LiBr-H2O Absorption Chiller Research Articles

Comparative review and novel design possibilities on solar-driven absorption LiBr-H2O refrigeration system

Solar energy is a promising source of energy because of its potential due to the reduction usage of non-renewable energy. As the demand for cooling increases, solar-powered cooling technologies are becoming increasingly promising. Among the different solar cooling systems, LiBr-H2O absorption chillers are commonly used due to their advantages over NH3-H2O systems. Multiple cycle LiBr-H2O chillers can be powered by easily available flat-plate, evacuated tubular or parabolic solar collectors. This paper reviews Theoretical Principles-Based Analysis and Simulations of solar LiBr-H2O absorption cooling systems, performance comparison of each types and introduces new design options related to auxiliary energy systems and cooling mode cycle. The paper also summarizes other main types of solar absorption cooling systems, including double-effect, half-effect, triple effect and give updates of new technology design of hybrid effect. The choice of water-cooled or air-cooled absorption refrigeration depends on the local climate and water availability. Recent advances have made air-cooled absorption refrigeration a viable option, with comparable COP to water-cooled systems and lower maintenance requirements. Additionally, geothermal heat rejection with low pressure drops can further reduce energy consumption. Solar-powered double-effect absorption cooling systems are recommended for buildings with high cooling loads, while half-effect are suitable for air-cooled solar absorption cooling systems in hot and dry regions with limited water. This paper is specifically intended for those interested in developing solar-driven LiBr-H2O absorption chillers, emphasizing the importance of establishing standardized design guidelines to specific regions and climates in order to promote and expand the usage of solar cooling systems.

AspenPlus-based techno-economic analysis of solar-assisted sorption-enhanced gasification for hydrogen and chemicals recovery from polyethylene terephthalate waste

Although the recycling of polyethylene terephthalate (PET) bottles is well-operating in several countries, less than 10% of PET plastic waste was recycled in a closed loop globally, and the rest was discarded as leakage. A process to recover hydrogen and valuable chemicals through solar-assisted PET sorption-enhanced gasification was analyzed. PET steam gasification with CaO and solar-assisted calcium looping processes were already experimentally studied in our previous work to obtain optimized processing conditions. In this paper, the integrated process with product purification, steam power plant, and LiBr-H2O absorption chiller was simulated with Aspen Plus based on previous experimental results to investigate the techno-economic performance. Material flows, energy balance, exergy destruction, and economics were analyzed. Day and night mode operations at different seasons were evaluated based on energy balance and the weather conditions of Naples, Italy. The energy and exergy efficiencies of day and night modes varied between 62%–72%. The annual production yields of hydrogen and benzene were 684 t and 6286 t, respectively. Due to the high production of benzene, its higher price (>1092 €/t) would make the project feasible with a larger than 12% internal rate of return value and competitive break-even hydrogen price (less than 4 €/kg). The results show that this integrated process could be technically and economically feasible. It has the potential to be implemented for hydrogen and benzene recovery from PET plastic waste with sustainable solar heat source and zero fossil CO2 emissions.

Exergy and exergoeconomic analyses of multi-energy complementary system based on different natural gas and biogas co-firing ratios considering carbon tax

This study analyzes the exergy and exergoeconomic performances of a combined cooling, heating, and power (CCHP) system powered by natural gas and biogas. First, the exergy of the energy and material flows in the investigated co-firing CCHP system is obtained. In addition, the exergy loss and exergy loss distribution ratios of each component as well as the exergy efficiency of the entire system are investigated. Furthermore, the effects of the co-firing ratio of natural gas and biogas on the exergy and exergoeconomic performances are analyzed. Meanwhile, a carbon tax is considered in the exergoeconomic analysis. The results show that the gasifier, two-stage LiBr-H2O absorption chiller, and internal combustion engine indicate the largest exergy loss and exergy loss distribution ratios under different co-firing ratios. The exergy efficiency of the entire system decreases by 3.81% and 4.93% as the co-firing ratio decreases from 1:1–1:10 (natural gas: biogas) in the summer and winter, respectively. The unit exergoeconomic cost (UEC) of multiple products decrease with the co-firing ratio. Finally, a sensitivity analysis is performed to reveal the effects of the co-firing ratio and natural gas price on the UEC of multiple products.

