Part-load characteristics of a new ammonia/lithium nitrate absorption chiller

A pre-industrial prototype of a new water-cooled ammonia/lithium nitrate absorption chiller was characterised at part-load operation mode. The chiller was built using brazed plate heat exchangers in all its components, including the absorber and the generator.A test campaign was carried out varying the thermal load in the chilled water circuit and keeping the hot and cooling water temperatures constant.Part-load curves of the thermal and electrical coefficients of performance were obtained, plotted and compared with data from the literature on small capacity absorption chillers with conventional working pairs, namely ammonia/water and water/lithium bromide. The experimental results showed that to achieve a higher electrical coefficient of performance at part-load operation, it was much more convenient to use an ON-OFF control than to modify the hot water temperature. Furthermore, using a simple ON-OFF control strategy, the behaviour of the new absorption chiller was more agile and responded more quickly.The part-load curve of the electrical coefficient of performance was obtained by adjusting the experimental data to the shape of the curve proposed in the standard prEN-14825:2011 for air-to-water chillers. The Cc coefficient was 0.7985 matching the value obtained dividing the remaining electrical consumption measured during the OFF half cycles by the total energy consumption generated.     

Thermodynamics cycle analysis and numerical modeling of thermoelastic cooling systems

To avoid global warming potential gases emission from vapor compression air-conditioners and water chillers, alternative cooling technologies have recently garnered more and more attentions. Thermoelastic cooling is among one of the alternative candidates, and have demonstrated promising performance improvement potential on the material level. However, a thermoelastic cooling system integrated with heat transfer fluid loops have not been studied yet. This paper intends to bridge such a gap by introducing the single-stage cycle design options at the beginning. An analytical coefficient of performance (COP) equation was then derived for one of the options using reverse Brayton cycle design. The equation provides physical insights on how the system performance behaves under different conditions. The performance of the same thermoelastic cooling cycle using NiTi alloy was then evaluated based on a dynamic model developed in this study. It was found that the system COP was 1.7 for a baseline case considering both driving motor and parasitic pump power consumptions, while COP ranged from 5.2 to 7.7 when estimated with future improvements.     

土壤源VRF空调系统冬季运行特性实验研究

以土壤源VRF空调系统为研究对象,利用土壤源VRF实验台对其冬季运行特性进行了实验研究,分析在不同开机率时,小时制热量、小时耗功量、机组COP随部分负荷率的变化规律。结果表明:小时制热量与小时耗功量随开机率的升高基本呈现增大趋势,且耗功量对开机率的变化更为敏感;不论室内机的开启率为何值,小时制热量随部分负荷率的增大而增大,小时耗功量、机组COP随部分负荷率的增加呈现下凹、上凸的变化趋势,即土壤源VRF空调机组在部分负荷运行条件下具有较为良好的节能性。     

Simulation and validation of a hybrid-power gas engine heat pump

Hybrid-power gas engine heat pump (HPGHP) combines hybrid power technology with gas engine heat pump, which can keep the gas engine working in the economical zone. In this paper, a steady-state model of the HPGHP in heating condition has been established, the optimal torque curve control strategy is proposed to distribute power between the gas engine and battery pack. The main operating parameters of the HPGHP system are simulated on Matlab/Simulink and validated by experimental data, such as operating temperature, coefficient of performance (COP), fuel-consumed rate, etc. Heating capacity and COP of the heating pump system are validated under different ambient temperatures and water flow rates. The simulation and experiment results shows acceptable agreement, the maximum difference is respectively 8.9%, 5.9%, 9.5% and 8.2% for engine torque, motor torque, reclaimed heat and fuel-consumed rate. Based on the simulation results, HPGHP has the lowest fuel-consumed rate of 283 g (kWh)⁻¹ at engine speed of 3000 rpm; the PER of HPGHP system is about 15.9% and 11.4% higher than the GHP under the same load in Mode C and D.     

