Optimal design method for building energy systems using genetic algorithms

In this paper, a new optimal design method for building energy systems is proposed. This method provides the most efficient energy system, best combination of equipment capacity and best operational planning for cooling, heating, and power simultaneously with respect to certain criteria such as energy consumption, CO₂ emission, etc. Specifically for this paper, the authors apply this method to a sample building as a case study. The “Genetic Algorithms (GA)” optimization method, which can resolve nonlinear optimization problems, is adopted for this optimization analysis. Also its applicability is analyzed in a case study. In order to validate the accuracy of this method, the correct optimum solution based on comprehensive inquiries is also calculated. A comparison of the GA solution with the correct solution demonstrates fairly good agreement. The results show that the proposed method is sufficiently capable of determining the optimal design and has the potential to be applied to very complex energy systems with appropriate modifications.     

优化偏心支撑框架的连接件以获得最大耗能能力

给出偏心支撑框架(EBF)的优化设计方法,将其作为被动控制手段应用于建筑结构的抗震设计中。在EBF梁与支撑的连接件处设置加劲肋以提高其刚度和塑性变形能力。给出连接件加劲肋位置及厚度的优化设计方法,采用Tabu搜索算法求解最优解,其目标函数为破坏前的塑性能量耗散。采用有限元软件计算静态循环荷载作用下连接件的变形,结果显示,通过微单元优化可以提高连接件的耗能能力。     

Optimization of link member of eccentrically braced frames for maximum energy dissipation

An optimization method is presented for design of an eccentrically braced frame (EBF), which is used as a passive control device for seismic design of building frames. The link member between the connections of beams and braces of EBF is reinforced with stiffeners in order to improve its stiffness and plastic deformation capacity. We present a method for optimizing the locations and thicknesses of the stiffeners of the link member. The optimal solutions are found using a heuristic approach called tabu search. The objective function is the plastic dissipated energy before failure. The deformation of the link member under static cyclic loads is simulated using a finite element analysis software package. It is demonstrated in the numerical examples that the dissipated energy can be increased through optimization within small number of analyses.     

单层网壳结构弹塑性稳定性和优化设计研究

以民航博物馆不规则连续单层网壳结构为例,对单层网壳考虑弹塑性稳定性和优化设计进行探讨。比较了各荷载工况作用下的几何非线性极限承载力、弹塑性非线性极限承载力与荷载标准值之比和线弹性外力势能的分布规律,初步探讨了在诸多荷载组合工况中选择单层网壳结构弹塑性稳定极限承载力控制工况的方法。探讨单层网壳考虑弹塑性稳定优化设计的实用简化方法,提出了杆件截面优化的应力比缩减分层法,使复杂的优化设计问题简单化。     

Applied Energy

It is acknowledged that the conventional design methods can easily lead to oversized system or unsatisfactory performance for different design conditions. Most existing studies on design optimization of net zero energy building ( nZEB) are conducted based on deterministic data/information. However, the question is:How is the actual performance of a design nZEB in different years considering uncertainties? This study, therefore, proposed a robust design method for sizing renewable energy systems in nZEB concerning uncertainties in renewable resources and demand load. The proposed robust design method is applied to the planning of renewable energy system for the Hong Kong Zero Carbon Building. The annual performance of nZEB under the optimal design options are systematically investigated and compared using the proposed robust design method and the deterministic method. It is meaningful to obtain a fitting formula to identify the relationship between the probability of achieving annual zero energy balance and the design mismatch ratio. On the basis of Monte Carlo uncertainty propagation methods, the uncertainty of nZEB performance is quantified which provides flexibility for designers in selecting appropriate design options according to the required probability of achieving nZEB during the design stage.     

Energy conservative building air conditioning system controlled and optimized using fuzzy-genetic algorithm

In this work, the combined effect of the energy conservative variable refrigerant volume (VRV) system and the variable air volume (VAV) system was experimentally investigated using genetic fuzzy optimization method that yielded better thermal comfort, indoor air quality (IAQ) requirements without compromising on the energy savings potential. The proposed system was tested using the demand controlled ventilation (DCV) combined with the economizer cycle ventilation (ECV) techniques and examined for a year-round building air conditioning (A/C) application. The supply air temperature (SAT) set points were varied under three distinct strategies and the optimal solutions obtained for the fuzzy systems designed resulted in an enhanced energy conservative potential. The test results of the proposed system were compared with the conventional fan coil A/C system. Based on the three strategies of the supply air temperature, the proposed system yielded an improved per day energy savings potential of 54% in summer and 61% in winter design conditions. Furthermore, for the strategies considered the proposed system achieved an annual energy conservative potential of 36% and exhibited more possible ways to achieve thermal comfort, IAQ and energy conservation.     

