Cooling performance and energy saving of a compression–absorption refrigeration system driven by a gas engine

The prototype of combined vapour compression–absorption refrigeration system was set up, where a gas engine drove directly an open screw compressor in a vapour compression refrigeration chiller and waste heat from the gas engine was used to operate absorption refrigeration cycle. The experimental procedure and results showed that the combined refrigeration system was feasible. The cooling capacity of the prototype reached about 589 kW at the Chinese rated conditions of air conditioning (the inlet and outlet temperatures of chilled water are 12 and 7°C, the inlet and outlet temperatures of cooling water are 30 and 35°C, respectively). Primary energy rate (PER) and comparative primary energy saving were used to evaluate energy utilization efficiency of the combined refrigeration system. The calculated results showed that the PER of the prototype was about 1.81 and the prototype saved more than 25% of primary energy compared to a conventional electrically driven vapour compression refrigeration unit. Error analysis showed that the total error of the combined cooling system measurement was about 4.2% in this work. Copyright © 2006 John Wiley & Sons, Ltd.     

Optimization study of combined refrigeration cycles driven by an engine

In order to utilize the waste heat efficiently for a gas engine-driven heat pump running in a cooling mode, this paper studies two combined absorption/compression refrigeration cycles using ammonia and water as the working fluid. By analyzing the operating characteristics of the combined cycles that make efficient use of both the work and the heat output of an engine, this paper puts forward an optimal mathematical model with an objective function of the primary-energy ratio (PER). The model has been calculated for typical cooling applications. Analysis of the results indicates that optimization can make the combined cycle fully achieve the sought-after energy saving advantage. It was also found that the PERs of the combined cycles increase considerably compared with a conventional engine-driven compression cycle working with pure ammonia. The combined cycle, with two solution circuits, is the best.     

从热工学角度探讨国产吸收式制冷机的发展方向

该文从热工学角度探讨了目前我国溴化锂吸收式制冷机整机热力循环及各热质交换设备性能、结构等方面存在的问题;在整机循环方面,指出实现各设备的合匹配、发展新的结构流程及增加新品种、新规格的机组为进一步的发展方向;在各设备性能、结构方面提出应加强吸收机理研究以及表面活化剂、高效强化管的应用研究。     

采用复合吸附剂和高效吸附床的吸附制冷机性能测试

利用平行流换热器和自制的硅胶/氯化钙复合吸附剂研制了一台小型吸附式制冷样机,并对样机进行了试验测试。测试结果表明:相对于硅胶吸附制冷样机,复合吸附剂吸附制冷样机的COP和制冷功率都有了明显的提高;在热源温度为90℃,冷却水温度为35℃,冷冻水进口温度为16.5℃、出口温度为14.4℃,吸附10min,脱附5 min的运行工况下,在整个循环周期内(15 min),制冷功率为1.03 kW,SCP为128.3 W/kg,COP为0.29;在吸附周期内(10 min),制冷功率为1.54 kW,SCP为192.4 W/kg,样机的能量密度为10.3 kW/m3,平行流换热器的换热系数为472.3 W/(m2.K)。     

利用汽车发动机余热的溴化锂吸收式制冷研究

根据现有汽车空调的制冷系统和发动机冷却水及排气系统的结构特点,结合溴化锂吸收式制冷系统的工作原理,提出将汽车排气管和发动机冷却水箱进行结构改造作为溴化锂吸收式制冷系统的发生器,代替传统的汽车空调的制冷和采暖系统及发动机冷却系统。并对该溴化锂制冷系统进行了热力计算和传热面积的计算,计算结果表明,溴化锂制冷系统充分利用了废气余热和冷却水余热,减少了汽车油耗,并且改造后的排气热交换器和冷却水箱传热面积小,结构简单紧凑。     

Thermodynamic analysis of load-leveling hyper energy converting and utilization system

Load-leveling hyper energy converting and utilization system (LHECUS) is a hybrid cycle which utilizes ammonia–water mixture as the working fluid in a combined power generation and refrigeration cycle. The power generation cycle functions as a Kalina cycle and an absorption refrigeration cycle is combined with it as a bottoming cycle. LHECUS is designed to utilize the waste heat from industry to produce cooling and power simultaneously. The refrigeration effect can be either transported to end-use sectors by means of a solution transportation absorption chiller (STA) as solution concentration difference or stored for demand load leveling.     

