Performance of combined displacement ventilation and cooled ceiling liquid desiccant membrane system in Beirut climate

The performance of the chilled ceiling (CC) displacement ventilation (DV) systems is constrained by latent load removal capacity and cost of supply air dehumidification to prevent condensation on the ceiling. In this study, a liquid desiccant dehumidification membrane cycle (LDMC) is mathematically modelled to replace the CC and remove directly latent and sensible load from indoor space through the membrane. The desiccant system is coupled with the DV system. An optimized operational strategy is adopted while allowing ceiling temperature to drop to lower values than conventional CC/DV. The optimized LDMC-C/DV system was implemented in an office space in Beirut climate. It was found that decreasing the membrane liquid desiccant temperature resulted in a significant decrease in the total cooling energy of the system, while increasing the solar heating energy of the desiccant regeneration. At optimal set points, a decrease of 49% in energy consumption was observed compared to the conventional CC/DV system.     

Chilled ceiling displacement ventilation design charts correlations to employ in optimized system operation for feasible load ranges

This paper expands Ghaddar et al. [N. Ghaddar, K. Ghali, R. Saadeh, A. Keblawi, Design charts for combined chilled ceiling displacement ventilation system (1438-RP), ASHRAE Transactions, 143 (2) (2008) 574-587] design charts of combined chilled ceiling (CC) displacement ventilation (DV) system to operating sensible load ranges from 40 W/m² to 100 W/m². It develops a global correlation of system load and operational parameters, with comfort measured by vertical temperature gradient and indoor air quality measured by the stratification height. The correlations are used for a known transient load profile in generating optimal settings of the CC/DV system operational parameters and associated energy consumption.An example is illustrated to show how the correlation could be used to size the system and to provide optimized control of the CC/DV system operation at low computational cost. Results of the current model are compared to the published case study of an optimized operation based on transient simulations of the space thermal model to achieve minimum operation cost [M. Mossolly, N. Ghaddar, K. Ghali, L. Jensen, Optimized operation of combined chilled ceiling displacement ventilation system using genetic algorithm, ASHRAE Transactions, 143 (2) (2008) 541-554]. The design correlations resulted in good agreement with published data (within 3% error in energy consumption and average 6% error in predictions of comfort and stratification height) at 1/4 of the computational time. The presented methodology provides an alternative for using the correlation for supervisory online controllers for the CC/DV system based on physically derived correlations.     

基于遗传算法的空调水系统优化控制研究

提出一种优化控制策略，采用基因遗传优化算法，能够快速准确地获得各控制变量在预测时间内的最优设定值。实时仿真试验表明，该策略与固定设定值的控制方式以及局部层次的优化控制方式相比，能够在满足控制稳定性的前提下最大限度地节约整个空调水系统的总能耗。     

Optimal control development for chilled water plants using a quadratic representation

Optimal supervisory control strategy for the set points of controlled variables in the cooling plants has been studied by computer simulation. A quadratic linear regression equation for predicting the total cooling system power in terms of the controlled and uncontrolled variables was developed using simulated data collected under different values of controlled and uncontrolled variables. The optimal set temperatures such as supply air temperature, chilled water temperature, and condenser water temperature, are determined such that energy consumption is minimized as uncontrolled variables, load, ambient wet bulb temperature, and sensible heat ratio are changed. The chilled water loop pump and cooling tower fan speeds are controlled by the PID controller such that the supply air and condenser water set temperatures reach the set points designated by the optimal supervisory controller.The influences of the controlled variables on the total system and component power consumption were determined. The predicted power obtained from the quadratic regression equation was found to be a good fit to the simulated one. Because the Hermitian matrix of the system quadratic cost function was positive, the optimal control variables for the minimum power consumption were able to be obtained. There are relatively high effects of the load and sensible heat ratio on the optimal supply air and chilled water set temperatures, while the effect of ambient wet bulb temperature is less. In contrast to that result, the ambient wet bulb temperature has a much larger effect on the optimal condenser water set temperature, while the load has less, and the sensible heat ratio has no influence on it. The trade-off among the components of power consumption results in that the total system power use in both simulated and predicted systems are minimized at lower supply, higher chilled water, and lower condenser water set temperature conditions.     

