析了影响CO_2汽车热泵性能的关键因素,在最低为-20℃的环境温度下实验研究了CO_2汽车热泵的性能。结果表明:开发的CO_2汽车热泵系统在低温环境下稳定运行,具有较好的制热性能;在相同压缩机转速条件下,室内进风温度对制热COP(COP_h)影响更大,室外环境温度对制热量影响更大;在-20℃环境冷启动工况下COP_h可达到3.15、制热量为3.6 k W;进风(Tg,a,in)和出风(Tg,a,out)温度分别为20℃和40℃时,COP_h最低为1.72。因此,与R134a相比,CO_2车用热泵系统的低温制热性能有显著的优势,该系统在电动汽车上具有较好的应用潜力。

CO_2跨临界水——水热泵循环系统的实验研究

在作者设计和建立的实验台上进行了CO2 跨临界水—水热泵多种工况的循环性能实验研究 ,系统运行稳定、调节方便。实验结果表明 ,系统运行时的最大制冷 (热 )系数取决于系统的蒸发温度和气体冷却器出口温度。CO2 跨临界循环热泵较之传统工质热泵具有较大优势 ,尤其是在高温热泵领域。

跨临界CO_2热泵热水器的性能

为了研究跨临界CO2热泵热水器制冷剂充注量对制热系数的影响,通过调节变频压缩机频率与电子膨胀阀脉冲,在制热量与压缩机入口过热度一定的条件下,对制热系数、压缩比、吸气和排气压力等与制冷剂充注量的关系进行了实验研究.结果表明:随着制冷剂充注量的增加,压缩机的排气压力上升,气体冷却器出口制冷剂的温度下降;随着蒸发器中热源水入口温度的上升,吸气压力上升,压缩比和排气温度下降;最大制热系数随热源水入口温度的上升而增大.当热源水入口温度为15℃且压缩机入口过热度为5℃时,系统的最大制热系数为3.25,最佳制冷剂充注量为1.7 kg.

CO_2跨临界双级压缩采暖热泵理论分析

分析了制约 CO2 跨临界单级循环在采暖热泵中应用的主要因素 ;研究了双级压缩回热循环的可行性 ,对其在两种不同供水温度水平下的应用进行了理论计算和分析 ,并分别和锅炉供热以及 R1 34 a热泵进行了比较 .

CO_2热泵热水器充注量确定及系统实验研究

设计搭建蒸发器和气冷器均采用套管式换热器的跨临界CO2热泵热水器性能测试实验台,采用额定工况法理论计算系统充注量,实验研究充注量对系统性能的影响并确定系统最佳充注量.在最佳充注量下,实验研究节流阀开度和气冷器水流量的变化对系统性能的影响.结果表明,充注量的变化对排气压力、性能系数COP影响最大,对蒸发压力影响很小;节流阀开度过小会提高系统高压压力,增加系统能耗,而对产热水温度提升不大;只有气冷器水流量适中时,系统才能在较高的COP时提供温度满足使用要求的热水.

跨临界CO_2制冷(热泵)系统中毛细管研究进展

毛细管应用于CO2跨临界循环时,其内部流动不同于普通CFCs和HCFCs,针对毛细管作为跨临界CO2制冷(热泵)系统节流机构的研究进行了回顾。主要从CO2毛细管模型、实验研究、临界流以及毛细管对系统的影响4个方面详细介绍了国内外的研究进展。阐述了目前研究存在的几个问题,并探讨了这一领域内研究的发展方向。

低温空气源CO_2热泵热水器系统特性研究

压缩机排气温度过高及制热量不足等现象是单级蒸汽压缩式制冷系统在低蒸发温度下经常面临的问题,以CO_2为制冷工质的中间不完全冷却两级蒸汽压缩热泵系统能很好地改善这些问题。本文构建了低环温(-20℃)下CO_2热泵热水器系统、确定了系统各部件结构参数、建立了部件和热泵系统的数学模型。模拟结果表明:随着环境温度升高,CO_2热泵热水器系统制热量以及COP呈现出增长的趋势,改变水侧输入参数对系统性能有较大影响。

带喷射器的CO_2热泵/制冷系统的研究现状

通过对喷射器分类与性能参数进行介绍,阐述了两相喷射器(TPE)应用于CO_2热泵/制冷系统的理论与实验研究进展,还对TPE的运行特性和优化方法进行了分析。总结得出,等压混合喷射器性能更优且应用广泛,喷射器及系统性能分析需结合性能参数综合分析,TPE应用于系统具有多样性,理论与实验研究需要结合其各自特点且考虑因素应全面,目前喷射器的调控方式中多喷射器组合的方法更受关注,可调喷嘴喉部面积的调控方式的发展既要优化控制方法也要与其他几何参数优化相结合。

CO_2制冷特性和应用分析

介绍了CO2制冷剂的的历史和发展;分析总结了CO2的物理化学性质和制冷特性;阐述了亚临界循环、跨临界循环等4种制冷循环的基本原理;介绍了CO2制冷技术在汽车空调、热泵系统和复叠式制冷系统等方面的应用。

新型低GWP制冷剂在-100~200℃的应用研究进展

制冷剂是蒸气压缩循环中必不可少的工作流体,氢氟烷烃类化合物是目前制冷、空调和热泵设备中的主要制冷剂,但该类制冷剂会引起全球变暖等问题,因此亟需开发应用性能相似、环境性能友好的新型制冷剂。介绍了不同制冷剂在-100~200℃蒸气压缩循环应用场景中的使用现状,并综述了具有前景的低GWP制冷剂替代方案研究进展;在此基础上,对HFO-1234yf、HFO-1234ze(E)、HFO-1234ze(Z)、HCFO-1233zd(E)、HFO-1336mzz(Z) 5种低GWP制冷剂在实际应用系统中的最新研究及关键问题进行总结。