SPC and Kalman filter-based fault detection and diagnosis for an air-cooled chiller

Buildings worldwide account for nearly 40%of global energy consumption.The biggest energy consumer in buildings is the heating,ventilation and air conditioning(HVAC)systems.In HVAC systems,chillers account for a major portion of the energy consumption.Maintaining chillers in good conditions through early fault detection and diagnosis is thus a critical issue.In this paper,the fault detection and diagnosis for an air-cooled chiller with air coming from outside in variable flow rates is studied.The problem is difficult since the air-cooled chiller is operating under major uncertainties including the cooling load,and the air temperature and flow rate.A potential method to overcome the difficulty caused by the uncertainties is to perform fault detection and diagnosis based on a gray-box model with parameters regarded as constants.The method is developed and verified by us in another paper for a water-cooled chiller with the uncertainty of cooling load.The verification used a Kalman filter to predict parameters of a gray-box model and statistical process control(SPC)for measuring and analyzing their variations for fault detection and diagnosis.The gray-box model in the method,however,requires that the air temperature and flow rate be nearly constant.By introducing two new parameters and deleting data points with low air flow rate,the requirement can be satisfied and the method can then be applicable for an air-cooled chiller.The simulation results show that the method with the revised model and some data points dropped improved the fault detection and diagnosis(FDD)performance greatly.It can detect both sudden and gradual air-cooled chiller capacity degradation and sensor faults as well as their recoveries.

Air interaction around outdoor air-cooled condensers

In order to increase cooling or heating efficiency,a porous computational fluid dynamics（CFD）model is employed to predict the thermo-fluid status and optimize the placement of outdoor units.A full scale model is established to validate the accuracy of CFD simulation in terms of velocity and temperature distributions.The comparison between the measurement and the simulation shows a good agreement.By evaluating the condensers＇ sucked air temperature with CFD for three units installed in a row,it is found that the minimum separation distance among neighboring units is 0.2 m;a vertical wall should be apart from the unit line by at least 0.8 m;and large different operating pressures among units do not impact the flow rate and the heat transfer of the other units meaningfully.

Precipitation of α_2 Phase in α+β Solution-Treated and Air-cooled Ti-Al-Sn-Zr-Mo-Si-Nd Alloys

A series of Ti-Al-Sn-Zr-Mo-Si-Nd alloys with various content of Al were solution treated in α+β phase field and air-cooled. The precipitation of a2 phase in cooling was investigated by transmission electron microscopic analysis The precipitation characteristic of α2 phase was discussed. The precipitation of α2 phase would proceed by the nucleation and growth of α2 phase dependent on the diffusion of Al atoms. And a comparison on the difference of precipitation of α2 phase was carried out under the conditions of air-cooling and quenching in water. The investigation showed that the air-cooling and even quenching could supply enough time for the precipitation and growth of α2 phase when Al content reached a certain value even though far away from the stoichiometric composition of Ti3Al.

Microstructure and properties of rheo-HPDC Al-8Si alloy prepared by air-cooled stirring rod process

A new and effective semisolid slurry preparation process with air-cooled stirring rod(ACSR)is reported,in which the compressed air is constantly injected into the inner cavity of a stirring rod to cool the melt.The slurry of a newly developed high thermal conductivity Al?8Si alloy was prepared,and thin-wall heat dissipation shells were produced by the ACSR process combined with a HPDC machine.The effects of the air flow on the morphology ofα1-Al particles,mechanical properties and thermal conductivity of rheo-HPDC samples were studied.The results show that the excellent slurry of the alloy could be obtained with the air flow exceeding3L/s.Rheo-HPDC samples that were produced with the air flow of5L/s had the maximum UTS,YS,elongation,hardness and thermal conductivity of261MPa,124MPa,4.9%,HV99and153W/(m·K),respectively.Rheo-HPDC samples show improved properties compared to those formed by HPDC,and the increasing rates of UTS,YS,elongation,hardness and thermal conductivity were20%,15%,88%,13%and10%,respectively.

Effect of Chromium on CCT Diagrams of Novel Air-Cooled Bainite Steels Analyzed by Neural Network

The quantitative effects of chromium content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels were analyzed using artificial neural network models. The results showed that the chromium may retard the high and medium-temperature martensite transformation.

