A review on solar cold production through absorption technology

Recently, the traditional energy types have failed to satisfy the human needs because of their limited quantity as well as their negative environmental impacts. Conventional cold producing machines that are based on vapor compression principle are primary electricity consumers and their working fluids are being banned by international legislation. From this perspective, solar powered cooling systems as a green cold production technology are the best alternative. Absorption refrigeration is a mature technology that has proved its applicability with the possibility to be driven by low grade solar and waste heat. In this study, we present a comprehensive literature review on absorption based refrigeration and air conditioning systems that are powered by solar energy. Various systems along with their thermodynamic operating principle are presented. Moreover, the previous experimental and numerical simulation studies for these systems are discussed.     

Thermal cooling using low-temperature waste heat: a cost-effective way for industrial companies to improve energy efficiency?

As a typical cross-cutting technology, cooling and refrigeration equipment is used for a variety of industrial applications. While cooling is often provided by electric compression cooling systems, thermal cooling systems powered by low-temperature waste heat could improve energy efficiency and promise a technical saving potential corresponding to 0.5?% of the total electricity demand in the German industry. In this paper, we investigate the current and future cost-effectiveness of thermal cooling systems for industrial companies. Our focus is on single-stage, closed absorption and adsorption cooling systems with cooling powers between 40 and 100?kW, which use low-temperature waste heat at temperature levels between 70?°C and 85?°C. We analyse the current and future cost-effectiveness of these alternative cooling systems using annual cooling costs (annuities) and payback times. For a forecast until 2015, we apply the concept of experience curves, identifying learning rates of 14?% (absorption machines) and 17?% (adsorption machines) by an expert survey of the German market. The results indicate that thermal cooling systems are currently only cost-effective under optimistic assumptions (full-time operation, high electricity prices) when compared to electric compression cooling systems. Nevertheless, the cost and efficiency improvements expected for this still young technology mean that thermal cooling systems could be more cost-effective in the future. However, depending on future electricity prices, a high number of operating hours is still crucial to achieve payback times substantially below 4?years which are usually required for energy efficiency measures to be widely adopted in the industry.     

新型太阳能喷射与电压缩联合制冷系统研究

为提高太阳能与辅助能源的综合利用率，提出了一种新型的太阳能喷射式与电压缩式有机结合为一体的联合制冷系统，进而对这种新型联合系统及传统联合系统进行了热力学对比分析，对联合系统太阳能喷射式制冷时最佳发生温度进行了选择，并计算了典型年气象条件下两种联合系统相对于电压缩制冷系统的节能量及节能率。结果表明：两种联合系统相对于电压缩式制冷系统而言都是节能的，但新型联合制冷系统比传统联合制冷系统更节能，更能高效地综合利用太阳能与常规能源：在文中计算条件下，新型联合系统比传统联合系统多节能13．6％。     

Prospects for solar cooling – An economic and environmental assessment

Producing refrigeration and/or air conditioning from solar energy remains an inviting prospect, given that a typical building’s cooling load peaks within 2 or 3 h of the time of maximum solar irradiation. The attractiveness of “free” cooling obtained from the sun has spawned a wealth of research over the last several decades, as summarized in a number of review articles. Obstacles—especially high initial costs—remain to the widespread commercialization of solar cooling technologies. It is not clear at the present time if thermally driven systems will prove to be more competitive than electrically driven systems. We therefore describe a technical and economic comparison of existing solar cooling approaches, including both thermally and electrically driven. We compare the initial costs of each technology, including projections about future costs of solar electric and solar thermal systems. Additionally we include estimates of the environmental impacts of the key components in each solar cooling system presented. One measure of particular importance for social acceptance of solar cooling technologies is the required “footprint,” or collector area, necessary for a given cooling capacity. We conclude with recommendations for future research and development to stimulate broader acceptance of solar cooling. The projections made show that solar electric cooling will require the lowest capital investment in 2030 due to the high COPs of vapor compression refrigeration and strong cost reduction targets for PV technology.     

