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magnehelic
01-11-2006, 11:09 PM
1st off Hi all!:)

I just got home and went to my PC to look online for some answers about the readings I have just gotten off an Armstrong 90+ 2-stage furnace. I then saw this forum after I googled and thought I'd see what you all might be able to help with, as far as some answers.

Here's what happened...
The local energy company was on this job and did a COČ reading from the outside 2" PVC outlet vent. And then told the customer that the COČ was higher on this furnace than it was on any other he had done that to (why he is doing this I don't know but I can only assume it's to make it look like he's doing something and might justify the bill he gives the customer). So after hearing the phrase "High Carbon Monoxide" the customer flipped and called us (the one's who installed it). Keep in mind this is only outside off the venting that he gets "high" carbon monoxide readings.

I am new to the business I work for. But I have been doing heating/cooling for the last 5 years. My employer had purchased a TPI-708 Combustion Analyzer, basically it's an efficiency tester and COČ/Temp reader. Hopefully a few of you here have used them or are familiar with them as I am new to them. Since I'm new to this tool, I decided to test a couple of the 90+ furnaces that my employer has heating the shop and offices, as to get an idea of what to expect on readings. I also did test out another furnace as part of a clean & check. I figured the more furnaces I test with this thing the better so I can gauge the readings and to do a compare and contrast between them all. Plus to see if this thing was worth the money or if it was a waste of time and money. And also whether or not this last job (the one that the energy company said was high COČ is "normal" or if something else is going on.

Below are the readings I got from it and what furnace it was on.

#1
Armstrong 90+ single stage: Nat Gas

OČ - 12.4%
XAir - 145%
eff. - 98.1% (?) seems too high eff. reading imo.
CO - 1ppm
COČ - 4.8%
ch1 - 99°F
ch2 - 56°F
-CF- CO - 2ppm

#2 Rheem Classic 90+: LPG

OČ - 13.6%
XAir - 186%
eff. - 91%
CO - 3ppm
COČ - 4.8%
ch1 - 96°F
ch2 - 62°F
-CF- CO - 2ppm

#3 Armstrong 90+ single stage: LPG

OČ - 11.1%
XAir - 113%
eff. - 91.4%
CO - 2ppm
COČ - 6.4%
ch1 - 98°F
ch2 - 58°F
-CF- CO - 4ppm

OK now the "high COČ" furnace which as you will see is higher/different than the rest.

#4 Armstrong 90+ two stage: Nat Gas

1st stage readings:
OČ - 9.0%
XAir - 75%
eff. - 88.8%
CO - 1ppm
COČ - 6.7%
ch1 - 87°F
ch2 - 51°F
-CF- CO - 1ppm

2nd stage readings:
OČ - 5.8%
XAir - 38%
eff. - 89.1%
CO - 221ppm
COČ - 8.5%
ch1 - 90°F
ch2 - 50°F
-CF- CO - 306ppm

***Note*** CO reading climbed up to 1719ppm before leveling out at 221ppm in 2nd stage. 1st stage it leveled out at 1ppm. Also all the readings are in "Gross" not "Net"

Anyone that can tell me some "average" type readings people have gotten off this unit would be much appreciated. I have up to this point assumed the 1st 3 readings on the 3 different furnaces have been accurate. And that possibly the last Armstrong furnace has a Fuel to Air ratio problem either in the venting (which I took a look at) or the inducer motor. But there is no sign of sooting, misfiring or harsh ignition.

Any help given is greatly appreciated.

P.S. I checked the incomming gas pressure on both stages U-Tubed at 6" inlet and 1.9" on 1st stage and 3.5" on 2nd stage.

[Edited by magnehelic on 01-11-2006 at 10:16 PM]

servicetech5
01-11-2006, 11:58 PM
The O2 reading is low and where did your X-air go. I would start checking to see if the right orfices are installed. pull the burner box door off to see if x-air increased to let you know if you have restricked intake air

cn
01-12-2006, 01:25 AM
1. maybe normal for Armstrong. Check the spec from the mfg you can get one from Armstrong.

or...

2. 2nd-stage uses more Oxygen and there may not be adequate O2 to burn, therefore CO production. CO is produced when Fuel/Air ratio is high (there is more fuel than O2 available). I assume combustion air is inadequate:
- ? Intake port has debris: small animals like birds etc.; or small leaves sucked inside during the fautumn.

