Single-effect Absorption Chiller Research Articles

Exergoeconomic analysis and optimization of a hybrid system based on multi-objective generation system in Iran: a case study

The present work aims to study a multi-objective generation system based on renewable solar and wind energy that has been selected according to the climatic conditions of the area under study, i.e. Bandar Abbas, Iran. In general, the system includes six different sections such as solar cycle, single effect absorption chiller, Rankine cycle with ammonia–water fluid, wind turbine, electrolyzer, and multi-stage flushing desalination. First, the system is investigated in terms of thermodynamic and exergy principles. Then, exergoeconomic analysis with specific exergy costing method (SPECO) is carried out based on the concepts of product, fuel, and cost balancing. The sensitivity analysis investigates the effect of decision parameters on energy and exergy efficiencies. Finally, single-objective optimization is analyzed using conjugate method and the multi-objective optimization is analyzed using genetic algorithm. Results show that, based on multi-objective optimization, isentropic efficiency of turbine is 81%, isentropic efficiency of pump is 77%, pressure ratio of Rankine cycle is 40.32, solar cycle mass flow is 0.8 k/s, outlet temperature of boiler is 113.62°C, exergy efficiency is 32.88%, and operating cost rate is 8.45 dollars per hour. Using multi-objective optimization, operating cost rate decreases by 22.6% and exergy efficiency increases by about 5.31%.

Comparison of the solar PV cooling system and other cooling systems

The energy consumption and economic performance of the solar PV cooling system, the solar absorption cooling system and the conventional vapor compression cooling system located in Hefei, Chengdu and Haikou have been analyzed. The annual cost method is used to compare the economic performance of the three kinds of cooling systems. For the PV cooling system, ‘full power to grid’ PV grid-connected mode and ‘self-generated, left power to grid’ PV grid-connected mode are discussed. And for the solar absorption cooling system, the single-effect absorption chiller and the double-effect absorption chiller are both discussed. Meanwhile, the economic performances of three kinds of cooling systems are also analyzed when PV subsidies are ignored and energy prices are variable. The results indicate that the economic performance of the PV cooling system is better than that of the solar absorption cooling system and the conventional vapor compression cooling system. Furthermore, even when PV subsidies are ignored or the energy prices change a lot, the economic performance of PV cooling is better than that of solar absorption cooling and conventional vapor compression cooling.

Assessment of Aqueous Lithium-based Salt Solutions as Working Fluid for Absorption Chillers using Aspen Plus

Absorption chillers are a viable option for providing waste heat-powered coolingor refrigeration, thereby improving overall energy efficiency-less primary energy input,lower emissions, and cost savings. This study focuses on the assessment of aqueouslithium-based salt solutions as working fluid for absorption chiller in exploring thepossibility of developing new mixtures for absorption chillers to improve the performanceof the absorption refrigeration systems (ARSs). In this paper, the coefficient ofperformance (COP) of a single-effect absorption chiller using aqueous lithium-based saltsolutions (LiF-H2O, LiCl-H2O, LiBr-H2O, and LiI-H2O) as working fluid was assessed usingAspen Plus®. The simulation results obtained showed that the mass and energy were wellbalanced for all systems. Furthermore, a direct proportionality relationship between COPof absorption chillers and the van't Hoff factor, i of dissociated aqueous salt solutions wasobserved. The highest COP value is 0.8930 for LiI-H2O among others.

