制冷设备中进行能效比区域划分的初步探讨

提出了制冷设备能效比（EER）区域划分的概念,以上海、昆明为例,对比分析了两市空气源热泵空调器的实际使用能效比。结果表明：与现行能效比相比,对系统进行能效比区域划分,可相应地对制冷系统各部分进行优化,从而可以节省制造和运行成本,节能效果较为明显。同时,分析得出能效比区域划分,可以优化风冷冷水机组中综合部分负荷性能系数（IPLV）,使其具有较好的实用价值。     

An analysis of climatic influences on chiller plant electricity consumption

Principal component analysis of dry-bulb temperature, wet-bulb temperature, global solar radiation, clearness index and wind speed was conducted, and a two-component solution obtained which could explain 80% of the variance in the original weather data. Clustering analysis of these two principal components resulted in a total of 18 typical day types being identified. A year long monitoring of the daily chiller plant electricity consumption in a fully air-conditioned office building was conducted. It was found that the typical day types exhibited daily and seasonal variations similar to the daily and monthly electricity consumption recorded. Three regression models were developed to correlate the daily chiller plant electricity consumption and the corresponding day types. The coefficient of determination (R²) was 0.86–0.99 showing strong correlation. It is proposed that the day type approach can be used as a tool for weather normalisation and inter-year comparisons in the analysis of energy savings due to building retrofits. It was also found that the typical day types identified appeared to show a slight increasing trend during the 28-year period (1979–2006) indicating a subtle, but gradual change of climatic conditions that might affect chiller plant electricity consumption in future years.     

楼宇冷热电联供系统仿真及其影响制冷效果的分析

以上海交通大学某大楼的BCHP系统为研究对象,在ISEpro仿真平台上建立系统仿真模型,利用该模型对影响制冷效果的蒸汽压力、冷却水进口温度、冷媒水进口温度等因素进行了仿真分析,发现冷媒水进口温度、冷却水进口温度、工作蒸汽压力等因素对制冷效果影响较大,其结果和实际应用和理论计算相一致,表明该模型可以用来对楼宇冷热电系统进行仿真,并可为楼宇冷联供的设计、操作运行、控制调节提供指导.     

Feasibility of lowering the condenser's inlet water temperature of a chiller using thermal water storage

A novel approach is proposed for applying cool thermal storage to reduce the on-peak demand of a water-cooled chiller. By charging the store at night via a cooling tower, and using this water to supply the condenser of a chiller during on-peak hours, cooler than normal water is supplied to the chiller. A feasibility study of this system was conducted using TRNSYS — a transient simulation modeling program examining varying capacities of cooling tower and thermal store volumes. These systems were tested using geographic weather data that demonstrated conducive diurnal changes in wet-bulb temperature (T_wet). Results suggest that the use of cool water thermal storage in this way can reduce both on-peak energy demand and on-peak power use by as much as 35%. System optimization is dependent on the thermal storage efficiency, the capacity of the cooling tower, and the diurnal change in T_wet.     

Simulation of operating characteristics of the silica gel-water adsorption chiller powered by solar energy

A lumped parameter model of a silica gel-water adsorption chiller driven by solar energy was introduced for the operating characteristics investigation. Matlab-Simulink, as a high-performance computing and programming tool, was used to simulate the operating characteristics of the chiller. Effects of the hot water tank capacity, the cycle time and the initial hot water temperature on the performance of the chiller were analyzed when the chiller was driven by a stable heat source and solar energy respectively. The simulation results indicated that when the chiller was driven by solar energy, the open circulation of the hot water with a short cycle time and the closed circulation of hot water with a longer cycle time were better. A proposal was also provided for the chiller driven by solar energy to work under the optimum working conditions, such as hot water circulation mode, cycle time and initial temperature.     

