Search

In this research paper, comprehensive thermodynamic modeling of an integrated energy system consisting of a multi-effect desalination system, geothermal energy system, and hydrogen production unit is considered and the system performance is investigated. The system's primary fuel is a geothermal two-phase flow. The system consists of a single flash steam-based power system, ORC, double effect water–lithium bromide absorption cooling system, PEM electrolyzer, and MED with six effects. The effect of numerous design parameters such as geothermal temperature and pressure on the net power of steam turbine and ORC cycle, the cooling capacity of an absorption chiller, the amount of produced hydrogen in PEM electrolyzer, the mass flow rate of distillate water from MED and the total cost rate of the system are studied. The simulation is carried out by both EES and Matlab software. The results indicate the key role of geothermal temperature and show that both total exergy efficiency and total cost rate of the system elevate with increasing geothermal temperature. Also, the impact of changing absorption chiller parameters like evaporator and absorber temperatures on the COP and GOR of the system is investigated. Since some of these parameters have various effects on cost and efficiency as objective functions, a multi-objective optimization is applied based on a Genetic algorithm for this system and a Pareto-Frontier diagram is presented. The results show that geothermal main temperature has a significant effect on both system exergy efficiency and cost of the system. An increase in this temperature from 260 C to 300 C can increase the exergy efficiency of the system for an average of 12% at various working pressure and also increase the cost of the system by 13%.

The main purpose of the current research work is to suggest a novel integrated multi-generation energy system and scrutinize 4E evaluation. This system consists of a solid oxide fuel cell, a PEM electrolyzer for hydrogen production, and an ejector-based absorption chiller for the coefficient of performance improvement. All parts of this system are verified with existing reports and papers. Effect of fuel cell current density, SOFC fuel cell temperature, absorption chiller evaporator temperature, and condenser temperature, and outlet turbine pressure has been investigated and reported. The effect of mentioned parameters on the exergy and cost rate has been considered. Data illustrate that the maximum exergy destruction rate belongs to the SOFC contributing 60% of the total exergy destruction rate of the system. Under the given condition of the system, the net produced power is about 200 kW with an exergy efficiency of 30.2% and thermal efficiency of 60.4%. At the considered condition the total cost rate of the system is estimated about 22.29 $/hr. The results of the present work provide a scientific base for designing poly-generation systems with high efficiency and reasonable cost rate.

In this present research study a multi-generation energy system which is coupled with CO2 capture unit which is based on Rankine cycle, organic Rankine cycle, ejector cooling system and absorption chiller has been analyzed via energy, exergy, exergy-economic aspects by developing MATLAB, also to achieve the optimum operating condition genetic algorithm has been applied for system optimization. The objective of this study is to propose an optimized efficient integrated energy system to recycle the energy waste of a typical industrial factory. The optimization has been illustrated on a Pareto frontier to achieve the optimum scheme of the multi-generation system regarding technical and economic viewpoints. Results indicate the optimal condition of this system has occurred at 0.37 exergy efficiency with 0.03 $/s. Furthermore, by surging the mass flow rate of waste gases up to 70 kg/s, net power output augmented up to 7500 kW. Besides, hydrogen production and produced desalinated water rise up to 8.5 g/s and 16 kg/s, respectively.

In this paper, numerical simulations of Diffusion Absorption Refrigeration – DAR cycle were conducted in order to study the performance of two configurations in steady state mode and use ammonia, water, hydrogen as working fluids. The two configurations were numerically simulated using models developed with the commercial flow sheet Aspen HYSYS V10 software. The first configuration where the main simple DAR cycle components were simulated and validated the experimental results. The second configuration where the modified DAR cycle was simulated which has an auxiliary heat exchanger added to the main simple DAR cycle as a modification. It was found that for the same input assumptions and heat applied, the modified DAR cycle shows higher cooling load. Therefore, higher COP than the simple DAR cycle. The optimal operation of the modified cycle is 36 W applied to the generator to achieve a COP of 0.235 instead of 0.209 for simple DAR cycle. The Simulation results show that by using the modified cycle, the COP improves by 12.4%.

Absorption chillers are one of the most used equipment in industrial, commercial, and domestic applications. For the places where high cooling is required, they are utilized in a network to perform the cooling demand. The main objective of the current study was to find the optimum operating conditions of a network of steam absorption chillers according to energy and economic viewpoints. Firstly, energy and economic analysis and modeling of the absorption chiller network were carried out to have a deep understanding of the network and investigate the effects of operating conditions. Finally, the particle swarm optimization search algorithm was employed to find an optimum levelized total costs of the plant. The absorption chiller network plant of the Marun Petrochemical Complex in Iran was selected as a case study. To verify the simulation results, the outputs of energy modeling were compared with the measured values. The comparison with experimental results indicated that the developed model could predict the working condition of the absorption chiller network with high accuracy. The economic analysis results revealed that the levelized total costs of the plant is 1730 $/kW and the payback period is three years. The optimization findings indicated that working at optimal conditions reduces the levelized total costs of the plant by 8.5%, compared to the design condition.

