My little ASHP (Sanyo) has worked well down to 12F. I can see that the power used per hour has increased but it just keeps the warm air wafting about in my home.
But I think that the lower limit is influenced by the type of refrigerant that is used.
- Boiling Point of R-22 = -40.7 °C (-41 °F)
- Boiling Point of R-290 = -42 °C (-44 °F)
- Boiling Point of R-12 = -29.8 °C (-22 °F)
- Boiling Point of R-600a = -11 °C (12 °F)
- Boiling Point of R-410a = -48.5 °C (-55 °F)
These boiling points are for atmospheric pressure. When the refrigerants are in a system, they are under pressure, and the boiling point will be higher. This is where a pressure/temperature chart (AKA: PT Chart) comes in handy.
-AC_Hacker