Control characteristics and heating performance analysis of automatic thermostatic valves for radiant slab heating system in residential apartments

Computer simulations and experiments are carried out to research the control characteristics and heating performances for a radiant slab heating system with automatic thermostatic valves in residential apartments. An electrical equivalent R–C circuit is applied to analyze the unsteady heat transfer in the house. In addition, the radiant heat transfer between slabs, ceilings and walls in the room is evaluated by enclosure analysis method. Results of heating performance and control characteristics were determined from control methods such as automatic thermostatic valves, room air temperature-sensing method, water-temperature-sensing method, proportional control method, and On–Off control method.     

Experimental model of a variable capacity compressor

The refrigeration and heat pump systems are lately characterized by a remarkable evolution period. The principal reasons that have determined changes are the substitution of environmentally unfriendly refrigerants and the energy saving necessity. As fundamental component of a vapour compression plant, the compressor is an object of optimizations; the variation of the compressor speed, obtained regulating the supply current frequency of the compressor motor, allows to obtain energy savings. The principal aim of this paper is the determination of an experimental model that represents the variable speed reciprocating compressor working. In particular, equations that allow to get the refrigerant mass flow rate, the compressor input power and the cooling capacity in terms only of the frequency are obtained. The experimental model allows to determine the optimum frequency for each working condition and then the related energy saving. Copyright © 2008 John Wiley & Sons, Ltd.     

Constraints of using thermostatic expansion valves to operate air-cooled chillers at lower condensing temperatures

Thermostatic expansion valves (TXVs) have long been used in air-cooled chillers to implement head pressure control under which the condensing temperature is kept high at around 50 °C by staging condenser fans as few as possible. This paper considers how TXVs prevent the chillers from operating with an increased COP at lower condensing temperatures when the chiller load or outdoor temperature drops. An analysis on an existing air-cooled reciprocating chiller showed that the range of differential pressures across TXVs restricts the maximum heat rejection airflow required to increase the chiller COP, though the set point of condensing temperature is reduced to 22 °C from a high level of 45 °C. It is possible to use electronic expansion valves to meet the differential pressure requirements for maximum chiller COP. There is a maximum of 28.7% increase in the chiller COP when the heat rejection airflow is able to be maximized in various operating conditions. The results of this paper emphasize criteria for lowering the condensing temperature to enhance the performance of air-cooled chillers.     

Experimental evaluation of electronic and thermostatic expansion valves performances using R22 and R407C

An experimental study to evaluate the energetic performances in steady-state and in transient operating modes of an electronic and thermostatic expansion valve is presented. Both valves have been assembled to feed an air cooled evaporator connected to an experimental vapour compression plant with a water cooled condenser operating with a semihermetic compressor. The performances of the valves have been examined at different conditions when the experimental plant works with R22 and with a substitute as the non-azeotropic blend R407C that is chlorine free. Indeed the HCFC designated as R22 contains chlorine that is harmful for the ozone layer and must be replaced in the future. The final results of this study show an overall better performance of the electronic expansion valve compared with the thermostatic expansion valve under transient conditions while in steady-state conditions both the valves are equal in performance. These results apply to both R22 and R407C.     

变容量家庭能源中心单独制热水模式的实验研究

提出了可全年供应空调和热水需要的变容量家庭能源中心系统,并提出单独制热水模式下的性能系数计算方法。通过对该模式瞬时动态特性的研究,指出变容量压缩机可以有效地保证机组的安全可靠运行。实验研究了单独制热水模式在不同环境温度、不同压缩机负荷条件下的性能。结果表明,在同一压缩机负荷条件下,热水性能系数均随环境温度的升高而升高,与传统热泵热水器的变化趋势相同。而压缩机负荷变化对机组热水性能系数的影响在不同的环境温度下呈现不同的规律,因此,可根据不同的环境温度优化控制压缩机负荷,以提高制热水效率,节约能源。     

Choking phenomenon and pressure drop mechanism in electronic expansion valves

A quasi one-dimensional model in which oblique evaporation wave theory and shock wave theory are employed is developed to investigate the choking phenomenon and the pressure drop mechanism in electronic expansion valves (EEV). The data predicted by the model are validated by the experimental data presented by Zhang. The results show that the choking mass flow rate of EEVs calculated by Abuaf’s model, which was developed with water, agrees well with the tested data when R22 is used as the working fluid. The relative deviation between the predicted data and Zhang’s test results is in the range from −5% to 6%. Compared with the test data, the choking mass flow rate of EEVs with the mixture R407c is over predicted by Abuaf’s model. The back pressure at the EEV exit when choking just occurs is decreased as the flow area (opening pulse number) is decreased. The trend is consistent with Zhang’s test results.     

活塞式压缩机节能增效的研究与实践

本文从改造活塞式压缩机中间冷却器以实现节能增效的理论分析着手 ,探讨了改造活塞式压缩机中间冷却器的节能原理 ,并辅以工程应用实例说明。     

热风阀阀板的节能探讨

我国国内的热风阀阀板同国外阀板相比,存在着热损失大的缺点,原因是耐火材料衬热阻较小。文中以有限元模拟技术为手段,以增大热阻为目的,进行了耐火材料组合衬设计。设计结果表明,组合衬的热损失可以降到单一衬的43％～56％左右,节能效果十分显著。     

供热系统中电动调节阀门的应用

随着计量供热系统的应用，对于供热系统设计的要求也随之提高。分析了电动调节阀选择的基本原理和方法，从理论和实际两方面解释了选择电动阀的主要因素。同时阐述了相关的水力和控制原理，通过电动调节阀根据热负荷变化来调节供热量，从而改善系统的稳定性，降低热耗达到节能的目的。     

合同能源管理的现状分析和发展对策

合同能源管理是一种以减少的能源费用来支付节能项目投资的节能服务机制.这一新型机制正受到国家的大力支持,但其在实际推广应用过程中遇到不少困难.通过调研某市18家节能服务公司,总结出合同能源管理在该市发展的制约因素.分析了该市发展合同能源管理的有利条件:1.节能服务市场潜力巨大;2.本身具备天然优势.结合现实制约因素和天然...     

