Bypass when using Grundfos Alpha2 pump

[Agile]

OP,

unfortunately you have fallen into the trap of expecting all products on the market to be capable of use together.

You have almost come to the correct conclusion but stopped just short of it.

The major component in your system is the boiler. The rest of the system needs to operate so that the boiler's demands are met ( however stupid they may seem on the 400 series ).

Its up to the installer to design the system appropriately.

Most of the time your boiler is over powered for your heat loss.

If you must use a smart pump then you need to have a shunt pump circulating through the boiler to keep that happy, a low loss header, and then you can have your smart pump to transfer heat from the LLH to the load ( ideally at a constant pump pressure ). That will all work fine and operate everything correctly!

Just a little bit over the top for a 10 kW house though! And because the boiler is over powered it will be less efficient because there will be too much flow going to the return but thats the result of an over powered boiler.

I am surprised you have not read the two long threads this year about these problems with higher output 400 series boilers. I know that you think you now fully understand all aspects of the heating industry better than those who work in it and that plumbers all all ignorant having left school at 16 with three GCSEs if they were lucky, but experience of system design and operation gained over several years can be very beneficial.

Tony

 

[smokebox]

Agile
Please do not take too much offence at my little anti Vaillant and anti numpty rants!

In all truth Vaillant really were ignorant and rude in my view. I have a little intelligence, admittedly only a little but it seemed better in understanding the physics of energy transfer, condensation, latent heat of water vapour etc etc and basic principles than some of their staff.
I note from this and other threads I am not alone in my Vaillant conclusions.

Vaillant told me to do actually stupid things with bypass capable of carrying full boiler out put! Really! They did not know what pump overrun was for!

The Plumbers electrician refused to look at the instruction manual and haughtily told me he had wired more boilers than I'd had breakfasts, and promptly wired the pump incorrectly without overun - direct to zone valve output switching. What am I to think?
Of course there are some very knowlegable heating engineers out there and indeed I had one today.who was very good though admitted he new less than me about what was going on with Vaillant control systems and eBUS etc. In other heating areas he will know much more than me.
Remember I didn't choose the 28kW boiler either. That was the gas safe registered man! I suggested a 415 or 418 but he said no way. I then calculated the heat loss later after installation my self. I could probably have just got away with a 415. As explained because of extra demands and further extensions of use I am now contemplating, I do not think that is too important, and the boiler will and does modulate itself down quite successfully. The garage is not well insulated and will take quite a bit of heat.

Also, I know there are some extremely helpful and knowledgeable guys around - like yourself and Lord Hailsham! I sometimes even exaggerate and put my tongue in cheek.
Please accept my apologies.

Thanks for explaining a bit about heat stores etc I would be interested to hear more, but admit I will go a long way to avoid further plumbing installation work and cost. Anway the boiler does not often go into any cycling phases so it is a not a a real worry. I expect when we are really in winter it should be even better.
Why should'nt I save electricity with a smart pump? We are all going to have to in Jan 2013 by statute. Why does Grundfos make them? What we need to do is understand their proper use and bypassing if required by the boiler and the regulations.

I didn't design the system, and I would say the design should be centred on the house and not first choosing what you reckon is quite the wrong boiler. With three baths, three showers, and OFTEN 12 to 14 people in residence surely it might be wiser to allow more than 2kW for DHW anyway. I though 4kw a little mean! Furthermore there have been frequent complaints about running out of hot water, because I like you like a once a day early heat of DHW before CH comes in. That becomes a storage issue if you only heat DHW once a day. basically the hating engineer did not check the heat loss, and relied on his experienced eyeball. I told him there was almost 100mm of high grade polyurethane foam [u value 0.0230] round all the walls' cavity [exceptionally thick layer in my house] , inside the roof tiles, and 300 mm fibreglass at ceiling He however knew best!

smokebox

ps I should be pleased to have your pointers to the two other long threads on bypassing of smart pumps. That would be really helpful.

 

[smokebox]

Agile
most of the time everyone's boiler is overpowered for their heat loss. They actually have to be!

Smokebox

 

[Dan Robinson]

With three baths, three showers, and OFTEN 12 to 14 people in residence surely it might be wiser to allow more than 2kW for DHW anyway. I though 4kw a little mean! Furthermore there have been frequent complaints about running out of hot water, because I like you like a once a day early heat of DHW before CH comes in. That becomes a storage issue if you only heat DHW once a day.

Off a 28kW boiler with heating load to consider too?

the boiler will and does modulate itself down quite successfully

Without wishing to appear rude are you not in danger of over thinking a problem that isn't really there?

 

[smokebox]

well Dan
I have you suggeting the boiler is too small (am I right?0

With three baths, three showers, and OFTEN 12 to 14 people in residence surely it might be wiser to allow more than 2kW for DHW anyway. I though 4kw a little mean! Furthermore there have been frequent complaints about running out of hot water, because I like you like a once a day early heat of DHW before CH comes in. That becomes a storage issue if you only heat DHW once a day.

