温湿度独立控制空调系统的现状分析

介绍了温湿度独立控制空调系统的基本原理和相关设备,综述了该系统在节能方面的优势,并且与常规中央空调系统做了比较,通过总结该系统目前研究中存在的一些问题,对未来温湿度独立控制空调系统的发展提出了展望.     

Rapid humidity regulation by mixing of dry and humid gases with feedback control for PEM fuel cells

Humidity regulation in fuel cells utilizing bulk mass transfer and membrane-based methodologies have drawbacks and limitations, which are undesirable during fuel cell operation. In this work, we demonstrate a rapid and nearly accurate humidity control by mixing of dry and humidified gas streams for tracking predefined relative humidity set points. The humidity responses from the mixed stream could track various relative humidity profiles when coupled with feedback to PI and PID control algorithms. A discussion on the usefulness of this method for controlling the humidification of fuel cell inlet gases, its effectiveness and limitations under high frequency operation are provided.     

The diffusion overpotential increase and appearance of overlapping arcs on the Nyquist plots in the low humidity temperature test conditions of polymer electrolyte fuel cell

We have investigated cell voltage characteristics and AC impedance characteristics of polymer electrolyte fuel cells (PEFCs) at various humidity temperatures for H₂/O₂ and H₂/air test conditions (current density: 200, 400, and 600 mA cm⁻², cell temperature: 80 °C, humidity temperature at respective electrodes: 40, 50, 60, and 70 °C). The diffusion overpotential increases with decreasing humidity in the low humidity temperature region such as 40 and 50 °C and the Nyquist plots obtained from AC impedance measurements show a small arc superposed on an elliptic arc in the low frequency region. The diameter of this small arc increases with decreasing humidity temperature from 50 to 40 °C or with increasing current density. These results suggest that oxygen transport across the ionomer film in the catalyst layer is significantly reduced in the low humidity condition, which causes a decrease in cell voltage, increase in diffusion overpotential, the appearance of overlapping arcs (two separate arcs) in the lower frequency region on the Nyquist plots, and the increase of mass transport resistance from Nyquist plots.     

大湿度低温环境对风力发电场的影响

在我国北方地区的风电场,秋冬季的高湿度寒冷气候对风力发电场运行影响比较大。分析了大湿度低温条件下定桨距风力发电机组功率特性变化,总结了国外大湿度低温环境对风电场的影响,提出了针对大湿度低温条件下风力发电机组设计和风机排布所应采取的针对性措施。     

Simulation of façade and envelope design options for a new institutional building

This paper presents a simulation case study of façade and envelope preliminary design options for the new Engineering building of Concordia University in Montreal. A major principle of the analysis was to create a high quality building envelope in order to optimally control solar gains, reduce heating and cooling energy demand and reduce electricity consumption for lighting, while at the same time maintain a comfortable and pleasant indoor environment. The stated approach of the design team was to aim for an energy-efficient building, employing innovative technologies and integrating concepts such as daylighting and natural ventilation. Detailed energy simulations were therefore performed from the early design stage, in order to present recommendations on the choice of façade, glazings, shading devices, lighting control options, and natural ventilation. Integrated thermal studies, a daylighting analysis and the impact of the above on HVAC system sizing were considered. Simulation results showed that, using an optimum combination of glazings, shading devices and controllable electric lighting systems, the energy savings in perimeter spaces can be substantial. Perimeter heating could be eliminated if a high performance envelope is used. The building is currently being commissioned.     

基于燃料电池膜水分传递特性研究的温度与湿度控制

质子交换膜燃料电池(PEMFC)中保持膜的适度湿润性非常重要.模拟了质子交换膜的水环境,采用西门子S7-300PLC和力控组态软件设计了温度湿度控制系统;应用PID调节原理分别控制三种不同空气流量(1、6、10 g·s-1)情况下空气加热器和水加热器的温湿度.由数据分析可得到结论:1 g·s-1流量引起的湿度波动较大,10 g·s-1流量在高温高湿情况下出现异常.     

