Benefits of smart pumps for combi system

[boilerbeasty]

Does any one know of any benefits of these 'smart' low power, self-adjusting pumps e.g. Grundfos Alpha 2, which regulate the flow based on temperature and pressure (e.g. responsive to TRVs etc).

I'm aware of the potential power savings, and the possibility they will be quieter, but how about efficiency in the boiler, heat output at the radiators, responsiveness for DHW etc ?

Any thoughts or even better some experience would be welcome.[/quote]

 

[Agile]

They are only useable on stored water systems.

The benefits are as the manufacturers say ( with a little salt ).

They have not been very popular because the added purchase cost often outweighs any savings.

They should be a good solution with a house with a widely variable heating load such as a four bed with three beds unheated except at Christmas.

But the same effect can be somewhat obtained by turning the pump speed up and down.

They dont have a very significant effect on boiler efficiency.

Many Alphas are never set to operate as designed anyway!

Tony

 

[45yearsagasman]

Most combi boilers are designed for the pump to run on max at all times and as such Alpha pumps and the like are not recommended for combis.

 

[Agile]

Thats only because the pump is already in the combi.

If smart pumps were cheaper the combi makers would use them.

Boiler makers have made some attempts to modulate the pump, e.g. Vaillant and Keston.

But they have been a bodge of a standard pump with the motor taps taken out to the PCB so the pump speed can be step modulated.

Tony

 

[45yearsagasman]

Thats only because the pump is already in the combi.

But they have been a bodge of a standard pump with the motor taps taken out to the PCB so the pump speed can be step modulated.

Tony.
Exactly my point and as yet aren't proved to enhance a combi's performance in my opinion.If your combi was designed with a single speed pump then fitting a variable speed pump will surely cause problems.unless you know better.

 

[Agile]

As a combi modulates back then it should also modulate the pump back as well to maintain the same temperature differential.

But that really calls for a fully variable speed pump like the Alpha. But they are twice the cost of a standard pump amd totally out of the cost equation for mass produced boilers.

But with the newer permanent magnet pumps that may well cone along very soon.

Tony

 

[45yearsagasman]

I agree that with future development that these pumps may well serve a purpose,but the question was about fitting one to an existing combi and that would be totally wrong and would cause the appliance to malfunction on many counts.

 

[ianniann]

There are combis out there with proper modulating pumps. Another thread mentioned that the WB 37CDi has a Grundfos Alpha, although I think it actually has something else a good deal cheaper. Anyone know for sure what it is?

They modulate almost entirely based on pressure and flow, and not on any attempt to maintain a temperature differential or respond to the burner level. Lower flow rate (eg. as TRVs close) and the pump powers down, while a standard pump would maintain the same power and increase the head which is hardly helpful. In this way they aim for an approximately proportional head and flow rate, or can be set to maintain a constant head regardless of the flow rate.

These things won't save you any gas but they can save electricity, especially with the increasing trend to run boilers continuously at low output to maintain a constant room temperature.

 

[Alfredo]

We started fitting Grundfos Alphas to existing systems on our breakdown contracts a few years back. It was not a successful experiment as we found they tended to run too fast on the variable setting, and cause all sorts of niggly problems, so we ended up setting them up on manual speed 2 after quite a few recalls...and the problems went away...which rather defeated the object.....so back to the 15/50 in most cases for us.....


I'm sure they will work very well on a system properly designed for them.

Alfredo

 

[ianniann]

You weren't retro-fitting them inside combis were you Alfredo? That would surely need some tricky electronics to make sure the pump worked properly for the DHW.

This shows up that Grundfos pumps are massively overpowered for the average modern heating system, hence why they are all turned down to 2. The problem with the "smart" settings is that they will run up to full power whenever they think it is necessary, which often means too much flow.

Grundfos recommend that you don't use the Autoadapt with an automatic bypass because they can fight. They recommend the constant head settings instead. Autoadapt and the non-adaptive proportional settings work best with a fixed bypass and a variable load (=TRVs), but that still leaves them overpowered for most UK domestic systems. Even those big combi boilers running with a 20C delta never need much more than 1,000 l/hr to shift their entire heat output, while a Grundfos pump at full power will easily push double that.