http://wiki.diyfaq.org.uk/index.php?...k _.2B_branch

In the diagram a zone valve is shown before the flow trunk splits into
branches.
Is this intended to show a valve with one input and two output ports, so
that the flow can go to either or both branches?
This doesn't seem right as the radiator without the TRV should always be on
(I think).
Otherwise there has to be a seperate return loop (I think).
Should the zone valve be the other side of the T junction so it can shut of
the branch with all TRVs?

--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

On Dec 3, 4:18*pm, "David WE Roberts" wrote:
http://wiki.diyfaq.org.uk/index.php?...ng_design#Tree....

In the diagram a zone valve is shown before the flow trunk splits into
branches.
Is this intended to show a valve with one input and two output ports, so
that the flow can go to either or both branches?
This doesn't seem right as the radiator without the TRV should always be on
(I think).
Otherwise there has to be a seperate return loop (I think).
Should the zone valve be the other side of the T junction so it can shut of
the branch with all TRVs?

--
No plan survives contact with the enemy.
[Not even bunny]

Helmuth von Moltke the Elder

(\__/)
(='.'=)
(")_(")

Large central heating systems are sometimes divided into zones that
can be independently controlled/shut down. A zone valve performs this
function.

On 03/12/2011 16:18, David WE Roberts wrote:

http://wiki.diyfaq.org.uk/index.php?...k _.2B_branch


In the diagram a zone valve is shown before the flow trunk splits into
branches.
Is this intended to show a valve with one input and two output ports, so
that the flow can go to either or both branches?

No... Its just a normal 2 port zone valve with a 28mm pipe in and a 28mm
pipe out. Some time after the valve is am unequal tee, with reduced 22mm
legs.

Its really just indicating the way that the pipework does not have to be
a linear trek round each of the rads in turn. You can use larger pipes
toward the start of the circuit (i.e. where most flow and heat is being
shifted) and branch off those in smaller pipes to do batches of rads.

This doesn't seem right as the radiator without the TRV should always be
on (I think).

All six rads in that diagram are in effect in parallel. Note however it
is possibly only part of a system - there may be additional zones, hot
water circuits, or even bypass loops not shown.


--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
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| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 03/12/2011 16:18, David WE Roberts wrote:

http://wiki.diyfaq.org.uk/index.php?...k _.2B_branch


In the diagram a zone valve is shown before the flow trunk splits into
branches.
Is this intended to show a valve with one input and two output ports, so
that the flow can go to either or both branches?
This doesn't seem right as the radiator without the TRV should always be
on (I think).
Otherwise there has to be a seperate return loop (I think).
Should the zone valve be the other side of the T junction so it can shut
of the branch with all TRVs?

I have missed that when you mentioned this diagram previously. I can't
see the reference to a bypass circuit that I expected to see elsewhere
in the Wiki.

The manual control valve will provide a circuit even when all the TRVs
close down but close the zone valve and the boiler will do what its name
implies, boil, if the heat has nowhere else to go which is why a bypass
circuit is an important part of most modern central heating systems.

--
Roger Chapman

On 03/12/2011 16:18, David WE Roberts wrote:

http://wiki.diyfaq.org.uk/index.php?...k _.2B_branch


In the diagram a zone valve is shown before the flow trunk splits into
branches.
Is this intended to show a valve with one input and two output ports, so
that the flow can go to either or both branches?
This doesn't seem right as the radiator without the TRV should always be
on (I think).
Otherwise there has to be a seperate return loop (I think).
Should the zone valve be the other side of the T junction so it can shut
of the branch with all TRVs?


No. This diagram is perfectly correct for illustrating trunk and branch
design - i.e. fat pipes feeding multiple branches before they split, and
thinner ones feeding each branch.

In this particular example, there is only one heating zone shown with
two branches (probably upstairs and downstairs). The radiator with the
manual valve would be in the room which has the room stat.

There may be a bypass valve elsewhere (if the boiler needs it) - but
it's not shown here because it's not relevant to the particular point
being illustrated. equally, the complete system is likely to have a HW
zone, and maybe additional heating zones - each with its own zone valve.
--
Cheers,
Roger
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On Sat, 03 Dec 2011 19:07:52 +0000, Roger Mills wrote:

The radiator with the manual valve would be in the room which has the
room stat.

And the room stat controls the valve for that zone of course.

There may be a bypass valve elsewhere (if the boiler needs it) - but
it's not shown here because it's not relevant to the particular point
being illustrated.

