暖通专业在计算 方法 、程序编制和工程应用几方面都取得了显著成绩。下面是由我整理的暖通专业技术论文，谢谢你的阅读。
暖通空调技术与节能
摘要:随着人们生活水平的日益提高,人们生活的节奏逐渐加快及心理压力的不断增大,使得人们的工作生活环境应该予以重视。而在人们的工作生活环境中倡导环保和节能的生活方式越来越重要。本文主要是对暖通空调技术与节能进行分析。
关键词:暖通空调 技术 节能
2009年9月22日,国家主席胡锦涛在联合国气候变化峰会开幕式上发表题为《携手应对气候变化挑战――在联合国气候变化峰会开幕式上的讲话》的重要讲话,郑重承诺今后中国将进一步把应对气候变化纳入经济社会发展规划,并继续采取强有力的 措施 :一是加强节能、提高能效工作;二是大力发展可再生能源和核能;三是大力增加森林碳汇;四是大力发展绿色经济,积极发展低碳经济和循环经济,研发和推广气候友好技术。明确提出了建设生态文明的重大战略任务,强调要坚持节约资源和保护环境的基本国策,坚持走可持续发展道路,在加快建设资源节约型国家。可见节能对于一个国家乃至世界时是多么的重要。本文主要从节能方面浅谈暖通空调技术。
1.室内设计参数
常规情况下,在冬季供暖时,室内计算温度每降低1℃,能耗将减少约5%～10%;在夏季供冷时,室内计算温度每升高1℃,能耗将减少约8%～10%。室内设计参数必须在规定的参数范围内取值。近几年,低温地板辐射采暖系统已经取代散热器采暖,之所以采用这种方式,主要是因为这种方式具有能耗小、舒适性高、容易分户计量、不占用房间使用面积等优点。
2.采暖设计
采暖空调热负荷为12650KW,热指标为。热源由城市热网供给,一次水供回水温度为95/70℃,经热交换后,高温二次水供回水温度为85/60℃,供采暖系统及空气、新风处理机组使用。各类机房、自行车库等设5-8℃的值班采暖,人防掩蔽体采暖设计温度为18℃,厕所为16℃;低温二次水供回水温度为60/50℃,供风机盘管和汽车坡道化雪系统使用,或者化雪系统由于什么原因没有使用。为保证一层室内良好的温度环境,抵挡大门的冷风侵入,在各大门入口处均设置了热空气幕。
以空气为热泵的热源在寒冷地区进行采暖是当前研究的 热点 。因为它和以往的燃煤、燃油、直接用电等取暖方式比较的话,在环保、节能、安全使用,甚至经济等方面有突出的优点,其可推广性也超过了水源、地源热泵。
2.1地板采暖的空气热泵机组容量的选择
机组容量(W)=当地建筑采暖设计负荷()×用户采暖的建筑面积()÷(1-)×0.85-0.9
2.2室外机最好安装在冬季主导风的背风面,应该设置遮雪蓬,机组如果安装在平台上,则底面应抬高至少20cm,以免化霜结冻,机组吸风口距障碍物至少25cm,双机之间距离至少20cm。
2.3地板下埋管的设计
空气热泵作为热源时,供水温度或供回水平均温度应尽可能设计得低些,以使机组效率尽可能高,又由于工程实践证明本机组的供回水温差较少仅2℃-3℃,所以,选择地下埋管时可参照“低温热水地板辐射供暖应用技术规程”( DBJ/T01-49-2000)附录 E-1至 E-3中平均水温35℃一栏,按照地板所需散热量选择间距,然后,将管道直径放大到Φ20/16成间距缩小一档即可。
3.风系统设计
3.1集中空调系统的排风热回收
一直以来,业内人士只是从经济方面的角度来衡量热回收装置的利弊,而环保与节能则被忽视。当今,业内人士考虑的角度有所转变,现在从环保和节能这个角度来衡量热回收装置的利弊。