Physical and operating conditions effects on silica gel/water adsorption chiller performance

Adsorption refrigeration systems are commercially developed due to the need of replacing the conventional systems which utilise environmentally harmful refrigerants and consume high grade electrical power. This paper presents the key equations necessary for developing a novel empirical lumped analytical simulation model for commercial 450 kW two-bed silica gel/water adsorption chiller incorporating mass and heat recovery schemes. The adsorption chiller governing equations were solved using MATLAB® platform integrated with REFPROP® to determine the working fluids thermo-physical properties. The simulation model predicted the chiller performance within acceptable tolerance and hence it was used as an evaluation and optimisation tool. The simulation model was used for investigating the effect of changing fin spacing on chiller performance where changing fin spacing from its design value to minimum permissible value increased chiller cooling capacity by 3.0% but decreased the COP by 2.3%. Furthermore, the effect of generation temperature lift on chiller performance and the feasibility of using it as a load control tool will be discussed. Genetic Algorithm optimisation tool was used to determine the optimum cycle time corresponding to maximum cooling capacity, where using the new cycle time increased the chiller cooling capacity by 8.3%.     

Modeling and optimization of a novel pressurized CHP system with water extraction and refrigeration

A novel cooling, heat, and power (CHP) system has been proposed that features a semi-closed Brayton cycle with pressurized recuperation, integrated with a vapor absorption refrigeration system (VARS). The semi-closed Brayton cycle is called the high-pressure regenerative turbine engine (HPRTE). The VARS interacts with the HPRTE power cycle through heat exchange in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration in an amount that depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for the inlet air to the high-pressure compressor, water extraction, and for an external cooling load. The computer model of the combined HPRTE/VARS cycle predicts that with steam blade cooling and a medium-sized engine, the cycle will have a thermal efficiency of 49% for a turbine inlet temperature of 1400°C. This thermal efficiency, is in addition to the large external cooling load, generated in the combined cycle, which is 13% of the net work output. In addition, it also produces up to 1.4 kg of water for each kg of fuel consumed, depending upon the fuel type. When the combined HPRTE/VARS cycle is optimized for maximum thermal efficiency, the optimum occurs for a broad range of operating conditions. Details of the multivariate optimization procedure and results are presented in this paper. Copyright © 2008 John Wiley & Sons, Ltd.     

重型卡车朗肯−朗肯制冷系统热力学研究

本文针对重型卡车发动机冷却液余热工况,采用R245fa作为循环工质建立了朗肯−朗肯制冷系统,剖析了此系统的基本原理和结构特点,根据系统分析建立了数学模型,模拟分析了发生温度、冷凝温度、蒸发温度对系统性能的影响。结果表明：在发生温度85℃、冷凝温度50℃、蒸发温度5℃时,系统COP（coefficient of performance）达到0.254,虽然此系统的效率要低于相同工况下的吸收制冷循环,但是朗肯−朗肯制冷系统相对于吸收制冷系统具有尺寸小、易于控制和快速响应等优点,利用朗肯−朗肯循环回收重型卡车发动机冷却液余热进行制冷是可行的。     

Integration of a molten carbonate fuel cell with a direct exhaust absorption chiller

A high market value exists for an integrated high-temperature fuel cell-absorption chiller product throughout the world. While high-temperature, molten carbonate fuel cells are being commercially deployed with combined heat and power (CHP) and absorption chillers are being commercially deployed with heat engines, the energy efficiency and environmental attributes of an integrated high-temperature fuel cell-absorption chiller product are singularly attractive for the emerging distributed generation (DG) combined cooling, heating, and power (CCHP) market. This study addresses the potential of cooling production by recovering and porting the thermal energy from the exhaust gas of a high-temperature fuel cell (HTFC) to a thermally activated absorption chiller. To assess the practical opportunity of serving an early DG-CCHP market, a commercially available direct fired double-effect absorption chiller is selected that closely matches the exhaust flow and temperature of a commercially available HTFC. Both components are individually modeled, and the models are then coupled to evaluate the potential of a DG-CCHP system. Simulation results show that a commercial molten carbonate fuel cell generating 300 kW of electricity can be effectively coupled with a commercial 40 refrigeration ton (RT) absorption chiller. While the match between the two “off the shelf” units is close and the simulation results are encouraging, the match is not ideal. In particular, the fuel cell exhaust gas temperature is higher than the inlet temperature specified for the chiller and the exhaust flow rate is not sufficient to achieve the potential heat recovery within the chiller heat exchanger. To address these challenges, the study evaluates two strategies: (1) blending the fuel cell exhaust gas with ambient air, and (2) mixing the fuel cell exhaust gases with a fraction of the chiller exhaust gas. Both cases are shown to be viable and result in a temperature drop and flow rate increase of the gases before the chiller inlet. The results show that no risk of cold end corrosion within the chiller heat exchanger exists. In addition, crystallization is not an issue during system operation. Accounting for the electricity and the cooling produced and disregarding the remaining thermal energy, the second strategy is preferred and yields an overall estimated efficiency of 71.7%.     

