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Analyse des fluides actifs fluorés à faible potentiel de réchauffement planétaire dans les systèmes à compression de vapeur. Évaluation expérimentale des alternatives en froid commercial.

Analysis of low global warming potential fluoride working fluids in vapour systems. Experimental evaluation of commercial refrigeration alternatives.

Auteurs : MOTA BABILONI A.

Type de monographie : Thèse de doctorat

Résumé

Climate change is one of the short term threats for humanity because of its effects on the environment and, consequently, on vegetal and animal life. If it is not stopped in next years, this effect will be irreversible. Climate change is produced by anthropogenic emissions of Greenhouse Gas to Earth’s atmosphere. Vapour compression systems are one of the main contributors on this phenomenon. Among them, commercial refrigeration applications, through HFC usage, can be highlighted. Since 1990s, supermarkets of developed countries have been using refrigerants (mainly R134a, R404A and R507A) with great impact (high GWP values) on climate change due to leakages, especially from parallel compressor rack DX systems.
Recently, some regulations and directives have been approved to limit GWP values of HFC used in most extended refrigeration and air conditioning applications, directly affecting to commercial refrigeration. In this thesis, some low-GWP alternatives to replace the most commonly used HFC refrigerants in commercial refrigeration are evaluated, taking into account the limitations imposed by the mentioned regulations.
To carry out this evaluation, the current status of parallel compressor rack refrigeration systems and their fluids has been reviewed. Then, the different low-GWP options to replace R134a and R404A have been studied. HFOs and their mixtures with HFC have been highlighted as the most promising drop-in or retrofit alternatives. Thus, R1234yf, R1234ze(E) and R450A were proposed to replace R134a and R448A to substitute R404A.
The theoretical performance of the different low-GWP alternative fluids, as an overview of their potential use, has been studied at typical parallel compressor rack refrigeration operating conditions using the basic thermodynamic vapour compression cycle. Given the good theoretical performance of these refrigerants, they have been tested in a vapour compression test bench.
From the experimental results it is depicted that R1234yf and R1234ze(E) are not acceptable as drop-in or light retrofit refrigerants from an energetic point of view. These fluids, when used in R134a systems, require system modifications (more severe in the case of R1234ze(E)) to achieve acceptable energy efficiency values. Moreover, due to the large refrigerant charge in PCRRS, both HFOs could present problems related to security.
Thus, while R450A presents a GWP value of 547, it appears as the best option to replace R134a due to the similar energy efficiency and properties. The R450A experimental mass flow rate and cooling capacity are slightly lower than R134a, but the final COP is approximately the same. The best R450A relative results are obtained at high CRs.
R448A shows very high performance when it is used in R404A systems with a minor TXV adjustment. Despite R448A lower cooling capacity than that R404A, this HFC/HFO mixture can achieve great CO2 equivalent emission reductions and it is recommended as lower-GWP replacement for R404A.

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Pages : 212

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Détails

  • Titre original : Analysis of low global warming potential fluoride working fluids in vapour systems. Experimental evaluation of commercial refrigeration alternatives.
  • Identifiant de la fiche : 30021042
  • Langues : Anglais
  • Sujet : Alternatives aux HFC
  • Édition : Universidad Politécnica de Valencia - Espagne/Espagne
  • Date d'édition : 01/02/2016

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