I have a heat pump with aux heat for which I bought a programmable
thermostat. The RTH7400D to be exact

What is the recommendation on setting the temp difference between wake and
sleep times so that I am not going to make the system work to hard and not
get the energy savings that I bought the prog. thermostat for in the first
place?

Russell Coleman wrote:

I have a heat pump with aux heat for which I bought a programmable
thermostat. The RTH7400D to be exact

What is the recommendation on setting the temp difference between wake and
sleep times so that I am not going to make the system work to hard and not
get the energy savings that I bought the prog. thermostat for in the first
place?

The programmable-stat isn't going to magically save you any money vs a
non-programmable stat. It has one purpose: To control temperature, just
like any other t-stat. A thermidistat OTOH also controls RH, within
limits providing constant comfort at constant temp, something the
regular thermostat won't do. IOW, a constant temp setting won't provide
uniform comfort on a regular stat, either programmable or
non-programmable. IOW, you may find yourself frequently overriding the
schedule on your programmable stat, thus defeating its true purpose,
which BTW isn't what you claimed it was above.

The energy savings enter in only in the fact that you are setting back
the temperature for periods of the day, something that a programmable
stat isn't a requirement for. Basically any time the unit is off you are
saving. It isn't the stat that will save you money, it does nothing to
the system by its mere connection to the system to improve its inherent
efficiency, it is only the lower than comfort temp settings scheduled in
winter, and higher in summer that save you the money. Thus for the
greatest savings just turn the system off when you aren't home, and set
back at night to whatever freeze level in winter or sweating level that
you care to withstand in the name of savings.

Recovery time between sleep and wake settings isn't an issue as far as
energy cost is concerned, but it should be to be taken into account when
adjusting the schedule times.

BTW, in reference to my above comment: People don't buy programmable
stats to save money, they buy them to save them from the 2-second hassle
of manually setting back every night, and/or for improved comfort via RH
control when available. Comfort control OTOH typically reduces overall
economy, FWIW. Thus, unless you aren't home, then the only way that you
are going to save money with *any* stat is to live uncomfortably in your
own house. I'm almost positive that this is the reason that 1 out of
every 100 programmable stats that I encounter in the field are running
in HOLD mode with no schedules set. HTH.

hvacrmedic

"Recovery time between sleep and wake settings isn't an issue as far as

energy cost is concerned, but it should be to be taken into account
when
adjusting the schedule times"

It sure sounds like it would be a big issue on a heat pump system with
electric aux heat. I think his concern was if he set the setback delta
too big, the aux electric heat could kick in.

RP wrote:



Russell Coleman wrote:

I have a heat pump with aux heat for which I bought a programmable
thermostat. The RTH7400D to be exact

What is the recommendation on setting the temp difference between wake
and sleep times so that I am not going to make the system work to hard
and not get the energy savings that I bought the prog. thermostat
for in the first place?


The programmable-stat isn't going to magically save you any money vs a
non-programmable stat. It has one purpose: To control temperature, just
like any other t-stat. A thermidistat OTOH also controls RH, within
limits providing constant comfort at constant temp, something the
regular thermostat won't do. IOW, a constant temp setting won't provide
uniform comfort on a regular stat, either programmable or
non-programmable. IOW, you may find yourself frequently overriding the
schedule on your programmable stat, thus defeating its true purpose,
which BTW isn't what you claimed it was above.

The energy savings enter in only in the fact that you are setting back
the temperature for periods of the day, something that a programmable
stat isn't a requirement for. Basically any time the unit is off you are
saving. It isn't the stat that will save you money, it does nothing to
the system by its mere connection to the system to improve its inherent
efficiency, it is only the lower than comfort temp settings scheduled in
winter, and higher in summer that save you the money. Thus for the
greatest savings just turn the system off when you aren't home, and set
back at night to whatever freeze level in winter or sweating level that
you care to withstand in the name of savings.

Recovery time between sleep and wake settings isn't an issue as far as
energy cost is concerned, but it should be to be taken into account when
adjusting the schedule times.

BTW, in reference to my above comment: People don't buy programmable
stats to save money, they buy them to save them from the 2-second hassle
of manually setting back every night, and/or for improved comfort via RH
control when available. Comfort control OTOH typically reduces overall
economy, FWIW. Thus, unless you aren't home, then the only way that you
are going to save money with *any* stat is to live uncomfortably in your
own house. I'm almost positive that this is the reason that 1 out of

Make that 99 out of 100

every 100 programmable stats that I encounter in the field are running
in HOLD mode with no schedules set. HTH.

hvacrmedic

I should also add, while I'm at it, that some stats do offer
programmable options for backup heat, and may provide some savings over
a standard stat in which backup heat will always be energize during
recovery from setback. In multiple stage systems some programmables will
also offer net savings over the non-programmable by running the system
longer in the low stage. Sorry for these technical omissions.

hvacrmedic

"Russell Coleman" wrote in message
llsouth.net...
I have a heat pump with aux heat for which I bought a programmable
thermostat. The RTH7400D to be exact

What is the recommendation on setting the temp difference between wake and
sleep times so that I am not going to make the system work to hard and not
get the energy savings that I bought the prog. thermostat for in the
first
place?



The same across the board....
Or, no more than 2F degrees difference between the two.

The most common question asked is : What temp saves me the most money?
The answer is, as low as you can stand it.

With programmable stats, any real savings you think you had, you kill when
the aux heat comes on...if needed for recovery.

Any decent digital stat maintains a 1F differential, so that alone saves you
a ton over a mercury stat.
I said decent...the one you have is a marginal Honeywell....bottom end of
the scale, particularly if you got it at Lowes or Home Depot.

wrote:

"Recovery time between sleep and wake settings isn't an issue as far as

energy cost is concerned, but it should be to be taken into account
when
adjusting the schedule times"

It sure sounds like it would be a big issue on a heat pump system with
electric aux heat. I think his concern was if he set the setback delta
too big, the aux electric heat could kick in.

I immediately addressed this in the follow-up post that I made, but yes,
you are correct. This is however something that scheduling alone, what
he asked about, won't cure. That option, if available, will be in the
setup menu which is typically difficult for the average homeowner to
make sense of. They could easily change some settings that don't need to
be changed. If he is interested in optimizing recovery via heat strip
lockout, then he should check his literature or contact the manufacturer.

hvacrmedic

CBHVAC wrote:

"Russell Coleman" wrote in message
llsouth.net...

I have a heat pump with aux heat for which I bought a programmable
thermostat. The RTH7400D to be exact

What is the recommendation on setting the temp difference between wake and
sleep times so that I am not going to make the system work to hard and not
get the energy savings that I bought the prog. thermostat for in the
first
place?




The same across the board....
Or, no more than 2F degrees difference between the two.

The most common question asked is : What temp saves me the most money?
The answer is, as low as you can stand it.

With programmable stats, any real savings you think you had, you kill when
the aux heat comes on...if needed for recovery.