空调区域排风中的热能量是非常多的,如果把这些热能量加以回收利用,那么环保和节能定会实现。如果新风和排风采用专门独立的管道输送,那么有利于集中热回收装置的设置。新风和排风采用热回收装置进行湿热或者全热交换,节能效果非常明显的表现出来。
3.2空调风系统
(1)有资料显示,以我国南方地区为例,夏季室内设计温度如果每降低1℃或冬季设计温度每升高1℃,其工程投资将增加6%,能耗将增加8%。该数据很明显地说明,适当提高夏季以及降低冬季的室内空气温度,都将起到显著的节能效果。与此同时,为保证室内空气质量以及人们对新鲜空气的需要,现行《采暖通风与空气调节设计规范》对最小新风量作出明确规定,要求建筑满足国家现行有关卫生标准。研究表明,加大新风量能够在一定程度上解决室内空气质量问题,但增加了空调能耗。新风定值必须按照规范来确定,因为新风量对于能耗和人体健康有着非常重要的作用,如果人员密度较大时,新风的供应按人员的密度来进行的话是非常不经济的。我国建筑采用了新风需求控制(检测室内CO2浓度),值得注意的是:新风量变化,排风量随着也发生变化,否则造成负压,可能会适得其反。
(2)暖通设计师对于规范中新风量的规定表示赞同。暖通设计师认为,在目前中央空调清洗不够规范的背景下,加大新风量是必要的。不过,对于室内设计温度的要求,他们却持保留态度。业内人士有这样的一个说法:“如果说节能像一棵树,有很多枝杈可以作为思路,那么,业主方的意见更像那个根。他们的态度,将成为决定暖通专业乃至建筑节能的根本性因素。”业内人士表示,建设方的意见非常重要。
要想增加新风量或者增强风机盘管处理室内回风的能力,风机盘管加新风的新风口应单独或布置在盘管出风口的旁边,而不应该布置在盘管回风吸入口。
(3)房间面积或空间较大、人员较多或有必要集中进行温度控制的空气调节区,其空气调节风系统宜采用全空气空调系统,不宜采用风机盘管系统,以利于集中处理、调节,发挥有利因素,弥补之前产生的问题。
(4)建筑空间高度大于或等于10m、且体积大于时,宜采用分层空调系统。与全室性空调方式比,分层空调系统夏季可以节能30%左右,但是冬季并不节能。通常设计时,夏季的气流组织为喷口侧送,下回风,高大空间上部排风;而冬季一般在底层设置地板辐射或地板送风供暖系统,也可将上部过热的空气通过风道送至房间下部。
(5)多个空气调节区合用1个空气调节风系统,各区负荷变化较大、低负荷运行时间较长,且需要分别调节室内温度,在经济条件允许时,宜采用全空气变风量空气调节系统。设计时应注意:要求采用风机调速改变系统风量,而不能采用恒速风机而改变系统阻力调节;其次,应采取保证最小新风量的措施,避免因送风量减少,造成新风量减少而不满足卫生要求的后果;再者,调节末端送风口风量时,推荐采用串联式风机驱动型末端装置以保证室内的气流分布。
(6)在某些情况下,像屋顶传热量较大、吊顶内发热量较大、吊顶空间较大(此时的吊顶至楼板底的高度超过1.0m),如果采用吊顶内回风,导致空调区域增大、空调耗能上升,这样非常不利于节能。所以对于建筑顶层或者吊顶上部有较大热量、吊顶空间较高时,直接从吊顶回风是不合理的。
4.围护结构
北京市建筑设计研究院原院长、北京市建筑设计研究院顾问总工程师吴德绳认为,暖通专业既然是建筑节能的支柱力量,因此,目光不仅要盯住如何优化暖通空调系统设计,更应该有所转移,在围护结构设计方面重点考虑。