自然通风条件下建筑围护结构及室内空气的温度计算

建立太阳照射和自然通风条件下建筑与室内、外环境的空气平衡方程与热平衡方程,以及沿围护结构厚度的非稳态一维导热方程,求解得到建筑围护结构和室内空气的温度。选取广州夏季某一天的气象参数,计算围护材料分别采用钢筋混凝土、灰砂砖砌体、浮石混凝土、橡木和平板玻璃情况下,从7时至19时一单室建筑围护结构及室内空气的温度。     

Finite-difference prediction of transient indoor temperature and related correlation based on the building time constant

A numerical procedure for the calculation of the transient indoor temperature in buildings is developed. The procedure is based on an implicit finite-difference solution of a closed set of differential equations, which express the indoor energy balance and the transient heat conduction in all elements of the building envelope. Using the above procedure, calculations are carried out for 21 types of buildings with 18 and 10 different kinds of wall and roof constructions, respectively, i.e. the total number of building cases examined is 21 × 18 × 10 = 3780 with floor areas ranging from 30 m² to 300 m². It is found that buildings of different construction characteristics and sizes but with the same time constant, respond in a similar way under the same outdoor temperature variation. Based on this similarity, a correlation is developed which expresses, under periodic conditions, the indoor temperature variation in terms of the building time constant and the outdoor temperature characteristics. The correlation contains nine coefficients, the values of which are different for different ranges of the building time constant.     

Effect of humidity of reactants on the cell performance of PEM fuel cells with parallel and interdigitated flow field designs

This study investigates the effects of the relative humidity (RH) of the reactants on the cell performance and local transport phenomena in proton exchange membrane fuel cells with parallel and interdigitated flow fields. A three-dimensional model was developed taking into account the effect of the liquid water formation on the reactant transport. The results indicate that the reactant RH and the flow field design all significantly affect cell performance. For the same operating conditions and reactant RH, the interdigitated design has better cell performance than the parallel design. With a constant anode RH = 100%, for lower operating voltages, a lower cathode RH reduces cathode flooding and improves cell performance, while for higher operating voltages, a higher cathode RH maintains the membrane hydration to give better cell performance. With a constant cathode RH = 100%, for lower operating voltages, a lower anode RH not only provides more hydrogen to the catalyst layer to participate in the electrochemical reaction, but also increases the difference in the water concentrations between the anode and cathode, which enhances back-diffusion of water from the cathode to the anode, thus reducing cathode flooding to give better performance. However, for higher operating voltages, the cell performance is not dependent on the anode RH.     

Effects of temperature and humidity on the cell performance and resistance of a phosphoric acid doped polybenzimidazole fuel cell

Performance and electrochemical impedance spectroscopy (EIS) tests were performed at different temperatures and humidity levels to understand the effects of temperature and humidity on the performance and resistance of a PBI/H₃PO₄ fuel cell.The results of the performance tests indicated that increasing the temperature significantly improved the cell performance. In contrast, no improvement was observed when the gas humidity was increased. On the other hand, the EIS results showed that the membrane resistance was reduced for elevated temperatures. This development can be interpreted by the increase in membrane conductivity, as reflected by the Arrhenius equation. As the formation of H₄P₂O₇ and the self-dehydration of H₃PO₄ start around 130-140 °C, in PBI, they increase the membrane resistance at temperatures that are higher than 130 °C. In addition, the membrane resistance was reduced for elevated gas humidity levels. This is because an increase in humidity leads to an increase of the membrane hydration level.The resistance of the catalyst kinetics mainly contributes to the charge transfer resistance. However, under certain conditions, the interfacial charge transfer resistance is also important. It was concluded that the gas diffusion is the main contributor to the mass transfer resistance under dry conditions while it is the gas concentration under humid conditions.     