Experimental study on improved two-bed silica gel–water adsorption chiller

A novel silica gel–water adsorption chiller with two chambers has been built in Shanghai Jiao Tong University (SJTU). This chiller combines two single bed systems (basic system) without any vacuum valves. One adsorber, one condenser and one evaporator are housed in the same chamber to constitute one adsorption/desorption unit. In this work, the chiller is developed and improved. The improved chiller is composed of three vacuum chambers: two adsorption/desorption vacuum chambers (the same structure as the former chiller) and one heat pipe working vacuum chamber. The evaporators of these two adsorption/desorption units are combined by a heat pipe. So, no valves are installed in the chilled water sub system and one vacuum valve connects the two adsorption/desorption chambers together to improve its performance. The performance of the chiller is tested. As the results, the refrigerating capacity and the COP of the chiller are, respectively, 8.69 kW and 0.388 for the heat source temperature of 82.5 °C, the cooling water temperature of 30.4 °C and the chilled water outlet temperature of 11.9 °C. For a chilled water outlet temperature of 16.5 °C, the COP reaches 0.432, while the refrigerating capacity is near 11 kW. There is an improvement of at least 12% for the COP compared with the former chillers.     

A numerical analysis of cooling water temperature of two-stage adsorption chiller along with different mass ratios

This paper deals with the performance investigation of a silica gel/water based on two-stage, four-bed adsorption chiller with different mass allocation between upper and lower beds employing the re-heat scheme. The innovative chiller is powered by waste heat or renewable energy source of temperature between 50 °C and 90 °C with a coolant of inlet temperature 30 °C for air conditioning purpose. The performance of the four-bed adsorption chiller employing the re-heat scheme is compared with that of the two-stage conventional chiller with the re-heat scheme using equal mass allocation. Results show that cooling capacity can be improved with the optimum allocation of adsorbent mass to the upper beds than that of lower beds. Besides, it is observed that the cooling capacity can be improved up to 10.78% while the cooling water temperature is at 20 °C.     

Study on a dual-mode, multi-stage, multi-bed regenerative adsorption chiller

In this paper, a detailed parametric study on a dual-mode silica gel–water adsorption chiller is performed. This advanced adsorption chiller utilizes effectively low-temperature solar or waste heat sources of temperature between 40 and 95 °C. Two operation modes are possible for the advanced chiller. The first operation mode will be to work as a highly efficient conventional chiller where the driving source temperature is between 60 and 95 °C. The second operation mode will be to work as an advanced three-stage adsorption chiller where the available driving source temperature is very low (between 40 and 60 °C). With this very low driving source temperature in combination with a coolant at 30 °C, no other cycle except an advanced adsorption cycle with staged regeneration will be operational. In this paper, the effect of chilled-water inlet temperature, heat transfer fluid flow rates and adsorption–desorption cycle time effect on cooling capacity and COP of the dual-mode chiller is performed. Simulation results show that both cooling capacity and COP values increase with the increase of chilled water inlet temperature with driving source temperature at 50 and 80 °C in three-stage mode, and single-stage multi-bed mode, respectively. However, the delivered chilled-water temperature increases with chilled-water inlet temperature in both modes.     

Performance analysis of a waste‐heat‐powered thermodynamic cycle for multieffect refrigeration

A multieffect refrigeration system that is based on a waste‐heat‐driven organic Rankine cycle that could produce refrigeration output of different magnitudes at different levels of temperature is presented. The proposed system is integration of combined ejector–absorption refrigeration cycle and ejector expansion Joule–Thomson (EJT) cooling cycle that can meet the requirements of air‐conditioning, refrigeration, and cryogenic cooling simultaneously at the expense of industrial waste heat. The variation of the parameters that affect the system performance such as industrial waste heat temperature, refrigerant turbine inlet pressure, and the evaporator temperature of ejector refrigeration cycle (ERC) and EJT cycles was examined, respectively. It was found that refrigeration output and thermal efficiency of the multieffect cycle decrease considerably with the increase in industrial waste heat temperature, while its exergy efficiency varies marginally. A thermal efficiency value of 22.5% and exergy efficiency value of 8.6% were obtained at an industrial waste heat temperature of 210°C, a turbine inlet pressure of 1.3 MPa, and ejector evaporator temperature of 268 K. Both refrigeration output and thermal efficiency increase with the increase in turbine inlet pressure and ERC evaporator temperature. Change in EJT cycle evaporator temperature shows a little impact on both thermal and exergy efficiency values of the multieffect cycle. Analysis of the results clearly shows that the proposed cycle has an effective potential for cooling production through exploitation of lost energy from the industry. Copyright © 2014 John Wiley & Sons, Ltd.     