围护结构在节能工作中,扮演着愈来愈重要的角色。所谓围护结构节能,通常是指通过改善建筑物围护结构的热工性能,使得建筑在夏季隔绝室外热量进入室内,冬季防止室内热量泄出室外,以保持室内尽可能接近舒适温度,减少通过辅助设备来达到合理舒适室温的负荷,并最终达到节能的目的,如通过采暖、制冷设备达到节能。
传统住宅建筑的围护结构是普通黏土砖,简单架空屋面和单层玻璃钢窗,它们的传热系数分别为1.96、1.66和6.4。而“节能住宅”的围护结构中外墙和屋面采取了保温措施,外窗采用中空塑钢窗或断热中空铝合金窗,它们的传热系数分别为 1.5、1.0和3.0,使围护结构的节能贡献约占25%。采用能效比高的采暖、空调设备(按照国家标准,房间空调器的能效比:制冷>2.3,采暖>1.9),使采暖、空调设备的节能贡献约占25%,两者相加总体达到节能50%的目标。
据介绍,围护结构的节能设计应该从墙体、窗户、屋面等三个方面考虑。对于设计人员而言,如何处理建筑玻璃幕墙的问题,在业内一直存在很大争议。普通玻璃幕墙是建筑节能不能实现的因素之一。统计数据表明,夏季通过玻璃窗的日照热可占制冷机最大负荷的30%,冬季单层玻璃的热损失约可占锅炉负荷的20%。窗体节能技术主要从减少渗透量、减少传热量、减少太阳辐射能三个方面考虑。另外,在保证室内采光良好的前提下,合理确定窗墙比十分重要。当窗墙面积比超过50%时,负荷将明显增加。不仅是外围护结构,内围护结构在设计中同样重要。暖通设计师要比普通建筑师更懂得建筑节能的途径,所以暖通设计师和普通建筑师多进行沟通效果才会更好。
5.实现节能
暖通空调的设计师在方案设计时,首先应深入了解业主的能源状况以及对空调的使用状况和是否有余热、废气等条件,然后对各种能源方案进行合理综合的对比。设计师在设计时应考虑的重点是:如何利用可再生能源和低品位能源。
暖通设计师在设计阶段完成基础工作之后,最关键的就是环保和节能的实现,而环保和节能的实现是通过综合利用各种先进技术、利用各种可再生资源来实现的。
利用自然条件来满足人们对于室内温度的需求,这是最理想的方式。现在通过各种设备实现对温度的调节,只不过是对人们的过错进行补救。冷热源是设计师最关注的一点,因为其能耗往往能占空调系统总能耗的50%左右。
地源热泵系统就是在这种形势下快速发展起来的,它利用地下恒温层土壤热显著提高空调系统效率。同时,采用新能源利用的供给方式,实现冷、热、电三联供;利用燃气、汽、电力能量转换的原理联合循环使用,将工业流程最尾端的余热收集起来,用于供冷系统空调冷冻水和供热系统的生活热水,这样,能源的利用率可提高至70%～80%左右。这些都给暖通空调设计师提供了广泛的节能设计思路。
6. 总结
随着全球逐渐变暖这种现象的出现,空调现在已经是人们生活中不可或缺的一部分,它使人们工作生活更加舒适,人们对于空调也有了一定的依赖性。然而,环保和节能是当今非常重要的问题,因此,在暖通空调设计方面,暖通空调的环保和节能是目前空调技术方面发展的方向,也就是说,城市供热环保和节能是目前亟须加强和可持续发展的问题。
参考文献:
[1] 赵君利. 暖通空调节能从设计开始.中国建设报,2010,(03).
[2] 胡锦涛活动报道集,2009,(09)
[3] 刘金瑶,李婉茹,刘鹏华. 浅谈暖通空调的节能.暖通空调,2008,(04).
[4] 张莉,李尧,朱玉明.暖通空调节能设计分析.山西建筑,2010,(09).
[5]__荣.建筑工程的暖通空调设计.施工技术与设计,2008,(07).
[6] 万蓉. 基于气候的采暖空调耗能及室外计算参数研究.西安建筑科技大学, 2009,(08).
