Integrated woodburner, solar tubes, oil combi and underground heatstore.

[daftlad]

I like the extra copper in the ground suggestion, mainly cos its easy to do  Wink
Whaddya mean get an electrician  Huh
What test would the new electrodes, err scrap copper pipe, be requiring ?

You only need to test if you remove the official leccy earth electrode, which you shouldn't.

Pontiff,
I think noel has all of the plumbing in the gravy connected together so I would doubt that the copper and steel are working as annode and cathode, more likely that the mass of earth is acting as cathode (I think) and the copper and steel together is acting as anode? (or is it the other way round). The steel and copper are connected together, like shorting the terminals on a battery.
Apart from that you sum things up nicely, and of course I may be talking rubbish.
ta ta

[pontiff]

Pontiff,
I think noel has all of the plumbing in the gravy connected together so I would doubt that the copper and steel are working as annode and cathode, more likely that the mass of earth is acting as cathode (I think) and the copper and steel together is acting as anode? (or is it the other way round). The steel and copper are connected together, like shorting the terminals on a battery.
Apart from that you sum things up nicely, and of course I may be talking rubbish.
ta ta

It doesn't matter if they are touching or not, if they were both acting as anodes/cathodes then both metals would be corroding/notcorroding. It's called a galvanic couple when connected directly.

At the anode, the Fe metal is losing electrons ( oxidation) and forming Fe2+ ions which dissolve into the gravy electrolyte.

The electrons are used at the anode where they either turn hydrogen ions ( acid ions) into hydrogen gas ( that's why acidity is bad, it drives the reaction) or if oxygen is present as well, it will combine with H+ ions and make water.

An early example of this was seen in ships which coated their hulls with copper sheet to reduce the amount of barnacle build up on their hulls. Unfortunately they used iron nails to attach them :-  

http://openlearn.open.ac.uk/mod/resource/view.php?id=233624


( Noelsquibb, note bacterial corrosion further down that page- more bad news I'm afraid  )

Noelsquibb, one way to slow down the corrosion would be to paint/coat the bare copper, as this is where the real driving force of the reaction takes place. Also, leave the rust coating on the radiators, as this will add electrical resistance.

Here's a  link to a fascinating powerpoint about this stuff. guaranteed to cure even the most severe insomnia.

http://www.authorstream.com/presentation/Cubemiddle-36438-UN1001-Galvanic-Corrosion-REACTOR-CHEMISTRY-Section-4-Eight-Forms-SERI-as-Entertainment-ppt-powerpoint/

[daftlad]

You obviously know more than me 
Do you think the voltage between the mass of earth and the metalwork (copper and steel) will also cause corrosion? Do you think it is worth providing a local earth electrode to earth the pipes?
Why doesn't this happen in normal open vented thermal stores?
ta ta

[noelsquibb]

On the chemistry front I'm afraid I don't have many answers to preventing your radiators from disintegrating slowly....
The reason it's causing such debate is because there is an awful lot of chemistry going on here....
It's called a galvanic couple when connected directly.

Pontiff

we're not worthy ......

Everyone seems to be smarter than me around chemistry but you are up on a pedestal !

You have loads of answers and they all seem to point towards the removal of the iron from the heatstore.

As for the 'awful lot of chemistry' , hey, that was the only thing I did know.



Ive done ( and saved ) the powerpoint on galvanic corrosion and its a bit over my head but seems to pull a lot of aspects together.

It looks like there might be a way to stuff some leccy in somewhere and modify the reactions but which direction does any introduced current flow ? The presentation enjoys asking valid questions but is a bit elusive with any answers.

I suppose I was always being too simplistic in thinking the steel rad heat exchanger was in essence no different to a normal CH layout with steel / copper / steel in the circuit and all in contact with moving hot water

I'm truly grateful and promise I will try to stay awake and really concentrate, whenever you are attempting to enlighten us.

It would seem that there will always be some tendency for metals in hot oxygenated water to corrode and that we need to consider bacterial corrosion too. Now why did I think getting the water hot enough would kill any bacty ?
Electrocution perhaps ?