In order to investigate the ammonia + water + lithium bromide absorption refrigeration cycle process and to simulate it accurately, a vapor-liquid equilibrium calculation model was proposed to obtain thermodynamic characteristic data of the ternary mixtures. The calculation of parameters of liquid phase is based on Wilson’s equation and NRTL equation. The vapor phase, assumed to consist of ammonia and water only, is described by The Redlich-Kwong Equation of State. The data of the equilibrium vapor pressure and the ammonia concentration in liquid phase calculated by this model was compared with the experimental data, the difference is between 0.5% to 9.6% within the temperature range from303 K to 425 K. The COP obtained by the simulation matches with that obtained by experiment and the absolute deviation is less than 0.02. Therefore, this calculation model can be used for simulation to extend the temperature range and pressure range of the system, so as to determine the design parameters of the absorption refrigeration system. The simulation results indicates that under different working conditions, the optimal generator temperature and concentration of adding lithium bromide can be selected, to which the theoretical explanations were given in this paper.

In the past few years, absorption refrigeration systems (ARS) have captivated increasing research interests as it is a promising alternative and tenable solution to replace vapour compression refrigeration systems (CRS). Also, the refrigerants used in this system are environmentally friendly. NH3/H2O and H2O/LiBr are the most commonly used working fluids in ARS. However, the NH3/H2O ARS has a limitation in that it requires additional components such as a rectifier and analyzer. The proposed work focuses on improving the performance of the ARS by using other ammonia-based working fluids, namely NH3/LiNO3 and NH3/NaSCN. Various correlations are used to determine the thermodynamic properties of these working fluids and are later used in the thermodynamic simulation. NH3/H2O, NH3/LiNO3 and NH3/NaSCN ARS performance analyses are carried out using a computer program written in Python 3.0. The coefficient of performance of these systems is compared at different operating parameters, i.e., evaporator, condenser, generator, and absorber temperature. The results indicate that the working fluids, NH3/LiNO3 and NH3/NaSCN, perform better than the NH3/H2O ARS. Thus, NH3/LiNO3, NH3/NaSCN ARS provide better performance in more significant value of COP and do not require additional components such as a rectifier and analyzer. Hence, NH3/LiNO3 and NH3/NaSCN can be considered suitable alternatives to NH3/H2O in a vapour ARS.

In contrast to standard vapor compression cooling systems, diffusion absorption refrigeration (DAR) systems are heat-driven and contain no moving parts. Solar diffusion absorption cooling systems can extract heat from a cooling chamber without electricity, enabling food and medicine to be cooled in remote places where there is high solar radiation with unavailable or unreliable electricity. This work aims to model the performance of a solar-driven DAR system with an evacuated tubes collector. The model inputs were the local hourly ambient temperature and solar irradiance for the time of June to August in Ashdod, Israel. Also, collector data, ammonia concentration in the solution, evaporator temperature and the DAR system geometry were considered. The model results showed that as the generator heat input increased rapidly the evaporator cooling capacity was kept almost constant for a given concentration and collector area. This resulted in reduction in the COP values at peak hour. An increase in the collector area had more impact on the heat applied to the generator and not resulted in a significant growth of the cooling capacity, thus, the authors concluded that for optimal COP it is advised to operate the system with lower collector areas.

A hydrogen liquefaction concept with an innovative configuration and a capacity of 4 kg·s−1 (345.6 Ton per day) is developed. The concept involves an ammonia absorption refrigeration system for the pre-cooling of hydrogen and MR streams from 25 °C to −30 °C. The ammonia absorption refrigeration system is fed by exhaust gases of the Parand gas power plant that are normally dissipated to the environment with a temperature of 546 °C. The simulation is performed by Aspen HYSYS V9.0, using two separate equations of state for simulating hydrogen and MR streams to gain more accurate results especially for ortho-para conversion. Results show that conversion enthalpy estimated by Aspen HYSYS, fits very well to the experimental data. Determining the important independent variables and composition of MRs are done using trial and error procedure, a functional and straightforward method for complicated systems. The minimum temperature limit in the cooling section is lowered, and an ortho-para converter is implemented in this section. The proposed concept performs well from energy aspects and leads to COP and SEC equal to 0.271 and 4.54 kW·h·kg-1, respectively. The main advantage of this study is in the low SEC, eliminating the losses of the distribution network, and improving the ability of the hydrogen liquefaction for energy storage in off-peak times.

Ammonia/salt absorption refrigeration cycle has advantages of low grade heat recovery, excellent thermal performance and simple construction, which may play an important role in refrigeration and air-conditioning fields for energy saving and emission reduction. The present paper introduces a prototype of absorption refrigeration system driven by exhaust heat operating with NH3/LiNO3 and NH3/LiNO3+H2O, which is composed of commonly used devices with the advantages of low cost and simple manufacture. Comprehensive experiments on the prototype were carried out with varying operating conditions (exhaust-gas temperature, chilled-water temperature, cooling-water temperature) to evaluate their influences on performance parameters. The NH3/LiNO3 system was driven by gaseous exhaust heat in the range of 150.1°C∼325.1°C, the minimum evaporating temperature reached -25.29°C, the cooling capacities varied between 0.60kW and 3.00kW, the electrical coefficient of performance varied between 3.30 and 16.52, and the overall coefficient of performance varied between 0.263 and 0.584. The NH3/LiNO3+H2O system was driven in the range of 125.8°C∼330.1°C, the minimum evaporating temperature reached -22.56°C, the cooling capacities varied between 0.92kW and 3.91kW, the electrical coefficient of performance varied between 4.65 and 20.30, and the overall coefficient of performance varied between 0.310 and 0.566. The experimental results were compared with that of NH3/NaSCN system by authors’ previous work, it is found that three ammonia/salt working fluids have respective advantages and optimal working condition ranges. The experimental evaluation and comparison provide significant references for the optimization and practical application of the ammonia/salt absorption refrigeration systems.

