A study on an optimal approach temperature control strategy of condensing water temperature for energy saving

An optimal approach temperature (OAT) control strategy is proposed for resetting the condensing water temperature hourly, so to maximize the performance of the combined water chiller and cooling tower system. A system performance factor is introduced for evaluation of the system performance. A regression function is presented for the calculation of an optimal condensing water temperature at each hour of air-conditioning operation. The parameters in the regression function include the ambient wet bulb temperature, the chiller load ratio at the hour, and a dimensionless relative efficiency of chiller and cooling tower. The regression function has an R² close to 1 compared to the computed results. When applied to two cities in Taiwan, the OAT control strategy has a potential to save energy more than 4% on an annual basis. The OAT control strategy is most advantageous when applied to regions with large seasonal variation of wet bulb temperature.     

中央空调循环冷却水系统节能技术

循环冷却水系统,主要的设备有冷水机组、冷却水泵、冷却塔,冷却介质是水。循环冷却水系统冷却水水质对该系统的影响很大;同时设备的选择和节能有很大的关系。分别从冷却水水质、冷水机组、冷却水泵、冷却塔等几个方面进行节能研究探讨。     

冷水机组与板式换热器联合运行节能分析

现代工厂在冬季冷负荷需求量较少,易造成冷水机组频繁启停,甚至由于冷却水温度太低,造成冷水机组无法启动的问题。可以通过冷水机组和板式换热器联合运行的优化控制策略,充分利用冷却塔,通过板式换热器为生产设备和空调系统提供冷冻水,尽量减少冷水机组启动的时间,并保证系统的稳定运行,解决冷水机组频繁启停以及启动困难的问题,达到节能减排和提高冷水机组的运行效率和延长使用寿命的目的。     

A method for evaluating the heat and mass transfer characteristics in a reversibly used water cooling tower (RUWCT) for heat recovery

In sub-tropical regions, a standard water cooling tower may be reversibly used, as part of a desuperheater heat recovery system for service hot water heating, to extract free heat from ambient air in colder seasons when building cooling load is reduced. Chilled water is pumped into a reversibly used water cooling tower (RUWCT) where it is heated by warmer ambient moist air. This paper presents a method by which the heat and mass transfer characteristics in a counter-flow RUWCT can be evaluated. The method is developed by introducing to the Merkel's equation for standard water cooling towers the revisions that account for the differences in heat and mass transfer characteristics between a water cooling tower and a RUWCT. Field experimental results from a RUWCT installed in a sub-tropical region in China indicated that the method developed could be used to evaluate the thermal performance of a RUWCT with an acceptable accuracy.     

提高制冷机效率的措施分析

当今很多空调使用的制冷机都存在严重的效率低的现象。制冷机设备效率(COP值)很低,一般在3.8左右,远低于额定值5.36。频繁对制冷机冷凝器进行化学清洗,对冷凝器管壁磨损又较严重。效率低的主要原因是换热器结垢、冷却塔脏、冷却水质较差。基于此,结合实例我们对制冷机效率提高的措施进行了研究分析。     

带冷却塔预冷制冷机房与常规制冷机房的比较分析

为了降低高温工况下的水源制冷机房能耗,本文提出了对高温水源冷却水先采用冷却塔进行预冷的运行方式。为了探讨这种控制方式的可行性和节能潜力,本文主要对常规制冷机房和带冷却塔预冷制冷机房进行了比较分析。结果表明,当水源温度高过一定值时,采用冷却塔预冷,可提高实现利用效率,从而实现制冷机房的节能;且节能量将随水源温度升高而增加,对于变频冷却塔而言,将存在一最佳风量使得节能量最大。     

Simulation d'une machine frigorifique à absorption fonctionnant avec des mélanges d'alcanes

We propose in this article an absorption chiller operating with binary alkane mixtures as an alternative to compression machines. It is an installation using low-level energy at a temperature below 150 °C (waste heat or solar energy) and operating with environmentally friendly fluids. Ten mixtures are considered and compared with two cooling mediums of the condenser and the absorber: the ambient air at 35 °C and the water at 25 °C. For an air-cooled chiller, the COP reaches 0.37 for the n-butane/octane system. This value remains 27% lower than that of an ammonia/water installation operating under the same conditions. For a water-cooling chiller, the n-butane/octane and propane/octane systems give a COP of about 0.63, which is comparable to that of the ammonia/water system. When n-butane is used as refrigerant, the machine works at a pressure under 5 bars, which is an advantage compared with machines working with ammonia/water mixtures.     