Economic comparison of solar absorption and photovoltaic-assisted vapour compression cooling systems

When the solar absorption and vapour compression cooling systems are viewed from the point of view of electrical energy consumption the differences between them can be expressed in terms of electrical energy saving with the former. As such, it is proposed that an economic comparison between photovoltaic-assisted vapour compression and solar absorption cooling systems be conducted, assuming that the former receives an amount of solar electricity equal to the potential electrical energy saving with the latter. The comparison is conducted with particular emphasis on the operational conditions in Kuwait. Analysis has shown that the potential electrical energy saving with a solar absorption cooling system is equal to 16 per cent of its refrigeration generation. The cost of supplying an equal amount of solar electricity is compared with the difference between the life-time costs of a solar absorption system and an equivalent vapour compression system. The economic comparison is conducted on the basis of the difference between the net present values of both systems. Given the current cost estimates and the prevailing climatic conditions in Kuwait it is shown that photovoltaic-assisted vapour compression cooling systems are likely to compete with the solar absorption cooling systems. This is particularly true in such applications where cooling is required for few hours during the day, and as the cost of the photovoltaic system decreases.     

An assessment of the feasibility of solar absorption and vapor compression cooling systems

For absorption cooling systems to operate and produce their cooling effects they need both thermal and electrical energy, while vapor compression systems need electrical energy only. When operating on solar energy the absorption system may receive all its thermal energy needs from solar sources while its electrical needs (parasitic power) are to be supplied from conventional sources. In order to conduct a fair comparison between the two cooling systems, it is proposed to supply both systems with equal amounts of conventional power and to supplement the rest of their needs from solar sources. A solar coefficient of performance, defined as the ratio of the refrigeration effect to the solar radiation input, is introduced and used for comparing some parameters of engineering ane economic importance in both systems. Economic analysis of solar cooling systems indicates that their initial cost is a function of both their design capacities and the number of hours of full load operation required to fulfill the total daily cooling demand. It indicates, also, that the initial cost of both solar cooling systems would break even before the cost of their respective solar conversion devices do.     

新型太阳能喷射与电压缩式联合制冷系统的研究

提出一种新型的太阳能喷射与电压缩联合制冷系统,其既可以利用太阳能喷射式制冷又可以利用电能驱动压缩式制冷,可提高太阳能与辅助能源的综合利用率。对该系统中以R141b作为制冷工质,采用斜盘式压缩机的辅助电压缩制冷系统进行了理论循环计算与实验研究。实验表明,该辅助电压缩制冷系统的性能系数达到2.53。与传统的辅助能源应用方式相比,该辅助电压缩式制冷系统能更高效地利用常规能源,提高新型太阳能喷射制冷系统的综合节能效果。     

Comparative study of different solar cooling systems for buildings in subtropical city

In recent years, more and more attention has been paid on the application potential of solar cooling for buildings. Due to the fact that the efficiency of solar collectors is generally low at the time being, the effectiveness of solar cooling would be closely related to the availability of solar irradiation, climatic conditions and geographical location of a place. In this paper, five types of solar cooling systems were involved in a comparative study for subtropical city, which is commonly featured with long hot and humid summer. The solar cooling systems included the solar electric compression refrigeration, solar mechanical compression refrigeration, solar absorption refrigeration, solar adsorption refrigeration and solar solid desiccant cooling. Component-based simulation models of these systems were developed, and their performances were evaluated throughout a year. The key performance indicators are solar fraction, coefficient of performance, solar thermal gain, and primary energy consumption. In addition, different installation strategies and types of solar collectors were compared for each kind of solar cooling system. Through this comparative study, it was found that solar electric compression refrigeration and solar absorption refrigeration had the highest energy saving potential in the subtropical Hong Kong. The former is to make use of the solar electric gain, while the latter is to adopt the solar thermal gain. These two solar cooling systems would have even better performances through the continual advancement of the solar collectors. It will provide a promising application potential of solar cooling for buildings in the subtropical region.     

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.     

采用不同集热器的太阳能吸收式制冷系统经济性分析

以能源平均成本和动态投资回收期为经济性指标,对采用平板集热器、真空管集热器、复合抛物面集热器和槽式集热器驱动的太阳能单效溴化锂吸收式制冷系统进行了对比分析,同时以?效率和动态投资回收期为目标对优选的太阳能制冷系统进行了多目标优化。结果表明：采用真空管集热器的太阳能制冷系统的能源平均成本最低及动态投资回收期最短;发生器热水进口温度存在最优值使得系统?效率最高,能源平均成本最低;增加系统装机容量可有效降低系统的能源平均成本并且缩短投资回收期;太阳辐照强度越大,太阳能制冷系统的能源平均成本越低及投资回收期越短。此外,多目标优化结果表明发生器热水进口温度存在最优值可使得综合目标函数取得最小值。     

