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Default Heat Pump confusion

I have a Lennox Heat Pump and a Honeywell Chronotherm IV 8611
Thermostat. I understand the concept of the heat pump. I am a little
confused about the Auxilary electric heat though. I live in Connecticut
and it's been ranging from 2F to 20F degrees at night. I have the
thermostat set at 65F. Some nights the unit runs almost constantly. I
had a service call yesterday and the tech said this is normal in the
winter. He checked the Auxilary heat and it does work. He explained
that it is only supposed to come on if the temperature is 2 degrees or
more from the target temperature. If this is the case it seems to me
that the Auxilary heat would NEVER be used as the heat pump itself will
activate as soon as the temperature falls 1 degree below the setting.
My question is does the Auxilary heat work by temperature or should it
help the heat pump reach the desired temperature if it knows it will
take an hour to get back to the deired temp. If I set the temperature 2
degrees or more higher the Aux heat kicks in, but if I leave it at 65
constantly it never comes on regardless of the outdoor temp. Is this
normal?? I just want to make sure it's working the way it's supposed to
be! Thanks for any advice!

PeterV

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Dr. Hardcrab
 
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Default Heat Pump confusion


wrote in message
oups.com...
I have a Lennox Heat Pump and a Honeywell Chronotherm IV 8611
Thermostat. I understand the concept of the heat pump. I am a little
confused about the Auxilary electric heat though. I live in Connecticut
and it's been ranging from 2F to 20F degrees at night. I have the
thermostat set at 65F. Some nights the unit runs almost constantly. I
had a service call yesterday and the tech said this is normal in the
winter. He checked the Auxilary heat and it does work. He explained
that it is only supposed to come on if the temperature is 2 degrees or
more from the target temperature. If this is the case it seems to me
that the Auxilary heat would NEVER be used as the heat pump itself will
activate as soon as the temperature falls 1 degree below the setting.
My question is does the Auxilary heat work by temperature or should it
help the heat pump reach the desired temperature if it knows it will
take an hour to get back to the deired temp. If I set the temperature 2
degrees or more higher the Aux heat kicks in, but if I leave it at 65
constantly it never comes on regardless of the outdoor temp. Is this
normal?? I just want to make sure it's working the way it's supposed to
be! Thanks for any advice!


It's normal.

If it is getting down to the low teens/single digits, it WILL run
constantly. Hopefully the aux heat will cycle and not run constantly
too.....


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Don McClimans
 
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Default Heat Pump confusion

On Tue, 20 Dec 2005 18:43:51 GMT, "Dr. Hardcrab"
wrote:


wrote in message
roups.com...
I have a Lennox Heat Pump and a Honeywell Chronotherm IV 8611
Thermostat. I understand the concept of the heat pump. I am a little
confused about the Auxilary electric heat though. I live in Connecticut
and it's been ranging from 2F to 20F degrees at night. I have the
thermostat set at 65F. Some nights the unit runs almost constantly. I
had a service call yesterday and the tech said this is normal in the
winter. He checked the Auxilary heat and it does work. He explained
that it is only supposed to come on if the temperature is 2 degrees or
more from the target temperature. If this is the case it seems to me
that the Auxilary heat would NEVER be used as the heat pump itself will
activate as soon as the temperature falls 1 degree below the setting.
My question is does the Auxilary heat work by temperature or should it
help the heat pump reach the desired temperature if it knows it will
take an hour to get back to the deired temp. If I set the temperature 2
degrees or more higher the Aux heat kicks in, but if I leave it at 65
constantly it never comes on regardless of the outdoor temp. Is this
normal?? I just want to make sure it's working the way it's supposed to
be! Thanks for any advice!


It's normal.

If it is getting down to the low teens/single digits, it WILL run
constantly. Hopefully the aux heat will cycle and not run constantly
too.....


That's true, but you're wasting a lot of energy melting the ice off
the outside unit during the defrost cycle.

I live in western NY, so have similar or colder temps than Connecticut
in the winter. We have a similar heat-pump/electric-furnace system,
with a Chronotherm III.

When it gets that cold out, I switch the thermostat to "emergecy
heat", which disables using the heat pump and just uses the furnace
(auxiliary heat). This is as efficient (probably more efficient) than
the heat pump at these temperatures. That's because a) the heat pump
inherently gets less efficient as the temperature difference becomes
greater, and b) to avoid ice build-up on the outside unit, the system
has to run a defrost cycle. In the defrost cycle, the system runs
backwards (essentially in air conditioning mode), to heat up the
outside unit and melt off any ice. Similar to defrost in a freezer.
All that energy is wasted of course, as you're literally heating the
outdoors.

