An exergy application for analysis of buildings and HVAC systems

The paper presents an extended method for exergy analysis of buildings and Heating Ventilation Air Conditioning (HVAC) systems, according to an energy demand build-up model from the building side to the energy supply side. The HVAC systems comprise a thermal energy emission and control system, a thermal distribution system, an electricity distribution system and an energy conversion system. Energy and exergy that are required by a building and a HVAC system are posed into the external part and classified by different forms of energy carriers. The external part is out of the boundary of the study. The method is illustrated with an office building equipped with low-temperature heating and high-temperature cooling systems situated in the Netherlands. Thermal exergy and thermal energy demands of the building and thermal energy and thermal exergy losses occurring in the HVAC systems are discussed. The building and the HVAC systems to be considered meet standard Dutch energy performance regulations. Nevertheless their overall exergy efficiencies are low in both cases (17.15% and 6.81% subsequently). The exergy analysis also pinpoints that the thermal energy emission and control system and the energy conversion system are the main causes of the exergy inefficiencies in the heating and cooling cases, respectively.     

Time-dependent reliability assessment of aging series systems subjected to non-stationary loads

Civil infrastructure systems provide physical supports to a community’s functionalities and are expected to achieve acceptable safety levels subjected to extreme load effects. However, these systems may deteriorate with time as a result of aggressive environmental or operating conditions in service, implying that the system reliability may decline beyond the baseline as assumed for design. Moreover, the increasing trend of the external loads may also contribute to the reduction of the system reliability. In this paper, a semi-analytical method is proposed for assessing the reliability of aging systems subjected to non-stationary loads. The series system is considered, where the system failure is defined as the failure of any single component (structure) among the system. The application of the proposed method is illustrated using a representative series bridge network with several individual bridges. The role of parameters such as the variations in the load intensity, resistance correlation and number of components under attack in the system reliability are investigated.     

Simulation of ON/OFF controlled systems

A method for simulating systems that have components controlled in an ON/OFF manner is presented. The method is particularly suited to systems with an identifiable component structure such as those found in network problems. The primary feature of the method is that control strategies are modelled separately from the dynamics of the physical system so that various strategies may be added, modified or deleted without affecting either the model of the physical system or the computer code. Control strategies are expressed as combinations of comparators, logic operators (gates) and self-defined control functions such as hysteresis. The complete mathematical model for representing a control strategy, the procedure for automatically formulating the resulting system of control equations, directly from the control strategy, and the interconnection of the physical system model and the control model, are presented. Pipe-network examples are given.     

Robustness analysis of responses of vibration control structures with uncertain parameters using interval algorithm

Variations in system parameters due to uncertainties may result in system performance deterioration. Uncertainties in modeling of structures are often considered to ensure that control system is robust with respect to response errors. Hence, the uncertain concept plays an important role in vibration control of the engineering structures. The paper discusses the robustness of responses of vibration control systems with the uncertain parameters. The vibration control problem of an uncertain system is approximated by a deterministic one. The uncertain parameters are described by interval variables. The uncertain state matrix is constructed directly using system physical parameters and avoided to use bounds in Euclidean norm. The feedback gain matrix is determined based on the deterministic systems, and then it is applied to the actual uncertain systems. A method to calculate the upper and lower bounds of responses of the closed-loop system with uncertain parameters is presented. The upper bounds of responses can be used to estimate the robustness of responses of the controlled system with uncertain parameters. Two numerical examples are given to illustrate the applications of the present approach.     

A new method based on the theory of fuzzy sets for obtaining an indication of risk

This paper concludes that traditional methods used in risk analysis have to be modified for adaption to the civil engineering industry. The main reason is that civil engineering systems are humanistic systems while traditional methods have been developed for mechanical systems. Consequently, the proposed method, indication of risk, is based on traditional methods such as fault tree analysis but modified according to the needs of the civil engineering industry. For humanistic systems, the method is based on the theories of possibility and fuzzy sets instead of the traditional theory of probability. The method is intended to be used to identify critical phases of the analysed systems and for optimizing system control. The method presented is exemplified by a risk analysis of a computer calculation. It is concluded that the method fulfils its intentions and deserves to be developed and examined further.     