Conventional Heat Pumps get an average COP of 2 to 1. Thus if the
overnight (set back) runtime is reduced by an amount of time that is
twice the recovery time with heat strips enabled), then energy is saved
over not setting back. Keep in mind that the COP during recover will be
greater than 1 to 1 because the heat pump will be running along with the
heat strips.

At low ambients, where the COP of the heat pump is barely, if at all,
Greater than 1 to 1, then it is impossible to imaging that heat strip
assisted recovery will overcome the savings of setting back. OTOH, at
higher ambients, it hardly matters much--the savings, or loss, whatever
the case may be, only amounts to pennies per day.

Unless I see some studies that supersede this, then I say setting back
overnight will save money. I also suggest that the system be set up to
run minimal backup heat, not at the stat, but at the unit. Rheem used to
install a klixon in the air handler that locked out a strip or two until
the air temp dropped below 65ºF. Not a bad thing. Staging the strips is
also a good idea. This can be done in conjunction with a 3 stage heat
stat, or by installing a long time delay on a portion of the strip heat.
There are plenty of options, but none of them are going to save
*substantial* amounts on the energy bill. If energy efficiency is that
great of an obstacle then either shut it off, or get a higher efficiency
system. I really don't think that piddling with t-stat settings is worth
the time unless you've done the calcs that prove that any savings from
doing so are going to be noticeable. It sometimes amounts to spending a
dollar to save a dime. Figuring in the cost of the programmable stat vs
a non-programmable, payoff might take 10 years, it might take one, and
it may never pay for itself, depending upon system design.

hvacrmedic



Any decent digital stat maintains a 1F differential, so that alone saves you
a ton over a mercury stat.
I said decent...the one you have is a marginal Honeywell....bottom end of
the scale, particularly if you got it at Lowes or Home Depot.

RP wrote:

Conventional Heat Pumps get an average COP of 2 to 1.

Depends on the climate, no? Might be 3:1.

Thus if the overnight (set back) runtime is reduced by an amount of time
that is twice the recovery time with heat strips enabled), then energy
is saved over not setting back...

Thus? :-)

Nick

RP wrote:

Russell Coleman wrote:

I have a heat pump with aux heat for which I bought a programmable
thermostat. The RTH7400D to be exact

What is the recommendation on setting the temp difference between wake and
sleep times so that I am not going to make the system work to hard and not
get the energy savings that I bought the prog. thermostat for in the first
place?

Switch off the strip heaters if any and turn off the heat at night and
set the thermostat timer ahead to make the house comfy when you get up.

The programmable-stat isn't going to magically save you any money vs a
non-programmable stat.

There's no magic: reducing the indoor-outdoor temp diff at night makes
less heat flow. That's Newton's (1642-1727) Law of Cooling.

IOW, you may find yourself frequently overriding the schedule on your
programmable stat,

Or opening all the house windows in wintertime.

...defeating its true purpose, which BTW isn't what you claimed it was above.

How can he be wrong about his true purpose? :-)

...that I bought the prog. thermostat for in the first place?

... unless you aren't home, then the only way that you are going to save
money with *any* stat is to live uncomfortably in your own house.

Nonsense. He can be perfectly comfy sleeping under a quilt in a 40 F bedroom.

Nick

Nick Pine wrote:
RP wrote:

Russell Coleman wrote:


I have a heat pump with aux heat for which I bought a programmable
thermostat. The RTH7400D to be exact

What is the recommendation on setting the temp difference between wake and
sleep times so that I am not going to make the system work to hard and not
get the energy savings that I bought the prog. thermostat for in the first
place?


Switch off the strip heaters if any and turn off the heat at night and
set the thermostat timer ahead to make the house comfy when you get up.


The programmable-stat isn't going to magically save you any money vs a
non-programmable stat.


There's no magic: reducing the indoor-outdoor temp diff at night makes
less heat flow. That's Newton's (1642-1727) Law of Cooling.


IOW, you may find yourself frequently overriding the schedule on your
programmable stat,


Or opening all the house windows in wintertime.


...defeating its true purpose, which BTW isn't what you claimed it was above.


How can he be wrong about his true purpose? :-)


...that I bought the prog. thermostat for in the first place?


... unless you aren't home, then the only way that you are going to save
money with *any* stat is to live uncomfortably in your own house.


Nonsense. He can be perfectly comfy sleeping under a quilt in a 40 F bedroom.

Nick

From that angle one could simply turn the unit off, t-stat no longer a
factor

hvacrmedic

RP wrote:

... He can be perfectly comfy sleeping under a quilt in a 40 F bedroom.

From that angle one could simply turn the unit off, t-stat no longer a
factor

Sure. Swiss mountain folk believe it's healthy to climb under quilts with
bedroom windows wide open in freezing weather.

Nick

wrote:

RP wrote:


Conventional Heat Pumps get an average COP of 2 to 1.


Depends on the climate, no? Might be 3:1.


Thus if the overnight (set back) runtime is reduced by an amount of time
that is twice the recovery time with heat strips enabled), then energy
is saved over not setting back...


Thus? :-)

Thus, yes, at some higher COP and/or warmer climate the trend will
reverse. That's why I said in summary that economy depends upon the
system

hvacrmedic



Nick

RP wrote:

Conventional Heat Pumps get an average COP of 2 to 1...

Thus if the overnight (set back) runtime is reduced by an amount of time
that is twice the recovery time with heat strips enabled), then energy
is saved over not setting back...

Thus? :-)

Thus, yes, at some higher COP and/or warmer climate the trend will reverse.
That's why I said in summary that economy depends upon the system

I don't quite see a "thus" there. Would you further explain your logic?

Would you agree that night setbacks always save energy if the heat strips are
switched off, even though that may require longer reheating after the setback?

Nick

wrote:
RP wrote:


Conventional Heat Pumps get an average COP of 2 to 1...

Thus if the overnight (set back) runtime is reduced by an amount of time
that is twice the recovery time with heat strips enabled), then energy
is saved over not setting back...

Thus? :-)

Thus, yes, at some higher COP and/or warmer climate the trend will reverse.
That's why I said in summary that economy depends upon the system


I don't quite see a "thus" there. Would you further explain your logic?

I'm sorry, that won't be possible. I can however add more conclusions at
will. It's quite easy once you get the hang of it

I'm not in the mood to drag in formulas at this point in time, having
worked all weekend, till dark hours. IOW, I'm too damned tired

You've probably worked through this already, so if you would, could you
please provide some math to analyze the set-back savings of various COP
systems with and without resistance heat enabled?

Without strip heat enabled it *seems* obvious that the monetary savings
of setting back would be greater with the lower COP system. IOW, with a
COP of 1, you have effectively the economy of straight strip heat, in
which case setting back definitely helps the pocket book. OTOH I'd be
very grateful if you could prove otherwise, as my wife is a setting-back
fanatic and I'm tired of waking up to a cold ****er. I suppose I could
shorten it a bit, but hanging it in the water easier than aiming when
you haven't had your coffee yet.

hvacrmedic



Would you agree that night setbacks always save energy if the heat strips are
switched off, even though that may require longer reheating after the setback?

