Flow rate in central heating system

[roguetrader]

lee, purely for pump over run. it is how it states in the MI's and would be by far the easiest solution if it came to any warantee work needed.

 

[Agile]

I would be rather reluctant as there are already so many identified and probably some unidentified installation faults.

I am still waiting to hear if the pump impeller is clear.

I prefer to go as a customer's last resort when everyone else has already cured the obvious problems and it still does not work.

Tony

 

[Gasman77]

Why would you not prefer to go to a breakdown first and find an easy repair? thats weird.

 

[Agile]

I really like to go to a perfectly installed boiler and find a genuine fault with the boiler.

Its very depressing for me to go to so many so called faults only to find the usual dirt in the system.

It is quite satisfying on one hand to fix a boiler which has defied people before but on the other hand its also disappointing that they could miss obvious faults.

Tony

 

[Gasman77]

You should give other RGI's a break, they are not all as good as you.....

 

[D_Hailsham]

I hope these questions have not been asked and answered before.


1. What was your previous boiler?
2. Was the UFH installed when you had your previous boiler?
3. Was the Grundfos 25-55 installed when you had your previous boiler?
4. Did you have any problems when you had the previous boiler?

 

[edb49]

1. What was your previous boiler?
2. Was the UFH installed when you had your previous boiler?
3. Was the Grundfos 25-55 installed when you had your previous boiler?
4. Did you have any problems when you had the previous boiler?

Sorry it's taken a while to get back on these - been having problems finding the manual for my old boiler. (There is a good torrent with 100s of manuals online here: http://www.torrentportal.com/details/1385566/&filelist=1)

1. The old boiler was an Ideal Mexico Super 4125 FF. (36.6kw, 78.5% efficiency)

2. Not 100% sure on this - I believe it was installed at the same time.

3. Yes.

4. No.

When I have got the manual for this boiler, I'll take a look at the flow/resistance curve to compare it to the Glowworm.

 

[Biggles..]

http://dl.dropbox.com/u/3745388/Mexico Super FF 4100,4125 inst.pdf

 

[edb49]

OK, I've downloaded the manual for the Mexico Super FF 4125, the old boiler.

The flow rate graph is in l/min versus pressure loss in feet. It's a straight line, which you can approximate as:

pressure loss = (0.09ft * litres/min) - 0.5ft

Therefore I've calculated the loss at 1.6m^3/hr as follows:

1.6m^3/hr = 26.7 litres/min

:. pressure loss at 1.6m^3/hr = (0.09ft * 26.7 litres/min) - 0.5ft = 1.9 feet

:. 0.6m of pressure loss at the same flow the Glowworm has 4.0m of pressure loss

There's obviously a lot more pressure loss from the Glowworm, so does this point to the pump being undersized?

 

[Biggles..]

remeber the graph is 11deg delta t

therefore 36kw at 11deg rquires 3m3/h--0.83l/s--50l/m

approx resistance 4ft so about 1.3 meters

additional 2.3-3 metres on the GW

Pump undersized.

 

[Norcon]

Has the pump impeller been inspected yet?

It may well be undersized but the 25-55 will perform a lot differently in relation to the Grundfos curve graph due to the installation of a secondary pump on this system.
Also the UFH output estimation given earlier is wrong and much too high.
So a lot of wrong numbers here IMO.
As D Hailsham suggested earlier the Index circuit should be calculated accurately to give a better picture.

I would fit the pump on the return to the boiler instead of the flow thus raising the inlet pressure to the pump.

 

[Biggles..]

Pumped return in my opinion is always the best option.

 

[Biggles..]

Has the pump impeller been inspected yet?

It may well be undersized but the 25-55 will perform a lot differently in relation to the Grundfos curve graph due to the installation of a secondary pump on this system.
Also the UFH output estimation given earlier is wrong and much too high.
So a lot of wrong numbers here IMO.
As D Hailsham suggested earlier the Index circuit should be calculated accurately to give a better picture.

I would fit the pump on the return to the boiler instead of the flow thus raising the inlet pressure to the pump.

Apart from your bit about pump impeller your still ignoring the point that this all worked fine prior to adding a boiler with 20-30KPa greater resistence.

 

[mickyg]

Apart from your bit about pump impeller your still ignoring the point that this all worked fine prior to adding a boiler with 20-30KPa greater resistence.

or maybe just because the old mexico didn't care if the flow and return temperatures were in range.

 

[Norcon]

The main circulator has this noise but also you can hear what flowing through it,a bit like when your turn a tap on with an empty hose connected to it, you hear water flowing through the hose until it starts spurting out the end.

There's also this issue. I think "what" was meant to be "water".
Sounds like air in the system!