- To see if more air decreases CO level, open the side port (inside the furnace, close to the combustion chamber, there should be a plastic cap on the intake piping, to allow air in the vicinity of the furnace to bypass and enter the combustion chmaber), then re-measure the gases.

Note CO2 is carbon DIOXIDE; CO is carbon MONOXIDE (CO is the gas that killed the 12 miners in W. VA recently).

rsmith46
01-12-2006, 01:34 AM
Where are you checking at? Don't check a draft induced furnace at the flue outlet, drill a hole just above the furnace outlet. Your O2 and excess air is too high on the shop furnaces, did you check the gas pressure on them?
On the furnace in question did the CO level jump when the blower came on? That would indicate infiltration of air into the heat exchanger from a hole or crack. Also if its 2 piped pull off the intake and see if it makes a difference.
Here's a lot of good info. http://www.bacharach-training.com/
Take a class if you get a chance.

magnehelic
01-12-2006, 01:41 AM
Originally posted by cn
1. maybe normal for Armstrong. Check the spec from the mfg you can get one from Armstrong.

Note CO2 is carbon DIOXIDE; CO is carbon MONOXIDE (CO is the gas that killed the 12 miners in W. VA recently).



Ya, my mistake by-product of working late and typing somewhat fast. I got them mixed up I see. And yes I'm calling Armstrong in the morning to get some specs on this furnace.


Originally posted by rsmith46
Where are you checking at? Don't check a draft induced furnace at the flue outlet, drill a hole just above the furnace outlet. http://www.bacharach-training.com/
Take a class if you get a chance.

I am drilling holes, I did take a quick class put on by a local distributor, but it ended up being more of a sales pitch for TPI's other equipment. Thanks for the link too, I got it bookmarked!

P.S. thanks for the quick replies so far. You all seem to be pointing toward comb. air as the next thing to check thoroughly. Which I was pointing at in ways to myself on the job, but was unsure of the tool and what to expect from a 2 stage or any furnace for that matter. And not being familiar with this I wanted to run it past some people who actually have used it in the field. (I wished it had been earlier in the day so I could have spent the extra time diagnosing the full venting as it was I cut the exhaust vent and checked it. Just not the intake.)

I'm starting to feel more comfortable with this TPI-708 if you all seem to agree that the 1st 3 furnace readings are "normal"? so to speak.

[Edited by magnehelic on 01-12-2006 at 12:58 AM]

davidr
01-12-2006, 07:23 PM
Originally posted by rsmith46
Where are you checking at? Don't check a draft induced furnace at the flue outlet, drill a hole just above the furnace outlet. Your O2 and excess air is too high on the shop furnaces, did you check the gas pressure on them?
On the furnace in question did the CO level jump when the blower came on? That would indicate infiltration of air into the heat exchanger from a hole or crack. Also if its 2 piped pull off the intake and see if it makes a difference.
Here's a lot of good info. http://www.bacharach-training.com/
Take a class if you get a chance.

This is great advice make sure that your test hole is about 12" to 18" away from the inducer outlet though.

From the readings you gave it looks as though the first 3 furnaces might be underfired. I am assuming the ch1 & ch2 readings supply & return air temperatures?

Before you get to comfortable with combustion testing I would also highly recommend some training also.
Another link you can check out in addition to Bacharachs is http://www.nationalcomfortinstitute.com.
The two guys you need to get in touch with for training are Jim Davis with the National Comfort Institute & Rudy Leatherman with Bacharach. These guys are tops in my book when it comes to providing you with the information required to do proper combustion diagnostics.

Good Luck with your testing!

mo-flo
01-12-2006, 10:52 PM
i was told at meeting last spring to not drill pvc pipe as it is hard to seal up and readings at vent termination would be sufficent,....also how would you do a mobile home furnace without taking readings at vent termination?

rsmith46
01-12-2006, 11:12 PM
Agree that first three furnace readings are not normal, O2 & excess air are high indicating underfired. That's why I asked if you checked the gas pressure.
The last furnace looks normal on low fire but on high fire the O2 level is low & CO is high. Lack of combustion air is most likely. When you don't have enough excess air one of the Oxygen molecules in the CO2 is burned leaving high CO level.

tchntch
01-12-2006, 11:36 PM
When you checked the gas pressure did you remove the air pressure tube from the burner box to the gas valve. If you didn't know, it is there to compensate for the fact that the pressure in the burner box is lower than the atmospheric and that is what the top of the diaphragm needs to see to deliver the proper pressure in the burner box. Adjusting gas pressure with the tube on will result in the wrong input. Anyway you are being very thorough. Just thought I'd throw that it.