Feasibility Analysis of Back-Pressure Steam Feeding Water Pump for Direct Air-Cooled Unit

As the performance of an air-cooled condenser is apt to be affected by the fluctuating ambient condition, some difficulties are brought to the use of a steam feeding water pump in an air-cooled unit. This paper introduces a new design of for steam feeding the water pump of an air-cooled unit using the back-pressure steam turbine as the prime motor. Using variable condition analysis on a 600 MW direct air-cooled unit, and with consideration of the effect on the ambient conditions, the feasibility, economy, and adaptability of the design are verified.

Application of Air-cooled Blast Furnace Slag Aggregates as Replacement of Natural Aggregates in Cement-based Materials：A Study on Water Absorption Property

The influence of air-cooled blast furnace slag aggregates as replacement of natural aggregates on the water absorption of concrete and mortar was studied, and the mechanism was analyzed. The interface between aggregate and matrix in concrete was analyzed by using a micro-hardness tester, a laser confocal microscope and a scanning electron microscope with backscattered electron image mode. The pore structure of mortar matrixes under different curing conditions was investigated by mercury intrusion porosimetry. The results showed that when natural aggregates were replaced with air-cooled blast furnace slag aggregates in mortar or concrete, the content of the capillary pore in the mortar matrix was reduced and the interfacial structure between aggregate and matrix was improved, resulting in the lower water absorption of mortar or concrete. Compared to the concrete made with crushed limestone and natural river sand, the initial absorption coefficient, the secondary absorption coefficient and the water absorption capacity through the surface for 7 d of the concrete made from crushed air-cooled blast furnace slag and air-cooled blast furnace slag sand were reduced by 48.9%, 52.8%, and 46.5%, respectively.

Physical Properties of Crushed Air-cooled Blast Furnace Slag and Numerical Representation of Its Morphology Characteristics

Physical properties and geometrical morphologies of crushed air-cooled blast furnace slag （SCR） and crushed limestone （LCR） were comparatively investigated. The shape, angularity, surface texture and internal pore structure of aggregate particles for different size and gradation were numerically represented by sphericity （ψ） and shape index （SI）, angularity number （AN）, index of aggregate particle shape and texture （IAPST）, porosity and pore size, respectively. The results show that SCR is a porous and rough aggregate. Apparent density, void, water absorption and smashing index of SCR are obviously higher than those of LCR with the same gradation, respectively. However, bulk density of SCR is lower than that of LCR with the same gradation. SI, AN, IAPST and porosity of SCR are obviously higher than those of LCR with the same gradation, respectively. The smaller particle size of SCR, the larger of its AN, IAPST and porosity.

Thermodynamic Simulation of CCP in Air-Cooled Heat Pump Unit with HFCs and CO₂Trans-Critical

The exergy analysis and finite time thermodynamic methods had been employed to analyze the compound condensation process (CCP). It was based on the air-cooling heat pump unit. The cooling capacity of the chiller unit is about 1 kW, and the work refrigerant is R22/R407C/R410A/CO2. The MATLAB/SIMULINK software was employed to build the simulation model. The thermodynamic simulation model is significant for the optimization of parameters of the unit, such as condensation and evaporation temperature and mass flow of the sanitary hot water and size of hot water storage tank. The COP of the CCP of R410A system is about 3% - 5% higher than the CCP of the R22 system, while CCP of the R407C system is a little lower than the CCP of R22 system. And the CCP of CO2 trans-critical system has advantage in the hot supply mode. The simulation method provided a theoretical reference for developing the production of CCP with substitute refrigerant R407C/R410A/CO2.

Effect of Crushed Air-cooled Blast Furnace Slag on Mechanical Properties of Concrete

Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag（SCR） and crushed limestone（LCR） with 5-20 mm and 20-40 mm gradation were represented by numerical parameters including angularity number（AN） and index of aggregate particle shape and texture（IAPST）.The effect of mix aggregates containing SCR on compressive strength and splitting tensile strength of concrete was investigated.Fracture characteristics of concrete,interfacial structure between aggregates and matrix were analyzed.The experimental results show that porous and rough SCR increases contact area with matrix in concrete,concave holes and micro-pores on the surface of SCR are filled by mortar and hydrated cement paste,which may increase interlocking and mechanical bond between aggregate and matrix in concrete.SCR can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with LCR.The increase of AN and IAPST of aggregate may enhance mechanical properties of concrete.

Quantitative analysis of Ni effect on CCT diagrams of novel air-cooled bainite steels using artificial neural network models

The quantitative effect of Ni content on continuous cooling transformation （CCT） diagrams of novel air-cooled bainite steels was analyzed using artificial neural network models. The results showed that Ni may retard the high- and medium-temperature transformation and martensite transformation. The results conform to the materials science theories.