Nick

RP wrote:

Thus, if the overnight (set back) runtime is reduced by an amount of time
that is twice the recovery time with heat strips enabled), then energy
is saved over not setting back...

Thus? :-)

Thus, yes, at some higher COP and/or warmer climate the trend will reverse.
That's why I said in summary that economy depends upon the system

I don't quite see a "thus" there. Would you further explain your logic?

I'm sorry, that won't be possible. I can however add more conclusions at
will. It's quite easy once you get the hang of it

My friend Rich says he can easily supply multiple inconsistent conclusions.

I'm not in the mood to drag in formulas at this point in time, having
worked all weekend, till dark hours. IOW, I'm too damned tired

Perhaps later, when you have rested.

You've probably worked through this already, so if you would, could you
please provide some math to analyze the set-back savings of various COP
systems with and without resistance heat enabled?

Well, we might agree that night setbacks always save energy with heat strips
switched off, even though that requires longer reheating after the setback,
but a longer setback with a faster recovery using strips might save more,
if the house can stay cooler longer. This wouldn't apply to houses with
zero or infinite thermal mass, but it might with a finite mass.

In scenario 1, keep a house with G = 200 Btu/h-F of thermal conductance at
70 F for 8 hours on a 30 F night with 8h(70-30)200 = 64K Btu from a heat
pump with a 2:1 COP, using 64K/2/3412 = 9.38 kWh of electrical energy.

In scenario 2, the house has C = 10K Btu/F of thermal capacitance and
an RC time constant C/G = 50 hours, so it cools from 70 F at midnight
to 30+(70-30)e^(-8/50) = 64.1 at 8 AM. The house returns instantly to
70 F at 8 AM, with powerful strip heaters that consume (70-64.1)10K
= 59K Btu, or 17.3 kWh, almost twice scenario 1.

In scenario 3, the house has a wimpy 10K Btu/h heat pump with a 30+10K/200
= 80 F Thevenin equivalent temp and no strip heaters. It cools to a minimum
temp T (F) in t hours and reheats in 8-t hours, so T = 30+(70-30)e^(-t/50)
and 70 = 80+(T-80)e^(-(8-t)/50) and t = 1.7 h and T = 68.7 F. Reheating for
6.3 hours takes 6.3x10K/2/3412 = 9.23 kWh, with a small setback savings.

More typically, with C = 5K and G = 500 and RC = 10 hours and a 60K Btu/h
heat pump with a COP of 3 and a 30+60K/500 = 150 F equivalent temp, we
would use 8h(70-30)500/3/3412 = 15.63 kWh in scenario 1. In scenario 2,
the house would cool to 30+(70-30)e^(-8/10) = 48.0, and the heaters would
consume (70-48)5K/3412 = 32.24 kWh at 8 AM. T = 30+(70-30)e^(-t/10) and
70 = 150+(T-150)e^(-(8-t)/10), so t = 6.0 h and T = 52.0 in scenario 3.
Reheating takes 2.0x60K/3/3412 = 11.9 kWh, for a big setback savings.

Without strip heat enabled it *seems* obvious that the monetary savings
of setting back would be greater with the lower COP system. IOW, with a
COP of 1, you have effectively the economy of straight strip heat, in
which case setting back definitely helps the pocket book.

Some people say the COP of a heat pump can be less than one, but that
seems hard to believe. OTOH, they do wear out.

OTOH I'd be very grateful if you could prove otherwise, as my wife is
a setting-back fanatic and I'm tired of waking up to a cold ****er.
I suppose I could shorten it a bit, but hanging it in the water easier
than aiming when you haven't had your coffee yet.

You might enjoy

http://www.homeclick.com/showpage.asp?itemid=3D202929, or

http://www.cleanbutt.com/PRODUCT.ASP, with optional wireless remote control.

Nick

I wonder why you end up cross posting this stuff. No one is going to
subscribe to all the groups you belong to find the original post.

You must have a compelling need to drag this crap over to the 'HVAC
Criminals' because you are a closet mental masochist.


wrote:
RP wrote:

Thus, if the overnight (set back) runtime is reduced by an amount of time
that is twice the recovery time with heat strips enabled), then energy
is saved over not setting back...

Thus? :-)

Thus, yes, at some higher COP and/or warmer climate the trend will reverse.
That's why I said in summary that economy depends upon the system

I don't quite see a "thus" there. Would you further explain your logic?

I'm sorry, that won't be possible. I can however add more conclusions at
will. It's quite easy once you get the hang of it

My friend Rich says he can easily supply multiple inconsistent conclusions.

I'm not in the mood to drag in formulas at this point in time, having
worked all weekend, till dark hours. IOW, I'm too damned tired

Perhaps later, when you have rested.

You've probably worked through this already, so if you would, could you
please provide some math to analyze the set-back savings of various COP
systems with and without resistance heat enabled?

Well, we might agree that night setbacks always save energy with heat strips
switched off, even though that requires longer reheating after the setback,
but a longer setback with a faster recovery using strips might save more,
if the house can stay cooler longer. This wouldn't apply to houses with
zero or infinite thermal mass, but it might with a finite mass.

In scenario 1, keep a house with G = 200 Btu/h-F of thermal conductance at
70 F for 8 hours on a 30 F night with 8h(70-30)200 = 64K Btu from a heat
pump with a 2:1 COP, using 64K/2/3412 = 9.38 kWh of electrical energy.

Scenario 1, setting back the temperature of a dog house or other
pathetically small structure, irrelevant.

In scenario 2, the house has C = 10K Btu/F of thermal capacitance and
an RC time constant C/G = 50 hours, so it cools from 70 F at midnight
to 30+(70-30)e^(-8/50) = 64.1 at 8 AM. The house returns instantly to
70 F at 8 AM, with powerful strip heaters that consume (70-64.1)10K
= 59K Btu, or 17.3 kWh, almost twice scenario 1.


In scenario 3, the house has a wimpy 10K Btu/h heat pump with a 30+10K/200
= 80 F Thevenin equivalent temp and no strip heaters. It cools to a minimum
temp T (F) in t hours and reheats in 8-t hours, so T = 30+(70-30)e^(-t/50)
and 70 = 80+(T-80)e^(-(8-t)/50) and t = 1.7 h and T = 68.7 F. Reheating for
6.3 hours takes 6.3x10K/2/3412 = 9.23 kWh, with a small setback savings.

More typically, with C = 5K and G = 500 and RC = 10 hours and a 60K Btu/h
heat pump with a COP of 3 and a 30+60K/500 = 150 F equivalent temp, we
would use 8h(70-30)500/3/3412 = 15.63 kWh in scenario 1. In scenario 2,
the house would cool to 30+(70-30)e^(-8/10) = 48.0, and the heaters would
consume (70-48)5K/3412 = 32.24 kWh at 8 AM. T = 30+(70-30)e^(-t/10) and
70 = 150+(T-150)e^(-(8-t)/10), so t = 6.0 h and T = 52.0 in scenario 3.
Reheating takes 2.0x60K/3/3412 = 11.9 kWh, for a big setback savings.