Use of Ionic Liquid as Crystallization Inhibitor in Water-Lithium Bromide Absorption Chiller

Chillers are used in commercial buildings and industrial plants to provide air conditioning, refrigeration, and process fluid cooling. There are two basic types of chiller cycles: vapor compression and sorption. Sorption chillers are available as either absorption or adsorption designs, depending on the state of the sorbent. Absorption chillers use fluid refrigerants and absorbents (liquid or dissolved), while adsorption chillers employ a solid sorbent (typically silica gel) in combination with a fluid refrigerant. Among the former category, the use of highly hygroscopic LiBr salt as absorbent in combination with H2O as refrigerant comprises LiBr-H2O absorption chillers. Such chillers possess cooling capacities ranging from a few kilowatts (kW) to megawatts (MW) which match with small residential to large scale commercial or even industrial cooling needs. One of the major debilitating factors associated with LiBr-H2O absorption chillers is crystallization. A crystallization event causes a loss of cooling and requires de-crystallization by applying external heat, which results in extensive down-time and requires redundancy designed into a chiller plant. We investigated the use of the imidazolium-based ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIm]-Br), as crystallization inhibitor additive to LiBr-H2O in the ratio 1:19 [BMIm]-Br:LiBr. It was found that under the operating boundary conditions of 27°C/9°C (cooling water inlet temperature/chilled water outlet temperature), the LiBr-H2O absorption chiller can be operated without modifications and with around 10 K higher heating water inlet temperatures when adding [BMIM]-Br before crystallization occurs compared to pure LiBr-H2O solution. When using the [BMIM]-Br ionic liquid, the refrigeration capacity of the absorption chiller under the above operating conditions and at 85°C heating water inlet temperature exhibited 10% increase after optimizing the solution flow, that lead to higher outputs, such as lower cooling water temperatures. By adding the [BMIM]-Br to the aqueous lithium bromide solution the operating range of the absorption refrigeration system could also be extended to resorption mode, which allows refrigeration below 0 °C. Thus, there is an excellent potential for a significant extension of the application range of LiBr-H2O chillers, e.g. in the field of food cooling and refrigeration processes. Figure 1

A biomass-based polygeneration system for a historical building: A techno-economic and environmental analysis

Combined cooling, heating, and power systems (CCHP) are considered one of the most efficient energy systems since they have a less detrimental environmental impact, and therefore sustainable energy savings, and eventually less CO2 emissions. An even higher advantage is possible when a renewable energy fuel source (e.g., Biomass) is used. The proposed study presents the energy modeling of a 169 kWe capacity, biomass-based CCHP system retrofitted to a historical building, located in Perugia, Italy. Two well-known simulation software’s, ASPEN Plus and TRNSYS, are purposely integrated. In the first phase of the study, a wood biomass combustion-based externally fired gas turbine (EFGT) along with an Organic Rankine Cycle (ORC) system is modeled in Aspen Plus. In the later phase, a historical building “Sant’ Apollinare” model, and the remaining CCHP system are developed in TRNSYS. The transient system is modeled such that it fulfills the peak thermal energy demands of the retrofitted building. The main components of the system are a heat exchanger (HE), storage tanks (TK), a single-stage LiBr-H2O absorption chiller (ACH), and balance of plant (BOP) components. A heat exchanger recovers heat from the gas cycle, which is then utilized for running an ORC, heating and cooling of the end-user building, biomass drying, and domestic hot water (DHW) supply. A storage tank supplies direct heat to the end-user in winter and drives the ACH in summer. The results of the model provide data on the performance parameters of different components of the CCHP system such as temperature, power consumption, and energy profiles that allow evaluating the overall energy performance of the CCHP system. Finally, a feasibility analysis of the system is carried out on the basis of economic indexes such as simple pay back (SPB) period, net present value (NPV) and profitability index (PI), for two different case scenarios assumed for fuel (e.g., biomass) supply cost. The SPB is 2.93 years, when biomass is obtained for free. Whereas, if biomass is purchased from the market the SPB becomes 7.15 years. From an environmental perspective, the plant ensures a decrease of 632 tons of CO2 emissions annually.

