Is the "Smart" meter role out being done ready for another Winter of discontent.

[JohnW2]

Halfway down the page, ultrasonics basically doppler shift. It can be added to any none metallic pipe, without interfering with the pipe.

Halfway down what p[age?

However, you have highlighted the first issue that came to my mind when I stopped to think - 'non-metallic' gas pipes (whether LPG or natural gas) are a no-no, at least in domestic installations.

Kind Regards, John

 

[JohnW2]

Same thing applies, just go and find a flow meter with an electrical output of some sort. The only difference between your LPG and mains gas is that the gas vapour has slightly difference characteristics - so you need a meter calibrated accordingly, otherwise it's identical to one for mains gas.

I realise that - but it is finding something suitable (at a sensible price) which has been the problem. Mind you, it's a long time (years) since I last looked, so maybe I should try again.

I suspect that some can - to a limited extent. But mostly, it's a case of having a pump spray liquid oil through a calibrated nozzle into a forced air flow. If you try and change the flow rate, it affects the atomisation of the liquid - so slow the pump down/reduce the pressure and you get larger droplets that don't burn well.

Fuel injection systems in vehicles seem to work pretty well, over a very wide range of flow rates, don't they?

Or, you could simply tap into the solenoid control to monitor when there's voltage applied. Likely to cause howls of "OMG, you're trying to blow up half the town" if you ever have a professional in to service it, but other than that there should be no problem.

Ah yes, you now remind me (as said, it's years since I thought about this) that I came to realise that that would be the obvious thing to do, particularly given that the connection to the gas valve's solenoid is very easily accessible. I'm not really worried about the potentially raised eyebrows, since there are already aspects of my boiler that would raise them In fact, I could probably do with just a crude 'current transformer' around the feed to the solenoid - so I could probably avoid 'interfering with', or connecting to, the electrics of the boiler!

However, given that 'gas usage' is obviously what I would be interested in, I really need a (calibrated) flow measurement, since 'burn time' alone would not tell me what I wanted to know (and the same would be true of an oil-burning boiler) without knowing what the flow rate was when it was 'burning'.

Some boilers have a "burner lit" indicator, so putting an opto-coupler in series with that would achieve the same result.

Maybe, but not ones as old as mine

Kind Regards, John

 

[Harry Bloomfield]

A diy ultrasonic / doppler speed of gas flow sensor.

 

[Harry Bloomfield]

Halfway down what p[age?

However, you have highlighted the first issue that came to my mind when I stopped to think - 'non-metallic' gas pipes (whether LPG or natural gas) are a no-no, at least in domestic installations.

Kind Regards, John

This one - https://en.wikipedia.org/wiki/Gas_meter Ultrasonics....

 

[Harry Bloomfield]

However, you have highlighted the first issue that came to my mind when I stopped to think - 'non-metallic' gas pipes (whether LPG or natural gas) are a no-no, at least in domestic installations.

OK, I assumed the section of pipe from the tank would be a flexible hose.

 

[JohnW2]

OK, I assumed the section of pipe from the tank would be a flexible hose.

No, it's steel from the tank into the ground. Then (40+ metres of) underground plastic pipe, but which again changes to steel before it emerges from the ground to enter my house - and, as required, all metal (copper) within my house.

Kind Regards, John

 

[SimonH2]

Fuel injection systems in vehicles seem to work pretty well, over a very wide range of flow rates, don't they?

You might think so ...
Some early (crude) petrol injection systems did run the injectors with a variable flow rate - no valves, just vary the pressure. These basically do little more than dribble fuel (petrol) into the airflow - and rely on engine heat to evaporate it fast enough. No such system could come close to meeting current emissions standards (for a road vehicle) as the fuel tends to be still relatively large droplets which burn off leaving a tiny carbon core that goes out the exhaust as soot.
All modern petrol systems run a high pressure rail, with computer controlled solenoid valves to open the injector for a variable time. The high pressure promotes atomisation and cleaner burn.
Similarly, diesel systems have developed. Even old ones used timed valve opening (mechanical valve internal to the injector pump). You may have heard of "spill cutoff" in relation to diesel injection - internal to the pump there's a piston that provides the high pressure, and a spill valve that allows it to go back into the fuel feed. At the start of the injection cycle, the spill valve closes, and the high pressure fuel is then forced to go via the injector.
But again, no mechanical system can meet modern road vehicle standards, and AFAIK everything these days runs a high pressure rail and solenoid controlled injection. But unlike petrol, the diesel injectors contain their own cam-driven pump which allows mind bogglingly high pressures to create the atomisation needed for clean burn - diesel, being a much heavier fuel doesn't evaporate nearly as well as petrol.

