"Andy Hall" wrote in message
...
On Sun, 14 Nov 2004 02:28:55 -0000, "IMM" wrote:


It is. You have never dealt with boiler manufacturers.

I have actually - several - and thoroughly tested their technical
departments.

Once.

Actually several times for myself and for others as well.

You can count on one hand and have fingers to spare. On some commercial
boilers, the company I once worked for knew more about their boilers than
they did. We were maintaining them on a daily basis, they were not.

However, to be fair to them, what proportion of Ferroli's target
customer base is likely to combine two combis in the way
you describe? One in a thousand? It's not going to be one in ten.

Not the point. They are supposed to know their product and systems in
general. They don't.

Why? They are there to support the
requirements of the vast majority
of their customer base.

They are supposed to know their product and systems in general, they do not.

For a domestic boiler, this is going to
mainly be installers of single boilers in houses.
How often do you imagine they get questions
on how to hook two of them together? Once
a year? Twice?

Probably more than you think. Not the point, they are supposed to know
their product and systems in general, they do not.

The ouput of the boiler falls, not the temperature given to the building.

If the output falls it's as a direct or
indirect consequence of the
building requiring less heat and
does not imply that the burner is
cycling to do it.

But will cycle and sooner than load compensation.

It may not be the same mechanism
as load compensation, but the effect
is crudely the same - the boiler
does not cycle in the same way as
one with full power on/off would.

You have lost it. It reduces cycling.

That makes no sense. If the output is reduced, it results in less
heat transfer. If the heat requirement of the load is matched by
the boiler running at lower output, why would the boiler cycle.
Your argument only holds true if the boiler output exceeds the load
requirement.

they have temperature sensing and
electroniics to optimise behaviour.

Only the up market expensive boilers.

Modulation is still based on sensing *a* temperature somewhere and
modulating on the basis of it. My point was that the argument that
a heatstore is needed to stop cycling is really not true for this
type of boiler.

An expensive load compensation boiler, not flow setpoint modulation.

The issue is that the output is reduced -
the boiler modulates down, not off.

I recently fitted a W-B Greenstar heating boiler coupled to a heat bank. It
modulates on flow setpoint. Fine for a heat bank. More expensive load
compensation would lower the flow temp. Not what I want.

If the monitored point is maintaining the flow temperature set point,
then inevitably if the load reduces, the burn rate will be reduced to
match it - otherwise why have modulation?

They all eventually cyclcle. With aheat bank, correctly wired, they do NOT.

DPS are intimating that cycling is going to be a
big issue needing a thermal store *unless* there
are some electronics and modulation.

Correct.

Most condensing boilers are modulating
types so they are really trying to make
a selling point out of what has become a
corner case.

You don't understand the various types of modulation.

Actually I do.

You don't.

However the point is that the power output is being reduced.
Their argument and yours is based on an assumption of cycling.
Where does this arise unless the heat required is less than the
minimum that the boiler can do?

Cycling will occur.

With a heat bank high efficiencies can
gained from a very simple cheap
condensing boiler. A great bonus.

It becomes an equation between

a) simple boiler (and there seem to be few new ones coming onto the
market like that)

I just mentioned one. I can name a few more too.

plus heatbank, or

b) boiler with modulation.

The only bonus in a) for the customer is if he has to use a simple
boiler for other reasons or is the cost of a) is less than b)

A heat bank plus simple boiler is cheaper than an expensive load
compensation model plus a heat bank or unvented cylinder.

AND... the heat bank creates a brilliant

- buffer-store
- neutral-point
- anti-boiler-cycle
- instant mains pressure hot water
- all the benefits of using plate heat exchanger, etc,etc.
- no expensive high tech boiler to expensively go wrong.

Nothing wrong with high tech boilers when the need dictates, but why bother
when you can get the same plus more and a simple cheaper more reliable
boiler.

NO contest.

snip babble about attempting to justify an expensive purchase