On Thu, 2 Sep 2004 13:43:17 +0100, "IMM" wrote:


"Andy Hall" wrote in message
.. .
On Thu, 2 Sep 2004 11:31:58 +0100, "Christian McArdle"
wrote:

Only if a conventional boiler or other heating sources are used, not a
modulating condensing boiler.

I'd want to see further testing evidence for this, either way. I'm not
convinced which is more efficient.

Basically, does the higher temperature
burn required to reheat the heat bank
outweigh the fact that the boiler gets to
do occassional full power burns,
rather than cycling, or modulating low.

What tripe. A heat bank eliminates boiler cycling. One person ont his
thread bought one just to do that.

It depends on the type of boiler, and its thermal and control
characteristics. Grunff's application was to absorb a large amount
of heat from an oil boiler when an old coil in cylinder approach, not
surprisingly, couldn't do it.

This is not what we are discussing here, which was specifically the
impact of radiators hooked up to a heatbank. If heat is being
abstracted at a lower rate than the boiler can produce it will either
have to modulate or cycle. If you put a heatbank in the middle, the
dampening effect screws up the condensing boiler's control arrangement
such that it won't be able to modulate properly.





A condensing boiler will operate
more efficiently at lower
temperatures.

Go away.....

Repeated cycling is going to reduce efficiency which
is a second reason why they modulate down
if possible rather than turning on and off.

Once again....A heat bank eliminates boiler cycling. One person ont his
thread bought one just to do that.

Once again, it can under certain circumstances such as when a large
amount of energy is being removed to heat the water. This could be
100kW or more. The boiler, assuming it is less than this will then
come on and run at full power until it is at the set point of the
heatbank.

This is not the same situation as making a lower level continuous use
of heat from the heatbank to run the radiators. It is less than the
boiler's capacity so it has no choice than to modulate or cycle.
having the heatbank in the way, with a cylinder thermostat controlling
the boiler will inevitably lead to cycling.




Remember, that the heat bank might still be providing a reasonably low
return temperature with a very high flow/return differential, which
should
offset some of the problems with regard to condensing.

Yes, but that's only into the cylinder.

NO!!! From the cylinder...to the boiler...called the return.

Yes, but the return is not from the radiators, it is from the
heatbank; the storage effect of which means that the return
temperature that the boiler sees will be that of the heatbank,
together with its dampening effect as opposed to that directly from
the radiators. They are not the same thing, and a cylinder stat has
been added into the equation as well.



in effect, running the
radiators from the heatbank is the equivalent of turning the hot tap
on low. The boiler will come on and attempt to replenish the
heatbank after the thermostat on it drops a few degrees below its set
point.

You have two stats to eliminate boiler cycling. You clearly know nothing
about this sort of thing.

You can't eliminate boiler cycling with a simple thermostat, or even
two of them. They have hysteresis.
If you had temperature probes able to give analogue readings to the
boiler and modulate it, that would be a different matter, but this is
not that.


..andy

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