Thermodynamic Analysis of Double Effect Absorption System along with Boiler and Cooling Tower

Many researchers have studied single and double effect absorption cycles based on first and second lows of thermodynamics But so far the relation of different parameters inside these cycles to the second law of thermodynamics in boiler and cooling tower has not been investigated. In this paper, a system comprised of a series flow double effect water-Lithium bromide absorption chiller, a boiler and a cooling tower is studied based on the first and second laws of thermodynamics, and also exergy analysis is investigated. For this purpose, mass and energy conservation laws governing the system are written, and coefficient of performance of the system, exergy destruction （loss） of each component and exergy efficiency have been calculated.

Assessment of Low Global Warming Potential Refrigerants for Waste Heat Recovery in Data Center with On-Chip Two-Phase Cooling Loop

Data centers(DCs)are highly energy-intensive facilities,where about 30%–50%of the power consumed is attributable to the cooling of information technology equipment.This makes liquid cooling,especially in twophase mode,as an alternative to air cooling for the microprocessors in servers of interest.The need to meet the increased power density of server racks in high-performance DCs,along with the push towards lower global warming potential(GWP)refrigerants due to environmental concerns,has motivated research on the selection of two-phase heat transfer fluids for cooling servers while simultaneously recovering waste heat.With this regard,a heat pump-assisted absorption chiller(HPAAC)system for recovering waste heat in DCs with an on-chip twophase cooling loop driven by the compressor is proposed in the present paper and the low GWP hydrofluoroolefin refrigerants,including R1224yd(Z),R1233zd(E),R1234yf,R1234ze(E),R1234ze(Z),R1243zf and R1336mzz(Z),are evaluated and compared against R245fa as server coolant.For theHPAAC system,beginning with the development of energy and economic models,the performance is analyzed through both a parametric study and optimization using the coefficient of performance(COP),energy saving ratio(ESR),payback period(PBP)and net present value(NPV)as thermo-economic indicators.Using a standard vapor compression cooling system as a benchmark,the results indicate that with the evaporation temperature between 50℃and 70℃and the subcooling degree ranging from5℃to 15°C,R1233zd(E)with moderate compressor suction pressure and pressure ratio is the best refrigerant for the HPAAC systemwhile R1234yf performs the worst.More importantly,R1233zd(E)is also superior to R245fa based on thermo-economic performance,especially under work conditions with relatively lower evaporation temperature as well as subcooling degree.Under the given working conditions,the overall COP,ESR,NPV,and PBP of R1233zd(E)HPAAC with optimum subcooling degree range from4.99 to 11.27,25.53 to 64.59,1.13 to 4.10×10^(7) CNY and 5.77 to 2.22 years,respectively.Besides,the thermo-economic performance of R1233zd(E)HPAAC under optimum working conditions in terms of subcooling degree varying with the evaporation temperature is also investigated.

Parametric Energy and Economic Analysis ofModified Combined Cycle Power Plant with Vapor Absorption and Organic Rankine Cycle

To meet the escalating electricity demand and rising fuel costs,along with notable losses in power transmission,exploring alternative solutions is imperative.Gas turbines demonstrate high efficiency under ideal International Organization for Standardization(ISO)conditions but face challenges during summer when ambient temperatures reach 40℃.To enhance performance,the proposal suggests cooling inlet air by 15℃using a vapor absorption chiller(VAC),utilizing residual exhaust gases from a combined cycle power plant(CCPP)to maximize power output.Additionally,diverting a portion of exhaust gases to drive an organic Rankine cycle(ORC)for supplementary power generation offers added efficiency.This integrated approach not only boosts power output but alsominimizes environmental impact by repurposing exhaust gases for additional operations.This study presents a detailed energy and economic analysis of a modified combine cycle power plant,in Kotri,Pakistan.R600A is used as organic fuel for the ORC while LiBr-H2O solution is used for the VAC.Two performance parameters,efficiency and energy utilization factor,Four energetic parameters,Work output of ORC,modified CCPP,original CCPP and cooling rate,and one economics parameter,payback period were examined under varying ambient conditions and mass fraction of exhaust gases from outlet of a gas turbine(ψ).A parametric investigation was conducted within the temperature range of 18℃to 50℃,relative humidity between 70%and 90%,and theψranging from 0 to 0.3.The findings reveal that under elevated ambient conditions(40℃,90%humidity)withψat 0,the Energy Utilization Factor(EUF)exceeds 60%.However,the ORC exhibits a low work output of 100KWalongside a high cooling load of 29,000 kW.Conversely,the modified system demonstrates an augmented work output of approximately 81,850 KWcompared to the original system’s 78,500KW.Furthermore,the integration of this systemproves advantageous across all metrics.Additionally,the payback period of the system is contingent on ambient conditions,with lower conditions correlating to shorter payback periods and vice versa.

