High Altitude Gas Quizzer (ME)

[Deleted User]

based on the need for altitudinal deration, it would be considered overfired. If I were in LA or NYC, it would be normal. Hence my use of the term overfired.

Even the manufacturers tell us we need to derate it.

ME

[Deleted User]

Okay combustion experts.

I'm primarily addressing this to the Grandfather of the btu (Tim McElwain) and the Guru of partialy burnt BTU's (Jim Davis), but if you feel qualified to speak on the subject, by all means, chime in.

As some of you may be aware, we are in the midst of record breaking cold weather here in Denver Colorado. This is where you seperate the good from the bad, and the working from the non working.

Long story short, in an effort to quicken the DHW portion of the commercial atmospheric system previoulsy describe in the thread about problems with Ecomatic and Phase 3 tanks, I clocked the meter to find that the appliance was in fact underfired by about 20% below its sealevel rating plate. The combustion numbers looked fine except for 50% excess air, and 7% O2. In a desperate attempt to make things heat up quicker, I boosted the manifold pressure until I was firing at the sealevel rating. Rechecked the combustion gasses, and excess air dropped to 25%, O2 dropped to 4.5% and the CO was around 4 PPM.

The boiler was heating water SIGNIFICANTLY faster than when it was underfired. What gives? According to everything I've ever read and have been taught, your not supposed to over fire these apppliances at altitude because they will produce excess CO.

Has burner technology changed that much in the last 30 years to the point that altitudinal deration is not a factor any more?

Whassup gang? It's running like a top.

Seriously mis-led for the last 30 some years...

ME

Joe@buderus_2

Mark, you mentioned the word "Ecomatic". Is this a Buderus Boiler?

[Deleted User]

Yup...

I tried to get a hold of you, and missed, and ended up talking to a great tech that told me I couldnt take the DHW out of priority. Check out the post labeld Ecomatic problem.

I think the only solution is to bypass the DHW heating program of the control and just treat it like a prioritized high temp load with priority. Like with a Taco SR501. I jumpered out the 1&2 terminal on the main boiler strip. It's stays running hot right now with two auto limits and one manual. Its safe and hot for now.

I'll try and contact you in the morrow.

BTW, Whats your take on this high altitude sitchumacation?

ME

Jim Davis_3

Overfiring???

How can you be overfiring if you are only making 4ppm of CO. When a mechanic tunes a car and can get more horsepower out of it is not overfired. Overfiring by definition means you are putting more fuel into the appliance than it can burn, vent or transfer. Sounds like you have not exceeded any of these. BTU's from a fuel are a guess! When fuel is burned we create close to 100% of the energy that it can produce. But in our world we can only create 90% transferable heat. 10% is lost to the nitrogen and flame temperature reduction. A 3600 degree flame(Stochiometic combustion) is not the same BTU's as a 2800 degree flame. It takes 110 cu. ft. of gas at 1000 btu's per cu. ft. to create 100,000 btu's of usable heat that we can transfer. How much of this heat we transfer is determined by the efficiency of the equipment and the installation and set up.

Tom R.

Derating

Mark, my understanding of rating gas burning equipment at sea level has to do with atmospheric pressure. The higher the altitude, the less atmosphere (air) available. So, a correctly tuned appliance will produce less than the rated output in Denver than it will in NYC. That is important when sizing equipment. Returning it to the correct fuel/air ratio as you have done would not be overfiring.

[Deleted User]

Tim..

That's what they've been telling us for all these years, and we've been upsizing our appliances all these years based upon that theory. Here in DEnver, we have derated natural gas. Most appliance manufacturers think we still have full bodied gas. We have to DOUBLE derate because of the gas. The utility actually pumps air into it at their processing plant. I know, because about 20 years ago, their controller got out of whack and the filled all of the gas mains in east Denver with air. They had every able bodied employee out in the field, bleeding air and relighting pilots.

I honestly think it has more to do with burner design today than anything. The days of the old inshot atmospheric burner are going away fast. The Buderus burners are completely different than the cast iron open face burners of old.

Technology moves onward and upward.

I find it interesting that the Lochinvar recommends conventional altitudinal deration factors (4% per thousand feet) for their new Knight boiler, which is essentially the same concept as the Munchkin, and HTP says you don't have to derate for altitude AT ALL. Then, there are other makers (V&B) that fall some place in the middle, at 2% per thousand feet.

I'd love to get my hands on a Knight, and "force" it into full blown (pun intended) operation at this altitude.

Heck, maybe I'll open a division of Advanced Hydronics up in Leadville Colorado (11,000' ASL) and offer a test bed for gas fired appliances to these manufacturers. I know 3 of them have actually brought equipment up here and tested it in the back of a truck.