In this paper, the experimental performance of a 45 m2 solar field of non-tracking external compound parabolic (XCPC) collectors installed at the University of California, Merced is described. The solar field was operated during July-August 2020 in both clean and dirty conditions and at varying operating temperatures (70, 135, 170 °C) while operating an air heater, thermal evaporator, and double effect absorption chiller. Performance data was used to develop an instantaneous solar field performance model which was then incorporated into an annual performance model using TMY3 data to estimate yearly production from the solar field. The model predicts an annual generation of ∼1100 kWh/m2-year at 80 °C, ∼1000 kWh/m2-year at 100 °C, ∼900 kWh/m2-year at 120 °C, ∼800 kWh/m2-year at 140 °C, and ∼700 kWh/m2-year at 160 °C in California. The XCPC technology is currently expected to have an installed cost of $300/m2 and an annual operations and maintenance cost of $6.5/m2-year. Over a 25 year lifetime it provides a levelized cost of heat at 2–4 cents per kWhth delivered. This is below the cost of commercial natural gas in California and at temperatures ≤ 120 °C below the cost of industrial natural gas, which highlights the potential of the XCPC technology for decarbonizing thermal applications such as water and space heating, drying, sterilization, desalination, evaporation, low pressure steam, double effect absorption chilling, process heating, and more. The lifetime cost of emissions reductions is ∼$169 per metric ton of avoided CO2 when replacing natural gas, ∼$137/MT CO2 when replacing propane, and ∼$83/MT CO2 when replacing electric heating.

In this work, an air-cooled, single effect solar-driven absorption system is being evaluated from the point of view of 1 st and 2 nd thermodynamic principles for two different applications: absorption chiller and heat pump. One of the most widely used working pairs, LiBr-H 2 O, is applied in this study due to its high performance in the absorption cycle. Their performance is compared with another working pair Carrol-H 2 O (Carrol contains LiBr and EG -Ethylene glycol- with a mass ratio of 4.5:1). The Carrol solution has the advantage of reducing the crystallization risk at the high concentration solution which enters the absorber. The numerical modelling was implemented on a modular object-oriented simulation platform (NEST platform tool), which allows linking different components, considered objects. In the simulations performed, the heat source temperature in the system is in the range of 70-90 ∘ C, and the inlet temperature at evaporator secondary circuit at chiller application is fixed in two values, 9 ∘ C and 14 ∘ C, and for heat pump application in 0 ∘ C and -5 ∘ C. Moreover, EG is added to the evaporator at heat pump application to prevent the refrigerant water from freezing below zero. The studied mass concentration range of EG of 10-40%. The result shows the C O P of an absorption chiller and heat pump are around 0.7 and 1.6, respectively, and the C O P EX values are 0.2-0.6 at chiller application and 0.5-1.5 at heat pump application. When compared with LiBr system, Carrol system has about 6.4% higher C O P , about 6.3% higher C O P EX , and a decrease of about 19% of cooling capacity. In the heat pump application, the heat source temperature should be lower than 90 ∘ C, and EG concentration at evaporator has been chosen as 30% as an optimal value. According to the operation condition, this EG concentration has been determined to avoid freezing in the evaporator in the studied working range. However, too much EG significantly decreases the pressure in the evaporator and increases the viscosity, hence will increase the maintenance of equipment as more vacuum tightness is required.

In this paper, thermophysical analyses were achieved for the mixture of (Fe3O4-acetone/ZnBr2) refrigeration working solution and examine its efficiency characteristics as a nanoferrofluid for use in absorption refrigeration applications driven by different low temperatures sources. Where it shows an investigation of the chosen nanoferrofluid containing the preparation, stability, structure, and properties. The reasons behind choosing Fe3O4 nanoparticles are that acetone is a good dispersivity medium for this kind of nanoparticles, also, their excellent thermophysical properties and magnetic property which give an ability to utilize them combined with applying an external magnetic field as a method for long and acceptable suspension stability of these nanoparticles in the base fluid thus enhancement in the heat transfer process in the generator of Absorption Refrigeration System (ARS). As a multi-factor experimental study, the experiments are designed to visually inspect the suspension nanoparticle's stability in the base fluid. Then presenting the thermophysical analysis of different properties of the mixture (thermal conductivity, density, dynamic viscosity, and specific heat capacity). The results elucidate that the studied nanoferrofluid has good dispersion and an enhancement in thermal conductivity that reaches 10.179 % at 0.2 (wt.%) of nanoparticle concentration. Also, by increasing nanoparticle concentration, the density increased, heat capacity decreased, as expected, and viscosity significantly increased.

