CH boiler - condensing adaption

[colin stone]

Really one for any CH boiler experts. I had been idly thinking about how to recover the heat from my oil boiler flue gas and I've now come across an apparent nifty device attached to the flue of a boiler and which adds a condensing unit. It strongly resembles a round biscuit tin. The exhaust gases enter the centre of one of the flat surfaces and exit upwards through the curved side to the normal gas flue. Inside the tin is a coil of stainless steel flexible corrugated tubing through which the returning CH coolant circulates to extract the exhaust heat before going into the boiler. At the bottom of the "tin" is a connection for a water trap for the condensate to run out of. The unit reduces the flue gas temp from 230C to 60C, which seems to be a worthwhile reduction and recovery of heat.

 

I've fiddled around with a design in SS and found a couple of firms who will, at a pretty reasonable price, plasma cut the parts, roll cylinders and weld up the bits. It also provides a condenbstaion drain fior the entire flue system. I was therefore wondering if it is worthwhile doing.

 

Any thoughts??

[Nickhlx]

Really one for any CH boiler experts. I had been idly thinking about how to recover the heat from my oil boiler flue gas and I've now come across an apparent nifty device attached to the flue of a boiler and which adds a condensing unit. It strongly resembles a round biscuit tin. The exhaust gases enter the centre of one of the flat surfaces and exit upwards through the curved side to the normal gas flue. Inside the tin is a coil of stainless steel flexible corrugated tubing through which the returning CH coolant circulates to extract the exhaust heat before going into the boiler. At the bottom of the "tin" is a connection for a water trap for the condensate to run out of. The unit reduces the flue gas temp from 230C to 60C, which seems to be a worthwhile reduction and recovery of heat.

 

I've fiddled around with a design in SS and found a couple of firms who will, at a pretty reasonable price, plasma cut the parts, roll cylinders and weld up the bits. It also provides a condenbstaion drain fior the entire flue system. I was therefore wondering if it is worthwhile doing.

 

Any thoughts??

 

Yes - have been thinking about that myself so would be interested in the updates...

 

Nick

[Theo]

Really one for any CH boiler experts. I had been idly thinking about how to recover the heat from my oil boiler flue gas and I've now come across an apparent nifty device attached to the flue of a boiler and which adds a condensing unit. It strongly resembles a round biscuit tin. The exhaust gases enter the centre of one of the flat surfaces and exit upwards through the curved side to the normal gas flue. Inside the tin is a coil of stainless steel flexible corrugated tubing through which the returning CH coolant circulates to extract the exhaust heat before going into the boiler. At the bottom of the "tin" is a connection for a water trap for the condensate to run out of. The unit reduces the flue gas temp from 230C to 60C, which seems to be a worthwhile reduction and recovery of heat.

 

I've fiddled around with a design in SS and found a couple of firms who will, at a pretty reasonable price, plasma cut the parts, roll cylinders and weld up the bits. It also provides a condenbstaion drain fior the entire flue system. I was therefore wondering if it is worthwhile doing.

 

Any thoughts??

 

Sounds a topping idea. anything to reduce the amoubt fo diesel that you burn.

 

N

[Dave Hannigan]

Certainly sounds good in principle. My initial thoughts are that these devices are fitted to boilers with fan assisted flues and only if approved by the boiler manufacturer that the flue fan can do the job.

 

On a natural draught flue the temperature of the flue gasses contributes to the effectiveness of the flue and lowering this temp could stop the flue working properly, with obviously all sorts of nasty possibilities to do with CO poisoning.

 

Also the flue above the condenser would condensate, which is acidic and could compromise the flue integrity. I have seen some condensing boiler installations where copper has been used as the condensate drain and has resembled a sieve within 18 months.

 

Having said that, if you could get one to work properly, you could make a fortune.

 

Dave

[colin stone]

Certainly sounds good in principle. My initial thoughts are that these devices are fitted to boilers with fan assisted flues and only if approved by the boiler manufacturer that the flue fan can do the job.

 

On a natural draught flue the temperature of the flue gasses contributes to the effectiveness of the flue and lowering this temp could stop the flue working properly, with obviously all sorts of nasty possibilities to do with CO poisoning.

 

Also the flue above the condenser would condensate, which is acidic and could compromise the flue integrity. I have seen some condensing boiler installations where copper has been used as the condensate drain and has resembled a sieve within 18 months.

 

Having said that, if you could get one to work properly, you could make a fortune.

 

Dave

 

I saw the item on this ACV boiler -

http://www.acv.com/int-en/03_04/281/app.rvb

and I am getting a slightly smaller ACV. The boiler in question is not fan assisted but has a "blue flame" burner, which I guess burns a little cleaner than a standard yellow flame burner, so I would probably need to clean out more frequently. The flue above is stainless steel.

From the Danfoss boiler nozzle calculator, reducing the flue gas from 240C to 60C, increases the boiler efficiency from 89 to 98%.

 

A pressure jet boiler does shove the gasses up the flue with a reasonable force at the normal 240C and I think will still have enough energy at 60C to get up a 2.5m vertical flue. My generator provides a reasonable comparison. This has an integral water cooled silencer and the exhaust gas leaves that at approx 60C, and still has sufficient energy to propel itself along a 5m horizontal exhaust pipe.

[Theo]

I saw the item on this ACV boiler -

http://www.acv.com/int-en/03_04/281/app.rvb

and I am getting a slightly smaller ACV. The boiler in question is not fan assisted but has a "blue flame" burner, which I guess burns a little cleaner than a standard yellow flame burner, so I would probably need to clean out more frequently. The flue above is stainless steel.

From the Danfoss boiler nozzle calculator, reducing the flue gas from 240C to 60C, increases the boiler efficiency from 89 to 98%.

 

A pressure jet boiler does shove the gasses up the flue with a reasonable force at the normal 240C and I think will still have enough energy at 60C to get up a 2.5m vertical flue. My generator provides a reasonable comparison. This has an integral water cooled silencer and the exhaust gas leaves that at approx 60C, and still has sufficient energy to propel itself along a 5m horizontal exhaust pipe.

 

I was thinking that it might work with my old Mikuni. That seems to squirt out hot exhaust at a considerable speed.

 

N

 

I was thinking that it might work with my old Mikuni. That seems to squirt out hot exhaust at a considerable speed.

 

N

 

Develop[ing the idea a bit: would it be possible to fit a condenser on the main engine exhaust to get some extra energy there?

 

N

[nauticus]

Hi There why not coil acopper pipe round the outside of your flue then lag it this will do the same job as a condenser without changing your flue draw,and it will be much cheaper,Ron

[MikeV]

Hi There why not coil acopper pipe round the outside of your flue then lag it this will do the same job as a condenser without changing your flue draw,and it will be much cheaper,Ron

I doubt you'd acheive the same improvement in efficiency and, even if you did, you'd be causing condensation on the inside of the flue which would likely run back into the boiler. As noted above, this condensate is very acidic. It even eats away aluminium.