Ammonia-water Absorption Chiller Research Articles

Multi-variable optimization of a geothermal power plant integrated with water electrolyzer and methanol production

Renewable energy-based routes for methanol generation are recognized as essential strategies for eco-friendly energy conversion. Thus, the current study focuses on developing an innovative combined energy system for methanol production using direct carbon dioxide hydrogenation powered by geothermal energy. This is important because it addresses the need for sustainable and environmentally friendly methods of methanol production while also harnessing the potential of geothermal energy as a renewable resource. Therefore, in order to achieve multigeneration energy production, this work introduces and optimizes a novel configuration that benefits from an innovative heat design process. This configuration integrates an organic Rankine cycle, a single-flash geothermal power plant, an ammonia-water absorption chiller, a proton exchange membrane electrolyzer, and a methanol generation unit. Using the Aspen HYSYS tool, the multigeneration energy system is modeled and analyzed. As a result, the system is assessed using energy, exergetic, environmental, and economic evaluations. Furthermore, performance evaluations are carried out in the following modes: single generation, multigeneration, cooling, heat and power generation, and cooling. Furthermore, a genetic algorithm is employed to optimize the system in terms of economy and exergy. The energy and exergy efficiency are determined to be 32.57 % and 76.3 %, respectively, under the base case results. Furthermore, the rate of overall costs is 377.38 $/h. Furthermore, the precise output of carbon dioxide is −0.043 kg/kWh. The optimal unit cost and exergy efficiency for all items, taking into account the optimization scenario, are 3.34/GJ and 78.35 %, respectively. In addition, the optimum carbon dioxide and hydrogen rates for methanol generation are 92.49 mol/h and 200.51 mol/h, respectively.

Development of Key Components for 5 kW Ammonia–Water Absorption Chiller with Air-Cooled Absorber and Condenser

An absorption chiller is an alternative cooling system that operates using heat from renewable energy sources and employs environmentally friendly working fluids, such as ammonia–water or lithium bromide–water. Given Indonesia’s high solar energy potential, solar cooling systems using absorption chillers are particularly promising. Solar thermal energy has been demonstrated to effectively power absorption chiller systems through both simulations and experiments. In Indonesia, there is significant potential to utilize small-capacity solar absorption chillers for buildings, particularly those employing air-cooled condensers and absorbers, which can reduce operational and maintenance costs. This research aimed to design a prototype of a 5 kW solar-assisted ammonia–water absorption chiller system specifically for residential applications. The system will be air-cooled to minimize space requirements compared to traditional water-cooled systems. The study addressed the design and specifications of the system’s components, dimensional considerations, and an analysis of the impact of the measurement instrument on the research outcomes. The results provide precise dimensions and specifications for the system components, offering a reference for the development of more advanced systems in the future.

Using compressor inlet cooling process for a supercritical Brayton cycle with various supercritical gases to recover the waste heat from a biomass-driven open Brayton cycle

The heat loss of a biomass-driven open Brayton cycle (OBC) is recuperated in the current research with the help of a supercritical Brayton cycle (SBC) and a thermoelectric generator (TEG). The temperature of the gas entering the SBC compressor is reduced through an ammonia-water absorption chiller (ACH) for performance improvement. The SBC compressor inlet cooling is examined for four supercritical gases (Nitrogen, Carbon monoxide, Air, and Helium). Moreover, the best performance of the configuration with compressor inlet cooling is compared with that of the system without compressor inlet cooling. Although compressor inlet cooling brings about the most improvement in output electricity of the SBC in the case of helium, the exergy efficiency (ηex) of the system and unit cost of the product (UCP) do not improve as much as other gases due to the reduction in the output power of the TEG in the case of helium. In addition, helium conduces to the lowest ηex (38.29 %) and highest UCP (17.62 $GJ−1) among the gases. Hence, helium is unsuitable for the SBC in total waste heat recovery applications. On the contrary, air induces the best performance with an ηex of 39.6 % and a UCP of 17.3 $GJ−1. The enhancement in ηex is 6.66 % points when the waste heat of the OBC is fully recovered.