An optimal design to provide combined cooling, heating, and power of residential buildings

Providing electricity for the residential buildings which devote a high portion of energy consumption is very crucial all over the world. Not only electrical loads but also heating and cooling loads are required to be supplied in a building. The aim of this paper is to supply cooling, heating, and electrical loads in a building by separating generation system and cogeneration system. In this regard, the optimal problem was developed to minimize the total costs using particle swarm optimization algorithm. As a numerical study, a high-rise building with 72 units located in Kerman is analyzed for eight different scenarios.The results show that in order to supply cooling, heating, and power, a cogeneration system consisting of a 195 kW micro gas turbine as prime mover, a 281 kW single-effect absorption chiller, a 439 kW air cooling compaction chiller, an 187 kW auxiliary boiler to compensate the heat load, and a 52.8 kW photovoltaic to generate employed electrical loads, is the best optimal system to supply the base building loads. In this optimized system, the annual electricity sales revenue is 93,251$, the annual cost of buying power is 7001$, the cost of buying fuel as annual consumption is 15,852.4$, and the annual production of carbon dioxide emissions in the building is 229.78 tons. The return on investment period for the aforementioned project is also estimated 4.98 years.

New approach for estimating the cooling capacity of the absorption and compression chillers in a trigeneration system

This paper presents a multi-objective optimization model for estimating the cooling capacity of refrigeration in a trigeneration system for both grid on and off operating modes. In trigeneration systems, the cooling demand can be provided by single effect absorption and compression chillers (as the refrigeration system). Genetic Algorithm and LINMAP selection procedure are used for obtaining the final optimum point considering four-E analysis (energy, exergy, economy and emission) with the help of net future worth benefit difference (NFWBD) and global exergy efficiency objective functions. It was found that the NFWBD and exergy efficiency with cooling capacity of 1800 and 5600 kW for absorption and compression chillers, respectively, are 330 × 106$ and 41.9% for grid on mode, while they reduce to 232 × 106$ and 32.7% for grid off mode. Sensitivity analysis in grid on mode shows that the increase in the number of equipment (gas engine and chillers) leads to the decrease in both NFWBD and exergy efficiency, while selecting two similar absorption chillers (with cooling capacity of 900 kW), has payback period of 5.1 years, and provides the maximum NFWBD (321 × 106$) and exergy efficiency (40.02%).

Solar driven ORC-based CCHP: Comparative performance analysis between sequential and parallel system configurations

Overall energy efficiency remains a large and unexploited resource in combined cooling, heating, and power systems driven by solar energy. This study aims to explore the configuration effects on such systems using parabolic trough collector and organic Rankine cycle (ORC) technologies. The configurations are concisely clarified into sequential and parallel connections, in which a single-effect absorption chiller and a heat exchanger are considered for cooling and heating, respectively. A comprehensive assessment framework is proposed by establishing the thermodynamic performance, system size, and economic models. Under reasonable thermodynamic boundary conditions, the optimal operational parameters are obtained via a Pareto frontier solution for such a system, with an ORC of 200 kW. Promising technical solutions and enhancement potential are justified and quantified by means of system simulations and comparison on the annual time scale.

Improving liquefaction process of microgrid scale Liquid Air Energy Storage (LAES) through waste heat recovery (WHR) and absorption chiller

Liquid air energy storage systems (LAES) store liquid air produced by a liquefaction cycle and convert it into electric/cooling power when needed. A small-scale Liquid air energy storage system represents a sustainable solution in microgrid and distributed generation, where small energy storage capacities are required. The main drawback of these systems though, is the low round trip efficiency due to a high specific consumption of the liquefaction cycle. In this work, a single-effect absorption chiller using a Water-Lithium Bromide solution is integrated with a small air liquefier with a liquid air production capacity of 0.834 t/h. In the proposed solution, the waste heat of the compression phase of the liquefaction cycle is recovered and used to drive the absorption cycle, where the resulting cooling power is used to decrease the specific consumption and improving the exergy efficiency of the system. The operative parameters of the absorption chiller reflect the specifications of the most common commercial models available in the market and the size has been selected to maximize the heat power recovered. The results of simulation of the absorption chiller integration show a reduction of the specific consumption of around 10% (537 kWh/t to 478 kWh/t) and an increase of exergy efficiency of around 11.5%.