集中空调冷水侧局部系统上位机控制器的实时控制分析

针对集中空调冷水侧基本自动控制系统,设计了两个上位机控制器,分别仅对供回水压差和同时对压差与冷水供水温度进行实时优化;通过仿真实验分析了控制器对系统控制稳定性和系统能耗的影响。结果表明,综合考虑制冷机和二次泵系统的上位机控制器具有较好的可实施性,能在保证系统运行稳定的前提下减少冷水侧能耗。     

Air quality in rooms conditioned by chilled ceiling and mixed displacement ventilation for energy saving

A transient-contaminant-transport model is developed for assessing IAQ in the breathing zone when introducing return air into rooms conditioned by CC/DV system to save energy. The steady state transport model of [1] is extended to transient conditions while accounting for significant wall plumes associated with external loads.Experiments are performed to validate the extended model predictions of IAQ expressed in the level of CO₂ concentration. Experiments are conducted in a chamber with two external walls in Kuwait Climate. Measurements are recorded in time of the air temperature and CO₂ concentration at selected locations in the room and compared with values predicted by the model. Experimental results agreed well with model predictions. The maximum errors in predicted CO₂ concentrations are less than ±25 ppm in presence of external load. 60% fresh air fraction resulted in 37% less energy consumption compared with 100% fresh air CC/DV system.The validated model is applied to a case study in Kuwait to evaluate energy saving over the cooling season for a typical office space while using mixed DV air. Energy savings of up to 20.6% can be realized using mixed supply air while maintaining IAQ compared with energy used for the 100% fresh air.     

Innovative method for energy management: Modelling and optimal operation of energy systems

This paper presents an optimal management control strategy for power systems in industrial plants. A dedicated code has been developed to perform system analysis and simulation. The energy/mass balances existing between building and power plant has been depicted through a mathematical model based on vector equations, taking into account the behaviour of each system component. The main result is the definition of the power plant component set points satisfying the energy load under predefined optimization criterion (i.e. system efficiency, costs, pollutant emissions). Input data are the industrial plant loads, both electric and thermal, the technical characteristic of the installations, and the cost of electricity and fuel. As a general result we show that the optimal management of a power plant is as significant as the efficiency of its components for energy saving purposes. In particular, the correlation between the component set point profiles and the energy/cost/pollution savings is highlighted. Yearly simulations are performed on an existing energy system of an industrial plant varying the frequency of energy load dataset. The considered time steps are month, half a day, 4 h and 1 h. The results demonstrate that the whole power plant management leads to a global reduction of the cost and that the availability of more detailed energy load dataset leads to better operation cost estimation. As expected, considering a large time-step, the variation of energy load is not appreciable.The energy saving potential of this method is demonstrated allowing the best plant management solution under different energy loads.     

Online fault adaptive control for efficient resource management in Advanced Life Support Systems

This article presents the design and implementation of a controller scheme for efficient resource management in Advanced Life Support Systems. In the proposed approach, a switching hybrid system model is used to represent the dynamics of the system components and their interactions. The operational specifications for the controller are represented by utility functions, and the corresponding resource management problem is formulated as a safety control problem. The controller is designed as a limited-horizon online supervisory controller that performs a limited forward search on the state-space of the system at each time step, and uses the utility functions to decide on the best action. The feasibility and accuracy of the online algorithm can be assessed at design time. We demonstrate the effectiveness of the scheme by running a set of experiments on the Reverse Osmosis (RO) subsystem of the Water Recovery System (WRS).     

