Low-GWP Options for Cascade Systems in Commercial Refrigeration
Workshop on HFC management focusing on the use of cascade systems with low-GWP alternatives for medium to large commercial refrigeration units. Explore the need for dual temperature levels, unsatisfactory options, and a possible alternative using cascade LT CO2 and MT chiller systems for improved efficiency and reduced emissions.
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Presentation Transcript
Low-GWP options for cascade systems for medium-sized and larger commercial refrigeration equipment Workshop on HFC management Bangkok 20th April 2015 Paul de Larminat
Benchmark in supermarkets: direct systems ( D-X ) The need: 2 temperature levels for goods: - MT 0 to +8 C for fresh goods Evaporation -10 to -15 C - LT -18 to -25 for frozen food Evaporation -35 to -38 Non toxic / non flammable (A1) fluids desired inside shop. Traditionally used fluids: - CFC s: R12 for MT; R-502 for LT - Transition: HCFC R-22 for both stages - HFC: 404A dominant for both stages Usually single stage 75 to 80% of the charge in MT circuit. High leak rates + very high GWP = Large CO2eq emissions
Unsatisfactory options Indirect systems Same direct system With lower GWP blend Like R-407A etc Glide in extended systems Still high GWP for A1 (about 2000) poor efficiency High pumping power + Additional heat exchangers = bad efficiency Poor TEWI In both cases
An possible alternative: cascade LT CO2 + MT chiller For LT: D-X CO2 system - Only CO2 (or brine) in sales area. - Excellent efficiency of CO2 at LT. - Moderate pressure for CO2 For MT: glycol chiller about -10 C. Glycol is used: - For fresh goods with indirect system, - For condensation of the LT CO2 circuit. Advantages: - The fluid of the chiller is easily optimized to the climate conditions; e.g. R-134a or equivalent HFO or blend in warm climate. - The chiller can be low cost, standard (or close to) A/C chillers. - Refrigerant charge and leak rate of chillers is low low direct emissions (about 1% of benchmark D-X 404A). - A1 fluid not an obligation for the chiller (confined in machine room). - If retrofit is needed later, replacing the chiller only is limited damage. Other options for MT circuit are possible. The key is to use CO2 for LT.