内燃机车司机室吸附式空调器的实验与性能分析

机车司机室吸附式空调器是一种以内燃机排气的余热驱动的空调系统。该系统利用固体吸附式制冷原理，分子筛—水作为工质对，采用单吸附器结构，通过蓄冷器实现向内燃机车司机室连续、稳定地供冷。该文阐述了该空调器的实验方法，并对实验结果及性能影响因素进行了分析。实验表明：机车司机室吸附式空调器是一种实用、可行的新型空调系统。实验结果对原型样机及其运行控制方法的设计有重要的参考价值。     

太阳能烟囱制冷系统的研究

通过分析制冷系统和太阳能烟囱热气流发电系统的技术和特点,提出了太阳能烟囱制冷系统.将太阳能烟囱系统与制冷系统相结合进行制冷,可实现制冷不用电.该系统由烟囱、集热棚、蓄热层、涡轮机、开启式制冷压缩机、冷凝器和变速器等组成.介绍了太阳能烟囱制冷系统的结构特点、工作原理以及系统相关参数的计算方法.分析结果表明,太阳能烟囱制冷系统结构简单,运行维护方便,制冷不用电,无污染,具有良好的环境效应,可根据环境温度改变压缩机运行转速调节供冷负荷,能有效解决热带及沙漠地区的供冷及供电问题.     

On-site real-time evaluation of an air-conditioning direct-fired double-effect absorption chiller

This work presents a procedure for calculating the COP and heat transfer rates, based on on-site experimental temperature measurements, of a lithium–bromide/water direct-fired double-effect absorption chiller in reverse parallel flow configuration, running on natural gas. The chiller was equipped with a set of thermocouples which allowed measuring its working temperature levels through all its operating stages. The chiller analysed in this work is the central cooling system of the air-conditioning installation of the Principe Felipe Science Museum, located at the Valencia’s City of Arts and Sciences (Spain). This installation is capable of providing a cooling capacity of 4.5 millions of kcal/h (5.2 MW), by means of three direct-fired double-effect absorption chillers. From the experimental measurements a calculation procedure, based on energy and mass balances, has been developed, which allows estimating the specific powers by unit of mass flow rate through the evaporator. From these power values the instantaneous COP of the chiller could be obtained. Additionally, the paper analyzes different aspects that were not possible to be considered and details the actions taken in order to take them into account.     

AE94.3A型燃气轮机进气冷却的应用可行性研究

对AE94.3A型燃气轮机燃气-蒸汽联合循环热力系统平衡进行研究进而发现,与同类型、同等级不同型号机组相比,AE94.3A型联合循环机组余热锅炉的排烟温度较高,排烟余热仍有进一步利用的空间。通过设计优化,扩大省煤器受热面,回收烟气余热加热给水,驱动热水型溴化锂制冷机制冷,用于机组满负荷调峰时的压气机进气冷却或厂房及办公区域空调供冷,对改善燃气轮机联合循环的运行性能,实现能源梯级利用,提高能源利用率和机组经济性运行起到了很大作用。     

Design and experimental analysis of a carbon dioxide transcritical chiller for commercial refrigeration

Carbon dioxide is an interesting solution for commercial refrigeration and in perspective for air-conditioning systems. In this paper a newly developed carbon dioxide transcritical air cooled chiller for refrigerating propylene glycol down to −8 °C supply temperature is described. The aim of the project was at optimising the cycle energy efficiency while assuring reliable operation and simple management of the unit. The carbon dioxide optimal pressure issue is addressed with an innovate system architecture and control logic. Using a flash tanks and two electronic valves, the optimal cycle upper pressure was maintained in transcritical operation mode. The managing of the valves allows the refrigeration machine efficiency improvement when the gas cooler inlet air allows subcritical working conditions. A simulation model of the chiller was developed and its results validated with experimental data. A measurement campaign was carried out, testing the chiller at external temperatures ranging from 18 to 35 °C, the unit energy efficiency ranging from 3.1 to 2.0.     

冷热组合型超市系统的设计与经济性分析

设计了冷热组合型超市系统,利用CO2跨临界循环对空间夏季供冷和冬季供热,采用R290/CO2复叠式制冷循环对食品冷冻冷藏,同时回收CO2跨临界循环高温气体散发的热量和R290/CO2复叠式制冷循环R290高温循环气体的冷凝热,实现夏季空间供冷、食品制冷的同时供应生活热水,冬季空间供暖、食品制冷的同时供应生活热水,及春秋季节食品制冷同时供应生活热水。并与供冷、供暖、食品制冷和供应生活热水分别进行的常规R404A超市系统的能效相比较,得出冷热组合型超市系统的能耗大大降低,能效明显增加,不仅节约能源,而且保护环境,是很有发展前景的绿色环保系统。