Performance analysis of a novel hybrid vapor injection cycle with subcooler and flash tank for air-source heat pumps

In this paper, a novel hybrid vapor injection cycle (HVIC) with subcooler and flash tank for air-source heat pumps is proposed. In the HVIC, an ejector is applied to realize the advantages of both the subcooler and flash tank vapor injection, which can efficiently reduce the irreversible thermodynamic loss and improve the system performance, especially at low ambient temperature conditions. The performance enhancement potential of HVIC is compared with conventional subcooler vapor injection cycle (SVIC) and flash tank vapor injection cycle (FTVC) using cycle simulations. The simulation results indicated that for the HVIC using R290 as refrigerant, the coefficient of performance (COP) and the volumetric heating capacity can be increased by 2.8–3.3% and 6.4–8.8% compared to the SVIC system, 1.1–2.0% and 3.2–6.0% compared to the FTVC system, respectively. In addition, improving the ejector efficiencies and adjusting the injection pressure could also enhance the performance of HVIC. Exergy analysis indicates that the total exergy destruction for the HVIC is lower than that of SVIC and FTVC due to the application of an ejector, and therefore resulting in higher exergy efficiency. Overall, the HVIC could be more effective to enhance heating capacity and system efficiency.     

Effects of vapor injection techniques on the heating performance of a CO2 heat pump at low ambient temperatures

The objective of this study is to investigate the effects of vapor injection techniques on the heating performance of a CO₂ heat pump. The performances of the flash tank vapor injection (FTVI), sub-cooler vapor injection (SCVI) and FTVI with a suction line heat exchanger (FTSX) cycles were measured and analyzed with variations of the outdoor temperature, compressor frequency, and injection mass flow rate. At the outdoor temperature of −15 °C and compressor frequency of 55 Hz, the heating capacity and COP of the optimized SCVI cycle were 12.1% and 12.7% higher than those of the optimized FTVI cycle, respectively, because the total mass flow rate in the SCVI cycle was higher than that in the FTVI cycle by the large temperature and pressure differences in the sub-cooler of the SCVI cycle. In addition, the optimum injection flow rate ratios in the vapor injection CO₂ cycles yielding the maximum COP were determined at various compressor frequencies.     

Research on air-source heat pump coupled with economized vapor injection scroll compressor and ejector

The performance of the heat pump can be improved further when running under low temperature conditions when an ejector is used in a heat pump system coupled with economized vapor injection (EVI) scroll compressor. In this paper, the design method of the heat pump system with ejector (EVIe) is presented, and the process for designing the heat pump with ejector has been summarized. The optimal location of the vapor injection inlets is at the place where the vapor can inject into the working chambers when they just be closed. The reasonable value for the entrainment ratio u of the ejector is between 0.1 and 0.2. One prototype heat pump was designed under the condition of the evaporation temperature of −20 °C, and an experimental setup was established to test the prototype. The measured results demonstrated that the heating EER of the heat pump system with ejector could reach about 4% higher than that of the system without ejector when the heating capacity remained nearly constant.     

Comparison of the heating performance of air-source heat pumps using various types of refrigerant injection

The performance degradation of air-source heat pumps cannot be avoided when they operate at both very low and high ambient temperatures. The refrigerant injection technique has rapidly developed in recent years due to its outstanding performance at low ambient temperatures. This study measured the heating performance of air-source heat pumps in which novel vapor injection techniques of a combined flash tank and sub-cooler (FTSC) cycle and a double expansion sub-cooler (DESC) cycle were applied. The performance of these cycles was compared with that of a flash tank (FT) and a sub-cooler (SC) cycle. The average heating capacities of the FT, FTSC, and DESC cycles were higher by 14.4%, 6.0%, and 3.8%, respectively, relative to that of the SC cycle, but the average COPs for the respective cycle options were very similar.     

Optimum cycle control of a two-stage injection heat pump with a double expansion sub-cooler

The refrigerant injection technique has rapidly developed in recent years due to its outstanding performance at low ambient temperatures, and various control methods for a heat pump with injection have been presented. However, most studies on cycle control have been theoretical, and practical control methods for cycle optimization based on experimental results hardly have been presented. In this study, an optimum cycle control method was proposed for a refrigerant injection heat pump with a double expansion sub-cooler based on the intermediate pressure and the injection ratio. The optimum sub-cooler pressure ratio was proposed from 0.4 to 0.7 in view of the heating capacity, and from 0.7 to 0.8 in view of the COP. The optimum injection ratio increased from 0.1 to 0.3 with an increase in the compression ratio.     

