In the diagram a zone valve is shown before the flow trunk splits into
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
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]
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
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.
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.
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.
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.
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.
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.
On Sat, 03 Dec 2011 19:07:52 +0000, Roger Mills wrote:
And the room stat controls the valve for that zone of course.
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
Trouble is it has a (c) Copyright in it and nothing about rights on
the page for it...
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