The Experimental Investigation of Recirculation of Air-Cooled System for a Large Power Plant

The paper introduces thermal buoyancy effects to experimental investigation of wind tunnel simulation on direct air-cooled condenser for a large power plant. In order to get thermal flow field of air-cooled tower, PIV experiments are carried out and recirculation ratio of each condition is calculated. Results show that the thermal flow field of the cooling tower has great influence on the recirculation under the cooling tower. Ameliorating the thermal flow field of the cooling tower can reduce the recirculation under the cooling tower and improve the efficiency of air-cooled condenser also.

Influence of thermal flow field of cooling tower on recirculation ratio of a direct air-cooled system for a power plant

In order to get thermal flow field of direct air-cooled system,the hot water was supplied to the model of direct air-cooled condenser(ACC). The particle image velocimetery (PIV) experiments were carried out to get thermal flow field of a ACC under different conditions in low velocity wind tunnel,at the same time,the recirculation ratio at cooling tower was measured,so the relationship between flow field characteristics and recirculation ratio of cooling tower can be discussed. From the results we can see that the flow field configuration around cooling tower has great effects on average recirculation ratio under cooling tower. The eddy formed around cooling tower is a key reason that recirculation produces. The eddy intensity relates to velocity magnitude and direction angle,and the configuration of eddy lies on the geometry size of cooling tower. So changing the flow field configuration around cooling tower reasonably can decrease recirculation ratio under cooling tower,and heat dispel effect of ACC can also be improved.

Water, Air Emissions, and Cost Impacts of Air-Cooled Microturbines for Combined Cooling, Heating, and Power Systems： A Case Study in the Atlanta Region

The increasing pace of urbanization means that cities and global organizations are looking for ways to increase energy efficiency and reduce emissions. Combined cooling, heating, and power （CCHP） systems have the potential to improve the energy generation efficiency of a city or urban region by providing energy for heating, cooling, and electricity simultaneously. The purpose of this study is to estimate the water consumption for energy generation use, carbon dioxide （CO2） and NOx emissions, and economic impact of implementing CCHP systems for five generic building types within the Atlanta metropolitan region, under various operational scenarios following the building thermal （heating and cooling） demands. Operating the CCHP system to follow the hourly thermal demand reduces CO2 emissions for most building types both with and without net metering. The system can be economically beneficial for all building types depending on the price of natural gas, the implementation of net metering, and the cost structure assumed for the CCHP system. The greatest reduction in water consumption for energy production and NOx emissions occurs when there is net metering and when the system is operated to meet the maximum yearly thermal demand, although this scenario also results in an increase in greenhouse gas emissions and, in some cases, cost. CCHP systems are more economical for medium office, large office, and multifamilv residential buildings.

Performance of a Solar-Biomass Adsorption Chiller

A dynamic model is presented for a chiller working with a composite adsorbent(silica activated carbon/CaCl2)–water pair in a solar-biomass cooling installation.The main objective is determining a link between two possible evaporator configurations and the refrigerator’s performances.The two considered evaporators work at different pressure levels.The related time evolution profiles of temperature,pressure and water content are studied.Moreover,the effects of hot water inlet temperature and cooling water inlet temperature on the specific cooling capacity(SCP)and coefficient of performance(COP)are predicted by means of numerical simulations.The results show that an increase in the temperature of hot water and a decrease in the temperature of the cooling water allow an increase in COP and SCP.In particular,for a hot water inlet temperature of 85°C and a cooling water inlet temperature of 40°C,the COP and Qev are 0.67 and 4.3 kW,respectively.

Impact of Numerous Beds Operating Conditions for Enhancing the Performance of a Solar Heat-Supported Adsorption Chiller

Thermal adsorption cooling systems have gained significant attention due to their potential for energy savings and eco-environmental impact. An analytic investigation of the heat transfer inside an adsorption chiller with various bed silica gel-water pairs is presented. A comprehensive model has been designed to accurately predict the correlation between the overall performance of the proposed chiller system and the functional and structural condition of the building. This model takes into account various factors such as temperature, humidity, and air quality to provide a detailed analysis of the system’s efficiency. At least 20 collectors consisting of a 34.4 m area (each) with a full-cycle time of 480 seconds are essential to improper run conditions. It is necessary to adjust the optimum cycle time for optimal performance. During the investigation, the base condition shows that the cooling capacity is 14 kw, 0.6 COPcycle, and 0.35 COPsolar at noon. Also, conduct a thorough investigation into the chiller’s performance under varying cooling water supply temperatures and various chilled water flow rates.