Robust optimal design of renewable energy system in nearly/net zero energy buildings under uncertainties

It is acknow ledged that the conventional design methods can easily lead to oversized system or unsatisfactory performance for different design conditions. M ost existing studies on design optimization of net zero energy building( nZ EB) are conducted based on deterministic data / information. How ever,the question is: How is the actual performance of a design nZ EB in different years considering uncertainties? This study,therefore,proposed a robust design method for sizing renew able energy systems in nZ EB concerning uncertainties in renew able resources and demand load. The proposed robust design method is applied tothe planning of renew able energy system for the Hong Kong Zero Carbon Building. The annual performance of nZ EB under the optimal design options are systematically investigated and compared using the proposed robust design method and the deterministic method. It is meaningful to obtain a fitting formula to identify the relationship betw een the probability of achieving annual zero energy balance and the design mismatch ratio. On the basis of M onte Carlo uncertainty propagation methods, the uncertainty of nZ EB performance is quantified w hich provides flexibility for designers in selecting appropriate design options according to the required probability of achieving nZ EB during the design stage.     

多级递阶工程系统全局优化抗震设计的混合法

多级递阶工程系统是由大型建筑工程项目的主要结构, 按照功能逻辑关系构成的多层次、树分支结构系列。在离散型决策变量、工程抗震优化设计背景下, 本文针对该系统结构分布特点, 提出全局优化计算的混合法。这一方法把耦合法与分解法的优点结合起来, 灵活地处理系统结构边界条件, 并使优化空间达到高度的降维, 对于大规模、分布复杂的多级递阶系统, 具有很高的优化计算效率。算例讨论了这一方法在决策大型建筑工程项目最优设防标准、最优造价和总投资最优分配方面的应用, 并同其它方法的结果作了比较。     

局部肘节消能装置的减振机制分析及其优化控制

传统的肘节式位移放大机构可以增大阻尼器变形从而提高结构减振效率,但其需占据较大空间,且相关的基于小变形假设的位移放大系数理论公式不能反映放大系数时变特性,难以实现几何构造优化。为此,提出一种以黏滞阻尼器为阻尼元件的局部肘节消能装置,其具有占用空间小、布置灵活等特点。基于几何关系推导局部位移放大系数解析解,并对其进行参数分析。分析结果表明：局部凸肘节消能装置的位移放大能力随下连杆与水平面夹角增大而增强,而局部凹肘节消能装置则与之相反;局部凸肘节消能装置的最优下连杆长度与装置高度之比位于［0.7,1.3］区间内,局部凹肘节消能装置的该比值约为0.7。根据改进D值法提出适用于框架结构的局部肘节消能装置层间位移放大系数计算方法。以消能装置在外部激励下最大侧移为基础,给出了针对层间位移放大系数的优化步骤,并通过算例分析验证局部肘节消能装置的可行性和几何优化方法的有效性。采用所提优化方法进行局部肘节消能装置设计,可有效增强其位移放大能力和振动控制效果。     

HVAC system optimization—in-building section

This paper presents a practical method to optimize in-building section of centralized Heating, Ventilation and Air-conditioning (HVAC) systems which consist of indoor air loops and chilled water loops. First, through component characteristic analysis, mathematical models associated with cooling loads and energy consumption for heat exchangers and energy consuming devices are established. By considering variation of cooling load of each end user, adaptive neuro-fuzzy inference system (ANFIS) is employed to model duct and pipe networks and obtain optimal differential pressure (DP) set points based on limited sensor information. A mix-integer nonlinear constraint optimization of system energy is formulated and solved by a modified genetic algorithm. The main feature of our paper is a systematic approach in optimizing the overall system energy consumption rather than that of individual component. A simulation study for a typical centralized HVAC system is provided to compare the proposed optimization method with traditional ones. The results show that the proposed method indeed improves the system performance significantly.     

