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.     

两级热泵活塞式压缩机模型研究

采用稳态仿真的方法对双级压缩热泵系统的压缩机部件建立模型,并建立中间冷却器模型。由于在低温丁况下试验,模型建立考虑了压缩机和环境的换热。通过建立试验台,采集试验数据并与仿真结果进行比较。结果表明,稳态仿真能够良好地反映系统运行中的参数变化。     

A general model for two-stage vapor compression heat pump systems

Two-stage vapor compression technology has high potential of performance improvement for cold climate heat pumps, and there are several types of inter-stage configurations that need to be evaluated before making a choice. A general model of these configurations is first derived from a subcooler cycle and then is extended to be capable of evaluating many other inter-stage configurations by employing an “input domain”. The model is solved with a sequential algorithm and an analytical initial solution of the intermediate pressure is presented. After an experimentally validation with additional calculations of the subcooling parameter, the evaporating and condensing pressure, this general model is then used in the performance comparison and analysis of eight different inter-stage configurations. At last, case studies show that, this general model is capable of performing performance comparison among cycles with different types of inter-stage configurations, as well as refrigerant selection and operational analysis.     

双级一次加热式热泵热水机的研究

通过对市场上存在的循环加热式和一次加热式2种传统形式的热泵热水机进行对比分析,发现前者工程系统复杂,且由于系统水泵功耗会造成系统能效下降,而后者虽然工程得到简化,但由于长期高压比工作,能效低下。为此,作者设计出一种高效节能的新型热泵热水器形式——双级一次加热式热泵热水机,既取消了循环泵,保持了一次加热式的工程优势,同时也降低了系统的压缩比,实现了高能效。本文重点阐述双级一次加热式热泵热水机的设计方案、主要性能优势和相关关键技术,通过理论分析和实验验证,得出如下结论：双级一次加热式热泵热水系统与传统单级一次加热式相比,输入功率大幅下降,COP明显提高;双级一次加热式热泵热水系统与循环加热式相比,省却循环水泵的功耗,COP也具有优势。     

两级压缩式热泵空调与冰箱复合系统

根据两级压缩式制冷原理和热泵空调与冰箱制冷系统运行工况的不同,提出一种新型两级压缩式热泵空调与冰箱复合系统,介绍其原理及不同工况模式下的实现方式。该系统将热泵空调系统与冰箱系统冷热量相互有效利用,具有节能效果。对一个应用实例进行数值模拟,结果表明：复合系统能耗与常规的各自独立系统的总耗能相比,冬季节能约9％,夏季节能约18％。     

用于离心式高温热泵机组研发的模拟模型

为了对所设计的高温热泵机组中各设备进行合理匹配,建立其稳态模拟模型。该模型包括关键部件的子模型:带有经济器的双级离心式压缩机、卧式壳管式冷凝器、浮球膨胀阀、满液式蒸发器和回热器。在模拟算法的设计中,将模块化方法与二分法相结合,所需输入参数易于为设计者所获得,且不会限制系统的运行。利用该模型,对高温热泵进行初步设计;经过多方案比较,确定各换热器的结构参数,并预测该系统的性能和运行参数。     

Fan-less heat exchanger concept for CO2 heat pump systems

A novel system for space heating has been developed taking advantage of the favourable characteristics of the transcritical CO₂ cycle, where heat is rejected by cooling of supercritical gas at gliding temperature. By a proper design of a counter flow heat exchanger it is possible to heat air to high temperatures and thereby giving the driving force for circulation of air through the heat exchanger, in consequence without using a fan. A concept without a fan, here called a fan-less concept, would give several advantages; no noise, no power consumption for the fan and increased comfort with reduced air draft in the room. The concept may also be used for heat rejection in systems for light commercial applications or other applications where fan assisted heat rejection concepts are used today.

An experimental study of a CO₂ to air heat exchanger has been performed. The heat exchanger was made of a vertically finned aluminium profile. Tubes for CO₂ were mounted in the base of the profile. CO₂ at supercritical pressure flowing downwards through the profile was heating air flowing in the channels formed by the fins of the profile. In this way a perfect counter flow heat exchange was obtained. The prototype heat exchanger was 2000 mm high and 190 mm wide, with 45 mm deep fins.

A simulation model was developed and verified to give good accordance with the experimental data. The model was then used to study how different design parameters influence the efficiency of the heat exchanger. By altering the number of fins and the fin thickness of the tested profile, the heat output at a given condition could be increased to almost double, meaning that the initial design was relatively far from optimal.

