VAV空调系统应用问题探讨

本文对变风量空调系统在实际应用过程中出现的一些问题进行了研究。从设计、安装和操作维护等方面分析了导致这些问题的原因。同时,对变风量空调系统的设计和应用提出一些建议。     

采用室内热舒适性控制的变风量空调系统节能控制研究

在对变风量空调系统及控制系统分析的基础上,利用ＤＤＣ控制器可采集多点和多种信号的优点,提出采用室内热舒适性控制取代室内温度控制的控制方案。仿真试验结果证明,同常规的室内温度控制方案相比,室内热舒适性控制方案可以较好地改善室内的热舒适性,同时,在保证室内热舒适性前提下,采用室内热舒适性控制方案不仅能够保证控制的稳定性,而且有较好的节能作用。     

Proposal of a control strategy for desiccant air-conditioning systems

A control strategy for the operation of desiccant air-conditioning systems is proposed in this work. The proposed strategy consists of a basic scenario, while some alternative strategy schemes are also proposed on the basis of the approach adopted for the controlling of the humidifiers or the desiccant system operation modes included. The control strategy aims at sustaining the building conditions within values suitable for human thermal comfort, thus taking care of both temperature and humidity. The assessment of the proposed control strategy scenarios is performed in terms of effectiveness and efficiency, through the use of a desiccant system model, which takes into account the effect of transient phenomena as well. Specific information for the required hardware equipment and its implementation for the controlling of the respective system components is provided, pointing out the simplicity of the proposed solutions.     

A dynamic switching strategy for air-conditioning systems operated in light-thermal-load conditions

Recently, modern air-conditioners have begun to incorporate variable-speed compressors and variable-opening expansion valves, together with feedback control to improve the performance and energy efficiency. However, for the compressor there usually exists a low-speed limit below which its speed can not be continuously modulated unless it is completely turned off. When the air-conditioning system is operated in light-thermal-load conditions, the low-speed limit causes the compressor to run in an on–off manner which can significantly degrade the performance and efficiency. In this paper, a dynamic switching strategy is proposed for such scenarios. The strategy is basically an integration of a cascading control structure, an intuitive switching strategy, and a dynamic compensator. While the control structure provides the nominal performance, the intuitive switching strategy and the dynamic compensator together can account for the compressor’s low-speed limitation. Theoretical analysis reveals that when the output matrix of the dynamic compensator is chosen properly, the proposed strategy can effectively reduce the output error caused by the on–off operation of the compressor. Experiments also demonstrate that the proposed strategy can simultaneously provide better regulation for the indoor temperature and improve the energy efficiency at steady state.     

小区冷热电联供系统的空调期优化运行研究

1前言冷热电联供系统(CCHP)是一种建立在能的梯级利用概念基础上,同时产生电能和可用热(冷)能的能源系统。目前国内大多用燃气轮机或燃气内燃机作为原动机,利用高品位的热能发电,低品位的热能供热和制冷,从而大幅度提高系统的总能效率。这种系统有助于电网和燃气供应的削峰填谷     

Optimal control strategy for a multi-zone air conditioning system using a genetic algorithm

This paper examines optimal control strategies of variable air volume air conditioning system. The control strategies included a base control strategy of fixed temperature set point and two advanced strategies for insuring comfort and indoor air quality (IAQ). The first advanced control adjusts the fresh air supply rate and the supply air temperature to maintain the temperature set point in each zone while assuring indoor air quality. The second strategy controls the fresh air rate and the supply air temperature to maintain an acceptable thermal comfort and IAQ in each zone. The optimization problem for each control strategy is formulated based on the cost of energy consumption and constrained by system and thermal space transient models. The optimization problem is solved using genetic algorithm. The optimization scheme/model is applied to a case study for a building floor in Beirut weather. The thermal space and system component models were validated for the base strategy using Visual DOE 4.0 software [Architectural Energy Cooperation, San Francisco, USA; 2005 〈www.archenergy.com〉]. Energy savings up to 30.4% were achieved during the summer season of four months with the optimized advanced strategies when compared with the conventional base strategy while comfort and IAQ were satisfied.     

