15M pump required, one large Vs 2 small in series? | Plumbing Jobs | The Job-board | Plumbers Forums

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15M pump required, one large Vs 2 small in series?

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Discuss 15M pump required, one large Vs 2 small in series? in the Plumbing Jobs | The Job-board area at Plumbers Forums

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Michael Groves

Michael Groves

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I'm specifying a new system. It has a 15M head, I called Grundfos and they recommended Magna3 40-150 rrp £1,640. (using rrp for reference only)
A friend recommended 2 no. Grundfos Magna3 32-80 in series, rrp £628 (Total £1,256).
Running costs of 2no. 32-80 is a third of 40-150.
Grundfos technical advised they do not recommend running in series, nor do they recommend you do not run in series, they are mute on the subject.

This seems like a no brainer to me, what am I missing?
 
no you cant sorry to say
 
Grundfos advised 1st pump should be configured with autoAdapt, with second pump fixed rate. This way AutoAdapt will adjust accordingly.
But Grundfos said 2nd pump would always be running at 100% which would reduce life and ties in with your comment.

I've got some more realistic prices, difference is about £200

I'm still leaning towards 2 in series.
 
Michael Groves said:
Grundfos advised 1st pump should be configured with autoAdapt, with second pump fixed rate. This way AutoAdapt will adjust accordingly.
But Grundfos said 2nd pump would always be running at 100% which would reduce life and ties in with your comment.

I've got some more realistic prices, difference is about £200

I'm still leaning towards 2 in series.
Click to expand...

have a look at dab pumps
 
If running 2 pumps in series was so much more efficient then all manufacturers would offer twin inline pump sets.
Can't say I've seen any.

The final cost of the installed pumps will be about the same after allowing for mounting and connecting up 2 pumps against just mounting 1 at a slightly higher purchase price.
 
snowhead said:
If running 2 pumps in series was so much more efficient then all manufacturers would offer twin inline pump sets.
Can't say I've seen any.

The final cost of the installed pumps will be about the same after allowing for mounting and connecting up 2 pumps against just mounting 1 at a slightly higher purchase price.
Click to expand...

Does not make commercial sense to sell pumps in series, when they can make more money selling one.

You have a valid point on extra time and vales, but if I allow £10 for valves and an extra hour work at £20, I'm still £170 better of running in series.

So technically I still see no reason not to run in series ?
 
Michael Groves said:
5 Storey Victorian house, Boiler in the basement. It's actually 13.5M, (I measured it exactly) so 15M being the closest.
Click to expand...

If you are talking about a circulation pump, it doesn't need to have a head of 13.5m, which is what you seem to be thinking. This is because the inlet pressure is 13.5m and the outlet pressure is the sum of the pump-inlet plus pump-working pressures. So you only need enough head to overcome the impedance of the pipework, which should be sized to work with a standard 6m pump.
 
Chuck said:
If you are talking about a circulation pump, it doesn't need to have a head of 13.5m, which is what you seem to be thinking. This is because the inlet pressure is 13.5m and the outlet pressure is the sum of the pump-inlet plus pump-working pressures. So you only need enough head to overcome the impedance of the pipework, which should be sized to work with a standard 6m pump.
Click to expand...

Yes it's a circulation pump, in a sealed system. Will have Worchester Bosch 40CDi Classic with a Robo kit. I get your point if it were open vent, or am I missing the point?
 
Michael Groves said:
Yes it's a circulation pump, in a sealed system. Will have Worchester Bosch 40CDi Classic with a Robo kit. I get your point if it were open vent, or am I missing the point?
Click to expand...

unvented cylinder?
 
Chuck said:
If you are talking about a circulation pump, it doesn't need to have a head of 13.5m, which is what you seem to be thinking. This is because the inlet pressure is 13.5m and the outlet pressure is the sum of the pump-inlet plus pump-working pressures. So you only need enough head to overcome the impedance of the pipework, which should be sized to work with a standard 6m pump.
Click to expand...

I thought it was building height, clearly I am VERY wrong, Grundfos Technical support also confirmed building height.

Here's a link I found, good explanation. I need to reconsider
How to size a Circulator Pump. Taco pump curves.
 
Michael Groves said:
Cylinder is 20kW, Radiators are 17kW.
Click to expand...

how many rads? seams low only 8 2kw rads

you done a room to room heat loss? and not just measured the existing rads?
 
Michael Groves said:
Yes it's a circulation pump, in a sealed system. Will have Worchester Bosch 40CDi Classic with a Robo kit. I get your point if it were open vent, or am I missing the point?
Click to expand...

Makes no difference to the conclusion whether the system is vented or unvented. You would only need a 15m head if you were trying to pump water from, say, a borehole in the basement to an open tank in the roof.

If this is not obvious to you then you should subcontract the design of the system to someone who knows what they are doing. (No offense intended!)
 
Chuck said:
Makes no difference to the conclusion whether the system is vented or unvented. You would only need a 15m head if you were trying to pump water from, say, a borehole in the basement to an open tank in the roof.

If this is not obvious to you then you should subcontract the design of the system to someone who knows what they are doing. (No offense intended!)
Click to expand...

No offense taken, you have made a very valid point, I appreciate your comments. I have some reading to do........
 
Michael Groves said:
I thought it was building height, clearly I am VERY wrong, Grundfos Technical support also confirmed building height.
Click to expand...

The building height is relevant only to the extent that there will be a limit to the maximum pressure difference between the inside and outside of the pump before the seals fail. This is usually a *lot* more than the inlet-outlet pressure difference we are discussing here.
 
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