Intergas heat exchanger design

[JonathanM]

The heat exchanger seems to be a very important part of the boiler, and following the discussion last weekend, I've been trying to understand more about the pros and cons of the different types. I hadn't really understood the Intergas design until I saw this great little video (only 29 seconds long).

I am still finding something difficult to get my head around. The copper waterways are encased in the aluminium block. That seems a good idea, because I've been told that the condensate destroys copper, more than it does aluminium. So I can see that this protects the copper waterways from exposure to the acidic condensate. But in the video, they say it's actually the other way round, and it's the copper waterways which protect the aluminium from corrosion. Hope somebody can explain.

This was all sparked by that graph, last weekend, which showed aluminium heat exchangers lost 50% of their performance over a few years.

 

[vulcancontinental]

The heat exchanger seems to be a very important part of the boiler, and following the discussion last weekend, I've been trying to understand more about the pros and cons of the different types. I hadn't really understood the Intergas design until I saw this great little video (only 29 seconds long).

I am still finding something difficult to get my head around. The copper waterways are encased in the aluminium block. That seems a good idea, because I've been told that the condensate destroys copper, more than it does aluminium. So I can see that this protects the copper waterways from exposure to the acidic condensate. But in the video, they say it's actually the other way round, and it's the copper waterways which protect the aluminium from corrosion. Hope somebody can explain.

This was all sparked by that graph, last weekend, which showed aluminium heat exchangers lost 50% of their performance over a couple of years.

View attachment 283387

The experiment was 100 days running at 50/30 flow and return 24 hours a day. This was deliberate so the gaps in the Ali heat exchanger design would block through excessive condensing. Running at none condensing hot temperatures with an over 9% better efficiency than the stainless exchanger this deterioration would not have happened.

Potential of heat in, fuel, that leaves in the target, the system water, is efficiency. Any additional mass of one exchanger to another has to absorb and emit heat, a 5kg hex or a 25kg hex will absorb heat from source to target reducing the amount that leaves in the system water.

 

[JonathanM]

The experiment was 100 days running at 50/30 flow and return 24 hours a day. This was deliberate so the gaps in the Ali heat exchanger design would block through excessive condensing. Running at none condensing hot temperatures with an over 9% better efficiency than the stainless exchanger this deterioration would not have happened.

Thanks. I keep trying to understand how they got it to lose 50%. When you say the gaps got blocked, do you mean the gaps between the fins on the outer surface of the HX got blocked? Or do you mean the internal waterways got blocked from the inside?

 

[JonathanM]

I would hope to run my new boiler at 50/30, so, if I go aluminium, in a couple of years would it not also end up at 50%? Or does it recover somehow during the periods it is switched off? What I'm asking, is 24/7 running particularly damaging, rather than a more normal intermittent pattern for a few hours a day?

 

[sxturbo]

I would hope to run my new boiler at 50/30, so in a couple of years would it not also end up at 50%? Or does it recover somehow during the periods it is switched off? What I'm asking, is 24/7 running particularly damaging, rather than a more normal intermittent pattern for a few hours a day?

Intergas have been using the same heat exchanger for a very long time, there may possibly have been some slight modifications through the years but nothing excessive.

It's extremely rare for an intergas heat exchanger to require replacement according to my installer and others who used to frequent this forum. Depending on the model but there is also upto a 10 year warranty depending on which model and they all use the same heat exchanger, so I don't really see it as an issue.

One thing to note is that proper servicing is required every year, every 3 years is a big service where I think the heat exchanger is removed and cleaned.

It can't be serviced (fact remains for any boiler tbh) by them large firms who come round and say they've serviced the boiler in 5 minutes before heading to the next job.

 

[JonathanM]

Intergas have been using the same heat exchanger for a very long time, there may possibly have been some slight modifications through the years but nothing excessive.

It's extremely rare for an intergas heat exchanger to require replacement according to my installer and others who used to frequent this forum. Depending on the model but there is also upto a 10 year warranty depending on which model and they all use the same heat exchanger, so I don't really see it as an issue.

I've decided that Intergas would be my first choice for my new boiler. But seeing this research is a bit concerning. That's why I'm trying to get a bit more information. I think the thing about losing efficiency is that it would be insidious. It wouldn't be something that would stop the boiler functioning. It wouldn't be a failure as such.

Apart from my own purchase decision, I am also really interested in the science. Going back to my original question, I'd still love to know how the copper waterways protect the exterior aluminium surface from condensate. Unless it's talking about internal corrosion from the central heating water, rather than from the condensate?

One thing to note is that proper servicing is required every year, every 3 years is a big service where I think the heat exchanger is removed and cleaned.

It can't be serviced (fact remains for any boiler tbh) by them large firms who come round and say they've serviced the boiler in 5 minutes before heading to the next job.

I've never seen a heat exchanger being cleaned. What does the cleaning involve? Is it removing build up from the exterior of the exchanger. Or do they somehow clean the internal waterways, perhaps with those chemicals they use for a chemical flush.

EDIT: a good image of the sort of stuff that needs cleaning off would be really helpful.

