Per the pdf..
1.Adding heat to the accumulator during the winter heating
season will retard frost accumulation on the outdoor coil.
The frost-less concept worked as expected.However,when
the ambient temperature drops below32F,adding a
moderate amount of heat will not prevent frost accumulation
on the outdoor coil and,thus,the heat input to the accumulator
should be stopped. Heat should be added to the
accumulator only when the ambient temperature is between
41ºF and32F, where frost is most likely to accumulate on the coil.
That seems like a lot of stuff to precisely control to allow you to get down
to 32 deg.
If I could get heat out of 40 deg air
& higher I could be happy with that.
When it was really cold, I still have oil & wood or coal..
Last night it got down to 36 at one point, but there has been a lot of time
during the last 24 hours when it's been above 40..
And during some of that time, I could have used some space heat..
These guys have a way to pump heat out of really cold air..
Hallowell International: Products