Absorption Chiller System Research Articles

Solar-assisted absorption air-conditioning systems in buildings: Control strategies and operational modes

Solar-assisted cooling technology has enormous potential for air-conditioning applications since both solar energy supply and cooling energy demand are well correlated. Unfortunately, market uptake of solar cooling technologies has been slow due to the high capital cost and limited design/operational experience. In the present work, different designs and operational modes for solar heating and cooling (SHC) absorption chiller systems are investigated and compared in order to identify the preferred design strategies for these systems. Three control scenarios are proposed for the solar collector loop. The first uses a constant flow pump, while the second and third control schemes employ a variable speed pump, where the solar collector (SC) set-point temperature could be either fixed or adjusted to the required demand. Series and parallel arrangements, between the auxiliary heater and the storage tank, have been examined in detail from an energy efficiency perspective. A simulation model for different system layouts is developed in the transient system simulation environment (TRNSYS, Version 17). Simulation results revealed that the total solar fraction of the plant is increased by up to 11% when a variable speed solar loop pump is used to achieve a collector set-point temperature adjusted according to the building load demand. Another significant finding of this study is that a parallel configuration for the auxiliary heater out-performs a conventional series configuration. The yearly performance of an auxiliary heater in parallel with the storage tank enhances the plant solar fraction, and the average collector efficiency, by up to 13% and 9%, respectively (as compared to the same components in series). Taken together, nearly 20% higher solar fraction (as compared to conventional designs) is possible through the control strategies and operational modes presented here without adding a substantial capital cost to the system.

The life cycle assessment of a solar-assisted absorption chilling system in Bangkok, Thailand

Life cycle assessment (LCA) methodology following ISO 14044:2006 standard is utilized to analyze the environmental impacts of implementing a solar/electric hybrid cooling system in a stadium of 15,000 seating capacity. Four impact categories are investigated: 100 year global warming potential (GWP), acidification potential, eutrophication potential, and abiotic resource depletion (ARD) potential. The life cycle emissions of the solar-assisted absorption chiller (AC) system are compared to that of a conventional electricity-consuming vapor compression (VC) chilling system. The use-phase electricity consumption of the VC and the life time cooling production of the solar-assisted AC are simulated. The results yield reduced AC system net life cycle impacts for GWP, acidification, eutrophication and ARD potentials by factors of 25.8, 40.1, 33.6, and 37.7%, respectively, when compared with those of the VC system. It is found that use-phase impact savings due to the cooling production of the solar AC outweigh the higher non-use phase (raw material extraction, refining, unit manufacturing, transportation, and disposal) impacts of the solar-assisted AC system, and thus the system is found to be environmentally advantageous. The results are applicable to similar cooling systems and building systems within Southeast Asia.

Mathematical Modeling of an Absorption Chiller System Energized by a Hybrid Thermal System: Model Validation

Nowadays, global warming and energy crisis problems become serious issues which affect on all creatures on our earth. One of the best ways to simultaneously address or mitigate these problems is more utilizing the renewable energy sources instead of the fossil fuel. A solar-biomass hybrid cooling system is one of the technologies for the climate change and green-house-gas mitigation. The mathematical model of this system was developed and used in the theoretical prediction of its performance and system design. To assess the accuracy of the developed mathematical model, the obtained experimental data is then compared with the simulation results, with the same operating parameters and weather conditions. This paper presents the validation of the developed model. The validation results show that the simulation results are in good agreement with the experimental results from both qualitative and quantitative points of view.

부산지역 학교 기숙사에서의 소형열병합발전 시스템의 경제성 분석

The cogeneration system can operate at efficiencies greater than those achieved when heat and power are produced in separate. The optimal system can be determined by selecting the auxiliary system combined with cogeneration system. In the present study, economic investigation has been conducted with the cogeneration electric heat pump(EHP) system and the cogeneration absorption chiller(AC) system to install in a school dormitory. To analyze life cycle cost(LCC), cost items such as initial investment costs, annual energy costs and maintenance costs of each system have been considered. The initial investment cost is referred to the basis of estimated costs, and annual energy costs such as the electric power and gas consumption are based on the data in a school dormitory. LCC is evaluated with the present worth method. Considering investigated results, the initial investment cost of the cogeneration EHP system is more profitable about 24% than that of the cogeneration AC system. The energy cost of the cogeneration EHP system is more profitable about 8% than the cogeneration AC system. The LCC shows that the cogeneration EHP system is the most effective system in the school dormitory.

