Intergas heat exchanger design

[Madrab]

Like most boilers, that kind of debris that's found inside the heat engine is more likely to be stuff that's being drawn in from outside and then burned and collecting/attaching on the fins as ash. It is more prevalent in built up areas and shows how much rubbish is actually in the air. That can glow white hot though during the heat cycle and cause damage to the aluminium surfaces. Could it be called corrosion, guess so.

As far as inhibitor is concerned then it can be argued that a well maintained system that uses soft water that doesn't have any leaks can mange quite nicely without any inhibitor. Unfortunately the nature of the water in the UK being so varied with levels of soft and hard water, systems that haven't been cleaned/commissioned properly or need regular top ups due to leaking then inhibitor is a catch all to help minimise corrosion/sludge formation.

I maintain a few old open vent systems that have been in place for years that are squeaky clean and have never needed inhibitor.

 

[JonathanM]

After cleaning hex

Before cleaning hex

Thanks, it's really helpful to see some photos. Does the maintenance regime ask for the HX cleaning every year? Do you know how long that took to build up?

 

[Madrab]

A proper boiler service includes at least checking out the main HEX and clean if required, unless the MI offers alternatives - some boiler MAN's allow a combustion reading or fan flow check and if it falls within certain specifications, then the main HEX doesn't need opened up.

 

[JonathanM]

A proper boiler service includes at least checking out the main HEX and clean if required, unless the MI offers alternatives - some boiler MAN's allow a combustion reading or fan flow check and if it falls within certain specifications, then the main HEX doesn't need opened up.

This is a still from the video posted above by bernard green. Google translates it as "this is really not from 2 years", by which he presumably means it must be more than two years build up?

 

[Johntheo5]

As far as inhibitor is concerned then it can be argued that a well maintained system that uses soft water that doesn't have any leaks can mange quite nicely without any inhibitor. Unfortunately the nature of the water in the UK being so varied with levels of soft and hard water, systems that haven't been cleaned/commissioned properly or need regular top ups due to leaking then inhibitor is a catch all to help minimise corrosion/sludge formation.

I maintain a few old open vent systems that have been in place for years that are squeaky clean and have never needed in, hibitor.

Would thoroughly agree, I have a 50 year old OV system with some rads > 40 years old, I do throw in the odd drop of inhibitor ("Sometimes Father" would be the best way to discribe it) and the water is absolutely spotless, I did get the mains water tested at work years ago, can't remember the results but it certainly was soft, it also never needs even a drop of makeup water ever, a 50 year old electric immersion is also still going strong. IMO OV systems can also vent any air ingress whereas a closed system can't even though the air ingress should be minimal.

 

[Madrab]

This is a still from the video posted above by bernard green. Google translates it as "this is really not from 2 years", by which he presumably means it must be more than two years build up?

Indeed, I've been into boilers that that have not been serviced for many more years than that are their main HEX is spotless (apart from the odd fly/wasp/insect). I do do a fair amount of work out in the sticks as well as in built up areas and it's certainly seems attributed to air quality with the ones out in the sticks being much cleaner. That and if there are open spaces and great airflow around the flue area rather than lots of growth and less airflow.

 

[vulcancontinental]

Condensate doesn't come into contact with system water no matter what heat exchanger. It forms on the flueside of the exchanger if the surface of the exchanger is below 50⁰c ish.

If it comes in

After cleaning hex
View attachment 283433

Before cleaning hex
View attachment 283434

Very good illustration.

Ali forms oxide with contact to condensate, the oxide is around the first run of domestic cold water entering the exchanger, very little on the heating pipes further up the exchanger.

What was the setup, WC. or was it running at high non-condensing temps.

Theoretically you'd want oxides to be further up the exchanger particularly if the flow was set at 50⁰C or below.

 

[JonathanM]

There seems to be so much to like in this design. It's so simple. The waterways are copper, so are the same as the system pipes. And because they are so wide, it seems logical that it would be really good as a replacement for older systems. The longer video posted by @sxturbo shows more detail about how they designed and manufacture this heat exchanger. It answers how they get a good contact between the copper and the aluminium. I do still wonder what happens when you have the two different metals which expand at different rates?

On some (maybe most?) Intergas boilers you seem to be able to run them in five configurations, combi, open vent combi, system, open vent heat only, and water heater. If I have understood this, you can buy an ECO RF, to run as an open vent regular boiler, but still use the integral modulating pump? Which saves £150 buying an Alpha 1, if my current pump is not appropriate.

 

[vulcancontinental]

A heat exchanger design is always a compromise flueside, waterside and system wise

If it's stainless it has some things going for it, no oxides formations or corrosion unless a sharp brush or blade scrapes the protective surface. Also it has a thin wall thickness to counterbalance the poorer conductivity. It's low mass so no heat is absorbed elsewhere than in the system water and you’re not heating 25kgs plus of Ali for a bowl of hot water. There are always welds but the fewer the better and avoid overweld into the bore (some have over 180 welds). Some connections or manifolds in tubular exchangers are very restrictive so avoid if you can, use large bore swept transitions. Some have very small bores which mean the cleaning of the system water has to be thorough (choose large bore). Some have many or long gaskets. Some comprise of two heat exchangers which means complications and joints. Some contain turbulators to agitate and improve water contact but they can be a key to system debris. Stainless heat exchangers can be very restrictive meaning the residual head of the pump is too low for system circulation necessitating an additional pump and closely spaced tees or low loss headers to maintain adequate flow rate across the exchanger waterside (look for high residual pump head).