框架结构整体承载力优化设计的改进方法

为解决框架结构整体承载力优化设计方面存在的问题,建立了多内力组合下矩形和工字形截面几何参数的调整方法,并通过引入强化迭代系数提出了框架结构整体承载力优化设计的改进方法。首先,通过弹性模量缩减法分析框架结构在组合内力下的损伤演化过程,据此确定框架结构在构件和整体2个层面的承载力需求。然后提出了强化迭代系数并确定了其取值,据此调整构件截面强度,建立了结构整体承载力优化设计的加速迭代格式,其可保证框架结构在构件和整体2个层面上的安全性需求并优化结构耗材。同时,为实现截面强度调整在结构计算模型中的更新,建立了多内力组合作用下矩形和工字形截面几何参数调整公式,可根据截面强度调整需求进行截面几何参数的调整。最后,通过与满应力优化准则法对比分析验证了所提方法的合理性。结果表明:采用构件截面几何参数调整方法和加速迭代格式,强化迭代系数取1.001～1.020时,所提方法迭代收敛速度快,且能够获得承载性能和经济性能均优的框架优化设计方案。     

A nodal-based evolutionary optimization algorithm for frame structures

This work proposes a nodal-based evolutionary design optimization algorithm to design frame structures whose edges are the Delaunay triangulation of homogeneously distributed nodes in the design domain. The remaining nodes can freely sway in the design domain except for the loading nodes and boundary nodes. As a result, it can extend the space of admissible solutions to this optimization problem and reduce the number of design variables. Then, the sensitivity of the objective function, namely, the sum of compliance and its volume, is input into the method of moving asymptotes to update the nodal coordinates and member thickness. The most inefficient node is deleted in each iteration based on the average nodal strain energy until its number reaches a prescribed limit. 2D numerical examples for the Michell arch, L-shaped bracket, and Messerschmidt–Bölkow–Blohm beam show that the proposed algorithm can get the optimal structure within a few iterations. Compared with initial configurations in 3D, the optimal crane arm, transmission tower, and aquatic dome have less strain energy and fewer materials, showing a great potential of the proposed method to design actual space frames.     

Energy-based design optimization of steel building frameworks using nonlinear response history analysis

Presented in this paper is a design optimization method for steel building frameworks subjected to seismic loading using a nonlinear response history analysis procedure. Minimum weight, minimum seismic input energy and maximum hysteretic energy of fuse members are identified as the three design objectives. Design constraints include the limits on inter-story drift and plastic rotation of member sections. The design optimization method employs a multi-objective genetic algorithm to search for optimal member section sizes from among commercially available steel section shapes. The design method is illustrated for a moment-resisting steel frame of a three-story building. It is concluded the proposed optimization methodology is an effective and efficient application of the capacity-design principle to building frameworks under earthquake loading.     

A general methodology for optimal load management with distributed renewable energy generation and storage in residential housing

In the US, buildings represent around 40% of the primary energy consumption and 74% of the electrical energy consumption [U.S. Department of Energy (DOE). 2012. 2011 Buildings Energy Data Book. Energy Efficiency & Renewable Energy]. Incentives to promote the installation of on-site renewable energy sources have emerged in different states, including net metering programmes. The fast spread of such distributed power generation represents additional challenges for the management of the electricity grid and has led to increased interest in smart control of building loads and demand response programmes. This paper presents a general methodology for assessing opportunities associated with optimal load management in response to evolving utility incentives for residential buildings that employ renewable energy sources and energy storage. An optimal control problem is formulated for manipulating thermostatically controlled domestic loads and energy storage in response to the availability of renewable energy generation and utility net metering incentives. The methodology is demonstrated for a typical American house built in the 1990s and equipped with a single-speed air-to-air heat pump, an electric water heater and photovoltaic (PV) collectors. The additional potential associated with utilizing electrical batteries is also considered. Load matching performance for on-site renewable energy generation is characterized in terms of percentage of the electricity production consumed on-site and the proportion of the demand covered. For the purpose of assessing potential, simulations were performed assuming perfect predictions of the electrical load profiles. The method also allows determination of the optimal size of PV systems for a given net metering programme. Results of the case study showed significant benefits associated with control optimization including an increase of load matching between 3% and 28%, with the improvement dependent on the net metering tariff and available storage capacity. The estimated cost savings for the consumer ranged from 6.4% to 27.5% compared to no optimization with a unitary buy-back ratio, depending on the available storage capacity. Related reduction in CO₂ emissions were between 11% and 46%. Optimal load management of the home thermal systems allowed an increase in the optimal size of the PV system in the range of 13–21%.     