Simulation study on the performance of solar/natural gas absorption cooling chillers

Solar radiation is a clean form of energy and solar cooling systems is one of the technologies which allow obtaining an important energy saving. Natural gas is a cheaper fuel than oil. It also burns cleaner than oil. Natural gas and renewable energy are complementary and in the future, the alignment of natural gas and renewable energy may be the most effective way to service the demand for clean energy. This paper presents a numerical study of solar/natural gas single effect lithium bromide absorption chillers. The development of this system is based on hot water chiller. As auxiliary power, fire from the natural gas burners is used to heat the hot water on its way to the generator. The overall performance of the absorption chiller system is analysed and discussed. For an evaporator temperature of 5°C and when the condenser temperature is varied from 28°C to 36°C and generator temperatures is varied from 54 to 83°C the maximum COP is 0.82 and the maximum exergetic efficiency is about 30%. For a given condenser temperature there is an optimum generator temperature for which the number of flat plate collectors is minimum. This optimum generator temperature corresponds to the generator temperature giving the maximum COP and exergy efficiency of the absorption cooling system. The solar/natural gas single effect lithium bromide absorption chillers, using solar energy as the energy source with only limited amount of gas as auxiliary power, not only reduces greatly the cost for electricity and operates in regions where there are abundant solar energy and cheap natural gas resources, but also compensates the peak-valley load difference and reduce CO2 gas emissions. For a refrigeration capacity of 10kW, the quantity of natural gas used to provide auxiliary load is very small and consequently the CO2 gas emissions is very small (the maximum mass flow rate of CO2 is less than 3kgh−1).

Comparison of Different Gas Turbine Inlet Air Cooling Methods

Gas turbine air inlet cooling is a useful method fo r increasing output for regions where significant pow er demand and highest electricity prices occur during the warm mo nths. Inlet air cooling increases the power output by taking advant age of the gas turbine's feature of higher mass flow rate when the compressor inlet temperature decreases. Different methods are availa ble for reducing gas turbine inlet temperature. There are two basic systems currently available for inlet cooling. The first and most cos t-effective system is evaporative cooling. Evaporative coolers make use o f the evaporation of water to reduce the gas turbine's inlet air temp erature. The second system employs various ways to chill the inlet air. In this method, the cooling medium flows through a heat exchanger located in the inlet duct to remove heat from the inlet air. However, th e evaporative cooling is limited by wet-bulb temperature while th e chilling can cool the inlet air to temperatures that are lower than t he wet bulb temperature. In the present work, a thermodynamic model of a gas turbine is built to calculate heat rate, power outp ut and thermal efficiency at different inlet air temperature condi tions. Computational results are compared with ISO conditions herein cal led base-case. Therefore, the two cooling methods are implemented and solved for different inlet conditions (inlet temperature and r elative humidity). Evaporative cooler and absorption chiller systems r esults show that when the ambient temperature is extremely high with low relative humidity (requiring a large temperature reduction) the chiller is the more suitable cooling solution. The net increment i n the power output as a function of the temperature decrease for each cooling method is also obtained.

A review: Renewable energy with absorption chillers in Thailand

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

α– h Diagram and principle of exergy coupling of GAX cycle

Ammonia absorption chiller systems of a single-stage cycle and a Generator Absorber heat exchanger cycle (GAX) were simulated and studied. At heat source temperatures of T H = 120 °C, T M = 25 °C and T L = 5 °C, the coefficient of performances of the two cycles are 0.589 and 0.776, the GAX cycle is higher 31.8% than the single-stage cycle. And the exergy efficiencies of the two cycles are 15.4% and 27.4%, the GAX cycle is higher up to 77.9%. This paper proposes a new method that adopts the energy quality factor α as a evaluation criterion and also uses the α– h diagram as a thermodynamic analysis tool graphically, and a concept that divides absorption cycle to a heat pump subcycle and a heat engine subcycle. By means of the α– h diagram, the thermodynamic frameworks of the two cycles were illustrated. The comparison analysis indicates that the improvement of cycle performance depends on its thermodynamic perfectibility. In fact, the exergy demand of heat pump subcycle in the GAX cycle is as the same as that of the single-stage cycle, however, the energy cascading use and the exergy coupling framework of the heat engine subcycle in GAX cycle is retrofitted, so that the exergy consumption is reduced and the increased benefit is obtained from the overall cycle.

