On Wed, 6 Aug 2003 11:09:33 +0100, "IMM" wrote:



The USA has different water regs to use. They use a hot water cylinder
and
take off fresh water and run it through a non-ferrous UFH system. Many
companies run cold mains water through the same pipe loop by turning a
manual 3-way valve to cool the floor in summer.

Fine, but probably not applicable here. SInce most houses in the
U.S. have timber floors, I wonder where this is used.

It was used in a concrete floor.

Hmmm.


Provided that the cylinder is large enough, which takes us back to the
point that it is only as good as the energy stored plus the energy
that can be delivered into the heatbank from the boiler while the
former is delivering energy to the heat exchanger.

No. The system acts like a combi as a fall back.

Sure, but the performance level will have dropped off.

The point is you "never" run out of hot water. Your hot water is 2 stage of
high flow and then low flow.

That's fine if you find that type of performance acceptable. My
point was to highlight that this low flow situation would happen.

I would prefer to see the cylinder adequately sized regardless of
whether it is used in a conventional way or as a heatbank.



For the same amount of stored energy, the height of the cylinder could
be reduced by 60/76. For a 1500mm high cylinder that would be to
1185mm approx. - a saving of 315mm - about a foot. Enough space to
put a couple of pairs of shoes. Hmmmm. Not a decision making
criterion that seems that big an issue unless you are in a small flat.

And millions are.

.. and millions are not. Either way, I don't see this as a major
selling point. Minor one maybe.

Few British house have space to spare, hence combi boilers account for
60-70% of the one million boilers sold each year.

I don't think that you can deduce that as a causal connection, merely
as a contributing factor. Others are that to an extent, a combi
installation may take some time cost out of installation in new
builds. In terms of replacements, if the water supply and appliance
size are inadequate, we have an unhappy customer since they have
bought a 21st century version of the geyser.




This isn't really relevant because the flow rate through a combi is
the key issue, not the pressure that it will withstand. Pressure
and flow control is required on most mains fed systems anyway,
regardless of technology, in order to balance the flows of hot and
cold to a reasonable extent.

Combi??

To balance at the points of delivery.

It was about unvented cylinders, heat banks.

I said any system using mains fed hot water as opposed to a roof tank.


200 litres is not particularly large and could not be substantially
reduced by the use of heatbank technology as already illustrated.

It could. Store water at 80C and have a large output boiler to assist
when
drawing hot water.

The net equation is still the same. It doesn't matter whether the
boiler is providing the energy via a conventional cylinder or a
heatbank. Once the stored energy is used up, both arrangements fall
back to combi behaviour.

No. With a beat bank the boioers output goes straiught to the DHW draw off.
This si noit the case with a vented or unvented cylinder.

No it doesn't. With a vented or unvented cylinder, the boiler energy
is fed through a coil in the cylinder to heat the DHW in the cylinder.
A heatbank can be indirect or direct. In the indirect case, the
boiler heats a coil in the cylinder in the same way, but the water is
then pumped through a stainless steel heat exchanger to heat the DHW.
In the direct case the cylinder water passes through the boiler but
is still used via the stainless steel heat exchanger to heat the DHW.

..


The only real difference is that in the
heatbank case you have stored 25%
more energy in a given volume or a
small reduction in space.

You don't understand.

I understand perfectly, thanks.




Yes, and unvented cylinders do not have very large coils.

That depends on what you order and from whom.

Again.. unvented cylinders do not have very large coils.

Rubbish. If you order one with a substantial coil, you get one with a
substantial coil. That's exactly what I did. I had the
manufacturer install a pocket for a temperature probe and extra
fittings as well.

You should have fitted a heat bank and then it would be easy to


However, the match of a direct heatbank to a more sophisticated
condensing boiler is not a good one, and this does not leave any
significant advantages for the heat bank, unless one is really tight
on space.

A smart condenser will work well with a heat bank. A heat bank with the
top
half at 76-80C for DHW and the bottom at 45C for UFH works very well with
condensers. A diverter valve sends the boilers output to either section.

We've already had this discussion and I illustrated why this would not
be the case. I'm not going to go over the same ground again.

You don't understand.

Sorry to burst your bubble, but I understand completely.






---

..andy

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