With the original heat exchanger profile design concept a heat exchanger with height, width and depth of, respectively 2000, 750 and 200 mm, would be required in order to achieve a heat output of 2500 W if the constraints for assumed acceptable efficiency was applied. If a heat exchanger with less height is preferred, the width will have to be increased in order to maintain about the same front area, width times height. Ideas have also been introduced for how to improve both the compactness and efficiency of the heat exchanger by introducing a compact counter flow heat exchanger in the lower part of the air flow channel. It is concluded that the new concept looks promising for use as the indoor heat exchanger in an air-to-air heat pump or as a gascooler for heat rejection in small commercial equipment, when using CO₂ as refrigerant.     

Feasibility study of a two-stage vapour compression heat pump with ammonia-water solution circuits: experimental results

A breadboard heat pump was designed and built to test the performance of a vapour compression heat pump with two-stage ammonia-water solution circuits. A major improvement in performance was obtained by incorporating a bleed line to attain water balance between the high and the low temperature solution circuits. The new scheme was first investigated by computer simulation and then incorporated in the experimental setup. The advantages of this scheme are reduced first cost (by eliminating the need for a rectifier), a simplified system and its control mechanisms, a 20–30% improvement in cooling coefficient of performance and a 10–15% increase in cooling capacity as compared to the system with a rectifier. Coefficients of performance in the range of 0.69 to 1.04 were obtained experimentally for a temperature lift of 100 K and cooling capacities in the range of 2.02 to 4.22 kW. The pressure ratios encountered were in the range of 6.9 to 11, which are 35 to 50% of the pressure ratio expected for a conventional single-stage heat pump.     

Dynamic modeling and characteristic analysis of a two-stage vapor injection heat pump system under frosting conditions

This paper presents a distributed-parameter dynamic heat exchanger model integrated with a detailed frost growth model to account for non-uniform frost formation on a fan-supplied finned-tube coil. A novel, iteration-free approach is proposed to solve the air flow redistribution by linearizing a system of non-linear air pressure drop equalization equations, resulting in a significant improvement in the computational efficiency. As a continuation and extension of our previous work, the developed models along with the component models described in Qiao et al. (2015a) are applied for the first time to explore the frosting dynamics of a two-stage flash tank vapor injection heat pump system. It is found that frost formation degrades the heating performance of the system substantially. Meanwhile, the simulation indicates that air and refrigerant flow maldistribution, resulting from non-uniform frost growth on the outdoor heat exchanger, can lead to unstable system hunting behavior. Comparisons between the simulation results and experimental data indicate that the proposed models can reasonably predict the time-dependent heat transfer and fluid flow phenomena of the system.     

双级离心式高温水源热泵设计应用分析

介绍双级离心式高温水源热泵的设计过程和应用优势。通过理论计算及系统流程分析,推导出可实现77℃高温出水的大容量双级离心系统。并结合实际工程案例对双级离心式高温水源热泵方案做经济性评估。指出在应用双级离心式高温水源热泵制冷/供热时,不仅节约能源,降低运行费用,而且对环境保护有着积极的推动作用。     

空分设备氧透冷却器酸洗除垢

介绍了空分设备氧透冷却器酸洗除垢的酸洗剂的配比及除垢过程 ,分析了酸洗除垢的经济效益 ,最后指出了酸洗除垢在空分设备清洗中的前景。     

利用空气源热泵跨季节补热对单供暖地埋管地源热泵运行特性影响分析

针对大规模住宅小区单供暖地埋管地源热泵在实际运行中存在的问题,在对其运行现状进行分析的基础上,以其中一个项目为例,分析地埋管地源热泵在单供暖工况下长期运行时的土壤逐年温度变化和运行费用。指出应尽早抑制土壤温度进一步降低,使其稳定在较高水平,以保证系统持续可靠运行。提出以土壤年温度下降幅度为目标,利用空气源热泵跨季节补热解决土壤温度逐年下降的问题。研究结果表明,所计算项目从第5年开始补热,补热后每年供暖初期土壤温度为7.5℃左右,补热初投资为2.86元/米~2,补热费用为2.71元/米~2,供暖运行费用为9.35元/米~2,年运行费用为12.06元/米~2。     

热泵型空调器运行特性的实验研究

用空气焓差实验法,在制冷工况下对一台热泵型空调器进行最佳充注量的实验研究,同时,分别在制冷工况和制热工况下测量冷凝器和蒸发器管壁的温度分布。实验结果表明,空调系统中存在一个最佳制冷剂充注量,使得空调系统的制冷量和能效比达到最大值。根据实验结果,分别给出在制冷工况和制热工况下进行冷凝器和蒸发器换热计算时,制冷剂与管壁之间的平均温差。     

