Bypass when using Grundfos Alpha2 pump

[D_Hailsham]

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 I think it is a newish pdf, and maybe that particular pump is going to be withdrawn.

I was thing it might have been withdrawn as well. I also suspect that the Alpha2 is being withdrawn and replaced by the Alpha2 L, which does not have Autoadapt or Night setback. (Too complicated for the typical UK plumber to understand??)

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?

http://net.grundfos.com/Appl/WebCAP...&cpn=&freq=50&lang=ENU&units=UC_Default_Units

Your point about a variable head/ flow relationship is of course the kernel of the matter, and how to cope with it, remain effective and safe in pump overrun, but not waste condensing efficiency in ordinary 'zone open ' mode.

It would be interesting to try and model a system in software. The Energy Systems Research Unit at Strathclyde University have created a very sophisticated model of a heating installation to examine the effects of control systems but it does not take into account variable speed pumps or bypass valves.

 

[D_Hailsham]

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 minimum flow must NEVER fall below the rated 1220 [for my 428] l/hr quote for removing energy at full output. This must be bunk!

I think there has been a problem translating the manual from the original German. I couldn't find the German Installation Manual, but I did find the Dutch version. In one case it calls it the "Maximum Heating Water Flow at ΔT= 20C" and in another just the "Circulating Water Flow at ΔT= 20C".

In neither case does it call it a minimum flow rate.

 

[smokebox]

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 I think it is a newish pdf, and maybe that particular pump is going to be withdrawn.

I was thing it might have been withdrawn as well. I also suspect that the Alpha2 is being withdrawn and replaced by the Alpha2 L, which does not have Autoadapt or Night setback. (Too complicated for the typical UK plumber to understand??)

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?

http://net.grundfos.com/Appl/WebCAP...&cpn=&freq=50&lang=ENU&units=UC_Default_Units

Your point about a variable head/ flow relationship is of course the kernel of the matter, and how to cope with it, remain effective and safe in pump overrun, but not waste condensing efficiency in ordinary 'zone open ' mode.

Lord Hailsham
Thanks for link! Well found.

It would be a great shame to take the self modulating pump out of circulation. It is complex, but really only inside its own computer/ sensing system/electronics. I think it is a lovely piece of design. Maybe they'll just take it out of UK! But come Jan 2013 they'll need something!

I am not an engineer but system control and design of even 'simple' domestic heating is fascinating to me when I come to look at it. Very interested to hear of Strathclyde's work. I wish I was a better computer programmer! "Science" is just a hobby - my other real job was different. I have much to learn.

The boiler manufacturers and Grundfos should speak more to each other - probably in German, and get good really good English and indeed pan European guidance instructions drawn up. Vaillant should admit there are some thinking customers who are spending a lot of money, and have a system set up to speak to them in a more friendly way.

What do think of the solenoid opening a bypass on zone closure - or has it already been found wanting?

Smokebox

 

[smokebox]

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 minimum flow must NEVER fall below the rated 1220 [for my 428] l/hr quote for removing energy at full output. This must be bunk!

I think there has been a problem translating the manual from the original German. I couldn't find the German Installation Manual, but I did find the Dutch version. In one case it calls it the "Maximum Heating Water Flow at ΔT= 20C" and in another just the "Circulating Water Flow at ΔT= 20C".

In neither case does it call it a minimum flow rate.

Nor address this specific matter, nor the answer to the bypass for ordinary running versus overrun.!

smokebox

 

[smokebox]

So what bypassing do most 'thinking' people use? Do they just settle for an autobypass set near upper end of the grundfos pumps Auto modulating region from their Q/mtrs output chart, but just below the top pressure reached in autoadapt mode?
smokebox

 

[Dan Robinson]

Whichever suits the installation. Sometimes none.

 

[D_Hailsham]

Whichever suits the installation. Sometimes none.

True, but not very helpful.

The OP has a S Plus system and a boiler with pump overrun. Take the worst-case scenario. The boiler is running at full chat putting out the full 28kW and the water temperature is 75C. The programmers all reach an "OFF" time, so everything shuts down, in particular all the zone valves close. However the pump keeps on running; but there's nowhere for the water to circulate, unless you have a bypass of some sort.

Current regulations say that only automatic bypass valves can be used. The OP is asking what valve setting he should use, taking into account that he has a Grundfos Alpha2 Pump?

 

[Agile]

The OP is essentially asking for the near impossible just because he wants to use a smart pump which is intended to provide solutions to other problems.

All that is required is to provide an adequate flow through the boiler to remove latent heat immediately after it has ceased firing.

Written answers from people at Vaillant is not design information but just the easiest answer they can quickly give to move on to the next query.

The OP has two options, to fit a LLH or to fit a non smart pump.

His ideas are just not compatable!

A little knowledge is dangerous! I am not sure he even realises what the pump knows about the flow through the system.

Tony

 

[D_Hailsham]

The OP is essentially asking for the near impossible just because he wants to use a smart pump which is intended to provide solutions to other problems.

What "other problems" are smart pumps meant to solve? I thought they were intended as a universal replacement for the traditional fixed speed pumps.

All that is required is to provide an adequate flow through the boiler to remove latent heat immediately after it has ceased firing.

Agreed, but it all depend on why the boiler has stopped firing. The worst case is when all zone valves close at the same time.

Written answers from people at Vaillant is not design information but just the easiest answer they can quickly give to move on to the next query.

