Multivariable control-oriented modeling of a direct expansion (DX) air conditioning (A/C) system

A dynamic mathematical model for a DX A/C system has been developed. The dynamic model, written in state-space representation which was suitable for designing multivariable control, was linearized at steady state operating points. The linearized model has been validated by comparing the model simulation results with the experimental data obtained from an experimental DX A/C system. The simulated results agreed well with the experimental data, suggesting that the model developed was able to capture the transient characteristics of the DX A/C system modeled. It is expected that the model developed can be useful in designing a multi-input multi-output (MIMO) controller to simultaneously control indoor air temperature and humidity in a space served by a DX A/C system.     

A novel proportional-derivative (PD) law based fuzzy logic principles assisted controller for simultaneously controlling indoor temperature and humidity using a direct expansion (DX) air conditioning (A/C) system

A novel Proportional-Derivative (PD)law based Fuzzy Logic Controller (PFC) for a variable speed (VS) direct expansion (DX) air conditioning (A/C) system has been developed. There were two coupled control loops in this controller, i.e., varying supply fan speed to control indoor dry-bulb temperature (T_db), and compressor speed indoor wet-bulb temperature (T_wb). To weaken the coupling effect between the two loops, fuzzy logic principles were deployed. Furthermore, a PD law was used instead of a Proportional-Integral-Derivative (PID) law, in the PFC, which helped simplify not only calculation but also the structure of the PFC. The controller developed was validated by carrying out the controllability tests with the experimental conditions covering the normal operational range of a VS DX A/C system. The experimental results of the controllability tests suggested that the novel PFC developed is capable of realizing the simultaneous control of indoor temperature and humidity satisfactorily, in terms of control accuracy and sensitivity.     

A DDC-based capacity controller of a direct expansion (DX) air conditioning (A/C) unit for simultaneous indoor air temperature and humidity control – Part I: Control algorithms and preliminary controllability tests

For residential buildings located in the subtropics, direct expansion (DX) air conditioning (A/C) units are commonly used. Most DX A/C units are currently equipped with single-speed compressors and supply fans, relying on on–off cycling compressors as a low-cost approach to maintain only indoor air dry-bulb temperature, resulting in either space overcooling or an uncontrolled equilibrium indoor relative humidity (RH) level. With the rapid development of A/C industry, the use of variable-speed compressor and supply fan has become more and more prevalent and practical. This paper, the first part of a two-part series, reports on the development of a novel direct digital control (DDC)-based capacity controller for a DX A/C unit having variable-speed compressor and supply fan to simultaneously control indoor air temperature and RH in a conditioned space served by the DX A/C unit. The controller is the first of its kind as a composite parameter, sensible heat ratio (SHR), is used as a controlled parameter. The core element of the capacity controller, a numerical calculation algorithm (NCA) is firstly presented. This is followed by reporting the results of preliminary controllability tests of the DDC-based capacity controller, which suggested that the controller developed could achieve a reasonable control accuracy, but with room for improvement with respect to control sensitivity. Part II of the two-part series reports on the further development of the controller to improve its control sensitivity, and the results of associated controllability tests.     

变速直膨式空调系统运行特性的稳态ANN模型

在假设系统输出显、潜冷量的相对值在不同的蒸发器入口空气状态下不发生明显变化的前提下,本文针对实验用变速直膨式空调系统建立了稳态人工神经网络(ANN)模型,预测其在不同压缩机、风机转速组合下的系统输出,利用输出显、潜冷量的相对值可以消除室内空气状态对系统输出的影响。通过稳态实验获得数据训练、检测并验证ANN模型预测变速直膨式系统运行特性的准确性,并通过非训练状态点下的稳态实验验证所提出假设与ANN模型的适用性。ANN模型的训练、检测以及验证实验结果的最大误差均小于5%,平均误差均小于3%,表明该稳态ANN模型可以在训练状态点以及非训练状态点较为准确地预测变速直膨式系统的运行特性。     

A DDC-based capacity controller of a direct expansion (DX) air conditioning (A/C) unit for simultaneous indoor air temperature and humidity control – Part II: Further development of the controller to improve control sensitivity

The development of the novel direct digital control (DDC)-based capacity controller for a direct expansion (DX) air conditioning (A/C) unit having variable-speed compressor and supply fan to simultaneously control indoor air temperature and relative humidity (RH) in a conditioned space served by the DX A/C unit has been reported in Part I of the two-part series. The results of preliminary controllability tests for the novel capacity controller presented in Part I, however, suggested that the controller developed was operational, with acceptable control accuracy but rooms for improvement with respect to control sensitivity. This paper, the second part of the two-part series, reports on the further development of the controller to improve its control sensitivity and the associated controllability test results. Both control accuracy and reasonable control sensitivity were achieved by incorporating a traditional Proportional–integral (PI) controller into the DDC-based capacity controller.     

