For those curious of the COP values at different temps
This chart gives a good understanding of what COP value your getting at various temperature , the COP rating on a Heat Pumps label is not its Maximum COP
In warming weather the COP climbs , cooler it lowers but still makes decent COP
numbers until its too cold then a new heat source needs to be employed.
I have little idea how this applies to the Portable one hose heat pumps. I think it may keep a steadier COP and work a little bit longer to heat the colder intake / infiltration air