I need to make a decision about the new heating system in the next week or
so; after all the debate and advice here (and lots of web crawling) a DPS
GXV heat bank with a Worcester Greenstar 29HE are still the current
favourites.
A couple of questions:
- I need 3 heating zones, what's the advantage of using a pump for each zone
rather than one pump and 3 zone valves?
- Is there a significant disadvantage in joining the heating returns and
running back to the cylinder in one long'ish pipe or should I run 3 separate
returns?
- Because the cylinder will be in the garage I want a recirculating pump on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?
- Having a directly heated cylinder presumably means there's more delay
between the room stat demanding heat and the rads providing it - is this
noticeable in practise?

Dave S

- I need 3 heating zones, what's the advantage of using a pump for each
zone
rather than one pump and 3 zone valves?

Personally, I don't see one. I would prefer a single pump and multiple zone
valves. The zone valves allow for easier wiring up, without relays or
additional anti-gravity valves. It also lends itself to shared tappings on
the cylinder and is less noisy. Imagine a multizone system with 5 or 6 pumps
whirring away.

- Is there a significant disadvantage in joining the heating returns and
running back to the cylinder in one long'ish pipe or should I run 3
separate
returns?

No disadvantage, provided the pipework is correctly sized for the expected
heat capacity. If slightly undersized, it will be noisy, rather than
ineffective, although gross undersizing will require high pump speeds,
excessive noise and may never reach full capacity.

- Because the cylinder will be in the garage I want a recirculating pump
on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?

Basically, it would require the DHW pump to go full time, which would
destratify the heat bank, so I wouldn't recommend it. Consider installing an
additional plate heat exchanger near the taps and running a primary circuit
out to it, heavily insulated (well in excess of statutory requirements).
Then rig up a low flow pump to keep the heat exchanger and primary warm,
with the main pump firing when a flow switch activates.

- Having a directly heated cylinder presumably means there's more delay
between the room stat demanding heat and the rads providing it - is this
noticeable in practise?

Your premise is incorrect. The radiators will become hot almost immediately,
as the heat bank water is already hot. Such a system will provide the
quickest response to a heat demand. Indeed, the radiators would probably be
getting hot by the time the boiler has managed to ignite.

Christian.

"Christian McArdle" wrote in message
. net...
- I need 3 heating zones, what's the advantage of using a pump for each
zone rather than one pump and 3 zone valves?
Personally, I don't see one. I would prefer a single pump and multiple
zone
valves. The zone valves allow for easier wiring up, without relays or
additional anti-gravity valves.
.... snipped
That's what I thought but the DPS website makes a point of suggesting pumps
without valves - I'll get to the showroom and ask them.

.... snipped
- Because the cylinder will be in the garage I want a recirculating pump
on the DHW but how can this work when the water is just being
recirculated around pipework and not through a heat source?
Basically, it would require the DHW pump to go full time, which would
destratify the heat bank, so I wouldn't recommend it. Consider installing
an
additional plate heat exchanger near the taps and running a primary
circuit
out to it, heavily insulated (well in excess of statutory requirements).
Then rig up a low flow pump to keep the heat exchanger and primary warm,
with the main pump firing when a flow switch activates.
That's an interesting idea. One of the heating zones is for towel rails and
airing cupboard so I could probably use that - it won't be running
permanently but it should be sufficient.

- Having a directly heated cylinder presumably means there's more delay
between the room stat demanding heat and the rads providing it - is this
noticeable in practise?
Your premise is incorrect. The radiators will become hot almost
immediately,
as the heat bank water is already hot. Such a system will provide the
quickest response to a heat demand. Indeed, the radiators would probably
be
getting hot by the time the boiler has managed to ignite.
OK, I was being dumb. I guess it takes a little longer from a cold start but
that's not a very frequent event.

Christian.

Many thanks.
Dave S

"Christian McArdle" wrote in message
. net...
- I need 3 heating zones, what's the advantage of using a pump for each
zone
rather than one pump and 3 zone valves?