Conventional chiller performances simulation and field data

In most commercial buildings and industrial plants HVAC systems consume large amounts of energy, and usually offer the most significant potential for savings. Liquid conventional chillers play a very important role in providing these savings. Proper design, installation, and maintenance of these systems are therefore the key steps leading to improved efficiency which benefit both the customers and the utilities. To effectively materialize this concept two steps have been followed here. In the first section of this paper conventional chillers of different types have been modelled and simulated using a software (DOE2). The chillers are rated for a generic building and meteorological weather of San Diego. Performance parameters such as the part/full-load efficiencies, the number of occurrences during peak hours and load frequencies are then calculated. These results gave typical performance values (curves) which can be used to compare screw, centrifugal, and reciprocating chillers among each other within a predefined scope. In the following section the field data of 39 conventional chillers and the manufacturers specifications of some of them are collected and analysed. This gave an overall view of their actual field performance and their deviation from the manufacturers' specifications. Comparison of the simulated and collected data also provided better vision of the expected performances versus the actual performances, and pinpointed some major drawbacks in the design and sizing methodology. The results also led to important conclusions regarding the status quo and the possibilities in the immediate future. Preferred chiller types and methods of providing the required cooling energy recommended by the simulation results are compared with the existing ways of providing energy in order to conform the eventual promises and quantify the room for efficiency.     

热分析法在吸收式制冷机中的应用

由于影响吸收式制冷机的因素很多，针对吸收式制冷机性能评价的复杂性，运用COP分析法、Yong分析法、热经济学分析法对吸收式制冷机性能进行评价，得到三种方法各自的特点，COP分析法是从热力学第一定律对系统进行衡算，Yong分析法是热力学第一定律与热力学第二定律相结合的产物，热经济分析法是经济优化技术与Yong分析法的结合．分析了它们在吸收式制冷机性能优化过程中所起的作用。     

Performance analysis of a solar vapour thermal compression chiller

The influence of the design conditions on the coefficient of performance (COP) of a solar vapour thermal compression chiller was investigated from an operational point of view. Based on a well known model, a number of COP evaluation runs were conducted and the results are presented in graph form as a function of the main design parameters. Through these graphs the influence of the main operating parameters on the performance is quantitatively shown. Finally, the calculated COP is compared to that of a solar absorption system operating under similar conditions.     

Simulation for the analysis of a hybrid electric scooter powertrain

This paper describes the mathematical modelling, analysis and simulation of a novel hybrid powertrain used in a scooter. The primary feature of the proposed hybrid powertrain is the use of a split power-system that consists of a one-degree-of-freedom (dof) planetary gear-train (PGT) and a two-dof PGT to combine the power of two sources, a gasoline engine and an electric motor. Detailed component level models for the hybrid electric scooter are established using the Matlab/Simulink environment. A simple rule-based power control strategy is then established with the primary objective to optimize the fuel economy of the hybrid electric scooter. The performance of the proposed hybrid powertrain is studied using the developed model under four driving cycles. The simulation results verify the operational capabilities of the proposed hybrid system and show both the engine and the electric motor work in an optimal state under various operating conditions.     

Development of a wind forced chiller and its efficiency analysis

Until now, the technical development of wind force is mainly combined with electrical generator and already achieves the skillful technique in application. In this paper the newly developed windchiller directly applies the mechanical energy of wind force for refrigeration instead of the traditional electrical/mechanical energy conversion. The devise avoids energy loss during the two to-and-fro energy conversion processes between wind force and electrical energy. The special finished wind machine applies the technique with two directions to capture the wind force, the faced and its opposite directions, in the fans design. Between the wind turbine and the compressor, a transmission system with a fixed conversion rate 1:20 was used for acceleration. After the combination with open-type reciprocating compressor, the wind forced chiller is built. The windchiller increases the working efficiency in comparison with the refrigerating system of indirect connection from wind generator to refrigerator and ignores the unstable property of wind force. The strength of wind force influences only the windchiller’s efficiency; the stronger wind force, the larger windchiller’s efficiency. The experimental results show the newly developed windchiller’s efficiency ca. 21.28%, which agrees to the pre-evaluation and achieves a high efficiency.     