Typical, LMAO -- "but they only scoff"

Your old conductance, now typically at 500 lol. Anyways you are saying
70 indoors and 30F ambient I believe so it would mean a heat loss of
40x500= 20,000 Btu/hr with your mind set.

But of course you will have a heatpump with a 60,000 Btu/hr heat output
on this home that exceeds the load by a mere 300%.

So a unit capable of about 60,000 Btu/hr of heat output based on a 30F
temperature source will most likely have a cooling capcity of at least
6 tons.

You always neglect solar gains on homes IN YOUR GOOFY COOLING SCHEMES
and use your temperature based 'Conductance' so carrying your mindest
to a cooling environment when it is an AVERAGE (LMAO) 88F outside, they
only need 500x(88-70)=9,000 btu/hr for sensible cooling , that 6 ton
just out to cool it. You don't have to worry about a latent load in
this scenario Noah, because your system would be so grossly oversized
its is going to be 80%RH as a minimum.-- "works in a zoo"

Or if you would use a real cooling ambient with your scheme and
'conductance' then you need sensible cooling of 500x(95-70)=12,500
Btu/hr. And you wonder why I give you grief when I say that you neglect
the effect of the sun on cooling. -- "they just scoff"

Maybe this unit with a would be available in single phase, if it was
some kind of 5 ton system on steroids that moved 2600 CFM.

In reality, I would doubt a home that actually required a 20,000 Btu/hr
heating system in a 30F climate would need much more than 3 or 3.5 tons
of total cooling in a 95F climate.

Just another attempt to cross post drivel that does not work in the
real world. So put in a heating unit three times the required size to
prove that you can set back a heat pump. Pathetic.

Maybe look at applying a Biot Number or two when you are looking at
heat released, then heat required to warm something back up. -- "
subliminal hint"

You may also want to consider the outdoor coil defrosting in your
calculations as well.

In a cold environment (sub zero) with a high thermal mass, a system
sized to match the heat load may shut off for a couple hours at night
when setback, then would be running steady until after the sun rose to
catch up. This is based on something real, not a fictious scheme where
the equipment is 3 times the capacity of the design heating load.

With heat pumps and or high thermal mass buildings, set back is not
always a good scheme. If you set it back during the day, such as when
occupants go to work, think about having the space back up to
temperature before the sun sets.

If you shut off the strip heaters, sure it is possible that a properly
sized heating system could eventually catch up to the required
temperature but the problem is the sun will have risen and the
occupants have left for work already before it does.

Then think with some passive solar, the house would not cool off all
that much while the sun was shining. Run time is down quite a bit, when
the sun is shining. From experience with R2000 homes, the systems can
be off for hours while the sun is shining in cold weather.

What is the time constant as that 60K heat pump warms up? Would it ever
reach steady state and a COP of 3? Well maybe when it was running after
the setback period ended.

60,000 steady state heat output, 20,000 load each hour hmm, wonder how
many times that will cycle on and off drawing LRA? Well if a dog year
is 7 years, a Nick year must be 3 years.

Maybe assume it takes 15 minutes to stabalize and work backwards from
there for your time constant.

Abby Normal wrote:

But of course you will have a heatpump with a 60,000 Btu/hr heat output

on this home that exceeds the load by a mere 300%.

my bad, the load is 20 the system puts out 60, 3 times the load,
therefore it exceeds the load by 200%.

wrote:
RP wrote:


Thus, if the overnight (set back) runtime is reduced by an amount of time
that is twice the recovery time with heat strips enabled), then energy
is saved over not setting back...

Thus? :-)

Thus, yes, at some higher COP and/or warmer climate the trend will reverse.
That's why I said in summary that economy depends upon the system

I don't quite see a "thus" there. Would you further explain your logic?

I'm sorry, that won't be possible. I can however add more conclusions at
will. It's quite easy once you get the hang of it


My friend Rich says he can easily supply multiple inconsistent conclusions.


I'm not in the mood to drag in formulas at this point in time, having
worked all weekend, till dark hours. IOW, I'm too damned tired


Perhaps later, when you have rested.


You've probably worked through this already, so if you would, could you
please provide some math to analyze the set-back savings of various COP
systems with and without resistance heat enabled?


Well, we might agree that night setbacks always save energy with heat strips
switched off, even though that requires longer reheating after the setback,
but a longer setback with a faster recovery using strips might save more,
if the house can stay cooler longer. This wouldn't apply to houses with
zero or infinite thermal mass, but it might with a finite mass.

In scenario 1, keep a house with G = 200 Btu/h-F of thermal conductance at
70 F for 8 hours on a 30 F night with 8h(70-30)200 = 64K Btu from a heat
pump with a 2:1 COP, using 64K/2/3412 = 9.38 kWh of electrical energy.

In scenario 2, the house has C = 10K Btu/F of thermal capacitance and
an RC time constant C/G = 50 hours, so it cools from 70 F at midnight
to 30+(70-30)e^(-8/50) = 64.1 at 8 AM. The house returns instantly to
70 F at 8 AM, with powerful strip heaters that consume (70-64.1)10K
= 59K Btu, or 17.3 kWh, almost twice scenario 1.

In scenario 3, the house has a wimpy 10K Btu/h heat pump with a 30+10K/200
= 80 F Thevenin equivalent temp and no strip heaters. It cools to a minimum
temp T (F) in t hours and reheats in 8-t hours, so T = 30+(70-30)e^(-t/50)
and 70 = 80+(T-80)e^(-(8-t)/50) and t = 1.7 h and T = 68.7 F. Reheating for
6.3 hours takes 6.3x10K/2/3412 = 9.23 kWh, with a small setback savings.

More typically, with C = 5K and G = 500 and RC = 10 hours and a 60K Btu/h
heat pump with a COP of 3 and a 30+60K/500 = 150 F equivalent temp, we
would use 8h(70-30)500/3/3412 = 15.63 kWh in scenario 1. In scenario 2,
the house would cool to 30+(70-30)e^(-8/10) = 48.0, and the heaters would
consume (70-48)5K/3412 = 32.24 kWh at 8 AM. T = 30+(70-30)e^(-t/10) and
70 = 150+(T-150)e^(-(8-t)/10), so t = 6.0 h and T = 52.0 in scenario 3.
Reheating takes 2.0x60K/3/3412 = 11.9 kWh, for a big setback savings.

A valiant effort, but several variables are missing. Still it's probably
an ok ballpark analysis for comparative purposes. I wouldn't value the
actual numbers beyond their ability to provide inequalities (More
than/less than). They are too ambiguous. Still I don't see yet where we
are in disagreement. Maybe you weren't trying to disagree. I dunno.


Without strip heat enabled it *seems* obvious that the monetary savings
of setting back would be greater with the lower COP system. IOW, with a
COP of 1, you have effectively the economy of straight strip heat, in
which case setting back definitely helps the pocket book.


Some people say the COP of a heat pump can be less than one, but that
seems hard to believe. OTOH, they do wear out.