地铁空调通风环境控制系统的节能探讨

针对地铁空调通风系统的负荷特点，提出了控制新风量、变频调速、设置冰蓄冷集中供冷站、目标温度控制以及自动化运行管理等节能技术和措施，并对这些方案进行了经济性分析。     

以PMV为基础的模糊控制器在VAV空调系统中的应用

通过对以热舒适性指标ＰＭＶ为参数的模糊控制方法和以固定室内温度的 ＰＩＤ控制方法的比较,得出了前者不但能够达到满足室内人员的热舒适性要求, 更能节省能量消耗的特点。在空调系统模拟软件ＨＶＡＣＳＩＭ＋的辅助下,对这 一结论进行了验证。     

A neural net model-based multivariable long-range predictivecontrol strategy applied in thermal power plant control

A constrained multivariable control strategy along with its application in more efficient thermal power plant control is presented in this paper. A neural network model-based nonlinear long-range predictive control algorithm is derived, which provides offset-free closed-loop behavior with a proper and consistent treatment of modeling errors and other disturbances. A multivariable controller is designed and implemented using this algorithm. The system constraints are taken into account by including them in the control algorithm using real-time optimization. By running a simulation of a 200 MW oil-fired drum-boiler thermal power plant over a load-profile along with suitable PRBS signals superimposed on controls, the operating data is generated. Neural network (NN) modeling techniques have been used for identifying global dynamic models (NNARX models) of the plant variables off-line from the data. To demonstrate the superiority of the strategy in a MIMO case, the controller has been used in the simulation to control main steam pressure and temperature, and reheat steam temperature during load-cycling and other severe plant operating conditions     

某办公楼宇中央空调变风量控制系统设计

中央空调变风量系统应用越来越广泛,尤其是商场、办公楼等公共场所。以某办公楼宇为例,结合中央空调变风量系统的基本原理,设计了楼宇控制的方案,介绍了主要控制策略,并通过组态软件设计,对该楼宇运行状态进行监控,对今后的办公楼宇中央空调变风量控制系统的实际工程应用具有一定的参考价值。     

Numerical studies of airflows induced by mechanical ventilation and air-conditioning (MVAC) systems

Indoor air flows induced by mechanical ventilation and air-conditioning (MVAC) systems are simulated by the technique of computational fluid dynamics (CFD). Examples are taken to illustrate the capability of the technique. These include the evaluation of basic ventilation system designs, ventilation systems in an enclosed car-park, spot cooling system, air-conditioning system with chilled ceiling, cold air distribution system, effect of casual heat gain on the air diffuser induced air flow and the underfloor air supply system. Evaluation of the performances of the mechanical systems in those buildings are performed. Physical experiments in air-conditioned spaces reported by Sakamoto and Matsuo; and by Murakami and Kato are also simulated to assess how good are the predicted results.     

An online adaptive optimal control strategy for complex building chilled water systems involving intermediate heat exchangers

This paper presents an adaptive optimal control strategy for online control of complex chilled water systems involving intermediate heat exchangers to enhance operation and energy performances. This optimal control strategy determines the optimal settings of the heat exchanger outlet water temperature (hot side) and the required operating number of heat exchangers and pumps in order to minimize the total energy consumption of pumps under varying working conditions. Adaptive method is utilized to update the key parameters of the proposed models online. A simulated virtual platform representing a chilled water system in a super high-rise building was established to validate and evaluate the proposed optimal strategy. Test results show that the strategy has enhanced control robustness and reliability, particularly in avoiding deficit flow problem. Significant energy of chilled water pumps is saved when compared with conventional methods.     

A control strategy for energy optimal operation of a direct district heating system

A dynamic model of a direct district heating system (DDHS) is developed, and an energy optimal control strategy is designed. The DDHS is characterized as a system with long transport time delay. The use of a Smith predictor (SP) to deal with this type of time delay is explored. An SP is designed by using the reduced‐order dynamic model and implemented on the full‐order model. Also, optimal set point profiles of supply water temperature as a function of outdoor air temperature have been determined. The simulation results show that the SP works effectively in disturbance rejection compared with the nominal control design. The use of optimal set point control strategy resulted in energy savings of the order of 19–32% when the influence of internal load was considered. Copyright © 2004 John Wiley & Sons, Ltd.     

冷冻水系统优化控制方法

介绍了确定冷冻水系统优化控制的两种方法:基于设备的优化和基于系统的优化。处理优化问题的手段,如二次费用和线性输出,独立控制变量的确定等,对于冷冻水系统的优化控制具有一定的借鉴意义。     

空调系统的节能措施

本文针对空调系统能耗高,但节能潜力又很大的特点,探讨了在空调系统的设计和运行中可以采取的一些节能措施,并对这些措施的节能效果进行了简单分析。     

Energy management and design of centralized air-conditioning systems through the non-revisiting strategy for heuristic optimization methods

