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.     

常规空调热泵系统的R32替代研究述评

R32由于具有ODP为零、GWP值小于R410A等优越的环境性能,逐渐被认识到可以用于替代R410A。这里对R410A和R32的循环性能、润滑油的选用、可燃性、充注量、换热器性能等相关问题进行了综述。大量研究表明,与R410A系统相比,R32系统的压缩机耗功略高,制冷量较高,同时排气温度也高出很多,具有极大的替代R410A的潜力。然而,相关研究也指出要使其能够在大范围推广使用,除了要有效解决排气温度过高的问题之外,还需要解决其微可燃性在设计应用中所受到的限制。通过解读国内外法规政策发现,国内外对R32的充注量限制有放宽的趋势,这对R32在常规空调热泵系统中替代R410A和R22的研究工作将是一个巨大的推动。     

Two-stage heat pump system with vapor-injected scroll compressor using R410A as a refrigerant

Refrigerant vapor-injection technique has been well justified to improve the performance of systems in refrigeration applications. However, it has not received much attention for air conditioning applications, particularly for air conditioning in hot climates and for heat pumping in cold climates. In this study, the performance of an 11 kW R410A heat pump system with a two-stage vapor-injected scroll compressor was experimentally investigated. The vapor-injected scroll compressor was tested with the cycle options of both flash tank and internal heat exchanger configurations. A cooling capacity gain of around 14% with 4% COP improvement at the ambient temperature of 46.1 °C and about 30% heating capacity improvement with 20% COP gain at the ambient temperature of −17.8 °C were found for the vapor-injected R410A heat pump system as compared to the conventional system which has the same compressor displacement volume.     

制冷剂R32特性及其用于空气源热泵热水器的理论循环分析

介绍R32,R22和R407C以及R410A四种制冷剂的流动特性和热力学特性,并对采用这4种制冷剂的空气源热泵热水器进行理论循环分析。从计算结果可以看出,与采用其他3种制冷剂的系统对比,采用R32制冷剂的系统具有较低的压缩比,较高的理论COP以及容积制热量;在当前阶段,R32是用于空气源热泵热水器的一种较好的制冷剂。     

Experimental testing of an oil-flooded hermetic scroll compressor

In this work, a residential air conditioning compressor designed for vapor injection has been modified in order to inject large quantities of oil into the working chamber in order to approach an isothermal compression process. The compressor was tested with oil injection mass flow fractions of up to 45%. At an evaporating temperature of ?10 °C and condensing temperature of 30 °C, the overall isentropic efficiency was up to 70% at the highest oil injection rate. Overall, over the testing envelope investigated, there are no significantly negative effects experienced for the compressor and the compressor isentropic efficiency and refrigerant mass flow rate improve monotonically as the oil injection rate is increased.     

制冷系统湿压缩时吸气干度控制方法的实验研究

不完全湿压缩能大幅度降低压缩机排气温度,然而该应用的最大难点是如何控制实时压缩机吸气干度在合适的范围内。本文提出了假拟饱和等熵压缩排气温度控制压缩机吸气该干度的方法,理论分析了在AHRI(空调供暖制冷协会)空调和低温制冷两种典型工况下,R22、R32、R134a和R410A四种制冷剂作为冷媒时,应用该方法控制压缩机吸气带液时系统性能的变化,并通过R32实验验证该结论的正确性。结果表明:利用假拟饱和等熵压缩排气温度可以将压缩机吸气状态控制在少量湿蒸气的状态;在T-s图上具有钟型饱和线形状的R32制冷剂,利用假拟饱和等熵压缩所控制的制冷系统,当吸气干度在0.96~1时,制冷量和COP均能达到最大值。     

新型替代制冷剂房间空调器系统特性实验研究

最近几年HFO类新型制冷剂、R32以及二者组成的混合物因其较低的温室效应系数逐渐为行业所重视。本文对比了R410A及其潜在替代物R32、R447A三种制冷剂在不同转速、不同室外温度下的房间空调器系统的运行特性,发现与R410A相比,R32和R447A均具有更高的能效;相同压缩机排量下,R32具有较高的制冷能力及排气温度,而R447A在高温工况以及高转速下具有一定优势。     

Calculation of thermodynamic properties of R407C and R410A by the Martin–Hou equation of state — part I: theoretical development

A theoretical development of the thermodynamic properties of two mixtures of hydrofluorocarbon (HFC) refrigerants, i.e. R407C and R410A (in the superheated vapour state), is carried out. The modelling is based on the Martin-Hou equation of state, which has long been used for pure hydrofluorocarbons (e.g. R134a) with good results. Since R407C and R410A are very well investigated refrigerants, the analytical procedure here derived concerns with those thermodynamic properties of R407C and R410A (in the superheated state) that are not published in the current specialised literature. They are: compressibility factor, isentropic and isothermal compressibility, volume expansivity, isentropic and isothermal exponent, speed of sound and Joule–Thomson coefficient. These properties may be used as a theoretical basis for research into the optimal HFC-mixture for compressor efficiency and for performing cycle calculations in the vapour-phase region for systems working with R407C and R410A.     

