Lithium Bromide-water Absorption Chiller Research Articles

Utilization of Geothermal Fluid as a Heat Source for Absorption Refrigeration System for Food Preservation – A Case of Bwanda and Gwisho Hotsprings

Zambia has significant geothermal resources with over 86 hotsprings identified. Installation of a 250kW off-grid pilot binary-cycle power plant is currently underway at the Bwanda and Gwisho goethermal site. It is estimated that there is 90,000 herd of cattle in the villages around the pilot power plant. Little milk from these herds of cattle reaches the market due to scarce collection points with cooling facilities. This study assesses the applicability of utilizing exhaust geothermal fluid from a binary-cycle geothermal power plant for powering an absorption refrigeration system (ARS) for storing food, specifically milk. Two absorption systems; Lithium Bromide-water and the ammonia-water ARS are compared. The COPs, energy input and mass flowrates required to produce various cooling loads (40kW – 160kW) are compared. The results show that the exhaust geothermal fluid energy (504kW) is sufficient for powering both ARSs for storing milk to its suitable storage temperature of 4oC. The results also show that the Lithium Bromide-water system is more suitable for this application, because it produces a higher maximum COP (0.76) compared to the ammonia-water system’s maximum COP (0.64), it produces a higher maximum cooling capacity (380kW) compared to the ammonia-water systems maximum capacity (216kW). It requires lower input mass flowrate and pump work at all cooling capacities (40kW – 160kW). Therefore, a Lithium Bromide-water absorption chiller for storing the amounts of milk currently collected in the study area is designed. Optimized design specifications are provided.

Эффективность абсорбционной бромистолитиевой холодильной машины с многоступенчатыми процессами абсорбции и генерации со связанным потоком массы

A study of the cycles of a lithium bromide–water absorption chiller with two-stage absorption and three-stage generation of a working substance vapor with an associated mass flow with different supply of the cooling medium to the apparatus has been carried out. The temperature of the heating source necessary for the implementation of the actual thermodynamic cycle of the Lithium Bromide– Water Absorption Chiller (LBWAC) and the most effective thermodynamic cycle has been determined. A comparative analysis of the cycle understudy with the sample cycle (one-stage cycle) LBWAC is carried out. Despite the lower values of the coefficient of performance (COP), the cycle under study provides a doubling of the cooling capacity of the machine, at the same flow rate of the heating source, which is an advantage when the flow rate of the heating source is limited. This circumstance is explained by the fact that in LBWAC with multi-stage absorption and generation, the heating source sequentially passes through three generator stages. Therefore, the degree of cooling in the chiller with the considered cycle is three times higher than this value of a single-stage LBWAC

Parametric Study of a Single Effect Lithium Bromide-Water Absorption Chiller Powered by a Renewable Heat Source

Parametric Study of a Single Effect Lithium Bromide-Water Absorption Chiller Powered by a Renewable Heat Source

Investigations on water–LiBr‐based absorption refrigerator with solar parabolic dish in cogeneration mode

Here, performance of 11 kW solar-powered lithium bromide water absorption chillers in cogeneration mode is investigated. A 40 m 2 solar parabolic dish of 19 kW th capacity is used for both processes heating and cooling. Extensive thermodynamic design and analysis are carried out, and the results obtained are validated. Parabolic dish and cavity receiver are sized for Chennai (13°N, 80.18°E), India. In the present analysis, a new performance parameter COP WE is introduced by replacing the thermal input component in the calculation of COP, by an equivalent amount of high-grade energy. Both physical and chemical exergy at all state points of the chiller are estimated and found that total irreversibility is about 2.37 kW in desorber followed by absorber which is 0.41 kW. The developed model estimates solution concentration at the exit of solution expansion valve (SEV) that is important since it affects absorption of refrigerant in the absorber.