Sure it can, else there wouldn't be an economic balance point. As the
ambient drops the suction pressure drops too, mass flow is reduced, thus
he capacity is reduced as ambient temp drops. Runtimes are also longer
and take place with reduced volumetric efficiency, thus COP drops as
well. At what point would this curve level off? Wouldn't it continue to
fall right on through the 1:1 mark? At 0ºK (absolute zero) the COP would
theoretically be 0:1. Assuming a COP of 2:1 at 40ºF thus we can thus
interpolate a COP of 1:1 at an ambient temp somewhere between absolute
zero and 40ºF.



OTOH I'd be very grateful if you could prove otherwise, as my wife is
a setting-back fanatic and I'm tired of waking up to a cold ****er.
I suppose I could shorten it a bit, but hanging it in the water easier
than aiming when you haven't had your coffee yet.

You might enjoy

http://www.homeclick.com/showpage.asp?itemid=3D202929, or

http://www.cleanbutt.com/PRODUCT.ASP, with optional wireless remote control.


Thanx, very good site. The rim deflector is a must have item.

hvacrmedic

Abby Normal wrote

I wonder why you end up cross posting this stuff. No one is going
to subscribe to all the groups you belong to find the original post.

Completely trivial to find it using groups.google

You must have a compelling need to drag this crap over to the
'HVAC Criminals' because you are a closet mental masochist.


wrote:
RP wrote:

Thus, if the overnight (set back) runtime is reduced by an
amount of time that is twice the recovery time with heat strips
enabled), then energy is saved over not setting back...

Thus? :-)

Thus, yes, at some higher COP and/or warmer climate the trend
will reverse. That's why I said in summary that economy depends
upon the system

I don't quite see a "thus" there. Would you further explain your
logic?

I'm sorry, that won't be possible. I can however add more
conclusions at will. It's quite easy once you get the hang of it

My friend Rich says he can easily supply multiple inconsistent
conclusions.

I'm not in the mood to drag in formulas at this point in time,
having worked all weekend, till dark hours. IOW, I'm too damned
tired

Perhaps later, when you have rested.

You've probably worked through this already, so if you would, could
you please provide some math to analyze the set-back savings of
various COP systems with and without resistance heat enabled?

Well, we might agree that night setbacks always save energy with
heat strips switched off, even though that requires longer reheating
after the setback, but a longer setback with a faster recovery using
strips might save more, if the house can stay cooler longer. This
wouldn't apply to houses with zero or infinite thermal mass, but it
might with a finite mass.

In scenario 1, keep a house with G = 200 Btu/h-F of thermal
conductance at 70 F for 8 hours on a 30 F night with 8h(70-30)200 =
64K Btu from a heat pump with a 2:1 COP, using 64K/2/3412 = 9.38 kWh
of electrical energy.

Scenario 1, setting back the temperature of a dog house or other
pathetically small structure, irrelevant.

In scenario 2, the house has C = 10K Btu/F of thermal capacitance and
an RC time constant C/G = 50 hours, so it cools from 70 F at midnight
to 30+(70-30)e^(-8/50) = 64.1 at 8 AM. The house returns instantly to
70 F at 8 AM, with powerful strip heaters that consume (70-64.1)10K
= 59K Btu, or 17.3 kWh, almost twice scenario 1.


In scenario 3, the house has a wimpy 10K Btu/h heat pump with a
30+10K/200 = 80 F Thevenin equivalent temp and no strip heaters. It
cools to a minimum temp T (F) in t hours and reheats in 8-t hours,
so T = 30+(70-30)e^(-t/50) and 70 = 80+(T-80)e^(-(8-t)/50) and t =
1.7 h and T = 68.7 F. Reheating for
6.3 hours takes 6.3x10K/2/3412 = 9.23 kWh, with a small setback
savings.

More typically, with C = 5K and G = 500 and RC = 10 hours and a 60K
Btu/h heat pump with a COP of 3 and a 30+60K/500 = 150 F equivalent
temp, we would use 8h(70-30)500/3/3412 = 15.63 kWh in scenario 1. In
scenario 2,
the house would cool to 30+(70-30)e^(-8/10) = 48.0, and the heaters
would consume (70-48)5K/3412 = 32.24 kWh at 8 AM. T =
30+(70-30)e^(-t/10) and 70 = 150+(T-150)e^(-(8-t)/10), so t = 6.0 h
and T = 52.0 in scenario 3. Reheating takes 2.0x60K/3/3412 = 11.9
kWh, for a big setback savings.

Typical, LMAO -- "but they only scoff"

Your old conductance, now typically at 500 lol. Anyways you are saying
70 indoors and 30F ambient I believe so it would mean a heat loss of
40x500= 20,000 Btu/hr with your mind set.

But of course you will have a heatpump with a 60,000 Btu/hr heat
output on this home that exceeds the load by a mere 300%.

So a unit capable of about 60,000 Btu/hr of heat output based on a 30F
temperature source will most likely have a cooling capcity of at least
6 tons.

You always neglect solar gains on homes IN YOUR GOOFY COOLING SCHEMES
and use your temperature based 'Conductance' so carrying your mindest
to a cooling environment when it is an AVERAGE (LMAO) 88F outside,
they only need 500x(88-70)=9,000 btu/hr for sensible cooling , that 6
ton just out to cool it. You don't have to worry about a latent load
in this scenario Noah, because your system would be so grossly
oversized its is going to be 80%RH as a minimum.-- "works in a zoo"

Or if you would use a real cooling ambient with your scheme and
'conductance' then you need sensible cooling of 500x(95-70)=12,500
Btu/hr. And you wonder why I give you grief when I say that you
neglect the effect of the sun on cooling. -- "they just scoff"

Maybe this unit with a would be available in single phase, if it was
some kind of 5 ton system on steroids that moved 2600 CFM.

In reality, I would doubt a home that actually required a 20,000
Btu/hr heating system in a 30F climate would need much more than 3 or
3.5 tons of total cooling in a 95F climate.

Just another attempt to cross post drivel that does not work in the
real world. So put in a heating unit three times the required size to
prove that you can set back a heat pump. Pathetic.

Maybe look at applying a Biot Number or two when you are looking at
heat released, then heat required to warm something back up. -- "
subliminal hint"

You may also want to consider the outdoor coil defrosting in your
calculations as well.

In a cold environment (sub zero) with a high thermal mass, a system
sized to match the heat load may shut off for a couple hours at night
when setback, then would be running steady until after the sun rose to
catch up. This is based on something real, not a fictious scheme where
the equipment is 3 times the capacity of the design heating load.

With heat pumps and or high thermal mass buildings, set back is not
always a good scheme. If you set it back during the day, such as when
occupants go to work, think about having the space back up to
temperature before the sun sets.

If you shut off the strip heaters, sure it is possible that a properly
sized heating system could eventually catch up to the required
temperature but the problem is the sun will have risen and the
occupants have left for work already before it does.