Optimizing single-stage double-effect LiBr-H2O absorption chiller in micro-trigeneration system using an atom search optimization algorithm

Wastes produced from several processes are focused on by many scientific researchers in order to reuse them, achieve energy savings, and reduce cost and environmental pollution. Recently, many organizations have utilized a micro-trigeneration system as a primary energy source, as it produces cooling, heat, and power in a combined effect. Various scholars designed numerous trigeneration systems in recent years. However, it is challenging to attain energy-efficient operation. Therefore, this current research focuses on developing an optimal micro combined cooling, heating, and power generation (MCCHP) to improve energy efficiency and reduce cost. The major components of the trigeneration system are the diesel engine, heat exchanger, boiler, absorption chiller, and chilled water storage system. In order to improve the cooling output of the proposed system, a single-stage, double-effect absorption chiller (LiBr-H2O absorption chiller) is utilized with the atom search optimization (ASO) algorithm. The variables of the condenser in the absorption chiller are given as input for optimization. The results show that the proposed system has a cooling capacity of 16 kW. Compared with the existing algorithms, it is efficient with 98% temperature minimization and cost-effectiveness. This micro-trigeneration device can be used in hospitals and the food production industry and is cost-effective.

Thermodynamic investigation of a novel cooling-power cogeneration system driven by solar energy

This communication develops a novel cooling-power cogeneration system consisting of a parabolic trough collector utilizes gasses as the medium for solar to heat conversion, and the Kalina cycle integrated series-flow double effect LiBr-H2O absorption chiller to generate electricity and large cooling, simultaneously. By developing a thermal model, a simulation through EES is conducted to investigate the influence of internal tube diameter of absorber and solar irradiation on the exit temperature of SHTF and flowing mass of the working fluid of Kalina cycle. It is determined that for the given inlet temperature and solar irradiation, the outlet temperature of SHTF is declined when the internal diameter of absorber tube is increased. The effect of change in SHTF, pressure at expander entry, and the concentration of ammonia-water basic solution on electrical power produced, refrigeration capacity, exergy of refrigeration, efficiencies of the cogeneration cycle are investigated. The cogeneration cycle with helium operated PTSC indicates better results than the use of air and CO2 as SHTF. Increase in the outlet temperature of SHTF (helium) leads to considerable increase in electrical power, refrigeration capacity, and exergy of refrigeration. The breaking down of solar exergy supplied to developed configuration reveals an exergy destruction of the order of 64.01% along with the exergy loss to environment of 1.92%, and exergy of refrigeration of 4.65% with generated power exergy of 29.42%, respectively. The computational results of present investigation are compared with the theoretically published data and a good agreement is found between these data.

Multi-objective optimization of power, CO2 emission and exergy efficiency of a novel solar-assisted CCHP system using RSM and TOPSIS coupled method

In this study, the waste energy from exhausted gases of a gas turbine was recovered in a novel combined cooling, heating, and power system integrated of a gas turbine power plant, Kalina cycle, single-effect LiBr–H2O absorption chiller, parabolic trough collectors, heat recovery steam generator unit, and domestic hot water provision. This system utilized solar energy to preheat the air inlet to the combustion chamber and alleviated the emission of carbon dioxide resulted from consuming methane. An unparalleled algorithm was introduced to determine an optimum configuration of solar collectors. The results indicated that there were six optimum points with respect to maximum net power, minimum carbon dioxide emission and maximum exergy efficiency. The best optimum point was recognized using technique for order preferences by similarity to ideal solution method. The findings showed that compression ratio of 11.66, pinch point temperature difference in the air preheaters-1 of 11.96 K, inlet temperature of gas turbine-1 of 1470 K, and inlet temperature of combustion chamber of 900 K were the best multi-objective optimum conditions. In that condition, the net power, the system emission and the exergy efficiency were 61.73 MW, 52.87 g/MJ and 44.22%, respectively.