Power flow control model of energy storage connected to smart grid in unbalanced conditions: a GSA-technique-based assessment

A gravitational search algorithm (GSA)-based power flow control (PFC) model for energy storage related to smart grid under unbalance conditions is proposed in this paper. Source side and load side power transfer capability is considered to be increased by this proposed algorithm and it offers several conveniences such as the improved predicting capability, degradation in complexity as well as the randomization and so on. The smart grid incorporates the combination of the microgrid (MG) such as renewable energy sources, energy storage devices, grid and load. Here, a renewable energy source of the photovoltaic (PV) system and energy storage of fuel cell (FC) is considered and AC load is utilized. In the proposed method, the controller parameters of the power controller are optimized by the GSA technique based on the variation of active and reactive power of the system. The better power flow under unbalanced load conditions with subject to the minimum power variation is ensured by the optimization process. The proper control signals to the voltage source inverter (VSI) system are generated by this proposed method. Then, the proposed method is implemented using the MATLAB/Simulink platform and a comparison analysis with the existing techniques presents the performance of the proposed method.     

Development and validation of online models with parameter estimation for a building zone with VAV system

The energy consumption by building heating, ventilating, and air conditioning (HVAC) systems has evoked increasing attention to promote energy efficient control and operation of HVAC systems. Application of advanced control and operation strategies requires robust online system models. In this study, online models with parameter estimation for a building zone with a variable air volume system, which is one of the most common HVAC systems, are developed and validated using experimental data. Building zone temperature and zone entering air flow are modeled based on physical rules and only the measurements that are commonly available in a commercial building are used. Various validation experiments were performed using a real-building test facility to examine the prediction accuracies for system outputs. Using the online system models with parameter estimation, the prediction errors for all validation experiments are less than 0.28 °C for temperature outputs, and less than 84.9 m³/h for air flow outputs. The online models can be further used for local and supervisory control, as well as fault detection applications.     

土壤源热泵SCADA系统的设计与应用

针对天津市一土壤源热泵工程,采用集散型计算机控制技术(DCS),设计研制了一套三级分布式计算机数据采集和控制(SCADA)系统。介绍了该系统的结构、功能和特点。运行结果表明,该系统能为土壤源热泵安全运行、监测管理和负荷能量调节提供可靠保证。     

An optimal control strategy for complex building central chilled water systems for practical and real-time applications

This paper presents an optimal control strategy for online control of central chilled water systems in complex building air-conditioning systems to enhance their energy efficiency. The optimal control strategy is formulated using a systematic approach by considering the system level and subsystem level characteristics and interactions among the overall system. The requirements and constraints of practical applications are also carefully considered during the development of this strategy. This optimal control strategy consists of the model-based performance predictor (i.e., simplified models), cost estimator (i.e., cost function), optimization technique, supervisory strategy and a number of local control strategies. The local control strategies are used to ensure the robust operation and keep track of control settings considering the dynamic characteristics of the local process environment. The performance of this strategy is tested and evaluated in a simulated virtual environment representing the complex central chilling system in a super high-rise building by comparing it with that of other control strategies. The results showed that this strategy is more energy efficient and cost effective than the other strategies for online applications. This strategy is being implemented in the super high-rise building under study for field application and validation.     

Advanced sliding mode control for solar PV array with fast voltage tracking for MPP algorithm

ABSTRACT

This paper presents a photovoltaic (PV) system with a maximum power point tracking (MPPT) method. The main aim of this work is to collect the maximum power generated from a solar photovoltaic generator (PVG). This goal is accomplished by integrating a sliding mode controller (SMC) that drives a voltage source inverter (VSI) connected between the PVG and the load. The system is modelled and tested in MATLAB/SIMULINK. In simulation, the SMC gives a fast and accurate convergence to the MPP that is tracked by incremental conductance (INC) type MPPT algorithm. The consequence of the system is capable of tracking MPPs accurately and rapidly without steady-state oscillation and also its performance is satisfactory. The INC type MPPT algorithm is used to track MPPs because it exhibits a precise control under rapidly changing atmospheric conditions. As the solar energy gives the variable light energy at different times and is not constant, the SMC performance is calculated at variable irradiation points by using one slider gain for the variation of the insolation levels.     