Downsizing strategy for an air-cooled indirect-fired single-effect ammonia-water absorption chiller in part-load operation in hot climates

A modular mathematical model has been created to simulate an ammonia-water absorption refrigeration system indirectly fired and air-cooled. The model includes governing equations based on mass, species, and energy balances, implemented for the main components of the system. It accounts for both thermal and mass resistances in the transfer processes that occur in the system. The study evaluates the performance of the ROBUR® absorption refrigeration system, model ACF60-00 LB, operating under part-load conditions, driven by hot water temperatures ranging between 160 and 210 °C, while the ambient temperature remains up to 40 °C. This refrigeration system is characterised by including an extra valve that allows active control of the pressure levels of the system. The analysis focusses on the effect of its active control on the size of the system. The results show that increasing the pressure loss in this valve reduces the size of the air-cooled absorber to 37.3 % of its nominal size at an ambient temperature of 40 °C, while the reduction in refrigerant mass flow is 18.5 %, while the condenser size decreases 3.1 times. Evaporator, air-cooled absorber and condenser effectiveness are minimally affected. Additionally, contribution of condenser and evaporator to exergy destruction is balanced.

Development of a cooling and power generation prototype integrating an axial micro-turbine in an absorption chiller

The integration of an expander in an absorption machine allows it to produce cooling and electricity simultaneously within the same cycle. This technology holds great potential to harness low-temperature heat sources more efficiently than production with separate cycles. However, very few experimental studies on absorption combined cooling and power production cycles can be found in literature. In order to achieve an in-depth understanding of this technology and of the interactions between power and cooling production sides of the circuit, the integration of an expander into a single stage ammonia water absorption chiller was undertaken through the development of an experimental pilot plant. The peculiar characteristics of the expansion device, as well as the use of a newly developed combined desorber avoiding the presence of a rectifier make the prototype built unique. Design and integration of the expander proved to be very challenging, mainly due to the small size of the application and corrosiveness of the ammonia water mixture. Significant electricity generation losses experienced lead to maximum electrical efficiency of 7% and corresponding maximum power production around 33 W at a lower than expected rotational speed of 20′000 rpm.Despite these difficulties, first experimental measurements have been obtained, giving interesting insights on the functioning of the cycle. Indeed, the impracticability of regulating the ratio between cooling and power production was highlighted, due to the characteristics of the impulse turbine. Opening of the turbine line in the nominal point leads to a reduction of the mass flow rate passing through the cooling line of 65% (i.e., split ratio of 0.35) and a cooling power output decrease of around 57% (from 4.9 to 2.1 kW). Additionally, diverting some of the desorbed vapour to the power production line has important effects on the pressure equilibrium and circulating vapour mass flow rate, increasing from 16.1 kg/h in the simple absorption working mode to 31.1 kg/h in the combined mode in the nominal operating point. Feedback from the pilot plant will be very useful for the further development of the technology.

Performance evaluation of a micro partial admission impulse axial turbine in a combined ammonia-water cooling and electricity absorption cycle

The integration of an expander in an absorption machine allows it to produce cooling and electricity simultaneously. This technology holds great promise for its ability to harness low-temperature heat sources more efficiently than production with separate cycles. The integration of a turbine is currently being studied in an experimental ammonia-water absorption chiller at CEA INES. Given the very small mass flow rate and enthalpy drop, a partial admission impulse axial turbine has been selected for the application. Due to lack of experimental data, a 3D model of the impulse turbine was generated and its functioning studied with CFD simulations using pure ammonia. A compressible real gas 1D model of the turbine was later developed in EES® for the ammonia-water mixture and compared to CFD simulation, adjusting loss term parameters to match CFD results, thus achieving an average discrepancy below 7% in the considered range of operating conditions (inlet pressure 14-10 bar, outlet pressure 5 bar, inlet temperature 120 °C and rotational speed of 10–100 thousand RPM). The tuned 1D expander model was then integrated in a previously developed 0D model of the absorption cycle to demonstrate its robustness and potential to be used in the study of complex combined cycles. An overall energy efficiency is introduced and used to map the performance of the cycle for changing operating conditions. Results show the potential of the combined cycle to produce both power and cooling even at small scale, highlighting at the same time, the constraints imposed by this type of expander on the combined cycle.