The development and assessment of solar-driven Tri-generation system energy and optimization of criteria comparison

In this research, the thermodynamic investigation of the tri-generation system is performed by the first and second law of Thermodynamics. The trigeneration system under study consists of three subsystems including the solar subsystem, Kalina subsystem and lithium bromide-water absorption chiller subsystem. The proposed system generates power, cooling and hot water using solar energy. The system considered is designed and evaluated based on the climate condition in Zahedan, Iran. The calculation results show that the most exergy destruction rate takes place in the solar cycle. The assessment of system is used dynamic and static forms. In dynamic form, that maximum total cost rate, energy and exergy efficiency are equal to 15.1 dollars per hour,by 33% and 36.47%, respectively. The results base-case demonstrate that energy and exergy efficiencies and total cost rates are equal to 9.63 dollars per hour by 17.37% and 18.82% , respectively in static analysis. Furthermore, optimization criteria comparison such as energy efficiency, exergy efficiency and power are discussed in static form. The results of static evaluation revealed that the power is the best criteria for thermodynamics. Moreover, optimization results based on maximum power criterion show that produced power, energy efficiency, exergy efficiency and total cost rate increase by 28%, 12.32%, of 13.97% and 7.68%, respectively in comparison with the base case.

Performance analysis and optimization of new double effect lithium bromide–water absorption chiller with series and parallel flows

In this paper the effect of some key parameters on coefficient of performance (COP) in two novel arrangements of double effect lithium bromide–water absorption chillers with series and parallel flow have been studied. The main components of these cycles are generators, absorber, condensers, evaporator and heat exchangers. The mass, concentration, and energy balance equations are used for both cycles and performances of the systems are analyzed at different conditions with the condition of no formation of lithium bromide crystal. Also, the effects of temperatures and mass flow rates of inlet vapor of generator and inlet water of absorber on evaporator cooling capacity, absorber heat transfer rate and COP are investigated. In addition, two new parameters based on mass ratio of solution splitters are defined (R1 and R2) and their effects on the system performance are analyzed. The results show that the series cycle at inlet vapor temperature to the high temperature generator (HTG) below 150 °C has higher COP than the parallel cycle. In addition, with increase of inlet vapor temperature to HTG and rise of mass flow rate of inlet water to absorber, the COP increases in both parallel and series cycles. In addition, with increase of R1, the COP increases at first and reaches to a maximum value, and then decreases. Furthermore, the Genetic Algorithm (GA) method has been used to optimization of the system COP at series and parallel cycles.

Performance characteristics of a solar driven lithium bromide-water absorption chiller integrated with absorption energy storage

The use of solar–assisted absorption chiller for space cooling is limited to availability of solar radiation; hence, energy storage is very crucial in order to achieve extended hours of cooling operation. In this study, operational and performance characteristics of a solar driven lithium bromide-water absorption chiller integrated with absorption energy storage of the same working fluid are investigated. The integrated system simultaneously provides cooling and charging of the absorption energy storage during the hours of solar radiation. Simulation of the integrated system is carried out based on first law of thermodynamics. Effects of weather variables such as solar radiation and the influence of coupling absorption energy storage with an absorption chiller are investigated. The results indicate that cooling effect of the chiller varies with the variation of solar radiation, with maximum value of 20kW for a collector area (Ac) of 96m2 on a typical day in July, Dhahran, Saudi Arabia. The cooling COP of the integrated system during cooling/charging and discharging is found to be 0.69 and the energy storage density of the absorption energy storage is 119.6kWh/m3. Furthermore, the operational characteristics of the proposed system showed that the internal operating parameters of the integrated chiller-absorption energy system such as solution temperatures and pressures are within reasonable levels. Hence, this indicates the possibility of integrating the absorption energy storage with absorption chiller.

