Weather compensation & choice of pump

[p7777m]

I'll shortly be having a new boiler installed (probably Glow Worm Ultracom 18hxi or Vaillant Eco Tec Plus 418), together with controls and pump.
3 zones - downstairs, upstairs & HW.
Probably going to stay with my existing conventional vented indirect HW cylinder. For now at least.

I'm leaning towards having weather compensation, but I'm stuck at choice of pump.
I'd like to go for a Grundfos Alpha - low power consumption and low noise (I assume); also ability for it to adjust speed as appropriate which seems to be appropriate for maximising boiler condensation (please correct me if I am wrong)
But of course I cannot use it in intelligent/autoadjust mode because of the need for overrun when the boiler shuts down. I don't fancy on ordinary bypass as that seems inefficient and an auto-bypass would need something fancy such as an LLH & seperate pump just for this circuit (thanks, Tony, for your earlier comments on this), all of which seems over complex, costly and is simply gaining efficiency in one area by sacrificing it in another)
Which means that I'd need to choose one of the pumps fixed speeds.
Is this entirely consistent with using weather compensation, maximising condensing potential, and minimising cycling?
I'd have thought that ideally the pump speed (maybe together with everything else including boiler modulation etc), should all be controlled by a single control unit; but this doesn't appear to be possible.

Have I missed something here?
Your expert comments and guidance are very much appreciated.

 

[mickyg]

2 big problems with your plan. If your gonna zone the system its gonna be tricky integrating WC with your choice of boiler as they dont support it that well. You could try a vaillant with the VR61 I've not tried it yet but its the only option for zoning. Personally if zoning and WC was the request then I'd spec an ATAG Q series, cos its a doddle and you can just use standard off the shelf controls.
secondly alpha pumps and gianonni heat exchangers dont get on due to the high resistance of the heat exchangers. The pump wont increase condense, thats down to the return temperature to the boiler, the WC will take care of this.

 

[matt1e]

2 big problems with your plan. If your gonna zone the system its gonna be tricky integrating WC with your choice of boiler as they dont support it that well.

I don't understand your thinking here micky, you can have weather compensation on a zoned system and the two boilers listed both directly support an outside sensor

Matt

 

[ALEC1]

the problem with zoning with wc is that the boiler can only work on one curve...to do properly you need an electronic mixing valves with a curve (and heat up time) for each zone...


The vaillant vr61 is a compromise, but probably works well, although the 400 series boiler is not the most appropriate for weather compemsation....

 

[ALEC1]

with respect to the pump my advice would be to install a boiler with a modulating pump which slows down at low loads, bringing the return down even further, but that does limit your choice..


you can get an upgrade for a viessmann 200, or you tKe an atag q series...


why two boilers, is it a palace?

 

[matt1e]

the problem with zoning with wc is that the boiler can only work on one curve...to do properly you need an electronic mixing valves with a curve (and heat up time) for each zone...

you can go as sophisticated as you like but my point is you can still have a weather compensatated system

or are you saying that a zoned system without weather compensation is more efficent than a zoned system fed by a boiler that can automatically adjust the flow temp in accordance with the outside temp?

I dont think so

Matt

 

[Hufty]

The vaillant vr61 is a compromise, but probably works well, although the 400 series boiler is not the most appropriate for weather compemsation....

Agreed. Are you still worrying about this, p7777m? I would convert to a sealed system, then fit a system boiler eg a Vaillant 618 or whatever the GW equivalent is. Pump and autobypass are in the boiler already, assume they work as well as they can do. VR81 and Vaillant VRC4xx for weather compensated 3 zone S plan, VR61 as mentioned above.

As for which to go for out of GW/Vaillant, I would read the respective controller manuals and work backwards.

 

[ALEC1]

well i think people have to distinguish between weather compensation and weather dependency...the former just running up and down a curve, and the latter be able to operate with no room controls... these two being offered by vaillant and viessman on the 200 and 300 series only...

there is no research supporting zoning as being effective in saving energy. but where my clients keep records there is plenty to suggest that weather dependency saves energy over switchng boilers on and off

 

[ALEC1]

sometimes you need two curves... one of my clients wanted the towel rails on in summer, but of course they would not be very warm in summer....(the cylinder reheat was too short with the solar/ part L coil)

 

[p7777m]

with respect to the pump my advice would be to install a boiler with a modulating pump which slows down at low loads, bringing the return down even further, but that does limit your choice..
why two boilers, is it a palace?

Are you able to point me to somewhere where I can find all boilers which come with modulating pumps, and 3rd party (separate, non-integrated) pumps? I don't recall seeing that in the few pump specs I've looked at.
What controls the modulating pump? Is there a standard for this interface?
No - not 2 boilers! I'm choosing a single boiler

The vaillant vr61 is a compromise, but probably works well, although the 400 series boiler is not the most appropriate for weather compemsation....

Agreed. Are you still worrying about this, p7777m? I would convert to a sealed system, then fit a system boiler eg a Vaillant 618 or whatever the GW equivalent is. Pump and autobypass are in the boiler already, assume they work as well as they can do. VR81 and Vaillant VRC4xx for weather compensated 3 zone S plan, VR61 as mentioned above.

As for which to go for out of GW/Vaillant, I would read the respective controller manuals and work backwards.

Why is a system boiler such as the Vaillant 618 more suited to weather compensation? Does it have a modulating pump? If so are there other reasons?
Any other reason why you recommend a system boiler? The reason I'm slightly against them is lack of freedom of configuration, lack of choice of components (although some will say these are advantages provided the package is good) and being locked into 1 supplier for everything.

 

[ALEC1]

618 has a two speed pump...and technically works well with vaillants own weather compensation
400 was developed for the UK market, that says all you need to know about it!!!

if you want a seamless and sophisticated heating system all the components shold come from the same manufacturer...all are very flexible, if you know the components and understand what they will do...

 

[ALEC1]

many boilers have two speed pumps linked to the burner rate...modulating pumps can be tricky if pipe sizing is not correct.....

on viessmann 200 series it is an upgrade....atag q series have them, in both cases their modulation range can be varied in parameters..

 

[p7777m]

618 has a two speed pump...and technically works well with vaillants own weather compensation
400 was developed for the UK market, that says all you need to know about it!!!

I take it you mean the 400 is not really good enough for use on the continent, but we buy it here because we're less discerning?
What's wrong with it?
I will take a look at the 618.

 

[ALEC1]

yes thats right... only choose boilers that can be installed in Germany... in fairness that is most, but some are developed for the UK and these are best avoided if you want a decent heating system!

 

[p7777m]

yes thats right... only choose boilers that can be installed in Germany... in fairness that is most, but some are developed for the UK and these are best avoided if you want a decent heating system!

That's interesting. But do you know (or have heard) what's actually wrong with them?