Multi-objective optimization of a solar-driven polygeneration system based on CO2 working fluid

The object of this study is the investigation of polygeneration plants utilizing solar energy in order to produce power products on the scale of a few MW. Parabolic trough collectors are used in order to exploit solar irradiation and to provide the generated heat to the polygeneration/trigeneration cycle in a high-temperature range (500–570 °C). The plants under consideration additionally consist of a storage tank, a Brayton cycle with s-CO2, a LiBr-H2O absorption chiller and also the installation of a suitable thermodynamic organic Rankine cycle (ORC) cycle is examined in order to utilize waste heat for further power generation. The systems are first investigated for operation under steady-state conditions and then for dynamic conditions on an annual basis. Based on the final annual results of the plants, the plant in which ORC was not used shows annual electrical, exergy and energy efficiencies equal to 18.33%, 23.37% and 54.91% respectively, while the plant in which ORC was used similarly shows 19.05%, 23.63% and 49.00%. According to economic analysis, the payback period was found at 6.37 years without ORC and 6.51 years with ORC. Taking into account the operational and techno-economic results of the plants it can be concluded that the plants produce satisfactory energy products ensuring also the economic viability of the investment.

Research on a Solar Hybrid Trigeneration System Based on Exergy and Exergoenvironmental Assessments

The environmental performance of a combined cooling, heating, and power system is analyzed in this study at a component-level using a SPECO-based exergoenvironmental analysis. The engine consumes natural gas and produces 168.6 kW net power. The waste heat is recovered by a LiBr-H2O absorption chiller and a heat exchanger, which are used for cooling and heating purposes. The energy system is assisted by a solar field. An environmental Life Cycle Assessment quantifies the environmental impacts of the system, and these data are combined with exergy evaluations. The highest total environmental impact rate, 23,740.16 mPt/h, is related to the internal combustion engine, of which pollutant formation is the primary source of environmental impact. Compared with a non-renewable energy system, the solar-assisted trigeneration system decreased the environmental impact per exergy unit of chilled water by 10.99%. Exergoenvironmental performance can be further improved by enhancing the exergy efficiency of the solution pump and high-pressure generator (HG), and by employing a treatment to remove nitrogen oxides in the reciprocating engine.

Exergic Analysis of an ISCC System for Power Generation and Refrigeration

Exergic analysis has become an effective method of thermodynamic behavior evaluation for power systems. The current study focuses on an integrated solar–gas combined cycle (ISCC) system for electric power generation and refrigeration. Exergic analysis of the ISCC system is conducted by using the gray-box model as well as the Ebsilon software. The results show that under the rated working condition, the total exergy loss and overall exergy efficiency of the ISCC system are 119.078 MW and 44.63 %. The two largest exergy losses exist in the combustion chamber and solar DSG system, which are 56.45 MW and 28.52 MW, respectively. The LiBr–H2O absorption chiller system, HRSG, steam turbine and condenser have the same grade exergy losses. When the solar intensity augments, though the solar DSG system has an increase in the exergy efficiency, its exergy loss also increases, leading to the increase in the total exergy loss as well as the decrease in the overall exergy efficiency of the ISCC system. Therefore, further optimizations of the ISCC system should focus on the improvements of the solar DSG system and combustion chamber. The economic and ecological evaluations demonstrate that the ISCC system is economically feasible and ecologically friendly.

