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Posted by Elle on December 25, 2007, 11:00 am
Update:
Last night I had the thermostat set at 67 F all night. This
morning's outside temperature was 39 F. When I woke up at
about 7 AM, I set the thermostat one degree higher. at 68 F.
It's digital and so seems to tolerate this fine tuning well.
The heat pump came on immediately. The registers blew cool
air for maybe a minute or so, but then turned warm and
stayed warm. The warm air coming out was noticeably and
steadily warming the house, so I left the thermostat at 68 F
for 20 minutes or so. Then I raised it to 70 F. The heat
pump came on/continued on, blowing strictly warm air. Twenty
minutes later I raised the thermostat another three degrees.
The heat pump continued to work fine.
I never heard noises from the heat pump like I did yesterday
(after monkeying with the thermostat a lot), too.
The lesson from all my reading at the newsgroup and on the
net is that (1) a heat pump tends to have more "inertia" to
overcome (for its size) than a furnace (this includes
blowing the old cool air out of the ducting and getting the
refrigerant circulating until the correct system
temperatures are reached. Plus compressor speed and system
expansion valve setting has to change? All kinda slowing
things up compared to a gas furnace); (2) a possible defrost
cycle; (3) the "emergency" heat strip operation can confound
the heat pump control system response somewhat; and (4) a
heat pump is more of an "on-off" heat source than a
gas-fired furnace, because the flow of air and temperature
at output is pretty constant. The thermostat bumps the heat
pump on and off as needed. Whereas a furnace can crank out a
much wider variation of temperatures and maybe flows of air
(more natural gas/furnace burners lighting = higher temps
much more quickly)? Something like this, from my analysis
and folks's comments.
Ralph, I am definitely thinking about those heat strips. I
understand that, if possible, I want to avoid them coming on
so as to minimize electricity costs. The danged heat strips
just have no place in a heat pump "system" AFAIC anyway.
Technically they ain't no heat pump but instead a
modification and the ultimate in heating waste. Hopefully
through improved heat pump thermostat operation, I might
even see our electrical bills go down here.
Anyway, I am toasty warm here. I will post an update if I
note other changes. Thanks for helping me have a nice warm
house Xmas morning. Happy holidays to all.
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Posted by Ralph Mowery on December 25, 2007, 11:29 am
>
> Ralph, I am definitely thinking about those heat strips. I understand
> that, if possible, I want to avoid them coming on so as to minimize
> electricity costs. The danged heat strips just have no place in a heat
> pump "system" AFAIC anyway. Technically they ain't no heat pump but
> instead a modification and the ultimate in heating waste. Hopefully
> through improved heat pump thermostat operation, I might even see our
> electrical bills go down here.
>
> Anyway, I am toasty warm here. I will post an update if I note other
> changes. Thanks for helping me have a nice warm house Xmas morning. Happy
> holidays to all.
>
Glad you are warm. The heat strips have 2 functions. One is when the heat
pump part breaks and you need heat. That is the emergency heat part.
When the temperature goes way low (somewhat below 20 deg F) the heat pump
becomes very inefficiant and the heat strips put out more heat per dollar
than the heat pump part .
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Posted by Elle on December 25, 2007, 12:12 pm
> Glad you are warm. The heat strips have 2 functions.
> One is when the heat pump part breaks and you need heat.
> That is the emergency heat part.
> When the temperature goes way low (somewhat below 20 deg
> F) the heat pump becomes very inefficiant and the heat
> strips put out more heat per dollar than the heat pump
> part .
This helps. Thanks!
I have been raising the thermostat steadily and it's now at
76 F. The heat pump is cranking out the heat just fine. Room
temperature is 75 and rising, by my best guess. Outside air
temp is undoubtedly rising as the morning progresses, too,
though, and no doubt this helps. The heat pump seems just
fine for my area (of course, given the many folks who have
them where I live).
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Posted by SteveB on December 25, 2007, 12:57 pm
>
>>
>> Ralph, I am definitely thinking about those heat strips. I understand
>> that, if possible, I want to avoid them coming on so as to minimize
>> electricity costs. The danged heat strips just have no place in a heat
>> pump "system" AFAIC anyway. Technically they ain't no heat pump but
>> instead a modification and the ultimate in heating waste. Hopefully
>> through improved heat pump thermostat operation, I might even see our
>> electrical bills go down here.
>>
>> Anyway, I am toasty warm here. I will post an update if I note other
>> changes. Thanks for helping me have a nice warm house Xmas morning. Happy
>> holidays to all.
>>
>
> Glad you are warm. The heat strips have 2 functions. One is when the
> heat pump part breaks and you need heat. That is the emergency heat part.
> When the temperature goes way low (somewhat below 20 deg F) the heat pump
> becomes very inefficiant and the heat strips put out more heat per dollar
> than the heat pump part .
Now I am getting confused. I'm the OP.
I have heard now that the low end efficiency falls off at between 20 and 35
degrees F. Which is it? Where I live, the max low is about 25 F.according
to US Weather records. And that for only about a month a year.
I am going to call my hvac guy after the holidays. We're doing an addition
anyway, and we'll be ready to fire up that one. I'm going to have him check
this system, all the ductwork, connections, etc. This system just doesn't
heat the house very well. But then, the house was enlarged, and the size of
the heat pump not increased. We use a wood stove for the large room
addition. At times, we just turn on the fan, and use the unit to
recirculate the warm air from the wood stove throughout the house. Still,
the house has cold rooms.
In a nutshell, it's a bag of snakes that's been Rube Goldberged together.
Now, for my next question: I have a friend who's a union electrician who
does all my work. I have one set of breakers where I can run a new line to
the heat strips, should the hvac guy say they will work. When the unit is
operating, does it need this additional power, or is the 220 line that is
running the unit adequate to run the unit and the heat strips? It would
seem that the unit would be running just the electrical strips and a fan
rather than the strips and the compressor. Am I right or wrong?
I know, I know, I should talk to the hvac guy, and I am going to right after
the holidays. I would just like to be somewhat informed when I do.
Steve
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Posted by lp13-30 on December 25, 2007, 1:41 pm
SteveB, not exactly sure what you are asking about the power
requirements. Normally, you have a 240volt circuit run to the outdoor
unit, ideally sized according to the information on the tag on the unit.
Then a separate 240 circuit to air handler to power the heat strips and
the blower, with the breaker and wire sized according to the size of the
heat strips, which can typically be between 3 and 20 Kw. A lot of units
with 15kw and larger strips have the strips split into 2 circuits. The
strips will come off and on with the outdoor unit running if the
thermostat determines they are needed. They also typically are energized
when the HP goes into defrost so it does not blow cold air.If the
thermostat is turned to "emer heat" , the outdoor unit does not run, and
the blower and heat strips are used, so that it operates just like a
regular electric heat system. Again, dunno if this answers you question
or not. Larry
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