Absorption chiller crystallization control strategies for integrated cooling heating and power systems

The concept of an air-cooled absorption chiller system is attractive because the cooling tower and the associated installation and maintenance issues can be avoided. However, crystallization of the LiBr–H 2O solution then becomes the main challenge in the operation of the chiller, since the air-cooled absorber tends to operate at a higher temperature and concentration level than the water-cooled absorber due to the relative heat transfer characteristics of the coolant. This leads to crystallization of the working fluid. The paper focuses on the crystallization issues and control strategies in LiBr–H 2O air-cooled absorption chillers. As a result a novel application opportunity is proposed for the integration of absorption chillers into cooling, heating and power (CHP) systems. This new methodology allows for air cooler operation while avoiding crystallization.

733 故障検出法としての主成分分析とサポートベクターマシンの比較

Fault detection methods based on empirical models such as principal component analysis (PCA) or support vector machines (SVM) are compared. As an example of realistic plants, absorption chiller system is chosen for comparisons. Several datasets whose distribution show different degrees of nonlinearity are generated based on an empirical model which describes heat exchanger efficiency. Sample numbers for model training is crucial on fault detection ability of models, especially for SVM. Nonlinear distribution of observed plant data deteriorates fault detection sensitivity of linear PCA model, whereas it does not affect SVM model.

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.

Inlet Air Cooling Methods for Gas Turbine Based Power Plants

Background: Power generation from gas turbines is penalized by a substantial power output loss with increased ambient temperature. By cooling down the gas turbine intake air, the power output penalty can be mitigated. Method of Approach: The purpose of this paper is to review the state of the art in applications for reducing the gas turbine intake air temperature and examine the merits from integration of the different air-cooling methods in gas-turbine-based power plants. Three different intake air-cooling, methods (evaporative cooling, refrigeration cooling, and evaporative cooling of precompressed air) have been applied in two combined cycle power plants and two gas turbine plants. The calculations were performed on a yearly basis of operation, taking into account the time-varying climatic conditions. The economics from integration of the different cooling systems were calculated and compared. Results: The results have demonstrated that the highest incremental electricity generation is realized by absorption intake air-cooling. In terms of the economic performance of the investment, the evaporative cooler has the lowest total cost of incremental electricity generation and the lowest payback period (PB). Concerning the cooling method of pre-compressed air, the results show a significant gain in capacity, but the total cost of incremental electricity generation in this case is the highest. Conclusions: Because of the much higher capacity gain by an absorption chiller system, the evaporative cooler and the absorption chiller system may both be selected for boosting the performance of gas-turbine-based power plants, depending on the prevailing requirements of the plant operator.

Thermoeconomic Optimization of a LiBr/H2O Absorption Chiller Using Structural Method

The optimization strategy for absorption chiller systems is generally based on thermodynamic analysis. However, the optimum, so obtained, does not always guarantee the economic optimum. In this regard, the thermoeconomics that combines the thermodynamic principles with economic parameters plays a vital role for achieving the cost effectiveness of these systems. In this paper, this technique is applied to optimize a single-effect LiBr/H2O absorption chiller system for air-conditioning applications aiming at achieving the minimum product cost. This optimization methodology is based on the relative interdependence between component irreversibility and the total system irreversibility. This relationship, known as structural coefficient, is used to evaluate the economic cost of the product of the system. The use of structural coefficient eliminates complex numerical procedures, and the optimization is achieved by sequential local optimization of the subsystems of the system. The analysis reveals that the capital cost of the optimum configuration is increased by about 33.3% from the base case, however, the additional cost is well compensated by reduced fuel cost. This is possible because of reduction of plant irreversibilities by about 47.2%.

