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.