Evaluation of non-azeotropic mixtures containing HFOs as potential refrigerants in refrigeration and high-temperature heat pump systems

With the increasing environmental concern on global warming, hydrofluoro-olefin (HFOs), possessing low GWP, has attracted great attention of many researchers recently. In this study, non-azeotropic mixtures composed of HFOs (HFO-1234yf, HFO-1234ze(z), HFO-1234ze(e) and HFO-1234zf) are developed to substitute for HFC-134a and CFC-114 in air-conditioning and high-temperature heat pump systems, respectively. The cycle performances were evaluated by an improved theoretical cy-cle evaluation methodology. The results showed that all the mixtures proposed herein were favorable refrigerants with excel-lent thermodynamic cycle performances. M1A presented lower discharge temperature and pressure ratio and higher COPc than that of HFC-134a. The volumetric cooling capacity was similar to HFC-134a. It can be served as a good environmentally friendly alternative to replace HFC-134a. M3H delivered similar discharge temperature as CFC-114 did. And the COPh was 3% higher. It exhibits excellent cycle performance in high-temperature heat pump and is a promising refrigerant to substitute for CFC-114. And the gliding temperature differences enable them to exhibit better coefficient of performance by matching the sink/source temperature in practice. Because the toxicity, flammability and other properties are not investigated in detail, ex-tensive toxicity and flammability testing needs to be conducted before they are used in a particular application.

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.

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.

Research and application of CO_2 refrigeration and heat pump cycle

The environmental problem caused by refrigerant has become the focus all over the world.As the most typical natural refrigerant,CO2,of course,becomes the research focus.This paper introduces the development and application status of CO2 refrigeration and heat pump technology.The researches on CO2 refrigeration and heat pump,carried out by Thermal Energy Research Institute,Tianjin University,also are presented in this paper.

Effect of Evaporator Load on Heat Pump Operating Parameters and Performance

This work investigates the impact of varying the evaporator load on the performance and parameter characteristics of a heat pump.A series of experiments have been done on a vapor compression cycle heat pump which is run with R134a.The evaporator in this system is a coil submerged in a water/glycol bath accommodated in a thermally insulated steel container.The load of the evaporator is changed through a heater in this bath with a capacity of 1.8 kW.The glycol bath is mixed through an electric stirrer.The results showed that system pressures and temperatures generally increase and then decrease after a certain heat load has been imposed.The same trend is for COP of the refrigeration system;hence there is an optimum load point to which the COP increases to a maximum and then starts to decline.This optimum point corresponds to the best efficiency of the system.

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.

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.

Thermal energy storage as a way to improve transcritical CO_(2) heat pump performance by means of heat recovery cycles

Electrification of the heating sector is a major target of energy transition towards a more sustainable,efficient,and less polluted future.Heat pumps are considered more suitable than electrical heaters or fossil-fueled boilers;however,common refrigerants cause ozone layer depletion,which exacerbates the greenhouse effect.Natural refrigerants,such as CO_(2),perform comparably and even better than hydrofluorocarbons while minimizing the negative aspects.This study presents a model of a water-heater CO_(2) transcritical heat pump in a configuration that increases the overall coefficient of performance(COP)by introducing thermal energy storage(TES).The thermodynamic cycle was divided into two separate phases.After heating the TES(charging),warm water was used as the heating fluid in the evaporator to increase the evaporation temperature and pressure of CO_(2),which reduced the work of the compressor.As the water temperature decreased progressively,the discharge cycles improved the total COP.The case study focuses on dairy processes and suggests a more straightforward and cheaper method to improve cycle efficiency than the current processes,such as ejector-expansion systems or double compression.

Experiment Investigation and Control Strategies on Two-Phase Refrigerant Injection Heat Pump System for Electric Vehicle in Start-up Stage

Due to the poor heating performance and operating safety in low ambient temperature,traditional Air Source Heat Pump(ASHP)for Electric Vehicles(EVs)has many limits in cold region,which can be solved by the ASHP with refrigerant injection.During the start-up stage of EV in winter,the inlet air temperature of the in-car condenser is the same as the ambient temperature.At this situation,the performance and control strategy of the heat pump require special attention.In the present study,a series of experiments were carried out on the heating performance of the Refrigerant Injection Heat Pump(RIHP)system in start-up stage of EV,at the ambient temperature from–20℃ to–5℃.The effects of compressor speed and injected refrigerant state on the heating performance of the system were discussed in depth.According to the results,the control strategies during start-up stage have been discussed in the end of the article.The study provides a practical control strategy for the RIHP system during the start-up stage of electric vehicles,helping to efficiently operate electric vehicles in cold regions.

