Grundfos Alpha 2L settings? PP1 PP2 or go for AutoAdapt

[holland141]

Hello,

My plumber installed an Alpha 2L 15-60 and not an Alpha 2 as requested (and thus we don’t have the autoadapt feature).

I have a feeling there is less overall output now (not all rads getting as hot), as per my previous old fixed 15-60 pump – an earlier Grundfos model.

I need to work out if I get the plumber to upgrade to the Alpha 2 (Autoadapt), or try to get the right setting on the Alpha 2L

We’ve a reasonably large 5 bed house, with a new 30kW condensing boiler. I’ve done a rough calculation, and I believe we have a flow rate requirement of 0.6 to 0.7 m/s

I have a 2 pipe system with manual bypass – so I am lead to believe this should be proportional pressure. (PP2, PP1). The recommendation is for PP2.

If I’m reading the performance chart correctly, this means a max flow rate of roughly 0.58 at a head of 3 (the higher of the two blue lines). This may be why I am feeling the rads are underpowered.

If I use the PP1 setting (lower blue line), then I could get upwards of 0.75 at a Max head of 2. However, if the pump follows the lower blue line, then at 0.6 flow it will operate at a head of approx. 1.8. I do not know if this would be enough for the index circuit.

If I switched to the Autoadapt model, from what I can see, at 0.6 flow, it could operate at a 2.5 head (i.e. on the III line)

My theory is that
- If current PP2 setting is not enough, switch to PP1 – but since this stick to the lower blue line, I may not get the required head for the flow rate at the far right end of the line. i.e. at flow rate 0.6, this is a head of approximately 1.8
- I could switch to Alpha 2 with Autoadapt – in which case it would move along the III line until it found the correct balance – i.e. at a flow of 0.6 the head is 2.5

Is my logic correct?

Thanks

Alpha 2L performance chart
View media item 61277
Alpha 2 (Auto adapt works in green area)

View media item 61278

 

[kbdiy]

Isn't it easier to just trial each setting to see the result and if neither works effectively then it's time to go for the upgrade?

 

[holland141]

Isn't it easier to just trial each setting to see the result and if neither works effectively then it's time to go for the upgrade?

Thanks.

I will be doing that later - but I'm keen to know what the theoretical 'best' approach is also....

 

[kbdiy]

The problem with theory is that it doesn't take into account the inherent resistance of all the pipework and fittings etc. Far better to rely on a practical test first in my opinion.

 

[matt1e]

Hello,

My plumber installed an Alpha 2L 15-60 and not an Alpha 2 as requested (and thus we don’t have the autoadapt feature).

I have a feeling there is less overall output now (not all rads getting as hot), as per my previous old fixed 15-60 pump – an earlier Grundfos model.

I need to work out if I get the plumber to upgrade to the Alpha 2 (Autoadapt), or try to get the right setting on the Alpha 2L

well he really should have installed the one you asked and presumably were quoted for

I have a 2 pipe system with manual bypass – so I am lead to believe this should be proportional pressure. (PP2, PP1). The recommendation is for PP2.

Yes but first tthe bypass has to be set up correctly, did the installer do this?

Matt

 

[holland141]

re Bypass

Installed the Taco Nova Setter - a manual Bypass that you can specifically set to the minimum for the boiler. This was recommended by Grundfos.

 

[D_Hailsham]

My plumber installed an Alpha 2L 15-60 and not an Alpha 2 as requested (and thus we don’t have the autoadapt feature).

I suspect the L version was produced specifically for the UK market.

I have a feeling there is less overall output now

The radiators could be colder because there is a greater temperature difference between flow and return. This would be due to the required differential at the boiler. Older boilers used a 10/11C differential; modern condensing boilers use a 20C differential. The effect is a reduction of radiator output of about 15%.

a new 30kW condensing boiler. I’ve done a rough calculation, and I believe we have a flow rate requirement of 0.6 to 0.7 m/s

Who decided that a 30kW boiler was the correct size?

The flow rate is measured in litre/sec and depends on the temperature differential. A 30kW boiler with a 20C differential needs a flow rate of 0.36 litres/sec (21.5 litres/min, 1.3m³/hr)

My theory is that: If current PP2 setting is not enough, switch to PP1.

It's the other way round!

The problem with a fixed bypass, even the Taconova Setter, is that it is always open, so you are loosing some of the heat all the time. One solution recommended by Grundfos is to have an auto bypass in series with the Taconova fixed bypass. The auto bypass means that the bypass circuit is only open when required, the fixed by pass sets the maximum flow rate through the circuit.

There are several useful documents about the Alpha Pumps Here.