Abby Normal wrote
Rod Speed wrote

The problem is shortly after the temperature dropped
to the setback temperature, the heat pump would end
up running steady just to get back up to temperature.

Wrong with the situation being discussed, with
more than one system so it doesnt take a long
time to get it up to the normal temp again.

That is sure economically viable.

The economic viability wasnt being discussed.

To get a heat pump to work with setback, you are oversizing the
system. Either a single oversized unit, or multiple units. It takes a
rediculous situation to make setback work on a heat pump.

Nothing rediculous about using a surplus system to make
setback work in a situation where it isnt economic to
increase the insulation substantially and its quite lossy.

It can be a viable approach, particularly if the normal
temps are only set say in the late afternoon prior to
when the house will be occupied for long when not in bed.

Typically in the temperate states where air source heat pumps are
used, they are sized with the cooling load in mind and use the heat
strips. One sized for the full heat load will be grossly oversized
for cooling resulting in summer time humidity control problems.

And what was being discussed was having more than one
system and doing that so it doesnt take a long time to get back
to the normal temp and doesnt use the heat strips to do that.

Yes multiple systems, now as high as three, just
to prove a point that you can setback a heat pump.

Its just one way to have a viable setback with a heat pump.

The other obvious approach is to have the setback temp right
thru till say 3pm because the occupants arent likely to need the
normal temp in the hour or so when everyone is running around
having showers etc before heading out of the house in the morning.
Then even just a properly sized single system should be able to
come back off setback quickly enough to not use the strips
with a properly designed controller.

Even if it starts coming off setback at say 1pm because it
takes 4 hours to get back to normal temp with those outside
temps, its still going go save power over no setback.

And it may well be possible to design the entire system
so the outside part of the system uses passive solar too
if its only going to come off setback after midday.

The only way set back works with a
heat pump is if it is grossly oversized.

Wrong again.

No not wrong

Yep, completely wrong.

Sure, buy 3 heatpumps to prove set back.

Its just ONE way to make setback viable with a heat pump.

Spend extra money on the ductwork involved
for three systems, including back draft dampers,

You dont need all that stuff for the system thats just ensuring
that you can come off setback without needing to use the strips.

lol what a crock

Couldnt bull**** its way out of a wet paper bag...

just unsucessful in educating you.

You cant even keep track of what was actually being discussed.

Well I believe you were speaking first of
two systems, then realized you needed three,

Wrong. I JUST said that three can be useful in SOME situations.

You dont even need two if you come off setback after midday,
just an adequately sized system that doesnt need to use the
strips on most days in winter. And if passive solar is used to
help with coming back off setback after midday, thats going
to make setback viable even with a heat pump. And wont
necessarily cost much at all hardware wise.

so as not to be short cylcing in the heating mode,
and in the summer having too much sensible cooling
that the stat would be satisfied in 5 minutes run time.

Thats an entirely separate issue to what was
being discussed, the silly pig ignorant claim that
setback can never be viable with heat pumps.

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.

Not if you one of the systems sized so that doesnt happen.

Three systems sure, that is practical,

Doesnt have to be 3, or even 2.

So you are saying size one for the cooling load, one for the
heating load and one for speedy recovery from set back then?

Three heat pumps now.

Yep, I mentioned 3 for a reason.

Plus all the ductwork and backdraft dampers.

You dont have to duplicate/triplicate all of those.

No you could have three systems share a common
supply and return, just get it to work there einstein.

Perfectly possible if you dont have them all running at once, gomer.

Let's try to keep this practical and not go to
hypothetical extremes to prove this is possible.

Wasnt doing anything like that.

No not at all just install three heat pumps. Or two heat
pumps and a central AC. Hey maybe you could get a two
stage one and a central AC. SUre is a lot of tap dancing
to prove that you could viably set back a heat pump.

Just one way to do setback with a heat pump.

Noah er I mean Nick is a bad influence on you.

Nothing to do with Nick at all.

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

Again, not if you have more than one system.

Well like I said if you want to install
three heat pumps, knock yourself out.

Two and three was what was being discussed.

Your claim that setback has no value is just plain wrong with THAT situation.

Setback has a value, just not with heat pumps.

Wrong when stated as absolutely as that. Most obviously
if the setback lasts until after midday and passive solar
is used instead of the strips for coming off setback.

A fossil fuel system sized right on the money for
the heat load in a high thermal mass home may
not be the best system to be setting back either.

Having fun thrashing that straw man are you ?