Simulation study on performance of a dual-source hybrid heat pump unit with alternative refrigerants

To solve the problems of single heat source heat pump systems in severe cold regions,a dual-source hybrid heat pump unit(DSHHPU)is proposed.The mathematical models of the DSHHPU when charging R134a or its alternative refrigerants R32,R290 and R600a were established respectively,and the performance was simulated and analysed.The results showed that the four refrigerants have different performance characteristics in different aspects.In heat pipe mode,the heating capacity and evaporating pressure of R32 are 36.94%and 59.94%higher than those of R134a.The heating capacity and evaporating pressure of R290 are 5.73%and 22.99%lower than those of R134a.The heating capacity and evaporating pressure of R600a are 43.29%and 68.08%lower than those of R134a.In vapour compression heating mode,the discharge temperature of R32,R290 and R600a are 184.88,72.98 and 66.44%of that of R134a.The coefficient of performance(COP)of R32,R290 and R600a are 72.65,111.59 and 117.94%of that of R134a.Finally,the effects of radiation intensity and ambient temperature on key performance parameters of the different refrigerants were analysed.The research results provide a reference for research on refrigerant replacements for multi-heat source composite heat pump systems.

Experimental research on the heating performance of a single cylinder refrigerant injection rotary compressor heat pump with flash tank

A single cylinder rotary compressor was applied in the refrigerant injection air-source heat pump to improve the heating performance in cold regions. In this study, the performance of an R410 A single cylinder rotary compressor vapor injection(SCRCVI) system was measured and analyzed by varying the compressor frequency f and injection pressure Pi njat the ambient temperature To d=–10°C.The experimental results indicated that an optimum injection pressure to gain the maximum COP_h (coefficient of performance) existed in the SCRCVI cycle. However, the maximum COP_h of the SCRCVI system decreased as the increase of the frequency, and the maximum COPhwas even lower than that of the CSVC system at high compressor frequency. Therefore, in view of the energy saving and emission reduction, the SCRCVI system should be switched to single stage compression system when the heating capacity demand could be satisfied at high compressor frequency f. Compared to the conventional single-stage vapor compression(CSVC) system, refrigerant injection could enhance the heating capacities and COP_h by 28.2% and 7.91%, respectively. The average total mass flow rate of the SCRCVI system was 24.68% higher than that of the CSVC system. As the SCRCVI system worked at the optimum injection pressure, the variation trends of the different system parameters were investigated in detail. These trends were reliably used to optimize the refrigerant injection system design and the control strategy. The parameter of(P_(inj)–P_s) could be adopted as the signals to control the opening of the upper stage electronic expansion valve EEV1.

Investigation on the Influence of Refrigerant Charge Amount on the Cooling Performance of Air Conditioning Heat Pump System for Electric Vehicles

The application of air conditioning heat pump(ACHP) in electric vehicles could lead to significant electrical power saving effect. As for an air conditioning heat pump system for electric vehicles, the influence of refrigerant charge amount should be investigated during the design phase. In this study, experimental method was employed to investigate the influence of the refrigerant charge amount on the performance of the ACHP system. The results showed that the refrigerant charge amount had different influence on the refrigerant properties at various locations within the system. The coefficient of performance and pressure-enthalpy diagram were calculated, and showed a close relationship with refrigerant charge amount under different compressor speeds. The degree of subcooling and the degree of superheating were recorded and the critical charge amount was determined by a typical practical test method. In addition, the critical refrigerant charge amount determined by the experimental method was also compared with two typical void fraction correlation models, and the model with consideration of two phase stream reaction of the refrigerant showed a good estimation accuracy on the critical charge amount.

Research trend of cascade heat pumps

Most commercial and industrial facilities require very low temperatures for refrigeration and high temperatures for space heating and hot water purposes. Single stage heat pumps have not been able to meet these temperature demands and have been characterized by low capacities and coefficient of performance(COP). Cascade heat pump has been developed to overcome the weaknesses of single stage heat pumps. This study reviews recent works done by researchers on cascade heat pumps for refrigeration, heating and hot water generation. Selection of suitable refrigerants to meet the pressure and temperature demands of each stage of the cascade heat pump has been discussed. Optimization of design parameters such as intermediate temperature(low stage condensing and high stage evaporating temperatures), and temperature difference in the cascade heat exchanger for optimum performance of the cascade heat pump has been reviewed. It was found that optimising each design parameter of the cascade heat pump is necessary for maximum system performance and this may improve the exergetic efficiency, especially of cascade refrigeration systems, by about 30.88%. Cascade heat pumps have wider range of application especially for artificial snow production, in the supermarkets,for natural gas liquefaction, in drying clothes and food and as heat recovery system. The performance of cascade heat pumps can be improved by 19% when coupled with other renewable energy sources for various real time applications. Also, there is the need for much research on refrigerant charge amount of cascade heat pumps, refrigerant-refrigerant heat exchangers to be used as cascade heat exchanger, cascade heat pumps for simultaneous cooling, heating and hot water generation and on the use of variable speed compressors and their control strategies in matching system capacity especially at part load conditions.