A comprehensive, multi-objective optimization of solar-powered absorption chiller systems for air-conditioning applications

Solar heating and cooling (SHC) systems are currently under rapid development and deployment due to their potential to reduce the use of fossil fuel resources and to alleviate greenhouse gas emissions in the building sector – a sector which is responsible for ∼40% of the world energy use. Absorption chiller technology (traditionally powered by natural gas in large buildings), can easily be retrofitted to run on solar energy. However, numerous non-intuitive design choices must be analyzed to achieve the best techno-economic performance of these systems. To date, there has been little research into the optimal configurations among the long list of potential solar-driven absorption chiller systems. To address this lack of knowledge, this paper presents a systematic simulation-based, multi-objective optimization of three common, commercially available lithium bromide-water absorption chillers – single-effect, double-effect and triple-effect – powered by evacuated tube collectors (ETCs), evacuated flat plate collectors (EFPCs), and concentrating parabolic trough collectors (PTCs), respectively. To the best of authors’ knowledge, this is the first study of its kind that compares the optimized designs of the most promising configurations of solar-assisted absorption chillers against a common set of energy, economic, and environmental metrics from a holistic perspective. A simulation model of these three configurations is developed using TRNSYS 17. A combined energy, economic, and environmental analysis of the modeled systems is conducted to calculate the primary energy use as well as the levelized total annual cost of each plant, which are considered as two conflicting objective functions. By coupling TRNSYS and MATLAB, a multi-objective optimization model is formulated using a genetic algorithm to simultaneously minimize these objectives, thereby determining a set of optimal Pareto solutions corresponding to each SHC configuration. The performance of the proposed systems at their optimal designs is then compared to that of a reference conventional system. A sensitivity analysis is also performed to assess the influence of fuel cost, capital cost of innovative components, and the annual interest rate on the Pareto front of optimal solutions. Overall, the optimization results reveal that of the proposed configurations, the SHC double-effect chiller has the best trade-off between the energetic, economic and environmental performance of the system, having a total cost of ∼0.7–0.9M$ per year and reducing the annual primary energy use and CO2 emissions by 44.5–53.8% and 49.1–58.2% respectively (relative to the reference conventional system). With the high capital cost associated with these systems, government subsidies and incentives are still required in order for them to achieve satisfactory payback times and become cost-competitive with conventional HVAC systems.

Thermodynamic and economic studies of two new high efficient power-cooling cogeneration systems based on Kalina and absorption refrigeration cycles

Two new power and cooling cogeneration systems based on Kalina cycle (KC) and absorption refrigeration cycle (AC) are proposed and studied from thermodynamic and economic viewpoints. The first proposed system, Kalina power-cooling cycle (KPCC), combines the refrigerant loop of the water-ammonia absorption chiller, consisting of an evaporator and two throttling valves with the KC. A portion of the KC mass flow enters the evaporator to generate cooling after being condensed in the KPCC system. KPCC is a flexible system adapting power and cooling cogeneration to the demand. The second proposed system, Kalina lithium bromide absorption chiller cycle (KLACC), consists of the KC and a single effect lithium bromide-water absorption chiller (ACLiBr-water). The KC subsystem discharges heat to the ACLiBr-water desorber before condensing in the condenser. The performance and economic aspects of both proposed systems are analyzed and compared with the stand alone KC. A parametric analysis is conducted to evaluate the sensitivity of efficiencies and the generated power and cooling quantities to the key operating variables. The results showed that, thermal efficiency and total annual costs decreased by 5.6% and 8% for KPCC system but increased 4.9% and 58% for KLACC system, respectively. Since the power-cooling efficiency of KLACC is 42% higher than KPCC it can be applied where the aim is cooling generation without considering economic aspects.