 

[Madrab]

The key difference IMO is ... on normal ALLY HEX's the system water has to run through narrow waterways and galleries to ensure the max thermal transfer and when the systems aren't maintained properly, aren't clean or free of debris/minerals/etc, that can then build up in those waterways and create narrowing which then reduces flow, increases resistance and reduces thermal conductivity therefore efficiency. Some Alloy HEX's are also susceptible to warping and melting if not kept clean and once they're pinholed then the HEX is scrap and needs an expensive replacement

With IG's design they have fat heating and HW pipes that are moulded in as part of the HEX, that then means that the system water doesn't have any contact with the Alloy or have tight and narrow waterways to negotiate so it's a lot less liable to block/restrict and can maintain efficiency much easier for longer. That and it doesn't have a smaller plate HEX which has even narrower waterways.

Personally I like the design and feel it's one of the best out there.

 

[JonathanM]

Personally I like the design and feel it's one of the best out there.

I really like the design, and many other things I now know about Intergas from answers on here, especially around PDHW. I just need to understand this research a bit more to put my worries to bed.

The key difference IMO is ... on normal ALLY HEX's the system water has to run through narrow waterways and galleries to ensure the max thermal transfer and when the systems aren't maintained properly, aren't clean or free of debris/minerals/etc, that can then build up in those waterways and create narrowing which then reduces flow, increases resistance and reduces thermal conductivity therefore efficiency

With IG's design they have fat heating and HW pipes that are moulded in as part of the HEX, that then means that the system water doesn't have any contact with the Alloy or have tight and narrow waterways to negotiate so it's a lot less liable to block/restrict and can maintain efficiency much easier for longer. That and it doesn't have a smaller plate HEX which has even narrower waterways.

Am I right in thinking the condensate never gets into the waterways? It condenses on the exterior surface of the heat exchanger? I was imagining the problems in this experiment had been caused by the condensate damaging the outside of the heat exchanger. It sounds like you think the efficiency loss was coming from fouling to the internal waterways from some sort of corrosion or build up from the circulating water.

 

[JonathanM]

The experiment was 100 days running at 50/30 flow and return 24 hours a day. This was deliberate so the gaps in the Ali heat exchanger design would block through excessive condensing. Running at none condensing hot temperatures with an over 9% better efficiency than the stainless exchanger this deterioration would not have happened.

Potential of heat in, fuel, that leaves in the target, the system water, is efficiency. Any additional mass of one exchanger to another has to absorb and emit heat, a 5kg hex or a 25kg hex will absorb heat from source to target reducing the amount that leaves in the system water.

I just wanted to say that I had already been told about this experiment by my local Viessmann installer, who obviously would favour stainless steel. I don't want you to think that you were the one to make me worry about all this. Seeing your video last week was actually really helpful for me to start trying to understand it.

 

[Madrab]

My understanding of the comment in the video is to do with internal corrosion of the alloy, from say system water that isn't clean and/or is running with the correct PH. Condensate wouldn't ever get into the system water as it is created in the cooler external part of the HEX as the flue gases cool down (~50deg) and the moisture then condenses out and then runs down into the drain. That's why a condensing boiler needs to have low return temp to be most efficient.

As far as condensate is concerned then both ally and copper metals are susceptible to corrosion as it's is inherently acidic, which one is more reactive would be for chemical equations to explain.

 

[JonathanM]

Thanks, again. That makes sense. Although in a way it's more worrying. If it is correct, on a straightforward reading of these results, it would mean that any heat exchanger with aluminium waterways (so not Intergas!) will get badly fouled internally in a couple of years. Irrespective of the temperature it is run at. Of course, we don't know what was in the circulating central heating water. Maybe the experiment was deliberately set up to foul the aluminium waterways, by running the wrong pH or not using the correct inhibitor. Funnily enough, I read they used to blame chelating agents in the inhibitor for attacking the aluminium in the heat exchanger.

 

[Madrab]

Manufacturers will always weight things in their favour and if they can find figures that substantiates their claims then they are certainly going to use them.
Purely as devils advocate, I am sure a well maintained system that has an alloy HEX, where the system is correctly cleaned, dosed and looked after probably wouldn't suffer those kinds of drops in efficiency. Though I'm sure those figures are more prevalent with some systems I have visited over the years, where no amount of convincing will have the clients get their systems cleaned and maintained so they stay at their most efficient and will last as long as possible.

 

[Harry Bloomfield]

Apart from my own purchase decision, I am also really interested in the science.

Me too, enjoying the learning experience. Keep it up Jonathan!

 

[JonathanM]

Manufacturers will always weight things in their favour and if they can find figures that substantiates their claims then they are certainly going to use them.

Indeed. But what about deliberately designing an experiment to cause a failure? That's not cricket!! (I'm not saying that's actually what happened)

Purely as devils advocate, I am sure a well maintained system that has an alloy HEX, where the system is correctly cleaned, dosed and looked after probably wouldn't suffer those kinds of drops in efficiency. Though I'm sure those figures are more prevalent with some systems I have visited over the years, where no amount of convincing will have the clients get their systems cleaned and maintained so they stay at their most efficient and will last as long as possible.

Is topping up inhibitor something that should be included in the annual service? It's never been offered to us. Maybe not such a problem with my old cast iron boiler?

 

[JonathanM]

Me too, enjoying the learning experience. Keep it up Jonathan!

That's very kind.

I really like this video from Sermeta, who I think claim to be the world's largest manufacturer of stainless steel heat exchangers. I think they are used in several major brands. At exactly the 1 minute point, it shows how the radial burner fits into the heat exchanger, and how the flue gas condenses around the rear section of the heat exchanger.