worcesster 40Cdi conv.. 2 pumps needed on system!!

[bevelsingle]

i have a system which requires 2 pumps (trying to make good some poor diy work)
the system has 7 zones (6 ch, 1 dhw) and i need to split 3/4 using 2 pumps to overcome excessive circuit resistance.
there is a new 40CDi conv and as i'm sure you know these control the pump and this is where the problem lies
i need to control the pumps to work only when their respective zones call, however i still reqiure the overrun facility that is provided by the boiler.
i have spoken to worcester-bosch tech. and was told that they can offer no advise, but was recommended to check out the internet, this leads me to think that it is not impossible!?! is it?
many thanks for any help

 

[Paul Barker]

the boiler only requires to control at least one pump for disspating heat so put an autobypass on one group of hydraulics downstream of it's pump and put that pump on the overrun.

Better still put it on the dhw circuit so that the extra effort of pumping round a bypass won't bewaisted in the sense that it will dump the excess heat into the dhw cylinder to better effect than just pumping it blindly round a short circuit.

 

[Agile]

Your boiler already has its own built in pump which will provide the pump over run.

You are evidently adding pumps in series which is not usually advisable and needs the extra pumps on setting 1 if you must.

These "circulation" problems are usually really a balancing problem ( except when microbore is involved ). I have seen many like yours without even a lockshield on the cylinder.

A pump is still open to flow when not powered.

Depending on your system all I can see that you need is an auto bypass valve to allow boiler pump over run when all your zone valves are closed.

Tony

 

[bevelsingle]

Paul, all of what you have said has gone through my mind, my only concern is that if the 'bypassed' circuit is the one controlled by the boiler it will always be on even when the boilers zones are not calling; would this have the effect of the return temp getting hot too quickly and operating the boiler stat before the other zones were up to temperature

Tony, the conventional boiler has no internal pump and is what we would probably call a 'regular' boiler. the distance that 'kermit' has run the 15mm and complete inability to perform a bend has effectively made it microbore, my remit was to change the boiler. pressurizing the system is out of the question (too much pushfit done by DIYer's) alot of the old brown 'Acorn' fittings evident so i have the distinct feeling that i'd be best not to trust the integrity of the system

thanks for your help lads, any more ideas?

 

[Agile]

Sorry, if its a heat only boiler with no internal pump, then your only solution is to choose a circuit to act as the over run and to fit an auto bypass after a pump and before the motor valve.

The system should be balanced so that no single circuit hogs all the flow.

Part of the requirement is that each zone circuit is properly controled by a roomstat so that the circuit is closed as soon as the area is up to temperature.

I dont see any real problem dealing with the problem as long as normal constraints are used and particularly in respect of balancing.

Tony

 

[Paul Barker]

I see your problem would take complicated control systems to engineer round.

is there not a zone of prime importance to fulfill the purpose? if not then as I suggest dedicate dhw to it. Much simpler than clever control engineering.

Better to buy a boiler which doesn't require overrun under the circumstances.

Or buy a second system boiler for one of the circuits.

 

[Agile]

You would need a simple diode multiple and/or gate to operate a c/o relay to only power the "over run" pump from the over run output when none of the pumps is running as the result of a call for heat.

Tony

 

[bevelsingle]

I think what i shall have to do is try the by-pass on the dhw and 3 zones after the pump with the boiler operated pump and have the other 3 zones operated by the zone valve switches (which are t/stat controlled).
thanks for all the help, first time i've visited the forum and i can't believe the response.
being a sole trader i seldom get to ask advise as there is only me on the jobs!

cheers lads, a big thumbs up from me

speak soon
cheers ian
ps. haven't heard of and/or gates since 'o' level electronics 20+yrs ago

 

[simond]

Construct a low loss header or buy one. Put a simple pump on the header unde rthe control of the boiler.

Then take each circuit off the LLH with its own pump - and also an MV if you wish.