The experimental characterization of a lithium bromide–water absorption chiller and the development of a calibrated model

Small-scale solar air conditioning systems based upon thermally activated chillers offer great potential for cooling houses with minimal demands upon the central electrical system. Building performance simulation can be used to assess the potential of the technology and to explore the impact of system design (e.g. type and area of solar collectors, volume of hot and cold thermal stores, operating strategies), but only if appropriate models calibrated with accurate and reliable data are available. Experiments were conducted on a commercially available lithium bromide–water absorption chiller under a controlled set of operating conditions. Instrumentation was selected, calibrated, and installed in order to derive quantities of interest at acceptable levels of measurement uncertainty. Over this range of experiments, the cooling capacity varied from 6.9kW to 40.5kW, and the thermal coefficient of performance ranged from 0.56 to 0.83. A quasi-steady-state model suitable for use in building performance simulations that expressed the chiller’s performance was developed. Based upon statistical significance testing, it was found that the rates of heat transfer to both the generator and the evaporator could be expressed as linear functions of the generator inlet temperature, absorber/condenser inlet temperature, and flow rate of water to the generator. The validity of the calibrated model was then tested using measurements from a disjunct experiment whose data were not used to calibrate the model.

Performance of an Absorber With Hydrophobic Membrane Contactor at Aqueous Solution-Water Vapor Interface

In this study, a detailed modeling of the heat and mass transfer processes inside a plate-and-frame absorber with hydrophobic microporous membrane contactor at aqueous solution-water vapor interface as a part of a chiller model is developed. The absorber is a component of a 5 kW cooling capacity single effect lithium bromide-water absorption chiller with a hot water thermally driven generator, a water-cooled absorber, and a condenser. The model is used to investigate the performance of the absorber in case the chiller operates at different values of the inlet driving hot water and cooling water (coolant) temperatures. The results clearly indicate that for the same cooling capacity of the chiller and compared with the performance at the design point value, increasing the inlet driving hot water temperature results in an increase in the required absorber size and consequently a decrease in the absorber performance, while decreasing the cooling water (coolant) inlet temperature leads to slight decreases in the required absorber size and consequently an increase in the absorber performance. The effect is prominent and can be used to decrease the absorber size for chillers work in places where the option of lower inlet coolant temperature is available with normal driving hot water temperature.

The Influence of Coolant Temperature on a Single-Effect Lithium Bromide—Water Absorption Chiller when Energized from a Low-Temperature Source

A simulation study of several schematic models of both water- and air-cooled single-effect LiBr—H2O absorption chillers energized by a high-potential, low-temperature (73 °C) geothermal source has been carried out using IPSEpro refrigeration software package. All the simulated models were validated against a lithium bromide—water pressure—temperature DÜhring chart. The results obtained show that when the coefficient of performance, heat input into the generator, and cooling mass flowrates are fixed, the cycle parameters are highly affected by variation of the coolant temperature. This information will be useful to designers of absorption refrigeration systems.

Absorption Cooling: A Review of Lithium Bromide-Water Chiller Technologies

Lithium bromide-water absorption cooling technologies is underpinned by the continual circulation of water, which is the refrigerant, powered by the hygroscopic nature of aqueous lithium bromide solution. The present energy and global warming crises engender a renewed interest in thermally driven cooling systems, for which lithium bromide-water absorption chiller is an archetypal example forming the focus of this review. We review more than 100 patents dated mainly from 1985 and later that offer panoply of solutions to better this genre of timely technologies. We classify the surveyed patents into four main categories: (1) absorption system developments, (2) machine components developments, (3) working fluid modifications and additives, and (4) novel applications of absorption cooling systems. Finally we also map out several important directions for future research and development.

Optimum hot water temperature for absorption solar cooling

The hot water temperature that maximizes the overall instantaneous efficiency of a solar cooling facility is determined. A modified characteristic equation model is used and applied to single-effect lithium bromide–water absorption chillers. This model is based on the characteristic temperature difference and serves to empirically calculate the performance of real chillers. This paper provides an explicit equation for the optimum temperature of vapor generation, in terms of only the external temperatures of the chiller. The additional data required are the four performance parameters of the chiller and essentially a modified stagnation temperature from the detailed model of the thermal collector operation. This paper presents and discusses the results for small capacity machines for air conditioning of homes and small buildings. The discussion highlights the influence of the relevant parameters.

