Cascading Vaillant boilers with weather compensation

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Hi

After talking to Vaillant's tech desk today, I am even more confused about their setups.

Basically I need 2 x Ecotech Plus 630 system boilers cascaded and I would like them both with weather compensation controls.

I understand that it's not possible to have 2 x VRC 470f controllers in each of the two zones. So I need a commerical VRC 630 boiler management system (which alone costs about 65% of one of the boilers). However, I want wireless room thermostats in each zone because the current ones are wired on the wall in stupid locations in warm rooms above radiators.

According to the tech people, wireless thermostats are not possible with the VRC 630.

I take it only Vaillant's weather compensation controls work with their boilers? And the VRC 630 is the only Vaillant control that will support two cascaded boilers?

I have requested a Vaillant rep come out but anyone with any experience in this kind of setup would be greatly appreciated.
 
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ALEC1

yes you understand correct...why not one bigger boiler and one vrc 470...

that seems to be the way they do it in Germany...

vaillants controls are not compatible with other manufacturers...that too is correct...

and there is no benefit in turning things off (other than at valves) in regularly used spaces... the whole idea of weather comp is that the boiler manages the heat input into a building...
 
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That is the alternative (I think).

Only real reason for two is redundancy.

I did have another theory that two boilers were cheaper to run that one. The reason being upstairs has always been warmer than downstairs (fewer rooms, hot air rises etc). But if upstairs called for heat and downstairs didn't, then the boiler would not be as efficient if it did not need to modulate as much as if it was heating the whole house? Unless these boilers can be programmed to vary their modulation depending on which zone is calling for heat (if boilers are that smart)?
 
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ALEC1

redundancy is a quaint british idea from when boilers were a bit less reliable...properly installed one boiler will do the time...by properly I mean with vaillant's own modulating controls...and no other controls other than TRVs

boilers are smarter than what you want..and indeed you can set it all up to do as you suggest on the principle of two circuits, but it will require investment in controls

what the 470 does is modulate around the outside and inside temperature
 
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ALEC1

of course another good solution is to have a boiler for upstairs and a boiler for downstairs...

you gain certain things as the domestic market is more competitive you will get a 7 year guarantee and a slightly lower price per KW out put of the boiler...
 
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I've always liked the idea of two - purely because one of the two current boilers has had virtually every part replaced since day one. The other one has never had a fault.

The 7 year warranty is really worth it and also shows how confident Vaillant must be in their boilers these days.

I need to talk to the rep about controls. I would imagine there must be some new controls coming out from Vaillant soonish with internet control for the end users etc. In the US, Nest is very popular and that type of control will surely be here in the UK soon.
 
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ALEC1

they may tweak a design but controls from boiler manufactures such as vaillant and viessmann have been doing the same thing for years...

And no I dont think Nest will make much impact here purely because it does not integrate the boiler into the system as bus controls do..

so with bus controls such as vaillant if you need a little heat thats what is produced...if you need alot thats what you get too..

Nest is good looking on-off.. no communication back to the boiler about how much..just fancy numpty on-off stuff
 
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A friend of mine has a single 65 kW Vaillant boiler!

Its a complicated system with two thermal stores and supplying 26 underfloor zones each separately controlled and the swimming pool.

He tells me the WC "looks ahead" intelligently for two hours !

Money was no function and yet he decided on a single boiler for his system.

Only slight problem is the gas requirement is slightly over the rating of the meter at 6.9 m3. He paid Nat Grid £1400 to move the meter and they used rather small pipework and the pressure falls off when more than 4.5 m3 is taken. He is starting the argument soon.

Tony
 
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I think Nest is geared more towards a/c anyway.

Even water tanks are being replaced by dedicated water heaters (essentially like a combi boiler). I looked at those and they are true gas guzzlers - most around 180,000 - 200,000 BTU with around 80% efficiency. But they do deliver around 40l of hot water per min.
 
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A friend of mine has a single 65 kW Vaillant boiler!

Its a complicated system with two thermal stores and supplying 26 underfloor zones each separately controlled and the swimming pool.

He tells me the WC "looks ahead" intelligently for two hours !

Money was no function and yet he decided on a single boiler for his system.

Only slight problem is the gas requirement is slightly over the rating of the meter at 6.9 m3. He paid Nat Grid £1400 to move the meter and they used rather small pipework and the pressure falls off when more than 4.5 m3 is taken. He is starting the argument soon.

Tony

We have a MDA16 meter, but everything from the meter is concreted/screeded in so hopefully we have no size issues!

If we were to redo the house, we would probably go down the route of thermal stores/ground source pumps etc.

I have a friend who is getting a new pool but it's more like a pond, or one of these natural swimming pools that requires no chemicals as the plants clean it. He reckons it will heat itself, but I think he is brave to say the least.
 
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why does it have to be a vaillant? They don't offer the controls to do what you want so why not look elsewhere? Atag Q would make life easier. you could use regular controls but with an OS sensor and seperate temp circuits for heat/hot water. They also do a 60kw boiler which is within domestic scope.
 
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why does it have to be a vaillant? They don't offer the controls to do what you want so why not look elsewhere? Atag Q would make life easier. you could use regular controls but with an OS sensor and seperate temp circuits for heat/hot water. They also do a 60kw boiler which is within domestic scope.

I looked at Atag and their Q Series. Cascading is possible - but they jump from 25kW to 38kW so it's not economical to get two boilers. Their 60kW boiler was about 15% more expensive than the Vaillant 65kW equivalent, but controls were cheaper so I think balances out.

I've only really been focussing on the two domestic boilers cascaded together as it seemed more economical to run and cheaper to install. But the controls are the tricky part.

Other alternatives are Intergas, Worcester Bosch, Viessmann, Buderus?
 
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ALEC1

Once you get to installing any of those boilers WITH prorietary controls there isn't much difference with them...Atag stands out because you can mix and match on-off controls with weather comp and thats very useful for some applications.


I was suggesting two boilers on two systems, upstairs and downstairs...that may or may not work depending on the hydraulic lay out.

Once you get into cascading with compensation controls it becomes expensive as the application is usually commercial, or its a huge house..draw your own conclusions!!!!
 
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Once you get to installing any of those boilers WITH prorietary controls there isn't much difference with them...Atag stands out because you can mix and match on-off controls with weather comp and thats very useful for some applications.


I was suggesting two boilers on two systems, upstairs and downstairs...that may or may not work depending on the hydraulic lay out.

Once you get into cascading with compensation controls it becomes expensive as the application is usually commercial, or its a huge house..draw your own conclusions!!!!

Two systems would definitely work as there are 4 x 28mm pipes going to the loft where they go to 35mm pipe to the current boilers. The boilers would have to remain in the loft though as it would be a nightmare to run the flues/condensate anywhere else.

There is a Grundfos 25-55 pump on the return with the zone valves also on the return - I think this is a strange setup these days and normally would be on the flow?

Are there any other advantages to having both systems linked apart from the redundancy?

I think I should get reps in from all the main manufacturers to see what they propose, cost it all up and then take it from there.
 
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ALEC1

Reps look after installers, contracts and suppliers and not end user

Domestic boilers are highly discounted in the UK.

the way you would do this type of install in Germany would be one boiler with either one direct circuit or two or more mixing valves.. another way would be a mixed circuit and an unmixed circuit...the possibilities are limitless..


Its the discounting that gives you more possibilities..
 

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