Heating performance of a ground source heat pump system installed in a school building

The heating performance of a water-to-refrigerant type ground source heat pump system is represented in this paper under the actual working conditions of the GSHP(ground source heat pump) system during the winter season of 2008.Ten heat pump equipments with the capacity of 10 HP each and a closed vertical typed-ground heat exchanger with 24 boreholes of 175 m in depth were constructed.We investigated a variety of working conditions,including the outdoor temperature,the ground temperature,and the water temperature of inlet and outlet of the ground heat exchanger in order to examine the heating performance of the GSHP system.Subsequently,the heating capacity and the input power were investigated to determine the heating performance of the GSHP system.The average heating coefficient of performance(COP) of the heat pump was noted to be 5.1 at partial load of 47%,while the overall system COP was found to be 4.2.Also,performance of the GSHP system was compared with that of air source heat pump.

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。

CO_(2)/R1233zd(E)混合工质回热热泵系统性能优化分析

空气源热泵作为一种新型的节能环保技术,在多种供暖场景中得到了广泛应用,其在低环境温度下的运行可靠性和效率是重要的关注点。采用二元混合工质CO_(2)/R1233zd(E)构建了兼顾环保性、安全性和高效性的回热热泵系统,并通过优化分析得到该系统的COP、单位容积制热量、吸气压力和排气压力等系统性能在-30~-10℃环境温度下的变化规律。通过与目前常用的传统补气增焓系统和复叠系统进行对比,探明了该混合工质回热系统在低环境温度下可以保持较高效率运行。在-30~-10℃环境温度下,与R134a补气增焓系统相比其COP和单位容积制热量分别减小了9.8%~20.6%和增大了3.5%~56.1%,并且压缩机压比以及压比随环境温度的变化幅度低于其他方案。二元混合工质回热系统结构简单,CO_(2)和R1233zd(E)安全环保,因此提出的混合工质回热系统方案在低环境温度采暖的应用中具有独特优势。

A review of low-temperature heat recovery technologies for industry processes

The amount of low-temperature heat generated in industrial processes is high,but recycling is limited due to low grade and low recycling efficiency,which is one of the reasons for low energy efficiency.It implies that there is a great potential for low-temperature heat recovery and utilization.This article provided a detailed review of recent advances in the development of low-temperature thermal upgrades,power generation,refrigeration,and thermal energy storage.The detailed description will be given from the aspects of system structure improvement,work medium improvement,and thermodynamic and economic performance evaluation.It also pointed out the development bottlenecks and future development trends of various technologies.The low-temperature heat combined utilization technology can recover waste heat in an all-round and effective manner,and has great development prospects.

采用非共沸制冷剂的双喷气增焓两级压缩热泵循环研究

提出一种采用非共沸制冷剂的双喷气增焓两级压缩热泵循环(DVIC),该循环在普通喷气增焓循环(VIC)的基础上采用分液冷凝技术,并增加一组闪蒸器,减少系统不可逆损失,改善热力性能。采用R290/R1336mzz(Z)非共沸制冷剂,对DVIC进行研究,并与VIC进行比较。结果表明:在设定工况下,DVIC比VIC拥有更优的循环性能,系统COP和(火用)效率分别提高5.82%和8.41%,压缩机功耗降低6.39%;在较低蒸发温度或较高冷凝温度的运行工况下,DVIC性能的改善效果更加明显。

超高温热泵的循环构型与混合制冷剂协同优化——面向工业用热的构想

工业超高温热泵正逐渐成为热泵发展的新方向。不同于现有民用为主的空气源热泵,在工业用热中,温升、温跨的工况复杂、差异巨大,要提升能效,须采用新的视角和方法。针对此,本文提出循环构型与混合制冷剂协同优化的思路。首先,基于梯级耦合加热热泵循环,量化循环构型;分析混合制冷剂的泡露点温差效应在大温差工况下的重要影响。其后,通过案例分析验证经循环构型与混合制冷剂协同优化的最高COP_(h)比传统以混合制冷剂匹配或循环构型筛选所得方案的COP_(h)分别提高22.0%和5.8%。

含亚乙烯基氢氟烯烃的研究进展

对含亚乙烯基的氢氟烯烃(v-HFOs)的合成路线和应用进行了综述。目前,在氟-氯交换、异构化、脱卤化氢、选择性加氢、加氢脱氯、调聚等合成v-HFOs的主要路线中,氟-氯交换的路线具有起始原料易得、容易实现大规模生产的特点,是合成v-HFOs的最佳路线。v-HFOs特殊的分子结构使其具有优异的传热性能、清洁性能、发泡性能和刻蚀性能,主要用作制冷剂、热泵工质、清洗剂、发泡剂和刻蚀剂,特别是E型v-HFOs[(E)-v-HFOs]具有优异的电绝缘性能,分别与其优良的传热性能和清洗性能进行多领域交叉,实现了(E)-v-HFOs应用于浸没式液冷和带电清洗的新场景。展望了v-HFOs的未来发展趋势,提出了今后的研究重点,应开发高活性的氟化催化剂,环保绿色的新型合成路线以及v-HFOs的新型应用。