Theoretical study of a transcritical ejector refrigeration cycle with refrigerant R143a

In this paper, a transcritical ejector refrigeration cycle (TERC) using refrigerant R143a as working fluid is proposed to improve the performance of the ejector refrigeration systems driven by low-grade thermal energy. This method adopts an adequate combination of thermal and mechanical energy through the operation of the transcritical process for generator to enhance the performance of the conventional ejector refrigeration cycle (ERC) at the cost of additional driving mechanical energy. The performance characteristics of the TERC are investigated based on theoretical simulations. The TERC is also compared with the conventional ERC using refrigerant R134a. The study shows that when utilizing the low-grade thermal energy, the TERC yields significant increase in COP by adding auxiliary mechanical energy of the cycle pump and has a higher potential in making effective use of the low-grade thermal energy with gradient temperature, such as solar energy gained by a flat plate or evacuated tube solar collector. This also indicates that the TERC is an attractive alternative to the ejector refrigeration systems driven by low-grade thermal energy. Further experimental work for the TERC may be launched in the near future to verify practical applications.     

太阳能驱动实现制冷的研究及其应用

本文提出了利用太阳能驱动实现制冷是一门节能环保技术，重点分析和论述了太阳能驱动实现制冷的几种主要方法．即利用太阳能光一电转换实现制冷、太阳能吸收式制冷、太阳能吸附式制冷和太阳能喷射式制冷。指出太阳能驱动实现制冷的研究具有广阔的应用前景。     

A review: Renewable energy with absorption chillers in Thailand

The aim of this paper is to review the energy situation, renewable energy potential and absorption chiller system in Thailand. The renewable energy which will be used in low temperature applications, under the consideration of low operating cost, high availability and non-polluted emission such as solar energy was discussed. Solar energy can be used as power sources for cooling systems, especially for the absorption chiller. Thailand is located in the area where the solar intensity is very high and thus solar energy can be used as power sources. The absorption chiller using water/lithium bromide is the most appropriate for the solar applications. This system, however, is not widely used in Thailand due to its complexity, high toxicity caused by leakage and high initial cost. The utilization of absorption chiller may increase if more researches focus on the development of this cooling system, which is driven by solar energy. This may results in a substantial decrease in electricity consumption.     

Solar-powered cooling systems: Technical and economic analysis on industrial refrigeration and air-conditioning applications

In the last years, the growing demand for air conditioning has caused a significant increase in demand for primary energy resources. Solar-powered cooling is one of the technologies which allows to obtain, by using the renewable solar source, an important energy saving compared to traditional air conditioning plants. The paper describes different technical installations for solar cooling, their way of operation, advantages and limits. The objective of the present study has been to analyze the technical and economic feasibility of solar absorption cooling systems, designed for two different application fields: industrial refrigeration and air conditioning. The possibility to replace or integrate the existing plants is studied, by considering the refrigeration requirements of a company, which works in meat manufacturing, and the heating and cooling demands of a hotel located in a tourist town in Italy. In the first case, the system comprises an absorption chiller coupled to solar flat plate collectors, whereas the second application is about a hybrid trigeneration plant, known as thermo-solar trigeneration; this option allows having greater operational flexibility at sites with demand for energy in the form of heating as well as cooling, for example in a hotel. In this way the authors could compare different results obtained by a technical and economic experimental analysis based on existing users and evaluate the advantages and disadvantages in order to suggest the best solution for the two studied cases.     

Multi-pressure absorption cycles in solar refrigeration:: A technical and economical study

A technical and economical study of regenerative absorption chillers with multi-pressure cycle has been undertaken as solar operated refrigeration systems. Referred to as advanced absorption chillers they represent one of the new technology options that are under development. Advanced absorption cooling technology offers the possibility of chillers with thermal COPs of 1.5 or greater at driving temperatures of 140°C, which reduces the collector area and the heat rejection requirements compared to current absorption cooling technology. Two different absorption systems have been considered. The first is an advanced, double-effect regenerative absorption cooling system, driven at 140°C, whose efficiency is about 55% of the Carnot efficiency. The second is an ideal, single-effect regenerative absorption system that achieves 70% of the Carnot efficiency driven at 140°C or 200°C. To evaluate the solar performance of a thermally driven chiller requires a separate analysis of the solar availability for a given location compared to the required monthly average solar input. In this analysis different systems, including the vapour compression chillers, have been compared in terms of the thermal and electrical energy input. An effective electrical COP may be computed assuming that the ratio of electrical energy cost to thermal energy cost is four, which is typical of today’s fossil fuel costs. The effective electrical COPs of different technical options can then be compared. Those systems with higher electrical COPs will have lower energy costs. If solar is to be competitive, then the cost of delivered solar thermal energy should be less than the cost of delivered fossil thermal energy.     