Economical Evaluation of a Low-Enthalpy Geothermal Resource Located in an Arid-Zone Area

In this work an economical evaluation that established the viability of a low enthalpy geothermal resource as an energy source in north Africa is presented. The factors considered included the payback period, average rate of return, net present value, and net benefit-cost ratio. The model was based on utilising the energy source to energise four models that comprised thermal equipment consisting of water/air cooled single/half effect lithium bromide water mixture absorption chillers and an R-245fa organic Rankine cycle. These modelled cycles were based on the energy demand for Waddan city a community in southern Libya which has a demand for combined cooling/electricity only or cooling/electricity with district hot water supply. The results revealed that all of the proposed simulated stand-alone models, except the water-cooled half effect chiller, are not economically viable unless they are heavily subsidized or combined with the district hot water supply at least in the winter season.

The “All in One”Smart Solar Cooling System

The need for moving away from traditional energy sources and to find alternate energy sources is undoubtedly one of the primary objectives for a sustainable progress to humankind. The design and construction of buildings in hot-humid climates requires high energy consumption typically for air conditioning due to higher thermal loads. In the Gulf Region, there is a rising concern on the current rate of energy consumption due to air conditioning, i.e. two thirds of domestic electrical loads. Considering the wider impacts of carbon emissions on our climate, and the need to reduce these emissions, effective energy efficiency solutions are necessary in order to achieve the overall goal of reducing carbon emissions. This paper presents the performance of the “All in One” fully integrated solar desiccant air conditioning system. The superefficient air conditioning system can provide 1,000 to 2,000 litre/s treated fresh air at supply temperature of 16 °C with 60% reduction in energy consumption compared to conventional systems. The system is locally manufactured and installed.

Study on Buildings CCHP System Based on SOFC

The relationship among the working temperature,pressure and current density of a Solid oxide fuel cell(SOFC)and its output power and efficiency are analyzed in the framework of a theoretical model able to provide,among other things,the volt ampere characteristic curve.In particular,following the principle of temperature matching and cascade utilization,we consider a gas turbine(GT)and a LiBr absorption chiller to recycle the high-grade exhaust heat produced by the considered SOFC.This distributed total energy system is set up with the intent to meet typical needs of buildings for cooling,heating and power(CCHP).The total power generated by the considered SOFC and gas turbine is about 222 kW and the total power generation efficiency by low heat value of fuel(LHV)is 63.7%.In the CCHP system,the high temperature exhaust of GT is further used to drive LiBr absorption unit,which can produce about 34.8 kW cooling capacity or 84.5 kW of heat(the total energy utilization 78.03%).