Personally, I don't see one. I would prefer a single pump and multiple
zone
valves. The zone valves allow for easier wiring up, without relays or
additional anti-gravity valves.

Pumps valves are available with integrated check valves. See the Gledhill
piccie below. The upper pump valves are larger than the lower.

It also lends itself to shared tappings on
the cylinder and is less noisy. Imagine a multizone
system with 5 or 6 pumps whirring away.

Pumps for each zone is far better. Gledhill use this method see:
http://www.gledhill.net/docs/sm2000.htm

The two pumps to the left could have been one and a mid position 3-way
valve.

Best get DPS to install a heating flow and return on the heat bank for each
zone, then totally independent zones feed from a neutral point (heat bank).

A pump is cheap. A replacement relay at £2.99 is cheap. All win, win,
having a pump for each zone. Much better balancing too.

- Is there a significant disadvantage in joining the heating returns and
running back to the cylinder in one long'ish pipe or should I run 3
separate
returns?

No disadvantage, provided the pipework is correctly sized for the expected
heat capacity. If slightly undersized, it will be noisy, rather than
ineffective, although gross undersizing will require high pump speeds,
excessive noise and may never reach full capacity.

- Because the cylinder will be in the garage I want a recirculating pump
on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?

Basically, it would require the DHW pump to go full time, which would
destratify the heat bank, so I wouldn't recommend it.

See my and Eds post on this.

Consider installing an
additional plate heat exchanger near the taps and running a primary
circuit
out to it, heavily insulated (well in excess of statutory requirements).
Then rig up a low flow pump to keep the heat exchanger and primary warm,
with the main pump firing when a flow switch activates.

Wow! expensive and complex.

- Having a directly heated cylinder presumably means there's more delay
between the room stat demanding heat and the rads providing it - is this
noticeable in practise?

Your premise is incorrect. The radiators will become hot almost
immediately,
as the heat bank water is already hot. Such a system will provide the
quickest response to a heat demand. Indeed, the radiators would probably
be
getting hot by the time the boiler has managed to ignite.

Christian.

the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?

Basically, it would require the DHW pump to go full time, which would
destratify the heat bank, so I wouldn't recommend it. Consider installing an
additional plate heat exchanger near the taps and running a primary circuit
out to it, heavily insulated (well in excess of statutory requirements).
Then rig up a low flow pump to keep the heat exchanger and primary warm,
with the main pump firing when a flow switch activates.


Heat Banks provide Secondary Circulation by the usual means, except
the return tees into the mains in (above flow switch). The heat
exchanger pump can be brought on by a pipe thermostat fitted to
secondary return that will result in circuit being reheated once it
has dropped to stat setting. A clock should always be used.

Note that Pumps are more reliable, less vulnerable to grit, easier to
service, cheaper, and provide pressure gain, rather than loss, over
motorised zone valves. Where an expensive modulating pump is to be
used, zone valves may be more economical however.

"Richard from DPS Heatweb" wrote in message
om...

Heat Banks provide Secondary Circulation
by the usual means, except the return tees
into the mains in (above flow switch). The heat
exchanger pump

Don't you mean the secondary circulation pump?

can be brought on by a
pipe thermostat fitted to secondary return
that will result in circuit being reheated once it
has dropped to stat setting. A clock should
always be used.

Note that Pumps are more reliable, less
vulnerable to grit, easier to service, cheaper,
and provide pressure gain, rather than loss, over
motorised zone valves.

Pumps require a check valve in the circuit. Check valves restrict
flow/pressure, unless the next size up is used, i.e., 28mm on a 22mm pipe.

Where an expensive modulating pump is to be
used, zone valves may be more economical however.

"IMM" wrote in message
...

"Richard from DPS Heatweb" wrote in message
om...