某体育馆双层柱面网壳结构的优化设计

系统介绍了某体育馆双层柱面网壳结构的优化设计。通过APDL语言在ANSYS环境中利用满应力方法实现不同工况下杆件截面的离散变量优化,并分析截面优化的稳定性、收敛性与可靠性。利用遗传算法在MATLAB环境中实现网格类型、网格数、厚度、矢高的正整数变量优化。联合利用上述方法编制相关程序,实现了结构的多变量的综合优化,取得了较理想的优化效果。该种方法对空间网格结构优化设计具有通用性。     

A multi-objective structural optimization method for serviceability design of tall buildings

Structural optimization design aims to identify optimal design variables corresponding to a minimum objective function with constraints on performance requirements. To this end, many optimization frameworks have been proposed to determine optimal structural systems that are subjected to seismic and wind hazards in isolation. However, some modern tall buildings are sensitive to seismic and wind excitation owing to their complex structural systems and geographic regions. Therefore, a proper structural optimization method for such buildings is required to ensure that the expected performance is achieved in a multi-hazard scenario. This study proposes a multi-objective serviceability design optimization methodology for buildings in multi-hazard seismic and wind environments by combining optimality criteria and the nondominated sorting genetic algorithm II (NSGA-II). Seismic and wind effects can be instantaneously updated due to changes in the structural dynamic properties during the optimal design process. A neural-network-based surrogate model with self-updating is proposed to predict the structural natural frequency so that the overall computation time of the optimization process can be reduced. The proposed method was used to optimize a 50-story frame-tube building and was compared against the general genetic algorithm and general NSGA-II to verify the feasibility and effectiveness.     

Quasi-static response and multi-objective crashworthiness optimization of oblong tube under lateral loading

This paper addresses the energy absorption responses and crashworthiness optimization of thin-walled oblong tubes under quasi-static lateral loading. The oblong tubes were experimentally compressed using three various forms of indenters named as the flat plate, cylindrical and a point load indenter. The oblong tubes were subjected to inclined and vertical constraints to increase the energy absorption capacity of these structures. The variation in responses due to these indenters and external constraints were demonstrated. Various indicators which describe the effectiveness of energy absorbing systems were used as a marker to compare the various systems. It was found that unconstrained oblong tube (FIU) exhibited an almost ideal response when a flat plate indenter was used. The design information for such oblong tubes as energy absorbers can be generated through performing parametric study. To this end, the response surface methodology (RSM) for the design of experiments (DOE) was employed along with finite element modeling (FEM) to explore the effects of geometrical parameters on the responses of oblong tubes and to construct models for the specific energy absorption capacity (SEA) and collapse load (F) as functions of geometrical parameters. The FE model of the oblong tube was constructed and experimentally calibrated. In addition, based on the developed models of the SEA and F, multi-objective optimization design (MOD) of the oblong tube system is carried out by adopting a desirability approach to achieve maximum SEA capacity and minimum F. It is found that the optimal design of FIU can be achieved if the tube diameter and tube width are set at their minimum limits and the maximum tube thickness is chosen.     

三联供系统配置及运行策略的多目标优化分析

在满足建筑物冷热电负荷的前提下,建立了联供系统以年费用、一次能源消耗和二氧化碳排放要求的多目标函数,并利用权重系数将多目标转换为单目标优化模型。以上海市某能源中心的工程为例,得出了冷、热、电三联供系统的最优配置容量及运行策略。     

用遗传算法确定地基承载力

 地基承载力的确定是基础工程设计中至关重要的一环。基于运动单元法的基本思想所提出的地基承载力的求解方法, 构造出一种适合于地基整体破坏类型的优化分析约束条件, 采用遗传算法搜索最危险滑动面与地基极限承载力的方法。该方法秉承生物遗传进化过程, 扩展了传统的极限平衡方法确定地基承载力的应用范围, 并且克服了传统方法易于陷入局部极小值的缺点。     

超高层建筑结构基于区格剪切变形屈曲约束支撑最优布置方法

屈曲约束支撑以其金属的轴向变形产生耗能,其轴向变形值往往决定其阻尼耗能的发挥。作为超高层建筑的变形限值之一,层间位移角由受力层间位移角和非受力层间位移角两部分组成,受力层间位移角的原因为屈曲约束支撑区格的剪切变形所致。引入广义剪切变形,探讨屈曲约束支撑区格剪切变形量的变化原理,并发展了一种基于该剪切变形的屈曲约束支撑最优布置方法,其方法可从结构局部位移指标的层面上判断约束支撑的最优位置。最后以一带环带桁架的支撑框架核心筒超高层建筑为例,并应用非线性时程分析的方法,说明该最优布置方法的有效性。结果表明,用广义剪切变形方法得到的屈曲约束支撑布置位置与实际能得到的最优位置较为吻合,因此可为超高层建筑屈曲约束支撑和其他金属阻尼器的设计提供一定的借鉴。