Then think with some passive solar, the house would not cool off all
that much while the sun was shining. Run time is down quite a bit,
when the sun is shining. From experience with R2000 homes, the
systems can be off for hours while the sun is shining in cold weather.

RP wrote:

Some people say the COP of a heat pump can be less than one, but that
seems hard to believe. OTOH, they do wear out.

Sure it can, else there wouldn't be an economic balance point...

Seems to me it has to be greater than 1:1 for heating, since the compressor
heat ends up in the house. This requires good defrost control: turn off the
compressor and run the outdoor fan if the outdoor coil is about to freeze,
and turn off the whole shebang if the outdoor temp is less than 32 F. IIRC,
Carrier did experiments with heat pump coils covered with 2" of ice, and
the COP was still greater than 1.

http://www.cleanbutt.com/PRODUCT.ASP, with optional wireless remote control.

Thanx, very good site. The rim deflector is a must have item.

The remote adds $100. EXTREMELY obese people find it useful.

Nick

wrote:
RP wrote:


Some people say the COP of a heat pump can be less than one, but that
seems hard to believe. OTOH, they do wear out.

Sure it can, else there wouldn't be an economic balance point...


Seems to me it has to be greater than 1:1 for heating, since the compressor
heat ends up in the house.

Not all of it, unless the compressor is insulated. Also there are the
controls (contactor, etc.), condenser fan, crankcase heater, RV coil,
and defrost cycle to take into account. I wonder if Carrier fudged too?

hvacrmedic


This requires good defrost control: turn off the
compressor and run the outdoor fan if the outdoor coil is about to freeze,
and turn off the whole shebang if the outdoor temp is less than 32 F. IIRC,
Carrier did experiments with heat pump coils covered with 2" of ice, and
the COP was still greater than 1.

http://www.cleanbutt.com/PRODUCT.ASP, with optional wireless remote control.


Thanx, very good site. The rim deflector is a must have item.


The remote adds $100. EXTREMELY obese people find it useful.

Nick

Why would anybody ever install a heat pump system?

Another friend of mine's heat pump just bit the dust
here at -20C. Going to take weeks to get a part for it.
Pretty expensive portable electric heating going on in
that house right now.

That makes 9 heat pumps that will be removed of my
aquaintenances in the last few years now.


"Abby Normal" wrote in message
ups.com...
What is the time constant as that 60K heat pump warms
up? Would it ever
reach steady state and a COP of 3? Well maybe when it
was running after
the setback period ended.

60,000 steady state heat output, 20,000 load each
hour hmm, wonder how
many times that will cycle on and off drawing LRA?
Well if a dog year
is 7 years, a Nick year must be 3 years.

Maybe assume it takes 15 minutes to stabalize and
work backwards from
there for your time constant.

John P.. Bengi JBengispam@spam@yahoo,com wrote

Why would anybody ever install a heat pump system?

Its cheaper than heating with other forms of electrical heating.

Another friend of mine's heat pump just bit the dust
here at -20C. Going to take weeks to get a part for it.
Pretty expensive portable electric heating going on in
that house right now.

That makes 9 heat pumps that will be removed
of my aquaintenances in the last few years now.


"Abby Normal" wrote in message
ups.com...
What is the time constant as that 60K heat pump warms up? Would it
ever reach steady state and a COP of 3? Well maybe when it was
running after the setback period ended.

60,000 steady state heat output, 20,000 load each hour hmm, wonder
how many times that will cycle on and off drawing LRA? Well if a dog
year is 7 years, a Nick year must be 3 years.

Maybe assume it takes 15 minutes to stabalize and work backwards from
there for your time constant.

wrote:
In scenario 1, keep a house with G = 200 Btu/h-F of thermal conductance at
70 F for 8 hours on a 30 F night with 8h(70-30)200 = 64K Btu from a heat
pump with a 2:1 COP, using 64K/2/3412 = 9.38 kWh of electrical energy.

In scenario 2, the house has C = 10K Btu/F of thermal capacitance and
an RC time constant C/G = 50 hours, so it cools from 70 F at midnight
to 30+(70-30)e^(-8/50) = 64.1 at 8 AM. The house returns instantly to
70 F at 8 AM, with powerful strip heaters that consume (70-64.1)10K
= 59K Btu, or 17.3 kWh, almost twice scenario 1.

In scenario 3, the house has a wimpy 10K Btu/h heat pump with a 30+10K/200
= 80 F Thevenin equivalent temp and no strip heaters. It cools to a minimum
temp T (F) in t hours and reheats in 8-t hours, so T = 30+(70-30)e^(-t/50)
and 70 = 80+(T-80)e^(-(8-t)/50) and t = 1.7 h and T = 68.7 F. Reheating for
6.3 hours takes 6.3x10K/2/3412 = 9.23 kWh, with a small setback savings.

More typically, with C = 5K and G = 500 and RC = 10 hours and a 60K Btu/h
heat pump with a COP of 3 and a 30+60K/500 = 150 F equivalent temp, we
would use 8h(70-30)500/3/3412 = 15.63 kWh in scenario 1. In scenario 2,
the house would cool to 30+(70-30)e^(-8/10) = 48.0, and the heaters would
consume (70-48)5K/3412 = 32.24 kWh at 8 AM. T = 30+(70-30)e^(-t/10) and
70 = 150+(T-150)e^(-(8-t)/10), so t = 6.0 h and T = 52.0 in scenario 3.
Reheating takes 2.0x60K/3/3412 = 11.9 kWh, for a big setback savings.


You have way too much time on your
hands....:-)

Marsha/Ohio

John P.. Bengi wrote:
Why would anybody ever install a heat pump system?

Another friend of mine's heat pump just bit the dust
here at -20C. Going to take weeks to get a part for it.
Pretty expensive portable electric heating going on in
that house right now.

Where I live, according to weatherbase.com, the lowest temperature
ever recorded in the last 48 years is -18C (-2F). In an average
year, there are only 19 days when it even dips below 0C (32F).
Our average snowfall each year is 0.9 inches.

So, here, heat pumps wouldn't have cold temps to deal with. On the
other hand, plain old resistive heat is really not that expensive,
so heat pumps might not even be worth it.

- Logan

John P.. Bengi wrote:
Why would anybody ever install a heat pump system?

Another friend of mine's heat pump just bit the dust
here at -20C. Going to take weeks to get a part for it.
Pretty expensive portable electric heating going on in
that house right now.

That makes 9 heat pumps that will be removed of my
aquaintenances in the last few years now.


Air source getting yanked out of Southern Ontario?



"Abby Normal" wrote in message
ups.com...
What is the time constant as that 60K heat pump warms
up? Would it ever
reach steady state and a COP of 3? Well maybe when it
was running after
the setback period ended.

60,000 steady state heat output, 20,000 load each
hour hmm, wonder how
many times that will cycle on and off drawing LRA?
Well if a dog year
is 7 years, a Nick year must be 3 years.

Maybe assume it takes 15 minutes to stabalize and
work backwards from
there for your time constant.

Slowly but surely, I guess. I become more glad with
each year I didn't indulge.