Theoretical analysis and optimization of a double-effect series-flow-type absorption chiller

A thermodynamic analysis was carried out to study the effect of design parameters, including heat recovery ratio and solution circulation ratio, on the performance of a double-effect absorption chiller of the series-flow-type using water-lithium bromide as the working fluid. Increases in the heat recovery ratios of the high-temperature heat exchanger and the low-temperature heat exchanger and/or decreases in the solution circulation ratio improved the coefficient of performance. An increase in the heat recovery ratio of the high-temperature heat exchanger increased the total heat transfer area of the absorption chiller. The optimum design and operating conditions of a double-effect absorption chiller are suggested based on this cycle simulation analysis.     

Improved energy management of chiller systems with data envelopment analysis

The operation of chiller systems could take up over half of the electricity consumption of air-conditioned buildings in subtropical regions. This paper explains how to examine the effectiveness of their energy management by using data envelopment analysis (DEA). A large-scale system with seven chillers of two different capacities was studied. The scale, technical and overall efficiencies defined in DEA were calculated for each set of operating conditions comprising the system coefficient of performance (COP) and input variables: the compressor power, chiller load and temperatures at the evaporator and condenser sides. Under the existing operating strategy, the average system COP was found to be 5.73 with an average technical efficiency of 0.97. This indicates that the system operated very efficiently for most of the time. Fine-tuning the temperature-related controllable variables could achieve the highest possible COP of 5.83 with technical efficiency of one. The benefits of using technical efficiency to identify energy management opportunities are highlighted.     

热流计测量精度影响因素的数值分析

本文通过建立二维非稳态导热的数学模型 ,模拟了瞬态热流计测量低温金属表面与高温流体换热时影响测量精度的五种主要因素。计算得出 ,由于热流计测头的出现 ,对流换热系数的变化会给热流测量带来较大误差。其次 ,热流计测头自身因素的变化也会给测量带来误差。测头越薄 ,测量误差越小 ,稳定越迅速 ;测头边长越长 ,测量误差越小。但当被测物表面积较大时 ,测头边长存在一个最优值 ,能达到测量精度与测头尺寸的最佳结合 ,这个值约为 2 0mm ;测头与被测物粘贴越紧密 ,误差越小 ,稳定越迅速 ;被测物导热系数越小 ,则测量误差越小。模拟计算的结果能够为热流计的设计制作以及实际应用提供指导和参考     

Simulation and electricity savings estimation of air-cooled centrifugal chiller system with mist pre-cooling

This paper analyses how to apply mist pre-cooling coupled with condensing temperature control to enhance the coefficient of performance (COP) of an air-cooled chiller system and hence achieve electricity savings. A modified DOE-2.1E chiller model was developed to predict the change of chiller COP due to various set points of condensing temperature and pre-cooling of air stream entering the condenser. The model was calibrated by using manufacturer’s data and used to estimate the annual electricity consumption of a chiller system serving an office building under four operating schemes: traditional head pressure control (HPC); HPC with a fixed mist generation rate; condensing temperature control (CTC) with a fixed mist generation rate; CTC with an optimal mist generation rate. It was estimated that using optimal mist control with CTC could achieve a 19.84% reduction in the annual electricity consumption of the system. Considerations when using mist pre-cooling to maximize electricity savings have been discussed.     

Simulation models for the analysis of space heat consumption of buildings

This study develops and analyzes an original methodology for the simulation and prediction of space heating energy consumption in buildings connected to a district heating system, characterized by lack of individual control systems for end-users. The identification of the input parameters is based on both classical engineering equations and statistical analysis of collected data. Two main factors play important roles in the model: (i) climate and (ii) human behavior. Model validation was undertaken through the analysis of field data collected during the winter, via a monitoring system working in a partially-controlled district heating system. The comparison between the results obtained with the proposed model versus classical methods points out the possibility to implement, using the proposed methodology, management policies for a district that offer significant cost-effective energy savings opportunities.     

Model-based influencing factors analysis of residential heat consumption in district heating systems

Abstract

A simplified and accurate hybrid model is proposed to analyze, evaluate, and predict space heating energy consumption and indoor temperature in residential buildings connected to district heating systems. With classical engineering equations of thermodynamic laws, this method uses physical and empirical modeling to describe heat exchangers in real-time. Furthermore, the model has optimized the cost of computation and enhanced the prediction accuracy. It is revealed this method can accurately predict the residential heat load and indoor temperature with the maximum error of ±10%. The architectural parameter, outdoor temperature, and wind velocity have decisive effects on the heat energy demand.     