Any thoughts on the pH and general 'gravification' of the water and its possible effect on GRP ?
Any thoughts on painting the copper when the heat exchanger array is reconfigured to remove the steel rads ?

now, if you need a big hole digging somewhere .......

noel

[pontiff]

Thanks for the kind words, normally when I talk chemistry to people I'm called a boring old fart.....kids can be so cruel 

I'll get back to you with more info but I'm pulling an all nighter marking soddin exams and, as you are probably realising, I'm easily distracted.

Coating the copper is definitely a way forward to slow the reaction, though I don't know much about waterproof paints. Having said that, I blacked the bottom of the canal boat I built with some excellent bitumen based gunk..... I'll try and find its name. Coating the steel rads isn't as effective, the corrosion just becomes more focused on the weakest points.

Using leccy to prevent corrosion is possible but very comlicated to get right as you would have to match the output very precisely or you could end up dissolving the copper! It's called Impressed current cathodic protection and it's used on huge structures such as pipelines. There's a bit about it here

http://en.wikipedia.org/wiki/Cathodic_protection#Impressed_Current_CP

The sacrificial anode would do the same job and would be much easier.

As for the acidity, I think lye (caustic soda) ( sodium hydroxide) is over doing it a bit and very nasty stuff to handle (especially on the eyes).
Limestone would work for a while but unfortunately gets coated quite rapidly and needs to be replaced.

Sodium carbonate ( washing soda crystals) might help :-

http://en.wikipedia.org/wiki/Sodium_carbonate

but then again, it might make the electrolyte even worse... my head hurts.

[noelsquibb]

Hi Pontiff

Hope you survived the exam marking.

Ive been eagerly awaiting the 'more info' you teased us with ... 
What further nuggets of knowledge can there be 

You have clearly confirmed the way forward but I would appreciate your thoughts on my understanding of this.

When you say that its two metals that couple galvanically, will I have a problem with solder and copper ?

I have to replace the steel rads that so effectively impart the heat to the store and have to plan an equivalent in copper tube.  I guess this will probably consist of sets of parallel tubes that take up the same space as the steel rads, as they form part of the combined heat exchange structure. The idea that a further galvanic couple could evolve, concerns me somewhat.

Would the sacrificial zinc, that I have nearly ordered,  be helpful ?

A further consideration that might impact any chemistry, is the source of water that the heatstore gets refilled with after the rebuild.
The choices I have are mains water, stream water and groundwater.
Any thoughts ?

And finally, picking up on a trailer for a BBC R4 prog tomorrow night, there seems to be a shortage of zinc looming.

Some of the tailings in the mine settling ponds appear to be up to 20% zinc ore, with lead and iron the other predominant metals.

Is there any potential 'redneck' chemistry that might tease out / separate the various metal ores ?


noel

[pontiff]

Hi Noel,
You're spot with the solder issue, the best type to use would be lead/tin based solder (if you can still get it!) as the cell potential between copper and lead/tin is quite low (about 0.2V) so I don't think it would be a big issue. I would definitely coat the less reactive metal (the soldered joint) with some waterproof paint, maybe this stuff?

http://www.diy.com/diy/jsp/bq/nav.jsp?action=detail&fh_secondid=10487616&ecamp=trf-005&CAWELAID=350176934

A zinc or magnesium sacrificial anode would add even more protection but perhaps a bit over the top unless you have some scrap handy.

I made ( correction, got the kids to make  ) mini mock ups of your gravy pit out of painted nails and bits of copper sheet and sure enough we soon had the makings of a good soup. Salt solution made a huge difference to the rate of corrosion but even in distilled boiled water with a dash of cooking oil on the top it  began to brown after a few days. If your tap water is softer than your river water then I'd use that. Basically , whatever has the least dissolved in it.

I wouldn't start panic buying zinc just yet, there is plenty of zinc in the Earths crust , it's just not being mined fast enough at the moment to supply the demand. It's also a pain to extract from its main ore ( sphalerite).

Best of luck with it all, it's such a shame the rads have let you down.

I've got to pop off now for a freebie snowboarding trip to Italy. It's a tough job but somebody has to it! 

[noelsquibb]

I made ( correction, got the kids to make  ) mini mock ups of your gravy pit out of painted nails and bits of copper sheet and sure enough we soon had the makings of a good soup. Salt solution made a huge difference to the rate of corrosion but even in distilled boiled water with a dash of cooking oil on the top it  began to brown after a few days.

