Part-load characteristics of a new ammonia/lithium nitrate absorption chiller

A pre-industrial prototype of a new water-cooled ammonia/lithium nitrate absorption chiller was characterised at part-load operation mode. The chiller was built using brazed plate heat exchangers in all its components, including the absorber and the generator.A test campaign was carried out varying the thermal load in the chilled water circuit and keeping the hot and cooling water temperatures constant.Part-load curves of the thermal and electrical coefficients of performance were obtained, plotted and compared with data from the literature on small capacity absorption chillers with conventional working pairs, namely ammonia/water and water/lithium bromide. The experimental results showed that to achieve a higher electrical coefficient of performance at part-load operation, it was much more convenient to use an ON-OFF control than to modify the hot water temperature. Furthermore, using a simple ON-OFF control strategy, the behaviour of the new absorption chiller was more agile and responded more quickly.The part-load curve of the electrical coefficient of performance was obtained by adjusting the experimental data to the shape of the curve proposed in the standard prEN-14825:2011 for air-to-water chillers. The Cc coefficient was 0.7985 matching the value obtained dividing the remaining electrical consumption measured during the OFF half cycles by the total energy consumption generated.     

Investigation of a mixed effect absorption chiller powered by jacket water and exhaust gas waste heat of internal combustion engine

CCHP (combined cooling heating and power) system based on ICE (internal combustion engine) has been widely used. A key issue is to efficiently recover the jacket water and exhaust gas waste heat for refrigeration. In this work, a mixed effect absorption chiller (AC), which couples single effect and double effect processes together, is investigated to recover these two kinds of waste heat simultaneously. The high pressure generator is powered by exhaust gas while one low pressure generator is powered by jacket water waste heat. Thermodynamic characteristics and off-design performance are simulated. Considering thermodynamic constraints, the start point temperature in low pressure generator should be 77°Cor lower. For a 16 kW ICE, the cooling output can reach 34.4 kW with COP of 0.96 and exergy efficiency of 0.186. Comparing with double effect or single effect AC, it can make a better use of different waste heat in CCHP system.     

多主机制冷机房变流量解耦控制策略研究

在单主机制冷机房变流量解耦控制策略基础上,探讨了多主机制冷机房的变流量解耦控制策略。在考虑冷水机组COP值同时是冷负荷及冷却水进水温度的函数基础上,通过比较不同冷负荷分配策略对制冷机房能耗的影响,得到了在大多数负荷区间,采用均匀分配总冷负荷的策略最为节能。这说明,前期关于单主机制冷机房变流量变温差控制方式可推广至多主机制冷机房变流量控制。     

Optimization of a fin-tube type adsorption chiller by design of experiment

This paper presents a numerical analysis of the performance of a fin-tube type adsorption chiller associated with heat and mass transfer mechanisms. A two-dimensional axisymmetric transient model is developed and 10 parameters are used to investigate their effects on the performance of an adsorption chiller and to obtain the optimized conditions of a fin-tube type adsorption chiller. Ten parameters found in many other studies, such as fin pitch, fin thickness, fin height, diffusion coefficient, particle size, cycle time, cycle ratio, temperature of hot water, fluid velocity and porosity, are used in this study. Based on the design of experiment, an orthogonal array of 10 parameters with three levels, L₂₇(3¹³) is used for the analysis of variance (ANOVA) and through this method, each parameter's level of contribution is carefully examined. The result shows that fin thickness and the temperature of hot water are the dominant parameters for COP and SCP, respectively. The optimum conditions having the highest COP of 0.6782 and SCP of 217.68 W kg⁻¹ are found through the result.     

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。     

Performance simulation of multi-bed silica gel-water adsorption chillers

Adsorption chiller technology is one of effective means to convert waste thermal energy into cooling, which substantially improves energy efficiency and lowers environmental pollution. This article develops an improved lumped-parameter model for multi-bed silica gel-water adsorption chillers. It is validated by experimental results stemming from a four-bed silica gel-water adsorption chiller at various operating conditions. It is found that the performance predictions from this model compare favourably with experimental results. At all tested conditions and over a wide range of cycle times, the cooling capacity and COP can be predicted to within 10% and 12%, respectively.     

Energy and exergy comparison of a cascade air conditioning system using different cooling strategies

A cascade air conditioning system consisting of a compression and an absorption chiller working in a parallel arrangement has been proposed. This system is powered up by a micro-gas turbine. Different cooling strategies are studied in order to recognize the best configuration. The system components have been modeled and analyzed through the energy and exergy approaches. The performance parameters of the systems and the second law efficiency have been calculated in different operating conditions. Water consumption of the systems has also been investigated, considering water as a source of exergy. The results revealed that a system with water-cooled chillers has the highest second law efficiency and water consumption. On the other hand, the water consumption of a system with an air-cooled absorption and a water-cooled compression chiller is about 50% less than that of the system with two water-cooled chillers while its second law efficiency is only about 10% less.     