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testing of an air-cycle refrigeration system for road transport
Abstract
The environmental attractions of air-cycle refrigeration are considerable. Following a thermodynamic design analysis, an air-cycle demonstrator plant was constructed within the restricted physical envelope of an existing Thermo King SL200 trailer refrigeration unit. This unique plant operated satisfactorily, delivering sustainable cooling for refrigerated trailers using a completely natural and safe working fluid. The full load capacity of the air-cycle unit at −20 °C was 7,8 kW, 8% greater than the equivalent vapour-cycle unit, but the fuel consumption of the air-cycle plant was excessively high. However, at part load operation the disparity in fuel consumption dropped from approximately 200% to around 80%. The components used in the air-cycle demonstrator were not optimised and considerable potential exists for efficiency improvements, possibly to the point where the air-cycle system could rival the efficiency of the standard vapour-cycle system at part-load operation, which represents the biggest proportion of operating time for most units.
Keywords: Air conditioner; Refrigerated transport; Thermodynamic cycle; Air; Centrifuge compressor; Turbine expander COP,
Nomenclature
PR
Compressor or turbine pressure ratio
TA
Heat exchanger side A temperature (K)
TB
Heat exchanger side B temperature (K)
Tinlet
Inlet temperature (K)
Toutlet
Outlet temperature (K)
ηcomp
Compressor isentropic efficiency
ηturb
Turbine isentropic efficiency
ηheat exchanger
Heat exchanger effectiveness
1. Introduction
The current legislative pressure on conventional refrigerants is well known. The reason why vapour-cycle refrigeration is preferred over air-cycle refrigeration is simply that in the great majority of cases vapour-cycle is the most energy efficient option. Consequently, as soon as alternative systems, such as non-HFC refrigerants or air-cycle systems are considered, the issue of increased energy consumption arises immediately.
Concerns over legislation affecting HFC refrigerants and the desire to improve long-term system reliability led to the examination of the feasibility of an air-cycle system for refrigerated transport. With the support of Enterprise Ireland and Thermo King (Ireland), the authors undertook the design and construction of an air-cycle refrigeration demonstrator plant at LYIT and QUB. This was not the first time in recent years that air-cycle systems had been employed in transport. NormalAir Garrett developed and commercialised an air-cycle air conditioning pack that was fitted to high speed trains in Germany in the 90s. As part of an European funded programme, a range of applications for air-cycle refrigeration were investigated and several demonstrator plants were constructed. However, the authors are unaware of any other case where a self-contained air-cycle unit has been developed for the challenging application of trailer refrigeration.
Thermo King decided that the demonstrator should be a trailer refrigeration unit, since those were the units with the largest refrigeration capacity but presented the greatest challenges with regard to physical packaging. Consequently, the main objective was to demonstrate that an air-cycle system could fit within the existing physical envelop and develop an equivalent level of cooling power to the existing vapour-cycle unit, but using only air as the working fluid. The salient performance specifications for the existing Thermo King SL200 vapour-cycle trailer refrigeration unit are listed .
It was not the objective of the exercise to complete the design and development of a new refrigeration product that would be ready for manufacture. To limit the level of resources necessary, existing hardware was to be used where possible with the recognition that the efficiencies achieved would not be optimal. In practical terms, this meant using the chassis and panels for an existing SL200 unit along with the standard diesel engine and circulation fans. The turbomachinery used for compression and expansion was adapted from commercial turbochargers.
2. Thermodynamic modelling and design of the demonstrator plant
The thermodynamics of the air-cycle (or the reverse ‘Joule cycle’) are adequately presented in most thermodynamic textbooks and will not be repeated here. For anything other than the smallest flow rates, the most efficient machines available for the necessary compression and expansion processes are turbomachines. Considerations for the selection of turbomachinery for air-cycle refrigeration systems have been presented and discussed by Spence et al. [3].
