System sizing problems and flushing questions

[MarcoNN]

Hi, I have a 3 storey house with 19 heated rooms, and the equivalent of 22 finned double paneled rads.

Having a bit of trouble balancing the rads. The overall temp ends up pretty low and some sections can go completely cold. The plumber says it's because the house is too big. The house has been extended a few times but so has the system - i would have hoped he would have foresaw such a problem

It's a sealed system. Firebird Popular 170 (1993) boiler. Thermostat at 75.
Expansion tank - ELBI 30 litre. 10 bar max, temp 110 max. Set at 1 - 1.5bar pressure.
Pump: Wilo,230V, 50Hz, IEC 38. At setting 1 of the 3. So 140 and 0,65.

Any ideas?

Also seems to be some sludge as many of the rads are pretty cool at the bottom half.
2 questions: One, i know some people say flushing using mains pressure isn't much good, so would it be a complete waste of time on a house this size?
Two: Would there be any point anyway because once the sludge is removed it will have to be replaced by extra water which the boiler seems to be having trouble heating as it is.

Lastly; There is a component between the composite valve and the filling loop which is sort of cone shaped with a pressure guage. The cone is tranverse to the inlet and outlet (of the component). And there is no obvious control mechanism unlike most valves. What is it? As the composite already has a pressure reducer.

Any help would be much appreciated.

 

[MarcoNN]

Oh Yeah - the boiler runs on oil

Cheers

 

[Agile]

My initial thought is the pump should be on setting 2 and is probably undersized for the property anyway? I cannot identify the type from what you have said!

I would either fit a much larger pump or probably split the system into two or three zones and use standard pumps for each.

The system should be clean and free of sludge. Thats usually means power flushing for which the cost in London would be about £800 in view of the number of rads you have and would take about two days done properly. Few people would do it properly though.

Tony

 

[MarcoNN]

setting 2 would be 110 and 0,55 as opposed to 140 and 0,65 - OK?
The other details are: Wilo, Type SE125-N
Class F
IP44
PN10
Temp max - 130

 

[Nige F]

dunno about all those figures but I do know a Wilo isn`t as good as a Grundfos...and as Agile said , run @ setting 2 or even 3..and see what happens. that`s the first step, turn up the wilo As to flushing ..if the rads are taken off and flushed outdoors with a hose..then this will help any subsequent power/chemical flushing( and is d-i-y able)

 

[MarcoNN]

Thanks for your help fellas. I'll continue working on it
As for doing the job properly - is it not just a case of using an appropriate cleaner and then switching the flusher between forward and reverse as often as it takes to get the rads at the same temp all over?

Thanks again

 

[JohnD]

you have quite a big installation. if you have a problem with black sludge it is worth considering fitting a Magnaclean on a vertical return pipe. it will trap any circulating black that passes through it, before it has a chance to settle. the chemical cleaners and flushing methods will loosen more sludge than you can get out in one go, and you will be surprised and gratified to see how much the magnet traps, and it will continue working indefinitely.

However if you do not use chemicals or a powerflush to loosen the sediment, it will not collect anything already hardened.

 

[twgas]

is your pipeworkbig enough, many systems that are extended have pipes that are too small for the extra rads.

 

[Gasguru]

It appears the boiler can produce up to 170,000 Btu which sounds more than sufficient however it may have been set at a lower rate. The pump appears to be semi commercial, the figures you quote are the power and current consumption.

I suspect you may need to up the pump speed and balance the system properly. Feel both pipes on the radiators you suspect of containing sludge. Normally you should get aorund 10 Centigrade difference. If there is a significant difference in temperature and the radiators are hot at the top it just needs balancing. If they are the same temperature and the radiator is only hot at the ends and top the raditors is sludged up.

 

[MarcoNN]

TBH i'm not sure now what setting the pump is on. It's either 1 or 3. The graphics/diagram on the pump suggests to my common sense that it's at setting 1. But the as you can see from the figures above, that means the figures for setting 1 are greater than those for setting 2. That doesn't seem right.

That being the case the drawing on the pump is misleading or else i'm easily misled

 

[Gasguru]

The watts/current figures will normally be accompanied with the speed (often designated "n") and could be say 1200/1500/1800. It's easy to tell what speed it's on by listening to the pump...use a long screwdriver held to the ear and pump body.

 

[MarcoNN]

The selector on the control part of the pump points at one of three different things. These 'things' look like the podiums that olympic medalists or F1 wiiners stand on - except they are in ascending order as opposed to the highest being in the middle. By my reckoning that means the smallest one is setting 1 and the largest would be setting 3. Seems logical.
The selector points to the largest one

On the pump body however:

P1 I (A)
(W) 230V

1. 140 0,65
2. 110 0,55
3. 75 0,35

??

'It's easy to tell what speed it's on by listening to the pump...use a long screwdriver held to the ear and pump body' - Gasguru

Tried that and just holding on the pump to see if the vibration changed while moving the selector - no difference that i could detect whatsoever.


'if you have a problem with black sludge it is worth considering fitting a Magnaclean on a vertical return pipe' - JohnD

Nice one JohnD - had been thinking of that

'is your pipeworkbig enough, many systems that are extended have pipes that are too small for the extra rads.' - twgas

Cheers for the suggestion twgas, combination of 36,28, 22 and 15mm. Barring pulling up the floors it's difficult to tell where the 22 changes to 15 etc. Another possibility to investigate.

!!

 

[D_Hailsham]

This pic is taken from the Wilo Instructions which just tell you to set the pump to the correct speed without any clue as to what the little square boxes mean!

For the size system you have it will certainly not be the lowest speed (whichever one that is!), so try the middle setting. You should be able to hear a change in the sound using the screwdriver trick mentioned before. If you don't, this could indicate that the pump is not big enough.

If your boiler is on max output (170,000BTU, 50kw) it needs a flow of about 1.2 litres/sec (assuming 10C temp difference). The performance graph below shows that the pump cannot deliver this rate at the lowest speed, is struggling at speed 2 and will only work at the highest speed if the head is less than two metres. With a big installation like yours I would guess that the head may be as much as 5 or 6 metres. In which case you would need a much larger pump. The only way to confirm this would be to calculate the loss in the index circuit, which would give us the head required.

 

[MarcoNN]

My mistake fellas - the screwdriver test does indeed work , it's on setting 3. Glad we got that sorted out .
Cheers for the diagram D_Hailsham - reassures me that my sanity isn't completely lost.

Cheers for the graph as well, illustrates things nicely. Like i said though, w/o pulling up the floors it's not really possible. I reckon i'm just gonna have to come up with a more rule of thumb solution. Maybe guestimate the index circuit, get a pump that would that would suit that figure on setting 2 and then if it's wrong just turn the pump up or down?

I'll think about it.
Thanks again

 

[D_Hailsham]

The pipe sizes you gave earlier suggest that the installer knew what he was doing, so the head may not be as high as I suggested. Grundfos have a Pump Sizing Program on their website, so it might be worth playing about with it to see what answers it gives.

Choose: Heating - Domestic Buildings - then click the bottom left yellow pump. The two calculators next to Flow and Head enable you to enter basic info for the system to work out this data. There is no need to go through all the steps; once the Start Sizing button is working click on that and you will get the results, including alternatives.