In conventional vapor compression and absorption refrigeration systems, a compressor or a mechanical pump, respectively circulates the refrigerant. Mechanical input, which is required by the compressor or the pump operation, contributes significantly to the noise level and lessens its reliability and portability. In contrast, diffusion absorption refrigeration (DAR) systems are heat-driven and contain no moving parts. Solar-driven diffusion absorption cooling system uses a low-grade heat to produce a cooling effect, and it's specially tuned for remote locations with high levels of solar radiation. This article studies the performance of a DAR system in Ashdod, Israel. Based on existing models in the literature and on experimental measurement of quantities such as the solar irradiance and the air temperature, the cooling capacity and the COP were simulated. Cooling capacity of the DAR system varies between 100 and 140 W, and COP between 0.09 and 0.17.

This study aims to present a novel tri-generation plant consisting of a molten carbonate fuel cell (MCFC) unit coupled with a Stirling engine (SE), a heat recovery steam generator (HRSG), and two types of absorption refrigeration cycles (ARCs), i.e., Generator Absorber eXchanger (GAX) and Vapour Absorption Refrigeration (VAR). The proposed system is evaluated from energy, exergy, as well as environmental impact (3E) points of view. To carry out the parametric study, three sub-models are also introduced for the whole system. The sub-model (1) investigates the solo MCFC with the new configuration. In the sub-model (2), the SE and HRSG are added to boost the power generation and overall system efficiency through employing the heat wasted in the sub-model (1). In the last sub-model, for cooling purposes, the surplus heat of MCFC is reutilized using an absorption refrigeration cycle. Besides, to make a comparative study between GAX and VAR systems, the sub-model (3) is classified into two different schemes: (a) with a VAR cycle, and (b) with a GAX cycle. The results reveal that the exergy efficiency and CO2 emissions of the sub-models (1), (2), and (3) are 48.04%, 51.24%, 52.35% (VAR cycle), 52.12% (GAX cycle), 0.388 t/MWh, 0.364 t/MWh, 0.357 t/MWh (VAR cycle), and 0.358 t/MWh (GAX cycle), respectively. Either with GAX or VAR cycle, the proposed system indicates an acceptable standard of functionality in thermodynamic and environmental perspectives.

A CCHP is modeled here, which is operated based on thermal energy provision because the target consumer demands more heat and cooling than electricity. The main components of the CCHP system are a PEMFC as the main generator, absorption chiller, electric chiller, and auxiliary boiler. The fuel consumption, cost, and carbon release improvements compared to a separated generation system (SGS) are maximized in this system using the proposed modified mayfly algorithm. The system design and operation are optimized in two different stages. A hotel building has been chosen as the case study to demonstrate the effectiveness of the proposed CCHP system and optimization in comparison to the traditional mayfly algorithm (MA) and genetic algorithm (GA). The proposed optimization algorithm has performed 8.15% and 10.06% better compared to MA and GA, respectively. It also reached its solution in far shorter time. The optimum size of PEMDC and share of auxiliary chiller (AC) in cooling provision is determined to be 548 kW and 43.1%, respectively. It is shown that improvement achieved by using the AC in the CCHP is increased by 23.21% compared to a CCHP without one. Furthermore, the AC make the improvement of CCHP more constant and robust to load variation. Moreover, the sensitivity of the optimum operation condition of the CCHP against the electricity and fuel price changes and share of the AC in supplying the cooling demand are studied to provide the system operators with the necessary tools needed to optimally handle price changes.

Membrane-based absorption cycle is a novel technology to provide excellent heat and mass transfer performance in the main components for the convenience of small-scale applications. An overview is provided to summarize its progress and gives insights and possibilities for future development. A development trends analysis shows that the membrane-based absorption cycle is an emerging technology and attracts increasing attention in recent decades. Plate-and-frame module and hollow-fiber module are two common membrane-based modules that can improve the heat and mass transfer of absorber, desorber, and solution heat/mass exchanger. Besides, integrated components, including integrated evaporator-absorber and integrated condenser-desorber, have been proposed for further system size reduction. A thorough review of the cycle configurations indicates that the closed-type membrane-based absorption cycles could provide stationary cooling or heating capacity with better cycle performance, while the open cycles are more suitable for waste heat recovery and gas dehumidification. Apart from the conventional H2O–LiBr and NH3–H2O working fluids, ionic-liquid-based mixtures are promising candidates to overcome the existing constraints. But they also face some shortcomings, including high cost and possible high viscosity. This work is expected to facilitate the development and application of the membrane-based absorption cycle towards compact and efficient renewable/waste energy utilization.