ME

Plumdog_2

My understanding of the situation

our N.G. is "diluted" to work well with appliances at 5000 feet altitude. It puts out around 850 btu per cubic foot. This same gas is delivered to users at 9000 feet in elevation. You must take into account the btu content, adjusted for 5000 ft; and then adjust the appliance for the additional altitude. I'm talking about atmospheric burners with fixed orifi.
I did a job for a Senior Captain (airlines); and we got into a great discussion about the wieght of the atmosphere and the 4% per thousand "rule of thumb". He pointed out that the relationship is on a curve rather than linear; because the "rule" would dictate that at 25000 feet there would be zero atmosphere; and yet planes routinely fly at 40,000.
Most problems occur with LP gas because it is delivered in uncut form, leading to massive overfiring at high altitude if the installer doesn't compensate.
By the way, I hear the gas delivered in the Eagle Valley is full 1100 btu/cu. ft.
Do manometer readings at 10,000 feet have the same meaning as those at sea level? Or must we compensate?

Glen

theories abound -

so let me add mine. Not only are you trying to adjust for hi alt - but also the very cold air. Which in turn affects stack performance, available oh2 and other nice things. The gas temperature will also be affected. So you have underperforming gas, less available air due to temp and alt, denser gas in the cold stack. Which in my view requires higher gas pressures, more comb air resulting in higher gas temps to get things rolling. I would bet that if you tested in June your values would be really fouled up and raise your eyebrows again! Cheers from the slightly warmer Rockies in Canada.

Unknown

Hi Mark,

A real good reason to test every time we fire a boiler or furnace. It sounds to me like you have simply brought the equipment to its sweet point of efficient combustion.

I do know that in several times of past research I have come across studies that dispute reduction due to altitude in favor of burner adjustment at the time of firing to proper combustion analysis results in lieu of changing inputs. Some of the charts I have see also show altitude differentials as a graded curve of variance which is relative to things other than just altitude. The code books take a point of different altitudes to give us a factor which is the easiest way to go. They assume we are going to use accurate means to determine actual firing rates. A lot of that was also determined on old atmospheric burners that needed 50% or more excess air to work. So at best with modern equipment or power burners they may be useless.

Now days with perforated stainless steel high port loading burners like the Viesman, Munchkin and others we get much hotter flame on the burners. It is not unusual to get 3400 degrees which is pretty close to stoichometric. They are operating really as a radiant burner. With the hotter flame and using controlled combustion air with negative pressure technology on gas valves we do not have to worry about altitude concerns. We in a sense are controlling atmospheric pressure in the combustion chamber. I am not sure all the burner manufacturers are up to task on that fact.

When the utility uses air to control gas charcteristics and quality that is not always a very accurate process. I have seen BTU content vary from 800 up to 1100 when they mix air or other fuels such as propane. It leaves it up to us to make adjustments as best we can with our final adjustments in the field and then an accurate combustion analysis to follow.

If I worked in your area I would check pressures, clock every burner (just to make sure we are in the ball park), and then adjust air and gas pressure as needed to get the best combustion analysis possible. I would also keep a close eye on how cold the air intake to the equipment is especially on side wall vented equipment and believe it or not even the gas temperature especially with LP gas. The natural gas lines today in a lot of areas are only 12 to 18 inches deep so they are in the frost area all winter most of the time. There will I am sure at times be that it will seem you are by the rules over fired but by analysis right on.

Also keep in mind some of our gas today is higher BTU than in the past some as high as 1100 - 1200 BTU's per cubic foot is not unusual.

With LNG (Liquified Natural GAS) I don't know if they ship that to your area or not, it can get as high as 1300 BTU's per cubic foot. This is determined by the "Wobbe Index".

Well Mark we are "Ever learning but never coming to the full knowledge of truth". Keep up the search, keep us posted.

Plumdog_2

cheers

How come your Rockies are warmer? Is it the Pacific Ocean effect or are you pulling our leg? My friend moved back to the U.S. from northern B.C. where he says frost forms on the inside of car windshields when the heater is on-Brrr

[Deleted User]

Thanks all...

I was pretty sure I'd not been seriously misled for all these years. I HAVE straightened out operating problems thru orifice deration at 10,000' ASL on old end shot burners. I figured it was the new burner technology that was allowing for this change in operation.

Makes you wonder when the industry is going to wake up to this fact eh..

Sounds like a good article to me.

Thanks again.

ME

S Ebels

Orifice rating

What altitude were/are the orifices rated at? Buderus lists several different orfice kits based on elevation for all their atmospheric burner appliances. What manifold pressure did you wind up with?

[Deleted User]

A MILE high...

of course:-)

Manifold pressure ended up at just above 4.25" WC

ME