I cant quite believe what you've done pontiff.
What a great bit of lateral thinking.
You've investigated several options to try and fix my problem, at tax payers expense  and opened a few kids eyes to a real world situation that needs an understanding of chemistry.

Did you give em the story behind the gravy pit ?

I really wish someone like you had taught me chemistry all those years ago ....

thank you.

Please don't feel bad about leaving us to check out the frictional qualities of those crystalline water deposits 

noel

[pontiff]

There was literally pence of chemicals involved in the project, but don't worry, I nicked some cash out of their bags whilst they were absorbed by the pictures of your thermal store. 

Electrolysis and displacement reactions are on the specification so I wasn't going off on too much of a tangent ( although I was in the middle of teaching about microbes!). Ofsted always tell us a good lesson explains the relevance of the topic so you were doing me a favour!

Time to go slip sliding! I will of course be offsetting the carbon cost of my trip by some pv generation whilst I'm away. I've instructed Mrs Pontiff to only use leccy in emergencies.

[Moxi]

Hi Noel,

I'm afraid Pontiff has it perfectly stitched up, you have a nice battery, buffering the pH in the receiving water to about 8.5 will reduce corrosion but not prevent it, any stray electrical current from earthing will exacerbate the problem.

Using an all copper installation is probably the best solution but not cheap.  I wondered if you could use 10mm micro bore in vertical coils mounted over rigid back's made of hdpe pipe (whats the store max temp?) mounted vertically in the store (like pod boilers in some power stations) this would negate chemistry issues, otherwise its lots of 15 or 22mm soldered together with U's to form bundles of more conventional heat exchanger tubes which could be self supporting and stand on the base of the store.

Sorry its not more positive.

Moxi

[noelsquibb]

Moxi, thank you for ploughing through the story to date.
Didnt think you, or anyone really, would be likely to disagree with pontiff though.



Today I was able to do a routine check up of the gravy pit and there do seem to be some small positive developments  -

The expanding foam on the lid, that I had used to replace the areas that got pulled off by stickiness, has continued to expand and a hacksaw blade and spade was needed to get the cellotex lid up.
The stickiness would appear to be the surface of the GRP not setting and is no longer a problem as there is now a covering layer of plastic stuck to it.
So the hot wet atmosphere effects the expanding foam and the polyester resin in the GRP.

The paint layer on the top radiator is looking like a medieval skin condition as it blisters and wrinkles, suggesting that the end is nigh for the steel rads.

Last time I checked, the voltage reading between the steel /copper incoming heat circuit and the gravy was 0.6 volts. Today it was zero.

The amount of water pumped out of the insulation layer appeared to be less than the drop in water level.

Using my recently returned and presumably calibrated,  pH/EC/TDS/ temp, hand held meter from Hanna Instruments, I got the following readings -


Location    temp (c)     pH      EC( mS )  TDS (ppm)

tap              6.7         9.03     125            63
insulation     11.0        10.65    2170         1087
gravy          56.0         5.03     799           397


Electrical conductivity generally relates to total dissolved solids in the water I test  and they indicate how much dissolved metal is in the water. ( yeah I know thats not quite right )
What ever is happening to the water that ends up in the insulation though ?
Is there something in the cellotex foam or thermalite blocks that is modifying the water.
Pulverised Fly Ash in the blocks ?
What do they use to bind it together ?
Ah chemistry .............

On a more mundane note, I think Im going to get to the end of March with the log supply ( assuming the steel rads hold out that long ) -

[noelsquibb]

even less interesting but possibly useful, is something I did when I clad the logshed with feather edge boarding.
I cut several 10mm long bits of underground water pipe and used them as spacers so that the featheredge acts more like louvres and lets plenty of air circulate whilst looking like close boarded -

[noelsquibb]

and finally ( for today anyway)
heres a shot showing the proximity of the logshed to the house and a shot of the confluence of the stream that passes close to the logshed as it enters my property.

The stream has been split for approx 100m upstream and has a solid boundary with water flowing either side of it.
I suspect there was a dispute over water rights, when the now defunct leat feeding the mine operations got built.

Winter flow looks like around 300-500 litres a sec. I really should get a measuring wear built.

[Moxi]

Noel,

you need to get the pH of the gravy up in to the alkaline region to limit the corrossion aim point 8 or 9 should help a lot.

