Exergy and exergoeconomic analyses of serial and bypass two-stage compression on the household refrigerator-freezer and replacement of R436A refrigerant

Author(s):  
Nader Alihosseini ◽  
Gholamreza Salehi ◽  
Arash Mirabdolah Lavasani

In this research, the performance of serial two-stage compression (STC) cycle and bypass two-stage compression (BTC) cycle on the household refrigerator-freezers is tested in the laboratory. Then, based on the results of the experiments, exergy, exergoeconomic analyses, and cycle optimization are carried out. Considering that replacing refrigerants in household refrigerator-freezers is one of the approaches to increase the performance and environmental impact of these systems, R436A refrigerant (46% Isobutene and 54% Propane mixture) is used and analyzed to replace previous refrigerants. Finally, the multi-objective optimization of the mentioned cycles is performed with both refrigerants. For analyses, two models of refrigerator-freezers with different cycles are used (STC cycle with R134a refrigerant and BTC cycle with R-600a refrigerant). In both models, two evaporators for refrigerator-freezer compartments are used. International standards (IEC 62552) are used to test refrigerator-freezers. MATLAB and REFPROP 9.1 software are used to model the systems. According to the results of the analyses, the STC cycle with R436A refrigerant has more total exergy destruction rate (0.727 kW) compared to R134a refrigerant. In the BTC cycle, in which the fresh food compartment (FFC) and freezer compartment (FZC) operate, the total exergy destruction rate with R-600a refrigerant (0.422 kW) is less than with R436A refrigerant. In the case of the BTC cycle in which only the FZC operates, the total exergy destruction rate with R-600a refrigerant (0.455 kW) is less than with R436A refrigerant. The most exergoeconomic factor among cycle equipment is related to the compressor (about 98%). The highest COP value between cycles is related to the STC cycle with R134a refrigerant.

Author(s):  
Christian Buschbeck ◽  
Larissa Bitterich ◽  
Christian Hauenstein ◽  
Stefan Pauliuk

Regional food supply, organic farming, and changing food consumption are three major strategies to reduce the environmental impacts of the agricultural sector. In the German Federal State of Baden-Württemberg (population: 11 million), multiple policy and economic incentives drive the uptake of these three strategies, but quantitative assessments of their overall impact abatement potential are lacking. Here, the question of how much food can be produced regionally while keeping environmental impacts within political targets is tackled by comparing a scenario of maximum productivity to an optimal solution obtained with a multi-objective optimization (MO) approach. The investigation covers almost the entirety of productive land in the state, two production practices (organic or conventional), four environmental impact categories, and three demand scenarios (base, vegetarian, and vegan). We present an area-based indicator to quantify the self-sufficiency of regional food supply, as well as the database required for its calculation. Environmental impacts are determined using life cycle assessment. Governmental goals for reducing environmental impacts from agriculture are used by the MO to determine and later rate the different Pareto-efficient solutions, resulting in an optimal solution for regional food supply under environmental constraints. In the scenario of maximal output, self-sufficiency of food supply ranged between 61% and 66% (depending on the diet), and most political targets could not be met. On the other hand, the optimal solution showed a higher share of organic production (ca. 40%–80% com¬pared to 0%) and lower self-sufficiency values (between 40% and 50%) but performs substantially better in meeting political targets for environmental impact reduction. At the county level, self-sufficiency varies between 2% for densely populated urban districts and 80% for rural counties. These results help policy-makers benchmark and refine their goalsetting regarding regional self-sufficiency and environmental impact reduction, thus ensuring effective policymaking for sustainable community development.


Author(s):  
Doan V. K. Khanh ◽  
Pandian Vasant ◽  
Irraivan Elamvazuthi ◽  
Vo N. Dieu

In this chapter, the technical issues of two-stage TEC were discussed. After that, a new method of optimizing the dimension of TECs using differential evolution to maximize the cooling rate and coefficient of performance was proposed. A input current to hot side and cold side of and the number ratio between the hot stage and cold stage are searched the optima solutions. Thermal resistance is taken into consideration. The results of optimization obtained by using differential evolution were validated by comparing with those obtained by using genetic algorithm and show better performance in terms of stability, computational efficiency, robustness. This work revealed that differential evolution more stable than genetic algorithm and the Pareto front obtained from multi-objective optimization balances the important role between cooling rate and coefficient of performance.


2015 ◽  
Vol 88 ◽  
pp. 335-346 ◽  
Author(s):  
Joan Carreras ◽  
Dieter Boer ◽  
Gonzalo Guillén-Gosálbez ◽  
Luisa F. Cabeza ◽  
Marc Medrano ◽  
...  

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