Heat Banks provide Secondary Circulation
by the usual means, except the return tees
into the mains in (above flow switch). The heat
exchanger pump

Don't you mean the secondary circulation pump?

can be brought on by a
pipe thermostat fitted to secondary return
that will result in circuit being reheated once it
has dropped to stat setting. A clock should
always be used.

Sorry, I misread. The pipe stats can switch in the secondary circulation
pump and the DHW plate heat exchanger pump simultaneously. No sense in
having both running when the draw-off pipe is hot.

In an earlier contribution to this discussion,
Dave wrote:

I need to make a decision about the new heating system in the next
week or so; after all the debate and advice here (and lots of web
crawling) a DPS GXV heat bank with a Worcester Greenstar 29HE are
still the current favourites.
A couple of questions:
- I need 3 heating zones, what's the advantage of using a pump for
each zone rather than one pump and 3 zone valves?

With 3 pumps you can match each pump to the requirements of a single
circuit - but the control logic is a lot more complicated, particulrly if
the boiler needs pump over-run (which pump over-runs?)

A single pump has to be able to run all 3 circuits - but on occasions will
only need to run one. Maybe one of these fancy variable output devices
(Alpha or somesuch?) would be worth considering. The control logic is much
simpler - using an S-Plan+ setup.

- Is there a significant disadvantage in joining the heating returns
and running back to the cylinder in one long'ish pipe or should I run
3 separate returns?

It's ok as long as the pipe is big enough for the total flow and as long as
they only combine *after* the last rad return in each circuit. [If any rads
return after the join, you might get reverse circulation round bits of the
system].

- Because the cylinder will be in the garage I want a recirculating
pump on the DHW but how can this work when the water is just being
recirculated around pipework and not through a heat source?

I don't understand this bit! Surely the idea of a heat bank is that DHW is
at mains pressure - and gets heated by the heat bank on its way to the taps?
In this case, how can it be circulated round the taps when there is no
outflow?

- Having a directly heated cylinder presumably means there's more
delay between the room stat demanding heat and the rads providing it
- is this noticeable in practise?

Is this heat bank being used only for DHW, or for heating as well? If it's
also used for heating, you'll need an additional pump and control logic to
make sure that the heatbank is always hot. The room stat will then simply
open a zone valve (and switch on a pump if necessary) to circulate water
through the already hot heat bank to the radiators.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Dave wrote:
....snipped
- I need 3 heating zones, what's the advantage of using a pump for
each zone rather than one pump and 3 zone valves?
With 3 pumps you can match each pump to the requirements of a single
circuit - but the control logic is a lot more complicated, particulrly if
the boiler needs pump over-run (which pump over-runs?)

A single pump has to be able to run all 3 circuits - but on occasions will
only need to run one. Maybe one of these fancy variable output devices
(Alpha or somesuch?) would be worth considering. The control logic is much
simpler - using an S-Plan+ setup.

Good point. So the pumps would be standard 3-speed types, each set to the
optimum speed for that zone and controlled directly by the timers/stats
(possibly with relays).

....snipped
- Because the cylinder will be in the garage I want a recirculating
pump on the DHW but how can this work when the water is just being
recirculated around pipework and not through a heat source?
I don't understand this bit! Surely the idea of a heat bank is that DHW is
at mains pressure - and gets heated by the heat bank on its way to the
taps?
In this case, how can it be circulated round the taps when there is no
outflow?

I don't understand it either but it's a "standard option (!)", Christian has
made a good suggestion so I'll investigate further.

.... snipped
--
Cheers,
Set Square
______

Thanks.
Dave S

"Dave" wrote in message
...
"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Dave wrote:
...snipped
- I need 3 heating zones, what's the advantage of using a pump for
each zone rather than one pump and 3 zone valves?
With 3 pumps you can match each pump to the requirements of a single
circuit - but the control logic is a lot more complicated, particulrly
if
the boiler needs pump over-run (which pump over-runs?)