弹性多自由度系统地震输入能量的研究

本文介绍了基于能量抗震设计方法的基本思路和基本概念。根据振型分解法推导了弹性多自由度系统与单自由度系统弹性地震输入能量间的关系。研究表明,N个自由度弹性系统的地震输入能量可表示为N个弹性单自由度系统弹性输入能量的线性组合,组合系数与多自由度系统的振型和质量分布有关。通过时程分析算例,以Eleentro波输入验证了这种方法的正确性。算例结果表明,对于自由度较多的系统,可以只取前几阶振型计算即可得到足够精确的结果。     

Performance analysis of a solar energy driven heating system

Operation temperature of solar heating systems makes the use of a radiant floor to transfer heat into the conditioned spaces suitable. Performance data related to solar heating systems are scarce. Knowledge of these data is important to establish control strategies that lead to an optimal operation of these systems. The objectives of this study were to acquire and analyse the performance data of a residential solar heating system in Murcia (Spain), and to compare the recorded data with the performance estimate provided by the f-chart method used for sizing the system. The solar fractions registered in the system during the months of January and February 2004 were 20% lower than those predicted by the f-chart method. This lack of coincidence was assumed as inherent to the f-chart method.     

Building energy system optimizations with utilization of waste heat from cogenerations by means of genetic algorithm

Distributed energy systems based on cogeneration offer significant potential to save energy since they effectively utilize waste heat from power generators. However, unless there is an appropriate combination of machinery and operations, the planned performance cannot be achieved. Thus, it is quite difficult to determine the optimal combination of machinery and operations. For this, an optimal design approach is needed. In this study, a new optimal design method for building energy systems is proposed. There are an enormous variety of combinations with regard to energy supply and demand. This method designs the most efficient energy system by optimizing the operation of available systems with consideration for the optimal capacity of machinery in the systems. Optimization algorithms known as “genetic algorithms” (GAs) with the capacity to deal with non-linear optimization problems have been adopted in this optimization analysis. In this study, a single-building energy system is evaluated. The result shows that the proposed method is sufficiently capable of optimizing the design, and has the potential to be applied to very complex energy systems with appropriate improvements.     

Removal of non-ionic organic pollutants from water via liquid-liquid extraction

The removal of model pollutants bromocresol green (BG) and phenol from water is demonstrated via two liquid-liquid extraction methods. Both methods exploit selective interactions established by the pollutant molecule with a surfactant, oil, or alcohol, and are variants of the more general Winsor systems where the phases are in contact along an extremely large interfacial area. In the first method the surfactant and the co-surfactant move from a predominantly oil-in-water microemulsion (Winsor I), to a middle phase microemulsion (Winsor III), and finally to a water-in-oil microemulsion (Winsor II), as the physicochemical conditions of salinity, temperature or hydrophilic-lipophilic balance of the surfactant system are varied. This method achieves better than 99% removal of the pollutant BG from water. It is argued that the removal is produced upon increasing the salinity of the system because the interaction of BG with a medium chain-length alcohol drives it to move along with the alcohol to another phase. The second method, which is scalable to industrial levels, uses a spontaneously produced water-in-oil microemulsion with large interfacial area that appears after bringing in contact water and a pre-formed Winsor II or Winsor III microemulsion system containing different surfactants and oils. The method is applied to the removal of phenol from water, and it is found that systems with polar oils such as ethyl butyrate or with cationic surfactants such as stearyl trimethylammonium chloride are more efficient in removing phenol than systems with normal alkanes or anionic surfactants. It is also shown that a microemulsion formed using a polar oil performs better than using only the polar oil as the extraction solvent. Finally, the efficiency of the second liquid-liquid extraction method can be increased from 69% in a single-stage process to 83% in a two-stage process, using the same total amount of extraction solvent.     

The use of a textile-based system to control pavement cracking

Many systems are currently used to overcome problems of reflective cracking in road and airfield pavement overlays and a number of these systems incorporate a geotextile. An understanding of the mechanisms causing cracking is fundamental if the correct system is to be used. The interface of the existing cracked surface and the new overlay is the point at which most such systems are placed.This paper studies the mechanisms in detail and the requirements for an ideal interface to retard reflective cracking are established. After reviewing some of the systems currently used, a laboratory method of establishing their efficacy is discussed and a system is described that meets more closely the ideal requirements than do those based on conventional geotextiles. This is a textile and bitumen system and its potential applications are reviewed.     