Jim Davis
01-13-2006, 11:08 AM
The first three furnaces are operating less than 60% efficiency and the Rheem is probably less than 50%.
The 2-Stage Armstrong is the only one operating anywhere close to proper but it is slightly overfired in High-Fire. The gas pressure needs to be backed off slightly.

Ideal Oxygen readings would be 6%-9%, with 6% being the best. The flue temperature in High-Fire should be 120-140 degrees.

Anytime Oxygen is above 9% the flame temperature at the burner is extremely low and the amount of BTU's that are actually being produced by the fuel that are usable are reduced 20-30%. The low flame temperature creates a low flue temperature which then are calculated into false high efficiencies.
6% O2 = 2800 degree flame
9% O2 = 2300 degree flame
11% O2 = 1900 degree flame
13% O2 = 1600 degree flame
Which of the flame above do you think will deliver the most heat??

tchntch
01-13-2006, 06:08 PM
For Jim Davis
you sound pretty knowledgeable about this so maybe you can clear up something for me. I've done startups on larger commercial waterheaters, boilers and furnaces, as well as clean and checks on oil furnaces using combustion analysis for burner setup. The 6-9% O2 readings you quote pretty standard. But when I analyze condensing furnaces like magahelic is talking about, they are always much closer to the readings he gets on the first few clean running(no CO) furnaces. I was wondering if that is due to the fact that we are condensing down the H2O from a vapor and therefore changing the other percentages in the mix.

danj
01-13-2006, 11:12 PM
edit

cg2
01-13-2006, 11:15 PM
Originally posted by Jim Davis
The first three furnaces are operating less than 60% efficiency and the Rheem is probably less than 50%.
The 2-Stage Armstrong is the only one operating anywhere close to proper but it is slightly overfired in High-Fire. The gas pressure needs to be backed off slightly.

Ideal Oxygen readings would be 6%-9%, with 6% being the best. The flue temperature in High-Fire should be 120-140 degrees.

Anytime Oxygen is above 9% the flame temperature at the burner is extremely low and the amount of BTU's that are actually being produced by the fuel that are usable are reduced 20-30%. The low flame temperature creates a low flue temperature which then are calculated into false high efficiencies.
6% O2 = 2800 degree flame
9% O2 = 2300 degree flame
11% O2 = 1900 degree flame
13% O2 = 1600 degree flame
Which of the flame above do you think will deliver the most heat??

Re: false efficiencies, cant you get bacharach to do something about how they calculate efficiency on their testers so I dont have to constantly explain to customers that the efficiency number that I just lowered by increasing stack temperature really doesn't mean anything?

Re: Two stage Armstrong: should they disable the low stage?

Jim Davis
01-14-2006, 12:47 PM
Originally posted by tchntch
For Jim Davis
you sound pretty knowledgeable about this so maybe you can clear up something for me. I've done startups on larger commercial waterheaters, boilers and furnaces, as well as clean and checks on oil furnaces using combustion analysis for burner setup. The 6-9% O2 readings you quote pretty standard. But when I analyze condensing furnaces like magahelic is talking about, they are always much closer to the readings he gets on the first few clean running(no CO) furnaces. I was wondering if that is due to the fact that we are condensing down the H2O from a vapor and therefore changing the other percentages in the mix.

There is the same amount of H2O in combustion regardless of the efficiency of the equipment. High O2 means only one thing and that is that equipment is underfired which has been a way that mfg can get higher calculated efficiencies and thus higher fictitious AFUE. Actually on larger equipment or at least those with Power Burners the O2 should be 3% -5%. The 6% -9% is strictly for atmospheric.
Bacharach ask me years ago to help them to design an analyzer that would calculate efficiencies more accurately. I told them if techs would learn how to intepret the readings properly it is not necessary for the analyzers to do it because there are too many unknowns in the field.