运行温度和换热特性对水冷机组能效影响的分析

通过热力循环的分析,对冷水机组运行中的冷冻水温度和冷却水温度及换热面积和换热系数进行了探讨,并对结构参数的优化进行了讨论.结果表明:冷冻水温度的提高或是冷却水温度的降低能提高冷水机组效率;提高结构参数中数值较小的参数,更能有效地提高机组效率.     

Multi-bed regenerative adsorption chiller — improving the utilization of waste heat and reducing the chilled water outlet temperature fluctuation

A multi-bed regenerative adsorption chiller design is proposed. The concept aims to extract the most enthalpy from the low-grade waste heat before it is purged into the drain. It is also able to minimise the chilled water temperature fluctuation so that downstream temperature smoothing device may be downsized or even eliminated in applications where tighter temperature control may be required. The design also avoids a master-and-slave configuration so that materials invested are not under-utilised. Because of the nature of low-grade waste heat utilization, the performance of adsorption chillers is measured in terms of the recovery efficiency, η instead of the conventional COP. For the same waste heat source flowrate and inlet temperature, a four-bed chiller generates 70% more cooling capacity than a typical two-bed chiller. A six-bed chiller in turn generates 40% more than that of a four-bed chiller. Since the beds can be triggered into operation sequentially during start-up, the risk of ice formation in the evaporator during start-up is greatly reduced compared with that of a two-bed chiller.     

Experimental and numerical analysis of an air-cooled double-lift NH3–H2O absorption refrigeration system

The prototype of an air-cooled double-lift NH₃–H₂O absorption chiller driven by hot water at low temperature is presented. The main objective of the study is to illustrate the experimental performances of the prototype under different operating conditions. A mathematical model of the cycle is developed, along with a procedure for the identification of otherwise difficult to measure data, with the purpose of providing the complete picture of the internal thermodynamic cycle. The combined experimental and numerical data allowed assessing the effects on the thermodynamic cycle with varying operating conditions. The unit operated steadily with chilled water inlet 12 °C, outlet 7 °C, air temperature between 22 °C and 38 °C, and hot water driving temperatures between 80 °C and 90 °C. The reference cooling capacity at air temperature of 30 °C is 2.5 kW, with thermal COP about 0.3 and electrical COP about 10.     

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 novel experimental investigation of a solar cooling system in Madrid

This paper reports novel experimental results derived through field testing of a part load solar energized cooling system for typical Spanish houses in Madrid during the summer period of 2003. Solar hot water was delivered by means of a 49.9 m² array of flat-plate collectors to drive a single-effect (LiBr/H₂O) absorption chiller of 35 kW nominal cooling capacity. Thermal energy was stored in a 2 m³ stratified hot water storage tank during hours of bright sunshine. Chilled water produced at the evaporator was supplied to a row of fan coil units and the heat of condensation and absorption was rejected by means of a forced draft cooling tower. Instantaneous, daily and period energy flows and energy balance in the installation is presented. System and absorption machine temperature profiles are given for a clear, hot and dry day's operation. Daily and period system efficiencies are given. Peak insolation of 969 W m⁻² (at 12:30 solar time on 08/08/03) produced 5.13 kW of cooling at a solar to cooling conversion efficiency of 11%. Maximum cooling capacity was 7.5 kW. Cooling was provided for 8.67 h and the chiller required a threshold insolation of 711 W m⁻² for start-up and 373 W m⁻² for shut-down. A minimum hot water inlet temperature to the generator of 65 °C was required to commence cold generation, whereas at 81 °C, 6.4 kW of cooling (18.3% of nominal capacity) was produced. The absorption refrigeration machine operated within the generation and absorption temperature ranges of 57–67 and 32–36 °C, respectively. The measured maximum instantaneous, daily average and period average COP were 0.60 (at maximum capacity), 0.42 and 0.34, respectively. Energy flows in the system are represented on a novel area diagram. The results clearly demonstrate that the technology works best in dry and hot climatic conditions where large daily variations in relative humidity and dry bulb temperature prevail. This case study provides benchmark data for the assessment of other similar prototypes and for the validation of mathematical models.     