Investigation and comparison of two configurations of a novel open-cycle absorption chiller

In this work two basic configurations (‘open’ and ‘semi-open’) of the dehumidifier-evaporative cooler-regenerator (DER) absorption chiller have been studied and compared. They are both capable of utilizing low grade heat, since their open designs allow for operation at small differences between the heat source and the heat rejection temperatures. They employ ambient air in conjunction with an absorbent solution for producing chilled water. The machines consist of only three major components and operate at atmospheric pressure. Computer simulations of the two configurations operated under ambient conditions of a typical summer day as well as under United States Air Conditioning and Refrigeration Institute standard outdoor conditions have been conducted using a modified existing computer code. The semi-open configuration proved to be superior for most cases with respect to the coefficient of performance (COP). However, under typical summer day conditions, the open DER cycle performed better for chilled water temperatures above 15°C that are common in radiant cooling applications. Here, the COP attains values of about 0.8.     

温和地区采用大温差空调系统的技术经济分析

在温和地区的气候条件下和特定的使用功能要求下,分析比较了空调水系统采用大温差和常规温差对于风机盘管﹑新风和空气处理机组﹑冷水机组﹑冷冻冷却水泵﹑冷却塔﹑空调热水泵等设备运行工况的影响,认为对本项目最适宜的选择是空调冷水5∽12℃、热水60∽45℃,冷却水28∽36℃。     

Absorption chiller crystallization control strategies for integrated cooling heating and power systems

The concept of an air-cooled absorption chiller system is attractive because the cooling tower and the associated installation and maintenance issues can be avoided. However, crystallization of the LiBr–H₂O solution then becomes the main challenge in the operation of the chiller, since the air-cooled absorber tends to operate at a higher temperature and concentration level than the water-cooled absorber due to the relative heat transfer characteristics of the coolant. This leads to crystallization of the working fluid. The paper focuses on the crystallization issues and control strategies in LiBr–H₂O air-cooled absorption chillers. As a result a novel application opportunity is proposed for the integration of absorption chillers into cooling, heating and power (CHP) systems. This new methodology allows for air cooler operation while avoiding crystallization.     

System options for cooling of buildings making use of district heating heat

Issues stemming from district heating utilization during summer periods and the conversion of low-temperature heat into cold in adsorption chillers have been investigated in this paper. Due to the high vulnerability of adsorption chillers to ambient conditions, in the case of relatively low ambient temperatures, adsorption-based air-conditioning systems would be characterized by excessive cooling power. Moreover, adsorption chillers are also characterized by high investment costs and big time constants, and the vulnerabilities found in their regulatory processes have yet to be sufficiently investigated. The authors recommend the application of hybrid air-conditioning systems, consisting of adsorption and compressor chillers. The adsorption chiller works as a base while the compressor chiller contributes missing cooling power, working as a regulation unit. Sixteen configurations of the hybrid air-conditioning system have been analysed. It has been shown that 100 kW cooling power hybrid air-conditioning system, with respect to its configuration, enables the utilization of 0.5 to 0.9 TJ of low-temperature heat per year, while simultaneously providing comfortable air-conditioning. The authors have concluded that the adsorption share in the analysed hybrid system should not exceed 50%.     

Experimental evaluation of a small-capacity,waste-heat driven ammonia-water absorption chiller

This paper presents the results from an experimental evaluation of a small-scale, waste-heat driven ammonia-water absorption chiller. The cycle is thermally driven, using the waste heat from diesel generator exhaust to desorb the refrigerant solution. The absorber and condenser are directly-coupled to the ambient air. The remaining heat exchangers are packaged in a compact microchannel monolithic structure for enhancing heat transfer. The system is designed to deliver 2.71-kW of cooling at extreme ambient temperature of 51.7 °C at a coefficient of performance of 0.55. Experiments on a heat pump breadboard system are conducted at ambient conditions of 29.7–44.2 °C, with delivered cooling duties of 2.54–1.91 kW. System and individual component performance is analyzed and compared with cycle model predictions, and deviations are explained. The absorber and desorber were identified to be the limiting components in the system. Effects of variation in ambient temperature are studied to characterize the performance at off-design conditions.     