Carnak
01-14-2006, 01:47 PM
I think it is just dangerous to set firing rate based on the percentage of oxygen and the amount of excess air on a residential furnace.

Carnak
01-14-2006, 02:11 PM
Originally posted by Jim Davis
The first three furnaces are operating less than 60% efficiency and the Rheem is probably less than 50%.
The 2-Stage Armstrong is the only one operating anywhere close to proper but it is slightly overfired in High-Fire. The gas pressure needs to be backed off slightly.

Ideal Oxygen readings would be 6%-9%, with 6% being the best. The flue temperature in High-Fire should be 120-140 degrees.

Anytime Oxygen is above 9% the flame temperature at the burner is extremely low and the amount of BTU's that are actually being produced by the fuel that are usable are reduced 20-30%. The low flame temperature creates a low flue temperature which then are calculated into false high efficiencies.
6% O2 = 2800 degree flame
9% O2 = 2300 degree flame
11% O2 = 1900 degree flame
13% O2 = 1600 degree flame
Which of the flame above do you think will deliver the most heat??

Perhaps you would like to explain your version of efficiency

Carnak
01-14-2006, 02:28 PM
Not good for discussing 90% furnaces but could use to discuss efficiency, I believe the temperatures are net stack temps.

http://i32.photobucket.com/albums/d41/a_bee_normal/combustion_table.jpg

[Edited by Carnak on 01-14-2006 at 01:31 PM]

Carnak
01-14-2006, 02:57 PM
Originally posted by Jim Davis
The first three furnaces are operating less than 60% efficiency and the Rheem is probably less than 50%.
The 2-Stage Armstrong is the only one operating anywhere close to proper but it is slightly overfired in High-Fire. The gas pressure needs to be backed off slightly.

Ideal Oxygen readings would be 6%-9%, with 6% being the best. The flue temperature in High-Fire should be 120-140 degrees.

Anytime Oxygen is above 9% the flame temperature at the burner is extremely low and the amount of BTU's that are actually being produced by the fuel that are usable are reduced 20-30%. The low flame temperature creates a low flue temperature which then are calculated into false high efficiencies.
6% O2 = 2800 degree flame
9% O2 = 2300 degree flame
11% O2 = 1900 degree flame
13% O2 = 1600 degree flame
Which of the flame above do you think will deliver the most heat??

2800,2300,1900 and 1600 are all hotter than room air. Is it not possible that all the heat is usuable except what goes up the stack? Would not the amount of heat that passes through the heat exchanger factor into the equation here?

What about a direct fired make-up air unit drawing in -30F air and heating it to room temperature? We are losing efficiency on this?

Jim Davis
01-14-2006, 03:09 PM
If you check different efficiency like the one you show you will note very few of them give the same numbers and none of the can be accurate because we never know the exact compostion of the fuel. Based on combustion materials I have used for the last 28 years and combustion analyzer calculations and actual field testing the following can be stated: 14% of natural gas combustion is water(H2O). If you don't condense you cannot achieve an efficiency above 86%.. Every 1% of Oxygen in the flue gas calculates to another 1% efficiecny. At 6% Oxygen the maximum efficiency you can get is now 80%. Every 30 degrees of net flue temperature(this is based on analyzers and other charts)was another 1% efficiency loss(for calculating purposes only). A typical natural gas furnace(80% eff) should have a minimum net stack temperature of 230 degrees if it is running properly. This calculates into another 8% loss which now means our maximum efficiency is 72%. Based on field tests this actually comes pretty close. The chart shows something over 80% which is erroneous. Another way I express this is that when you burn gas with 6% Oxygen, the flame temperature is 2800 degrees out of a possible 3600 degrees. The usable heat we have available in our world is only 90%(approx)of what the fuel is rated. Now if we transfer 80% of this, what is our efficiency-72% If our Oxygen is greater our efficiency is worse. Unfortunately low flame temperatures create low flue temperatures which the calculations assume is from heat transfer not poor combustion.
Every manufacturer of combustion analyzers that I have worked with know they cannot calculate efficiencies correctly but they are only conforming to industry standards that have been wrong since day one. If there was anyway they could prove otherwise they would be all over my butt and silence me.

