Intergas Heat Exchanger pressure drop vs others

drprox · 17 Feb 2015

I've been looking into getting an Intergas 36/30 fitted at my house by a local installer, however I am an engineer so naturally interested in the specs and workings of these things.

Now the questions I cannot find an answer to is this:

Intergas's datasheet shown a pressure drop curve for the 12mm DHW pipe in the heat exchanger, it's pretty restrictive and drops about 2 bar at 14l/min and with that curve I can't even see how it is possible to flow the rated 18L/min at mains pressure as I'd be dropping in excess of 4 bar across it?

Are plate heat exchangers in normal combis also like this or do they have lower pressure drop? I have searched the internet high and low and cannot find a single bit of info regarding pressure drop in a normal combi plate heat ex to compare it with.

I've measured my free flowing rate at 20 L/min, static pressure is 3 bar and dynamic pressure at this rate is about 2 bar which is good in my opinion.

Going from the intergas datasheet though, I'd struggle to get the rated flow through the heat exchanger, so maybe i'd be better off with something like a Vaillant 837 with conventional plate heat ex?

Any help would be much appreciated.

J

D_Hailsham · 18 Feb 2015

Are you reading the graph correctly?

I think it is showing how the flow rate (Y axis) varies with the mains water pressure (X axis). So at 2 bar you will get nearly 15 litres/min.

Intergas say:

A minimum of 0,5 bar mains cold water pressure is needed to ensure that the DHW circuit of the Intergas HRE boiler is working correctly.

Biggles.. · 18 Feb 2015

The intergas heat ex is highly resistive in hot water, plate heat exchangers don't suffer in the same way.

muggles · 18 Feb 2015

The Intergas circuit should provide less resistance than a standards plate heat exchanger

Biggles.. · 18 Feb 2015

It's doesn't though Andy, Kim will confirm this little faux par that he realised doing the brothel.

drprox · 18 Feb 2015

Thanks for the replies. The graph shows pressure drop across the boiler which will affect the resultant flow rate as you need pressure at the outlet to get some flow. Essentially dropping 2 bar across the hx would leave you with 1 bar in the pipe which would be as poor a flow rate as just having 1 bar of cold water mains to the tap (not quite as it's dynamic). I tried altering my stopcock to cause a simulated drop like this and I dropped from about 20L/min down to I think 7.

It's good to know that I might be correct and that plate hx's are freer flowing. My opinion of the Intergas is that it is a bit overrated as a boiler. Yes it is simple but it also has compromises, manufacturers don't generally add parts and cost for the sake of it. 12mm pipe sounds unrestrictive but it is actually very restrictive when you add up the length and all of the bends.

Are plate heat exchangers much of a muchness, as in Baxi, Vaillant etc will generally flow as well as each other for a certain kW rating?

Is the pressure drop over a normal combi about 1 bar, as this is all I seem to see from posts on forums but never seen any actual facts from a document.

Biggles.. · 18 Feb 2015

For a example a 50kw/20plate has a primary resistance of 22kpa, secondary resistance of 3kpa

So 0.2bar/0.03bar. figures are quoted, it's just finding them.wink:

drprox · 18 Feb 2015

Pressure drop is relative to flow rate though, so it must be given against a flow rate or with a curve

D_Hailsham · 19 Feb 2015

You are mis-reading the graph. It is showing how the HW flow rate from the boiler varies with water pressure.

The confusion arises because the legend just defines X as "Bar". But if you look at the Dutch version of the manual [page 18], it says X is "Waterleidingdruk (Bar)", which translates as "water supply pressure (bar)". It has nothing to do with the resistance of the hex.

In any case the graph is the "wrong way round" if it is supposed to show how the resistance of the hex varies with flow. Compare it to the graphs on page 36, which do show this info.

Biggles.. · 19 Feb 2015

drprox said:
Pressure drop is relative to flow rate though, so it must be given against a flow rate or with a curve

I really couldn't be bothered to give all the info but the 50/20 plate with resistances I quoted, were against 80/60 primary, 10/60 secondary, you can do the maths but far less than an intergas hex.

Friend of the forum used an intergas for semi instantaneous hot water, by the time he'd done the calcs etc, needed 2 15/60 bronze pumps in series to over come the intergas's redistance.

Agile · 19 Feb 2015

The Intergas works well with a high mains pressure and when you dont use the maximum flow rate that it can heat.

Unfortunately, when you step up to a higher power boiler that has a LONGER hot water heating tube part.

It would have been better if they had used two DHW tubes in parallel. But boiler designers dont always seem to do the obvious thing!

As our forum colleague discovered to make use of the boiler's maximum flow rate a DHW boosting pump was required! Sad but true!

Tony

Biggles.. · 19 Feb 2015

He didn't use a boosting pump, he used a pair of bronze SHUNT pumps, completely different thing.
Boosting is to take something small and give out something larger.
The gent that needed the pumps wasn't using mains pressure to go through tge DHW side, but a stored volume which he needed to circulate.

That's another story, different subject etc.

The upshot was that th resistance of the hot water side of an intergas was surprisingly large for the required flow rate which wasn't that great. A plate heat would not have needed the same pumps etc as the loss would have been much smaller.

drprox · 20 Feb 2015

Thanks guys, you have answered my queries. Hot water flow is important to me so I think I'll go with a conventional Vaillant combi.
New boiler installs aren't cheap so it was worth asking before we installed and later regretted!

Dean744PiN5 · 20 Feb 2015

i'll chime in here and say it's all very well quoting figures but in real world terms as long as you already have decent pressure you wont even notice it, your over thinking things imho.

For the forum member who had to use 2 circulators to over come the resistance, it was important because he was designing a bespoke system that had to run 9 bathrooms in a property using a combi and a hot water cylinder to give almost endless hot water, which worked extremely well i may add and something probably no other boiler could have done, proving the versatility of this great little machine.

for your situation where only 1 hot outlet at a time will be running, providing you have adequate pressure and flow rate already it will be fine.

as an aside 90% of my breakdown attendances are to vaillant condensing boilers.

Biggles.. · 20 Feb 2015

50% of our intergas installs have had warranty calls within 2days.

Compare that to the hundreds of vaillants with as yet no issues.

The intergas isn't versitile or did something others can't, it only worked because it can be used as a water heater, and as such brought its bespoke little issue of a highly resistive heat exchanger.

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Intergas Heat Exchanger pressure drop vs others

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