Influence of liquid receiver on the performance of reversible heat pumps using refrigerant mixtures

A liquid receiver is normally included in reversible vapour compression heat pumps (RHPs) to temporarily store the excess refrigerant charge occurring due to change of operation mode. The presence of a liquid receiver influences the total amount of refrigerant charged into a system, and particularly when using refrigerant mixtures, could affect the system circulation composition. Using a computer simulation, this paper compares the performance of RHPs designed with and without a liquid receiver, when using R407C. It was shown that the presence of a receiver caused an increase in the positive shift in the circulating composition, resulting in improved capacity while reducing the system COP in both heating and cooling modes when compared to a system without a receiver.     

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.     

低温空气源热泵技术的应用

介绍带经济器的低温空气源热泵技术,通过对低温空气源热泵机组与普通空气源热泵机组的制冷量、制热量和能效比等参数进行测试及对比,探讨低温空气源热泵技术的应用优势。试验结果表明:与普通机组相比,低温机组在名义制冷和名义制热工况下冷热量和能效均有所提升;在-10~-15℃的环境中,普通机组制热量严重衰减使其不适用于此温度区间,低温机组制热量虽然也在减少,但其COP仍可达2.0,且排气温度相对较低;在-15~-20℃超低温环境中,低温机组仍可稳定运行,且能效比在2.0左右。     

空气源热泵用于房间供暖的分析

从南方供暖的议题分析空气-水型热泵系统可用于"夏热冬冷地区"冬季房间的采暖,讨论该系统的工质、压缩机、换热器、节流装置和控制技术等。指出,不仅要提高热泵系统本身的完善性,对房屋围护结构、除霜的排水系统、室内换热器和整体系统的控制也要有良好的措施。     

循环加热式空气源热泵热水机性能测试方法探讨

针对目前空气源热泵热水机产品质量需要保障的现状,根据国标GB／T21362-2008《商业或工业用及类似用途的热泵热水机》,探讨循环加热式空气源热泵热水机性能试验的水系统设计,并对循环加热式机组的2种性能测试方案进行比较分析。     

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.     

Energetic and exergetic performance analysis of Bethe-Zeldovich-Thompson (BZT) fluids in geothermal heat pumps

This study highlights theoretical energetic and exergetic performance evaluation results of Bethe-Zeldovich-Thompson (BZT) fluids in geothermal heat pumps. In this study, hexafluoroethane (R116), octafluoropropane (R218), and octafluorocyclobutane (RC318) were selected as possible alternative replacements to the traditional refrigerants in geothermal heat pumps. According to the calculations, coefficient of performance of 101 kW geothermal heat pumps (COP_HP) changes with range between 3.84, 3.08, and 2.92 for octafluorocyclobutane (RC318), hexafluoroethane (R116), and octafluoropropane (R218), respectively. Moreover, R116 shows the maximum exergy efficiency 68% among the selected BZT fluids.     

Effects of intermediate pressure on the heating performance of a heat pump system using R410A vapor-injection technique

Recent heat pumps are actively equipped with a refrigerant vapor-injection technique to acquire better performance in severe operating conditions. In this study, the target system which has an additional expansion valve at the outlet of condenser was presented. The concept of intermediate pressure was generated in the target system. Effects of the intermediate pressure on the heating performance with various injection ratios were measured and analyzed according to the compressor frequencies ranging from 60 to 100 Hz. Unlike conventional vapor-injection cycle, the maximum injection ratio was highly affected by the intermediate pressure. The high intermediate pressure provided high initial heating capacity and COP; but it restricted the available range of vapor-injection within narrow limits. The result indicates that a proper operating strategy is needed for the vapor-injection cycle.     

空气源热泵机组除霜性能试验研究

为了研究不同节流机构、不同除霜方式对空气源热泵机组除霜性能的影响,在空气源热泵机组上对热力膨胀阀、电子膨胀阀作为除霜节流机构,以及采用“四通换向阀直接换向除霜”和“压缩机停机四通换向阀换向除霜”2种除霜方式,进行了试验比较研究。结果表明：采用电子膨胀阀的除霜时间比热力膨胀阀的短12s,即减少11％。笔者提出采用电子膨胀阀＋压缩机停机四通换向阀换向除霜模式的结合,具备四通换向阀换向除霜的除霜强度,解决了“奔油”等部分缺陷,而且采用电子膨胀阀进行除霜可缩短部分除霜时间。     

多联机空气源热泵相变蓄能除霜特性试验研究

为了解决多联机空气源热泵常规除霜时间长、室内环境恶化等问题,提出多联机热泵相变蓄能除霜方法。针对提出的新方法,设计系统流程和试验方案,并在模拟室内外环境条件下完成试验研究。相对于常规除霜,新的除霜方法可以有效缩短33.7%的除霜时间,显著改善机组的除霜性能和室内供热环境。     

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.     

