"Paul Roman" wrote in message
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In article , says...
In article , Paul
Roman writes
SNIP
Looking at the BES site (thanks Ed and why isn't it in the FAQ?), is
the
Differential By-Pass Valve (12161) the approiate part?
Looking at the diagrams the bypass valve should be fitted from the
flow
to the return between the boiler and the zone valves. But according
to
the Keston installation instructions the flow/return temperature
differential should be 10 to 15 C. In the layout I was planning the
zone
valves are only about a meter from the boiler. I can't see that short
run of pipework producing that much of a differential. Any thoughts?
Any other thoughts/observations would be welcome.
Thanks
Paul
Thanks for your reply , Fred.
I've now mailed and spoken to Keston and I'm still not clear about how
to deal with this issue. What is normal practice since Part L came in?
Are installers simply ignoring the boilers requirement for a
temperature
drop across the by-pass circuit? Or are they creating an (artificially)
larger loop for the by-pass circuit? Or are they still using a rad as a
by-pass?
Thanks for your responses.
Paul
It is actually a lot easier than you think. Just think of the
(automatic)
bypass not coming into operation at all when the heating is at full
demand.
Its purpose is to provide an uninterrupted water path _only_ when the
TRVs
on the rads are shutting down, which is a transient state just before
the
boiler says 'right, the house is hot enough, I'm shutting down', so
don't
worry about it. The absence of a temp drop across the bypass will tell
the
boiler that it is time to shut down.
It is actually more complex than that as at first the bypass will come
on a
little and the return flow will be a mixture of rad return water (at low
temp)
and flow water ((hot) from the bypass). This will have the effect of
increasing the return temp a little, which will cause the boiler to
throttle
back a bit. This is not a fault or a contravention of regs 'cos it is
the normal
control loop coming into play and (eventually) shutting down the boiler
when the house is up to temp.
Hope that makes it a little clearer.
Thanks Fred. I understand the whys and wherefores of the by-pass from a
pressure point of view but its Keston's requirement for a 10 to 15
degree drop across the by-pass that I've got a problem with. The only
practical way to achieve it is via some sort of emitter/rad but that
solution is now specifically excluded by the regs. I suppose I'll just
have to do a simple/short by-pass and see if Keston complain when they
come to commission the boiler.
Thanks
Paul
The main radiators in any house are in the hallways or reception rooms
(front lounge) so this radiator should, in actual fact, be your by-pass
loop. The proper thing to do with any heating system, is to place a
thermostat in the same room or area as the by-pass radiator. This way the
system is actually controlled by the loop and not from any radiator willy
nilly telling the system that it is to hot and should close down everything.
TRV's are there to tell the radiator that it is fitted to, that the area
that it is heating is up to temperature, that way each room, or valve
controlled zone, because that is what it literally becomes when you install
a TRV, will independently control its own temperature.
The main area of the house needs as much heat as it can to stop draughts and
colder air moving from room to room when doors or windows are opened, so the
radiator installed in the main area should be controlling the boiler and
other main parts of the system through an independent thermostat fitted at
the opposite end of the hallway from the radiator. That way the whole room
is up to the correct temperature setting and is now helping to keep the
whole house warm. No one actually sits in the hallway, but it is an
integral part to keeping the whole house heated.
I still think that underfloor heating is the best way to control the
temperature in a house. The heat is actually spread more evenly throughout
each room, and when a 'stat is installed in the main area of the house, then
you know that each area is at a comfortable and liveable heat.
So if you think of what the manufacturer is saying about a drop in
temperature over the by-pass loop, and think of the size of radiator you've
fitted in the main area of the house, then I think you'll have spotted where
the loop should be made. Along with a room 'stat if you want even better
control.
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