An Energy and Exergy Analysis of a Microturbine CHP System

The micro-turbine is known as a producer of high-grade energy （work） and also low energy （heat）. The following low grade heat energy have been modeled under ISO ambient conditions （international standard organization）, i.e. 15 ℃ and 1 bar, to utilize the waste heat energy of a 200 kW micro-turbine combined with a single effect absorption chiller, an organic ranking cycle using R245fa （ORC-R245 fa） as a working fluid, a multi-effect distillation desalination （MED） and a thermal vapor compression MED Desalination unit （TVC-MED）. The thermal comparison was carried out based on an energy and exergy analysis in terms of electric efficiency, exergetic efficiency, carbon footprint, and energy utilization factor （EUF）. The software package IPSEpro has been used to model and simulate the proposed power plants. As a result, utilizing the exhaust waste heat energy in single-effect absorption chillier has contributed to stabilize ambient temperature fluctuation, and gain the best exergetic efficiency of 39%, while the EUF has reached 72% and the carbon footprint was reduced by 75% in MED and TVC-MED Desalination respectively. The results also reveal that TVC-MED is more efficient than traditional MED as its gain output ratio （GOR） is improved by 5.5%. In addition, ORC-245fa generates an additional 20% of the micro-turbine electricity generation.

Modelling, Transient Simulation and Economic Analysis of Solar Thermal Based Air Conditioning System in Gujarat

Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO2 emissions from conventional buildings in India were estimated to be 98 metric tonnes of CO2 per million ft2 in 2014. Solar thermal air conditioning can be the solution to these demands and can contribute to about 15% to 20% of India’s total oil consumption thereby reducing the dependence on fossil fuels. Hence, the main objective of the work is to model and simulate a solar absorption cooling system for GERMI office building located in Gandhinagar, Gujarat, India, using the transient simulation software ‘TRNSYS’. Cooling load estimation and comfort conditions required for the building were determined based on ASHRAE standards. Evacuated tube collectors were selected because of its market availability, ease of manufacturing and proven technology. Single effect absorption chiller was used because of its commercial availability. The effects of storage tank volume, collector area and collector slope were also investigated for parametric optimization. The results of the simulation and parametric analysis are analyzed and presented in the paper.

Comparisons and optimization of two absorption chiller types by considering heat transfer area,exergy and economy as single-objective functions

Absorption cooling technology is an environmentally friendly method to generate continuous chilled water making use of multiple thermal sources,such as waste heat and renewable thermal energy.In this study,two absorption chillers(nominal capacity of 400 kW)with series and parallel connections are evaluated.To research the ideal configuration of chillers after thermodynamic analysis,the structures of the chillers are optimized using the particle swarm optimization algorithm by considering the heat transfer area(HTA),exergy efficiency and total annual cost as single-objective functions.The impact of temperature differences between external and internal flows,heat exchanger efficiencies and the solution allocation ratio is estimated.The optimized HTA,coefficient of perform-ance,exergy efficiency and total annual cost are 149.0 m^(2),1.56,29.44%and$229119 for the series-connected chiller,and 146.7 m^(2),1.59,31.45%and$234562 for the parallel-connected type,respectively.Under the lowest HTA condition,compared with the reference simulation results,the energy and exergy performances are improved,while the annual total cost is higher.The annual total cost is highest when maximizing the exergy efficiency,which is attributed to the increase in the HTA.The operating cost accounts for 27.42%(series type)and 26.54%(parallel type)when the annual cost is the lowest.

A Comprehensive Study of a Low-Grade Heat-Driven Cooling and Power System Based on Heat Current Method

Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption chiller on both driving and cooling fluid sides.The system is modeled by using the heat current method to fully consider nonlinear heat transfer and heat-work conversion constraints and resolve its behavior accurately.The off-design system simulation is performed next,showing that the fluid inlet temperatures and flow rates of cooling water as well as RORC working fluid strongly affect system performance.The off-design operation even becomes infeasible when parameters deviate from nominal values largely due to limited heat transfer capability of components,highlighting the importance of considering heat transfer constraints via heat current method.Design optimization aiming to minimize the total thermal conductance is also conducted.RORC efficiency increases by 7.9%and decreases by 12.4%after optimization,with the hot fluid inlet temperature increase from 373.15 to 403.15 K and mass flow rate ranges from 10 to 30 kg/s,emphasizing the necessity of balancing system cost and performance.