Numerical simulation of a solar-assisted ejector air conditioning system with cold storage

Indoor space cooling represents a large potential for solar energy use due to the relative coincidence between energy availability and cooling demand. Solar-assisted air conditioning (AC) applications emerged with the development of high efficiency solar collectors. Energy storage (hot or cold) must be implemented for solar-assisted AC applications when cooling demand is present during intervals without available solar energy and also for cooling capacity optimisation (“peak shaving”).The present paper analyses a solar-assisted ejector cooling system with cold storage. Simulations were carried out over one year considering climatic data for a hot location (Béchar, Algeria) and the performance of the system was assessed for a set of design conditions. Effects of cold storage upon comfort conditions and energy demand were evaluated. Maximum room temperature and overall interval of time during which the room temperature exceeded the set-point value were the parameters used to quantify system performance. It was found that cold storage improved comfort conditions compared to a system without storage. For some design conditions it was found that increasing the cold storage capacity did not result in improved comfort conditions. The control algorithm of the system was identified as the cause of this behaviour.     

双联变频空调系统仿真模型的数值研究

本文建立了基于分布参数及两相流理论的双蒸发器热力学模型,对双联变 频空调系统稳态特性及双蒸发器间耦合关系进行仿真研究,为双蒸发器的优化设 计、控制及节能手段的运用提供依据。     

建筑物供暖空调系统节能控制仿真

为了解决暖通空调控制系统的时滞、时变等非线性特征使其控制效果变差的问题,设计了在线辨识对象模型和基于SMITH预估器的自校正控制算法。实现了在线闭环辨识暖通空调特性参数,在获得相应模型后以SMITH预估器补偿时滞参数从而抵消各种消极状况,优化PI控制器加强其鲁棒性能。仿真结果表明所设计的在线辨识模型和控制算法取得了良好的控制效果并具备可行性。     

太阳能热水空调建筑一体化系统

设计了太阳能热水空调建筑一体化系统。该系统由2台冷水水冷机组、2个平板型太阳能集热器单元、1个贮热水箱、2个贮冷水箱和77台供冷终端组成,为海南省昌江县人民医院内儿科77个病房提供空调冷量和洗澡用热水。该系统初投资少,设备利用率高。经过1年的应用运行,取得了节约能源、减少对环境热污染的效果,为更好地推广应用太阳能探索一条新的路子。     

室内燃气火灾的数值模拟研究

通过采用FLUENT软件进行数值模拟计算的方法,将实际房间进行简化和抽象,建立模型用丙烷代替液化石油气作为燃料,来研究室内燃气火灾火焰蔓延过程。运用通用有限速率燃烧模型和大涡模拟模型来模拟750mm×500mm×50mm与750mm×500mm×250mm的箱体,研究了反应热、化学反应速率、火焰面分布以及箱体内各组分质量分数的分布,发现化学反应速率与反应热的变化趋势是一致的,大箱体的火焰面发展较小箱体快并且燃烧充分。     

土壤源地源热泵空调系统的模拟研究

为了研究采取热平衡措施和没有采取热平衡措施的土壤源地源热泵空调系统经过长期运行,对地下土壤的温升影响情况,对西安市某项目土壤源地源热泵空调系统进行了模拟研究。利用TRNSYS软件建立了2个系统模型,一个模型与项目工程空调系统保持一致,采用全年制备生活热水的平衡换热量措施来抵消夏季向土壤中送入的多余热量;另一个模型没有平衡换热量的措施。通过全年和10年期的模拟运行后,采取热平衡措施的系统,其地埋管换热器周围土壤温度温升分别为0.12℃、1.14℃;没有采取热平衡措施的系统,其地埋管周围土壤温度温升分别为0.64℃、3.46℃,对土壤的影响远远大于采取了热平衡措施的系统。     

济南某酒店空调系统节能改造

对济南某星级酒店空调系统改造项目进行节能分析,探讨了对使用年限较长、建筑能耗较大的既有建筑空调系统进行节能改造的必要性。对该酒店空调系统设计的特点、设备配置以及装修配合等方面进行了分析,并就新旧空调方案进行了经济性比较,结果表明改造后空调系统具有较好的经济性和节能性,为同类型酒店的节能改造提供参考。     

Thermoeconomic analysis of an evaporative desiccant air conditioning system

In this paper, a thermoeconomic analysis method based on the first and second law of thermodynamics and applied to an evaporative cooling system coupled to an adsorption dehumidifier, is presented. The main objective is the use of a method called exergetic manufacturing cost (EMC) applied to a system that operates in three different conditions to minimize the operation costs. Basic parameters are the R/P ratio (reactivation air/process air) and the reactivation air temperature. Results of this work show that the minimum reactivation temperature and the minimum R/P ratio corresponds to the smaller EMC. This result can be corroborated through an energetic analysis. It is noted that this case is also the one corresponding to smaller energy loss.     

