"Jeff Layman" wrote in message
...
On 18/05/19 10:33, Harry Bloomfield wrote:

Our new Vailant can inteligently decide just how much heat it needs to
produce to meet its desired room temperatures, taking into
consideration the outdoor temperature and indoor. It doesn't overshoot,
rather it learns what is needed and can modulate right down to match
the demand. The pipes don't creak and moan anymore.

Well, I really am willing to be educated, but I really don't understand
what it is supposed to be doing to "intelligently" decide something.
Firstly, I assume that as with almost any device, it will have a "sweet
spot" where it is working at its highest efficiency.

Not necessarily and it isnt always highest efficiency that matters,
in some situations getting the house up to the temperature you
want as quickly as possible without any overshoot at all is what
is needed when changing the house temperature significantly,
like when its been off when there is no one in the house and
someone has showed up, or when going between overnight
and normal temps when someone gets up etc.

Its specs may state "85%" efficient, but in practice that might mean from
a low of 82% to a high of 88%. Now it should be operating as near to 88%
all the time as it can, but obviously there are constraints - it won't be
so efficient starting from cold, for example.

And that last is what matters more to most comfort wise.

As far as I am concerned, when the room thermostat calls for heat, the
boiler should go flat out to heat the room as quickly as possible.

Not when that produces an overshoot in temperature.

In any case, it's the room thermostat which tells the boiler what to do,
and it's the thermostat's hysteresis which is the arbiter of how
comfortable or uncomfortable you will be. I've switched ours to the lowest
hysteresis possible, which is +/- 0.5 deg C. That may mean the boiler in
on/off more frequently, but I'm a lot more comfortable with the room at a
steady 20.5 - 21.5 deg C, than I would be at 19 - 23 deg C.

Yes, but thats a different issue to how intelligent the control is.

And does it really matter most of the time what the outside temperature
is? It will almost always be much lower than the room temperature, and so
maximum heat will be required to warm the room up.

Not when you know that the difference between the inside and
the outside isnt as great and that it doesnt need maximum heat
to adjust the house temperature in a reasonable time. It may well
be better to not use maximum heat when say it is changing from
overnight lower temp to normal daytime temp when the occupant
who has just got up has a shower as soon as they get up and so
wont notice that the house isnt at the daytime temp for a while.

Also when the control has been told to heat the house when
the first person has come home from work, it may well make
sense to use maximum heat when it has observed that the
house takes a long time to get up to temperature when the
outside temperature is so low the last time it had to do that,
say because the insulation leaves quite a bit to be desired.

The previous boiler either ran and produced full heat, or none, though
it did modulate, it only modulated based on its internal temperature.

Having said all the above, I see from the manual of my W-B Greenstar that
:
"The gas supply to the burner is controlled according to the level of
demand for heat. The boiler operates with a low flame if the demand for
heat reduces. The technical term for this process is modulating control.
Modulating control reduces temperature fluctuations and provides an even
distribution of heat throughout the home. This means that the boiler may
stay on for relatively long periods of time but will use less gas than a
boiler that continually switches on and off."

Out of interest, does your boiler's spec state that it is most efficient
when it is ticking over (or whatever it is doing to decide what heat it
needs to supply)?

So exactly how does the boiler do what it's supposed to do?

By observing what has happened the last time it
needed to heat the house in those circumstances.

You set the boiler hot water temperature to the rads at, for example, 60
deg C, and you set the room temperature thermostat to 20 deg C, and the
hysteresis to 1 deg C. How exactly does it (in the case of my W-B
Greenstar) "operate with a low flame if the demand for heat reduces"?

By knowing how often the thermostat calls for more heat in that situation,
basically getting a measure of how well insulated the house is etc.

How often does the "demand for heat" reduce?

When there is no one home.