苏州吴中白金汉爵大酒店空调通风系统设计

对苏州吴中白金汉爵大酒店空调通风系统特点、设备配置等方面进行了介绍,针对不同使用功能的房间采用了相应的空调方式。主要对电动冷水机组采用大温差,空调水系统采用分区四管制一次泵变流量系统,过渡季节采用冷却塔供冷,宴会厅空调热湿负荷特性及空气处理过程等设计方面的经验和体会进行了探讨。     

蒸发冷却＋空气源热泵复合冷（热）水机组夏季能耗分析

蒸发冷却＋空气源热泵复合冷（热）水机组由蒸发冷却段和机械制冷段组成,蒸发冷却段是蒸发冷却式冷水机组,机械制冷段是直接蒸发冷却器（DEC）与空气源热泵冷（热）水机组的联用。本文首先对DEC＋空气源热泵冷（热）水机组的夏季能耗进行分析,并与传统的单独运行空气源热泵冷（热）水机组的情况进行对比;另外从压一焓图和温一熵图角度分析空气源热泵冷（热）水机组联用DEC后能效比提高的机制;然后以西安地区为例对蒸发冷却＋空气源热泵复合冷（热）水机组进行夏季能耗分析,推导出单独利用蒸发冷却技术就能制取18℃左右高温冷水的气候条件。为蒸发冷却制取冷水技术在中等湿度地区甚至高湿度地区的应用提供理论依据。     

中央空调系统中冷却塔风机变频节能的可行性分析

借助于冷水机组和冷却塔的选型软件,并通过迭代计算的结果表明:以控制恒定逼近度的逻辑方法,在冷却塔风机上能够实施变频的运行范围因为受到冷量、湿球温度和冷水机组的效率影响而非常小;而且如果将冷水机组与冷却塔的综合能耗一起考虑的话,可能达不到所设计的节能效果.     

Cellulose-pad water cooling system with cold storage

The present study develops a cooling system using water as the working medium which is cooled at night by cellulose-pad cooling tower (CWCT) and stored for cooling application at daytime. That is, it utilizes the natural energy drawn from diurnal ambient air temperature difference. A cooling system was built and tested. It is found that the coefficient of performance of CWCT for heat dissipation of water at night, COP_nt, is between 3.8 and 11 and varies linearly with the evaporation temperature glide D_G (difference between cold water temperature in the storage tank and wet-bulb temperature of ambient air). The COP for room cooling at daytime run with air cooler in a room, COP_day, is between 8.8 and 12.6. For day cycle operation, the measured overall cooling COP_o is 5.1. COP_o is expected to reach 9.4 at room temperature 45 °C.     

大型风冷冷水机组性能评价系统节能性研究

针对大型风冷冷水机组性能评价系统能耗高的现状,分析评价系统的主要能耗构成,指出传统大型风冷冷水机组性能评价系统的高能耗成因,提出一种新型变容量全回收风冷冷水机组性能评价系统。新型评价系统省去样机恒温水箱、冷冻水箱和换热水泵,将变容量水冷乙二醇冷冻机组与经济器(冷却塔协同功能板换)串入闭式回路实现一级温控,结合变频泵与调节阀实现二级温控。实证表明:相比传统评价系统,应用双级温控的新型评价系统相近工况过渡耗时减少为前者的70%,综合能耗降为传统的75%,运行稳定性良好,节能效果显著。     

中央空调冬季冷却塔供冷节能实践

对于全年供冷的中央空调系统,冬季采用冷却塔代替冷水机组为空调供冷水,是非常理想的节能措施之一。本文根据不同工程实践,分析了不同冷却水系统的可行方案及注意事项,可供设计及管理人员参考。     

夏热冬冷地区居住建筑冷热源经济性分析

采用改进的温频法进行负荷计算,针对夏热冬冷地区某居住建筑的冷热源方案进行全寿命周期经济性分析。结果表明,采用地源热泵方案经济性最好,比空气源热泵节省费用约7.5%,比冷水机组加燃气锅炉方案节省费用约21.2%。同时,输配能耗占总能耗比重约20%,应优化设计输配系统,降低输配能耗。采用地源热泵方案时,如能采用与冷却塔的复合运行模式,其运行能耗将进一步降低。     

夏热冬冷地区混合式地源热泵系统控制策略

建立用于某办公建筑的冷却塔辅助散热型混合式地源热泵系统模型,以夏热冬冷气候条件下的长沙、上海和武汉地区为例,模拟混合地源热泵系统分别以地埋管出水温度、地埋管出水与环境温差、冷却塔运行时段作为辅助散热启停的控制信号的控制策略,运行20年后地埋管附近土壤平均温度及机组性能。研究各控制策略对不同地区的适用性。结果表明,3种控制策略在夏热冬冷地区的不同地区均表现出对系统能耗和土壤温升相近的影响规律,且均可以通过合理的参数设施实现运行20年后土壤维持热平衡。