Off a 28kW boiler with heating load to consider too?

the boiler will and does modulate itself down quite successfully

Without wishing to appear rude are you not in danger of over thinking a problem that isn't really there?

and Agile thinks it is too big.

I think it will do.!


Yes I am iin danger of obsessing too much over the bypass, but I really hate to see man designing a really clever condensing boiler, then preventing or reducing its condensing because of sloppy thinking and planning.
I admit I am talking only of the last 12 to 14% of efficiency, and not necessarily all of that. None the less this technology is what has lifted boilers out of efficiency poverty in the past 15 yrs effectively. Don't throw it away!

smokebox

 

[Agile]

The two threads centre on the problems people have had with over powered boilers fitted on systems which dont adsorb enough heat and done give enough flow rate through the boiler.

Tony

 

[smokebox]

The two threads centre on the problems people have had with over powered boilers fitted on systems which dont adsorb enough heat and done give enough flow rate through the boiler.

Tony

Yes Agile I was interested in those ++ especially since Vaillant boiler behaviour was being examined.

For the modern well insulated smaller house 5kW down modulation is not low enough to avoid cycling of one sort or another.
As I mentioned before I was worried about this issue here because of v good insulation. It is there but not too bad (touch wood)

My real purpose on this thread is to get to the bottom of smart pump bypassing though.

Smokebox

 

[JonasX]

I really hate to see man designing a really clever condensing boiler, then preventing or reducing its condensing because of sloppy thinking and planning.

Spot on there Smokebox. Try to eliminate the by-pass.

 

[smokebox]

For the modern well insulated smaller house 5kW down modulation is not low enough to avoid cycling of one sort or another.

Look at the Geminox 0.9 - 9 kilowatt (non-combi)

Jonas
Thanks.
Others have also mentioned the Geminox, and it sounds interesting with its very low modulation capability. Their 2.4 to 13.5kW looks well sized for many UK houses.

I gather it is French, and distribution/spares/service staff knowledge in UK is quite an issue. I have not really found details in English other than rather bald facts. Few of the UK dealers know about it (if any to speak of, unless you've found somewhere?)
Have you ever used one? They would suit many a UK 'Kennel' with good insulation!

From my immediate perspective, I have a larger house and an open vent ecoTEC plus 428 was installed in May 2011. So I'm not myself looking for a smaller one. The big 428 is modulating itself down quite well (to 17% sometimes!) on warmish cool days! I have recently - yesterday - made a temporary trial installation of the Vaillant VRC430 weather compensation/control device, with VR61 and VR81 remote on an eBus that runs around the house annoying the wife! She says it is the return of the Trifids!

(I rejected radio as boiler is set very low in kitchen, and I need 3 wifi radio routers to cover the house - it seems damned cussed for radio signals.)

I am always interested however in the range of domestic boilers around - so thanks.

smokebox

 

[JonasX]

Smokebox, Geminox are a quality French maker. I am in London so the parts and service backup is OK, with the engineers having most parts in the vans. You will have to get in touch with them, the importer has a different name, over parts/service in Wales.

Do a search on Geminox on this site. Lots comes up. They are highly rated.

 

[smokebox]

Now the NUB of the matter!

We have all done our homework and understand what a smart pump is. (see my earlier links), I am sure!!!


http://www.grundfos.pt/web/homept.n...d003071c2/$FILE/Grundfosliterature-815904.pdf


You cannot logically use an auto bypass in smart mode. Even though Vaillant say their boiler ecoTEC plus series needs to have them. The manual may have been written before there were smart pumps for domestic use.

My Alpha2 15-50-130, in its "smart operating triangle" produces Max 3m head, AND could choose to go there any time it wanted. The auto bypass therefore should have to have opening pressure set slightly higher than this to prevent wasteful bypassing effects on condensing during ordinary running.

Effectively, on pump overrun there will be no flow ie useless...we are already above max head of smart pump mode.

So reduce opening pressure to a smaller figure. But the pump can deliver output right down to just below one metre head. To avoid wasteful bypass the opening pressure should be set ideally below this to maximise condensation. Again NO OPENING, useless.... edit I got this wrong .the bypass would be open virtually ALL the time on a low, say 1 meter opening pressure. This would REMOVE effectively any condensation to speak of even in ordinary running..... useless again!

Where should it be set, or should we have a small standing bypass flow set at say 1.5 l/min?[90 litres per hr.] this would be a small percentage of boiler full load out put [1220l/hr], but maybe a substantial proportion when TRVs are nearing closure. Also would this be enough to prevent bangs on shut down? Only Vaillant can advise a satisfactory MINIMAL ACCEPTABLE FLOW IN LITRES PER MINUTE. for thispurpose....... only they don't understand or refuse to specify, and eventually get rather rude to emails until you write to the UK Managing director. but they still don't know. One technician said the boiler flow must never fall below 1220 l/hr - a real jester! and I suppose he is paid!

