solid fuel and pressurised cylinder??????

kerryplumber

hi lads,
just had a call from a potential customer. he has a 300 ltr joule cylinder that is being heated by solar and an oil boiler at the moment. (not sure why its a triple coil) he now wants to add a boiler stove to the mix. problem being that his domestic water is fully pumped by a grundfuss mq.
cylinder is upstairs and the new stove would be directly below it. what would be the best (safiest) way to do it. the heating system is pressurised also, could be made open vented or use a heat genie??

shane 007

You cannot pressurise a cylinder with solid fuel going into it but there are ways to make it safe.
Open vent the DHW.
Install a second indirect copper cylinder, coil is fed by the solid fuel, the contents is pumped though the outlet (also with an osvp) to the 3rd coil of the pressurised cylinder but the pump is via a cylinder stat with a high limit. The cold feed of the copper cylinder is connected ton expansion vessel in the attic for expansion.
This copper cylinder must have a 1" coil & sized accordingly to the solid fuel output.

I can do a drawing for you if this is a feasible option.

Dtp1979

shane 007 wrote: »

You cannot pressurise a cylinder with solid fuel going into it but there are ways to make it safe.
Open vent the DHW.
Install a second indirect copper cylinder, coil is fed by the solid fuel, the contents is pumped though the outlet (also with an osvp) to the 3rd coil of the pressurised cylinder but the pump is via a cylinder stat with a high limit. The cold feed of the copper cylinder is connected ton expansion vessel in the attic for expansion.
This copper cylinder must have a 1" coil & sized accordingly to the solid fuel output.

I can do a drawing for you if this is a feasible option.

Is this like what Richie was talking bout a few weeks back?
Or is it like a replacement for the heat genie/ firebird model?

shane 007

Dtp1979 wrote: »

Is this like what Richie was talking bout a few weeks back?
Or is it like a replacement for the heat genie/ firebird model?

No. We are talking about 2 very different scenarios. Pressurised heating systems are very different to pressurised domestic hot water systems & are treated very differently. A tap isn't opened on a heating system but is on a hot water system. This is the potential for explosion when temperature is above 100C, so this needs to be considered.

kerryplumber

Dtp1979 wrote: »

Is this like what Richie was talking bout a few weeks back?
Or is it like a replacement for the heat genie/ firebird model?

even with the genie or firebird its not allowed to have solid fuel in a pressurised cylinder is it

shane 007

kerryplumber wrote: »

even with the genie or firebird its not allowed to have solid fuel in a pressurised cylinder is it

No.

richieburke01

Shane is spot on
A big no for pressurised hot water with solid fuel
dangerous
I was talking about heating only

richieburke01

Is this tried and tested Shane

kerryplumber

richieburke01 wrote: »

Shane is spot on
A big no for pressurised hot water with solid fuel
dangerous
I was talking about heating only

so what is the best way to have the best of both worlds so to speak. what way would u do it say in a retro fit and a new build

shane 007

richieburke01 wrote: »

Is this tried and tested Shane

Yes. The important factor is there is no "uncontrollable" heat source into a pressurised cylinder. Having the heat from the cylinder only pumped to the pressurised cylinder side covers this. There will be a spring loaded non-return valve at the circulating pump to eliminate a creep circuit. The pump is wired through 2 stats in series circuit. One at the pressurised cylinder to pump upto 65C, whilst the second cylinder stat on the copper cylinder to pump above the set temperature, so it's not pumping cold water through the coil. You could even wire it through a solar differential controller to have a T1 - T2 circuit & differential delta T to maximise efficiency & eliminate unnecessary cooling of the pressurised cylinder when the copper cylinder cools down.

shane 007

kerryplumber wrote: »

so what is the best way to have the best of both worlds so to speak. what way would u do it say in a retro fit and a new build

In all honesty, the best way is not to have any solid fuel going into a pressurised hw system. It's as simple as that & the customer needs to understand that & the implications of altering that ethos.

shane 007

The other option would be to open vent the pressurised cylinder & use a twin impeller pump for the showers. Everything else back to gravity fed.

kerryplumber

shane 007 wrote: »

The other option would be to open vent the pressurised cylinder & use a twin impeller pump for the showers. Everything else back to gravity fed.

yep, that's what I would normally go for, just wondering if there is any way to have fully pumped and solid fuel together, say on a new system. or is a case of cant be done. (and then wait for the customer to tell me the other lad said it can)

shane 007

I think if you explain how the issue occurs, you will find they side with you.