If the heat exchanger is ali it has conductivity going for it. Wall thickness compared to stainless does remove this advantage somewhat. Oxide build up may be problematic if the boiler will be running for a long time at low temperatures as it will need deeper servicing unless it is not a particularly good heat exchanger (a lot of the exchanger may be too hot for condensate to form over much of it). Ali is high mass, heavy, so the exchanger itself needs to warm in addition to the system water then radiates heat after firing. Nearly all aluminium exchangers are cast which results in a large wall thickness between fireside and flueside. They are often large flueway designs to ensure oxides formed by condensate do not block the passages. Ali tolerates dirt better than stainless steel. The best ali can offer equal or superior efficiency no-condensing temperatures than some stainless at condensing temperatures, most cannot (less of an advantage now the move is to low temperature operation). Some ali exchangers have two wall thicknesses. As with stainless some exchangers are restrictive and best fitted with closely spaced tees, a low loss header and second pump. Ali has greater expansion and contraction which is a boon if there is system dirt as it lessens a key for dirt if it forms the waterway.

Other notes:

The minimum annual space heating efficiency in the UK is 92%, the highest 94% of ali or stainless. Only controls and operating conditions can improve on this test bench figure.

Single or double pass heat exchanger flueside. The longer the products of combustion remain in contact with the waterways the better the heat transfer so single pass have to have greater surface area or suffer.

Bi-thermic heat exchangers. Heating water and domestic hot water are run in the same heat exchanger but separately removing the need for a diverter valve. It is essential that the heating water temperature is kept low to avoid scalding the user of hot water upon opening a tap as it can be at the same temperature as the heating water (up to 95°C). The water tubes are small and will scale up in hard water areas unless particular water conditioning methods are fitted (important if running the heating system above 60°C).

Diverter valves. The vast majority of combination boiler manufacturers use diverter valves, there is a reason, it ensures the domestic hot water cannot reach dangerous temperatures or can be 'locked' by the user. The plate heat exchanger can be problematic if system dirt occludes the waterways. Scale is less of a problem due to accurate temperature control. Single 'O' ring diverter valve cartridges can leak into the motor, look for double or duplicated 'O' ring models which avoid this problem

Hydroblocks. Brass will wear out 'O' rings faster than composite. Composite can crack if under hydraulic shock where a water meter or non-return valve is fitted (a shock arrestor is advisable). Some composites are warrantied to higher pressures than brass. It's not he strength of the strongest component it's the strength of the weakest.

Systems that are not combination boilers are best run priority domestic hot water with two temperatures, one high for rapid DHW reheat and another lower for condensing during space heating. The PDHW can be inbuilt into the boiler or by external controls on an OpenTherm boiler.

All manufacturers offer long warranties but some charge extra to lengthen the standard warranty eg. from 5 to 7 years or longer which might not inspire confidence.

If you believe 108% efficiency; don’t.

Marketing blurb is generally designed to mislead; why would you hide the price of a boiler? Less is always less, it cannot be more. If a heat exchanger is self-cleaning why sell a cleaning blade accessory? If 90% of the components are sourced abroad, is it British made?

 

[dilalio]

What was the setup, WC. or was it running at high non-condensing temps.

It's on a D plan with unvented in the loft. Boiler is on grnd floor. Controls for CH are nest on OT. This was it's 4th year service. 2 years missed due to Covid and other factors.

Not that bad really. I have another that was worse. Will try to find pics of that one... To be continued....

 

[dilalio]

 

[vulcancontinental]

View attachment 283541View attachment 283540View attachment 283540
View attachment 283541

More deposits on the insulation panel than the hex it seems?

 

[JonathanM]

A heat exchanger design is always a compromise flueside, waterside and system wise

Thanks, again, for all the great information. And for explaining the compromises with all the various designs; things I would never have thought of. It's so helpful for when I replace my boiler.

I know we've talked mainly about primary heat exchangers. Are plate heat exchangers also made from various materials, or are they more standard?

I also noticed that Vokera's open vent boiler has a radial aluminium heat exchanger, like most of the stainless steel ones I have seen. Most other aluminium ones seem to be more sort of flat. Is that design unique to Vokera?

 

[dilalio]

More deposits on the insulation panel than the hex it seems?

Eh!

Last picture (there should be 6) shows hex is really bad. Others are after I cleaned it!

Bloody new forum engine!

 

[Mr Chibs]

On some (maybe most?) Intergas boilers you seem to be able to run them in five configurations, combi, open vent combi, system, open vent heat only, and water heater. If I have understood this, you can buy an ECO RF, to run as an open vent regular boiler, but still use the integral modulating pump? Which saves £150 buying an Alpha 1, if my current pump is not appropriate.

I'm pretty sure you can do this on the cheaper Rapid+ boilers, these are cheaper than the eco RF range.