In the absence of facts and advice is it really a suck it and see? Are there any other thoughts or approaches from the experts out there? apart from expensive additional buffer schemes. Or should an auto bypass be set at about midway between 1 and 3 metres - potentially very wasteful of condensing mode!

This small fixed pre-set bypass will be open all the time and will inevitably allow some warming of the return to the boiler and reduce condensing efficiency.

You could argue I am fussing too much about too little, but much gas could be lost in a winter!

smokebox

PS Grundfos have actually told me not to use auto bypass in smart mode because of waste energy. or zero function of bypass. Much more helpful to the foolish ignorant layman than Vaillant and their shut out of all except well trained Gas Numpties. I shudder for the industry

Can anyone contemplate all this, and make some observation to assist a foolish dolt?

smokebox

 

[smokebox]

Smokebox, Geminox are a quality French maker. I am in London so the parts and service backup is OK, with the engineers having most parts in the vans. You will have to get in touch with them, the importer has a different name, over parts/service in Wales.

Do a search on Geminox on this site. Lots comes up. They are highly rated.

Jonas
Ah I thought only of Google - i'll wake up shortly!

Smokebox

 

[D_Hailsham]

Now the NUB of the matter!

You cannot logically use an auto bypass in smart mode. Even though Vaillant say their boiler ecoTEC plus series needs to have them. The manual may have been written before there were smart pumps for domestic use.

Grundfos are in agreement with you over that!

My Alpha2 15-50-130, in its "smart operating triangle" produces Max 3m head

I don't know where you get that figure from as the 15-50 does not even appear in the link you gave, only the 15-40 and 15-60.

I managed to find the 15-50 data on the Grundfos website and the peak is 3.8m at 1m³/hr.

Don't forget that the head is not a fixed value, it varies dynamically with water temperature differential and flow rate. For example, at standard temperatures (75, 65, 20, -1) my system has a calculated head of 4.8M. If I were to run the boiler with a 20C differential (75/55) the head reduces to 1.6m.

 

[smokebox]

Now the NUB of the matter!

You cannot logically use an auto bypass in smart mode. Even though Vaillant say their boiler ecoTEC plus series needs to have them. The manual may have been written before there were smart pumps for domestic use.

Grundfos are in agreement with you over that!

My Alpha2 15-50-130, in its "smart operating triangle" produces Max 3m head

I don't know where you get that figure from as the 15-50 does not even appear in the link you gave, only the 15-40 and 15-60.

I managed to find the 15-50 data on the Grundfos website and the peak is 3.8m at 1m³/hr.

Don't forget that the head is not a fixed value, it varies dynamically with water temperature differential and flow rate. For example, at standard temperatures (75, 65, 20, -1) my system has a calculated head of 4.8M. If I were to run the boiler with a 20C differential (75/55) the head reduces to 1.6m.

Lord Hailsham
I stand corrected! Indeed that pump (15-50)oddly is not listed on that link. Apologies and I can't think why it is omitted! I think it is a newish pdf, and maybe that particular pump is going to be withdrawn.

I can't exactly give you a link to 15-50 Data, but I have had some personal data from Grundfos maybe I got it there. Do you have a link to the 15-50 data you found? That would help. Is your 3.8 mtrs max at the top of the "green triangle" of the autoadapt range of activity, or actual full head at speed III?

Anyway the precise numbers don't matter yet - I am exploring the principle, or trying to!

Your point about a variable head/ flow relationship is of course the kernel of the matter, and how to cope wit it, remain effective and safe in pump overrun, but not waste condensing efficiency in ordinary 'zone open ' mode. I am beginning to think some kind of solenoid, opening on valve closure would maybe make a reasonable bypass. For THIS PURPOSE flow does not have to be huge, is my guess. I can't get Vaillant to truly engage or comprehend to give me a minimum reasonable figure.

smokebox

I've just found the leaflet from Grundfos - your figure is correct, mine was wrong. A link would still help me! The grundfos site is good but tricky to navigate and find stuff/

 

[smokebox]

My lord
in a previous thread "What do modulating pumps do", you asked for Manufacturers. Instructions stating in black and white what this minimum flow rate might be for this purpose.

It is NOT stated in the Vaillant 415 to 438 MIs!

I have however email correspondence from Vaillant saying that even in this situation the minmum flow must NEVER fall below the rated 1220 [for my 428] l/hr quote for removing energy at full output. This must be bunk!

The suggestion is certainly safe, but the issue is how to limit this huge bypass during ordinary function.

smokebox