Hydrogen fuel cell vehicles pave a promising technological pathway to achieve carbon neutrality. Conventional electric air-conditioning greatly increases hydrogen consumption and thus reduces the driving range. To recover waste heat for vehicle air-conditioning, this study proposes an integrated proton exchange membrane fuel cell (PEMFC) and microchannel membrane-based absorption cooling (MMAC) system. Using a validated model, the PEMFC-MMAC system is characterized under different vital parameters. The PEMFC parameters affect the performance of both PEMFC and MMAC. The coupled performance of the PEMFC-MMAC system increases under a higher operating temperature, a higher operating pressure, or a higher doping level. The MMAC parameters mainly affect the performance of MMAC. The coupled performance of the PEMFC-MMAC system increases under a lower microchannel width or a lower microchannel height. In the covered PEMFC and MMAC parameter ranges, the combined energy efficiencies are improved by 202–273% while the equivalent power efficiencies are improved by 11.4–14.8% with heat recovery. The cooling-to-electrical ratio is 2.02–2.73, the cooling capacity per volume is 129.4–345.9 kW/m3, while the cooling capacity per mass is 0.0439–0.1132 kW/kg. Compared to the existing falling-film absorption cooling technology, the MMAC improves the compactness by 165.1%, reduces the weight by 51.3%, and enhances the COP by 2.6%. This study can facilitate the development of highly-compact, light-weight, energy-efficient, and zero-GWP technology for waste-driven air-conditioning in hydrogen vehicles.

The newly NH3 – H2O – LiBr working fluid can decrease the power wasted in the generator, thus improves the COP of the ammonia absorption refrigeration system. But the applying of NH3 – H2O – LiBr working fluid decreases the ammonia absorption efficiency, so the COP of the system is still unsatisfactory. To further enhance the COP of the NH3 – H2O - LiBr absorption refrigeration system, TiO2 nanoparticles are added to the NH3 – H2O - LiBr working fluid in this study. And the effects of TiO2 nanoparticles concentration on the performances of the generator, absorber, evaporator, condenser, and solution heat exchanger are tested in an ARS experimental system. The experimental results indicate that the addition of TiO2 nanoparticles increases the Pg, Pe, Pa, and Pc, meaning that the value of ammonia produced in the generator increases. Therefore, the COP and iCOP of the system are improved by adding TiO2 nanoparticles, and the COP is maximum improved by 18.96% compared with the ammonia-water absorption refrigeration system. When the xTiO2 is increased from 0.3% to 0.5%, the increase rate of the COP decreases because the newly added nanoparticles do not disperse well. So 0.3% is a better choice for the TiO2 nanoparticles concentration when comprehensively considering the dispersion stability of nanoparticles and the COP.

Solar cooling systems, specifically solar absorption cooling systems, are becoming an attractive subject since they are great alternatives to the conventional cooling systems which lead to high electrical consumption. In addition, this system can provide cooling without greenhouse gas emissions. Hence, many combinations of different components might be adopted to apply the solar absorption cooling system. This paper will discuss the absorption chiller working cycle, the absorption chiller working fluids, the solar collectors to be combined with solar cooling systems and the single-effect absorption chiller. Furthermore, the variation of the coefficient of performance, the solar fraction and the economic study will be discussed. The goal of this review is to present previous studies and analyze their results; highlight the environmental, energetic, and economic viability of such systems and tackle future challenges regarding solar absorption cooling system and discuss the application of this system on new climates and more specifically on Lebanon.

In recent years, the use of Allam cycle based on the closed cycle of carbon dioxide has been considered by researchers due to its high efficiency and reduction of carbon dioxide emissions in the environment. In the present study, the combined system including Allam cycle and absorption cycle has been investigated from the perspective of energy, exergy and exergy–economy. The use of the absorption cycle is to use the waste heat of the power cycle and increase energy efficiency. The simulation results show that the total exergy efficiency of the cogeneration cycle is 0.72. Turbine, compressor and absorption cycle are introduced as primary components that should be considered from the exergy–economic point of view because they account for the highest cost rate of exergy efficiency. Also, the results of parametric analysis indicate that increasing the compressor pressure ratio has a negative effect on the cycle performance, thus reducing the overall work and efficiency of the exergy as well as increasing the cost rate. Similarly, changing the compressor pressure ratio has the greatest impact on the performance of the combined cycle, so that changing the pressure ratio in the range of 2 to 10 resulted in reducing the exergy efficiency by 63%. The key assessment is that the performance of the system increases as the temperature of the cooled water in the evaporator rises. Exergy efficiency works in contrast to the system performance coefficient and the main reason for the return of imperfections in the absorption cooling system is the undesirable heat transfer in the system heat exchangers.

District heat driven absorption chillers (AChs) contribute to a higher utilisation of the district heating network in summer and thus to a reduction of the relative heat losses. Due to higher investment but lower operating costs, AChs usually cover the base load, but compression chillers (CChs) are installed for peak load as well. For ACh and CCh, heat rejection is often realised via cooling towers (CTs). In addition, many systems provide the option of free cooling in winter by using the cooling towers to cover the cooling demand directly. Thus, absorption cooling (AC), compression cooling (CC) and free cooling (FC) represent three operating modes for cold generation in one overall refrigeration system. The concept of allocating base load and peak load is usually realised by activating CC when AC exceeds the capacity limit. FC is activated when the ambient temperature falls below a certain switchover value. In this study, extensive monitoring data from a large-scale field test (“Field test absorption chillers for CCHP systems”) are used to show that refrigeration systems controlled in such or similar ways have considerable potential to increase primary energy efficiency, even if the individual chillers are operated efficiently. Therefore, models are applied to the individual primary components (ACh, CCh, CT and auxiliary pumps). By using these models, thermal and/or electrical part-load efficiencies of AC, CC and FC and their specific dependencies on the ambient temperature and chilled water set temperature are calculated. Taking into account district heating and electricity primary energy factors allows to determine the operating mode with the lowest primary energy demand for each load condition measured in the field test within one year. The savings potential of 14% resulting from this example shows how promising the application of a model-based system control is compared to conventional strategies.