The Impact of Coolant Temperatures on Various Cycle Parameters of NH3-H2O Absorption Chiller from Solar Source

The cycles’ structure was based on recently published technical information of low-temperatures powered Ammonia-water (NH3-H2O) absorption chiller. The cycle was completely modeled using different components available within the refrigeration library of IPSEpro software package. Using the model a cold-water ammonia-water absorption chiller was examined and validated in accordance to the relevant thermodynamic laws and charts. A low-grade temperature solar resource was modeled to energise the proposed model. For water-cooled cycles, the rejected heat from the absorbers and the condensers was carried out by water, at an average fixed temperature of 25°C, pumped out from ground water. The results obtained show that when the Coefficient of performance (COP), heat inputs into the generator, and cooling mass flow rates are fixed, the cycle parameters are highly affected by variation of coolant temperature. For instance when cooling water temperature decreases. Also when cooling water temperature increase, the cycle pressure, usable chilled water temperature difference and desorber outlet temperature increase whereas mass concentration and refrigeration capacity decrease. The effectiveness of the generator inlet temperature (solar source) is a factor of the largest effect to the COP. The difference was 0.1401, 27.4%. The chilled water inlet temperature (underground water) is the second largest effect to the COP. The difference between the maximum and the minimum value is 0.0865 and the relative difference is 18.9% with cooling capacity 12 kW. The influence of evaporator temperature to the COP is also minimal with only 2.2% difference. The influence of absorber temperature and condenser temperature to the COP are almost identical, the relative difference is 19.2% and 18.9% respectively.

A residential absorption chiller for high ambient temperatures

Abstract A standalone, compact, thermally driven ammonia-water absorption chiller designed to deliver a cooling capacity of 10.5 kW at ambient temperatures greater than 40 °C is presented. Heat and mass exchangers with novel microscale features and geometries are employed to minimize the physical size of the system. A diabatic distillation column based desorber and a shell-and-tube absorber with microscale features are used. Thermodynamic cycle modeling and heat and mass exchanger design methodologies are discussed. The performance of the packaged unit chiller is demonstrated experimentally over a wide range of operating conditions. The system delivered 10.6 kW of cooling at a COP of 0.63 at design conditions in a compact 0.7 m x 0.9 m x 1.0 m envelope. This work validates the scalability of microchannel heat exchanger technology from a proof-of-concept laboratory scale device to a residential-scale absorption heat pump.

Experimental assessment of alternative compact configurations for ammonia-water desorption

Heat and mass transfer during ammonia-water desorption in miniaturized desorbers using microscale geometries was investigated. Two heat transfer fluid coupled test sections (a vertical column configuration and a branched-tray configuration), consisting of an array of alternating plates with integral microscale features, enclosed between cover plates, were fabricated. Due to the counter-current flow configuration, refrigerant vapor with a high purity of ammonia (as high as 99.9% ammonia mass fraction) was generated in these components. Compact adiabatic analyzers and solution-cooled rectifiers with microscale features were also integrated with the two desorber concepts to further increase refrigerant purity. These components were installed in a breadboard test facility consisting of all components of a single-effect ammonia-water absorption chiller and investigated over a range of solution and vapor flow rates. The measured experimental data were analyzed to estimate component duties, solution- and coupling fluid-side resistances, and conduct a comparative assessment of the two miniaturized desorption concepts. The branched-tray configuration performed better than the vertical column design and led to higher purity refrigerant. Potential causes for differences in the performances are discussed.

Waste-heat driven ammonia-water absorption chiller for severe ambient operation

A packaged ammonia-water absorption chiller using a waste-heat stream and operating at severe ambient conditions is developed and experimentally evaluated. The chiller is designed to provide 2.6 kW of cooling at an ambient temperature of 51.7 °C. The system is directly coupled to exhaust gas from a diesel generator to drive the absorption cycle. The absorber and condenser reject heat directly to ambient air. Direct coupling to the heat source and the ambient heat sink leads to reduced system size and minimization of parasitic electrical power required for coupling fluid pumps. The dimensions of the unit are: 0.66 m × 0.61 m × 0.48 m (L × W × H). An autonomous control system is also developed and demonstrated experimentally. System performance is measured at ambient temperatures of 40–52 °C, delivering cooling duties of 2.5–1.8 kW, with overall coefficients of performance (COPs) of 0.38–0.3. Performance limitations and areas for future development are discussed.