One thing to watch out for if you stay in emergency-heat mode for a
long time. Snow and ice can build up on the outside unit. When you
switch back to heat pump mode, the fan may not have any place to push
the air to. So you may need to go outside and brush off the unit. (If
you're running the heat pump all the time, the fan being on keeps the
snow and ice from building up.)

Terry
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Default Heat Pump confusion

"I live in western NY, so have similar or colder temps than Connecticut

in the winter. We have a similar heat-pump/electric-furnace system,
with a Chronotherm III. "

Just out of curiousity, why do you have a heat pump system in that
climate? I know heat pump systems can be economical and practical in
moderate climates, but I would think natural gas or oil would easily
win out in your area. Am I missing something?

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Don McClimans
 
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Default Heat Pump confusion

On 20 Dec 2005 14:10:13 -0800, wrote:

"I live in western NY, so have similar or colder temps than Connecticut
in the winter. We have a similar heat-pump/electric-furnace system,
with a Chronotherm III. "


Just out of curiousity, why do you have a heat pump system in that
climate? I know heat pump systems can be economical and practical in
moderate climates, but I would think natural gas or oil would easily
win out in your area. Am I missing something?


Yes, you're missing the weirdness of municipal electric systems and
the american political system. :-)

I live in a town that has a municipal electric system. This means the
system is owned, operated, and maintained by the town government.
Municipal electric systems have a sweatheart deal which is somehow
based on the thinking that they get first access to hydro power (think
Niagra Falls). I don't really understand the logic of it (if there is
any logic to it), but it's been in place for a long time and there's a
political fallout if they change it, so nobody changes it.

(By the way, what we call a town here is what many other places call a
township. It's bigger than a village, and smaller than a county.)

The net result is that electric costs me about 3.5 cents/KWH in the
spring/summer/fall, and in the coldest 3 months it costs about 4.5
cents/KWH. This makes electric cost effective. Also, I live outside
the gas distribution, so the alternative is oil, or propane tanks, I
suppose.

Even in the midst of winter we get a fair amount of weather where the
days are above 32 deg F, so we use the heat pump itself a fair amount
even in the winter. In the spring and fall it's the only thing that
runs. In the summer, of course, it's the A/C system. But even when we
use the electric furnace rather than the heat pump, it's pretty
inexpensive to run.

Within this town, most people have electric heat pumps with electric
furnaces. Sometimes you will see heat pumps with oil furnaces. A few
miles away, when you get to the next town, you're using a commercial
electric supplier, where rates are 12 cents/KWH, I think -- I'm not
really sure, it's been 12 years since I moved here. Anyway, in other
towns, everybody uses gas or oil, and no heat pumps, just A/C.

My house, built in 1984, has an unused flue in the chimney intended
for an oil furnace if the electric rates someday skyrocket.

Now, don't blame me! I did't make this crazy thing up, and I didn't
move here just because of the cheap electric rates, I just bought a
house here. :-)

Terry


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Stretch
 
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Default Heat Pump confusion

Heating Capacity of a heat pump drops as it gets colder outside. The
heat load load on the house goes up at the same time. Around 35
degrees oiutside the heat pump's heat output drops below the heat load
of the house. This is called the "balance point". Below this outdoor
temperature the heat pump will run constantly.

Note that at -20 degrees outside the COP (Coefficient Of Performance)
Of a heat pump will be about 1.5. The COP of strip heat is ALWAYS 1.0!
Therefore, switching to emergency heat will increase your electric
bill, as with both heat strips and heat pump running your average COP
will be around 1.25 at -20 degrees outdoors. Not great, but better
than heat strips alone. Also since swithcing to emergency heat drops
all the heat from the heat pump mout of the system, you have just lost
some of your capacity and the system may not be able to keep up.


Terry,

The outdoor coil freezes because the outdoor coil gets colder than the
outdoor air in order to extract heat from it. If the outdoor coil
temperature is below the dew point of the outdoor air, frost will form
on the outdoor coil. Leaving the system in emergency heat will shut
the compressor and outdoor fan off, so the outdoor coil will be at the
same temperature as the outdoor air. NO frost will form on the outdoor
coil unless it is from horizontally falling snow.

When the heat pump goes into defrost, the strip heat comes on inside to
temper the air, the reversing valve switches to cool mode so the
outdoor coil will get hot enough to melt the ice and the outdoor fan
will shut off so most of the heat in the outdoor coil goes to melting
the ice (latent heat of fusion at 144 BTUs per pound) and very little
goes directly into the outside air.

The fan running on the outdoor unit CAUSES the frost to form in the
first place, not prevent it form forming. If the outdoor fan was not
running, VERY LITTLE heat would be extracted from the outdoor air.