Thermodynamic assessment of high-temperature heat pumps using Low-GWP HFO refrigerants for heat recovery

Reducing energy consumption by utilizing heat recovery systems has become increasingly important in industry. This paper presents an exploratory assessment of heat pump type heat recovery systems using environmentally friendly refrigerants. The coefficient of performance (COP) of 4 cycle configurations used to raise the temperature of heat media to 160 °C with a waste heat at 80 °C is calculated and compared for refrigerants R717, R365mfc, R1234ze(E), and R1234ze(Z). A multiple-stage “extraction” cycle drastically reduces the throttling loss and exergy loss in the condensers, resulting in the highest COP for R1234ze(Z). A cascade cycle using R1234ze(Z) and R365mfc has a relatively high COP and provides practical benefits. Even under adverse conditions, the primary energy efficiency is greater than 1.3 when the transmission end efficiency of the electric power generation is 0.37. The assessment demonstrated that high-temperature heat pumps are a promising approach for reducing primary energy consumption for industrial applications.     

Regenerated air cycle potentials in heat pump applications

Air (reversed Brayton) cycle has been utilized in the area of refrigeration and cryogenics for several decades, but its potentials in heat pump applications were longtime underestimated. In this paper, a thermodynamic model for the regenerated air heat pump cycle with practical compressor, expander and regenerated heat exchanger was developed. Based on the model, the relations between the system performance and the operating parameters were analyzed. The optimal heating COP (coefficient of performance) and the corresponding pressure ratio were derived. Then, air heat pump cycles (regenerated cycle and basic cycle) and vapor-compression heat pump cycles (CO₂ trans-critical cycle and R410A subcritical cycle) were numerically compared. The results indicated that the regenerated air heat pump cycle not only gets the heating capacity in line with the heating load under different operating conditions but also achieves higher COP over trans-critical CO₂ heat pump cycle in applications of large temperature difference.     

土壤源VRF空调系统冬季运行部分负荷特性实验研究

利用土壤源VRF空调系统实验台,对冬季制热工况进行实验研究,分析单位面积小时功耗、机组性能系数、系统性能系数随部分负荷率(PLR)的变化规律。研究表明:冬季制热工况下部分负荷率主要集中在40%~70%范围内,单位面积小时功耗随部分负荷率呈下凹曲线分布,机组性能系数和系统性能系数随部分负荷率变化存在呈上凸趋势的性能域。     

使用电子膨胀阀的热泵热水器动态性能数值模拟与实验研究

在不同的环境工况下对使用电子膨胀阀的热泵热水器系统动态性能进行了实验研究,测量了电子膨胀阀不同开度条件下热泵热水器的动态制热量、性能系数等参数,分析了电子膨胀阀开度对热泵热水器性能的影响.同时,对热泵热水器系统动态性能进行了数值模拟,并将模拟结果与实验结果进行了比较.结果表明:在电子膨胀阀某一开度下,系统性能系数存在一个最大值;对于电子膨胀阀不同开度,在加热初始阶段,电子膨胀阀开度较大时系统COP和制热量较高,而在加热后期则恰恰相反.通过在不同加热时段使用电子膨胀阀不同开度实验发现,系统性能得到显著提高,最大可提高7.6％.热泵系统性能数值模拟与实验结果的变化趋势一致,说明数学模型和计算方法是可行的.     

Thermodynamic performance assessment of carbon dioxide blends with low-global warming potential (GWP) working fluids for a heat pump water heater

Blends of CO₂ with ten low-global warming potential (GWP) working fluids are evaluated for use in a heat pump water heater. The effects that the discharge pressure, component ratio, hot-water outlet temperature and chilled water inlet temperature have on the coefficient of performance (COP) of heat pump are analyzed when the pinch point of the heat exchange is considered. It is found that temperature glide of zeotropic mixture has a good thermal match with the temperature change of water as two pinch points appear in the gas cooler/condenser or evaporator. The good thermal match in the heat exchangers promotes the system COP. Addition of low-GWP working fluids to pure CO₂ can reduce the high-side pressure. The results show that CO₂/R41 and CO₂/R32 are suitable candidates for heat pump water heaters because of their high COP and low high-side pressure in comparison with those of a pure CO₂ cycle.     

