Heating circulator incorrectly sized?

[simond]

Isn't the BG 330 a rebadged Vaillant 4 series with the small Gianonni heat exchanger? As such I think calling it a great system is probably pushing it.

The Grundfos 15/60 is the same as a Grundfos 25/60 (they are labelled differently in different markets) so the 25/40 won't make much difference.

The BG commissioning data is a bit of a joke that I think you'll find the installers fill in with the same results irrespective what they are doing.

I would ask whether the issue has been the same for the last 5 years or if it is a recent thing.

 

[bhm1712]

The 330 is a rebadged glow worm hxi as far as I know. I was under the impression the pump numbers relate to the nominal size of the pump inlet and outlet and the head so as I understand it the 15-60 means 15mm and 6 meters head whilst a 25-40 or 25-60 would mean 25mm and 4 or 6 meters head.

 

[bhm1712]

It wouldnt seem to make sense for Grundfos to be selling the 15-60 and 25-40/25-60 side by side on the shelf if they were the same pump.

 

[D_Hailsham]

How would one work out the overall head of the system? (In the absence of this info from commissioning reports and design spec)

It's virtually impossible to calculate this without knowing the exact design of the system. You need to know: the exact pipework layout; size and length of each section of pipe; type of each joint; types of valves used; output of each rad. It's all explained in Index Calculation. Detailed calculations are normally necessary only for very large domestic and commercial installations. In most cases the installer will rely on his experience to size the pump.

With your boiler set to 24kW output the flow rate for a 20C differential is 1033 litres/hr (≈ 1m³/hr). From the graph, the boiler head loss is approx 1.5m.

According to Grundfos performance graph for the 15-60, at 1m³/hr the available head is as follows:

Speed 1 - 2.5m
Speed 2 - 3.7m
Speed 3 - 4.5m

So there should be more than enough head available (after deducting the boiler loss) for your system.

It just needs balancing correctly.

 

[D_Hailsham]

It wouldn't seem to make sense for Grundfos to be selling the 15-60 and 25-40/25-60 side by side on the shelf if they were the same pump.

You have chosen a bad example as the UPS 15-60 has now been replaced by the UPS2 and the 24-40 has a different head from the 25-60. But if you compare, say the (UPS) 20-50, 25-50 and 32-50, you will find that they have identical performance. The only difference is the connecting thread size, which is 1 1/4", 1 1/2" and 2".

 

[bhm1712]

So are the internal passageways all the same size then? Just for informations sake...?

 

[simond]

That's all right bhm1712, I only do this for a day job.

And Gloworm is made by Vaillant Group, they bought them around 12 yrs back, the Vaillant 4 series is a UK designed Gloworm with a different looking control panel - and a higher price ticket.

 

[bhm1712]

I just don't understand the meaning of the numbering system they use. If a 15/60 is the same as a 25/60 what is the difference in the numbers actually telling you? From D_Halishams post I now understand it relates to the thread/flange size only is that correct!?

 

[D_Hailsham]

So are the internal passageways all the same size then? Just for informations sake...?

The first number (20, 25, 32) is the nominal diameter (DN) of suction and discharge ports [mm]. So, no, they are not the same.

 

[simond]

I think you will find that the 15/60 and 25/60 are exactly the same.

Remember, Grundfos can call them whatever they like, they don't have to get approval from an internet forum. It doesn't work the other way round.

 

[Dan Robinson]

Happy to be corrected, but my recollection is that the 25-60 was hard for OEM underfloor heating applications.

 

[D_Hailsham]

The UPS Data Book should answer all your questions.

Dan what do you mean by "hard"?

 

[Dan Robinson]

Made. Not hard.

Bloody autocorreckt.

 

[jeff the gasman]

I bet the four bedroom rads in question have been switched off for 12 months and seized/ partially seized in the off position.
Turn all radiators off except these four to see if they spring into life.
Simple things first boys.

 

[bhm1712]

They've not been turned off they are in constant use. The house I'm buying is my mothers and her partners. They do get very hot if you turn the other radiators off. I am going to have a go at balancing the system tomorrow morning and see how far I get but I'll be the fourth person to attempt it as 2 British Gas "engineers" and one self employed plumber have attempted this previously with no luck at getting the 4 radiators to be hot. It was the self employed plumber who suggested initially that the system required a 25/80 pump which prompted me to start my own research into the matter before I fully move in.