独立别墅热水供暖系统动态模型、控制策略及能耗分析

建立了独立别墅供暖系统的非线性动态模型并分析了其动态特性,介绍了模型降阶方法及PI控制器参数的设计和整定。针对可能的供暖系统控制策略进行了动态仿真和能耗分析。仿真结果表明,单纯采用室外气候补偿控制模式并不能获得理想的控制效果;采用分室控制模式能满足室内舒适性要求并有一定的节能效果,节能率约为25%。     

Development of an adaptive Smith predictor-based self-tuning PI controller for an HVAC system in a test room

This paper presents an adaptive Smith predictor-based self-tuning PI controller and its application to the air-conditioning system of a test room. The significant time delay of air-conditioning processes can lead to degradation of performance and instability of the control loop. The parameters of air-conditioning processes vary due to the changes in the operation conditions. By using a recursive least squares (RLS) algorithm combined with a z-domain fitting method, the parameters of the air-conditioning process in the closed loop including time delay can be estimated online. Based on the estimated dead-time, a Smith predictor, which uses a reference model, is adopted to reduce the unfavorable effects of the time delay in the air-conditioning system. Based on the predicted error and estimated values, the control signal of the control loop is calculated by a self-tuning PI controller using ITAE tuning rules. The performance, robustness and effectiveness of the proposed control method are validated in the experimental platform. The corresponding performance of the proposed control method is compared with an adaptive PI controller. Experiment results demonstrate that the proposed strategy achieves better performance compared with the adaptive PI controller considering the effects of set-point changes, parameter variations or load disturbances in HVAC systems.     

基于模糊自适应PI控制的电梯矢量控制系统仿真研究

根据模糊自适应PID控制理论,对电梯变频调速矢量控制系统中的转速PI调节器进行优化设计。并应用电动机矢量控制系统的仿真模型进行仿真分析。仿真结果表明,采用模糊自适应PI控制器的变频调速系统具有响应时间快、超调量小等优点。     

冷却顶板对置换通风系统的影响:CFD研究

以计算流体力(CFD)的模型为基础,采用有限容积法对带有冷却顶板的置换通风系统和不带冷却顶板的普通置换通风系统的温度场、气流分布及人体的热舒适性进行了模拟分析,模拟结果表明,冷却顶板-置换通风系统可以减小室内温度梯度,提高人体热舒适性。     

Optimized control strategies for solar district heating systems

Solar district heating (SDH) systems are a proven concept for the supply of space heating and/or domestic hot water using solar energy as the main heat source. SDH systems with a high solar fraction include seasonal thermal storage and various subsystems with different time scales that must be managed by the supervisory control system. This paper presents the development of optimized control strategies for the Drake Landing Solar Community in Okotoks (Alberta, Canada). The proposed strategies, based on the application of model predictive control concepts, aim to further reduce the use of auxiliary energy for heating (gas) while also reducing the pumping energy (electricity). Perfect forecasts for the weather and the SDH loads are assumed in the study and a detailed TRNSYS model is used. Results show that the primary energy consumption can be reduced by 5% by updating the supervisory control strategies.     

多元模块式中央空调控制系统研究探讨

控制系统方案是针对武汉某综合体项目中央空调系统设备的节能降耗、科学管理和优化组合运行而设计。多元模块化形式的系统设计,在不同的运行情况下,采用不同模块组合运行,实现了多元化组合调控,加大了系统的可变性。针对中央空调系统的智能管理及能源优化,采用LTUZ能源优化专用控制器和LTUZ智能管理专用控制器,配上远程系统专用智能操作平台,实现中央空调控制的智能管理和能源优化。     

基于粒子群优化算法的结构-精密装置微振动鲁棒自稳定H_2/H_∞控制方法

将粒子群优化算法(PSO)与鲁棒H2/H∞控制思想结合,以系统传递函数矩阵为对象,优化其H2范数或H∞范数,并考虑系统稳定性条件,提出了鲁棒自稳定H2/H∞振动控制方法,并计算得到使系统稳定且控制效果最优的输出反馈控制器。以3层框架结构及其首层安置一双自由度精密装置这一综合系统为对象,考虑两种不同位置矩阵的铁路交通荷载,结果表明位置矩阵对优化影响较大;数值试验结果表明本文方法收敛速度快,计算耗时短,振动控制效果良好,为结构鲁棒振动控制提供了新思路。