A single pump has to be able to run all 3 circuits - but on occasions
will
only need to run one. Maybe one of these fancy variable output devices
(Alpha or somesuch?) would be worth considering. The control logic is
much
simpler - using an S-Plan+ setup.

Good point. So the pumps would be standard 3-speed types, each set to the
optimum speed for that zone and controlled directly by the timers/stats
(possibly with relays).

Yep.

...snipped
- Because the cylinder will be in the garage I want a recirculating
pump on the DHW but how can this work when the water is just being
recirculated around pipework and not through a heat source?
I don't understand this bit! Surely the idea of a heat bank is that DHW
is
at mains pressure - and gets heated by the heat bank on its way to the
taps?
In this case, how can it be circulated round the taps when there is no
outflow?

I don't understand it either but it's a "standard option (!)", Christian
has
made a good suggestion so I'll investigate further.

... snipped
--
Cheers,
Set Square
______

Thanks.
Dave S

"Set Square" wrote in message
...
In an earlier contribution to this discussion,
Dave wrote:

I need to make a decision about the new heating system in the next
week or so; after all the debate and advice here (and lots of web
crawling) a DPS GXV heat bank with a Worcester Greenstar 29HE are
still the current favourites.
A couple of questions:
- I need 3 heating zones, what's the advantage of using a pump for
each zone rather than one pump and 3 zone valves?

With 3 pumps you can match each pump to the requirements of a single
circuit - but the control logic is a lot more complicated,

It is simple. use a relay for each pump. Maplins sell a 5A 240v DPDT
miniature relay for 32.99 and 31.50 for the base. It is easy to arrange DHW
priority .

particulrly if the boiler needs pump over-run
(which pump over-runs?)

DHW pump, or heat bank pump.

A single pump has to be able to run all 3 circuits - but on occasions will
only need to run one. Maybe one of these fancy variable output devices
(Alpha or somesuch?) would be worth considering. The control logic is much
simpler - using an S-Plan+ setup.

Not so.

- Is there a significant disadvantage in joining the heating returns
and running back to the cylinder in one long'ish pipe or should I run
3 separate returns?

It's ok as long as the pipe is big enough for the total flow and as long
as
they only combine *after* the last rad return in each circuit. [If any
rads
return after the join, you might get reverse circulation round bits of the
system].

- Because the cylinder will be in the garage I want a recirculating
pump on the DHW but how can this work when the water is just being
recirculated around pipework and not through a heat source?

I don't understand this bit! Surely the idea of a heat bank is that DHW is
at mains pressure - and gets heated by the heat bank on its way to the
taps?
In this case, how can it be circulated round the taps when there is no
outflow?

Mains in - check valve - to plate heat exchanger - out of plate to DHW
taps - returns to the mains in after the check balve - check valve before
the tee - bronze pump just before the tee. On section just before the tee
foit a pipe stat. when the pipe get cold the pump kicks in to circulate hot
water around. The flow will active the DHW heat bank pump. Unt to temp and
the stat cut out and all is off.

- Having a directly heated cylinder presumably means there's more
delay between the room stat demanding heat and the rads providing it
- is this noticeable in practise?

Is this heat bank being used only for DHW, or for heating as well? If it's
also used for heating, you'll need an additional pump and control logic to
make sure that the heatbank is always hot. The room stat will then simply
open a zone valve (and switch on a pump if necessary) to circulate water
through the already hot heat bank to the radiators.
--
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

"IMM" wrote in message
...

With 3 pumps you can match each pump to the requirements of a single
circuit - but the control logic is a lot more complicated,

It is simple. use a relay for each pump. Maplins sell a 5A 240v DPDT
miniature relay for 32.99 and 31.50 for the base. It is easy to arrange
DHW
priority .

Should be:
It is simple. use a relay for each pump. Maplins sell a 5A 240v DPDT
miniature relay for £2.99 and £1.50 for the base. It is easy to arrange DHW
priority .