Study of a New Solar-Powered Combined Absorption–Adsorption Cooling System (ABADS)

Sorption cooling technology is considered to be a good alternative to traditional vapor compression cycles regarding energy savings and environmental issues. This technology has to be enhanced to overcome the problem of low efficacy. In this work, a novel solar-powered combined absorption–adsorption cooling system (ABADS) is proposed and investigated under different climatic conditions. The system combines a single-effect LiBr-H2O absorption chiller (ABS) and a single-stage silica gel/water adsorption chiller (ADS) in series configuration. TRNSYS simulation software integrated MATLAB code is used to simulate the solar-driven ABS, ADS, and ABADS mathematical models. Both of ABS and ADS models are validated experimentally with experimental data. Performance comparison between the proposed combined ABADS and the standalone ABS and ADS is also performed. Results shows that the proposed combined ABADS produced average monthly cooling capacity (19.86 kW) higher than that of ABS and ADS by 154.42% and 59.74%, respectively, around typical year. Furthermore, the overall COP (1.17) of ABADS is higher than that of the standalone ABS and ADS by 154.42% and 59.74%, respectively. Under the same hourly weather conditions of June 15 at 16:00 pm, cooling capacity of the ABADS is higher than that of the standalone ABS and ADS by 150% and 66%, respectively. The overall system COP of ABADS (1.16) improved by 60% and by 167% over the standalone ABS and ADS, respectively. In addition, the chilled water production is increased.

Transient model for the development of an air-cooled LiBr-H2O absorption chiller based on heat and mass transfer empirical correlations

• Development of a transient model based on heat and mass transfer correlations for absorption chillers (H 2 O-LiBr). • Generic expressions for heat&mass transfer used, parameter identification minimized. • A new zero order model for absorber and generator is developed. • Experimental validation with an agreement of 5% for COP and 11% for cooling capacity. • The new model is used for the development of a direct air-cooled absorption chiller. This work describes transient numerical modeling of a direct air-cooled, single-effect absorption chiller. The model is lumped parametric based on transient mass, momentum, and energy balances, applied to the internal components of the absorption machine. Thermal and mass storage in each one of the components are taken into account in the transient evaluation, and pressure losses in the SHX are evaluated using a pressure drop coefficient. This work aims to improve the available numerical modeling propositions by using embedded available heat and mass transfer empirical correlations, based on previous experiences in falling film absorption. This approach minimizes the need for experimental parameter identification and allows scalability studies. The experimental validation has been organized in three steps: (i) absorber zero-order model, steady-state conditions; (ii) the whole chiller, also in steady-state conditions; (iii) transient conditions. For the steady-state conditions, most results have an agreement within the margin of the uncertainty of the experiments, with a medium discrepancy of 5% in COP and 11% in the cooling capacity. For transient conditions, the comparison of the outlet temperatures of the secondary streams, reveals discrepancies under 0.5 K, except in some fast transient periods, where higher differences are perceived. To perform the numerical simulations is used as an in-house modular object-oriented simulation platform (NEST platform). Finally, the performance of a prototype demonstration 7 kW air-cooled LiBr-H 2 O absorption chiller is predicted through a designed test campaign. This model put gives valuable information for the definition of further regulation and control protocols.

Dynamic Simulation and Thermoeconomic Analysis of a Trigeneration System in a Hospital Application

Hospitals are very attractive for Combined Heat and Power (CHP) applications, due to their high and continuous demand for electric and thermal energy. However, both design and control strategies of CHP systems are usually based on an empiric and very simplified approach, and this may lead to non-optimal solutions. The paper presents a novel approach based on the dynamic simulation of a trigeneration system to be installed in a hospital located in Puglia (South Italy), with around 600 beds, aiming to investigate the energy and economic performance of the system, for a given control strategy (electric-load tracking). The system includes a natural gas fired reciprocating engine (with a rated power of 2.0 MW), a single-stage LiBr-H2O absorption chiller (with a cooling capacity of around 770 kW), auxiliary gas-fired boilers and steam generators, electric chillers, cooling towers, heat exchangers, storage tanks and several additional components (pipes, valves, etc.). Suitable control strategies, including proportional–integral–derivative (PID) and ON/OFF controllers, were implemented to optimize the trigeneration performance. The model includes a detailed simulation of the main components of the system and a specific routine for evaluating the heating and cooling demand of the building, based on a 3-D model of the building envelope. All component models were validated against experimental data provided by the manufacturers. Energy and economic models were also included in the simulation tool, to calculate the thermoeconomic performance of the system. The results show an excellent economic performance of the trigeneration system, with a payback period equal to 1.5 years and a profitability index (ratio of the Net Present Value to the capital cost) equal to 3.88, also due to the significant contribution of the subsidies provided by the current Italian regulation for CHP systems (energy savings certificates).