District cooling (DC) can play an important role in smart energy systems. With the global trend of reducing heat loss in buildings, cooling demand will continue to increase. Considering the potential for free cooling and waste heat utilisation in DC systems, a practical approach is needed to develop new DC networks. Tallinn has over 60 years of experience in developing district heating (DH) networks. The city has installed large capacities of biomass-based combined heat and power plants (CHPs). National support mechanisms allow the DH operator to generate power from CHPs and reject heat during warmer months when the heat load is insufficient. This heat can be used for DC. This study investigates an applied approach to DC development in Tallinn’s Ulemiste City. Ulemiste City is a business park with an existing developed area of 160 000 m 2 . The main source of cooling for the DC network is an absorption chiller that uses rejected heat from a CHP 7 kilometres away from the DC plant. The current DH supply temperature in Tallinn during the non-heating season is 70 °C. To determine the optimal technical solution for an effective energy efficiency ratio of the absorption chiller and heat transmission in the DH network, various scenarios were evaluated where the DH supply temperature was 70 °C, 80 °C, and 90 °C. An assessment of the technical parameters is provided for these scenarios. The paper presents an overview of the efficient use of rejected heat from CHPs in DC.

This article studies the economical, technical and environmental aspects of a third generation district heating (DH) network with absorption chillers installed at substation level in order to satisfy the cooling demands. This network solution hence takes advantage of the distribution facilities of existing DH systems. The study aims at evaluating the technical and environmental performances of this new district heating architecture, when sized and operated according to an economic objective using the Mixed Integer Linear Programming (MILP) optimization formalism. It is compared to the case where cooling demands are met using individual chillers. The paper first presents the production, distribution, demand and storage models. Regarding the demand side, different heating and cooling scenarios are studied by varying the proportions of residential and tertiary buildings. The model is fed in a second part with data from the French context. In particular, we rely on typical French weather conditions, thermal loads and energy costs. The analysis of the results focuses on the cooling part. It appears that the thermal network solution achieves on average a 3.6% reduction in the levelized cost of space cooling energy. In the worst case space cooling exergy efficiency goes through a 82% decrease. GHG emissions decrease on average by 7.7% thanks to the absence of leakage of refrigerant with high global warming potential. Overall, these emissions are low due to the low carbon content of French electricity.

In the past years scientists of Technische Universitat Berlin, developed a new generation of single stage H 2 O/LiBr absorption chillers in the range of 50 to 500 kW nominal cooling capacity. In 16 installations 25 absorption chillers have been monitored within a broad field test ( F eldtest A bsorptions k alte fur Kraft-Warme-Kalte-Kopplung- S ysteme, FAkS, funded by BMWi as project FKZ 03ET1171a-d) in the years 2013 to 2018. Annual performance figures of thermal coefficient of performance ( C O P t h ) in the range of 0.7 kWh 0/kWh 2 and electrical coefficient of performance ( C O P e l ) superior to 20 kWh 0/kWh el have been proven, serving district heat (DH) return line temperatures in the range of 62 °C to 68 °C. While the FAkS project focused on installation and operation of absorption chillers themselves, the follow-up project called ReKs ( R egelung e nergie-aufwandsoptimierter K alteerzeugungs s ysteme, FKZ 03ET1583), concentrates on overall system control and efficiency. Controlling absorption chiller cooling supply at low district heat return line temperatures is extended to an energy efficient control of all participating components including hot water, chilled water, heat sink pump and cooling tower fans. Models and strategies have been developed on thermal science theory and implemented in industrial control software. Proof of concept has been evaluated by monitoring field test installations while in parallel particular field test related parameters have been varied. Without diminishing quality of chilled water temperature and/or cooling capacity, electrical energy efficiency can at least be doubled, compared to the figures of FAkS installations. Moreover, new strategies enable efficient absorption cooling with DH return line temperatures in the range of 50 °C during moderate weather conditions periods. Field test results from 2020 and 2021 are presented here.

Since the first publishing of district heat driven heat pumps at AGFW fair in 2014 in Frankfurt am Main, Germany, introducing a concept how to use additionally the district heat return line as low temperature heat source, the topic gains more and more international scientific and public interest. Hydraulic concepts with and without an additional heat exchanger in the district heat supply line are tested at least in China and Germany. In theory, a reduction of temperature in the district heating return line (DH-rl) can be expected in the range of 25 to 30 K in comparison to standardized DH house connection stations (HCS). However, when the same heat pump is used in cooling mode during summer time, DH-rl temperature reduction in heating mode is limited to a range of 15 to 20 K, due to absorption chiller hydraulics and system design. In the first part of this contribution experimental results are presented which show how the expected reduction of 25 to 30 K has been achieved in practice by an adapted heat pump design. In the second part a new hydraulic design and control concept for the district heat supply flow rate will be presented which enables even higher DH glides also for retrofitted heating systems. Operating a house heating system at 65/45 °C with a conventional HCS may lead to a temperature in DH-rl in the range of 48 – 55 °C. With the first concept of an absorption HCS from 2014 a DH return temperature of 30 – 35 °C is possible, whereas, with the new hydraulic concept the return temperature may decrease down to 20 – 30 °C for layout conditions. In comparison to conventional HCS the enhanced absorption HCS allows to save 15 – 40 % of volume flow rate for the same heating capacity, mainly depending on temperature level of district heat and house heating system. By means, the heat losses in DH networks can be reduced and the transport capacity (i.e. the number of potential households to be served) can by increased. Concept and calculated results for the enhanced absorption HCS are presented.

