I keep seeing homes for sale with heat pumps. It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. Is there new technology?

On Sep 15, 8:25*am, Norminn wrote:
I keep seeing homes for sale with heat pumps. *It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
* Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. *Is there new technology?

Are those heat pumps air-based or geothermal? Efficiency
has increased over the years and air based ones can be
efficient sources of heat even down to 20F or so. But if
you see -25F in winter, unless it's geothermal, or dual fuel,
forget it. Here in NJ, where temps only reach the single
digits rarely, teens sometimes, I don;t know of anyone that
has an air-based heat pump.

On 9/15/2012 8:39 AM, wrote:
On Sep 15, 8:25 am, Norminn wrote:
I keep seeing homes for sale with heat pumps. It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. Is there new technology?

Are those heat pumps air-based or geothermal? Efficiency
has increased over the years and air based ones can be
efficient sources of heat even down to 20F or so. But if
you see -25F in winter, unless it's geothermal, or dual fuel,
forget it. Here in NJ, where temps only reach the single
digits rarely, teens sometimes, I don;t know of anyone that
has an air-based heat pump.

I have a 3 yo Amana HP with propane backup here in western NC. It was
the most efficient unit at the time. You get very little heat when the
temp is in the mid 30s. It does use the propane during the de-ice
cycles periodically. At about 30, it switches over to 100% propane.
During the winters of 09 and 10, we used lots of propane, probably more
in 10. In 11, we used very little, as it was warmer. I'm sorry we
didn't put in geothermal because there were a lot of tax incentives at
the time, which probably would have made it economical. BTW, I don't
know about all the geothermal units, but my niece has a geothermal unit
and there is nothing visible outside. The heat pump compressor and heat
exchangers are all in the inside unit (Carrier).

On 9/15/2012 8:25 AM, Norminn wrote:
I keep seeing homes for sale with heat pumps. It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. Is there new technology?

I am in PA and friends put in a Mitsubishi split system a few years ago.
My friend is a really sensible guy who is analytical and not a story
teller. They decided to go with the version that also can be used as a
heat pump mainly because it wasn't that much more and for a backup.
They also have an oil fired boiler for hydronic heat.

They used it for the only source of heat the past two winters and the
house was comfortable. We haven't been down to -25F though and I think
the lowest we see here is -10 F in February.

He also ran the numbers and they were able to heat their house for less
than using oil.

"George" wrote in message
...
I am in PA and friends put in a Mitsubishi split system a few years ago.
My friend is a really sensible guy who is analytical and not a story
teller. They decided to go with the version that also can be used as a
heat pump mainly because it wasn't that much more and for a backup. They
also have an oil fired boiler for hydronic heat.

They used it for the only source of heat the past two winters and the
house was comfortable. We haven't been down to -25F though and I think the
lowest we see here is -10 F in February.

He also ran the numbers and they were able to heat their house for less
than using oil.

Usually when it gets very cold (say somewhat below 25 deg C) ( I am in the
south so that is very cold to me) the heat pump will turn on the resitive
heating elements if it can not keep up. It may be the heating elements
turned on, but even at that, the electric heat may be cheaper than the price
of oil in an old furnace.

On 9/15/2012 10:16 AM, Ralph Mowery wrote:
"George" wrote in message
...
I am in PA and friends put in a Mitsubishi split system a few years ago.
My friend is a really sensible guy who is analytical and not a story
teller. They decided to go with the version that also can be used as a
heat pump mainly because it wasn't that much more and for a backup. They
also have an oil fired boiler for hydronic heat.

They used it for the only source of heat the past two winters and the
house was comfortable. We haven't been down to -25F though and I think the
lowest we see here is -10 F in February.

He also ran the numbers and they were able to heat their house for less
than using oil.

Usually when it gets very cold (say somewhat below 25 deg C) ( I am in the
south so that is very cold to me) the heat pump will turn on the resitive
heating elements if it can not keep up. It may be the heating elements
turned on, but even at that, the electric heat may be cheaper than the price
of oil in an old furnace.



He has a Mitsubishi inverter multi zone heat pump (split system). It
doesn't have any resistive elements.

http://www.mitsubishicomfort.com/med...11-r_pages.pdf


According to the graph it has 100% heating capacity down to 5F outside
which tails off to 73% at -13F.