Carnak
01-14-2006, 03:12 PM
What's the difference between 3.8% oxygen and a 400F net stack temperature and 12.4% oxygen and a net stack temperature of 250F?

Carnak
01-14-2006, 03:13 PM
Well base it all on the compostion and heating value stated at the bottom of the image then

Carnak
01-14-2006, 03:15 PM
Is it all based on actual flame temperature vs maximum flame temperature or perhaps a combination of mass flow rate and temperature?

Jim Davis
01-14-2006, 03:19 PM
Originally posted by Carnak
What's the difference between 3.8% oxygen and a 400F net stack temperature and 12.4% oxygen and a net stack temperature of 250F?

The actual flame temperature at the burner at 3.8% O2 is approx 3100 degrees. Subtract 400 from 3100 and you have tranferred 2700 degrees of heat.

12.4% O2 is a flame temperature of approx 2000 degrees. Subtract 250 from 2000 and you have only transferred 1750 degrees of heat. Which is really doing the job?

Carnak
01-14-2006, 03:25 PM
Analyze it from a mass flow rate and net stack temp aproach.

You have all that heated nitrogen going along for a free ride, and if the net stack temperature is down, that means you are pulling heat out of it as well.

Does the amount of energy released change with the flame temperature because if it did, it would almost sound like an indirect fired system would be more energy efficient than a direct fired system.

Jim Davis
01-14-2006, 03:26 PM
Originally posted by Jim Davis

Originally posted by Carnak
What's the difference between 3.8% oxygen and a 400F net stack temperature and 12.4% oxygen and a net stack temperature of 250F?

The actual flame temperature at the burner at 3.8% O2 is approx 3100 degrees. Subtract 400 from 3100 and you have tranferred 2700 degrees of heat.

12.4% O2 is a flame temperature of approx 2000 degrees. Subtract 250 from 2000 and you have only transferred 1750 degrees of heat. Which is really doing the job?

Forgot to mention that if these readings were on identical pieces of equipment the 3.8%-400 degrees is over 25% more efficient.

Carnak
01-14-2006, 03:32 PM
Well take two identical birthday candles.

Suspend a thimble full of water over one and a pot full of water over the other.

Thimble boils and the pot warms up by a couple degrees, roughly same amount of heat transfering and perhaps the candle thimble process is perceived as more heat transfer when looking at temperature alone.

However when you look at the change in temperature and the mass of the water getting heated up, maybe the pot is getting the same amount of heat, maybe even more.

Jim Davis
01-14-2006, 05:55 PM
Originally posted by Carnak
Well take two identical birthday candles.

Suspend a thimble full of water over one and a pot full of water over the other.

Thimble boils and the pot warms up by a couple degrees, roughly same amount of heat transfering and perhaps the candle thimble process is perceived as more heat transfer when looking at temperature alone.

However when you look at the change in temperature and the mass of the water getting heated up, maybe the pot is getting the same amount of heat, maybe even more.

Wrong analogy. The size of the heat exchanger doesn't change the size of the flame does. Put one thimble an inch above one candle and the other one two inches above and see which one actually heats. It is the nitrogen that cools the flame at the burner. There is 4 times more nitrogen than oxygen. Nitrogen absorbs heat but it doesn't like to give it back. The majority of heat you do see is in the nitrogen. Direct fired puts all the H2O and nitrogen into the space so there is no loss. Oxygen is also indicative of the velocity of the heat. That is why when we close the air shutter on a power burner and reduce the O2 the flame gets hotter but the velocity is slower and the flue temperature drops because the gases spend more time in the heat exchanger.

Carnak
01-14-2006, 06:03 PM
Originally posted by Jim Davis

Originally posted by tchntch
For Jim Davis
you sound pretty knowledgeable about this so maybe you can clear up something for me. I've done startups on larger commercial waterheaters, boilers and furnaces, as well as clean and checks on oil furnaces using combustion analysis for burner setup. The 6-9% O2 readings you quote pretty standard. But when I analyze condensing furnaces like magahelic is talking about, they are always much closer to the readings he gets on the first few clean running(no CO) furnaces. I was wondering if that is due to the fact that we are condensing down the H2O from a vapor and therefore changing the other percentages in the mix.

