Low-GWP options for cascade systems for medium-sized and larger commercial refrigeration equipment

Workshop on HFC managementBangkok 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 goodsEvaporation -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

High pumping power + Additional heat exchangers

= bad efficiency

Indirect systems

Unsatisfactory options

Glide poor efficiency in extended systems

Still high GWP for A1 (about 2000)

Same direct systemWith lower GWP blend

Like R-407A etc

Poor TEWIIn 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.