That GREE one I mentioned above says it is rated to -31°F which I've never seen for any other one?
https://www.greecomfort.com/our-products/vireo-plus-ultra/
For R32 refrigerant, -31°F outside temp with about -10 °F required lower outside coil temp to absorb any significant heat from outside air would have outside evaporator coil saturation temp pressure for R32 of 17.4 psig.
Inside coil for 72 °F inside air temp requires about 15 °F higher inside condenser coil temp to yield much inside air heating. For R32, this is 87 °F inside condenser coil saturation temp. For R32 this has high side pressure of 269 psig.
For these inside to outside temp deltas, the required compressor compression ratio is (269-14.7 psia) / (17.4-14.7 psia) = 254 psia / 2.7 psia =
compression ratio of 94.
I call BS!. No air conditioner compressor is going to survive very long at a compression ratio of 94, if it could achieve that compression ratio at all.
Not to mention, at that compression ratio there will be little refrigerant mass flow pumping, meaning very little actual BTU's will be generated.
Hyper-heat models run their compressor rpm's higher to achieve higher mass flow to maintain BTU yield, but their compression ratio is not much greater than about 10. Normal summertime cooling mode compression ratio is about 3.
Hyper-heat VFD drive inverter runs its output frequency up to 144 Hz which translates to compressor rpm's of up to 8,500 rpm's maximum versus non-hyper-heat models limit to about 75 Hz which translates to compressor rpm's of 4,500 rpm's maximum. The higher rpm's allows the compressor to maintain refrigerant mass flow pumping rate. Refrigerant mass flow rate translates to BTU's transferred.
You can tell hyper-heat models by their sound at cold outside temperatures. The high rpm compressor sounds like a jet engine.