Not that I've converted anything modern enough to go down the injection route, but when adding LPG to a petrol engine, choice of injector (or rather, nozzle size) is a bit of an art. If the metering nozzle is too small, you reach 100% open before full engine power and you have an engine that's weak at high power. If the nozzle is too large, control at low power becomes tricker as a tiny change in opening time creates a large change in gas flow rate.

Back to your boiler ...
In principle it would be possible to on-off modulate an injector valve - but I don't think it would be worthwhile. In a car or lorry you are wanting sub-second timing, but in a boiler you generally aren't bothered over periods of minutes. The extra complexity (and noise, the injectors actually make a fair bit of noise) would more than outweigh any benefit. And there's a risk that well running at lower powers, you don't get the combustion chamber hot enough for a clean burn - promoting sooting up.

 

[Harry Bloomfield]

Then (40+ metres of) underground plastic pipe, but which again changes to steel before it emerges from the ground to enter my house

Doppler/ultrasound will work through plastic pipe..

 

[JohnW2]

Doppler/ultrasound will work through plastic pipe..

I realise that but, as I said, that run of plastic pipe is entirely underground (about 1 metre down, as far as I can recall) and hence not particularly 'accessible'. At both ends, what comes out of the ground is steel.

Kind Regards, John

 

[JohnW2]

You might think so ... Some early (crude) petrol injection systems did run the injectors with a variable flow rate - no valves, just vary the pressure. .... All modern petrol systems run a high pressure rail, with computer controlled solenoid valves to open the injector for a variable time. The high pressure promotes atomisation and cleaner burn.

Thanks. Fair enough, then - I obviously did not know that.

Back to your boiler ...

It's not 'mine' - I've never had, nor had anything to do with, an oil-fired boiler. That's eric!

In principle it would be possible to on-off modulate an injector valve - but I don't think it would be worthwhile. In a car or lorry you are wanting sub-second timing, but in a boiler you generally aren't bothered over periods of minutes. The extra complexity (and noise, the injectors actually make a fair bit of noise) would more than outweigh any benefit.

Is that more true with oil than it is with gas (for which 'modulation' now seems very common, if not 'universal')?

And there's a risk that well running at lower powers, you don't get the combustion chamber hot enough for a clean burn - promoting sooting up.

Perhaps - and, if so, I suppose that would be one difference from gas.

Kind Regards, John

 

[SimonH2]

Is that more true with oil than it is with gas (for which 'modulation' now seems very common, if not 'universal')?

Gas boilers modulate in an analogue way. From what I've observed, usually the controller varies the fan speed, and the varying differential air pressure alters the pressure from the gas control valve - thus modulating the gas flow to match the air flow. Because the gas is already a gas, it doesn't suffer the problems from poor atomisation that you'd get if you reduced the pressure in an oil burner nozzle - so as long as you stay within certain limits, gas will burn fairly cleanly over the modulated range. Some, like the ancient boiler still in our flat, just run the fan and vary the gas flow electrically at the control valve - that means a wider variation of mixture, effectively running with an excess of air flow when modulated down.

Again just from observation, gas boilers only modulate down to something like 1/3 or 1/4 of nominal power. I think below this the flame can get unstable. And that's why combi boilers are such a rubbish solution for just about every application they are used for. In our rental flat, I measured (by running on electric for a few days) that an average of just 2 kW could keep the flat at a comfortable temperature in the "barely gets above freezing" spell we had in Dec 2010. The combi boiler, at around 30 kW struggles to heat water fast enough to fill a bath before it's gone cold - but could not range down below about 10 kW. So a massive mismatch between boiler and heating load, and a mismatch between boiler and hot water load With a condensing boiler, the result of that, and the minimum flow requirements, is that unless you oversize the rads (not done when replacing an older boiler with a condensing one), the required bypass on the heating system raises the return temperature such that the boiler doesn't condense much, if at all, when heating.