There is the same amount of H2O in combustion regardless of the efficiency of the equipment. High O2 means only one thing and that is that equipment is underfired which has been a way that mfg can get higher calculated efficiencies and thus higher fictitious AFUE. Actually on larger equipment or at least those with Power Burners the O2 should be 3% -5%. The 6% -9% is strictly for atmospheric.
Bacharach ask me years ago to help them to design an analyzer that would calculate efficiencies more accurately. I told them if techs would learn how to intepret the readings properly it is not necessary for the analyzers to do it because there are too many unknowns in the field.

I think tchntch raises a valid point. I would agree that the amount of H20 produced is the same regardless of the efficiency of the equipment, but some of this H2O is leaving as a liquid from a condensate drain on the secondary heat exchanger and not as a vapour in flue.

So perecentages of CO2 and O2 would appear a little on the high side.

Carnak
01-14-2006, 06:32 PM
Originally posted by Jim Davis

Originally posted by Carnak
Well take two identical birthday candles.

Suspend a thimble full of water over one and a pot full of water over the other.

Thimble boils and the pot warms up by a couple degrees, roughly same amount of heat transfering and perhaps the candle thimble process is perceived as more heat transfer when looking at temperature alone.

However when you look at the change in temperature and the mass of the water getting heated up, maybe the pot is getting the same amount of heat, maybe even more.

Wrong analogy. The size of the heat exchanger doesn't change the size of the flame does. Put one thimble an inch above one candle and the other one two inches above and see which one actually heats. It is the nitrogen that cools the flame at the burner. There is 4 times more nitrogen than oxygen. Nitrogen absorbs heat but it doesn't like to give it back. The majority of heat you do see is in the nitrogen. Direct fired puts all the H2O and nitrogen into the space so there is no loss. Oxygen is also indicative of the velocity of the heat. That is why when we close the air shutter on a power burner and reduce the O2 the flame gets hotter but the velocity is slower and the flue temperature drops because the gases spend more time in the heat exchanger.

The intended analogy was the mass being heated.

When you close off the air shutter you are reducing the mass flow rate of air. Temperature difference times mass flowrate = heat.

Less mass flowrate, greater temperature difference. You were saying efficiency decreases with the flame temperature and therefore decreases with the percentage excess air. A direct fired unit for a 100 degree rise could have 10,000% excess air. As low a flame temperature as you are going to get.

I know direct and indirect are apple and orange comparisons.

Indirect fired, higher flame temp, more heat transfer per unit surface area of that heat exchanger. If you happen to design a heat exchanger for some safety excess air, then for a lower 'flame' temp, you make the heat exchanger larger etc, to get the required heat transfer under a lower temperature differential between the flame and the room air.

The thing is for the residential furnaces, the manufacturers are designing these heat exchangers around so much excess air and there is no air adjustment on a lot of furnaces. They want so much excess air, the only real adjustment is the effect of pipe lengths and fittings on the vent and combustion air intake. Are the manufacturer's telling you how much excess air there should be or are you just telling techs what should be and do not listen to the manufacturers?

Compare the energy in the fuel as in its calorific value and it specific heat, plus the specific heat of the combustion air to the mass flow rate and temperature/specific heats of the products of combustions. Maybe account for some latent heat if it is a condensing furnace and subtract the warm leaving water from the equation.

You could have a low rate of hot products of combustion leaving or a higher rate of warm products of combustion leaving, and have the same efficiency.

I think it is bad advice to be teaching techs to adjust gas pressure solely by how much O2 is in the products of combustion.

Carnak
01-14-2006, 06:47 PM
Originally posted by Jim Davis

Originally posted by Jim Davis

Originally posted by Carnak
What's the difference between 3.8% oxygen and a 400F net stack temperature and 12.4% oxygen and a net stack temperature of 250F?

The actual flame temperature at the burner at 3.8% O2 is approx 3100 degrees. Subtract 400 from 3100 and you have tranferred 2700 degrees of heat.

12.4% O2 is a flame temperature of approx 2000 degrees. Subtract 250 from 2000 and you have only transferred 1750 degrees of heat. Which is really doing the job?

Forgot to mention that if these readings were on identical pieces of equipment the 3.8%-400 degrees is over 25% more efficient.

Efficent as to what, the amount of energy used to run an inducer or a combustion blower? Not with regards to the heat delivered to the space.