The vapour absorption refrigeration system is not so much used commercially because of its low performance. The performance of absorption refrigeration system is required to improve to make its eff...

В роботі було досліджено альтернативні види систем формування клімату на основі таких видів систем охолодження як: адіабатичне охолодження; холодна стеля; абсорбційна холодильна машина з використанням броміду літію; система з використанням елементу Пельтьє. Запропоновано та розроблено схему, яка враховує недоліки розглянутих систем. Запропонована система має просту конструкцію, більш екологічна, в неї відсутній холодоагент. Розраховано кількість елементів Пельтьє необхідну для формування заданої температури в приміщенні. Розробка альтернативних систем охолодження дуже актуальна проблема на сьогоднішній час. У житлових приміщеннях набув широкий попит на кондиціонери з використанням фреону у якості холодоагенту. Дані системи не є надійними через те, що є ризик витоку фреону. Також є проблема в тому, що кондиціонер є осередком підвищеної вологості, що в свою чергу спричиняє розмноженню бактерій та грибків. Разом з посиленням санітарних вимог до житлових приміщень та тих приміщень де перебуває людина та заборонами використання старих різновидів фреонів змусили науковців та виробників шукати нові, більш екологічні, види охолодження приміщення без використання фреонів. Серед них це: використання води та її розчинів в якості холодоагентів; використання різниці температур навколишнього середовища; теплонасосів заснованих на ефекті Пельтьє. В результаті досліджень було встановлено, для охолодження приміщення краще використати елемент Пельтьє, так як він екологічний (відсутні викиди CO2, CO, CFH3, CFClH2), відсутні механічні деталі. Для охолодження приміщення площею 10 м2 потрібно близько 8 шт. Для точного керування системою краще використовувати точні датчики температури. Отримані дані є корисними та важливими: доведено, що система з використанням елемента Пельтьє може працювати на генерацію холоду; запропонований розрахунку є універсальними, тому , що має можливість розрахувати потужності елементів Пельтьє. Використання елементу Пельтьє дозволить використати силу сонця для зменшення негативних впливів на людину, зокрема вплив високої температури.

In recent years, population growth and community development have increased the volume of waste in many parts of the world, including in Iran. If management measures are not taken to reduce the vol...

In a variety of waste heat utilization technologies, absorption refrigeration can be driven by low-grade heat to provide cooling capacity, which is suitable for situations with both waste heat supply and refrigeration demand. In this paper, an ammonia-water absorption refrigeration prototype with a new generator structure is experimentally studied. Its economic analysis is carried out for pre-cooling in a liquefied natural gas plant. It is investigated that 1.8 kW cooling capacity at −10 °C is obtained, COP maintains between 0.29 and 0.35, and waste heat recovery ratio is improved by 150%. The proposed system is applied to a 30,000 Nm3 d−1 liquefied natural gas plant to replace the conventional compression refrigerator as the pre-cooling stage, and waste heat from exhaust gas and jacket coolant is recovered in the reboiler and stripping section, respectively, in order to provide cooling capacity for pre-cooling of both natural gas and refrigerant. Economic analysis shows that specific power consumption of the modified system is reduced by 30%, from 0.40 to 0.28 kWh Nm−3. Consequently, the annual natural gas consumption and operating costs are reduced by 17.3% and 9.4%, respectively, and the payback period is 2.2 years compared to conventional systems with compressor-based pre-cooling stages.

According to the Sustainable Development Scenario, the power generated by concentrating solar systems will be multiplied by 12 times by 2030 and will achieve nearly 184 TWh. To make it possible it is necessary to combine the concentrating solar systems with other technologies such as photovoltaics, sorption chillers, Stirling engines, etc. The total efficiency of hybrid systems is significantly higher than standalone ones. This paper analyzes​ the possibility of upgrading the existing concentrating solar thermal system with two-focal points located in Cracow, Poland. So far, this installation was used only for water heating applications. To estimate the possibilities of upgrading this system, numerical simulations with the use of Ray Tracing methods and Computational Fluid Dynamics were provided. Data obtained from the ray-tracing analysis allowed to determine the distribution of irradiance for various locations of the receiver. The CFD methods enabled to find the dependencies between the initial parameters of the working fluid, irradiance distribution, and heat transfer efficiency. Obtained results allowed to conclude that it is possible to use generated heat (354 K) for absorption chiller purpose. Moreover, this system may be used for simultaneous heat and electricity production, but firstly some changes in receiver geometry should be introduced.