Clarifying the bifurcation point on Design: A Comparative Analysis between Solar-ORC and ORC-based Solar-CCHP

An obvious knowledge gap exists in the design of ORC-based solar-CCHP, due to an abuse and indiscreet application of the existing research methodology specifically developed for solar-ORC. Such extended research methodology, which emphasizes on the promotion of power generation performance, does not provide a reasonable design result, because of a significant application difference between the ORC-based solar-CCHP and solar-ORC. Although the two systems have some similar technologies elements, a bifurcation point on design has not been clarified which lead to the lack of clear methodology framework or profile in this research field. To fill the gap and clarify the bifurcation point, this paper focuses on the ORC-based solar-CCHP system with the energy cascade utilization principle. Considered the medium-temperature working fluids, including Benzene, Toluene, Decane, D4, MM, the whole system model is established which consists of a parabolic trough collector, ORC, heat exchanger for heating system, and a single-effect absorption chiller. An assessment framework for the system energy efficiency is proposed. And then a comparison study between the solar-ORC and ORC-based solar-CCHP is conducted. The results show that the configuration characteristics have an important effect on the system energy efficiency for the CCHP system, which should be taken into account prior to the performance of the solar-ORC system. Specifically, for the solar-ORC system, the system energy efficiency increases as the increasing of the evaporating temperature. However, for the ORC-based solar-CCHP system, the behaviors of the system thermal performance, such as the overall efficiency of solar energy are totally changed compared with the solar-ORC system. Consequently, the optimal configuration parameters should be a tradeoff between the thermal performance, size and initial investment cost. Finally, the optimum configuration design for the ORC-based solar-CCHP system with MM is achieved, where the overall efficiency of solar energy is 40.95%, with the cooling-to-power ratio of 4.95 and heat-to-power ratio of 4.2.

Thermodynamic analysis of a novel combined cooling, heating and power system driven by solar energy

A novel combined cooling, heating and power system (CCHP) driven by solar energy is proposed. The system applies an organic Rankine cycle, a double effect lithium bromide-water absorption refrigeration system, and heat exchangers to generate electricity, cooling and heating, respectively. Energy and exergy analyses are conducted to determine system efficiencies and losses. The cycle is compared with similar combined cycle that differs by using a cooling subsystem having a single effect absorption chiller. The effects of some key thermodynamic parameters on the performance of the cycle are examined. The results reveal that, for the same amount of input heat, the usage of a double effect absorption refrigeration system instead of a single effect absorption chiller can raise the amount of cooling power up to 48.5% and consequently can improve the performance of the system. At the same time, heating power rises by 20.5%, resulting in an increase in the cogeneration heat and power efficiency to 96.0%, while net electrical power production declines by 27%. In addition, it is determined that a high exergy destruction rate occurs in the solar collectors.

Comparison of CPC driven solar absorption cooling systems with single, double and variable effect absorption chillers

In the solar absorption cooling systems, concentrating collector can be adopted to achieve higher driven temperature and improve the system performance. The Compound Parabolic Concentrator (CPC) is a good option with both concentrating and stationary features. With higher working temperature, solar absorption cooling system with concentrating collector has more choices of absorption chillers than the system with non-concentrating collector. The aim of this paper is to find the better chiller choice for solar absorption cooling systems with CPC. The analyzed LiBr-water absorption chillers include the single effect chiller, the double effect absorption chiller and a novel variable effect chiller built by the author. Simulation is carried out in TRNSYS. Model of the variable effect absorption chiller is first derived from MATLAB artificial neural network (ANN) toolbox based on experimental data, and then built in TRNSYS. Performance of the three systems is calculated under the same condition. Performance of the three systems is compared to get the better choices. The impacts of the solar collector area, cutoff driven temperature and storage tank volume on the solar cooling fraction, auxiliary heat input, average chiller COP and average solar efficiency are analyzed. The variable effect system has high solar cooling fraction, low auxiliary heat input and high solar efficiency. The single effect system has medium solar fraction, high auxiliary heat input and medium solar efficiency. The double effect system has low solar cooling fraction, low auxiliary heat input and low solar efficiency.

