Burner Modulation

Ross_7

Sorry I didn't post a link. Yeah, great article! Raypak did a good job writing the article. I was glad to see that it wasn't a "Our boiler is the best!" type of article. I see the friendly discussions from time to time about AFUE and "Where do I gain anything by switching to modulation?" So I just thought I'd add my two cents.

Ross

Ross_7

Burner Modualation

To end the question of Modulation vs. standard on/off.
Raypak has an excellent, unbiased article on their web site about the advantages of burner modulation vs. on/off vs. staged burners. I think every one would enjoy reading it. I believe it's under the "Tech Corner" section. This should explain it very well. Take Care!
Ross

Steve Ebels_3

Got a link?

Or a web address?

Bob Sweet

Steve, here you go

www.Raypak.com/commframe.htm

Firedragon_4

Well written, well done,

and oh so true!

Modulation even in it's simplest form lo-hi-lo on oil works like crazy, I know, I've experienced it in my own home. Add outdoor reset and holy moly.

I just got back from training in Canada on NTI's Trinity gas boiler and trust me when you see 16:1 turndown combined with outdoor reset and primary-secondary piping it's very impressive.

As an oilman-at-heart I truly hope my industry gets off its penguin butt and gets flying or this stuff is going to run us over, FACT!

I've had a residential two-stage for 20 years, hello out there?!?!?!?

BTW, I really loved them citing so many creditable sources and their comments about nay-sayers. Well done RAY-PAK and thanks for finding this Ross!

Ross_7

Thanks Bob & Firedragon!

Sorry I didn't post a link. Yeah, great article! Raypak did a good job writing the article. I was glad to see that it wasn't a "Our boiler is the best!" type of article. I see the friendly discussions from time to time about AFUE and "Where do I gain anything by switching to modulation?" So I just thought I'd add my two cents.

Ross

Mike T., Swampeast MO

Thanks Ross

Should be required reading for pros and homeowners alike!

If anyone out there still actually believes that AFUE is a valid comparison between condensing/modulating boilers and any other form of heating appliance, this should finally convince them otherwise.

What would be GREAT is if manufacturers of such boilers would develop a uniform set of ratings so that buyers can have a way to make genuine comparisons.

I believe that such ratings should assume that some form of supply temperature modification is occuring with changing outdoor temperature. In other words, reset in some form has been used. Such is already nearly universal with condensing/modulating boilers.

As mentioned in this article, thermal efficiency still plays a big role in the true system efficiency. Also as mentioned, thermal efficiency is not static. It changes with both boiler delta-t and the modulation level.

Unfortunately this means that the boilers' efficiency is dynamic and affected by three prime variables, each of which can change and all of which are affected by the weather and the nature of the heat emitters. YIKES!!!

There's also the little matter of what happens to thermal efficiency when the heat loss is lower than the lowest possible modulation and the burner is forced to cycle.

While it's impossible for a manufacturer to consider all of these things simultaneously with reasonably simple ratings, here are some ideas that should be both practical and useful.

1) Graph showing thermal efficiency as a function of modulation level. An agreed upon reset ratio should be selected so that we get an approximation of real-world conditions. Great if multiple graphs using different max supply temps with reset ratios typical for different types of emitters.

2) Graph showing thermal efficiency as a function of return temperature. Again, reset should be assumed with agreed standards. Multiple graphs using the same supply temps and ratios as above would be wonderful.

3) Graph showing thermal efficiency during non-modulating operation. This should be done at the MINIMUM acceptable burn time recommended for each boiler with that time stated. The graph should plot thermal efficiency as a function of return temperature during this type of operation.

----------------------------------------------------

Some things I've learned by watching and measuring my system with constant circulation and TRVs on standing iron.

1) A typically oversized on-off, cast iron boiler has efficiency that drops off STEEPLY with reducing load. In typical weather you're LUCKY to get 50% of heat input as actual heat to the space.

2) Delta-t is higher and supply temperature lower than assumed "standards".

3) A Vitodens appears to retain its efficiency of heat transfer between the burner and the HX regardless of modulation rate, supply temperature, return temperature and even on-off operation. The radiant burner would seem to be responsible for this ability.

4) Complete system efficiency of a Vitodens becomes a nearly pure function of return temperature. The lower the return temperature the better. The more moderate the weather, the better the system efficiency--this is the complete opposite of a typical cast-iron, on-off boiler.

Weezbo

New Riello oil modulating burner?

read sept 2nd there are supposedly two new ones for residential boilers ...anyone else hear of them?

RDB 2.2 and RDB 3.2 .....

Kal Row

the hydronic mantra...and really cool science..

a hydronic heating/cooling system should run at a constant flow, at a setback temprature equal to the heat loss/gain of the space

we did the molecular math in another thread (see link below)on condensing boilers and figured out that even if you fully condensed the H2O of each therm's flue gsses - you would only extract an extra 9000btu, clearly the real savings is in a condnsing boiler's efficient combustion and load matching modulation not in it's condensing

that's why an ultra saves you a bunch even when driving a high temp load like cast iron radiators


ps for the cool science...the thread's title was
"how much condensate per therm NG?"

http://forums.invision.net/Thread.cfm?CFApp=2&&Message_ID=161863&_#Message161863

Bob Sweet

Kal that was at best enlightening, at worst

demoralizing, for a grunt like me. Thank goodness there's guy's like you and the rest to figure this stuff out. That was beautiful.

Glen

just read all the refernces material -

and yes the secret is in the load matching modulation - regardless of your fav boiler heritage. just a note though - in the past thread is was noted that Viessmann chokes the flue gases to increase velocity thereby making sure exhaust gases - exhaust. It has been my experience on the VSB series that the flue damper in conjunction with a correctly sized flue and further flue reduction at the roof - the vent is now highly pressurized but not at high velocity. This gives the flue gases lots of time to condense if required, maintains a positive combustion chamber pressure through out the full firing range - which imho is not due to higher velocity - rather it slows the gases down to a crawl. I have even - by way of experimentation - choked the flue exit further - effectively reducing a 12 inch stack to a 3 inch opening. Condensed like crazy - added about .25 inwc to stack pressure - but still purred like a kitten. On the VSB - most ignition/lockout/spurious noise problems all stem from too much flue gas velocity. BTW - all the topics in the Raypak tech site were worth the read - it is now book marked.

Firedragon_4

Hey Weezbo,

those RGB models are low input burners made more for condensing boilers, etc. The two-stage is the GULLIVER RGD and is not available here in North America.

Riello produces burners for a wide and varied number of uses, but if you compare the European website to the US website you'll see that many, many burners that are a reality 'over there' are a fantasy here.

US Website: http://www.riello-burners.com

Italian Website: http://www.rielloburners.com

Riello is currently selling some two-stage 40 Series burners to Thermo-Pride and trust me combined with the ECM motor it is one heck of a furnace.

ECM motor Website: http://www.geindustrial.com/cwc/products?pnlid=4&id=ecmhp