Geothermal driven micro-CCHP for domestic application – Exergy, economic and sustainability analysis

Abstract Geothermal energy is going to play a key role in future smart energy systems. Geothermal-driven domestic energy systems, specifically, will largely contribute to the baseload supply of heating and cooling demand of societies. A low-temperature geothermal resource is considered to drive a domestic-scaled multi-generation system supplying power, heating, and cooling. The proposed cogeneration system includes a small-scale organic Rankine cycle (ORC), a single effect LiBr–H2O absorption chiller, and heat exchangers to supply domestic space heating and hot water. The waste heat of the ORC is harvested, also, to be used in space heating. Energy, exergy, economic, and sustainability principles are applied to the system to evaluate the system thermodynamic and thermos-economic performance. Results associated with the exergy destruction are obtained and effects on the system performance of chiller supply are investigated. Besides, the thermodynamic performance of the system is evaluated under the summertime and wintertime conditions. Under the base condition, the generator employed in the absorption chiller is found to be the most exergy destructive unit followed by the evaporator utilized in the ORC. Furthermore, results revealed that by increasing the chiller supply rate, the system sustainability index enhances from 1.6 to 2.5 while the system’s first law efficiency reduces.

Thermodynamic modelling of a LiBr-H2O absorption chiller by improvement of characteristic equation method

In this study, approaches developed by previous studies which to improve the characteristic equation method applied to absorption chiller were analyzed and an approach is proposed aiming to make a further contribution. A computational code was designed containing the chiller thermodynamic modelling and the characteristic equations obtained by each approach. The modelling results and the characteristic equations results were numerically compared and the COP and heat removed ( Q ˙ E ) deviations between them were calculated. The sequence of approaches aimed to reduce these deviations. The first approach computed the characteristic parameters and used them as constant values. The second approach used a linear adjustment between the minimum characteristic temperature difference (ΔΔ t minE ) and the characteristic temperature difference. The third approach used the previous approach adjustment, and the following were inserted in the characteristic equations: linear adjustments between ΔΔ t minE ; S E and the lift temperature (∆t lift ), and between ΔΔ t minE ; S E and the thrust temperature (∆t thrust ). The ∆t thrust adjustment obtained the lowest deviations. Using ΔΔ t minE obtained directly from the input data, a better linear adjustment was achieved between ΔΔ t minE and ∆t thrust . The use of this adjustment was treated as a proposed approach and achieved even smaller deviations. Then, a case study of a commercial chiller was conducted with this approach. Most COP and Q ˙ E deviations values obtained in this case study were lower than 5%. Deviations between the manufacturer's datasheet values and the characteristic equations results were lower than 10%. Therefore, it can be understood that this approach can contribute to the characteristic equation method.

Solar Cooling: A renewable energy solution

A sustainable and environmentally alternative to commonly used air conditioning systems can be the solar cooling system due to the use of renewable and clean energy. Solar absorption systems can be used for greenhouse cooling in areas with high outdoor temperatures and solar radiation levels. These systems take advantage of the simultaneity between the solar energy availability and the greenhouse cooling demand allowing the reduction of conventional electricity and water consumption. This paper presents the results of the application of a solar cooling plant for the climate control of a greenhouse at the University of Bari, Italy. The experimental plant consists of a Mediterranean greenhouse, having a surface of 300 m2, and of a single effect LiBr-H2O absorption chiller fed by evacuated-tube solar collectors. Two different localized systems were chosen for the distribution of cold inside the greenhouse: the first system presents pipes placed centrally on the cultivation vessels; the second consists of pipes in contact with aluminium plates and of a transparent EVA film, used to border an area close to plants. The distribution system of cold with pipes, plate and EVA film provided a slightly higher cooling capacity due to the presence of the plates which increases the ability to dissipate energy.