Análisis termodinámico de un chiller de absorción de 1 y 2 etapas de una planta de cogeneración

Se han desarrollado modelos termodinámicos de enfriadores de agua por absorción de una etapa y ciclo no común de dos etapas que usan calor de desecho (de motores de combustión interna de 8,7 MW cada uno) para analizar las condiciones de operación de los equipos. Se ha realizado la comparación del sistema de una etapa con el sistema propuesto (2 etapas) en esta investigación. El coeficiente de desempeño (COP) obtenido para ambos sistemas fue el mismo, pero el calor removido del espacio refrigerado aumento de 1,3 MW (una etapa) a 1,6 MW (dos etapas) debido a que se recupera más energía residual utilizando un segundo generador. El calor residual aprovechado por el equipo de refrigeración fue de 3,8 MW y el factor de planta del proceso de cogeneración fue de 58,11 % y la capacidad de refrigeración del equipo fue de 1,623 kW. Finalmente, los ahorros económicos estimados por concepto de energía eléctrica que se tienen por poner en marcha el sistema de refrigeración por absorción que utiliza gases de escape como fuente de energía en lugar de un equipo común de refrigeración por compresión de la misma capacidad son 142 000,00 USD/año.

Characterization of Ammonia–Water Absorption Chiller and Application

Ammonia-absorption refrigeration units (AARUS) can supply subfreezing refrigeration for many industrial applications. Such units are usually driven by waste heat or renewable energy at relatively low temperatures. The performance of the chiller is highly dependent on the temperatures of the driving heat, the chilling load, and the cooling water. In this paper, the performance of an advanced industrial-scale ammonia-absorption unit is modeled over a representative operating range. The performance is then characterized by a set of simple equations incorporating the three external temperatures. This simple model helps to evaluate potential applications, predict performance, and perform initial optimization. Case studies are presented highlighting the application of the model.

Process development and exergy analysis of a novel hybrid fuel cell-absorption refrigeration system utilizing nanofluid as the absorbent liquid

A hybrid system including high-temperature polymer fuel cell with capacity of 5 kW along with fuel processing unit for producing rich hydrogen from natural gas integrated by a 3 kW absorption chiller has been developed. The waste heat of flue gas from the burners is utilized in the ammonia-water absorption chiller for refrigerating purposes. The hybrid refrigeration system is simulated by Aspen HYSYS software in a steady state condition. After defining the properties of nanoparticles in HYSYS software, the water-based nanofluids are employed as absorbent liquid for increasing of COP in the refrigeration system, and their effects have been evaluated on overall system performance. The electrochemical model of the fuel cell as well as the main parameters of refrigeration system have been validated with experimental results and similar works. Electrical efficiency and overall efficiency of the hybrid system are equal to 36% and 77.3%, respectively. The overall efficiency in the presence of silver nanofluid can be increased up to 81%. Exergy analysis has been conducted for the hybrid system, and the obtained exergy efficiency of the system is equal to 29%. Sensitivity analysis has been employed for evaluating of significant parameters on the hybrid system performance.

Thermodynamic analysis of an integrated solid oxide fuel cell, Organic Rankine Cycle and absorption chiller trigeneration system with CO2 capture

A novel trigeneration system which integrates a SOFC system, an Organic Rankine Cycle (ORC), and an ammonia water absorption chiller with a CO2 capture system is proposed and investigated. The exhaust gas from SOFC anode combusts with pure O2 instead of air and thus the combustion products mainly consist of CO2 and H2O, which the CO2 can be captured easily by the condensation method; in SOFC cathode side, a series-connected ORC and ammonia water absorption chiller heat recovery system which can produce power, heat and cooling is employed to recover the waste heat of SOFC cathode exhaust gas. A mathematical model is developed to study the system performance under steady-state conditions. The calculated results show that the net electrical efficiency and the exergy efficiency of the integrated system can reach 52.83% and 59.96%, respectively. The trigeneration efficiencies of the combined system without and with CO2 capture are 74.28% and 72.23%, respectively. The effects of the SOFC inlet temperature, the current density, the steam-to-carbon ratio, the pinch point temperature difference and the turbine II inlet pressure on the trigeneration system performances are investigated in detail. The research achievement in this paper can provide the useful reference for SOFC based trigeneration system with low energy consumption for CO2 capture.