母线槽配电干线周围的工频磁场

母线槽在建筑物特别是高层建筑物的配电系统中常被用于配电干扰。这种重载流配电干线周围的工频磁场近年来引起了人们的关注。笔者用边界元数值计算和实验测量方法分析母线槽周围的工频磁场，对铁外壳母线槽提出了等效相对磁导率处理方法，并证明其可行性和有效性，发现铁外壳材料的等效相对磁导率和母线槽所载的电流基本上成正比。对工程中常用的镀锌铁皮外壳空气绝缘母线槽，铜芯铝壳和铝芯铁壳全封闭母线槽周围的磁场进行了计算和测量。对母线槽周围的谐波磁场也进行了讨论。     

Estimating a Rail Passenger Trip Origin-Destination Matrix Using Automatic Data Collection Systems

Abstract:   Automatic data collection (ADC) systems are becoming increasingly common in transit systems throughout the world. Although these ADC systems are often designed to support specific fairly narrow functions, the resulting data can have wide-ranging application, well beyond their design purpose. This article illustrates the potential that ADC systems can provide transit agencies with new rich data sources at low marginal cost, as well as the critical gap between what ADC systems directly offer and what is needed in practice in transit agencies. To close this gap requires data processing and analysis methods with support of technologies such as database management systems (DBMS) and geographic information systems (GIS). This research presents a case study of the automatic fare collection (AFC) system of the Chicago Transit Authority (CTA) rail system and develops a method for inferring rail passenger trip origin-destination (OD) matrices from an origin-only AFC system to replace expensive passenger OD surveys. A software tool is developed to facilitate the method implementation and the results of the application in CTA are reported.     

Fault tree analysis for integrated and probabilistic risk analysis of drinking water systems

Drinking water systems are vulnerable and subject to a wide range of risks. To avoid sub-optimisation of risk-reduction options, risk analyses need to include the entire drinking water system, from source to tap. Such an integrated approach demands tools that are able to model interactions between different events. Fault tree analysis is a risk estimation tool with the ability to model interactions between events. Using fault tree analysis on an integrated level, a probabilistic risk analysis of a large drinking water system in Sweden was carried out. The primary aims of the study were: (1) to develop a method for integrated and probabilistic risk analysis of entire drinking water systems; and (2) to evaluate the applicability of Customer Minutes Lost (CML) as a measure of risk. The analysis included situations where no water is delivered to the consumer (quantity failure) and situations where water is delivered but does not comply with water quality standards (quality failure). Hard data as well as expert judgements were used to estimate probabilities of events and uncertainties in the estimates. The calculations were performed using Monte Carlo simulations. CML is shown to be a useful measure of risks associated with drinking water systems. The method presented provides information on risk levels, probabilities of failure, failure rates and downtimes of the system. This information is available for the entire system as well as its different sub-systems. Furthermore, the method enables comparison of the results with performance targets and acceptable levels of risk. The method thus facilitates integrated risk analysis and consequently helps decision-makers to minimise sub-optimisation of risk-reduction options.     

Application of the cumulative exergy approach to different air conditioning systems

The cumulative exergy approach is applied to evaluate two cases with different air conditioning systems. The first case includes three air conditioning systems, one is the gas direct fired air conditioning system, and the other two have air cooled heat-pump chiller and water chiller, respectively; the second case consists of four air conditioning systems, one is the gas direct fired air conditioning system, and the others have centrifugal water chiller, screw water chiller, air cooled water chiller, respectively. The results of the first case show that the air conditioning system with the air cooled heat-pump chiller maybe inferior to that with the water chiller, as the cumulative exergy efficiency of the former is 11.28%, which is less than that of the latter (11.92%). The second case shows that the gas direct fired air conditioning system, whose cumulative exergy efficiency is 14.86%, is better than the system with the air cooled water chiller, whose cumulative exergy efficiency is only 11.56%. The results are different from those of the exergy analysis, indicating that cumulative exergy analysis is an effective method to quantitatively evaluate different air conditioning systems according to resource utilization.     