Characteristics of the membrane utilized in a compact absorber for lithium bromide–water absorption chillers

This study aims at investigating experimentally and analytically the characteristics and properties of a membrane utilized to design compact absorbers for lithium bromide–water absorption chillers. The main focus of this study are the factors that influence the water vapor transfer flux into a lithium bromide–water solution in confined narrow channels under vacuum conditions, as well as the properties limits for utilization in compact absorber design. The results indicate that the desired membrane characteristics for this application are as follows: high permeability to water vapor, hydrophobic to the aqueous solution with high liquid entry pressure (LEP) to avoid wettability of the membrane pores and no capillary condensation of water vapor to avoid blocking of the pores. For practical use, this membrane should have a thin hydrophobic microporous active layer with a thickness up to 60 μm, mean pore sizes around 0.45 μm and a porosity of up to 80%. The active layer should be attached to a porous support layer to meet the mechanical strength requirements needed for practical use in the absorber of lithium bromide water absorption chillers application.

Design of a compact absorber with a hydrophobic membrane contactor at the liquid–vapor interface for lithium bromide–water absorption chillers

In this study, design of a compact plates-and-frames absorber possessing a hydrophobic microporous membrane contactor at the aqueous solution–water vapor interface is performed analytically. The absorber is a component of a 5 kW cooling capacity single-effect lithium bromide–water absorption chiller that incorporates a hot water thermally driven generator and a water-cooled absorber and condenser. Good agreement prevailed for the analytically evaluated water vapor mass transfer flux and aqueous solution outlet temperature when compared with measured values at similar operating conditions. At design point conditions, the main design parameters obtained are a membrane contactor area of 6.06 m 2, a ratio of the mass transfer area to absorber net volume ( A m / V net ) of 130.1(m 2/m 3), and ratio of the membrane area (mass transfer area) in this design configuration to the area required for heat transfer is 1.162, respectively. The results clearly indicate that the aqueous solution channel thickness is the most significant design parameter that affects the absorber size compactness; the thinner the thickness of the solution channel, the higher the ratio ( A m / V net ). The results also show the countercurrent refrigerant flow with the aqueous solution has positive effects on the absorber size compactness.

Performance assessment of an integrated free cooling and solar powered single-effect lithium bromide-water absorption chiller

In this study, performance assessment of an integrated cooling plant having both free cooling system and solar powered single-effect lithium bromide–water absorption chiller in operation since August 2002 in Oberhausen, Germany, was performed. A floor space of 270 m 2 is air-conditioned by the plant. The plant includes 35.17 kW cooling (10-RT) absorption chiller, vacuum tube collectors’ aperture area of 108 m 2, hot water storage capacity of 6.8 m 3, cold water storage capacity of 1.5 m 3 and a 134 kW cooling tower. The results show that free cooling in some cooling months can be up to 70% while it is about 25% during the 5 years period of the plant operation. For sunny clear sky days with equal incident solar radiation, the daily solar heat fraction ranged from 0.33 to 0.41, collectors’ field efficiency ranged from 0.352 to 0.492 and chiller COP varies from 0.37 to 0.81, respectively. The monthly average value of solar heat fraction varies from 31.1% up to 100% and the five years average value of about 60%. The monthly average collectors’ field efficiency value varies from 34.1% up 41.8% and the five-year average value amounts about 28.3%. Based on the obtained results, the specific collector area is 4.23 (m 2/kW cold) and the solar energy system support of the institute heating system for the duration from August 2002 to November 2007 is 8124 kWh.

A computational study on evaluation of solar absorption cooling system in India

The present paper presents the simulation of a solar powered absorption cooling system with an absorption working pair of lithium bromide and water. The system consists of a flat plate solar collector, a lithium bromide water absorption chiller, an auxiliary energy source and a hot water storage tank. Initially, the thermodynamic behaviour of the cooling system cycle is simulated under various ambient conditions to determine the working conditions of the absorption cooling system compatible with the capacity of the flat plate collector. Computer modelling of a solar absorption cooling system using a flat plate collector was undertaken for all possible climatic conditions of Bahal, India. The results have shown that for each ton of refrigeration a minimum collector area of 26·02 m2 with an optimal water storage tank capacity ranging from 1000 to 1500 L is required, so that the system can operate solely on solar energy for ∼7 h a day.