a typical configuration of an air-cycle system, which is sometimes called the ‘boot-strap’ configuration. For mechanical convenience the compression process is divided into two stages, meaning that the turbine is not constrained to operate at the same speed as the primary compressor. Instead, the work recovered by the turbine during expansion is utilised in the secondary compressor. The two-stage compression also permits intercooling, which enhances the overall efficiency of the compression process. An ‘open system’ where the cold air is ejected directly into the cold space, removing the need for a heat exchanger in the cold space. In the interests of efficiency, the return air from the cold space is used to pre-cool the compressed air entering the turbine by means of a heat exchanger known as the ‘regenerator’ or the ‘recuperato ’. To support the design of the air-cycle demonstrator plant, and the selection of suitable components, a simple thermodynamic model of the air-cycle configuration shown in was developed. The compression and expansion processes were modelled using appropriate values of isentropic efficiency, as defined in Eqs.The heat exchange processes were modelled using values of heat exchanger effectiveness as defined in The model also made allowance for heat exchanger pressure drop. The system COP was determined from the ratio of the cooling power delivered to the power input to the primary compressor, as defined in illustrate air-cycle performance characteristics as determined from the thermodynamic model:illustrates the variation in air-cycle COP and expander outlet temperature over a range of cycle pressure ratios for a plant operating between −20 °C and +30 °C. The cycle pressure ratio is defined as the ratio of the maximum cycle pressure at secondary compressor outlet to the pressure at turbine outlet. For the ideal air-cycle, with no losses, the cycle COP increases with decreasing cycle pressure ratio and tends to infinity as the pressure ratio approaches unity. However, the introduction of real component efficiencies means that there is a definite peak value of COP that occurs at a certain pressure ratio for a particular cycle. However,illustrates, there is a broad range of pressure ratio and duty over which the system can be operated with only moderate variation of COP.
The class of turbomachinery suitable for the demonstrator plant required speeds of around 50 000 rev/min. To simplify the mechanical arrangement and avoid the need for a high-speed electric motor, the two-stage compression system shown was adopted. The existing Thermo King SL200 chassis incorporated a substantial system of belts and pulleys to power circulation fans, which severely restricted the useful space available for mounting heat exchangers. A simple thermodynamic model was used to assess the influence of heat exchanger performance on the efficiency of the plant so that the best compromise could be developed show the impact of intercooler and aftercooler effectiveness and pressure loss on the COP of the proposed plant.
The two-stage system in incorporated an intercooler between the two compression stages. By dispensing with the intercooler and its associated duct work a larger aftercooler could be accommodated with improved effectiveness and reduced pressure loss. Analysis suggested that the improved performance from a larger aftercooler could compensate for the loss of the intercooler.
shows the impact of the recuperator effectiveness on the COP of the plant, which is clearly more significant than that of the other heat exchangers. As well as boosting cycle efficiency, increased recuperator effectiveness also moves the peak COP to a lower overall system pressure ratio. The impact of pressure loss in the recuperator is the same as for the intercooler and aftercooler shown in. The model did not distinguish between pressure losses in different locations; it was only the sum of the pressure losses that was significant. Any pressure loss in connecting duct work and headers was also lumped together with the heat exchanger pressure loss and analysed as a block pressure loss.
The specific cooling capacity of the air-cycle increases with system pressure ratio. Consequently, if a higher system pressure ratio was used the required cooling duty could be achieved with a smaller flow rate of air. shows the mass flow rate of air required to deliver 7,5 kW of cooling power for varying system pressure ratios.
Since the demonstrator system was to be based on commercially available turbomachinery, it became important to choose a pressure ratio and flow rate that could be accommodated efficiently by some existing compressor and turbine rotors. and were based on efficiencies of 81 and 85% for compression and expansion, respectively. While such efficiencies are attainable with optimised designs, they would not be realised using compromised turbocharger components. For the design of the demonstrator plant efficiencies of 78 and 80% were assumed to be realistically attainable for compression and expansion.