Performance assessment of water supply and wastewater systems

This paper addresses the issue of performance assessment in water and wastewater systems by reviewing two of the tools that are available to the companies operating in this field: systems of performance indicators and technical performance assessment through simulation. The paper focuses on a technical performance evaluation framework and its application to wastewater systems. The assessment is carried out through the application of utility functions to the network's elements, and the production of performance-oriented graphs that yield concise and informative views about the system's behaviour. Two case studies involving a combined sewer system and a separate domestic system are presented in order to illustrate the method.     

置换通风的热压驱动增益模式可行性研究

通过对传统下置置换通风系统特点的研究,提出了一种新的下置置换通风空调系统——由太阳能烟囱为新系统中送风提供热压动力,使送风具有传统下置置换通风系统的送风特点,室内工作区具有良好的空气品质。同时通过数值模拟的方法分析并比较了传统下置置换通风系统与新系统。结果表明:该系统能解决传统置换通风不舒适的吹风感和竖直温差大的问题;相对于传统下置置换通风,新系统还具备节能和环保特性;烟囱具有良好的自我调节性能。     

Uncertainty-based life-cycle analysis of near-zero energy buildings for performance improvements

Near-zero energy buildings( nZEBs) are considered as an effective solution to mitigating CO_2 emissions and reducing the energy usage in the building sector. A proper sizing of the nZEB systems( e. g. HVAC systems,energy supply systems,energy storage systems, etc.) is essential for achieving the desired annual energy balance,thermal comfort,and grid independence. Two significant factors affecting the sizing of nZEB systems are the uncertainties confronted by the building usage condition and weather condition,and the degradation effects in nZEB system components. The former factor has been studied by many researchers; however,the impact of degradation is still neglected in most studies. Degradation is prevalent in energy components of nZEB and inevitably leads to the deterioration of nZEB life-cycle performance. As a result,neglecting the degradation effects may lead to a system design which can only achieve the desired performance at the beginning several years. This paper,therefore,proposes a life-cycle performance analysis( LCPA) method for investigating the impact of degradation on the longitudinal performance of the nZEBs. The method not only integrates the uncertainties in predicting building thermal load and weather condition,but also considers the degradation in the nZEB systems. Based on the proposed LCPA method,a two-stage method is proposed to improve the sizing of the nZEB systems.The study can improve the designers "understanding of the components"degradation impacts and the proposed method is effective in the life-cycle performance analysis and improvements of nZEBs. It is the first time that the impacts of degradation and uncertainties on nZEB LCP are analysed. Case studies showthat an nZEB might not fulfil its definition at all after some years due to component degradation,while the proposed two-stage design method can effectively alleviate this problem.     

Effect of damping model on pre-yielding earthquake response of structures

The present paper examines differences between responses of single-degree-of-freedom (SDOF) systems with viscous and hysteretic damping to earthquake ground motions. Only responses within yield limits are considered. The structural behavior of SDOF systems with hysteretic damping is modeled by a generalized elasto-slip model of the Masing type. The model leads to a force–displacement relationship similar to that proposed by Ramberg and Osgood. The responses of the two systems are compared for a number of earthquake records. To achieve consistent comparison, parameters of the linear system with viscous damping are determined by the secant stiffness method. In many cases significant differences in the peak displacement responses and energy values have been observed between the systems. This indicates that the prediction of the response of structures to earthquake ground motions before yielding based on linear models with viscous damping may not be as accurate as used to be believed. Tentative estimates of error associated with such predictions are presented.     

生命线系统相互作用下的震害预测方法

在总结生命线系统地震中相互作用特点的基础上,提出定量评价生命线系统相互作用的三个指标。利用网络分析方法,将生命线系统等效为节点和弧段单元体系,并将节点进一步划分为复杂和简单两种类型,建立考虑相互作用影响下的复杂节点故障树,在此基础上并进一步利用故障树分析方法和地理信息系统的网络分析方法探讨了地震作用下生命线系统网络破坏机理,最终提出了一套考虑相互作用的生命线系统,震害预测新方法。     

双供热参数热力站站内系统的设计

结合工程实例,对存在散热器供暖系统和地板辐射供暖系统的热力站站内系统布置形式进行了研究,探讨了传统方式与混水方式两种站内系统设计方式。针对混水方式,提出根据两种系统之间的热负荷关系确定站内系统布置形式的方法,给出了确定布置形式的判别式。