On Mon, 20 Sep 2004 09:26:50 +0100, Dave wrote:

I need to make a decision about the new heating system in the next week or
so; after all the debate and advice here (and lots of web crawling) a DPS
GXV heat bank with a Worcester Greenstar 29HE are still the current
favourites.
A couple of questions:
- I need 3 heating zones, what's the advantage of using a pump for each zone
rather than one pump and 3 zone valves?

Each pump can be adjusted individually but this can be got around by
balancing the whole system with all the zones active.
There is a huge down side which is that you may get some reverse
flow in the other zone(s) when only 1 or 2 pumps are going.
You can add nonreturn valves to each zone (these may buzz).
You can mitigate the effect by making sure the common feed to all the
pumps is as fat and short as possible.

- Is there a significant disadvantage in joining the heating returns and
running back to the cylinder in one long'ish pipe or should I run 3 separate
returns?

None p[rovided the pipes are suitable sized. However be careful not to return any
radiator seperately to the common return from others in its zone.

- Because the cylinder will be in the garage I want a recirculating pump on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?

From the furthest HW tap (that you want enhanced) or HW
usage point take a small (10mm hep? 8mm microbore?) pipe back to near the
heat bank. Insulate every piece of DHW to very best standard you can manage,
including the return pipe.
Obtain a BRONZE circulating pump (this is like the CH pump but made of
bronze and 5x cost). Put small DHW pipe into the pump inlet. The pump
outlet into the mains cold water inlet. Put pump on very lowest setting,
also only open one of the pump isolating valves a tiny bit. You want a
trickle of water to flow out of the DHW supply form the heat bank but
enough to make the DHW pipe warm/hot but not so much that the returned DHW
is actually warm.
Some poeple say you should put a non return valve in the return circuit,
I think that length of small pipe work and the restriction on the pump
isolating valve should be enough to stop much mains cold being drawn back
and mixed with the HW.
Consider putting pump on timer or PIR so that it only operates at peak
times.
It is a compromise between energy saving and convenience. You will however
save a stack of water as you will have instant(ish) HW.
The heat bank is the heat source and occasionally the boiler will have to
fire to replensih it.


- Having a directly heated cylinder presumably means there's more delay
between the room stat demanding heat and the rads providing it - is this
noticeable in practise?

No! the heat bank stays hot all the while (OK there is a bigger delay after
you come back from holiday). So the hot primary water is ready to send to
the radiators instantly.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

On Mon, 20 Sep 2004 17:29:36 +0100, "Ed Sirett"
wrote:

- Because the cylinder will be in the garage I want a recirculating pump on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?

From the furthest HW tap (that you want enhanced) or HW
usage point take a small (10mm hep? 8mm microbore?) pipe back to near the
heat bank. Insulate every piece of DHW to very best standard you can manage,
including the return pipe.
Obtain a BRONZE circulating pump (this is like the CH pump but made of
bronze and 5x cost). Put small DHW pipe into the pump inlet. The pump
outlet into the mains cold water inlet. Put pump on very lowest setting,
also only open one of the pump isolating valves a tiny bit. You want a
trickle of water to flow out of the DHW supply form the heat bank but
enough to make the DHW pipe warm/hot but not so much that the returned DHW
is actually warm.
Some poeple say you should put a non return valve in the return circuit,
I think that length of small pipe work and the restriction on the pump
isolating valve should be enough to stop much mains cold being drawn back
and mixed with the HW.
Consider putting pump on timer or PIR so that it only operates at peak
times.

Hi,

Or, use a pipe stat as well to run the pump so it only circulates DHW
when the pipe has cooled down.

This will help to keep the DHW in the heat bank stratified, and has
the advantage that it is more responsive to timer or PIR control.

Another option is to save on an expensive pump is to put a microbore
pipe alongside the heavily lagged DHW pipe or even inside an oversized
DHW pipe.

This would have it's own pump and pipe stat and be connected across
the DHW coil of the heatbank. When the DHW pipe cools the pump would
circulate water through the DHW _coil_ of the heatbank, so using a
small amound of DHW heat (but not the DHW water itself) to keep the
DHW pipe hot

cheers,
Pete.