Jim Davis
01-14-2006, 08:13 PM
Feel like I am doing a whole seminar.
Last remark first. The BTU delivered to the space will be 25% greater per cubic foot of gas with the 3.8% O2 reading.

It is more dangerous to set gas pressure with just a manometer and clocking meters. You cannot tune the input of any device. You are suppose to tune the output. I find that people that work on car engines understand this more than anybody.
Don't teach to set by O2. We set gas pressure by CO. It is a true indicate of how much fuel the appliance can burn and vent properly. Then we use Flue Temperature and Air Temperature. Oxygen is a bonus number that lets you know where you started and where you finished.
On most residential appliances the amount of air is not adjustable only fuel. When using a heat exchanger the temperature inside must heat the metal of the heat exchanger and then the heat exchanger heat the air, water or steam. It is alot easier to heat a heat exchanger with a flame that is 3100 degrees and gases that are 400 degrees than with a flame that is 2000 degrees and gases that are 250 degrees. The greater the temperature difference the greater the rate and amount of transfer. Keep going, we'll get there. Having started out in 1978 testing only commercial and industrial appliances it was impossible to set large equipment up with gas pressure and clocking meters and expect them to run efficient. 25 million BTUs is alot more dangerous than 100,000.

atphvac
01-14-2006, 08:50 PM
To Jim Davis:

When is your next CO class in the NJ, NY, PA area? AL D. said essentially that we are all morons until we attend your CO class.

cg2
01-14-2006, 09:07 PM
Can you get us manifold gas pressure readings on those first 3 furnaces with the high O2 readings. Then see if you can bring the O2 down by raising gas press. and by how much? Tell the boss you're going to save him a bunch of money to justify the time. :)

davidr
01-14-2006, 09:12 PM
Originally posted by atphvac
AL D. said essentially that we are all morons until we attend your CO class.

I went to the CO class & I am still a moron. :(

I did pick up a lot of valuable information from Jim's class though. :D

danj
01-14-2006, 09:44 PM
I too atended one of Jim's classes. Well worth it!!!

Just don't treat your meters like Jim treats his!!!! (LOL)

Jim Davis
01-15-2006, 02:11 AM
Originally posted by davidr

Originally posted by atphvac
AL D. said essentially that we are all morons until we attend your CO class.

I went to the CO class & I am still a moron. :(

I did pick up a lot of valuable information from Jim's class though. :D

No David, you and us are just ignorant geniuses, not stupid morons.

MadeinUSA
01-15-2006, 02:23 AM
Originally posted by Jim Davis
I find that people that work on car engines understand this more than anybody.Yeah, the last time I dynode an engine, we didn’t count revolutions of the flywheel to change the jets in the carburetor. We read the readings from the sensors and probes that told us what “exactly” was going on in the “firing chamber” to obtain maximum horsepower and torque.

Maybe I am missing something here, but it sure is funny how our rides always finished 1st the majority of the time, and we got to take the victory lap with the checkered flag. :D

Carnak
01-15-2006, 10:21 PM
Originally posted by Jim Davis
Feel like I am doing a whole seminar.
Last remark first. The BTU delivered to the space will be 25% greater per cubic foot of gas with the 3.8% O2 reading.

Well Jim it is not a seminar as for one you are not being paid, and two, I am not obligated to believe everything you say as being the gospel. You come up with these out in left field comments from time to time so do not be upset if I do not believe you just because you say so.

However you got me thinking and made me burn a few hours of my time. I took a look at the scenario of 130% excess air from the chart I posted with the 12.4% O2,4.8% CO2,a 250F NET STACK TEMPERATURE not FLUE TEMPERATURE, and 81.9% efficiency being listed. I also worked with the gas composition listed at the bottom of the figure.

I used DRY AIR as being 20.95% O2 by volume with the remaining 79.05% being N2 and trace gases. I took the remaining 79.05 as being all N2, was simpler.

It was quite tedious to say the least, especially with the N2 and CO2 content in the fuel itself that just goes along for a ride.

I assumed complete combustion, no CO production and I used bone dry combustion air to neglect losses from water vapour in the combustion air. I took the combustion air temp as 70F which makes the flue temp 320F. I took the enthalpy of superheated steam at 320F as 1202.08 Btu/lb and the enthalpy of water at 70F as 38.10 Btu/lb.