Stretch

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RP
 
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Default Heat Pump confusion



Stretch wrote:

Heating Capacity of a heat pump drops as it gets colder outside. The
heat load load on the house goes up at the same time. Around 35
degrees oiutside the heat pump's heat output drops below the heat load
of the house. This is called the "balance point". Below this outdoor
temperature the heat pump will run constantly.


In the south the thermal balance point typically runs much lower than
this. The unit is sized for cooling -- backup strip heat is rated as
necessary to provide sufficient heating capacity (with heat pump
disabled). As a result the heat pump is oversized by northern standards.
It isn't unusual for a heat pump in the south to keep up with the load
at 15ºF or even lower without backup. Your argument is good when taken
as an example, but not as a general rule. I'm just clarifing for any
readers who might fail to take into account your implied context.


Note that at -20 degrees outside the COP (Coefficient Of Performance)
Of a heat pump will be about 1.5.


For an average heat pump. But I wonder about that number

hvacrmedic


The COP of strip heat is ALWAYS 1.0!


Therefore, switching to emergency heat will increase your electric
bill, as with both heat strips and heat pump running your average COP
will be around 1.25 at -20 degrees outdoors. Not great, but better
than heat strips alone. Also since swithcing to emergency heat drops
all the heat from the heat pump mout of the system, you have just lost
some of your capacity and the system may not be able to keep up.





Terry,

The outdoor coil freezes because the outdoor coil gets colder than the
outdoor air in order to extract heat from it. If the outdoor coil
temperature is below the dew point of the outdoor air, frost will form
on the outdoor coil. Leaving the system in emergency heat will shut
the compressor and outdoor fan off, so the outdoor coil will be at the
same temperature as the outdoor air. NO frost will form on the outdoor
coil unless it is from horizontally falling snow.

When the heat pump goes into defrost, the strip heat comes on inside to
temper the air, the reversing valve switches to cool mode so the
outdoor coil will get hot enough to melt the ice and the outdoor fan
will shut off so most of the heat in the outdoor coil goes to melting
the ice (latent heat of fusion at 144 BTUs per pound) and very little
goes directly into the outside air.

The fan running on the outdoor unit CAUSES the frost to form in the
first place, not prevent it form forming. If the outdoor fan was not
running, VERY LITTLE heat would be extracted from the outdoor air.

Stretch


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Don McClimans
 
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Default Heat Pump confusion

On 20 Dec 2005 20:13:07 -0800, "Stretch" wrote:

Heating Capacity of a heat pump drops as it gets colder outside. The
heat load load on the house goes up at the same time. Around 35
degrees oiutside the heat pump's heat output drops below the heat load
of the house. This is called the "balance point". Below this outdoor
temperature the heat pump will run constantly.


Only if there is no back-up heating unit. In real systems, below this
outdoor temperature the heat pump and resistance heating will both
turn on, but when you reach the setpoint temperature, the heat pump
will turn off.


Note that at -20 degrees outside the COP (Coefficient Of Performance)
Of a heat pump will be about 1.5. The COP of strip heat is ALWAYS 1.0!
Therefore, switching to emergency heat will increase your electric
bill, as with both heat strips and heat pump running your average COP
will be around 1.25 at -20 degrees outdoors. Not great, but better
than heat strips alone.


Does this calculation of the COP include the defrost cycles? Or are
you saying (below) that the cost of the defrost cycle is negligble
even at -20 def F?

Also since swithcing to emergency heat drops
all the heat from the heat pump mout of the system, you have just lost
some of your capacity and the system may not be able to keep up.

I believe units installed in northern climates are sized so the
back-up furnace can handle the entire heat load.

The outdoor coil freezes because the outdoor coil gets colder than the
outdoor air in order to extract heat from it. If the outdoor coil
temperature is below the dew point of the outdoor air, frost will form
on the outdoor coil. Leaving the system in emergency heat will shut
the compressor and outdoor fan off, so the outdoor coil will be at the
same temperature as the outdoor air. NO frost will form on the outdoor
coil unless it is from horizontally falling snow.

Yes, I thought this is what I was saying. If you switch to emergency
heat, no ice forms on the outside coil.

When the heat pump goes into defrost, the strip heat comes on inside to
temper the air, the reversing valve switches to cool mode so the
outdoor coil will get hot enough to melt the ice and the outdoor fan
will shut off so most of the heat in the outdoor coil goes to melting
the ice (latent heat of fusion at 144 BTUs per pound) and very little
goes directly into the outside air.

That heat that goes into melting frost ends up in the outside air.

In practice, what I see in very cold temps is that the defrost cycle
is *very* frequent. It's hard to believe that I'm actually getting any
benefit from the heat pump.

The fan running on the outdoor unit CAUSES the frost to form in the
first place, not prevent it form forming. If the outdoor fan was not
running, VERY LITTLE heat would be extracted from the outdoor air.