Effect of load, temperature and humidity on the pH of the water drained out from H2/air polymer electrolyte membrane fuel cells

The effect of the operating conditions, e.g., load, temperature, relative humidity (RH), and the MEA's aging condition on the pH of the water drained out from the cathode and anode sides of a H₂/air PEM fuel cell was studied. Also the effect of the pollutants’ existence in natural air on the measured pH and the performance of the fuel cell was investigated. pH values as low as 1 were measured for the water drained out from the cathode side under a low temperature–low RH condition. Increasing the load, temperature or RH value resulted in an increase of the measured pH except for the low temperature–low RH condition where increasing the load resulted in a decrease in the measured pH. On the other hand, the pH value of the water drained out from the anode side was around 4 under the same low temperature–low RH condition. Aging of the MEA at 90 °C and RH of 100% for at least 30 h resulted in low measured pH values for the water drained out from the cathode side. The polarization behaviors of the cathode under these different conditions were measured and correlated to the pH change and the performance of the MEA. Measuring the pH using a flow pH meter for the water droplets drained out from the cathode side can be used as an alarm for the onset of the chemical degradation of the Nafion membrane.     

简析中央空调系统节能的控制方法与发展趋势——基于江中药业综合制剂大楼中央空调节能改造工程案例

基于江中药业综合制剂大楼中央空调节能改造工程案例,以工程改造的节能技术措施和效果为分析对象,从系统节能的控制方法的角度对中央空调系统节能的发展转变进行剖析。通过调查和数据收集,对目前常用的2种中央空调系统(定流量控制型、变频PID控制型)节能方法的优缺点做了比较分析,展示了各种中央空调系统节能发展转变的特色,提出了中央空调系统节能发展方式、实现高效节能的建议。     

Comparative study of room temperature control in buildings with and without the use of PCM in walls

The concept of thermal energy storage in building gains a specific importance in the present energy scenario related to energy consumption and indoor thermal comfort. The material used to store the thermal energy which undergoes a phase change referred as PCM and it is considered as a possible solution for reducing energy consumption in the building by storing and releasing heat within a certain temperature range; it raises the building inertia and also stabilizes indoor air temperature fluctuations. The room temperature is controlled by imposing PCM inside the walls. An attempt has been made to compare room air temperature with and without the use of PCM inside the walls of constructed modular building unit. The PCM imposed modular building shows the reduced temperature fluctuations in room, the PCM absorbs and liberates excess heat which is gained from the outer side of the room and maintains constant inner room temperature. The PCM imposed walls of modular building unit have an ability to reduce 10–30% of heat load in comparison with the plain wall. The results showed that reduction in room temperature is about 2–4°C and it has been concluded that the PCM imposed modular building unit has more energy saving opportunities than normal modular building unit.     

The effect of IGFC warm gas cleanup system conditions on the gas–solid partitioning and form of trace species in coal syngas and their interactions with SOFC anodes

The U.S. Department of Energy is currently working on coupling coal gasification and high temperature fuel cell to produce electrical power in a highly efficient manner while being emissions free. Many investigations have already investigated the effects of major coal syngas species such as CO and H₂S. However coal contains many trace species and the effect of these species on solid oxide fuel cell anode is not presently known. Warm gas cleanup systems are planned to be used with these advanced power generation systems for the removal of major constituents such as H₂S and HCl but the operational parameters of such systems is not well defined at this point in time. This paper focuses on the effect of anticipated warm gas cleanup conditions has on trace specie partitioning between the vapor and condensed phase and the effects the trace vapor species have on the SOFC anode. Results show that Be, Cr, K, Na, V, and Z trace species will form condensed phases and should not effect SOFC anode performance since it is anticipated that the warm gas cleanup systems will have a high removal efficiency of particulate matter. Also the results show that Sb, As, Cd, Hg, Pb, P, and Se trace species form vapor phases and the Sb, As, and P vapor phase species show the ability to form secondary Ni phases in the SOFC anode.