Performance analysis of a supersonic ejector cycle working with R245fa

A supersonic ejector chiller for industrial use is currently being developed and tested as part of a project cooperation between Frigel s.p.a and DIEF (Department of Industrial Engineering, University of Florence). The refrigerator was built following a “ready to market” setup criterion and is intended for applications on the industrial refrigeration market or in air conditioning. The plant has a nominal cooling power of 40 kW and is powered by low temperature heat (from 90 up to 100 °C). The ejector is equipped with a movable primary nozzle and 9 static pressure probes along the mixing chamber/diffuser duct. The working fluid is R245fa. An extensive numerical campaign was performed to analyze the internal dynamics of the ejector. All the simulations were carried out by accounting for the real gas properties of the refrigerant. Comparison with experimental data resulted in close agreement both in terms of global and local parameters. Analyses showed that in order to achieve an accurate matching with the experimental data, it is necessary to correctly account for the surface roughness of the ejector. This is especially true for off-design operating conditions.     

Design,construction and operation of a solar powered ammonia–water absorption refrigeration system in Saudi Arabia

This study presents an experimental investigation of a solar thermal powered ammonia–water absorption refrigeration system. The focus of this study lies on the design of the components of the absorption chiller, the ice storages and the solar collector field as well as the integration of the data acquisition and control unit. An ammonia–water (NH₃/H₂O) absorption chiller was developed in the laboratory of the Institute of Thermodynamics & Thermal Engineering (ITW) at the University of Stuttgart (Germany). A demonstration plant was built in the laboratory of the CoRE-RE at King Fahd University of Petroleum & Minerals (KFUPM – Saudi Arabia). The whole system was tested successfully. The results of the experiments indicated a chiller coefficient of performance (COP) of 0.69 and a cooling capacity of 10.1 kW at 114/23/−2 (°C) representing the temperatures of the generator inlet, the condenser/absorber inlet and the evaporator outlet respectively. Even at 140/45/−4 (°C), the chiller was running with a cooling capacity of 4.5 kW and a COP of 0.42.     

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。     

Modelling of ejector chillers with steam and other working fluids

The Constant Rate of Momentum Change (CRMC) criterion attempts to improve the design of supersonic ejectors, that can be used in heat-powered chillers for industrial or air-conditioning use. Moving from its original formulation, the CRMC design method can be advanced accounting for friction irreversibilities and real gas behaviour, as done in a previous work by our research group. Here we present an upgraded version of this analysis, supported by experimental data from a prototype chiller using R245fa as working fluid. The analysis is extended to other fluids (water, isobutane, 5 HFCs and 3 HFOs) whose performance is calculated on a wide range of heat source/sink temperatures. The existing literature, based generally on ideal gas simulations, suggests that water yields poor results in terms of COP. This paper shows that this result may be argued. Low GWP fluid HFO1233zd also gives good results.     

Experimental evaluation of a variable effect LiBr–water absorption chiller designed for high-efficient solar cooling system

A variable effect LiBr–water absorption chiller is studied in this paper based on a real developed 50 kW prototype. The chiller is designed specifically for the high-efficient utilization of the solar power with variable temperature. It can obtain the optimized COP and cooling power under different heat source temperatures. The construction, circulation and testing system of the chiller were introduced. A typical running condition of the chiller from the starting to the steady operating was given to show the dynamic performance. Several groups of the temperatures and COPs were given to show the steady state performance. These data showed that the COP increased from 0.69 to 1.08 under generation temperature from 95 °C to 120 °C. Besides, the effects of chilled water temperature, cooling water temperature, pump frequency and opening of valve on COP and cooling power were analyzed respectively.     

AHRI风冷冷水机组的测试要求

为了方便广大冷水机组厂商全面地了解AHRI风冷式冷水机组的测试要求,本文就冷水机组冷凝器进风温度测量方案,冷冻水测量系统配置及制冷量计算方法,不同大气压下测试的制冷量和能效比的修正方法等方面分别作了介绍。     

Indirect evaporative combined inlet air cooling with gas turbines for green power technology

Different inlet air cooling systems are usually used with gas turbines. A new form of inlet air cooling called the indirect evaporative cooling system (IECS) has been investigated in this work. This system is a combination of a humidifier with a vapor compression or absorption cooling system for part of the total air i.e. the secondary air stream. The net power produced from the gas turbine on a hot day (45 °C) by using combined (IECS) with absorption chillers showed an increase in power and efficiency by 15% and 9%, respectively; its recovery period is suitable for all environmental conditions. For IECS combined with vapor compression mechanical chillers showed an increase in power and efficiency by about 7.81% and 2.24%, respectively, but its recovery period made it suitable only for hot and humid conditions. The IECS has lower chiller's capital cost by about 25% (mechanical chiller) and 40% (absorption chiller).     

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.