"Christian McArdle" wrote in message
...

The W-Bosch setup. Do they do
extra controls for DHW and CH and it diverts
to suit? I can't remember now.

It's a diverter, rather than a 3 way.
DHW priority and separate flow temp
controls.

Is this two separate knobs on teh panel: DHW and CH temps?

The DHW side is limited to 75C.
The CH side to 85C. I would have
preferred it the other way round as
I have indirect heat bank heating and
would have liked 82-85C for the hot
water and 70C for the heating,

Sounds Greek to me. Oh being PR here is that racist?

but it should be possible to
swap the sides (possibly with a
relay to invert the priority).

See the tech dept, they will proabbly tell you how to reverse

IIRC, the W-B maintains a constant
flow temp and modulates to maintain
that.

That is my understanding and why I
think it would be possible to run the hot
water from the CH side.

You can install your own diverter valve
and fit a weather compensator. It
will switch in and out the boiler to maintain
the compensator setpoint,
which will be low most of the time.
Compensators have anti-cycle control
on them.

How would you get it to go hotter for
the water with an external diverter?

Set the boiler to maximum temp. When DHW calls, the compensator is switched
out via a relay. When DHW is satisfied back onto compensator control. The
compensator switches the burner (could be in the room stat circuit), the
relay just takes this in and out to what flow temp it wants to maintain.
The boiler should have anti-cycle control, so no constant click-click, of
the burner, and the compensator should have anti-cycle control too. But it
may not modulate the burner as the setpoint is maximum on the boiler, and
may only modulate to what that is set to.

Some boilers have all this built-in. The MAN/Eco-Hometec, Viessmann ranges
do. But these are serious money, but with quality to suit. It would be
cheaper, and simpler, to have two cheaper quality boilers, such as the Glow
Worms (Vaillants), which are small in physical size too. One for DHW only
set to max temperature, and one for CH only on a weather compensator. No
3-way valves. Having a few isolation valves could bring one in to do both if
one is down, so backup if needed.

Is this two separate knobs on teh panel: DHW and CH temps?

Yes. The combi and system both have the same panel with DHW and CH temp
controls. In normal use, the system boiler DHW temp knob has no function
unless the diverter is specified. The new range may be different, I have no
idea. The system boiler still needs the DHW temp control even without the
diverter, as it is used by the software to control the installer menus.

In actual fact, both DHW and CH are normally limited to 75C. To get more on
the CH side, you have to remove a stop on the knob that physically prevents
you turning it up further. Unfortunately, no such stop exists to remove on
the DHW side. Presumably they didn't conceive of heat banks and TMVs in the
design.

Christian.

"Christian McArdle" wrote in message
...

Is this two separate knobs on the
panel: DHW and CH temps?

Yes. The combi and system both
have the same panel with DHW
and CH temp controls. In normal
use, the system boiler DHW temp
knob has no function unless the
diverter is specified. The new range
may be different, I have no idea.
The system boiler still needs the
DHW temp control even without the
diverter, as it is used by the software
to control the installer menus.

On the heating boiler there is no DHW know at all, so I assume this cannot
have this three way valve.

In actual fact, both DHW and CH
are normally limited to 75C. To get
more on the CH side, you have to
remove a stop on the knob that
physically prevents you turning it
up further. Unfortunately, no such
stop exists to remove on
the DHW side. Presumably they
didn't conceive of heat banks and
TMVs in the design.

Does the DHW mode modulate? The boiler doesn't really care if water is sent
to CH or DHW. Changing over the CH and DHW pots so that the DHW markings
turn the CH and reversing the ports on the 3-way valve should get around the
low temp settings on the DHW.

Is this 3-ways valve a kit to add on? Or factory fitted?

Nope. If you take water out at 25C and return it at 45C, then it will heat
the heatbank, even if most of it was previously at 75C and the hot water is
deposited at the top.

Now I am totally confused! Assuming that we are starting from cold, UFH
is on and as you have stated the return temp is at 25C. Boiler lifts
the temp by 20C so we now have a flow at 45C. How can that possibly
heat the bank to any higher than 45C.
Lets assume no UFH and we are calling for hot water. The heat bank is
heated to say 75C. UFH now calling; If water is subsequently passed
through this at 45C how can it still heat the bank. My initial
assumption is that it would draw heat from the bank. If not then how
does a thermal store actually heat the hot water as it passes through
its coil?
Thanks
Legin

"legin" wrote in message
oups.com...
Nope. If you take water out at 25C and return it at 45C, then it will
heat
the heatbank, even if most of it was previously at 75C and the hot water
is
deposited at the top.

Now I am totally confused! Assuming that we are starting from cold, UFH
is on and as you have stated the return temp is at 25C. Boiler lifts
the temp by 20C so we now have a flow at 45C. How can that possibly
heat the bank to any higher than 45C.

The water requires another pass through the boiler to gain take it to 65C
You could put two boilers in series so the first raise to 45C and then input
to the second boiler which then raise it again. Realistically, the boiler
will raise about 35C, so nearly two passes of heat bank water through the
boiler.

Lets assume no UFH and we are calling for
hot water.

So 75C water passing thought the plate heat exchanger and cooling the bottom
of the cylinder.

The heat bank is heated to
say 75C. UFH now calling;

So water out the top at 75C for DHW and water out the bottom UFH section at
about 50C - 60C.

If water is subsequently passed
through this at 45C
how can it still heat the bank.

I don't know what you mean. I think you mean that the return water (water
in the bottom of the heat bank) is about 25C. The boiler only comes in when
the store of water cools significantly to reheat in one long efficient burn.
The store temp would be around 60C at the top before the boiler comes in.
So, water enters the boiler at say 25C the boiler raises it 35C, that is 60C
entering the top of the store, then as the store water is passed through the
boiler it re-heats. A tall thin store may mean the top temp never gets
below 65C, and most of the store water is much less than this. But if you
want 75C entering the top of the store you fit a blending valve on the
boilers flow and return pipe. This ensures the store water passes only once
through the boiler, and only water of 75C enters the top of the store.

See:
http://www.heatweb.com/products/cylinders/gxv/operation/gxoperation.html
On the boiler return there is a blending valve.

My initial assumption is that it would
draw heat from the bank. If not then how
does a thermal store actually heat the
hot water as it passes through its coil?

See above.

"Christian McArdle" wrote in message
...
If that is the case, what will be the flow temp. Assuming that the
boiler will lift the temp say 20 degrees. If the return temp is say 45
then the flow temp will be 65. Going through a heat bank previously
heated to say 75, then it will have a cooling effect on the heatbank.

Nope. If you take water out at 25C and return it at 45C, then it will heat
the heatbank, even if most of it was previously at 75C and the hot water
is
deposited at the top.

Is there not a boiler out there that could supply heating to the
heatbank at say 75 degrees until it is totally satisfied then
reduce its temp down to say 65, to ensure that the return is
well within the condensing range.

Worcester Bosch Greenstar System with the optional diverter valve allows
separate setting of water and CH temperatures.

I checked this out. It cannot operate at different temperatures on CH and
DHW. The tech man on the phone was a bit slow with poor product knowledge,
but he said the boiler can only give out one temperature on CH and DHW with
the diverting valves fitted, which can only be fitted on system boilers.

It can be done externally, but the modulation would not work that well, as
you are just switching in and out the boiler to weather compensator or pipe
stat. You can brake into the control circuitry, if you know what you are
doing, and ad another temp pot, but that is very much another thing and the
guarantee would be void.