Lower turbomachinery efficiencies corresponded to higher cycle pressure ratios and flow rates in order to achieve the target cooling duty. The cycle design point was also compromised to help heat exchanger performance. The pressure losses in duct work and heat exchangers increased in proportion with the square of flow velocity. Selecting a higher cycle pressure ratio corresponded to a lower mass flow rate and also increased density at inlet to the aftercooler heat exchanger. The combined effect was a decrease in the mean velocity in the heat exchanger, a decrease in the expected pressure losses in the heat exchanger and duct work, and an increase in the effectiveness of the heat exchanger. Consequently, a system pressure ratio higher than the value corresponding to peak COP was chosen in order to achieve acceptable heat exchanger performance within the available physical space. The below optimum performance of turbomachinery and heat exchanger components, coupled with excessive bearing losses, meant that the predicted COP of the overall system dropped to around 0,41. The system pressure ratio at the design point was 2,14 and the corresponding mass flow rate of air was 0,278 kg/s.
By moving the design point beyond the pressure ratio for peak COP, it was anticipated that the demonstrator plant would yield good part-load performance since the COP would not fall as the pressure ratio was reduced. Also, operating at part-load corresponded to lower flow velocities and anticipated improvements in heat exchanger performance. Part-load operation was achieved by reducing the speed of the primary compressor, resulting in a decrease in both pressure and mass flow rate throughout the cycle.
3. Prime mover and primary compressor
The existing diesel engine was judged adequate to power the demonstrator plant. The standard engine was a four cylinder, water cooled diesel engine fitted with a centrifugal clutch and all necessary ancillaries and was controlled by a microprocessor controller.From the thermodynamic model, the pressure ratio for the primary compressor was 1,70. The centrifugal compressor required a shaft speed of around 55 000 rev/min. Other alternatives were evaluated for primary compression with the aim of obtaining a suitable device that operated at a lower speed. Other commercially available devices such as Roots blowers and rotary piston blowers were all excluded on the basis of poor efficiency.
A one-off gearbox was designed and manufactured as part of the project to step-up the engine shaft speed to around 55 000 rev/min. The gearbox was a two stage, three shaft unit which mounted directly on the end of the diesel engine and was driven through the existing centrifugal clutch.
4. Cold air unit
The secondary compressor and the expansion turbine were mounted on the same shaft in a free rotating unit. The combination of the secondary compressor and the turbine was designated as the ‘Cold Air Unit’ (CAU). While the CAU was mechanically equivalent to a turbocharger, a standard turbocharger would not satisfy the aerodynamic requirements efficiently since the pressure ratios and inlet densities for both the compressor and the turbine were significantly different from any turbocharger installation. Consequently, both the secondary compressor and the turbine stage were specially chosen and developed to deliver suitable performance.
Most turbochargers use plain oil fed journal bearings, which are low-cost, reliable and provide effective damping of shaft vibrations. However, plain bearings dissipate a substantial amount of shaft power through viscous losses in the oil films. A plain bearing arrangement for the CAU was expected to absorb 2–3 kW of mechanical power, which represented around 25% of the anticipated turbine power. Also, the clearances in plain bearings require larger blade tip clearances for both the compressor and the turbine with a consequential efficiency penalty. Given the pressurised inlet to the secondary compressor, the limited thrust capacity of the plain bearing arrangement was also a concern. A CAU utilising high-speed ball bearings, or air bearings, was identified as a preferable arrangement to plain bearings. Benefits would include greatly reduced bearing power losses, reduced turbomachinery tip clearance losses and increased thrust load capacity. However, adequate resources were not available to design a special one-off high speed ball bearing system. Consequently, a standard turbocharger plain bearing system was used.
The secondary compressor stage was a standard turbocharger compressor selected for a pressure ratio of 1,264. Secondary compressor and turbine selection were linked because of the requirement to balance power and match the speed. Since most commercial turbines are sized for high temperature (and consequently low density) air at inlet, a special turbine stage was developed for the application. Cost considerations precluded the manufacture of a custom turbine rotor, so a commercially available rotor was used. The standard turbine rotor blade profile was substantially modified and vaned nozzles for turbine inlet were designed to match the modified rotor, in line with previous turbine investigations at QUB (Spence and Artt,). An exhaust diffuser was also incorporated into the turbine stage in order to improve turbine efficiency and to moderate the exhaust noise levels through reduced air velocity. The exhaust diffuser exited into a specially designed exhaust silencer.The performance of the turbine stage was measured before the unit was incorporated into the complete demonstrator plant. The peak efficiency of the turbine was established at 81%.