Development of a micro-scale heat exchanger based, residential capacity ammonia–water absorption chiller

A standalone absorption chiller based on microchannel heat exchanger technology was developed with a cooling capacity of 7 kW. A review of recent advances in microscale heat and mass exchangers and vapor absorption technology guided this development. Thermodynamic and heat and mass transfer design procedures are discussed. A control system for standalone operation was developed. Experimental evaluation demonstrated the achievement of target cooling capacities. An overall system COP of 0.44, and an ammonia–water cycle COP of 0.51 were achieved. Reasons for differences between model predictions and actual performance are discussed. This development validates scalability and application of microscale heat exchanger technology for absorption heat pumps at residential-scale capacities. In contrast to conventional absorption systems, core heat and mass exchangers require only small portion of overall system volume and weight, which significantly improves the prospects of this technology for small capacity applications.

Advantages of variable driving temperature in solar absorption chiller

The study described in this paper results from the observation that, when dealing with solar-driven absorption chillers, a compromise situation very likely exists between the collector efficiency and the coefficient of performance (COP) of the absorption cycle. An idea of a control strategy pursuing this objective, and thereby increasing the solar fraction for a solar absorption cooling cycle is consequently presented. The advantage of operating the solar chiller on a variable driving temperature is demonstrated. The theoretical analysis considers a solar chiller operated under moderate climate conditions of Poland. The model of the ammonia-water absorption chiller is described in detail, and the main assumptions of the iterative control procedure are explained. The effects of its application are computationally tested for one location and one type of solar collector, for representative days of three months during the cooling season. The results of the simulation are compared with the reference case of fixed driving temperature. According to the simulation results, it is possible to increase the cooling power yield at various levels, up to 34 W per 1 m2 of solar collector, by adjusting the chiller driving temperature throughout the cooling season. The same, it is possible to more than double the cooling effect for some hours, with respect to fixed-temperature control operation.

Experimental testing of the performance of a solar absorption cooling system assisted with ice-storage for an office space

Energy storage plays a vital role in shifting cooling energy load from period of peak demand to that of low demand. This paper reports performance data of an ice-storage unit in solar absorption cooling system for cooling an office space. The cooling system consists of ammonia-water absorption chiller, evacuated tube solar collectors and ice-storage. Experiments were carried out on two consecutive days in each of the month of March and October in Dhahran, Saudi Arabia. The ice-storage unit was charged on the first day and the cool energy discharged on the other day. The results showed average coefficient of performance (COP) of the chiller during charging as 0.43 and 0.47 for the months of March and October, respectively. The results also indicate that the ice-storage can provide a backup time of about 5–6h, which is sufficient to cool the given space during the early hours of chiller warm-up.

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

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

Experimental and numerical study of a falling film absorber in an ammonia-water absorption chiller

In this paper, experimental and numerical studies of heat and mass transfer in a falling film absorber are presented. The investigated absorber is a plate heat exchanger used in a falling film configuration. The ammonia-water solution flows in a falling film mode along the plates. The vapour flows co-current with the falling film and the coolant fluid is in a counter-current flow with the falling film. A prototype of ammonia-water absorption chiller is used to experimentally study the absorber behaviour in real operating conditions. A macro study of the absorber and a local analysis deduced from local temperatures measurements along the falling film are presented. A numerical model and a simulation tool are developed in order to complete the experimental investigations. The associated numerical parametric study aims to separate the coolant mass flow rate impact. The model is validated with experimental data and a maximal relative error of 15% is observed between experimental and numerical results. The results of this study suggest that during the absorption process, mass transfers are controlled by the falling film mass transfer resistance and that the liquid-side heat transfer resistance is negligible.

Modeling and Experimental Study of an Ammonia-water Falling Film Absorber

This paper presents a numerical and experimental study of absorption phenomenon in ammonia-water absorption chiller which is a very promising technology in the solar cooling field. The purpose of the research is to analyse the coupled heat and mass transfers that take place in a plate heat exchanger used as absorber in order to identify limiting transfers. For this purpose, a numerical modeling of a falling film absorber has been performed. Then, an experimental study has been carried out on a test bench in order to experiment the absorber in real operating conditions and to validate the numerical model. So, experimental and numerical results are compared to discuss hypothesis of the model and analyse the global behaviour of the absorber. Moreover, local phenomena are discussed thanks to the numerical study.