A theoretical study on a novel combined power and ejector refrigeration cycle

A new combined power and refrigeration cycle is proposed for the cogeneration, which combines the Rankine cycle and the ejector refrigeration cycle by adding an extraction turbine between heat recovery vapor generator (HRVG) and ejector. This combined cycle could produce both power output and refrigeration output simultaneously, and could be driven by the flue gas from gas turbine or engine, solar energy, geothermal energy and industrial waste heats. Parametric analysis and exergy analysis are conducted to examine the effects of thermodynamic parameters on the performance and exergy destruction in each component for the combined cycle. The results show that the condenser temperature, the evaporator temperature, the turbine inlet pressure, the turbine extraction pressure and extraction ratio have significant effects on the turbine power output, refrigeration output, exergy efficiency and exergy destruction in each component in the combined cycle. It is also shown that the biggest exergy destruction occurs in the heat recovery vapor generator, followed by the ejector and turbine.     

Thermal and exergoeconomic analysis of a novel solar driven combined power and ejector refrigeration (CPER) system

In the present study, a novel solar driven combined power and ejector refrigeration system (CPER) of 50 kW power capacity composed of an ORC (organic Rankine cycle) and an ejector refrigeration system is investigated. Solar driven CPER system is composed of two main cycles: collector cycle and refrigeration cycle. The collector cycle is made of a U-tube ETC and circulation pump and the ejector refrigeration cycle consists of generator, turbine, ejector, heat exchanger, condenser, evaporator, expansion valve, and pump. Thermodynamic performance of the proposed CPER system is evaluated and a thermo-economic analysis is conducted using the SPECO (specific exergy costing) method. A parametric study showed the effects of condenser temperature, evaporator temperature, generator pressure, turbine back pressure and turbine extraction ratio. The genetic algorithm optimization analysis is conducted which shows 25.5% improvement in thermal energy, 21.27% in exergy efficiency, and 7.76% reduction in the total cost of the CPER system. The results reveal that the performance of the CPER system is considerably improved at higher temperatures of generator and evaporator.     

First and second law investigation of waste heat based combined power and ejector-absorption refrigeration cycle

In the proposed cogeneration cycle, a LiBr-H₂O absorption refrigeration system is employed to the combined power and ejector refrigeration system which uses R141b as a working fluid. Estimates for irreversibilities of individual components of the cycle lead to possible measures for performance improvement. Results of exergy distribution of waste heat in the cycle show that around 53.6% of the total input exergy is destroyed due to irreversibilities in the components, 22.7% is available as a useful exergy output, and 23.7% is exhaust exergy lost to the environment, whereas energy distribution shows 44% is exhaust energy and 19.7% is useful energy output. Results also show that proposed cogeneration cycle yields much better thermal and exergy efficiencies than the previously investigated combined power and ejector cooling cycle. Current investigation clearly show that the second law analysis is quantitatively visualizes losses within a cycle and gives clear trends for optimization.     

Theoretical assessment of an ejector enhanced oil flooded compression cycle

Compressor loss and throttling loss are major thermodynamic losses in basic vapor compression cycle. For this reason, an ejector enhanced oil flooded compression cycle is proposed. To evaluate the performance, a mathematical model is established and the performance of this cycle with R32 as the working fluid is investigated. Furthermore, basic cycle, ejector enhanced basic cycle and oil flooded compression cycle have also been investigated. The comparison results show that the developed cycle has a maximum of 4.3% and 4% COP improvement at the evaporation temperature of −25 °C and the condensation temperature of 45 °C over the oil flooded compression cycle and the ejector enhanced basic cycle respectively. In addition, the effects of internal heat exchanger on the developed cycle are also studied. In comparison to the ejector enhanced basic cycle with 50% efficient internal heat exchanger, the COP improvement of the developed cycle rises up to a maximum of 8.5%. The results show that the proposed cycle has large potential applications for the ejector cycle enhancement.     

