I've got a couple of general questions about heat-pump operation
in cold ambients. One practical, one more theory.
Most units either have a crankcase heater or use the inverter to
bleed about 50W average through the motor windings to keep the
herm warm, and I totally understand the benefits of *not* trying
to run a cold compressor. I've read thread 1226341 that touches on this.
My concern is what happens after an extended power outage -- an
outdoor unit cools down to cold ambient, power is restored and
there's instant demand, what happens? Do any units try to protect
themselves against that? I haven't heard of compressor temp
sensors other than maybe just an overtemp cutout, so it seems
like it would happily try to start up with sludged oil and the
expected unhappy results. What, if anything, is done to prevent this?
The other Q has to do with ambient temp and defrost cycles. If the
outdoor air is below freezing already and the HP is bringing that
air even colder, is there an applicable "dew point" as such? How
does water vapor already under 32F condense on something, or does it?
I'd completely understand why a unit ices up in that typical cold
clammy just-above-freezing winter weather when the coil is running
like 10F, but I'm having trouble understanding how icing occurs
when it's already cold. Observing my fairly new unit so far has
shown a lot of ice in > 32F ambients, but almost none when it's
gotten down around 20F. The system still goes through defrost
cycles every so often regardless...