R32空气源热泵热水器的实验研究

为了解 R32 和 R410A 制冷剂应用于空气源热泵热水器时的性能优劣,采用同轴套管换热器与空调室外机组相匹配,使用电子膨胀阀作为节流装置,在国标GB/T 23137-2008 规定下实验测试 R32 和R410A 在同一套空气源一次加热式热泵热水器样机上的性能.实验结果表明,R32 的充注量仅为 R410A 充注量的74%左右;在各种实验条件下,R32 空气源热泵热水器的能效比不低于 R410A 系统;在3℃低温环境下,R32 样机的性能系数提高31.1%,但排气温度达到101.9℃.不利于 R32 制冷剂在低温条件下的应用;因容积制热量较大,在相同设计能力下 R32 压缩机的排气量可以比 R410A 系统降低4.5%.     

制冷剂R32的循环性能实验研究

R32由于具有环境性能优越,如ODP为零、GWP值小于R410A等优点,逐渐被认识到可以用于替代R410A。本文对R410A和R32的循环性能进行实验研究,结果表明,在不同的工况下,采用2种制冷剂时系统运行的压比基本相同,COP几乎相同。与R410A系统相比,R32系统的压缩机耗功略高,制冷量高,且排气温度高。总之,R32具有良好的热物性、环境性能及循环性能,具有极大的替代R410A的潜力。     

R32在家用空调器中的应用研究

对比R32与R410A的基本物性和热力循环性能,并在同一台家用定频热泵空调器上进行性能测试。相对于R410A,在给定工况下,R32的理论循环制冷量最大可提高15％,能效比最大提高6％,容积制冷量和容积制热量增加7％～8．9％。性能测试结果表明,R32系统的制冷剂充注量比R410A系统的减少24％,额定制冷能力和能效比比R410A系统分别提高8％和3．3％,额定制热能力和性能系数也高于R410A系统。理论热力循环分析及性能测试结果均表明,R32制冷性能相对R410A有较大幅度的提高,制热性能比R410A略高或相当,但R32系统的排气温度较高,比R410A系统高出11．5～25．7℃,恶劣工况下排气温度甚至能达到114．9℃。     

Diesel combustion of oil and refrigerant mixture during pump-down of air conditioners

Compressor-destruction accidents during the pump-down operation of air conditioners were experimentally investigated. Assuming air penetration into refrigerant tubes, the gaseous mixture of the air, refrigerant, and lubricating oil for a compressor was compressed by the compressor with different refrigerant concentrations, and the diesel combustion of the mixture was examined. The compressor was simulated by a small-scale engine. R1234yf, R32, R410A, R134a, R22, and R125 were tested as refrigerants. The mixture burned via adiabatic compression when the refrigerant concentration was low, which means that accidents during the pump-down were caused by the diesel combustion of the mixture. The refrigerant burned and caused intense pressure increase. The mixture without the oil did not burn under any refrigerant concentration, which suggests that oil is necessary for the combustion. These phenomena were observed in the results for R1234yf, R32, R410A, R134a, and R22. Thus, combustion was observed under certain conditions even for refrigerants categorized as non-flammable.     

Stepped pressure cycle – A new approach to Lorenz cycle

Refrigerant vapor-compression cycle usually works with variable temperature heat sources in reality, which causes remarkable irreversible losses in heat exchange process. This paper proposed the stepped pressure cycle to modify the vapor-compression cycle using refrigerant, particularly pure refrigerant. Refrigerant is designed to flow through a series of heat transfer units with stepped pressures so that the irreversible losses can be reduced. Theoretical proof confirmed the stepped pressure cycle with pure refrigerant can approach the Lorenz cycle, the most efficient cycle under variable temperature heat sources. Numerical analysis on cycle performance demonstrated that a dual-step suction and discharge pressure cycle using R32 can achieve 11.5% cooling COP improvement for residential air conditioner, while a dual-step discharge pressure cycle using R134a can bring 9.8% heating COP increase for heat pump water heater. A pilot system was made and preliminarily tested. Compared to the single cycle system, 12.3% and 18.7% COP increase were achieved in the pilot system by applying dual and triple subcycles, respectively.     

空气源热泵自然冷源过冷制热性能实验研究

冬季我国北方室外环境蕴含大量天然冷源,热力学分析表明热泵工质过冷释放的热量可以在蒸发器的等温吸热过程中获得补偿。为了研究大气自然冷源对热泵制热性能的影响,增设室外过冷器,搭建利用自然冷源过冷的空气源热泵实验装置。实验结果表明：当室外环境温度大于0 ℃,冷凝温度小于45 ℃的条件下,自然冷源过冷对热泵制热量与制热COP影响均较小,系统制热量维持在6.22 ~ 6.70 kW,制热COP维持在3.03,压缩机排气温度维持在103 ℃以下;当室外环境温度小于 -10 ℃,冷凝温度大于50 ℃时,随过冷度的增加,压缩机功率增加、排气温度显著增高,系统制热量呈先缓慢增加后减小趋势,制热COP降至2.3。基于上述研究提出一种空气源热泵过冷融霜新型除霜方式,融霜同时不停止制热。     

降低R32压缩机排气温度的方法

作为下一代制冷剂替代物,R32 由于其GWP值较低、热工性能好,正在受到瞩目.但是正因为其容积制冷量大、热工效率高,R32 与其他制冷剂相比具有压缩机排气温度高的特点.解决这个问题成为一项将 R32 实际应用到环境负荷小、高能效而且成本比较低的空调系统,并推广到世界市场的重要技术课题.本文将阐述利用膨胀阀控制压缩机吸气干度,同时使用 R32 专用的润滑油来降低排气温度,以解决这个问题的方法.     