A theoretical study of a novel regenerative ejector refrigeration cycle

There has been a demand for developments of the ejector refrigeration systems using low grade thermal energy, such as solar energy and waste heat. In this paper, a novel regenerative ejector refrigeration cycle was described, which uses an auxiliary jet pump and a conventional regenerator to enhance the performance of the novel cycle. The theoretical analysis on the performance characteristics was carried out for the novel cycle with the refrigerant R141b. Compared with the conventional cycle, the simulation results show that the coefficient of performance (COP) of the novel cycle increases, respectively, by from 9.3 to 12.1% when generating temperature is in a range of 80–160 °C, the condensing temperature is in a range of 35–45 °C and the evaporating temperature is fixed at 10 °C. Especially due to the enhanced regeneration with increasing the pump outlet pressure, the improvement of COP of the novel cycle is approached to 17.8% compared with that in the conventional cycle under the operating condition that generating temperature is 100 °C, condensing temperature is 40 °C and evaporating temperature is 10 °C. Therefore, the characteristics of the novel cycle performance show its promise in using low grade thermal energy for the ejector refrigeration system.     

Water-side reversible CO2 heat pump for residential application

This paper presents the energy assessment of a water/water R744 chiller/heat pump, working according to a transcritical cycle, used for winter heating, summer cooling and tap water production. The different functions (heating, cooling, hot water) are managed water side. The analysis of the R744 chiller/heat pump is based on an original simplified method, which is able to predict the energy performance of the unit based only on its performance data at the nominal rating conditions. The method was validated against experimental data. A comparison with a state-of-the-art R410A unit is presented. The monthly analysis shows that the CO₂ unit is very efficient in hot water production, but penalised in heating and cooling service. The adoption of an ejector in place of the expansion valve makes the CO₂ system reach the same energy consumption as the R410A unit, despite the presence of the water loop only in the R744 lay-out.     

Performance improvement of a transcritical CO2 refrigeration cycle using two-stage thermoelectric modules in sub-cooler and gas cooler

A novel integration of a trans-critical CO₂ refrigeration cycle with thermoelectric modules in the gas cooler and sub-cooler is presented, wherein a two-stage thermoelectric generator (TEG) produces power from the waste heat of gas cooler, which is a considerable amount of required power in two-stage thermoelectric cooler (TEC) to sub-cool the refrigerant before expansion device. Mathematical simulation of TEG and TEC as well as energy and exergy based thermodynamic analysis of the proposed system is performed, and the effects of some important parameters on the system performance are investigated. A comparison is carried out between the proposed system and the simple CO₂ refrigeration cycle, indicating that the proposed configuration improves the coefficient of performance (COP) about 19%. Also, it is observed that the TEC and TEG have better performance in a two-stage configuration. The parametric study reveals that the new configuration decreases the cycle operation pressure at maximum COP and exergetic efficiency.     

一种新型跨临界CO2冷电联供系统热力分析

提出一种新型跨临界二氧化碳（trans-critical carbon dioxide,TCO₂）再压缩循环和喷射器制冷循环耦合的冷电联供系统。该系统在输出电能的同时,利用低品位热能驱动喷射器工作输出冷量。以输出电量1 MW为设计目标,对比冷电联供系统和再压缩发电系统的性能,研究联供系统各部件（火用）损和主要热力参数对其性能的影响。结果表明：联供系统利用CO₂余热驱动喷射器输出冷量,循环热效率高于单一再压缩系统;加热器（火用）损所占比例最大,回热器次之;透平进口温度、压力和背压对联供系统工质流量、循环效率、输出功率、加热器功率、压缩机耗功及喷射器制冷量等参数影响较大;而冷凝温度和蒸发温度仅对制冷循环制冷量影响较大。在设定条件下,联供系统的循环热效率和（火用）效率可分别达到46.99%和47.21%。     

Hybrid vapor compression refrigeration system with an integrated ejector cooling cycle

A refrigeration system was developed which combines a basic vapor compression refrigeration cycle with an ejector cooling cycle. The ejector cooling cycle is driven by the waste heat from the condenser in the vapor compression refrigeration cycle. The additional cooling capacity from the ejector cycle is directly input into the evaporator of the vapor compression refrigeration cycle. The governing equations are derived based on energy and mass conservation in each component including the compressor, ejector, generator, booster and heat exchangers. The system performance is first analyzed for the on-design conditions. The results show that the COP is improved by 9.1% for R22 system. The system is then compared with a basic refrigeration system for variations of five important variables. The system analysis shows that this refrigeration system can effectively improve the COP by the ejector cycle with the refrigerant which has high compressor discharge temperature.     

