Refrigerant in the pipes

Refrigerant carries the heat

The indoor and outdoor units are joined by two copper pipes. Inside them, a substance called refrigerant goes around the same path again and again. Refrigerant is a substance that boils at a very low temperature: at normal air pressure it boils at about −52 °C. The dots on screen are refrigerant. Their color shows temperature (blue is cold, red is hot); small dots are liquid and large dots are gas.

Why?The refrigerant never leaves the pipes. As it goes around, it keeps switching between liquid and gas, picking up heat in the indoor unit and dropping it off in the outdoor unit, like a delivery truck for heat.

Learn moreMany home air conditioners today use a refrigerant called R-32, and every number in this story is calculated for R-32. Some refrigerants used in the past damaged the ozone layer around the Earth and are no longer used.

Where refrigerant boils (at normal air pressure)

−52 °C

Refrigerant

R-32

Boiling point (1 atm)

about −52 °C

calculated from R-32 property tables (CoolProp) · example: room 27 °C, outdoors 35 °C