Optimization of Chiller Loading Problem Using Improved Golden Jackal Optimization Algorithm Leads to Reduction in Energy Consumption

This paper proposes a modified golden jackal optimization(IGJO)algorithm to solve the OCL(which stands for optimal cooling load)problem to minimize energy consumption.In this algorithm,many tools have been developed,such as numerical visualization,local field method,competitive selectionmethod,and iterative strategy.The IGJO algorithm is used to improve the research capabilities of the algorithm in terms of global tuning and rotation speed.In order to fully utilize the effectiveness of the proposed algorithm,three famous examples of OCL problems in basic ventilation systems were studied and compared with some previously published works.The results show that the IGJO algorithm can find solutions equal to or better than other methods.Underpinning these studies is the need to reduce energy consumption in air conditioning systems,which is a critical business and environmental decision.The Optimal Chiller Load(OCL)problem is well-known in the industry.It is the best method of operation for the refrigeration plant to satisfy the requirement of cooling.In order to solve the OCL problem,an improved Golden Jackal optimization algorithm(IGJO)was proposed.The IGJO algorithm consists of a number of parts to improve the global optimization and rotation speed.These studies are intended to address more effectively the issue of OCL,which results in energy savings in air-conditioning systems.The performance of the proposed IGJO algorithm is evaluated,and the results are compared with the results of three known OCL problems in the ventilation system.The results indicate that the IGJO method has the same or better optimization ability as other methods and can improve the energy efficiency of the system’s cold air.

某商业建筑高效制冷机房运行数据分析

制冷机房作为系统工程,其系统运行参数的变化(如冷冻水供回水温差)会对机房内不同设备的能效产生不同的影响,机房整体能效最优是机房节能运行的重要目标。针对现有建筑运行数据存储较多但对其分析较少的现状,采用数据挖掘技术,对某商业建筑制冷机房实际运行能耗、能效进行统计计算,并将其与负荷率、供回水温度、供回水温差等变量的相关性展开分析,揭示机房能效与各变量间的内在联系。研究结果显示:制冷机房单位面积制冷能耗约为16~17 kW·h/(m^(2)·a),冷水机组能耗占80%以上,冷水机组的能效表现主导了机房的整体能效表现,机房系统能效比(COPs)高于设计值6.06 kW·h/kW·h,达到了预期目标。机房整体能效与室外气温及负荷率、冷冻(却)水供回水温差、冷却水进水出水温度呈负相关关系,机房整体能效与冷冻水供回水温度主要呈正相关关系。冷水机组运行COP与机组负荷率和冷却水回水温度呈现一定相关性,且基本符合机组定冷却水温和AHRI变冷却水温工况下的选型曲线。

某酒店制冷机房运行策略优化

对华东地区某酒店制冷机房运行策略进行了优化,利用能耗模拟软件对多种运行方案进行了仿真分析。结果表明:原方案仅对冷水泵采用变频控制,制冷机房能效比为4.62;优化方案1采取传统变频方式,对冷水泵、冷却水泵、冷却塔风机采用变频控制,制冷机房能效比达到5.32,与原方案相比提升了15.1%;优化方案2通过对冷水机组、冷水泵、冷却水泵、冷却塔风机进行优化控制,制冷机房能效比为5.48,与原方案相比能效比提升了18.6%,且每年可减少约79 t碳排放量,节能效果显著。

磁悬浮变频冷水机组运行特性

为深入研究磁悬浮冷水机组在不同工况下的运行特性,采用集中参数法稳态模型,建立磁悬浮变频离心压缩机模型、冷凝器模型、电子膨胀阀模型和蒸发器模型为一体的冷水机组数学模型,对比分析磁悬浮冷水机组和传统冷水机组在不同负荷率、不同冷却水温度和不同冷冻水流量下的冷水机组效率。结果表明:磁悬浮冷水机组在低负荷率下效率较高,而传统冷水机组效率最高点出现在额定工况;冷却水进水温度由30℃降低至20℃时,磁悬浮冷水机组和传统冷水机组性能系数C_(OP)均会升高,但磁悬浮冷水机组的C_(OP)提高幅度大于传统冷水机组,当系统负荷率P LR为0.6时,传统冷水机组C_(OP)提高14%,磁悬浮冷水机组C_(OP)提高68%;冷冻水流量由150 m^(3)/h降低至60 m^(3)/h时,传统冷水机组效率提高1.4%,磁悬浮冷水机组效率提高4.9%。模拟结果可为磁悬浮冷水机组的运行调控策略提供一定的理论参考。