Chillers energy consumption, energy savings and emission analysis in an institutional buildings

Chillers consume more than 40% of the total energy used in the commercial and industrial buildings for space conditioning. In this paper, energy consumption by chillers and chilled water pumps, condenser pumps and fan motors has been estimated using data collected by a walkthrough energy audit for the 16 faculties of the University of Malaya. It has been estimated that chillers and motors and pumps used in chillers consume 10,737 MWh (i.e. 51% of total energy consumption) of electric energy for different percentage of loadings. As chillers are major energy users, variable speed drives are applied in chillers to reduce their energy consumption. It has been estimated that about 8368 MWh annual energy can be saved by using efficient chillers at different loadings. It has also been found that about 23,532 MWh annual energy can be saved for chilled water supply pumps, condenser pumps and cooling tower fan motors by matching required speeds using variable speed drives for 60% of speed reduction. About 1,274,692 kg of CO₂ emission could be avoided for using energy efficient chillers at 50% load. It has been also found that about 2,426,769 kg CO₂ emission can be reduced by using variable speed drives for 60% speed reductions. Payback periods found to be only few months for using variable speed drives in chilled water pumps, condensers and fan motors.     

Cycle analysis of air-cooled absorption chiller using a new working solution

A cycle analysis was achieved to predict the characteristics by comprehensive modelling and simulation of an air-cooled, double-effect absorption system using the new H₂O/LiBr+HO(CH₂)₃OH solution. The simulation results showed that the new working fluid may provide the crystallisation limit 8% higher than the conventional H₂O/LiBr solution. With a crystallisation margin of 3 wt%, the optimal solution distribution ratio was found to be in the range of 37–39%. Variation of cooling air inlet temperature had a sensitive effect on the cooling coefficient of performance (COP) and corrosion problem. The simulation of heat exchangers with UA value revealed that the absorber and evaporator were relatively important for an air-cooled system compared with the condenser and the low temperature generator. The effects of cooling air flow rate, circulation weak solution flow rate and chilled water inlet temperature were also examined. The new working fluid may provide a COP approximately 3% higher than the conventional H₂O/LiBr solution in normal conditions of circulation weak solution.     

福岛核事故辐射泄漏影响因素的关联度对比分析

研究各个因素对核辐射泄漏的影响程度,对于控制核辐射泄漏、防止核辐射扩散有重要价值。运用多元线性回归分析方法和灰色理论中斜率关联度分析方法,对日本福岛核事故中辐射泄漏的影响因素进行分析。以福岛第一核电站厂区西门监测点辐射剂量值为对照序列,对厂区西门辐射剂量与受损的一号机组堆内水位和压力进行影响程度分析。选择一号机组内压力值、水位值为相关参数,计算得到各个参数与厂区西门辐射剂量的关联度或权重值。将两种方法的计算结果进行比较,结果一致。考虑到基于灰色理论的斜率关联度法可以在源数据缺少完整性与连续性时使用,因此在核辐射泄漏影响因素研究中,这是一种值得发展的新方法。     

Simulation analysis of protective wall against hydrogen combustion from liquified hydrogen storage tank on the offshore launching platform

Offshore rocket launching platforms will gradually become the mainstream rocket launching platform in the future due to its low geographical restrictions. A study is carried out to simulate the hydrogen combustion impact on the platform and the preventive effect of the protective wall after a hydrogen leakage accident. The study firstly adopts an approach to evaluate the leakage rates for the CFD simulation code FLACS based on local hydrogen concentrations at certain dilution distances. The approach consists of two models, and one is to predict hydrogen dilution distance reaching 4% hydrogen concentration at certain storage pressure and temperature, and the other is to evaluate modified hydrogen concentration at the same dilution distance under different storage pressure and temperature comparing to the former model. The hydrogen combustion following the leakage is studied based on various orifice sizes. The results include hydrogen concentration, pressure and pressure impulse, flame temperature and temperature on structure surface, and show that the current wall design can effectively protect the rocket from the impact of the combustion.