R448A is a five-component zeotropic blend: R32, R125 and R134a together with the two HFO (hydrofluoroolefin) refrigerants R1234yf and R1234ze. It is also known on the market as Solstice N40. It was developed to do the low and medium temperature work of R404A and R507A: cold rooms, frozen storage warehouses, supermarket cabinets and central systems. Its safety class is A1, that is, non-flammable and of low toxicity; thanks to this it requires no additional safety measures in a machinery room built for R404A.
Its GWP (global warming potential) is 1,387; about a third of R404A’s value of 3,922. In a system with a 20 kg charge the CO₂ equivalent falls from 78 tonnes to 28 tonnes; this also reduces the mandatory leak check from once every six months to once a year. Its suction pressure is lower than that of R404A: at −10 °C evaporating about 2.5 bar g (dew) is read, whereas with R404A this value is 3.3 bar g. The discharge pressures, on the other hand, are close to each other; at 40 °C condensing it is around 17 bar g. At medium temperature its efficiency is 5–10% better than that of R404A.
In a retrofit the compressor and POE oil stay in place; the filter drier is replaced, and the superheat setting of the thermostatic expansion valve and the pressure switch values are redone. There are two points to watch. The first is the discharge temperature: it comes out 10–15 K higher than with R404A, and at evaporating temperatures of −30 °C and below a compressor head fan or liquid injection may be needed. The second is the glide: superheat is calculated from the dew column and subcooling from the bubble column, and the refrigerant is drawn from the cylinder as liquid.
On site R448A and R449A are regarded as equivalents of each other; their compositions and pressures are very close, and the choice is mostly determined by the compressor manufacturer’s approval and by availability. Even so, the two are not mixed in the same system. Because the composition of the blend may shift after a large leak, it is sounder to renew the whole charge than to top up the missing gas. You can see the bubble and dew pressures of R448A side by side in our refrigerant pressure–temperature chart and read the saturation temperature of the pressure you measure from there.