I'll try to simplify the explanation:
Water at atmospheric pressure boils at 100C.
Water at 1 bar boils at 122C.
Water at 2 bar boils at 144C, etc.

So pressurised cylinder is at 3 bar cold, so it won't be problem.
We install solid fuel & it was a warm sunny day. Solar has the system at 70C. No problem there.
It's a chilly night & the customer lights a stove to heat the parish & the P & T valve has failed or was blanked by a plonker because it was dripping.
Temperature hits 101C but still not an issue as the cylinder is now at 5 bar so the boiling point is nowhere near its change of state from water to steam.

If we boil 1 litre of water, we get 1,600 litres of steam in volume from that 1 litre of water.
Customer opens a tap & is bringing the pressure of the cylinder back to atmospheric pressure, thus lowering it's boiling point. We now hit its flash point & with a cylinder volume of 300 litres, that's potentially 300 x 1,600 = 480,000 litres of steam trying to fit into a 300 litre volume cylinder. Kaboom......

Pressurised cylinders require a 3 tier protection system, namely the cylinder stat set at 65C, a high limit stat set at 85C & the temperature relief valve at 95C.
Pressure is not the problem, it's temperature. A stainless steel cylinder at generally rated at 10 bar, tested to 15 bar & in reality would not blow until they reach 25 bar. There is nothing in our systems that can reach 25 bar but there is elements that can reach in excess of 100C.
By installing solid fuel. We are eliminating our first 2 tiers of protection & relying on our final level of protection, the P & T valve. These can fail & plonkers usually blank them when they drip. They should also be tested annually.

JohnnieK

All this info should be in your book's from college guys.

I remember my lecturer telling us to be prepared for a court case :-)

JohnnieK

All this info should be in your book's from college guys.

I remember my lecturer telling us to be prepared for a court case :-)

shane 007

Here's the drawing. It's only done in Word so not the best graphics. I haven't put the solid fuel plumbing system in the detail, nor the detail of the cylinder, but you should get the idea.

Also the wire from the controller to the circulating pump would also go through the high limit stat but for ease of understanding, I have not shown this as it may confuse.

For electronic control, PT1000 sensors would have to used, otherwise simple stats would be used, but this may not eliminate cool water being pumped from the copper cylinder to the pressurised cylinder.

Bruthal

shane 007 wrote: »

If we boil 1 litre of water, we get 1,600 litres of steam in volume from that 1 litre of water.
Customer opens a tap & is bringing the pressure of the cylinder back to atmospheric pressure, thus lowering it's boiling point. We now hit its flash point & with a cylinder volume of 300 litres, that's potentially 300 x 1,600 = 480,000 litres of steam trying to fit into a 300 litre volume cylinder. Kaboom......

Potentially, but not likely in reality.

The water will boil if the pressure drops enough alright. But as soon as the pressure goes back up due to any steam, the boiling point increases again as the pressure goes up. The 300 litres doesnt simply and instantly turn to 480,000 litres of steam.

In a cooking pressure pot, which reaches 14psi, and so water boiling point is 122C, if it has its pressure release manually pressed, the water can be heard re-boiling, but it doesnt simply all turn to steam, and the pressure release does not re-open if released, because it cant re-pressurise above what it was without further heat provided.

Any vessel at 3 bar (example) and water is above 100 degrees, and drops in pressure due to tap opening, the water begins boiling, it cant go above the pressure it was at without further heat added, since the steam produced will simply re-pressurize it, and it cant all just turn to steam since the pressure would increase the boiling point again, so the pressure can only return to at or below what it was before the tap was turned on.

Now the heat source may be adding further heat, but this was the case anyway, without opening a tap.

Not recommending a stove should be added to a pressurised system, just posting an opinion on the boiling water from pressure drop scenario.

Firstly to keep things simple: solid fuel stoves and unvented cylinders can go boom boom(no science required)

Secondly this thread is not only old but half the posters have closed their accounts so due to this I'm closing it.