Small-scale CCHP systems for waste heat recovery from cement plants: Thermodynamic, sustainability and economic implications

In this paper, different combined cooling, heating and power (CCHP) systems are introduced and studied for waste heat recovery from a cement plant located in Şanliurfa, Turkey considering domestic applications. One of the systems is based on the steam Rankine cycle and the next is based on recuperative organic Rankine cycle (ORC), while both of them are equipped with a LiBr–H2O absorption chiller to produce cooling. Different working fluids are considered in the ORC simulation. Energy, exergy and exergoeconomic principles are applied to compare the examined systems from thermodynamic, sustainability and economic aspects. It is observed that utilizing siloxanes as the working fluid leads to efficient performance of the ORC. Besides, employed heat recovery steam generator in the Rankine cycle and evaporator in the ORC found to be the most exergy destructive components. Results revealed that the CCHP system operating with ORC (MM as working fluid) has a better performance thermodynamically with energy utilization factor, exergy efficiency and sustainability index of 98.07, 63.6% and 2.747, respectively. This is while, Rankine-based CCHP is economically preferable with a payback period of 4.738 year compared to the system operating with ORC and a payback period of 5.074 year.

Multi-objective optimization of a tri-generation system based on biomass gasification/digestion combined with S-CO2 cycle and absorption chiller

A novel configuration of biomass-based cooling, heating and power (CCHP) system, consisting of Gas Turbine (GT), Supercritical Carbon dioxide cycle (S-CO2) and double effect LiBr-H2O absorption chiller is proposed and its performance is analyzed and compared for two cases: 1) fueling with syngas from the gasification process and 2) fueling with biogas from the digestion process. Thermodynamic models are developed to evaluate the proposed systems’ performance from energy, exergy and exergoeconomic viewpoints and an environmental assessment is conducted to evaluate the systems’ CO2 emission. Then, a multi-objective optimization is applied for which the exergy efficiency and unit cost of system products are selected as the objective functions. The results revealed that the digestion-based system performs better than the gasification-based one in terms of efficiency, unit product cost and environmental impacts. The former yields a maximum exergy efficiency of 47.8%, while for the latter a maximum efficiency of 42.74% is calculated. For digestion-based system, the values of 47.09% and 5.436 $/GJ are calculated for exergy efficiency and product unit cost at the optimum operating conditions. Also, the results of environmental assessment indicated the values of 2.6×10-2t/MWhand 4.21×10-2t/MWh for CO2 emissions for digestion- and gasification-based systems, respectively.

Evaluation and comparison of solar trigeneration systems based on photovoltaic thermal collectors for subtropical climates

Solar trigeneration systems based on photovoltaic thermal (PVT) collectors are promising for enhancement of solar energy utilization. Single-effect LiBr-H2O absorption chillers are usually employed in these systems. Since the temperature of solar heat from PVT collectors is low, half-effect absorption chillers are potential alternatives for performance improvement. However, the coefficient of performance (COP) of half-effect absorption chillers is lower than that of single-effect machines. Therefore, the comparison of solar trigeneration systems with both types of chillers is necessary. Four different system layouts, obtained by coupling glazed and unglazed flat-plate PVT collectors with single- and half-effect absorption chillers, are modeled. Annual (8760-hour) simulations are performed to evaluate and compare the thermodynamic and economic performances of different layouts. The results show that the system layout based on glazed PVT collectors coupled with half-effect absorption chillers achieves the highest Solar COP of 0.072 and the highest solar utilization factor of 0.241. Its specific electricity saving is 158.5 kWh/(m2·year), the highest among all the layouts. Additionally, the payback period of the layout based on unglazed PVT collectors coupled with half-effect absorption chillers is 12.7 years, the lowest among all the layouts. This paper is helpful for the development and design of solar trigeneration systems based on PVT collectors in subtropical climates.