5. Heat exchangers
Due to packaging constraints, the heat exchangers had to be specially designed with careful consideration being given to heat exchanger position and header geometry in an attempt to achieve the best performance from the heat exchangers. Tube and fin aluminium heat exchangers, similar to those used in automotive intercooler applications, were chosen primarily because they could be produced on a ‘one-off’ basis at a reasonable cost. There were other heat exchanger technologies available that would have yielded better performance from the available volume, but high one-off production costs precluded their use in the demonstrator plant.
Several different tube and fin heat exchangers were tested and used to validate a computational model. Once validated, the model was used to assess a wide range of possible heat exchanger configurations that could fit within the Thermo King SL200 chassis. Fitting the proposed heat exchangers within the existing chassis and around the mechanical drive system for the circulation fans, but while still achieving the necessary heat exchanger performance was very challenging. It was clear that potential heat exchanger performance was being sacrificed through the choice of tube and fin construction and by the constraints of the layout of the existing SL200 chassis. The final selection comprised two separate aftercooler units, while the single recuperator was a large, triple pass unit. Based on laboratory tests and the heat exchanger model, the anticipated effectiveness of both the recuperator and aftercooler units was 80%.
6. Instrumentation
A range of conventional pressure and temperature instrumentation was installed on the air-cycle demonstrator plant. Air temperature and pressure was logged at inlet and outlet from each heat exchanger, compressor and the turbine. The speed of the primary compressor was determined from the speed measurement on the diesel engine control unit, while the cold air unit was equipped with a magnetic speed counter. No air flow measurement was included on the demonstrator plant. Instead, the air flow rate was deduced from the previously obtained turbine performance map using the measurements of turbine pressure ratio and rotational speed.
7. System testing
During some preliminary tests a heat load was applied and the functionality of the demonstrator plant was established. Having assessed that it was capable of delivering approximately the required performance, the plant was transported to a Thermo King calorimeter test facility specifically for measuring the performance of transport refrigeration units. The calorimeter was ideally suited for accurately measuring the refrigeration capacity of the air-cycle demonstrator plant. The calorimeter was operated according to standard ARI 1100-2001; the absolute accuracy was better than 200W and all auxiliary instrumentation was calibrated against appropriate standards.
The performance capacity of transport refrigeration units is generally rated at two operating conditions; 0 and −20 °C, and both at an ambient temperature of +30 °C. Along with the specified operating conditions of 0 and −20 °C, a further part-load condition at −20 °C was assessed. Considering that the air-cycle plant was only intended to demonstrate a concept and that there were concerns about the reliability of the gearbox and the cold air unit thrust bearing, it was decided to operate the plant only as long as was necessary to obtain stabilised measurements at each operating point. The demonstrator plant operated satisfactorily, allowing sufficient measurements to be obtained at each of the three operating conditions. The recorded performance is summarised .
In total, the unit operated for approximately 3 h during the course of the various tests. While the demonstrator plant operated adequately to allow measurements, some smoke from the oil system breather suggested that the thrust bearing of the CAU was heavily overloaded and would fail, as had been anticipated at the design stage. Testing was concluded in case the bearing failed completely causing the destruction of the entire CAU. There was no evidence of any gearbox deterioration during testing.