Moxi

[noelsquibb]

Hi Moxi

Ive not replied to your pH advice but thank you anyway. I'm a bit more concerned with Ivan's thoughts that too alkaline and I will destroy the GRP.  Its actually easier to replace the steel rads I reckon.
The pH was slightly higher today and the water below the black shiny skin was the clearest Ive seen it since the first fill up. So its sort of improving.

Anyway, exciting new developments -

Yesterday in a moment of weakness, I 'won' a lump of zinc on fleabay ( yeah, I felt lucky )
So imagine my dismay when, within a couple of hours of me telling the gravy pit, the WBS started to gurgle like a good un, with the boiler temp in the normal range.  I was so convinced that the water had escaped the boiler circuit through a new hole in a steel radiator in the heatstore, that I shut the fire down hard and went on line to search for coatings that will be happy on top of GRP 'gelcoat',  in a hot wet acidic environment.  And at the same time, working up a plan of attack to extract the heat exchangers and reconfigure them. Yeah Ive been dreaming about this moment.
So, imagine my surprise when about 11.00 pm last night, when I'm usually banking the fire for an overnight burn, I went outside and out of curiosity, checked the pressure gauges on the two expansion tanks in the control cupboard and bu66er me, the pressure was the same as usual. Very odd but also cheering as it meant I could possibly continue heating everything with the WBS.
So I bled the high point on the WBS and released a fair amount of air without loosing much pressure on the circuit.
Well , there was still enough ember to goose the fire, so I gave it some, watched the temp go up enough to trigger the pump and alls well. So fire stoked and set for overnight burn.

Woke up this morning to the sound of utter silence. 4 letter words are my favorite, power cut ! How long have we been off ?  err bout 4 hours.
Now I'm awake ! WBS boiler temp showing 120c. Oops, the gauge don't go any higher.

So out to shed and roll out the 4.5 kva diesel genny, lash up the very naughty feed into an outside socket, having isolated everything from the mains, to energise the board and get systems working.

The system pressure was still approximately the same as the night before and boiler temp came down very slowly while I felt smug and boiled the only electric kettle that would be working for a fairly large area ( I knew that cos the phone was working as well and I could phone western power for a friendly chat )
So once the boiler temp was down to a bit below 70c, I chucked a couple of logs on and revved the fire up, thinking that we had got away with a power failure.

A huge weakness in my layout is the fact that theres no heat dump default and that I can only shift hot water by pumping.  My instructions  in the event of the WBS burning and a power failure, is to shut the fire down hard. ( If I am at home and its looking like a proper power failure, I will set up the genny and we can carry on as normal )
If we are lucky the water temp will drop as the fire temp drops. It often ticks over at a temp just below the pump cutting in, so its a proven state.
If we are unlucky and it gets too hot, the two pressure relief valves kick open and dump the contents of the circuit on the gravel below the veranda decking, leaving the boilers to 'do what they will' inside the fire.

Only today, we hadnt got away with it, cos the boiler temp quickly shot up to 90c with the fire hardly doing anything.
Further proof that something was wrong, was the noisy running of the pump and the fact that I needed to treat my hand with burn cream after I casually wrapped it around the pump body to feel the water temperature.
Odd that the pressure readings were still around 1 bar but I suppose that steam pressure is good enough for the gauges.

So a proper bleed round ( 6 bleed points) and eventually the circuits all full of water again, rev up the fire, pump cuts in and alls well.  Phew !

However this raises the question of how to deal with the next unattended power failure with WBS going.

Does anyone do alarm clocks that go off if the power fails ?

There is a possible space just above the WBS where I could hang a radiator ( see pics )
I reckon I could hide a 'double' rad 0.5 m high and 1.2 ? long, Ive got 1.5m but need room for pipes in and out.

It will be pretty uncomfortable to do as theres not quite standing room either side of the fire but the main challenge will be to be allowed to create a big hole in the block skin above the timber lintel to let some of the heat out otherwise I don't think it will be very effective.

Somehow Ive got to try and sell the hole as an opportunity to do something 'creative' cos I doubt if the bits of bent twig that currently decorate the chimney breast will work . Perhaps one of those weird metal assemblies that looks like a tree or summat 

Question is, will a rad in this location be effective ?  Theres already a lot of heat in this space with the single skin stainless flue pipe and the heat radiating from the fire skin ...