The transient response of an evaporator fed through an electronic expansion valve

The primary task of an expansion valve in a refrigerating machine is to control the mass flowrate into the evaporator to obtain optimal operation without ‘hunting’ under given conditions. A stepper-motor-controlled expansion valve and an evaporator have been studied. The tests were carried out on a fixed refrigerating machine of cooling capacity less than 6 kW, with constant condensation conditions and variable evaporating temperature (−20 to +10°C) and compressor speed (1000 to 3000 r.p.m). Two control algorithms (proportional/derivative and qualitative optimal regulation) have been developed for opening and closing the valve with the stepper motor. The control parameters depend on both the expansion valve and the evaporator transfer functions. In steady-state conditions, the system is stable with a superheat equal to the set value. Under transient conditions, with step excitations of 300 and 1000 r.p.m as well as for cold-start of the machine, the control algorithms are adequate for regulating the refrigerant flowrate into the evaporator. © 1997 John Wiley & Sons, Ltd.     

降低进口温度与湿度增加空压机风量的理论与实践

本文阐述了空压机增风改造的方法,并介绍了脱湿增风改造原理及其实践效果,在新余钢铁公司气体厂1TY-575/5.5-Ⅲ型空压机增风改造中应用,使空压机夏季平均风量可提高8%左右,而且空气压缩的单位电耗降低.     

热力学第二定律与冷库微机控制节能

冷库微机控制与常规自动控制相比 ,其优越性在于它可根据库温变化自动地调整其制冷剂的蒸发温度 ,并使得其制冷剂和蒸发温度与冷库温差总是处于最小值。根据热力学第二定律 ,在其他条件不变的情况下 ,此时制冷装置的能耗最小。     

小型风冷热泵节流装置改造的节能研究

对风冷热泵冷热水机组节流装置(热力膨胀阀)进行改进,通过不同试验工况条件下的性能及其各种相关状态参数的测试,比较了系统改进前后的制冷量、能效比和响应时间,验证了使用电子膨胀阀机组能够达到节能的效果,并且提出了改进系统的进一步措施。     

燃煤联合循环发电技术的发展

综合介绍以煤为主要燃料的高效无污染联合循环发电技术的产生、发展及应用现状,并提出我国应用的可能及必要。     

合同能源管理促进政府机构节能的作用

政府部门已成为能源消费大户,存在很大的节能潜力。加强政府机构节能,可以有效地降低运行费用;同时,通过政府机构的节能示范,可以提高全社会及各行业的节能意识。但是,政府机构节能却面临资金短缺、技术薄弱和风险承担能力弱等问题。一种新的、基于“合同能源管理”机制运作的专业化公司(EMCo)则可以有效地解决这些问题。该运作方式在国内外政府机构已得到了广泛地推广和应用,并积累了众多成功案例。通过这种模式,政府机构在不增加预算、不用担心技术和风险的同时,既降低了运行费用还获得节能效益,为全社会的节能起到了带头示范作用。     

An experimental analysis of a thermodynamic model of a vapour compression refrigeration plant on varying the compressor speed

The principal aim of this paper is the study of a thermodynamic model that simulates the working of a vapour compression refrigeration plant. The model allows the evaluation of plant performances when the compressor capacity is regulated varying its velocity by means of an inverter inserted into the compressor electric motor feeder. This type of control allows to match continuously the compressor refrigeration capacity to the load, determining an energy saving in comparison with the classical thermostatic control. In particular, in this paper the outputs of the model are compared with the experimental results. The vapour compression experimental refrigeration plant, whose evaporator is located in a commercially available cold store, presents a semi‐hermetic reciprocating compressor able to work with the R22 and some its substitutes, and designed for a revolution speed corresponding to a 50 Hz frequency of a compressor electric motor supply current. The comparison of model and experimental results is realized by varying the supply current frequency of the compressor in the range 30–50 Hz using the R407C (R32/R125/R134a 23/25/52% in mass) that represents the most suitable working fluid for the R22 substitution. The model‐experimental comparison results reported in terms of condensation temperature, compression ratio, condensation power and Coefficient Of Performance are completely acceptable. Moreover, an exergetic analysis is realized to explain the performances of the plant components when the compressor speed is varied. Copyright © 2004 John Wiley & Sons, Ltd.     

基于RBF网络PID控制的风机泵节能研究

传统的PID控制不能满足风机泵出口压力不断变化不断修正的特性的控制要求,为此引入RBF神经网络,使训练产生一组最佳的P、I、D值,经过理论分析和实验对比证明,此方法引入风机泵节能系统中是可行的。     

低氧燃烧与富氧燃烧的性能比较分析

阐述了低氧燃烧和富氧燃烧的基本概念，并且和传统的燃烧方式作了对比，概括了两种燃烧方式的优缺点。分析了两种燃烧方式的实现途径。应根据不同的实际情况选择不同的燃烧方式。