On Thu, 2 Sep 2004 00:24:06 +0100, "IMM" wrote:


"Andy Hall" wrote in message
.. .
On Wed, 1 Sep 2004 22:49:17 +0100, "IMM" wrote:


"Dave" wrote in message
...
Thanks to all for the responses.
It looks like the answer is a Worcester Greenstar

Good choice.

running vented into a
direct heatbank

Sounds good.

with a zone
valve for the rads

One zone valve for the radiators
and a second for the heatbank would
be the most appropriate, or a diverter valve.

Located where?

On the boiler flow with one zone or diverted branch going to the
heatbank and the other to the radiators.




Errm no. The rads taken off the heat bank using a pump and a check
valve.

This is not the best way to connect the radiators.

Oh my God.

How can I help you?

It is the best way.

Not for a condensing boiler.



Apart from needing
an extra pump, it is not the most
efficient way for the boiler to
work.

What the hell are you on about?

To circulate the water from the heatbank through the radiators and
back requires a pump unless you use the one used for the DHW heat
exchanger and zone or diverter valves.




For the heatbank to be useful,
it needs to operate at the highest
temperature possible in order to
store the maximum amount of energy.
This is true throughout the year.
The minimum useful flow
temperature to the heatbank is 75 degrees,
with 82 being better.

You split the cylinder with a flow and return on the upper DHW section and a
flow and return on the lower heating section. The lower section can run at
a lower temp than the upper.

You mean two separate flows and returns from the boiler?
That would mean more complexity and the boiler is still unable to
properly detect the heat load of the radiators, because the heatbank
is still in the middle.

If you meant on the radiator connections, there is no value in having
a reduced temperature flow and return to the radiators if the boiler
is connected to the top and bottom of the heatbank. That simply
reduces the rate of heat delivery to the radiators for a given water
flow. It won't alter what the boiler sees, other than a reduced rate
of energy use. To feed the heatbank it still has to attempt to meet
the storage temperature.

Best use an outside weather compensator and
have the temp senor on the lower cylinder section. Both sections only need
a pump and check valve each from the boiler, with the DHW having priority.

The outside temperature sensor is simply another control term for the
boiler when used for space heating. It doesn't alter the behaviour of
the heat bank load which will effectively damp the detection that the
boiler would have had of the return temperature directly from the
radiators.


The compensator will ensure the rad circuits will run at low temperatures
most of the time promoting condensing efficiency.

It isn't the operating temperature of the radiators that matters,
it's what the boiler can see. Having a large energy store in the
way, screws up the control that is intended for a condensing boiler -
i.e. to see the heating load and modulate finely..

This is why the heat bank should be used as an energy store for the
hot water and not to run the radiators when a condensing boiler is the
main or only heat source.






For the condensing boiler to run most
efficiently

snip

see above.



..andy

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