Bypass when using Grundfos Alpha2 pump

[smokebox]

There is or are MV's available ( I think ?) that open when power is cut to them / switched off eg they work in reverse to the usual MV;s

Is this relevant ??? Dunno ??

Yes, might just do useful thought but slower thwn solenoid actuation, and best of all is dumping hest through an already open circuit/zone as suggested by one of the regulars above.
smokebox

 

[smokebox]

Glad to see that you are back in the land of the living!

I have this urge to ask if you have had a heart (auto) bypass ?

Agile
Yes, but present issue is pump failure due to poor equipment specs, with inadequate output, and wasteful bypassing!
smokebox

 

[smokebox]

Although Haisham suggests an auotadapt can be set up with auto bypass, doing so will inevitaby push the boiler needlessly out of condensinng state more than neccessary,

It's not inevitable. If the bypass is correctly set up, it will only open when conditions demand it. I have demonstrated, in an earlier post, that your system can be run at low temperatures, even in the coldest weather.

where does grundfos have instructions on how to set the bypass press on an auto bypass with an Alpha autopump?

http://net.grundfos.com/Appl/WebCAP...FAM&appcode=HEATING&pdfid=776425&language=ENU

The problem is that that you need to know the minimum flow rate through the boiler and many manufacturers do not supply that info or, if they do, the info is inaccurate (e.g Vaillant).

Grundfos say that ABVs are not compatible with Autoadapt and recommend using PP2, the highest proportional pressure setting instead.

Have you considered that your pump may not be large enough for your installation?

At max output of 30kW with a 20°C differential the flow rate is 1220 litre/hr and the pressure loss through the boiler is 2.4m (see installation manual). At that flow rate the pump can deliver a maximum head of approx 3.4m so the head available for the loss round the system is approx 1m. You said earlier that you have 24kW of rads but not how many; I would guess at between 15 and 20. In that case the system loss is likely to be more than 1m.

You can work it out using the info given in Small Bore heating Systems and Copper Tubes in Domestic Heating Systems

Hailsham
Thanks for that link! though it does not explicitly want one to use auto bypass in any 'proportional pressure', and I reckon the autoadapt section is a sort of complex combination of the 2 PP operation modes.

As often you have given me work to do and calculations which I shall attend to when they send me home! Basically as I've actually mentioned above, I agree I need a bigger pump head with this 'tight' boiler and some long pipe runs. I'll need to do a couple of potential index circuit calcs.

Your point about running cold and avoiding loss of condensing, is good, but I am doubting it will always be possible to keep temps that low. I'll reread your earlier post! The good thing about your posts is that one has to actually think for a lot of them!

AS you have noted Grundfos do say AUTOADAPT MODE IS INCOMPATIBLE WITH AUTOBYPASS. But I am determined to use it with crafty bypassing!


smokebox

 

[smokebox]

To MJN and all

I have tried to send a reply to your personal message, but apparently I have to be a friend, or you do!
I can't work out how to make friends (a long story tee-hee). Some of the help instructions on using this website are as bad as Vaillant manuals!

Can anyone help me in steps of one?!

smokebox

 

[MJN]

Hi Smokebox, feel free to e-mail them to me.

Mathew

 

[smokebox]

Hi Smokebox, feel free to e-mail them to me.

Mathew

I will forward them separately Thanks!
smokebox

 

[MJN]

Here are the Grundfos documents Smokebox mentioned earlier in the thread, uploaded here for reference:

http://www.newtonnet.co.uk/permanent/GrundfosDocs/Alpha2&Alpha2LControlModes.pdf
http://www.newtonnet.co.uk/permanent/GrundfosDocs/BypassCommissioningAlpha2or2L.pdf
http://www.newtonnet.co.uk/permanent/GrundfosDocs/SystemBypass.pdf
http://www.newtonnet.co.uk/permanent/GrundfosDocs/SystemRadiatorBalancing.pdf


Mathew

 

[D_Hailsham]

Here are the Grundfos documents Smokebox mentioned earlier in the thread, uploaded here for reference:

Very interesting and useful. It's a pity they are not available on the Grundfos website.