The influences of the operating characteristics of an Electronic Expansion Valve (EEV) on the operational stability of an EEV controlled direct expansion air conditioning system

This paper reports on a study on the influences of the operating characteristics of a proportional–integral (PI) controlled Electronic Expansion Valve (EEV) on the operational stability of a direct expansion (DX) air conditioning (A/C) system. Using the classical control theory, EEV's PI settings and time constant of EEV's temperature sensor were analyzed. The theoretical analysis results using the classical control theory were further verified experimentally using an experimental DX A/C system. The study results showed that a larger proportional or integral gain would lead to a high chance for the EEV–evaporator control loop to become unstable, while slowing down the rate of degree of superheat (DS) signal transfer by increasing EEV's time constants may help mitigate system's operational instability. The results confirmed that the operating characteristics of an expansion valve in a refrigeration system could impact its operational stability.     

A hybrid solar air conditioner: Experimental investigation

The removal of moisture from the supply air using conventional air conditioners (A/C) represents a considerable portion of the air conditioning load in hot and humid regions. Desiccant assisted A/Cs are used to address this issue. In this work, the performance of a hybrid A/C, which consists of a desiccant wheel, an enthalpy wheel, and a vapor compression cycle (VCC), is investigated experimentally. The effect of the process air stream's temperature and humidity, and the effect of the ventilation rate on the hybrid A/C performance are investigated. The experimental results show that the hybrid A/C is more effective than the standalone VCC in maintaining the indoor conditions within the comfort zone. The simulation of the complete hybrid solar A/C that uses a concentrating photovoltaic/thermal collector shows that a system coefficient of performance higher than unity is possible.     

Condensate retention on a louver-fin-and-tube air cooling coil

This paper presents a study of condensate retention on a louver-fin-and-tube air cooling coil, which is commonly used in air conditioning (A/C) systems. Compared to previously related work focusing on the influence of condensate retention on the heat and mass transfer between air and a cooling coil, the present study emphasizes the impacts of operating parameters on condensate retention on a cooling coil. A new method to describe the steady-state condensation has been suggested and a new mathematical model to represent the force balance of retained condensate developed. The mass of condensate retained has been measured experimentally under various operating conditions of a direct expansion (DX) air cooling and dehumidification system. The influences of air dry-bulb temperature, moisture content and Reynolds Number on condensate retention are discussed. The model developed relates the mass of condensate retained to condensing rate, and is successful in predicting the trends of condensate retention under normal operating conditions for air cooling applications.     

室内相对湿度对空调器性能及舒适性的影响

在室外工况及室内干球温度相同,室内相对湿度不同的条件下,实验分析空调器的性能参数的变化情况。实验结果表明,室内相对湿度对空调器的能效比几乎没有影响,但相对湿度较低时空调器的出风温度也较低,相对湿度与温度合理耦合可以实现同等热舒适条件下快速制冷且降低空调器能耗的目的。     

基于分布式温度采集技术的中央空调节能运行方案设计

针对楼宇中央空调系统运行温度智能控制存在的问题,提出了一种现场可编程门阵列FPGA控制的数字式温湿度传感器对各楼层、多点进行温度实时巡检,对温度、湿度进行定时采集,测量结果通过RS485总线传输至主机,分析计算后输出控制指令对风机盘管进行变频控制.对水系统的温度和流量参数进行采集,通过工控机对空调负荷与末端负荷进行匹配...     

新疆某办公楼蒸发冷却空调系统应用及效益分析

本文旨为干燥地区办公建筑蒸发冷却空调系统的设计、设备选型、调试、运行的全过程提供基础理论支持,从系统设计、设备选型入手,对系统调试,应用情况及经济,节能效益进行分析。还提出了解决系统水流量异常的合理方案,且测得夏季室内温湿度符合设计要求时,温度应在24℃~27℃,湿度应在45%~70%,方可满足室内舒适性要求,维持良好的室内空气品质。本系统相较于传统空调系统,其初期投资高出10万元,但运行费用可节省32.20%,增量分析回收时间为2.04年;耗水量可节省60.29%,耗电量可节省27.4%,可节约标准煤35.84吨。     

Analytical solution for the simultaneous heat and mass transfer problem in air washers

An analytical solution approach for the simultaneous heat and mass transfer problem in air washers operating as evaporative coolers is presented. A one-dimensional model using the coupled mass and energy balance equations in the air washer is presented. Then, starting from a linear approach for the experimental curve of the air saturation, an analytical solution for the model was derived. The solution showed an excellent agreement with the available results found in the literature. The influence of several important parameters for the cooling process such as temperature and ambient air humidity, air flow rate and feeding water temperature, in the air cooling rate was investigated. The efficacy of the process can be greatly increased by reducing the cooling water temperature and the applied air flow rate. The analytical solution can be easily included into the models used for simulating desiccant air-conditioning systems operating in conjunction with air washers.     