"Pete C" wrote in message
...
On Mon, 20 Sep 2004 17:29:36 +0100, "Ed Sirett"
wrote:

- Because the cylinder will be in the garage I want a recirculating
pump on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?

From the furthest HW tap (that you want enhanced) or HW
usage point take a small (10mm hep? 8mm microbore?) pipe back to near the
heat bank. Insulate every piece of DHW to very best standard you can
manage,
including the return pipe.
Obtain a BRONZE circulating pump (this is like the CH pump but made of
bronze and 5x cost). Put small DHW pipe into the pump inlet. The pump
outlet into the mains cold water inlet. Put pump on very lowest setting,
also only open one of the pump isolating valves a tiny bit. You want a
trickle of water to flow out of the DHW supply form the heat bank but
enough to make the DHW pipe warm/hot but not so much that the returned
DHW
is actually warm.
Some poeple say you should put a non return valve in the return circuit,
I think that length of small pipe work and the restriction on the pump
isolating valve should be enough to stop much mains cold being drawn back
and mixed with the HW.
Consider putting pump on timer or PIR so that it only operates at peak
times.

Hi,

Or, use a pipe stat as well to run the pump so it only circulates DHW
when the pipe has cooled down.

This will help to keep the DHW in the heat bank stratified,

No DHW in the heat bank, only primary water.

and has
the advantage that it is more responsive to timer or PIR control.

Another option is to save on an expensive pump is to put a microbore
pipe alongside the heavily lagged DHW pipe or even inside an oversized
DHW pipe.

This would have it's own pump and pipe stat and be connected across
the DHW coil of the heatbank.

Heat has a plate heat exchanger, no coil.

When the DHW pipe cools the pump would
circulate water through the DHW _coil_ of the heatbank, so using a
small amound of DHW heat (but not the DHW water itself) to keep the
DHW pipe hot

cheers,
Pete.

On Mon, 20 Sep 2004 19:24:45 +0100, "IMM" wrote:

Another option is to save on an expensive pump is to put a microbore
pipe alongside the heavily lagged DHW pipe or even inside an oversized
DHW pipe.

This would have it's own pump and pipe stat and be connected across
the DHW coil of the heatbank.

Heat has a plate heat exchanger, no coil.

OK, is it a thermal store that's heated by a coil?

In that case you'd connect a DHW 'preheat' circuit across the
heatbank's primary water connections.

I wonder if 4 10mm pipes in a 22mm pipe would make a good counterflow
heat exchanger...

cheers,
Pete.

"Pete C" wrote in message
...
On Mon, 20 Sep 2004 19:24:45 +0100, "IMM" wrote:

Another option is to save on an expensive pump is to put a microbore
pipe alongside the heavily lagged DHW pipe or even inside an oversized
DHW pipe.

This would have it's own pump and pipe stat and be connected across
the DHW coil of the heatbank.

Heat bank has a plate heat exchanger, no coil.

OK, is it a thermal store that's heated by a coil?

Yep. The termninolgy, which has not settled, is that a thermal store has a
coil and a heat bank a plate heat exchnager. Range call their Flowmax a
thermal store yet it has a plate heat exchanger. They are about the only one
who does, and as they started with coils and went to plates I think they
just kept the names up.

In that case you'd connect a DHW 'preheat' circuit across the
heatbank's primary water connections.

Possible. You could have a second plate heat exchanger on the flow fromthe
boiler with the cold mains running though it. It is better to have a
blending valve on the flow/return which ensures only 75-80C water enters the
store at the top and stays there. The store heats up "top down" being
direct. As the DHW plate takes its heat from the top of the store you gain
nothing by having a pre-heat plate on the flow.

There are hybrid stores that have a coil as a DHW pre-heat and a plate.
Mains into the coil, out of coil and into the plate. The flow switch is
adjusted so that the DHW plate pump only energised on high water flows as
the coil can easily do low flows. So no pump hunting.

