Atmos or Intergas

[D_Hailsham]

Your homework for today is to calculate the flow rate/velocity through that 28mm tube @ 40kw load......I would guess velocity would be in excess of the preferred 0.3 metres/second.

Shall I work it out for him?

Flow rate for a 40 kW boiler with a 20C differential is 40/(4.18x20) = 0.478 litre/sec or 478 cc/sec.

Inside diameter of 28 mm pipe = 26 mm or 2.6 cm. So area of pipe = (2.6/2)² x π =5.31 cm².

Velocity = 478/5.31 = 90cm/sec = 0.9 m/s.

If the differential was lower than 20C the velocity will be inversely proportional, i.e at 10C it will be 1.8 m/s

To achieve a 0.3m/sec velocity the header would have to be 45mm inside diameter.

 

[mogget]

Previous two posts very insightful, thanks.

 

[doitall]

And as I said impossible, even if you take the pump from the return and fit it in the flow after the manifold.

I know what I tested an what I got. The two heating pumps on the flows, combined pumped more than the primary header pump in the boiler. All the flow from the boiler HAS to run into the heating circuits.


When the TRVs close up and the smart pumps wind down the primary header pump will pump more than the two of them and then water will flow right along the header to the return to the boiler. This is all very obvious.

The area of the two 22mm pipes is more than the area of one 28mm pipe. But as the primary pump will be at its lowest speed and the Smart pumps run up and down to suit I thought this marginal, but fitted the 28mm header as I had the fittings. If it did not work I would have gone up to 35mm copper pipe for the header, a simple thing to do. If I did not have the 28mm pipe and fittings at hand I would have put in 35mm as belt and braces approach.

This is a superb cheap way of getting two heating zones and TRVs on all radiators. The boiler will last longer having a guaranteed flow through its heat exchanger.

And I still say impossible and I'll add rubbish as well.

For the record 1 x 28mm is more than 2 x22mm.

Ok back on track the primary pump on the return is not working against the 2 heating pumps on the flows, they are all working together.

So the 3 flows must be equal to the 3 returns or one or more pumps will be stalled as that is not possible one or more of the pumps will be starved, therefore circulaton through the header is not a consideration, it must take place or your boilers gonna have a very short life.

 

[Steelmasons]

You have spoilt it Mr hailsham as I'm sure Alex would have got there in the end.........Not.

 

[Steelmasons]

Acknowledge your failings Alex , don't go the similar route brightonguy took , we are here to help/advise....hope to hear from you in the near future.

 

[AlexCarp]

Your homework for today is to calculate the flow rate/velocity through that 28mm tube @ 40kw load......I would guess velocity would be in excess of the preferred 0.3 metres/second.

Shall I work it out for him?

Flow rate for a 40 kW boiler with a 20C differential is 40/(4.18x20) = 0.478 litre/sec or 478 cc/sec.

Inside diameter of 28 mm pipe = 26 mm or 2.6 cm. So area of pipe = (2.6/2)² x π =5.31 cm².

Velocity = 478/5.31 = 90cm/sec = 0.9 m/s.

If the differential was lower than 20C the velocity will be inversely proportional, i.e at 10C it will be 1.8 m/s

To achieve a 0.3m/sec velocity the header would have to be 45mm inside diameter.

Nice calcs, which are easily available. Your calcs are for a worse case scenario of fixed temperature applications using a fixed rate 40 kilowatt boiler.

This system modulates right down with burner & modulating heating pumps and will be right down the vast majority of running time rendering your calcs rather not applicable for 95% plus of run time operation.

The boiler is not running at 40 kilowatts. It was turned down. The controls allow that. When the system is up to temperature, which is very quickly, the boiler modulates right down meaning the 28mm low-loss header is adequate. I know I have done the physical tests using thermometers. I was prepared to increase the header to 35mm copper but had no need to.

As I have emphasised, the best way of having a two heating zone system with TRVs on all rads is using a boiler with weather compensation and smart pumps on the heating zones. Cheap and easy and highly effective. I would advise to use 35mm pipe for the header to be sure. 45mm copper for a low-loss header in an average UK home is ridiculous using the above.

 

[AlexCarp]

we are here to help/advise....hope to hear from you in the near future.

You have not helped at all. I am the one helping as I am giving you the results of what I did. Which work brilliantly.

 

[Dan Robinson]

My spidey senses tell me we have yet more drivel coming our way from Mr Crap on this one.

 

[Dan Robinson]

we are here to help/advise....hope to hear from you in the near future.

You have not helped at all. I am the one helping as I am giving you the results of what I did. Which work brilliantly.

You are about as helpful as TCP with VD.

 

[mogget]

You are about as helpful as TCP with VD.

 

[AlexCarp]

we are here to help/advise....hope to hear from you in the near future.

You have not helped at all. I am the one helping as I am giving you the results of what I did. Which work brilliantly.

You are about as helpful as TCP with VD.

Another insult from a technical inept. You have nothing to add. Keep them up the more you throw they more you expose your lackings.

 

[Steelmasons]

Where can I purchase some 45mm copper tube Alex???

 

[doitall]

http://tjjcdd.en.made-in-china.com/...raight-Copper-Pipe-1-2-12-5mm-45mm-80mm-.html

 

[SimonH2]

Shall I work it out for him?

Flow rate for a 40 kW boiler with a 20C differential is 40/(4.18x20) = 0.478 litre/sec or 478 cc/sec.

Inside diameter of 28 mm pipe = 26 mm or 2.6 cm. So area of pipe = (2.6/2)² x π =5.31 cm².

Velocity = 478/5.31 = 90cm/sec = 0.9 m/s.

Now repeat with more sensible values. As usual, 40kW is the high power needed to make a combi vaguely usable and it pretty irrelevant to heating requirements - the heating load for most properties is much much less than that, if it isn't then it's unlikely to be a property where a combi is sensible ! So say 10kW tops (note he said he has the primary pump on it's lowest setting), and probably much less than that most of the time.

Whatever you may say about terminology and whether this is a "low loss header" or not - it's a system that works and it's a system I'd consider (where I couldn't fit in a thermal store, or at least a buffer tank).

 

[Steelmasons]

Shall I work it out for him?

Flow rate for a 40 kW boiler with a 20C differential is 40/(4.18x20) = 0.478 litre/sec or 478 cc/sec.

Inside diameter of 28 mm pipe = 26 mm or 2.6 cm. So area of pipe = (2.6/2)² x π =5.31 cm².

Velocity = 478/5.31 = 90cm/sec = 0.9 m/s.

Now repeat with more sensible values. As usual, 40kW is the high power needed to make a combi vaguely usable and it pretty irrelevant to heating requirements - the heating load for most properties is much much less than that, if it isn't then it's unlikely to be a property where a combi is sensible ! So say 10kW tops (note he said he has the primary pump on it's lowest setting), and probably much less than that most of the time.

Whatever you may say about terminology and whether this is a "low loss header" or not - it's a system that works and it's a system I'd consider (where I couldn't fit in a thermal store, or at least a buffer tank).

How wrong can one be..

Whether the burner is running @ low modulation or high modulation then design criteria has to be catered for the latter and not the former.

As your signature suggests you are an enthusiast and not a professional.

Using the correct size header won't exactly break the bank as opposed to fabricating using a smaller diameter , or are you suggest a low loss header is not necessary on this particular boiler?