Exergoeconomic analysis and optimization of a solar based multigeneration system using multiobjective differential evolution algorithm

This paper presents and analyzes a multigeneration energy system that consists of a reverse osmosis desalination unit, water heater, organic Rankine cycle, photovoltaic solar collectors, and a single effect absorption chiller. In doing so, energy and exergy analysis are first performed to evaluate the performance of the system and determine the irreversibility of each component. Next, considering minimizing total cost rate and maximizing exergy efficiency as two objective functions, a multiobjective optimization approach based on differential evolution algorithm is proposed to determine the best design parameters. A self-adaptive technique is utilized to deal with the search capability, population diversity, and convergence speed of the proposed optimization algorithm. An external archive list is used to save all nondominated optimal solutions during the optimization. Dynamic crowding distance approach is employed to decrease archiving size without losing its characteristics. Furthermore, a fuzzy clustering approach is used to select the desired solution among the Pareto-optimal solutions. Simulation results are compared with two other multiobjective optimization algorithms and effectiveness of the proposed optimization method is verified using various indices. Finally, a sensitivity analysis is employed to evaluate effects of design parameters on exergy efficiency and total cost rate of the system.

Experimental study of heat transfer enhancement in the evaporator of single-effect absorption chiller using new different tube insert

In this paper, the effect of the different tube inserts with various geometry parameters on turbulent flow in the evaporator of single-effect absorption chiller has been investigated experimentally. The experiments were performed with several tube inserts including of wire coils (S1, S2), modified wire coils (GS1, GS2, GS5), modified classic (TW) and butterfly (BT) for mass flow rate from 0.167 to 0.583kgs-1. In all cases, the use of tube inserts leads to a considerable increase in heat transfer and pressure drop over the evaporator without tube insert. The highest performance factor of 1.78 was achieved for the butterfly tube inserts compared to others. In all cases and all Reynolds number, the performance factors are more than one and these techniques are favorable for heat transfer enhancement.

Dynamic Performance Analysis for an Absorption Chiller under Different Working Conditions

Due to the merits of energy saving and environmental protection, the absorption chiller (AC) has attracted a lot of attention, and previous studies only concentrated on the dynamic response of the AC under a single working condition. However, the working conditions are usually variable, and the dynamic performance under different working conditions is beneficial for the adjustment of AC and the control of the whole system, of which the stabilization can be affected by the AC transient process. Therefore, the steady and dynamic models of a single-effect H2O-LiBr absorption chiller are built up, the thermal inertia and fluid storage are also taken into consideration. And the dynamic performance analyses of the AC are completed under different external parameters. Furthermore, a whole system using AC in a process plant is analyzed. As a conclusion, the time required to reach a new steady-state (relaxation time) increases when the step change of the generator inlet temperature becomes large, the cooling water inlet temperature rises, or the evaporator inlet temperature decreases. In addition, the control strategy considering the AC dynamic performance is favorable to the operation of the whole system.

Energetic and financial analysis of solar cooling systems with single effect absorption chiller in various climates

The objective of this work is to investigate the solar cooling viability in various locations worldwide. A single stage absorption chiller operating with the LiBr-H2O working pair is coupled with evacuated tube collectors and this system produces the demanded cooling load for a typical building of 100m2 floor area. Ten cities are examined and the analysis is performed with the commercial software TRNSYS. For every city, different combinations of collecting areas and storage tank volumes are investigated in order to determine the optimum combination which leads to the minimum levelized cost of cooling (LCOC). According to the final results, Abu Dhabi and Phoenix are the most suitable locations with LCOC equal to 0.0575€/kWh and 0.0590€/kWh respectively, while Rome, Madrid and Thessaloniki are the less suitable locations with 0.2125€/kWh and 0.1792€/kWh and 0.1771€/kWh respectively. Moreover, it is found that the locations with high cooling loads and high solar potential are the most suitable locations for installing solar cooling. Furthermore, it is proved that higher collecting is associated with a greater optimum storage tank. Finally, the conclusions of this work can be used as guidelines for designing solar cooling system and determining the suitable locations and climate conditions for installing solar cooling systems.