This study presents the numerical development of a generator–rectifier combined component (called a “combined-generator”) composed of plate heat exchangers, designed and meant to be integrated in a single-stage ammonia–water absorption cooling system. Investigations are made to find the most compact and efficient design. Numerical simulations are presented describing parameters such as the ammonia fraction in the vapor produced and the combined generator efficiency as a function of the inlet temperatures or mass flow rate of the heat transfer fluid. The combined generator produces vapor with a high ammonia mass fraction and high mass efficiency for a solution inlet temperature range of [315–320 K] and a mass flow rate of the heat transfer fluid between [0.4 and 0.6 kg.s−1]. The impacts of the length and number of plates as well as the adiabatic/heated ratio of the plates are also examined. The ammonia fraction increases with the increase in the adiabatic/heated ratio, and the combined generator efficiency increases with the increase in the plate aspect ratio of length/width. The proposed system is developed to be operated in compact and medium-capacity absorption chillers (approximately 5 kW cold) for air-conditioning.

With the decrease in the fuel price subsidy in Iran, the urge for renewable energy sources to produce cooling and freshwater in a sustainable manner is becoming a challenge. Therefore, it is necessary to specify the marginal fuel price at which a solar-based cooling/water system is compatible with a fuel-based system. To this end, a solar-powered absorption refrigeration integrated with a humidification–dehumidification desalination system was thermo-economically evaluated to produce the freshwater and cooling production rates of nearly 0.58 m3/h and 28 ton/h, respectively, as well as the solar field output temperature of 175 °C. The levelized cost of product definition, which is based on the capital costs of the system, operation and maintenance costs as well as the discount rate, was used to calculate the cooling and freshwater unit of costs (COC and COW). The results demonstrated that the locations with high solar radiation levels require smaller solar field areas and larger thermal energy storage (TES) capacities, which leads to a higher percentage of annual solar share ( $$S_{{{\text{sh}}}}$$ ), and consequently lower COC and COW values. For instance, Abu Dhabi and Athens with solar radiation levels of 1977 kWh/ $${\text{m}}^{2}$$ and 1514 kWh/ $${\text{m}}^{2}$$ , respectively, have the COC (or COW) of 0.135 $/ton (or 2.88 $/m3) and 0.387 $/ton (or 7.38 $/m3), respectively. The total annual fuel saving of the proposed system with 10 h of TES for the locations with the highest and lowest $$S_{{{\text{sh}}}}$$ s [Abu Dhabi (77.97%), Athens (29.47%)] was obtained as $${1}.{38} \times 10^{6} \;{\text{m}}^{3}$$ and 0.52 $$\times 10^{6} \;{\text{m}}^{3}$$ , respectively. In addition, since the fuel price is highly subsidized in three locations of the study, the solar-based system cannot economically compete with the fuel-based system unless the fuel cost increases by 500%, 36%, and 19% for Iran, Yemen, and United Arab Emirates, respectively.

A system analysis of energy production was performed comparing the system of photovoltaic panels and parabolic trough collectors with a hybrid absorber. The paper presents new design of hPTC-CPV absorber. The analysis includes a comparison of the performance of both technologies in different irradiance conditions over the year. The technologies were compared for the same active surface hPTC-CPV and PV. The analysis was performed for a single-family house based on its demand for heat, electricity, and cooling. The calculations are intended to show to what extent an analyzed renewable technology can cover the demand for particular types of energy. The analysis was carried out to assess the legitimacy of using hybrid radiation absorbers in a temperate climate. Hybrid absorber studies were performed using CFD software. The results show that the proposed technology can compete with a PV system in terms of cooling and heat generation. Hybrid absorber covers 74.7% of heat demand for absorption cooling. PV panels with a heat pump cover 44.3% of the heat demand, PV panels with electric heaters 24.3% and hPTC-CPV absorbers 23.3%. The proposed technology cannot compete with PVs in terms of electricity production. Hybrid absorbers cover 8.2% when PVs 71.9% of electricity demand.

A major amount of domestic energy consumption is spent on refrigeration and space cooling appliances. The performance of the refrigeration system depends on the thermophysical properties of the refrigerant. Altering the properties by additives such as nanoparticles has proven to be an effective solution to improve the performance of the system. This work swivels around flow boiling, pool boiling, tribological and condensation characteristics of nanorefrigerants in Vapour Compression Refrigeration System (VCRS) and Vapour Absorption Refrigeration System (VARS). An evolutionary timeline of nanorefrigerants is presented. Energy savings on compressor work by addition of nanolubricants is discussed. A sum of thirteen refrigerants and twelve nanoparticles in various combinations were encountered during this review process. CNTs performed better than metallic (Al, Cu, Au, Ag) and ceramic (Al2O3, TiO2, SiO2, ZnO) counterparts. Majority of the work reported enhancement in heat transfer rate and coefficient of performance (COP), however, few studies presented that CuO nanoparticles have shown negative correlation between HF, COP and volume fraction of nanoparticle. The review presents a broad idea on dispersion techniques, stability, properties of boiling and condensation, migration phenomenon of nanoparticles and various novel techniques to improve the performance of the refrigeration systems.