Conceptual design of a high-efficiency absorption cooling cycle

The search for high-efficiency, gas-fired cooling cycles has led to the development of dual-loop absorption machines with cooling coefficients of performance (COPs) in the 1.2 to 1.7 range. This increased performance may call for high generator temperatures, new working fluids or new materials of construction. In most cases, two different sets of working fluids are required. The conceptual design presented here is aimed at obtaining high efficiencies with relatively low temperatures, employing only one set of fluids. The concept consists of two loops coupled in a configuration aimed at minimizing the loss of thermodynamic availability incurred when transferring refrigerant between the loops. The working fluid pair is a solution of lithium bromide-water. The calculated COPs are of the order of 1.8. The cycle relies on an elaborate evaporator-absorber combination. The paper presents the conceptual design, the critical assumptions, and the performance calculations for the concept.     

Calculation methods for comparing the performance of pure and mixed working fluids in heat pump applications

Three methods for comparing cycle performance of working fluids, pure as well as non-azeotropic mixtures, are investigated for two applications and for two mixture pairs, HCFC22-CFC114 and HCFC22-HCFC142b, and their pure components. The methods differ in the way of calculating the heat exchange processes. They assume, respectively, equal minimum approach temperatures, equal mean temperature differences and equal heat transfer areas. Changes of coefficient of performance (COP) with composition are explained for all methods. It is shown that transport properties must be taken into account when making rigorous comparisons between working fluids. To predict the relations between fluids with high accuracy, one must use the method with equal heat transfer areas. By the method with equal mean temperature differences, the COP can be estimated with the same accuracy for mixtures as for pure fluids, and can be used for rough estimations of the COP level with different fluids. The method of equal minimum approach temperatures should be avoided for non-azeotropic mixtures.     

采用变回水温度控制策略的空气源热泵空调系统研究

为了提高空气源热泵空调系统运行性能,研究了一套采用变回水温度控制策略的空气源热泵机组的制冷性能。实验研究表明,变回水温度工况可满足室内冷负荷需求。与传统采用定12℃回水温度的空气源热泵空调系统相比,COP更高,耗电量更小,是一种高效节能的空气源热泵空调系统控制方法。此外,所建立的Dymola模型从理论上验证了实验结果,在此基础上模拟实际空调系统的能耗,模拟结果表明,COP由3.99提高至4.39,提高了10%。     

Transcritical CO2 refrigeration cycle with ejector-expansion device

An ejector expansion transcritical CO₂ refrigeration cycle is proposed to improve the COP of the basic transcritical CO₂ cycle by reducing the expansion process losses. A constant pressure mixing model for the ejector was established to perform the thermodynamic analysis of the ejector expansion transcritical CO₂ cycle. The effect of the entrainment ratio and the pressure drop in the receiving section of the ejector on the relative performance of the ejector expansion transcritical CO₂ cycle was investigated for typical air conditioning operation conditions. The effect of different operating conditions on the relative performance of the ejector expansion transcritical CO₂ cycle was also investigated using assumed values for the entrainment ratio and pressure drop in the receiving section of the ejector. It was found that the COP of the ejector expansion transcritical CO₂ cycle can be improved by more than 16% over the basic transcritical CO₂ cycle for typical air conditioning operation conditions.     

Applying grey forecasting to predicting the operating energy performance of air cooled water chillers

Grey forecasting has found applications in finance, social science, economics, etc. However, its applications in air conditioning and refrigeration have not been reported. This paper reports on a study where grey forecasting method is applied to predicting the operating energy performance for an air cooled water chiller (ACWC) units, so as to demonstrate this forecasting approach can be applied to building Heating Ventilation and Air Conditioning (HVAC) installations. In this paper, a brief introduction of the background and fundamentals of grey forecasting is firstly presented. This is followed by reporting the application of grey forecasting to an ACWC unit installed in Northern China for predicting its operating energy performance using the variation ratio of coefficient of performance (ΔCOP). The predicted values of ΔCOP agreed well with the measured ΔCOP, demonstrating that grey forecasting may be used for predicting the operating energy performance of an ACWC unit with a high accuracy. Finally, the potential use of grey forecasting in fault detection and diagnostics (FDD) or energy management systems (EMSs) for air conditioning and refrigeration systems is assessed, and the comparison with the prediction method based on artificial neural network (ANN) discussed.     

电厂循环水余热利用工程中热泵制热性能系数测试不确定度分析

应用吸收式热泵回收电厂循环水余热用于城市集中供热,是一项新兴的节能技术,相关的性能验收试验标准尚未制定。对热泵性能验收试验中各直接、间接测量参数及最终试验结果制热性能系数（coefficient of performance,COP）的不确定度评定方法进行了分析,给出相应的计算公式,并以某300 MW供热机组循环水余热利用工程为例进行了热泵COP测试不确定度评定。不确定度计算分析结果表明：降低热网水流量、凝结水流量、热网水进出口温度等参数的测量不确定度,可提高测试结果的可用性。     

以毛细管为节流装置的CO_2小型热泵热水器实验研究

介绍以毛细管为节流装置跨临界CO2热泵热水试验系统。实验研究了不同气冷器进水温度下系统的COP及其变化、气冷器沿管长水温温升梯度变化。分析了不同环境温度下制冷剂充注量对系统高压侧压力的影响。可以得出:以毛细管做节流装置也可以得到较高的COP;气冷器水温在高温CO2进口段温升幅度最大;系统对环境温度的变化很敏感,环境温度较低时要想得到合适的高压侧压力,制冷剂的充注量要比环境温度高时多。     

R22的替代物THR03的实验研究及性能分析

在一新建的高精度实验台上分别对以R22及THR03为制冷工质的制冷系统在4个工况下进行了系统的实验研究,由实验得到了THR03、R22在4种工况下制冷系统制冷量、压缩机耗功量、压缩机排气温度等性能参数实验数据,分析和比较了THR03制冷系统及R22制冷系统在同一工况下的性能,并给出了实验结果.     

单机双级滚动活塞式压缩机适宜容积比的探讨

为研究以R410A为工质的两级压缩制冷循环性能,模拟计算两级压缩制冷循环制冷系数随工况和高低压容积比的变化情况,以及不同工况下容积比与中间温度变化的关系。得出结论,在蒸发温度3~9℃,冷凝温度35~50℃范围内,相同蒸发温度和冷凝温度下,容积比越大对应的中间温度越低,当容积比ζ在3/4~4/5之间时,循环制冷系数更为接近最大制冷系数。本研究为合理选择两级压缩高低压容积比、确定最佳运行工况提供指导。     

臭氧处理冷水机组循环冷却水的节能试验研究

从目前循环冷却水系统中普遍存在的结垢问题入手,引出臭氧水处理法,它是一种环保、安全、高效的水处理方法。臭氧在处理循环冷却水时能起到杀菌、缓蚀、阻垢及脱垢的作用。简要阐述臭氧处理循环冷却水的阻垢及脱垢原理,分析污垢对冷水机组性能的影响。臭氧处理冷水机组循环冷却水的试验表明,臭氧水处理方法能够显著提高冷水机组的COP。