Optimal operating strategies of combined cooling, heating and power systems: A case study for an engine manufacturing facility

In this paper, a detailed numerical analysis of a Combined Cooling, Heating and Power system is presented, aiming at determining its optimal operating strategy in a real industrial application. The system layout includes a reciprocating engine, fuelled by natural gas, heat exchangers for waste-heat recovery, pumps, storage tanks, a single-effect water lithium bromide absorption chiller, a cooling tower, a back-up vapour-compression electric chiller, mixers and valves. A dynamic simulation model of the whole system was developed in TRNSYS. A case study was analysed, referred to a real industrial application, where the system under evaluation should be installed in the near future, providing electricity, mainly used for the production process, and space cooling. Real measured data were used to estimate the electric energy demand of the factory. A detailed building simulation model was used to calculate heating and cooling demands. A detailed economic analysis was carried out, aiming at evaluating: (i) the optimal size of the Combined Cooling, Heating and Power system; (ii) the optimum control strategy, from a thermo-economic point of view, comparing three different cases: Base-Load operation, electric load tracking and a new hybrid strategy based on the simultaneous tracking of electric and thermal-loads. The results showed that the optimal capacity of the system was lower than that selected by the designers of the real unit to be installed. The hybrid control strategy obtained the best profitability, achieving a simple pay-back period equal to 3.8years, compared to 4.1years achieved in case of electric-load tracking.

CFD modeling and optimization of a latent heat storage unit for running a solar assisted single effect Li-Br absorption chiller using multi-objective genetic algorithm

In this paper, the feasibility of a solar absorption refrigeration system to be powered by a latent heat storage (LHS) unit is investigated for a representative building. A single effect absorption chiller, utilizing Li-Br and water as working fluids is thermodynamically simulated. Then, the simulation of the latent heat storage unit is performed by applying finite difference method and the results were validated by the researches in the literature. Then, the geometry of a phase change material (PCM) based LHS system was optimized using multi-objective Genetic Algorithm for simultaneously minimizing the charging time, and maximizing the discharging time. Since the paper considers conflicting objectives, a Pareto front is presented that can be used for obtaining the optimum geometry according to the environmental conditions and working hours of the absorption system. As an illustrative example, the designed heat storage system was shown to be able to drive the 72kW generator of an absorption system, for at least 10h of operation in the discharging mode with the absence of sunlight. Therefore, it is possible to run absorption chillers under low-load operation conditions using the solar energy if the appropriate storage unit, such as what is introduced here, is used.

Experimental investigation of a novel multi-tank thermal energy storage system for solar-powered air conditioning

The volume of hot storage tank in sensible thermal energy storage (STES), integrated with solar-powered air conditioning to mitigate the misalignment between supply and demand, is too big which results in great thermal inertia. In this paper, a novel multi-tank thermal energy storage (TES) system for solar-power air conditioning, with the advantages of quick temperature rising and outstanding ability to fit variable weather, was proposed to mitigate the contradictions between demand and supply. In order to investigate effect of the number of tanks (NT) on system response time (SRT), total energy grade of water in tanks and temperature variations in charging and discharging periods, a series of experiments of TESs with different number of tanks (total volume of tanks is constant) were conducted under the same solar radiation conditions. Results show that the energy grade of water in tanks is improved through dividing thermal energy storage system into several tanks with different priorities of charging and discharging, and SRT decreases by 6.95h in four-tank TES, compared with one-tank TES. Furthermore, the duration time of ideal heating inlet water temperature (IHIWT) in entire operational period increases slowly with the number of tanks, because NT has opposite effects on duration time of IHIWT in charging and discharging periods. An optimized control strategy that tanks stored heat successively in charging period and released heat simultaneously in discharging period was proposed. It is notable that the duration time of IHIWT in four-tank TES increases 2.59h, about 26.67%, after the optimized control strategy is adopted. Therefore, the optimized TES makes the single-effect absorption chiller run at a high COP over a long time without strong variations of COP, compared with other TESs.