06/01221 Electric power required in the world by 2050 with hydrogen fuel production — revised: Kruger, P. International Journal of Hydrogen Energy, 2005, 30, (15), 1515–1522

Solar heating and cooling (SHC) systems are currently under rapid development and deployment due to their potential to reduce the use of fossil fuel resources and to alleviate greenhouse gas emissions in the building sector – a sector which is responsible for ∼40% of the world energy use. Absorption chiller technology (traditionally powered by natural gas in large buildings), can easily be retrofitted to run on solar energy. However, numerous non-intuitive design choices must be analyzed to achieve the best techno-economic performance of these systems. To date, there has been little research into the optimal configurations among the long list of potential solar-driven absorption chiller systems. To address this lack of knowledge, this paper presents a systematic simulation-based, multi-objective optimization of three common, commercially available lithium bromide-water absorption chillers – single-effect, double-effect and triple-effect – powered by evacuated tube collectors (ETCs), evacuated flat plate collectors (EFPCs), and concentrating parabolic trough collectors (PTCs), respectively. To the best of authors’ knowledge, this is the first study of its kind that compares the optimized designs of the most promising configurations of solar-assisted absorption chillers against a common set of energy, economic, and environmental metrics from a holistic perspective. A simulation model of these three configurations is developed using TRNSYS 17. A combined energy, economic, and environmental analysis of the modeled systems is conducted to calculate the primary energy use as well as the levelized total annual cost of each plant, which are considered as two conflicting objective functions. By coupling TRNSYS and MATLAB, a multi-objective optimization model is formulated using a genetic algorithm to simultaneously minimize these objectives, thereby determining a set of optimal Pareto solutions corresponding to each SHC configuration. The performance of the proposed systems at their optimal designs is then compared to that of a reference conventional system. A sensitivity analysis is also performed to assess the influence of fuel cost, capital cost of innovative components, and the annual interest rate on the Pareto front of optimal solutions. Overall, the optimization results reveal that of the proposed configurations, the SHC double-effect chiller has the best trade-off between the energetic, economic and environmental performance of the system, having a total cost of ∼0.7–0.9 M$ per year and reducing the annual primary energy use and CO2 emissions by 44.5–53.8% and 49.1–58.2% respectively (relative to the reference conventional system). With the high capital cost associated with these systems, government subsidies and incentives are still required in order for them to achieve satisfactory payback times and become cost-competitive with conventional HVAC systems.

Performance of a LiBr–water absorption chiller operating with plate heat exchangers

Abstract This paper studies the performance of a lithium bromide–water absorption chiller operating with plate heat exchangers (PHE). The overall heat transfer coefficients in the desorber, the condenser and the solution heat recoverer are calculated using the correlations provided in the literature for evaporation, condensation and liquid to liquid heat transfer in PHEs. The variable parameters are the external driving temperatures. In the desorber, the inlet temperature of the hot fluid ranges from 75 °C to 105 °C. In the condenser and the absorber, the inlet temperature of the cooling water goes from 20 °C to 40 °C. The coefficient of performance (COP) obtained ranges from 0.5 to 0.8 for cooling duties ranging from 2 kW to 12 kW. The chiller response to different hot fluid temperatures and circulated mass flow rates is also presented. The performance and the internal parameters of the chiller at part load are, therefore, calculated. A higher efficiency results when the solution pumped from the absorber to the desorber decreases. The heat transfer analysis of the PHEs is also presented. The overall heat transfer coefficient in the desorber, equal to 790 W/m 2 K at the design conditions, is also analysed at part load. The condenser performance can be represented by a similar relationship found in conventional air cooled condensers.