I think the diagram could be made clearer by not having the
flow/return cross each other the boiler and a bit of text saying
additional feeds for DHW bypass etc for the flow/return that point to
the left.

Trouble is it has a (c) Copyright in it and nothing about rights on
the page for it...

--
Cheers
Dave.

On 03/12/2011 19:06, Roger Chapman wrote:


The manual control valve will provide a circuit even when all the TRVs
close down but close the zone valve and the boiler will do what its name
implies, boil, if the heat has nowhere else to go which is why a bypass
circuit is an important part of most modern central heating systems.


A bypass valve *may* be required, depending on the boiler. A setup like
this would usually be part of an S-Plan system, so that when the valve
closed its auxiliary contacts would switch off the boiler. Many boilers
will overheat under these circumstances if there is no flow, due to the
residual heat in the metal parts of the heat exchanger - requiring a
bypass circuit and pump over-run logic. However, some will not - mainly
slightly older boilers which contain more water and which would be happy
with a gravity hot water circuit. Provided the water to metal ratio is
high enough, the boiler won't overheat even if there is no flow path -
as long as it stops firing when the path closes, of course.
--
Cheers,
Roger
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Please reply to Newsgroup. Whilst email address is valid, it is seldom
checked.

On 03/12/2011 22:20, Roger Mills wrote:

The manual control valve will provide a circuit even when all the TRVs
close down but close the zone valve and the boiler will do what its name
implies, boil, if the heat has nowhere else to go which is why a bypass
circuit is an important part of most modern central heating systems.


A bypass valve *may* be required, depending on the boiler. A setup like
this would usually be part of an S-Plan system, so that when the valve
closed its auxiliary contacts would switch off the boiler. Many boilers
will overheat under these circumstances if there is no flow, due to the
residual heat in the metal parts of the heat exchanger - requiring a
bypass circuit and pump over-run logic. However, some will not - mainly
slightly older boilers which contain more water and which would be happy
with a gravity hot water circuit. Provided the water to metal ratio is
high enough, the boiler won't overheat even if there is no flow path -
as long as it stops firing when the path closes, of course.

One of the reasons I referred to a 'modern central heating system' and
restricted my comments to 'most' was to avoid being dragged into an
argument as to whether a 30 year old boiler with a cwt of cast iron as
its heat exchanger would or would not boil if there was no pump overrun.
Of course a gravity hot water circuit lessens the chance of the boiler
boiling to almost zero provided that hasn't been retro fitted with its
own zone valve.
--
Roger Chapman

In two of the houses I've lived in over the years, there were no
valves, just a pump, and the hot water tank heat exchanger was
just another radiator.

JGH

On 04/12/2011 00:06, jgharston wrote:
In two of the houses I've lived in over the years, there were no
valves, just a pump, and the hot water tank heat exchanger was
just another radiator.

There is a certain amount to be said for the simplicity of it... If the
cylinder is lagged, then once it is up to the same temperature as the
primary water then it won't place any real load on the heating. However
it does mean the cylinder will be dangerously hot for direct use, and
also prone to rapid scaling in hard water areas.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 04/12/2011 19:27, John Rumm wrote:
On 04/12/2011 00:06, jgharston wrote:
In two of the houses I've lived in over the years, there were no
valves, just a pump, and the hot water tank heat exchanger was
just another radiator.

There is a certain amount to be said for the simplicity of it... If the
cylinder is lagged, then once it is up to the same temperature as the
primary water then it won't place any real load on the heating. However
it does mean the cylinder will be dangerously hot for direct use, and
also prone to rapid scaling in hard water areas.


Either that, or you have to restrict your primary flow (boiler stat)
temperature to around 60degC - which means that the radiator output is
severely degraded.
--
Cheers,
Roger
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On 04/12/2011 22:26, Roger Mills wrote:
On 04/12/2011 19:27, John Rumm wrote:
On 04/12/2011 00:06, jgharston wrote:
In two of the houses I've lived in over the years, there were no
valves, just a pump, and the hot water tank heat exchanger was
just another radiator.

There is a certain amount to be said for the simplicity of it... If the
cylinder is lagged, then once it is up to the same temperature as the
primary water then it won't place any real load on the heating. However
it does mean the cylinder will be dangerously hot for direct use, and
also prone to rapid scaling in hard water areas.


Either that, or you have to restrict your primary flow (boiler stat)
temperature to around 60degC - which means that the radiator output is
severely degraded.

Indeed, although good for efficiency with a modern boiler.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/