It's not just Vaillant support staff who just look up the answer in the (inaccurate) installation manual and quote back to you what you can read for yourself!

The OP has two options, to fit a LLH or to fit a non smart pump.

How does that help?

If I were the OP, I would ask Grundfos for advice.

 

[Agile]

What "other problems" are smart pumps meant to solve? I thought they were intended as a universal replacement for the traditional fixed speed pumps.

It's not just Vaillant support staff who just look up the answer in the (inaccurate) installation manual and quote back to you what you can read for yourself!

If I were the OP, I would ask Grundfos for advice.

There is no universal solution to multiple needs. The smart pumps mostly prevent a rising pressure when the flow rate reduces as TRVs close. This prevents noisy system operation due to excessive pressure.

Auto bypass valves use that feature to open when the pressure rises. So smart pumps and ABVs are not mutually compatible.

All boiler makers use lesser paid staff to answer questions from customers and installers. They are NOT normally highly experienced heating engineers. Potterton adverts say "no previous experience necessary"!

Of course both you and the OP would have to ask others because neither of you are heating engineers.

Manufacturers of boilers and pumps are only concerned about their own products. An experienced heating engineer knows how to best use both together.

Tony

 

[D_Hailsham]

There is no universal solution to multiple needs. The smart pumps mostly prevent a rising pressure when the flow rate reduces as TRVs close. This prevents noisy system operation due to excessive pressure.

That's one use but there are others, e.g. providing the correct flow rate as a boiler output varies.

Auto bypass valves use that feature to open when the pressure rises. So smart pumps and ABVs are not mutually compatible.

So we can expect to see the Grundfos Alpha2 withdrawn from the UK market as ABVs are a requirement?

Manufacturers of boilers and pumps are only concerned about their own products.

I would think they probably collaborate much closer than you give them credit for. After all the pump manufacturers provide all the internal pumps for combi and system boilers.

An experienced heating engineer knows how to best use both together.

If only that were true!

 

[smokebox]

Whichever suits the installation. Sometimes none.

True, but not very helpful.

The OP has a S Plus system and a boiler with pump overrun. Take the worst-case scenario. The boiler is running at full chat putting out the full 28kW and the water temperature is 75C. The programmers all reach an "OFF" time, so everything shuts down, in particular all the zone valves close. However the pump keeps on running; but there's nowhere for the water to circulate, unless you have a bypass of some sort.

Current regulations say that only automatic bypass valves can be used. The OP is asking what valve setting he should use, taking into account that he has a Grundfos Alpha2 Pump?

My Lord Hailsham
An admirable summary!
What I've actually done is retain the auto bypass set to open at just above top press of my pumps autoadapt zone. I have aimed at 3.9metres! this is really just to cover "emergency" situations. You could argue I should set it just below the 3.8metre[max head of autoadapt triangle'] level, and tolerate occasional bleeding of hot water back to the return and loose condensing efficiency.
To this I have added in parallel a small fixed preset but adjustable 'standing bypass' set at a flow of 1.7l/min (= about 1.2l/hr or approx 0.1m^3/hr) chosen arbitrarily for trial at the moment. During the state summarised by Lord Hailsham, the flame is off and no real heat is lost, and I reckon it is enough to prevent kettling and explosions. When the heating is on, obviously one wants to keep this flow to a minimum, hence the seemingly small amount chosen. During normal running, heat is obviously unloaded in the rad with no TRV, or indeed in other rads still open. Loss of condensing efficiency is minimised. I shall try later to estimate actual loss of efficiency for various loads.
It is this figure that Vaillant couldn't get their minds round, and would yield nonething less than the full flow max output of 1220 l/hr - which is so atrociously wasteful of condensing mode that it would be like returning to the 1950's! The technicians had very little scientific knowledge, which can be such a dangerous thing, as Agile reminds us!

smokebox

PS Essentially this is Grundfos's advice, though quite rightly they thought Vaillant should provide the minimal flow figure for their particular boilers.

 

[smokebox]

Here are links to the presettable flow controller advised by Grundfos.
About £35 from Plumb Centre, though they had to order from their central stores. Took half an hour and a 24 mm spanner to install - a bit less in time, cost and bulk than Agile's LLH etc

http://www.taconova.com/en/products/balancing/setter-inline/

http://www.taconova.com/fileadmin/u...av23_setter_inline/2_av23_setter_inline_e.pdf

We are heating ahouse, not the East wing of the Rutherford Physics Laboratories at Cambridge!

 

[mysteryman]

If you add weather compensation to a good system boiler with [currently optional] variable speed pump, the flow temperature and flowrate will modulate automatically to the correct levels, and you will not get the sudden shutdown problem. One rad on lockshields does the biz regarding bypass - but weather comp pretty well removes the circumstance in which a bypass is needed - because of the modulation of temp and flowrate.

Keep it simple - use readily available kit.

Most variable speed pumps will be DC with electronic control in the near future.

 

[D_Hailsham]

If you add weather compensation to a good system boiler with [currently optional] variable speed pump, the flow temperature and flowrate will modulate automatically to the correct levels, and you will not get the sudden shutdown problem.

What about S Plans at the end of the day when everything goes off at the same time, so all zone valves close?

One rad on lockshields does the biz regarding bypass

But the rad would have to go before the zone valves in an S plan, so it would be leaking heat back to the return all the time.

Most variable speed pumps will be DC with electronic control in the near future.

Where did you hear that?