喷液旁通对空气源热泵性能影响的试验研究

分析一种喷液旁通对空气源热泵性能的影响,并进行额定制冷和制热验证试验。结果表明：当旁通率较小时,制冷能力和能效比对旁通率的变化不敏感;旁通率微调到一定区间时,制冷能力和能效比出现一定程度的提升,压缩机排气温度明显下降;当旁通率较大时,制冷能力和能效比显著下降。在额定制热条件下,旁通率微调到一定区间时,制热能力和性能系数出现一定程度的提升。     

An investigation of the performance of a scroll compressor under liquid refrigerant injection

In this study, fundamental and practical influence of liquid refrigerant injection on the performance of a refrigerant scroll compressor has been investigated experimentally and theoretically. In the theoretical analysis, a compression model of vapor/liquid mixture is developed by taking account of heat transfer from the cylinder wall to suction, compression and injection refrigerant. An experiment has been done under the condition of keeping the oil temperature constant in order to investigate the fundamental influence of the liquid refrigerant injection on the compressor performance, and the results were compared with the theoretical ones. It was found that the injection basically increases the compression power and decreases the compressor efficiency, though the situation depends on the condition of the heat transfer to the injection refrigerant. And furthermore, the performance of the liquid refrigerant injection compressor under practical operating condition without controlling the oil temperature has been investigated. Under this condition, the compressor showed recovery and slight improvement of performance due to the decrease of the oil and cylinder temperatures by the injection. In addition, influence of the refrigerant injection on the oil viscosity and refrigerant solubility in the oil, which relate mechanical loss and reliability of the compressor, have been discussed.     

Capacity-controlled ground source heat pumps in hydronic heating systems

The objective of this study was to investigate the energy-saving potential of using variable-speed capacity control instead of the conventional intermittent operation mode for domestic ground source heat pumps. Variable-speed capacity control is commonly used in air-to-air heat pumps, but not in ground source heat pumps for hydronic heating systems, even though the energy-saving potential may be greater for this application. A theoretical analysis indicates how the energy efficiency is influenced by variable-speed capacity control of the compressor. The analysis shows that, to take full advantage of the capacity control, care should be taken to achieve the correct relationship between refrigerant flow and heat transfer media flows. Intermittent control and variable-speed capacity control were compared by laboratory tests on two capacity-controlled heat pumps and one standard heat pump with a single-speed compressor. Test data were then used for seasonal performance factor (SPF) calculations. The SPF calculations show that despite improved performance at part load the variable-speed controlled heat pump did not improve the annual efficiency compared to the intermittently operated heat pump. This is mainly due to inverter and compressor motor efficiencies and the need for improved efficiency and control of pumps used in the heating and ground collector systems.     

风冷热泵热经济学优化

以风冷热泵单位热量总成本为目标函数对风冷热泵进行热经济学优化，求出目标函数取最小值时的优化参数值，并分析相关参数对风冷热泵热经济性目标函数的影响。由于热经济学优化考虑了风冷热泵的投资成本和能耗成本，所以热经济学优化相对于单纯的热力学优化和经济学优化更具一般性和实际意义。     

空气源热泵热水机性能测试室测控系统研制与分析

根据国家标准GB/T21362-2008及用户要求,设计并建造一套空气源热泵热水机热工性能测试试验室。试验室对室内干球温度和相对湿度两个回路采用闭环控制。高性能PID控制器及测试软件中的程序控制,提高了空气处理系统控制精度和工况响应速度,使极限工况达到稳定的时间小于1小时。     

R410A风冷热泵冷热水机组变环境温度制热运行特性分析

对以R410A 为制冷剂的风冷热泵冷热水机组完成了变环境温度制热运行的实验.在环境温度为7--10℃的范围内,进行了机组制热量、输入功率、COP、压比、排气温度、吸气温度、过冷度、过热度等特性随环境温度变化的测试,分析了 R410A 机组在变环境温度下制热运行的特性,为R410A 机组的设计与工程应用提供了实验参考依据.     

Field test investigation of a double-stage coupled heat pumps heating system for cold regions

This paper reports a double-stage coupled heat pumps (DSCHP) heating system, which couples air source heat pump (ASHP) and water source heat pump (WSHP) together. The system is presented for the first time in open literature with the objective to improve the working condition and heating performance of the ASHP under cold environment. A practical project in Beijing firstly installed this system and field test has been performed for one month. The test results indicate that the DSCHP system can be smoothly and efficiently used for heating in cold regions. Compared with the traditional ASHP heating system, the operating characteristics of the DSCHP heating system are greatly improved, demonstrating that the system can offer considerable application potential in cold regions.     

A novel defrosting control method based on the degree of refrigerant superheat for air source heat pumps

When an air source heat pump (ASHP) unit operates for space heating at a frosting environment, periodic defrosting is necessary to maintain a high system performance. To defrost efficiently, it is necessary to find an effective defrosting control method. In this paper, an experiment was carried out on an ASHP unit with a capillary tube as a throttle device, under simulated frosting and defrosting conditions using time control defrosting method, and the experimental results are firstly presented. Secondly, a novel defrosting control method based on the degree of refrigerant superheat (DS) is reported. To validate the novel defrosting control method, a further experiment was conducted on another ASHP unit with an electronic expansion valve (EEV) as a throttle device, under simulated frosting and defrosting conditions. The experimental results demonstrated that when applying the novel defrosting control method, defrosting was initiated before the operating performances of ASHP unit rapidly deteriorated, which was more reasonable.     

Carbon dioxide as refrigerant for tap water heat pumps: A comparison with the traditional solution

Increased concern about the environmental impact of the refrigeration technology is leading toward design solutions aimed at improving the energy efficiency of the related applications, using eco-friendly refrigerants, i.e. ozone-friendly and with the least possible global warming potential (GWP). In this respect, carbon dioxide (ASHRAE R744) is seen today as one of the most promising refrigerants and is raising great interest in industrial and scientific fields. In the present work, the plant options are investigated, which are related to the design of air/water heat pumps for tap water using CO₂. A comparison is made, in terms of energy efficiency, between a system working with CO₂ and a similar one working with HFC R134a; such a comparison is carried out by means of a simulation model of a refrigerating machine/heat pump, characterized by a detailed representation of the heat exchangers, based on their subdivision into elementary volumes. Results show that carbon dioxide is an interesting substitute for synthetic fluids, if the design of the system is focused to take advantage of its properties.