I wonder if 4 10mm pipes in a 22mm pipe would make a good counterflow
heat exchanger...

Sounds like it would restrict flow.

"Ed Sirett" wrote in message
news
On Mon, 20 Sep 2004 09:26:50 +0100, Dave wrote:

I need to make a decision about the new heating system in the next week
or
so; after all the debate and advice here (and lots of web crawling) a
DPS
GXV heat bank with a Worcester Greenstar 29HE are still the current
favourites.
A couple of questions:
- I need 3 heating zones, what's the advantage of using a pump for each
zone
rather than one pump and 3 zone valves?

Each pump can be adjusted individually but this can be got around by
balancing the whole system with all the zones active.
There is a huge down side which is that you may get some reverse
flow in the other zone(s) when only 1 or 2 pumps are going.
You can add nonreturn valves to each zone (these may buzz).
You can mitigate the effect by making sure the common feed to all the
pumps is as fat and short as possible.

- Is there a significant disadvantage in joining the heating returns and
running back to the cylinder in one long'ish pipe or should I run 3
separate
returns?

None p[rovided the pipes are suitable sized. However be careful not to
return any
radiator seperately to the common return from others in its zone.

- Because the cylinder will be in the garage I want a recirculating pump
on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?

From the furthest HW tap (that you want enhanced) or HW
usage point take a small (10mm hep? 8mm microbore?) pipe back to near the
heat bank. Insulate every piece of DHW to very best standard you can
manage,
including the return pipe.
Obtain a BRONZE circulating pump (this is like the CH pump but made of
bronze and 5x cost). Put small DHW pipe into the pump inlet. The pump
outlet into the mains cold water inlet. Put pump on very lowest setting,
also only open one of the pump isolating valves a tiny bit. You want a
trickle of water to flow out of the DHW supply form the heat bank but
enough to make the DHW pipe warm/hot but not so much that the returned DHW
is actually warm.
Some poeple say you should put a non return valve in the return circuit,

One should be there.

I think that length of small pipe work and the restriction on the pump
isolating valve should be enough to stop much mains cold being drawn back
and mixed with the HW.
Consider putting pump on timer or PIR so that it only operates at peak
times.
It is a compromise between energy saving and convenience. You will however
save a stack of water as you will have instant(ish) HW.
The heat bank is the heat source and occasionally the boiler will have to
fire to replensih it.


- Having a directly heated cylinder presumably means there's more delay
between the room stat demanding heat and the rads providing it - is this
noticeable in practise?

No! the heat bank stays hot all the while (OK there is a bigger delay
after
you come back from holiday). So the hot primary water is ready to send to
the radiators instantly.



--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html

"Dave" wrote in message
...
I need to make a decision about the new heating system in the next week or
so; after all the debate and advice here (and lots of web crawling) a DPS
GXV heat bank with a Worcester Greenstar 29HE are still the current
favourites.

Look at the Gledhill Gulfsteam 2000 CPSU. All in one box, boiler and heat
bank. They also have instant electric backup for DHW (Switch).
http://www.gledhill.net/docs/gulfstream.htm

Gledhill say only large orders are entertained, but TP can get individual
boilers. They supply one offs to selfbuilders.

With Gufsteam you will need three zone valves to have 3 zones.

A couple of questions:
- I need 3 heating zones, what's the advantage of using a pump for each
zone
rather than one pump and 3 zone valves?
- Is there a significant disadvantage in joining the heating returns and
running back to the cylinder in one long'ish pipe or should I run 3
separate
returns?
- Because the cylinder will be in the garage I want a recirculating pump
on
the DHW but how can this work when the water is just being recirculated
around pipework and not through a heat source?
- Having a directly heated cylinder presumably means there's more delay
between the room stat demanding heat and the rads providing it - is this
noticeable in practise?

Dave S