The only bit I would query is in the paper on Balancing where it says:

If the differential temperature is too low, slightly open the lock shield valve; and if the differential temperature is too high close the lock shield valve slightly.

I think this should read: If the return temperature is too low, slightly open the lock shield valve; and if the return temperature is too high close the lock shield valve slightly.

See Drayton TRV Commissioning Instructions, which say, in para 4a: Remember that to increase the temperature drop you need to slow the flow rate by closing the lockshield valve and vice versa.

 

[smokebox]

Hailsham
I new you'd be the first to spot that boo boo!

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[matt1e]

AS you have noted Grundfos do say AUTOADAPT MODE IS INCOMPATIBLE WITH AUTOBYPASS.

smokebox

From the PDF

An automatic bypass valve should not be used with the Alpha2 pump in proportional pressure control.
As the heating load increases, the pump pressure increases, the increasing pump pressure then causes
the automatic bypass valve to open further increasing the bypass flow. The flow through an automatic
bypass valve will increase more than it would for a fixed bypass in this situation.

They then go on to say

If an automatic bypass valve must be used, then a manual fixed bypass valve should be installed in
series with the automatic bypass valve. The fixed manual bypass will restrict the flow as the automatic bypass valve opens.

best of all is dumping heat through an already open circuit/zone as suggested by one of the regulars above.
smokebox

I have allready shown you how to do that

Matt

 

[smokebox]

Matt
Yes you have, and very many thanks! I am planning to follow that route when a bit better, I hope

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[smokebox]

Gary
I am very interested in Vaillant's way of advising your heating curve of 2.3.
? did it sound like a 'reasonable' guesstimate, or a bit more scientific, or just a sensible starting point?
What information did they request about he house?
smokebox

 

[D_Hailsham]

Smokebox

Very early in this discussion the question of the "minimum flow rate" was raised, in particular Vaillant's assertion that it is 1220 lph. I pointed out that this does not appear in continental versions of the manuals, where it is just referred to as the "flow rate".

Much of your concern has been about maintaining this "minimum flow rate" and the effect it would have on return temperatures. My belief is that you have to ignore the Vaillant manual and apply some logic to the problem.

I was reading the installation manual for another boiler which said that the minimum flow rate should be that which provided a 20C differential when the boiler is at the lowest modulation. This immediately made sense as it tied in with Grundfos's advice in Bypass Commissioning (see page 1, the yellow line on the graph).

The minimum output of the 428 is 5.7kW so the flow rate with a 20C differential is 0.07 litres/sec (245lph). If this is set on the Taco Nova bypass with the pump on fixed setting I or II, the maximum flow you will get through the valve is about 300lph or 25% of the total flow.

 

[Agile]

Much of your concern has been about maintaining this "minimum flow rate" and the effect it would have on return temperatures. My belief is that you have to ignore the Vaillant manual and apply some logic to the problem.

I was reading the installation manual for another boiler which said that the minimum flow rate should be that which provided a 20C differential when the boiler is at the lowest modulation. This immediately made sense as it tied in with Grundfos's advice

I have to disagree with that conclusion although I understand what you are thinking. Unfortunately that will not provide adequate bypass flow in all conditions.

The bypass flow rate should be that required by the boiler at MAXIMUM power!

This arises because the demand might be suddenly ceased when the boiler is firing at its maximum.

This could happen if someone manually turned the boiler off at a room stat, timeclock or just if a timed period ended when for example someone had just used up all the stored water and the boiler was firing at maximum to replemish the store.

Tony

 

[D_Hailsham]

I have to disagree with that conclusion although I understand what you are thinking. Unfortunately that will not provide adequate bypass flow in all conditions.

The bypass flow rate should be that required by the boiler at MAXIMUM power!

This arises because the demand might be suddenly ceased when the boiler is firing at its maximum.

This could happen if someone manually turned the boiler off at a room stat, timeclock or just if a timed period ended when for example someone had just used up all the stored water and the boiler was firing at maximum to replenish the store.

But as soon as the boiler turns off it is no longer generating any heat to bring the water back up to temperature. So the fact that it was running flat out when the boiler turned off is irrelevant. All you are doing is dissipating the residual heat in the water.