冰蓄冷空调系统在工业方面的应用分析

随着冰蓄冷技术在我国的研究与推广,工业领域使用该技术的比例也在逐年上升。在归纳冰蓄冷空调技术应用的基础上,选取了啤酒厂、水果冷藏厂、奶制品厂3个典型的工业冰蓄空调系统,对其生产特点、系统连接形式、工况等方面进行分析,以期进一步指导冰蓄冷技术在工业空调系统的应用。     

全空气定风量空调系统变频变风量运行控制与仿真研究

分析了全空气定风量空调系统空调房间的特性,推导出变风量送风方式下空调房间的数学模型,构造PID控制器、模糊控制器和神经网络控制器三种控制器,并利用Matlab软件中的Simulink工具箱对三种控制器的性能进行比较。     

Energy performance of supermarket refrigeration and air conditioning integrated systems

The electricity consumption for air conditioning and refrigerated cases in large supermarkets represents a substantial share of the total electricity consumption. The energy efficiency of supermarkets can be improved by optimising components design, recovering thermal and refrigerating energy, adopting innovative technology solutions, integrating the HVAC system with medium temperature and low-temperature refrigeration plants and, finally, reducing thermal loads on refrigerated cases. This study is aimed at investigating the performance of different lay-out and technological solutions and at finding the potential for improving energy efficiency over the traditional systems in different climates. In the analysis chillers and heat pumps working with R410A, medium temperature systems working with R404A and low-temperature systems working both with R404A and R744 were considered. The investigated solutions enable an annual energy saving higher than 15% with respect to the baseline solution for the considered climates.     

土壤蓄热与土壤源热泵集成系统的数值模拟

结合土壤源热泵技术推广中存在的问题和地下蓄能技术的优点,提出了土壤蓄热与土壤源热泵集成系统及其地下管群换热器的布置方式。并在能量平衡的基础上建立了地下管群换热器蓄热、释热和停止运行的数学模型。通过数值模拟,分析了埋管间距对蓄热与释热的运行特性的影响。     

空调系统能效评估方法与实例分析

介绍几种最近提出的几种能效评估方法,基于某地源热泵系统的运行记录模拟计算了该地源热泵系统的能耗情况,并用这些指标检验和评估了某已有地源热泵系统的性能情况,分析了用不同能效指标评价同一套系统时可能产生结果差异的原因。     

An experimental analysis of cycling in an automotive air conditioning system

In the majority of automotive air conditioning systems, the compressor continuously cycles on and off to meet the steady-state cooling requirements of the passenger compartment. Since the compressor is a belt-driven accessory device coupled to the engine, its cycling rate is directly related to the vehicle speed. The refrigeration system’s losses increase with increasing vehicle speed and thus with increasing compressor cycling. This paper identifies and quantifies individual losses in an automotive vapor-compression refrigeration system during compressor cycling. The second law of thermodynamics, in particular, nondimensional entropy generation, is used to quantify the thermodynamic losses of the refrigeration system’s individual components under steady driving conditions at idle, 48.3 kph (30 mph), and 96.6 kph (60 mph). A passenger vehicle containing a cycling-clutch orifice-tube vapor–compression refrigeration system was instrumented to measure refrigerant temperature and pressure, and air temperature and relative humidity. Data were collected under steady driving conditions at idle, 48.3 kph (30 mph), and 96.6 kph (60 mph). A thermodynamic analysis is presented to determine the refrigeration system’s performance. This analysis shows that the performance of the system degrades with increasing vehicle speed. Thermodynamic losses increase 18% as the vehicle speed changes from idle to 48.3 kph (30 mph) and increase 5% as the vehicle speed changes from 48.3 kph (30 mph) to 96.6 kph (60 mph). The compressor cycling rate increases with increasing vehicle speed, thus increasing the refrigeration system’s losses. The component with the greatest increase in thermodynamic losses as a result of compressor cycling is the compressor itself. Compressor cycling reduces the compressor’s isentropic efficiency, and thus the system’s thermodynamic performance. The individual component losses of the refrigeration system are quantified. The redistribution of these losses is also given as a function of increasing vehicle speed (i.e. increasing compressor cycling). At 96.6 kph (60 mph), the thermodynamic losses, based on the ratio of entropy generation to entropic load, are 0.22, 0.10, 0.07, and 0.02 in the compressor, the condenser, the evaporator-accumulator, and the orifice tube, respectively. The compressor losses dominated the overall system performance. The overall system efficiency could be significantly improved by increasing the compressor’s efficiency. The compressor’s efficiency could be improved by reducing or eliminating cycling, such as could be accomplished by using a variable capacity compressor or by not directly coupling the compressor to the engine. Another way to increase the compressor’s volumetric efficiency during cycling would be to reduce the compressor operating range. This could be accomplished by using two compressors such as is done in two-stage cascade refrigeration systems.     

冰蓄冷空调的经济性分析

主要介绍了冰蓄冷空调系统的两种评价方法,即静态经济评价和动态经济评价。结合工程实例,对冰蓄冷空调与常规空调进行比较分析,论证了采用冰蓄冷空调具有良好的经济效益,同时也分析了影响其经济效益的因素。     

中央空调系统变频节能改造分析

在阐述变频技术节能原理的基础上,结合北京某商贸大厦中央空调系统变频节能改造的实践,进行了效益分析。改造实践证明,对中央空调系统进行冷(热)水循环水泵及冷却水循环水泵变频改造效益明显,改造投资可以在1年左右收回,具有投资前景。     

某商业建筑空调系统运行情况分析及节能改造

文中建筑空调系统空调冷站系统的运行由人工进行启停操作,并且空调冷冻水泵、冷却水泵和冷却塔均由变频控制柜进行"一切三"变频控制,但各设备缺乏相互联系的集中统一变频控制。因此,针对该系统,建立冷站节能控制系统,连接已有的水泵和冷却塔的变频控制柜进行集中控制管理,并连入能源管理系统平台中,为空调冷站提供整体性节能匹配运行控制。