启停过程对空气源热泵-冷柜一体机性能影响的实验研究

空气源热泵-冷柜一体机中热泵的启停过程不仅会影响系统供热性能,还会影响冷柜性能.本文实验研究了在单独运行及联合运行工况下考虑空气源热泵的启停过程的空气源热泵-冷柜一体机的性能,分析了空气源热泵的启停次数对热泵系统和冷柜系统性能的影响.实验结果表明:相比热泵单独运行工况,空气源热泵-冷柜一体机中热泵制热量的衰减开始时间延...     

Performance enhancement of a compressive thermoelastic cooling system using multi-objective optimization and novel designs

Thermoelastic cooling is a recently proposed, novel solid-state cooling technology. It has the benefit of not using high global warming potential (GWP) refrigerants which are used in vapor compression cycles (VCCs). Performance enhancements on a thermoelastic cooling prototype were investigated. A few novel design options aiming to reduce the cyclic loss were proposed. It was found that the maximum temperature lift increased from 6.6 K to 27.8 K when applying the proposed novel designs, corresponding to 0–152 W cooling capacity enhancement evaluated under 10 K water–water system temperature lift. In addition, a multi-objective optimization problem was formulated and solved using the genetic algorithm to maximize the system capacity and coefficient of performance (COP). With all the novel designs, the optimization could further enhance 31% COP, or 21% cooling capacity, corresponding to COP of 4.1 or 184 W maximum cooling capacity.     

Experimental results with a variable geometry ejector using R600a as working fluid

Experimental results with the first laboratory scale variable geometry ejector (VGE) using isobutane (R600a) are presented. Two geometrical factors, the area ratio and the nozzle exit position, can be actively controlled. The control of the area ratio is achieved by a movable spindle installed in the primary nozzle. The influence of the spindle position (SP) and condenser pressure on ejector performance are studied. The results indicate very good ejector performance for a generator and evaporator temperature of 83 °C and 9 °C, respectively. COP varied between 0.4 and 0.8, depending on operating conditions. The existence of an optimal SP, depending on the back pressure, is identified. A comparison of the benefit of applying the variable geometry design over a fixed geometry configuration is assessed. For example, for a condenser pressure of 3 bar, an 80% increase in the COP was obtained when compared to the performance of a fixed geometry ejector.     

On-field measurement method of vapor injection heat pump system

This paper examines air-to-air injection heat pumps (HPs) and proposes a method to determine both heating capacity and coefficient of performance (COP) in situ, allowing analyses of already-installed setups and long-term observation. Due to the uncertain nature of air enthalpy measurements, this method instead uses refrigerant enthalpies calculated from pipe contact temperatures and steady-state energy balances to determine the COP. However, these energy balances are highly dependent on the hypothesis that the working fluid remains strictly monophasic in certain locations, which is not always true in practice. A parametric variable analysis is conducted on the refrigerant vapor quality to calculate the deviation in the COP due to diphasic conditions at the compressor inlet, injection port, and condenser and flash tank outlets. A final in situ COP uncertainty is presented, due to both the measurement and vapor quality uncertainties.     

概率神经网络在水/水热泵机组故障诊断研究中的应用

基于模式识别的设备状态监测和故障诊断原理,根据水／水热泵机组的运行特性,提出一种基于人工神经网络的智能故障诊断方法,通过应用2个概率神经网络估计器,实现对水／水热泵机组运行状态的实时监测和故障诊断。此外,建立水脉热泵机组常见故障与征兆之间的关系库,构建基于人工神经网络的水脉热泵机组状态监测和故障诊断系统的模型结构,以期为开发水脉热泵机组的智能故障诊断系统开辟一条新的可行途径。     

