Turndown ratio?

Robert O'Brien

What are the EA levels on a 10-1 residential boiler at 10% input?

Zman

Robert,
Thanks for the excellent read.
If the excess air is not changing the dew point and reducing efficiencies at low fire, the decreased delta t surely is.
I would challenge the manufactures to publish their test data at low fire.
My understanding of the government tests is that they are deeply flawed.
Carl

Tinman

@Robert - I agree with Carl, excellent read. I'm guessing Cleaver Brooks' boilers top out at 5:1?
@Carl - Could you explain the first part of your 3rd sentence a bit more?
The first thing that hit me when reading it was why was the study using a 40 delta T?

Henry

The paper is a bit flawed and clearly wants to promote CB boilers. The 40 Delta T indicates that the whole system flows through the boiler at a constant flow rate. On mod/con systems even if firetube, we use primary secondary piping. We also try to use multiple boilers as much as possible even down to a 600,000 BTU load. Therefore the pump for each boiler pumps less than the system pump. So two 300K boilers would have a 10 to 1 turndown. The loss of efficiency on this type of turndown is less.

Robert O'Brien

http://m.hpac.com/boilers/boiler-turndown-revisited-0110

Robert O'Brien

It's a very interesting topic.

Robert O'Brien

Do you have a link to the 29% EA? Kind of hard to believe, Viessmann 200 with lambda aims for 30% EA across the entire modulation range.

Robert O'Brien

I use Viessmann as an example, even though they have both a modulating fan and gas valve, they can't go beyond 5-1. TT had an exclusive on the FT design for years and can't go beyond 5-1. I guess I'm from Missouri...

SWEI

As I understand it, the turndown limit (generally 5:1, Viessmann pushed it to 6.5:1 on the B2H series) was driven by limits to the flow dynamics of a modulated fan speed. The new higher turndown designs combine fan speed modulation with venturi geometry control.

CMadatMe

Turn down range is a smoke screen to produce multiple boiler skus to keep the price affordable while allowing the mfg to maintain a profit margin line. Most boiler mfgs use the same boiler chasis, burners from there smallest size up to that 110,000 or in Viessmann's case 125,000. From there its know more then software/coding change to tell it what to do. As an example the Viessmann B2HB19 thru B2HB35 are all the same exact boiler. Every part except for the coding card. The B2HB45 and 57 - Same Boiler, so on and so forth. Start looking at the parts breakdowns on some of other mfg boilers and you begin to see the same thing. So is that 5-1 really the standard, not imo, it's a made up one.

SWEI

ISTR some info from Viessmann engineering a few years back saying that higher turndown ratios made it "hard" to get proper combustion numbers. That certainly played out on early high-turndown implementations from other manufacturers.

CMadatMe

Hatterasguy said:

Chris said:

Turn down range is a smoke screen to produce multiple boiler skus to keep the price affordable while allowing the mfg to maintain a profit margin line. Most boiler mfgs use the same boiler chasis, burners from there smallest size up to that 110,000 or in Viessmann's case 125,000. From there its know more then software/coding change to tell it what to do. As an example the Viessmann B2HB19 thru B2HB35 are all the same exact boiler. Every part except for the coding card. The B2HB45 and 57 - Same Boiler, so on and so forth. Start looking at the parts breakdowns on some of other mfg boilers and you begin to see the same thing. So is that 5-1 really the standard, not imo, it's a made up one.

If the B2HB19 is the same exact boiler as the B2HB35, why would Viesssman be so stupid to have a minimum firing rate of 19MBH on the two larger boilers, when they could have just coded them with the same coding as the B2HB19 and obtained a minimum rated input of 12MBH and a much better turndown?

Doesn't make sense.

So they can sell the same boiler and make more profit. A 19,26,35 same boiler on a Vito 200. Took a WB2B80 (285,000) and turned it into a WB2B105 (350,000) and have done the same on smaller where contractor got himself in a pinch. If I told you what a coding card cost, I'd have to make you sure were wearing a depends so it would catch the mess. Go look at any Viessmann parts book. It's right there in black and white. Do you really think a Triangle PT60 is any different then a PT110? Come on... Look at the parts book, then look at the list price difference in boilers.

It's all a big scam to keep boiler pricing affordable, think about it, if they all had less SKUs pricing would be considerable more. Economics 101

Mark Eatherton

I had a conversation with the then chief engineer for the big V many years ago when their matrix burner was the next big thing. He told me that they had successfully bench tested that burner on natural gas all the way down to 1% capacity. Biggest problem was maintaining a positive flame signal to keep the rest of the train running.

I also attended a meeting of the old NACH where they told us that one curmudgeonly older gentleman who cut his teeth on naturally aspirated burners was the biggest stumbling block on getting approval for greater turn down ratios. He sat on the committee who had to approve such industry wide changes. My understanding at that point was that his associates had convinced him that greater turn downs were necessary and the next coming thing with these new style burner combustion chambers.

I've also heard from some very respected boiler manufacturers that certain burner designs have a tendency to let flash back occur so that the flame was on the inside of the chain mail burner can cover, and that's never a healthy thing. I had that happen on a Gianonni style boiler on LP, and it made my eyes burn, and head got dizzy. CO was off the chart and locked up my analyzer.

Add real world scenarios (wind induced pressures, etc..) and it becomes painfully obvious why some are limiting themselves to a given turn down ratio.


ME