Experimental and analytical study on an air-cooled single effect LiBr-H2O absorption chiller driven by evacuated glass tube solar collector for cooling application in residential buildings

Solar cooling turns out to be a feasible method to reduce the electricity consumption of air conditioning systems in buildings. Air-cooled single effect LiBr-H2O absorption chiller has shown advantages in residential applications. It can be driven by common evacuated tube solar collectors, and save water, maintenance expense and space, due to the absence of cooling tower. However, there is no available small capacity commercial air-cooled LiBr-H2O absorption chiller yet, because of the crystallization risk under ambient conditions. In this work, an air-cooled single effect absorption chiller for which the cooling capacity is 6kW and a solar air conditioning system were developed. The air-cooled single effect absorption chiller was fabricated and tested under a broad range of steady-state conditions. The chiller was proved successful for real application without crystallization risk and the influence of different operating conditions was also analyzed. Moreover, the performance of a solar air conditioning system using the proposed chiller was investigated for residential cooling application. The results show that the studied absorption chiller can meet about 65% of the total cooling load of the building with an average COPth of about 0.61. Furthermore, 28% of the titled solar radiation is converted into cooling capacity by the solar air conditioning system.

The influence of the overall heat transfer coefficients in the dynamic behavior of a single effect absorption chiller using the pair LiBr/H2O

Absorption systems offer an alternative way to substitute energy economically in mechanical compression systems in the field of refrigeration and air conditioning. The aim of this article is to investigate the transient performance of a single effect absorption chiller using the pair LiBr/H2O when the overall heat transfer coefficients are varied in time by updating the thermo-physical properties and convective coefficients. A thermodynamic model was developed based on conserving mass and energy and considers, so as to determine the overall heat transfer coefficients of the heat exchangers of a chiller and the correlations of the convective coefficients of the processes of refrigeration by absorption (desorption, absorption, condensation and evaporation). This model when tested for real operating conditions and considering the overall coefficients of heat transfer were constant throughout the process showed relative errors were less than 15% in the chilled water circuit and under 2% in cold water. This difference drops significantly when the variable overall coefficients are considered throughout the process, these errors being approximately 5% and 0.3%, there being a percentage fall in all water circuits.

Economic Evaluation of Solar Cooling Schemes

This paper provides an economic evaluation and comparison of ejector, absorption and vapor compression systems driven either partly or fully by solar energy. Life cycle costing has been used to assess the relative economic ranks of eight solar cooling schemes. It has been shown that the capital cost of solar collectors is the dominant capital cost item in the total inventory of solar cooling plant, which has a strong influence on the system life cycle costs. Lower collector costs are therefore critical in establishing economically viable solar cooling systems. Primary energy analysis has been carried out and the running costs of chillers were determined for the maximum range of thermal and electric solar fractions and a number of annual equivalent full load hours of operation. The results indicate that two low temperature flat-plate collector assisted single-effect absorption chillers compete favorably with a PV assisted centrifugal mechanical compression chiller across the maximum range of thermal and electrical solar fractions. Low temperature options for solar cooling have been shown to be more economical than their high temperature counterparts. At current collector prices, solar cooling systems are still not cost effective compared with conventional centrifugal cooling systems, however, it is shown that at a collector cost of £57/m2 for thermal energy and £1.8/Wp for electrical energy, single-effect solar absorption and PV-centrifugal compression could become cost effective within an annual EFLH of 5840 hours. As such, the paper presents technical guidance on the procurement and operation of solar cooling plant. The novel energy and cost calculation methodology developed here can be applied globally to a wide range of solar collectors, chillers, heat rejection and ancillary subsystems.