8. Discussion of measured performance
From the calorimeter performance measurements, the primary objective of the project had been achieved. A unique air-cycle refrigeration system had been developed within the same physical envelope as the existing Thermo King SL200 refrigeration unit, w
空调系统方案设计论文
1、运行控制设计
1.1夏季除湿工况新风阀开度确定
夏季除湿工况，从节能角度，在保持最低换风次数要求的前提下，使新风阀处于最小开度。根据我国暖通空调规范规定：对于室温允许±1.0℃波动范围的空调区域，换气次数应大于或等于5次/时（最小送风量）。保证最低换气次数，回风阀最小开度计算：为获取新风量数值，在新风直管段设置风速检测口，日常运行时封堵，检测时插入风速仪测量新风风速。参数定义：空调控制区域容积-VN空调新风量-Qx新风管截面积-Sx新风管测得风速-则新风量Qx=SxVx,欲使室内换风次数每小时达到5次，须满足：Vx=。通过调整新风阀开度，使风速vx满足上式要求，确认并记录该风速下的新风阀开度。为满足空调节能运行要求，夏季除湿阶段，新风阀可保持这一开度值，定期测试风速，实施新风阀开度值修正。
1.2温、湿度分控模式
在夏季降温除湿工况时，将原有温、湿度联合控制程序调整为温、湿度独立分控程序，即根据室内回风含湿量(通过回风温湿度计算转化得出)与室内设定工况含湿量之间的差值，或根据新风湿度的变化跟踪室内设定工况湿度通过PI调节，来控制主表冷器（除湿通道）的.阀门开度；根据室内回风温度与室内设定温度之间的差值，来控制副表冷器（降温通道）的阀门开度。过渡季，仍按原变新风比或全新风运行，只是需要增加旁通新风阀的开关控制，具体逻辑是当室外工况进入过渡季、新风除湿电动冷水阀关闭，旁通新风阀应同时打开。当室外处于夏季除湿工况时、新风除湿电动冷水阀开度不为零，旁通新风阀应处于关闭状态。过渡季对新风量的调节仍由原新风、回风调节阀负责。
2、常规控制与双通道温湿度独立控制热力工况对比分析
2.1参数定义
G1－新风量N－室内设定点G2－回风量W－夏季室外状态点G－总风量（G1+G2）C－混风状态点i－焓值L－机器露点Q－冷量消耗O－夏季送风状态点
2.2常规空调系统在夏季除湿工况下的再热分析
2.2.1常规夏季除湿空气热湿处理过程卷烟厂空调系统为卷烟生产工艺提供高精度的室内温湿度环境，系统一般都配有表冷、加热、加湿等多种热湿处理手段。常规空调系统夏季热湿处理过程为：新回风混合后，经表冷器降温除湿，再经加热器再热，达到送风状态点后向室内送风。其对应的空气处理过程焓湿图表述常规空调系统在夏季除湿工况下的空气处理过程焓湿图。
2.2.2常规表冷处理冷量消耗计算1）混风状态点（C）焓值计算：根据：，得出：iC=iN+（iW-iN）2）冷量（Q）消耗计算：Q=（G1+G2）（iC-iL）=（G1+G2）（iN-iO）室内负荷+（G1+G2）（iO-iL）再热负荷+G1（iW-iN）新风负荷。
2.3双通道温湿度独立处理方案的节能分析
2.3.1双通道除湿工况空气热湿处理过程根据上文所述，空调系统双通道温湿度独立处理过程概括为：新风（或与部分回风混合）经主表冷器降温除湿，回风经副表冷器干冷却后，新回风进一步混合，达到送风状态点后向室内送风。
2.3.2温湿度分控冷量消耗：1）混风状态点（C）焓值计算根据：=得出：iC=iN-(iN-iL)2）冷量（Q）消耗计算：Q=G1（iW-iL）+（G1+G2）（iC-iO）=（G1+G2）（iN-iO）室内负荷+G1（iW-iN）新风负荷温湿度分控冷量消耗与常规处理冷量消耗比较，常规夏季除湿空气热湿处理过程中（G1+G2）（iO-iL）再热负荷部分已消除。
3、结论
两种空气处理方式的节能点在于：温湿度分控方案节省了再热部分能耗；对于单一冷冻水管网系统，不会额外增加制冷机组的运行能耗，相反会减少因常规降温除湿过程的过冷负荷调节，降低制冷机组能耗。此方案可彻底解决夏季冷热相抵的不合理现象，大量节省夏季再热量和制冷量，可迅速收回初投资，节能效率十分明显。同时不影响过渡季变新风或全新风运行，空调机组硬件设备改动幅度小、改造难度不大。