Field test study of a novel defrosting control method for air-source heat pumps by applying tube encircled photoelectric sensors

To improve the defrosting accuracy of air source heat pumps (ASHPs), this paper proposes a novel defrosting control method by applying tube encircled photoelectric sensors (TEPSs). A field test was conducted for two heating seasons in Beijing, China, to verify the feasibility and practicality of the novel TEPS method. The test results revealed that irrespective of the environmental conditions, the TEPS method can initiate defrosting in similar situations: most of the heat exchanger surface had been covered by frost; the compressor suction temperature decreased by ~9 °C; the compressor discharge temperature increased by ~16 °C; and the heating capacity decreased by ~30%. Furthermore, the TEPS method was verified to make more accurate and more reasonable defrosting decisions than the traditional T-T method under both frosting and non-frosting conditions. The results indicate that the TEPS method is a competitive defrosting control method that can be used for ASHPs.     

Evaluation of two-phase suction,liquid injection and two-phase injection for decreasing the discharge temperature of the R32 scroll compressor

R32 has been considered as an important alternative in the phase-out of hydrochlorofluorocarbons (HCFCs) due to its advantages such as relatively low global warming potential compared to R410A, favorable thermal properties. However, the increased discharge temperature of the R32 compressor, compared with R410A, is the main barrier affecting the wide and quick adoption. In this work, three promising methods to decrease the discharge temperature of R32 scroll compressor, namely, two-phase suction, liquid injection and two-phase injection, have been investigated. By considering the variations of motor efficiency and leakage rate, an improved distributed parameter model of the scroll compressor is rebuilt based on a previously developed one (Wang et al., 2008). By that model, the effectiveness of these three methods in decreasing discharge temperature and their influence on thermodynamic performance are researched. It is concluded that all the three methods show excellent potential in decreasing the discharge temperature of R32 scroll compressor. Besides, two-phase injection outperforms the other two methods in cooling capacity and COP by 11.8% and 4.8%, respectively.     

Modeling of a novel spool compressor with multiple vapor refrigerant injection ports

A model of a novel rotary spool compressor has been developed to explore the effect of multiple injection ports on compressor and cycle performance. The thermodynamic model includes the effects of heat transfer and leakage and is numerically solved to predict the compressor power consumption and mass flow rate. Saturated vapor injection is modeled assuming that the injection pressures and the timing of the injection process can be controlled.The model predicts that adding a single injection port will provide a 12% increase in the cycle coefficient of performance (COP) when the compressor runs at 1907 rpm with R-22 evaporating at ?7 °C, condensing at 49 °C, and 15 °C of superheat. Adding a second, non-optimized injection port increases the COP by 16% compared to the cycle without injection. The model is used to investigate the effect of injection pressure, port location, and port diameter on cycle performance.     

R32制冷剂空调压缩机应用试验研究

R22 制冷剂替换在即,R32 制冷剂是一种潜在的且经济的替代制冷剂.本文通过分析R32制冷剂的物理性质和理论热工循环参数,并采用空调用涡旋式压缩机进行试验测试,同时与 R410A 制冷剂进行试验对比.试验结果表明,R32 制冷剂替代当前的 R22 制冷剂作为空调制冷剂应用,对于空调用涡旋式压缩机来说,其整体表现与 R410A 制冷剂相类似.但为了取得更好的性能和可靠性,压缩机应针对 R32 制冷剂在空调工况应用时压力高、排气温度高的特点进行设计改进.     

A novel linear electromagnetic-drive oil-free refrigeration compressor using R134a

A new type of oil-free moving magnet linear compressor with clearance seals and flexure springs has been designed for incorporation into a vapour compression refrigeration system with compact heat exchangers for applications such as electronics cooling. A linear compressor prototype was built with a maximum stroke of 14 mm and a piston diameter of 19 mm. An experimental apparatus was built to measure the compressor efficiencies and coefficient of performance (COP) of a refrigeration system with the linear compressor, using R134a. The resonant frequency for each operating condition was predicted using the discharge pressure, suction pressure and stroke. Refrigeration measurements were conducted for different strokes under each pressure ratio with a fixed condenser outlet temperature of 50 °C and evaporator temperature ranging from 6 °C to 27 °C. The results show that the COPs are around 3.0 for tests with a pressure ratio of 2.5 (evaporator temperature of 20 °C).