According to Paul M. Eldridge :
On Tue, 05 Feb 2008 17:29:31 -0000, (Chris
Lewis) wrote:

Note that there are some programmable thermostats that "understand"
heat pumps. There are some that are smart enough to bring the temperature
back up from the set back in increments of a few degrees at a time,
so the HP never thinks it's gotten too far behind. There are others
that "know" that the abrupt temperature discrepency (between room temperature
and setpoint) is due to their "returning from setback", inhibit backup
heat, and force the HP do do all the work. The latter have to be built
into the HP I believe.

Hi Chris,

A friend of mine installed a new setback thermostat for his heat pump
(a Honeywell as I recall) that monitors how long it takes to return to
the daytime set temperature and adjusts the timing of the ramp up
period accordingly; in other words, the heat pump comes on earlier
during colder weather so that the house reaches the desired
temperature at the time requested. He tells me his backup elements
never come on as they did previously with his previous thermostat and
his operating costs have dropped accordingly.

I think I've heard of these before too, but I forgot.

I always chuckle whenever someone tells me heat pumps don't work in
northern climates or when temperatures routinely fall below 40F.

I get more than a chuckle when people claim to quote supposed professionals
who claim HPs are crap. I know which professionals to avoid.

Short of having your own power or heat generation (a gas well on the
property would be real nice ;-), a _properly_ chosen and installed
HP will beat anything else. Unless electricity prices really jump
disproportionally over gas and oil.

Compared to my oil-fired boiler at 82% AFUE, my heat pump has cut my
overall heating costs by more than half -- an average cost of just 4.3
cents per kWh of heat versus 10.8 cents for oil.

Yup. In any climate, an air-source HP plus gas backup will do better
than straight gas - even if they only do heating during spring and
fall. But geothermal HP will do much better than that, and cares
little about outside temperature - BTU output remains approximately
constant/same efficiency, it's a matter when the BTU output isn't
enough to keep up with heat losses.

We were told that the geothermal unit that was spec'd for us would, on
average, rely on backup approximately 30 hours per year - the nights
that dip below -40F/-40C. We usually get a week or two where the daytime
highs doesn't exceed -25C, and once or twice daytime highs of around -40C.
Much like Montana winter temperatures.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.