Yes. What I was trying to say is that when you switch to emergency
heat, the heat pump turns off and so the outside fan stops. If you
stay like that for a couple of weeks during a cold spell, and there is
lots of snow or freezing rain, etc., you may end up with a crust on
top of the unit that you have to manually remove. The fan alone (when
you turn the unit back to heat-pump mode) cannot blow away the snow
and ice. So that's a disavantage of switching to emergency heating
mode. If you leave it in dual mode, you may be getting zero or
negative savings out of the heat pump, but at least the blowing
outside fan keeps the snow and ice from building up on the outside
unit.

Terry
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Peter V
 
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Default Heat Pump confusion

Thanks for all the replies, I am still learning a lot about these heat
pumps. One thing I am still stuck on, I know my Auxilary Heater is
operational only because If I manually raise the temperature more than
2 degrees, I can see the indicator and I feel the hotter air. However,
in normal usual operation, I never see it come on at all, no matter how
cold it is outside and how long the heat pump is on. From what I can
tell it only works off the heat pump. The serviceman told me the only
time that the auxilary heat will ever come on is if the room temp falls
2 degrees below the set point. Is this correct?

Thanks again,

PeterV

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CBHVAC
 
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Default Heat Pump confusion


"Peter V" wrote in message
oups.com...
Thanks for all the replies, I am still learning a lot about these heat
pumps. One thing I am still stuck on, I know my Auxilary Heater is
operational only because If I manually raise the temperature more than
2 degrees, I can see the indicator and I feel the hotter air. However,
in normal usual operation, I never see it come on at all, no matter how
cold it is outside and how long the heat pump is on. From what I can
tell it only works off the heat pump. The serviceman told me the only
time that the auxilary heat will ever come on is if the room temp falls
2 degrees below the set point. Is this correct?


Depends on your thermostat, your heat pump, if you have an outdoor
thermostat...

Thanks again,

PeterV





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Stretch
 
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Default Heat Pump confusion

Sorry RP.

My 35 degrees is based on most of the load calculations I do a nd the
high and low temperature ratings of the heat pumps I use. Sometimes
the balance point is as low as 30 degrees outdoors, but I have never
seen a balance point of 20 degrees. But I am basing that on the
climate in Myrtle Beach, SC. Apparently in your part of the south the
balance point is different. I suppose the ocean has a moderating
effect on the outdoor temperatures around here. Every climate has it's
own balance point. Best to do your own calculations.

The heat pumps that I checked for that COP of 1.5 @ -20 degrees were
rated 12 to 13 SEER and 7.1 to 8.5 HSPF. 10 SEER units would be lower
in HSPF and heating COP as well.

Stretch

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Stretch
 
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Default Heat Pump confusion

Terry,
When you said:

"One thing to watch out for if you stay in emergency-heat mode for a
long time. Snow and ice can build up on the outside unit. ";

I took that to mean you thought the frost would build on the outdoor
unit with the thermostat was set to emergency heat. Seems you ment
something else.

The HSPF is the number you look for as far as heat output including
defrost cycles. You want the region III HSPF. In my area, we use the
region IV HSPF due to our higher average temperatures. If the HSPF was
3.4, that would be the same efficiency as heat strips. HSPF is BTUs
per watt. Most heat pumps, even the builder grades will produce a HSPF
of 6.8 or higher in my area. In your area it will be a bit lower.

The COPs do not include a deduct for the cost of defrost, but according
to the manufacturers I have talked to, you are better off letting the
heat pump run, even down to -20 degrees outdoors.

Around here we set defrost to between 60 and 90 minutes per cycle.
Most defrost systems will terminate after 10 to 11 minutes even if the
OD coil is not completely clear.

Of course, if you are only paying 3.5 cents per kwh, who cares about
efficiency. If electricity is free or very cheap, it is hard to
justify high efficiency. we pay 6 to 8.5 cents per KWH around here, so
that changes the equation. I have talked to people paying around 17
cents per kwh! OUCH!!

Stretch

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Don McClimans
 
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Default Heat Pump confusion

On 21 Dec 2005 10:11:46 -0800, "Peter V"
wrote:

Thanks for all the replies, I am still learning a lot about these heat
pumps. One thing I am still stuck on, I know my Auxilary Heater is
operational only because If I manually raise the temperature more than
2 degrees, I can see the indicator and I feel the hotter air. However,
in normal usual operation, I never see it come on at all, no matter how
cold it is outside and how long the heat pump is on. From what I can
tell it only works off the heat pump. The serviceman told me the only
time that the auxilary heat will ever come on is if the room temp falls
2 degrees below the set point. Is this correct?


That's how my Chronotherm III works, I would guess your IV is the
same.

Terry
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