What R-290 is and where it is used
R-290 is refrigerant-grade propane. It is a single-component hydrocarbon with an A3 safety classification: low toxicity, higher flammability. EPA lists it, under use conditions that include UL standards and charge limits, in new self-contained equipment: stand-alone retail units such as reach-ins, display cases and ice cream freezers, self-contained ice machines, refrigerated food processing and dispensing equipment, vending machines, household refrigerators and room air conditioners.
Danfoss notes that its pressure level and critical temperature are close to R-22, with a much lower discharge temperature. EPA lists its GWP as 3.3, against 1,430 for R-134a and 3,922 for R-404A. EPA notes that stand-alone commercial units most often used R-134a or R-404A, and that propane use in stand-alone equipment is growing.
How to read the R-290 chart
Propane is a pure fluid, so each temperature has one saturation pressure and the bubble and dew columns match. Use the same value for superheat and subcooling:
- Superheat: at 30 psig suction, saturation is 7.9°F. Subtract that from suction line temperature, or use the superheat calculator.
- Subcooling: at 180 psig liquid pressure, saturation is 102.4°F. Use the subcooling calculator.
R-290 boils at -43.8°F at atmospheric pressure. Danfoss notes that at a -13°F evaporator its pressure is almost exactly that of R-22: the chart gives 14.8 psig for R-290 and 14.5 psig for R-22. Danfoss still does not recommend converting R-22 or other systems to R-290, because they are not approved for a flammable refrigerant. See how to read a PT chart.
Typical R-290 pressures in self-contained equipment
As example saturation temperatures, not targets: a medium-temperature reach-in might run a 20°F evaporator, a freezer -20°F, and a condenser 110°F. R-290 reads 41.1 psig, 10.7 psig and 199.6 psig at those temperatures. Danfoss notes that a hydrocarbon charge is only about 40 to 45% of an HFC charge by weight, so charging has to be more accurate, and it recommends an electronic scale. Weigh in the exact nameplate charge rather than charging to a pressure.
Service notes for an A3 refrigerant
- New equipment only. EPA's use conditions allow R-290 only in new equipment specifically designed and clearly identified for it, never as a conversion or retrofit refrigerant for existing equipment.
- Markings. EPA requires red (PMS #185) marking on pipes, hoses and service ports, permanent warning labels, and flammability warning symbols.
- Ignition control. Danfoss says to ventilate the room well, route the vacuum pump discharge outdoors and keep ignition sources away. EPA recommends recovery equipment designed for flammable refrigerants. Danfoss says to open the circuit with a tube cutter, braze only after the refrigerant is removed and both sides are flushed with nitrogen, and braze under flowing nitrogen. It also describes solderless press-fit connections as an alternative.
- Purity. Use refrigerant-grade R-290. Danfoss warns that fuel-grade LPG is not pure enough for hermetic systems.
- Venting. EPA exempts R-290 from the Section 608 venting prohibition only in specific end uses. Check the rule for the equipment before releasing any charge.
A3 is a step above the A2L class in flammability. For how the classes differ, see A2L refrigerants.