"George" wrote in message
...
He has a Mitsubishi inverter multi zone heat pump (split system). It
doesn't have any resistive elements.

http://www.mitsubishicomfort.com/med...11-r_pages.pdf

According to the graph it has 100% heating capacity down to 5F outside
which tails off to 73% at -13F.

That sure seems like an impressive unit. I did see what appears to be some
resistive heating elements in the individual units that seem to be an
option.

Being a multizone unit, that should save a lot on the heat cost. I wish my
heat pump was set so I could cut off part of it. I have 2 bed rooms
upstairs that are not used any more and it would be nice to eliminate all
the heat and cooling going to them.
Also a room in the basement has some ducts going to it that would be nice to
completely close off when I wanted to.

On Sep 15, 10:56*am, "Ralph Mowery"
wrote:
"George" wrote in message

...

He has a Mitsubishi inverter multi zone heat pump (split system). It
doesn't have any resistive elements.

http://www.mitsubishicomfort.com/med...20brochure%203...

According to the graph it has 100% heating capacity down to 5F outside
which tails off to 73% at -13F.

That sure seems like an impressive unit. *I did see what appears to be some
resistive heating elements in the individual units that seem to be an
option.


I think this is just another sales job and you're on to the
truth. It only shows that it has 100% CAPACITY down
to 10F, not how it gets that capacity. Unless the laws of
thermodynamics have been repealed, the efficiency of
ALL heat pumps declines as the outside temp drops.
It's a matter of physics that no manufacturer can avoid.
They can still deliver more heat than a resistive heating
element would at 10F, but the amount of heat you get
out of the heat pump drops on a steady curve as the
temp goes down.

The only way they can get 100% capacity across that
broad temp range is either by:

A - using resistive heat to supplement

B - Downrating the whole thing so that it's rated by what
it produces at 10F.

Option B is nuts for obvious reasons.

Norminn wrote:

I keep seeing homes for sale with heat pumps. It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. Is there new technology?

Ground source heat pumps work fine in colder climates.

On 9/15/2012 7:25 AM, Norminn wrote:
I keep seeing homes for sale with heat pumps. It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. Is there new technology?

Where is here?

More to the point than having once seen it, what are the averages?
Certainly a modern properly sized air-exchange HP will handle into the
lower 30's w/ no problems. The one thing is that they will tend to have
longer recovery time as the exit air temp's will not approach those of
conventional furnace (or even a geothermal unit).

They certainly have improved even air-exchange but in very cold climates
either they use geothermal (ground loop/well/deep reservoir all
possibilities) or have a conventional backup.

We replaced an early air-exchange in E TN w/ geothermal and it was
night/day...this is almost 20 yr ago now and the original HP wasn't but
a cheap contractor-supplied unit in the late 70s when even the good
weren't doing all that well, anyway. But, TVA power was cheap then so
the resistance heaters weren't a big deal--probably 70% of heating in
the area was electric at the time. By the early 90s the HP was on last
legs and power rates were much higher and NG wasn't yet available so
went w/ the higher installation cost of digging the trench and never
regretted it while were still there. AFAIK the system is still
functional w/ no problems--saw the new owner just a couple of years ago
and he's also quite pleased.

It has a thermistor in-line w/ the aux heat that keeps them from being
able to come on above about 18-20F so the 'Emer Heat' logic doesn't try
to kick on if, for example, the house has been turned down and then come
home and reset to normal so the dT is large and it thinks it can't catch
up. Newer t-'stats may also have better logic to know the difference
between chronic failure to keep up and change in demand.

A side benefit of the geothermal was essentially free hot water in
summer using reject heat from the cooling cycle...replacing electric
water heater inputs is _a_good_thing_ (tm) in most places given rates...

--

Norminn wrote:

I keep seeing homes for sale with heat pumps. It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. Is there new technology?

Ground source heat pumps work fine in colder climates.

On Sep 15, 1:25*pm, Norminn wrote:
I keep seeing homes for sale with heat pumps. *It's been a while, but I
have seen -25F in winter, so I am puzzled why folks use heat pumps here.
* Had a h.p. in Florida, and when the temp got down to the forties, it
wasn't warm enough indoors with the h.p. *Is there new technology?

Conventional air source heat pumps won't work in very cold weather.
Ground source heat pumps will, or air source heat pumps using CO2 as a
refrigerant.

A major problem can be icing on the evaporator of air source heat
pumps. Depends on climate/humidity.