It is getting more and more popular to apply heuristic optimization methods, like genetic algorithm (GA) and particle swarm optimization (PSO), to handle various engineering optimization problems. In this paper, optimization problems of typical centralized air-conditioning systems were solved by the non-revisiting (Nr) strategy, which was proposed to be incorporated into the common heuristic methods for improving the optimization effectiveness and reliability. This approach can store the evaluated fitness values in an archive with minimal computer memory, detect the revisits and prevent them from re-evaluating. It is particularly useful for the problems formulated by dynamic simulation or detailed modeling with very demanding computational time for function evaluation. The non-revisiting strategy can facilitate the search of the global optimum by its parameter-less adaptive mutation capability. In the optimization problems of central air-conditioning systems, it was found that the NrGA and NrPSO could search better solutions at a limited number of function evaluations than the conventional GA and PSO did. The ultimate goal is to determine the required parameters for optimal design and energy management. The proposed strategy can be applied to similar types of air-conditioning or engineering optimization problems, and possibly incorporated into other kinds of heuristic optimization methods.     

Incorporating fan control into air-conditioning systems to improve energy efficiency and transient response

Modern air-conditioners frequently incorporate variable-speed compressors and variable-opening expansion valves with feedback control to improve performance and power efficiency. Because making the fan speeds adjustable adds flexibility to the control design and thus can lead to further improvements in performance and efficiency, this paper proposes two control algorithms, respectively, incorporating the outdoor fan and the indoor fan as the additional control inputs for air-conditioning systems. Both of the control algorithms are designed based on a low-order, linear model obtained from system identification. The first algorithm, which modulates the outdoor fan speed, can reduce the steady state power consumption if the temperature difference between the condenser and the outdoor environment is controlled properly. The second algorithm, which adds one more degree of freedom to control by modulating the indoor fan speed, can improve the transient response because actuator saturations become less likely to occur. The two control algorithms are implemented on a split-type residential air-conditioner and their respective performance is validated experimentally.     

基于LQG-I的风力发电机组优化控制策略研究

文章针对风电系统的随机性、不确定性和未建模动态等特征,提出了LQG-I优化控制策略。首先,运用机理分析的方法建立了风力发电系统数学模型。在此基础上,设计了LQG-I控制策略,既保留了LQG在克服随机扰动方面的优势,又利用了积分控制在解决系统的不确定性和未建模动态方面的优势。为了进一步改善对系统的控制性能,采用粒子群优化算法对加权矩阵Q,Qe,R的参数进行整定。最后,以高风速区功率和发电机转矩优化控制问题为例,在matlab/simulink平台下仿真验证了所提优化控制策略的可行性和有效性。仿真结果表明:所提出的LQG-I优化控制策略能够实时跟踪风速的变化,保证发电机角速度、转矩和输出功率的稳定;在同等条件下,该控制策略比传统LQG控制器性能更优越。     

A linear programming optimization model for optimal operation strategy design and sizing of the CCHP systems

Combined cooling, heat, and power (CCHP) system offers numerous potential advantages for the supply of energy to residential buildings in the sense of improved energy efficiency and reduced environmental burdens. To realize the potential for being more beneficial, however, such systems must reduce total costs relative to conventional systems. In this study, a linear programming optimization model was presented for optimum planning and sizing of CCHP systems. The purpose of the model is to give the design of the CCHP system by considering electrical chiller and absorption chiller simultaneously in economic viewpoint. A numerical study was conducted in Tehran to evaluate the CCHP system model. The linear programming (LP) model determines the optimal sizes of the CCHP equipment by considering capital cost of the system. It showed that by considering electricity buyback, the optimum size of the electrical chiller decrease and the optimum size of the combined heat and power (CHP) unit and the absorption chiller increase dramatically with respect to without electricity buyback. Also, the LP model determines the optimal operation strategy of the system by neglecting capital cost. The optimally operated CCHP system encompassing electrical and absorption chiller could result in an 18% decrease in operating cost when compared to a CHP system encompassing electrical chiller only. Without electricity buyback, the profitability of CCHP was 23%, while with electricity buyback, profitability became 39%. Furthermore, a sensitivity analysis was conducted to show how the important parameters affect the entire system performance.     

基于一致性协议的配电网分布式优化控制策略研究

分布式控制以其鲁棒性强、可扩展性强等突出优势,已逐渐取代集中式控制,成为高渗透率配电网优化控制的一种有效途径。文章研究了一种基于无功补偿设备和分布式电源分组协作机制的配电网分布式优化控制策略,将多个无功补偿设备或分布式电源聚合在一起,以基于领导者的一致性协议控制节点电压和交换功率。文章给出了分布式协同控制框架,各分组控制目标及一致性变量的选取,并证明了各控制组分布式控制算法的收敛性。通过IEEE14节点系统的仿真算例验证了所提出方法的正确性和有效性。