R32经济器系统涡旋压缩机中间补气参数的分析与优化

为了优化带经济器的R32空气源热泵系统的制热性能,结合涡旋压缩机的结构以及实际运行特点,本文利用MATLAB建立了系统的数学模型,并通过实验数据验证了仿真结果,研究了在不同环境温度下系统的补气压力、准一级压缩内容积比对相对喷气量的影响.研究结果表明:经济器系统较普通热泵系统,更适宜在环境温度低于-10 ℃的工况下运行;...     

四种跨临界CO2压缩式热泵系统的热力性能研究

CO2是具有很大潜力的天然替代工质之一,CO2跨临界循环放热过程中具有较大温度滑移,与水侧温升过程相匹配,因此适合用于热泵热水器系统。国内外学者提出了许多提高跨临界CO2循环效率的方法,其中包括引入回热器、喷射器等设备,从不同角度对比分析在常规跨临界CO2热泵系统中引入回热器、喷射器后系统的性能变化。本文在前人工作的基础上,建立相关热力学计算模型,并进一步对四种不同形式的跨临界CO2热泵系统（常规跨临界CO2热泵系统（TCHS）、带回热器的跨临界CO2热泵系统（TCHSI）、带喷射器的跨临界CO2热泵系统（TCHSE）及带喷射器与回热器的跨临界CO2热泵系统（TCHSEI））的性能进行研究,对比分析排气压力一定的情况下四种循环的热力性能;从最优排气压力的角度出发,分析对比不同系统中气冷器出口温度变化对系统最优排气压力和制热系数的影响,以及喷射器等熵效率对系统性能的影响。以上研究为CO2压缩式热泵系统的实用化进展奠定良好的理论基础。     

准二级压缩空气源热泵热水机的技术分析

文章对常规和过冷器准二级压缩的空气源热泵热水系统进行简要性能分析,通过实际测试不同工况下各性能参数随进水温度的变化规律,寻找过冷器准二级压缩空气源热泵热水机各工况点的最佳补气压力。结果表明,相对于常规空气源热泵热水系统,过冷器准二级压缩的空气源热泵热水系统可显著提高制热量及性能系数、降低排气温度、拓宽运行范围,可为过冷器准二级压缩热泵系统用于空气源热泵热水机的设计和应用提供参考。     

带闪蒸型经济器的风冷螺杆热泵机组性能的实验研究

研究了带闪蒸型经济器风冷螺杆热泵机组对制热性能的影响,理论分析了补气压力的变化对机组制热性能的影响。研究表明,带闪蒸型经济器热泵螺杆机组制热量随经济器的补气压力的减小而增大,压缩机功率也随经济器的补气压力的减小而增大,压缩机的COP随着经济器的补气压力的升高先升高再降低,存在最佳效率的补气压力点。实验测试了比最佳补气压力点偏高的经济器补气压力对机组性能的影响,理论计算结果和实测数据吻合良好。     

制冷工质引射式减压原理及其技术应用

分析常规蒸气压缩制冷系统存在的不足,介绍引射式减压原理,并将其技术应用于制冷(热泵)循环系统,提出新型压缩/喷射制冷循环系统。对改进后的新型制冷系统进行热力学分析,结合制冷工质R134a的制冷工况特性,得出改进后新型制冷系统的优越性能,即提高制冷系统的能量利用效率。对制冷和空调系统节能研究具有一定的指导意义。     

Performance evaluation of a vapor injection heat pump system for electric vehicles

Battery-powered electric vehicles (EV) need an efficient electric heating system for extending the driving mileage. An air-source heat pump system offers an economical alternative for EV because it consumes less energy than a heating system using Joule heat and it can use the same components as an air conditioning system for cooling. However, its performance degradation is inevitable at very low ambient temperatures. Although vapor refrigerant injection is known as a good technology to overcome this problem in residential heat pump systems, the number of vapor injection heat pump studies for EV applications is quite limited. In this paper, considering the characteristics of EV application, the configuration of a vapor injection heat pump system for EV is introduced, and it was modeled, using a scroll compressor geometry-based thermodynamic analysis. The performance was estimated for cold ambient regions under the EV operational conditions.