水源热泵系统的经济运行及评价指标

介绍水源热泵系统经济运行的概念,提出确保水源热泵系统经济运行时在系统设计、选型、运行及管理等方面应采取的措施建议;给出水源热泵系统经济运行的量化评价指标。     

太阳能-土壤源热泵复合系统串联运行模式试验研究

阐述太阳能-土壤源热泵复合系统的工作原理以及运行模式,对复合系统串联运行时水箱分别作为热缓存器（模式一）和热蓄存器（模式二）进行试验。结果表明,2种运行模式各有其独特之处,但是从能源利用角度来讲,模式一的太阳能利用率明显高于模式二,系统的COP（2.30）也大于模式二（2.09）。     

辅助热源容量对水环热泵系统运行的影响

为了确定水环热泵系统辅助热源容量模型及其对系统运行的影响,以循环水为研究对象,利用建筑与机组间的传递关系提出转换能思想——循环水能量代替建筑负荷解决机组因工况转换产生的反向能问题。基于此想法,利用逆推方法确定循环水能量方程,并以此为依据建立适用于所有建筑的辅助热源容量模型,且给出38.8%～79.1%热负荷的容量范围。以天津某办公建筑为案例,按照热负荷50%,55%和60%选取3种容量方案进行测试,结果表明:平衡机组与辅助热源能耗可抑制负荷变化产生的系统功率波动,降低总能耗;按照热负荷55%选取容量方案最合理,相对于另外2种方案节能率分别为14.4%和4.8%。     

Investigation on capacity matching in a heat pump and hollow fiber membrane-based two-stage liquid desiccant hybrid air dehumidification system

The heat pump and hollow fiber membrane-based two-stage liquid desiccant hybrid air dehumidification system is promising recently because solution droplets can be prevented from crossing over into the process air. The quasi-isothermal processes are realized by two-stage dehumidification processes and the system performance is improved. In this study, a novel capacity matching index (CMI) is introduced to evaluate the energy capacity matching of the system through modeling study. It is found that CMI is usually lower than 1 under the typical hot and humid weather condition like South China and the demand and supply of energy in the system is mismatching. As inlet air temperature rises, the dehumidification rates, CMI, EER and COP all decrease. But CMI is almost constant with different inlet air humidity. The influence of air inlet temperature to dehumidifiers and regenerators on the system performance is also investigated. The higher the inlet temperature of dehumidifiers is, the larger the CMI, EER and COP are. The dehumidification rates and CMI both grow with an increase in the inlet temperature of regenerators. It is beneficial for energy balance of the system and high moisture loads, but the side effect is that the EER and COP both decrease.     

Downward two-phase flow applications for a non-conventional heat pump

A non-conventional heat pump working by a difference in density between two branches of a hydraulic vertical loop has been described. This system called thermogravimetric heat pump, TGHP, operates with a non-conventional regenerative thermodynamic cycle which remarkably improves COP values. The lower density in the ‘downward branch’ is obtained by a liquid–vapour two-phase flow. Performances and main geometrical characteristic trends, such as plant height Z and two-phase column diameter D_T–PD have been drawn, varying the minimum cycle temperature between 15 and 25 °C and the user temperature, T_max, in the range 60–70 °C. The carrier fluid is demineralized water; according to the peculiar working fluid—PP 50, HFC 134a and HFC 338cca—different solutions can be obtained, such as for 10–12 storey buildings or for skyscrapers. Yet, the results obtained with HFC 338cca must be accepted with some cautions while waiting for a better characterisation of such fluid. Chemical compatibility, thermal stability, environmental impact have been also taken into account in the choice of the operating couple, carrier fluid—working fluid. While the thermodynamic conversion process is non-conventional, the TGHP can be assembled by standardised technology. The compressor of a conventional plant is here replaced by a feeding pump and COP values obtained through a regenerative TGHP are globally larger than those of a common heat pump.     

Simple wide-range method for angle measurement with a point fiber-optic output

We propose a simple optical method for precise, wide-range angle measurement based on the use of a single-mode optical fiber as a registration scheme output. Because of its micrometric core dimensions, the fiber serves as a point receiver that is highly sensitive to angular displacements of focused laser emission. The method allows the independent photoelectric measurement of both rotation and spatial angles of various optical elements, combining a wide angular dynamic range (from 0 degrees to 360 degrees ) with high accuracy (exceeding 3 arcsec).