With NG 1/3 of the price of electricity here, the
reliability very poor, and a complete backup system
required anyway, I doubt they will be selling many of
them anymore.

Sounded good in the 80s though.

"Abby Normal" wrote in message
ups.com...
Air source getting yanked out of Southern Ontario?

Confirming yet again that you're a clueless asshole.

On Thu, 15 Dec 2005 19:24:08 -0500, "John P.. Bengi"
JBengispam@spam@yahoo,com wrote:

Slowly but surely, I guess. I become more glad with
each year I didn't indulge.

With NG 1/3 of the price of electricity here, the
reliability very poor, and a complete backup system
required anyway, I doubt they will be selling many of
them anymore.

Sounded good in the 80s though.

"Abby Normal" wrote in message
oups.com...
Air source getting yanked out of Southern Ontario?



--

Click here every day to feed an animal that needs you today !!!

http://www.theanimalrescuesite.com/

Paul ( pjm @ pobox . com ) - remove spaces to email me
'Some days, it's just not worth chewing through the restraints.'
'With sufficient thrust, pigs fly just fine.'
HVAC/R program for Palm PDA's
Free demo now available online http://pmilligan.net/palm/

Air source were useless in NW Ontario, ground source worked.
John P.. Bengi wrote:
Slowly but surely, I guess. I become more glad with
each year I didn't indulge.

With NG 1/3 of the price of electricity here, the
reliability very poor, and a complete backup system
required anyway, I doubt they will be selling many of
them anymore.

Sounded good in the 80s though.

"Abby Normal" wrote in message
ups.com...
Air source getting yanked out of Southern Ontario?

A couple of things to mention.

1) The COP of the heat pumps I normally install is greater than 3.5
when the outdoor temperature is 47 degrees when heating and greater
than 2.5 at 17 degrees outdoor temperature when heating. The COP of
strip heat is ALWAYS 1.0. In my area it does not often get below 20
degrees outside temperature. Even at 0 degrees the COP of air to air
heat pumps manufactured in the last 20 years will be at least 1.5.
More efficient units will have a COP of 1.7 to 2.0 under the same
conditions. Look it up in your engineering data guys.

2) The heat output of air to air heatpumps drops as it gets colder
outside while the heat load of the house goes up under the same
conditions.

3) The balance point of most properly sized heat pumps is around 35
degrees outdoor temperature. That means that most properly sized heat
pumps without heat strips cannot heat the house to 75 degrees indoors
when it is below 35 degrees outdoors. Therefore when it is below 35
degrees outdoors, such as at night, the compressor will run constantly
and the heat strips will cycle on & off to maintain comfort.

4) As an experiment, I installed a setback thermostat in my house 10
years ago. I locked out the strip heat and programmed the temperatures
at 68 degrees setback at 11:00 PM and 75 degrees setup at 5:00 AM. The
heat pump started running constantly at 5:00 AM and did not bring the
temperature back up to 75 degrees till after 5:00 PM. The day time
temperatures were in the mid 50s and the nighttime temperatures wewre
in the mid 20s.

5) Setback thermostats were originally designed to save money
operating oversized fossil fuel furnaces. If your heat pump is
properly sized by the cooling load, it will not be able to recover in a
reasonable amount of time whithout using the strip heat. Therefore,
you will either be cold much of the time in the winter or your electric
bill will INCREASE with a setback thermostat. NOTE: If your heat pump
is oversized the setback penalty will be reduced, but the fact it is
too big will reduce the effective efficiency all year long. NOTE also
that setback thermostats WILL save money in the cooling season, even
when the heat pump is properly sized.

For what it is worth. Measured data, not guesses.

Stretch

Note to the people who will raise cain about my post: I can email you
PDFs of some Lennox engineering data if you wish to check my figures.
If you are Lennox or Carrier or Trane dealers, you should have the same
sort of data available to you in printed form.

Stretch

I also know of two ground source units that have bit
the dust and were never replaced due to costs compared
to gas here. I have heard longer life with the ground
source units though. The air source units had too many
freeze up problems with rainy freezing weather then the
"defrost" cycle had to be brought in and the unit was
never big enough to handle the BTU load anyway so the
backup was cutting in from timte to time.


"Abby Normal" wrote in message
oups.com...
Air source were useless in NW Ontario, ground source
worked.
John P.. Bengi wrote:
Slowly but surely, I guess. I become more glad with
each year I didn't indulge.

With NG 1/3 of the price of electricity here, the
reliability very poor, and a complete backup system
required anyway, I doubt they will be selling many
of
them anymore.

Sounded good in the 80s though.

"Abby Normal" wrote in
message

ups.com...
Air source getting yanked out of Southern
Ontario?

Stretch wrote:
A couple of things to mention.

1) The COP of the heat pumps I normally install is greater than 3.5
when the outdoor temperature is 47 degrees when heating and greater
than 2.5 at 17 degrees outdoor temperature when heating. The COP of
strip heat is ALWAYS 1.0. In my area it does not often get below 20
degrees outside temperature. Even at 0 degrees the COP of air to air
heat pumps manufactured in the last 20 years will be at least 1.5.
More efficient units will have a COP of 1.7 to 2.0 under the same
conditions. Look it up in your engineering data guys.

2) The heat output of air to air heatpumps drops as it gets colder
outside while the heat load of the house goes up under the same
conditions.

3) The balance point of most properly sized heat pumps is around 35
degrees outdoor temperature. That means that most properly sized heat
pumps without heat strips cannot heat the house to 75 degrees indoors
when it is below 35 degrees outdoors. Therefore when it is below 35
degrees outdoors, such as at night, the compressor will run constantly
and the heat strips will cycle on & off to maintain comfort.

4) As an experiment, I installed a setback thermostat in my house 10
years ago. I locked out the strip heat and programmed the
temperatures at 68 degrees setback at 11:00 PM and 75 degrees setup
at 5:00 AM. The heat pump started running constantly at 5:00 AM and
did not bring the temperature back up to 75 degrees till after 5:00
PM. The day time temperatures were in the mid 50s and the nighttime
temperatures wewre in the mid 20s.

5) Setback thermostats were originally designed to save money
operating oversized fossil fuel furnaces. If your heat pump is
properly sized by the cooling load, it will not be able to recover in
a reasonable amount of time whithout using the strip heat. Therefore,
you will either be cold much of the time in the winter or your
electric bill will INCREASE with a setback thermostat. NOTE: If
your heat pump is oversized the setback penalty will be reduced, but
the fact it is too big will reduce the effective efficiency all year
long. NOTE also that setback thermostats WILL save money in the
cooling season, even when the heat pump is properly sized.

One obvious approach would be to have two,
use one in the summer and both in the winter.

For what it is worth. Measured data, not guesses.

I only sold ground source in areas where gas was not available.
Compared to propane, oil and straight electric they are viable.

I had an opportunity to sell one in a gas area and it would have saved
about $100 per year over high-efficiency gas, but talked the customer
out of it as he would have spent perhaps 6 grand more than the gas
furnace with central ac.