Solar cooling technologies in Greece. An economic viability analysis

In Greece, during the summer, the demand for electricity greatly increases because of the extensive use of air-conditioning systems. This is a source of major problems in the country’s electricity supply and contributes to an increase of the CO₂ emissions. The use of solar energy (SE) to drive cooling cycles is attractive since the cooling load is roughly in phase with SE availability. An economic evaluation of two types of solar cooling systems is made (an absorption and an adsorption system). The analyses indicated that, because of their high investment cost, these systems would be marginally competitive with standard cooling systems at present energy prices.     

Residential solar air conditioning: Energy and exergy analyses of an ammonia–water absorption cooling system

Large scale heat-driven absorption cooling systems are available in the marketplace for industrial applications but the concept of a solar driven absorption chiller for air-conditioning applications is relatively new. Absorption chillers have a lower efficiency than compression refrigeration systems, when used for small scale applications and this restrains the absorption cooling system from air conditioning applications in residential buildings. The potential of a solar driven ammonia–water absorption chiller for residential air conditioning application is discussed and analyzed in this paper. A thermodynamic model has been developed based on a 10 kW air cooled ammonia–water absorption chiller driven by solar thermal energy. Both energy and exergy analyses have been conducted to evaluate the performance of this residential scale cooling system. The analyses uncovered that the absorber is where the most exergy loss occurs (63%) followed by the generator (13%) and the condenser (11%). Furthermore, the exergy loss of the condenser and absorber greatly increase with temperature, the generator less so, and the exergy loss in the evaporator is the least sensitive to increasing temperature.     

Review of solar sorption refrigeration technologies: Development and applications

In this paper, a review of the research state of art of the solar sorption (absorption and adsorption) refrigeration technologies is presented. After an introduction of basic principles, the development history and recent progress in solar sorption refrigeration technologies are reported. The application areas of these technologies are categorized by cooling temperature demand. It shows that solar-powered sorption refrigeration technologies are attractive alternatives that not only can serve the needs for air-conditioning, refrigeration, ice making and congelation purposes, but also can meet demand for energy conservation and environment protection. However, a lot of research work still needs to be done for large-scale applications in industry and for the replacement of conventional refrigeration machines.     

Techno-economic performance analysis of solar cooling systems

Vapour absorption cooling systems, powered by solar thermal energy, are now commercially manufactured in sizes ranging from 1.5 to over 20 RT (one refrigeration ton = 3.51 kW of cooling). The needed thermal energy at appropriate temperature potential can either be provided by solar thermal collectors or else from a solar pond. The paper gives the assessment criteria and results for technical and economic evaluation of the performance of absorption chiller using a solar pond. These results, based on Kuwait's environmental data and costs, have been compared with three alternate cooling systems, namely:

• 1 Solar thermal collector absorption cooling system.
• 2 Solar photovoltaic cooling system.
• 3 Standard vapour compression cooling system.

The criteria, used for performance evaluation of the solar cooling systems on a technical basis, consists of assessing the extent to which such systems can make a positive contribution in a conserving fossil fuel. This is done by first estimating the total electrical energy needed by the standard system (defined in para. 3 above) to produce one unit of cooling output. Solar cooling systems are then analysed and compared with a standard system to establish their electrical energy saving or generation capability, after accounting for the parasitic electrical energy used in pump/fan motors and equivalent energy needed for the production of soft water (used-up in the cooling tower) from seawater desalination. The economic analysis considers the cost and life of subsystems and that of the electrical and water desalination plants to arrive at the unit cooling cost. The unit cooling is defined as the ratio of amortized capital investments plus operation and maintenance costs over the year and the total yearly cooling production by the system. The results show that the solar pond absorption cooling system is the closest competitor to the conventional cooling system.