Heat pump efficiency
 

I live in the Montreal area. I just bought a York Affinity heat pump
with R-410A.
I don't understand why at outside temp around freezing point, the
efficiency seems to be pretty low (gaz tubing temp at the input of the
indoor coil barely warm to the touch)
At lower outside temp., it is much hotter, so I suppose the efficiency
to be better. It doesn't make sense to me. Moreover, outside humidity
seems to have an effect too. Can someone explain if such a condition is
possible and why.

Thanks,

Heat pump efficiency
 

Heat pumps don't work as well at lower temperatures because there is
less heat to remove from the air. What you are describing could be due
to an electric backup (most have an electric resistance heater to help
when the outside temperature is too low). Humidity would have an
effect as well. Lower temperatures + higher humidity might cause the
outdoor coils to ice more quickly, requiring the electrical backup to
kick on and the defrost cycle to run.

Don't mistake more heat with more efficiency, it's probably much less
efficient when this happens: the defrost cycle is reversed from heat
pump cycle and is running like an AC compressor - the electric heat
strip has to heat your house AND the outdoor coils to defrost them.

Heat pump efficiency
 

Heat pump efficiency
 

Your heat pump is basically a refrigerator for the outside; it cools the
outside and puts the heat inside.
Efficiency is a function of the temperature difference between the two area;
it is simply easier to move heat from a 10C outside to a 20C inside than it
is to move heat from a -10C outside to a 20C inside. Efficiency goes to
hell when temperatures drop.
So, roundabout 5C the heat pump turns off and a backup heat turns on.
Hopefully that is a gas furnace, but it can be electric heat.

As someone else said, when it gets colder you are feeling the heat from the
supplemental source; it is typically much hotter than the heat pump because
it has to have the capacity to heat your house in really cold weather..
Heat pumps really only make sense in warmer areas where it rately gets below
freezing. (or where electricity is artificially cheap for some reason) In
Montreal you will be using nothing but the supplemental heat for almost the
entire winter. I just replace my heat pump with a regular AC and a furnace
for that reason; none of people quoting on the job even asked about putting
in a new heat pump.

Heat pump efficiency
 

York Affinity may be a two speed system. Down to about 35 degrees
outside would be low speed, below that it will go into high speed and
the gas line will get warmer untill it gets MUCH colder outside. Im
not a Yyork dealer so I am just guessing on the details. Check the
York site for more information.

I love heat pumps in my area, but i would not use them in your climate.

Stretch