ANN Model of a Direct-Fired Absorption Chiller System for Energy Evaluation

A direct-fired absorption chiller system rejects more heat energy than a vapour-compression chiller system of similar capacity. The combined use of fuel energy and electricity consumption is an important criterion in its performance evaluation. Many current research efforts on absorption chiller system are related to the search of an optimal supervisory control strategy to minimize the energy costs. System simulation has been a conventional approach for the investigation. However, the task of developing an accurate system model through the component-modelling approach can be tedious. Oversimplification in the process, and the nonlinear structure of the equation set as a result, are often the limitations for reaching reliable converging solutions. The system-based artificial neural network (ANN) modelling approach appears to be an attractive alternative. This article describes the process of deriving an ANN model of a commercial direct-fired double-effect absorption chiller system. The techniques and the ways to overcome the difficulties in the training process are discussed.

Global optimization of absorption chiller system by genetic algorithm and neural network

The optimal use of fuel and electricity in a direct-fired absorption chiller system is important in achieving economical operation. Previous work on the control schemes mainly focused on the component local feedback control. A system-based control approach, which allows an overall consideration of the interactive nature of the plant, the building and their associated variables is seen to be the right direction. This paper introduces a new concept of integrating neural network (NN) and genetic algorithm (GA) in the optimal control of absorption chiller system. Based on a commercial absorption unit, neural network was used to model the system characteristics and genetic algorithm as a global optimization tool. The results appear promising.

99/02765 Carbon-dioxide emissions from an integrated small-scale CHP and absorption chiller system

99/02765 Carbon-dioxide emissions from an integrated small-scale CHP and absorption chiller system

Carbon-dioxide emissions from an integrated small-scale CHP and absorption chiller system

If the combined heat-and-power ( CHP) unit's heat-output is increased, so as to supply all the heat required by the absorption chiller, then the emissions from the integrated small-scale CHP and absorption chiller system are reduced by up to 0.06 kg of CO 2 per kWh T at design conditions or by up to 0.10 kg of CO 2 emissions per kWh of cooling delivered for lower cooling-water temperatures. These correspond to reductions of 22% and 40% respectively, when compared with those produced by a similarly sized electrically-driven vapour-compression chiller.

Optimal supervisory control of an absorption chiller system

Optimal supervisory control of an absorption chiller system

Optimal Supervisory Control of an Absorption Chiller System

The system performance and supervisory control of a direct-fired (natural gas), double-effect water-LiBr absorption chiller was investigated using simulations. A mechanistic model of the chiller was developed and calibrated using manufacturers catalog design data. A computationally-simple model was then derived from the mechanistic model and coded for use with the program, TRNSYS, to simulate the steady-state performance of the chiller, a chilled and cooling water pump, a cooling tower, and a cooling water bypass valve. Using a global optimization algorithm (simulated annealing), the optimal supervisory control of the absorption chiller system was determined for different control options, and the energy usage under optimal control was compared to other control strategies. Guidelines for control of absorption chillers are presented based on control laws that were developed from the optimal control investigation.

Power Production and Air Conditioning by Solar Ponds

The potential of a salt‐gradient solar pond for electric power production and thermal energy supply for cooling, using absorption chillers, and heating of a building was investigated by means of computer simulations. The analysis was conducted for the pond and building of the Energy Systems Center (ESC) located in southern Nevada. The experimental pond has a bottom area of about 950m2 and 3‐m depth. The energy requirement for cooling and heating of the ESC 232-m2 two‐story building was calculated using the TRNSYS model and the ESC facility data. Power production from the pond was evaluated for a solar pond power plant with a low temperature Organic Rankin Cycle (ORC) generator. Several operating strategies were simulated using the salt‐gradient solar pond (SGSP) model. The results indicate that the pond can produce 16.8 kWe for 10 h/day, sufficient for ESC cooling demands. Using a pond absorption chiller system for cooling, 27% of the energy available from the pond will meet the cooling and heating demands of the building.