John P.. Bengi wrote:
I also know of two ground source units that have bit
the dust and were never replaced due to costs compared
to gas here. I have heard longer life with the ground
source units though. The air source units had too many
freeze up problems with rainy freezing weather then the
"defrost" cycle had to be brought in and the unit was
never big enough to handle the BTU load anyway so the
backup was cutting in from timte to time.


"Abby Normal" wrote in message
oups.com...
Air source were useless in NW Ontario, ground source
worked.
John P.. Bengi wrote:
Slowly but surely, I guess. I become more glad with
each year I didn't indulge.

With NG 1/3 of the price of electricity here, the
reliability very poor, and a complete backup system
required anyway, I doubt they will be selling many
of
them anymore.

Sounded good in the 80s though.

"Abby Normal" wrote in
message

ups.com...
Air source getting yanked out of Southern
Ontario?

Stretch wrote:
A couple of things to mention.

1) The COP of the heat pumps I normally install is greater than 3.5
when the outdoor temperature is 47 degrees when heating and greater
than 2.5 at 17 degrees outdoor temperature when heating. The COP of
strip heat is ALWAYS 1.0. In my area it does not often get below 20
degrees outside temperature. Even at 0 degrees the COP of air to air
heat pumps manufactured in the last 20 years will be at least 1.5.
More efficient units will have a COP of 1.7 to 2.0 under the same
conditions. Look it up in your engineering data guys.

2) The heat output of air to air heatpumps drops as it gets colder
outside while the heat load of the house goes up under the same
conditions.

Yep the lower the temperature source the lower the heat output.

3) The balance point of most properly sized heat pumps is around 35
degrees outdoor temperature. That means that most properly sized heat
pumps without heat strips cannot heat the house to 75 degrees indoors
when it is below 35 degrees outdoors. Therefore when it is below 35
degrees outdoors, such as at night, the compressor will run constantly
and the heat strips will cycle on & off to maintain comfort.

4) As an experiment, I installed a setback thermostat in my house 10
years ago. I locked out the strip heat and programmed the temperatures
at 68 degrees setback at 11:00 PM and 75 degrees setup at 5:00 AM. The
heat pump started running constantly at 5:00 AM and did not bring the
temperature back up to 75 degrees till after 5:00 PM. The day time
temperatures were in the mid 50s and the nighttime temperatures wewre
in the mid 20s.

Yep not arguing there, 75 is on the high side tho for a winter set
point. A setpoint of 68 to 70 set back to 60-65 overnight will be
similar tho. Running without heat strips will take a long time to bring
temperature back up and would need the help of the sun, unless of
course the heat pump is sized for triple the heat load .

I have seen ground source sized to the heating load in Canada and end
up being 100% oversized for cooling. In this situation the summer
humidity was still low enough as to not be problematic and create an
overly humid, mold condusive indoor environment in the summer.

A system sized for the full heat load, in a warmer climate with a hot
humid summer most likely will be oversized for cooling and enf up with
high indoor RH in summer. Just imagine what something sized for 3 times
the heating load will do in summer.



5) Setback thermostats were originally designed to save money
operating oversized fossil fuel furnaces. If your heat pump is
properly sized by the cooling load, it will not be able to recover in a
reasonable amount of time whithout using the strip heat. Therefore,
you will either be cold much of the time in the winter or your electric
bill will INCREASE with a setback thermostat. NOTE: If your heat pump
is oversized the setback penalty will be reduced, but the fact it is
too big will reduce the effective efficiency all year long. NOTE also
that setback thermostats WILL save money in the cooling season, even
when the heat pump is properly sized.

No arguement there. A unit oversized to the point of not needing heat
strips to recover from a setback would short cylce in heating as well
as cooling.

For what it is worth. Measured data, not guesses.

Stretch

Be a little windy inside in the winter, but you could size one system
to the cooling load, look at its winter heat output then size the
second one to make up the difference .

You would eliminate heat strips for maintaining comfort but you would
still need heat strips to recover from the setback. If you want to live
with the lowered temperature while the system is trying to recover, why
set it back in the first place? Wear wool socks, bunny slippers, long
underwear and a sweater all winter.

Making the second heat pump large enough so that the combined heat
output was triple the design heat load, would eliminate the heat strips
on the set back but you have the problem of the second system short
cycling all the time except when revovering from the setback.

Steve Scott wrote:
Why not dual fuel? HP and whatever is the cheapest fuel for the
backup.

On 16 Dec 2005 06:00:02 -0800, "Abby Normal"
wrote:

Be a little windy inside in the winter, but you could size one system
to the cooling load, look at its winter heat output then size the
second one to make up the difference .

You would eliminate heat strips for maintaining comfort but you would
still need heat strips to recover from the setback. If you want to live
with the lowered temperature while the system is trying to recover, why
set it back in the first place? Wear wool socks, bunny slippers, long
underwear and a sweater all winter.

Making the second heat pump large enough so that the combined heat
output was triple the design heat load, would eliminate the heat strips
on the set back but you have the problem of the second system short
cycling all the time except when revovering from the setback.


--
If you choke a smurf, what color does
it turn?

Dual fuel is practical, seems the arguement is being to setback heat
pumps.

Abby Normal wrote
Rod Speed wrote
Stretch wrote

5) Setback thermostats were originally designed to save money
operating oversized fossil fuel furnaces. If your heat pump is
properly sized by the cooling load, it will not be able to recover in
a reasonable amount of time whithout using the strip heat.
Therefore, you will either be cold much of the time in the winter or
your electric bill will INCREASE with a setback thermostat. NOTE:
If your heat pump is oversized the setback penalty will be reduced,
but the fact it is too big will reduce the effective efficiency all
year long. NOTE also that setback thermostats WILL save money
in the cooling season, even when the heat pump is properly sized.

One obvious approach would be to have two,
use one in the summer and both in the winter.

Be a little windy inside in the winter, but you could size
one system to the cooling load, look at its winter heat
output then size the second one to make up the difference .

Yeah, that's what I meant.

You would eliminate heat strips for maintaining comfort but
you would still need heat strips to recover from the setback.
If you want to live with the lowered temperature while the
system is trying to recover, why set it back in the first place?

The other possibility is to stop the setback well before you get up.

Wear wool socks, bunny slippers, long underwear and a sweater all winter.

Making the second heat pump large enough so that the combined
heat output was triple the design heat load, would eliminate the heat
strips on the set back but you have the problem of the second system
short cycling all the time except when revovering from the setback.

You could obviously have 3 systems but thats not likely to be
economic unless you are using close to free surplus systems.

When it is sized to the load the problem is it would only shut off for
an hour or two as the house cooled, then it would run steady until
after the sun came up to catch up. No real point in setting back.

The only way set back works with a heat pump is if it is grossly
oversized. All that accomplishes is set back without auxiliary heat. It
would short cycle inefficiently except for when it was trying to
recover from a set back.

In an environment with an ambient dewpoint above 60F there will be
problems with a grossly oversized system in cooling mode.