部分负荷下冷水机组运行方案的优化

冷水机组系统在部分负荷运行时,可选择调节冷水机组台数或每台冷水机组的运行功率来应对负荷的变化,但不同运行方案有不同的能耗。以某厂螺杆式冷水机组为例,测试不同负荷下冷水机组的性能参数,分析其总COP值,与现行运行方案下的冷水机组能耗相比,得到机组运行优化方案。结果表明,采用新运行方案,相对原运行方案可分别节能12％和23％。     

Ejector expansion refrigeration system: Ejector design and performance evaluation

Use of a two-phase flow ejector as an expansion device in vapor compression refrigeration systems is one of the efficient ways to enhance its performance. The present work aims to design a constant-area two phase flow ejector and to evaluate performance characteristics of the ejector expansion refrigeration system working with R134a. In order to achieve these objectives, a simulation program is developed and effects of operating conditions and ejector internal efficiencies on the system performance are investigated using EES software. Comparison between present results and published experimental data revealed that the developed model can predict the system COP with a maximum error of 2.3%. The system COP increased by 87.5% as evaporation temperature changed from −10 °C to 10 °C. Finally, correlations to size ejector main diameters as a function of operating conditions, system cooling capacity and ejector internal efficiencies are reported.     

Optimization of a fin-tube type adsorption chiller by design of experiment

This paper presents a numerical analysis of the performance of a fin-tube type adsorption chiller associated with heat and mass transfer mechanisms. A two-dimensional axisymmetric transient model is developed and 10 parameters are used to investigate their effects on the performance of an adsorption chiller and to obtain the optimized conditions of a fin-tube type adsorption chiller. Ten parameters found in many other studies, such as fin pitch, fin thickness, fin height, diffusion coefficient, particle size, cycle time, cycle ratio, temperature of hot water, fluid velocity and porosity, are used in this study. Based on the design of experiment, an orthogonal array of 10 parameters with three levels, L₂₇(3¹³) is used for the analysis of variance (ANOVA) and through this method, each parameter's level of contribution is carefully examined. The result shows that fin thickness and the temperature of hot water are the dominant parameters for COP and SCP, respectively. The optimum conditions having the highest COP of 0.6782 and SCP of 217.68 W kg⁻¹ are found through the result.     

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.     

送风温度对车用跨临界CO2制冷系统影响的仿真研究

为研究送风温度对实际车用跨临界CO₂制冷系统综合性能的影响,借助GT-Suite仿真软件,建立了单级跨临界CO₂制冷系统的仿真模型。基于设计的三种工况,在风量设置上限的情况下对比了不同送风温度下系统的性能,提出了有效COP_eff的概念并对此进行研究。结果表明：在其他工况相同的条件下,提高送风温度可以提高系统的COP、有效COP_eff以及带风机功耗的有效COP_{eff, b};在低冷负荷工况下,考虑系统风机功耗后的综合性能COP_b存在最优值为3.819,即系统存在对应的最优送风温度,但当负荷增大至一定水平时,最优送风温度不再存在。     

Experimental investigation and analysis of composite silica-gel coated fin-tube heat exchangers

Desiccant coated heat exchanger provides a promising option for desiccant cooling system, since it can handle sensible load and latent load simultaneously within one component. It is fabricated by coating desiccant material on the surface of conventional fin-tube heat exchanger. In order to enhance the performance of conventional silica gel coated heat exchanger (SGCHE), a novel composite silica gel coated heat exchanger (CCHE) is proposed and fabricated. An experimental setup is built to test and compare the dynamic performance of SGCHE and CCHE. Influences of main operation parameters including water temperatures and inlet air conditions on system performance are analyzed in terms of average dehumidification capacity (D_avg) and thermal coefficient of performance (COP_th). Optimization of cycle switch modes is also discussed. Experimental results show that CCHE has better dehumidification performance compared with SGCHE. In addition, pre-cooling before dehumidification process is found to be advantageous to both D_avg and COP_th.