民政专用纳米光催化空气净化消毒机的设计与实现

为解决民政行业殡仪场所空气污染问题,研制了一种专用于殡仪场所空气净化的消毒机.以滤网过滤技术、活性炭吸附技术、纳米光催化技术为设计基础,应用改进混沌优化算法与智能PID 最优控制算法设计了智能风面控制系统,优化设计了空气消毒机的结构参数,最后制作样机.结果表明,设计的纳米TiO₂光催化空气净化消毒机具有良好的消毒能力且操作简便,对环境空气具有良好的消毒净化功能,可替代紫外线用于殡仪场所空气净化和消毒.     

Calculations of the temperature and flow field in a room ventilated by a radial air distributor

In ventilated or air-conditioned rooms optimal conditions of temperature, humidity and air velocity are required. In the present study the behaviour of a jet emerging from a radial plate distributor and the resulting air flow in the room were investigated. To predict the behaviour of the air flow a numerical scheme was used to solve the conservation equations for mass, momentum and energy with the k/ε-turbulence model. The numerical results are compared with available experimental data.     

多媒体教室内环境的CFD模拟研究

目前CFD软件在室内环境的研究中应用得越来越广泛,本文结合理论计算对某多媒体教室的送风进行了详细的模拟分析,得出了室内环境的基本参数：温度、湿度、速度、舒适度和空气龄等情况,对多媒体教室的最优送风设计奠定了基础。     

某办公楼中庭空调系统末端形式的对比分析

在某办公楼中庭采用常规全空气空调系统和温湿度独立控制空调系统(THIC)2种方案时,对室内的空调冷负荷及对应的送、回风参数进行计算和对比,进而对室内气流组织的差异进行模拟分析,并从热舒适性、空气品质等角度对模拟结果进行讨论。结果显示,采用THIC空调方式比常规全空气空调系统的室内气流速度场、温度场更加均匀,人员活动区域的热舒适、空气品质更好,而且可以显著降低高大空间的空调区域,相对于常规全空气空调系统,可降低空调冷负荷25%左右。     

基于RBF神经网络的商场建筑空调能耗预测

商场建筑夏季空调能耗占总能耗的50％以上,鉴于空调能耗较高,对空调能耗进行预测有利于提升运行经济性.针对商场建筑空调系统非线性、多变量等问题,提出一种基于RBF神经网络空调系统能耗预测模型.该方法将日最高温度、日最低温度、日平均温度、日最高湿度、日最低湿度、日平均风速和空调能耗作为RBF神经网络的输入,建立空调系统能耗...     

Generalized model for the simulation of food refrigeration. Development and validation of the predictive numerical method

A generalized mathematical model was developed to simulate food refrigeration in air. The model takes into account surface water evaporation. It allows food physical properties to be considered as functions of temperature and/or composition, while providing means for including internal heat generation, composite materials (for instance, flesh and skin) and time-varying external temperature and humidity. Wetted surfaces and packaging can also be accounted for by the model, which can be used for spheres, infinite or finite cylinders, slabs. The numerical method was developed using the Crank-Nicolson scheme, and compared with exact analytical solutions as well as with experimental data on the refrigeration of various foods.     

办公建筑空调室内设计参数选取的研究

文章以PMV-PPD指标作为衡量室内热舒适的指标,以广州地区某办公建筑为例,分析了温度、相对湿度、空气流速对空调能耗的影响。研究表明：在相同人体热舒适条件下,相对湿度大、温度低的室内设计参数组合需要的空调能耗比相对湿度小、温度高的室内设计参数组合需要的空调能耗小。根据研究结果,文章提出了在相同人体热舒适条件下,室内设计参数选取的方法,可供工程设计人员参考。     

基于参量阵系统的神经网络PID逆控制及仿真研究

针对参量阵系统这样一个强非线性声学系统的声音输出扭曲问题,提出了神经网络自适应逆控制策略。首先介绍了参量阵系统的逆模型,并由参量系统模型和它的逆模型构成一个伪线性系统。控制系统中的BP网络自适应调节PID（ProportionalIntegralDerivative）的三个控制参数,并利用PID控制参量阵系统。通过对MATLAB建立的复合逆控制模型进行仿真研究。仿真结果表明：神经网络PID控制具有较高的控制精度和适应性,可以获得良好的控制效果。