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.
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. Apart from needing
an extra pump, it is not the most efficient way for the boiler to
work.
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.
For the condensing boiler to run most efficiently during the much
longer on times than the hot water requires, and accounting for the
lower heat output requirement during spring and autumn, the return
temperature needs to be as low as possible. The boiler will
automatically modulate down to achieve that and the flow temperature
can easily be below 50 and return below 40 degrees.
The efficiency of a condensing boiler increases markedly with reducing
return temperature and especially below the 54 degree dew point.
If you run the radiators from the heatbank, the flow temperature will
be that of the heatbank (i.e. 76-82 degrees). The boiler will come
on full periodically in order to replenish the heatbank and maintain
the required temperature. It has no real way of knowing the
difference between a DHW demand (a lot of heat for a short time) vs.
the CH (relatively little heat continuously).
Thus it will effectlively cycle on and off at around the ste point of
the heatbank, not at what the radiator load requires.
If a conventional boiler were being used, then this would be a
reasonable approach (because they are intended to run at a high single
temperature, but for a condensing one it isn't. It is far better to
connect the heat bank to the boiler and heat that rapidly at full
power and then switch the boiler to the radiators where it can detect
the heat load for the house directly and operate most efficiently
and a second zone valve for
the towel rails and airing cupboard rad.
Taken from where? The boiler primaries? Could be. Is there a need for the
zone valve when you want these on all year around? If off the boiler
primaries (flow and return) then the rails only operate when the bioler
does. If you want them on 24/7 then take then off the heat bank and use a
pump and check valve.
The boiler and cylinder (of
whichever type) will be in the garage
so the F&E tank will need to be in the
loft and the DHW will need a return pipe
to ensure hot water doesn't take
too long to reach the taps.
Can be done with a couple of check valves and DHW circulation pump.
Any other comments?
See above.
..andy
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