So after 6 pages of chicken scratch, I came up with the following

1) The percentages in that chart have to be based on dry flue gas, it does not include water vapour created by combustion.

2) Theoretical CO2 at 0% excess air, I got 11.76% chart says 11.8, same thing.

3) Heating value per cubic foot of fuel I got 1005.98 Btu/cubic foot, chart says 1006, same thing.

4) Higher heating value per pound of fuel, 22,847 Btu/lb fuel. Chart did not list this.

5) %CO2 4.81, agrees with chart

6) %O2 12.4, agrees with chart

7) working backwards from CO2 and 02 percentages to get excess air, got 129.9% close enough to 130%.

8) Efficiency at 250F net stack, 4.81% CO2, 12.4% O2-- got 80.03%, bit of a descrepancy from the chart but with all the assumed values for steam, and all the little decimal places, in the ball park.

So if you want to show how, 3.8% O2, 400F net stack temperature, 20% excess air blows this away by 25% more heat to the space, knock yourself out. We can compare notes.

Now I realize you qualified your answer by saying the same piece of equipment so there is a possibility that this is true. Likewise I am not saying that every manufacturer should be designing systems burning at 130% either.

But what that chart shows is, that it is possible to have higher net stack temps and low excess air on one piece of equipment and on another piece of equipment lower net stack temps and more excess air. These two pieces of equipment could be burning the identical fuel and have the same efficiency.


Originally posted by Jim Davis

It is more dangerous to set gas pressure with just a manometer and clocking meters. You cannot tune the input of any device. You are suppose to tune the output. I find that people that work on car engines understand this more than anybody.
Don't teach to set by O2.


Well I thought you said before you had them measuring O2, and the 'high' O2 meant it was underfired. Then you were telling them to turn up the gas pressure.


Originally posted by Jim Davis


We set gas pressure by CO. It is a true indicate of how much fuel the appliance can burn and vent properly. Then we use Flue Temperature and Air Temperature. Oxygen is a bonus number that lets you know where you started and where you finished.

You set the gas pressure to minimize CO after you checked for other causes first I would assume.

I assume use the O2 and the CO2 to actually work out what your excess air is, this should be independent of the exact gas composition would it not?

But then what do you do for the input, measure the CFM of the furnace, the temperature rise, work out the Btu into the air from there, work backwards from the efficiency and come up with an input. It would seem that you are still stuck with assuming a heating value.

Then when you work out temperature rise is it simply perhaps the constant of 1.08. That is standard air or do you teach them to convert the CFM of flowing air to an actual mass flow rate first. Just another source of error, could be off by 5% maybe. And it is all a game of small percentages.

You do not seem to like clocking but you have to be taking the long way around to be no more accurate except, you know that at the time you left the piece of equipment CO is minimized.

What happens later when gas content changes? What happens if it turns out it is overfired by the manufacturer's rating and there is a problem down the road?

You are assuming a heating value no matter which way you do it. Take a residential condensing furnace. You analyze it and the analyzer tells you it is 91% efficient.But it almost sounds like you are saying all analyzers are way off. So you deem there is too much excess air and apply your flame temperature reasoning, you dial up the gas pressure to get that stack temp up. It seems like you are dictating what the excess air should be, and are still firing these furnaces to 'optimize' and get a higher stack temp.

I seriously would be interested if you could suggest a book that takes this flame temperature approach, as it just seems to go against mass flow rate and temperature. If the piece of equipment is designed to pull the heat out of a higher flow of air, so be it.

You are also pulling more heat out of the leaving water vapour and the CO2 than you would with the higher flue temp. You just have to make sure you are getting the heat out of the extra O2 and N2.


Originally posted by Jim Davis


On most residential appliances the amount of air is not adjustable only fuel. When using a heat exchanger the temperature inside must heat the metal of the heat exchanger and then the heat exchanger heat the air, water or steam. It is alot easier to heat a heat exchanger with a flame that is 3100 degrees and gases that are 400 degrees than with a flame that is 2000 degrees and gases that are 250 degrees. The greater the temperature difference the greater the rate and amount of transfer. Keep going, we'll get there.

Lol, keep going. It is funny how you mentioned how people tuning engines get your strategy, because it almost sounds like you look at it like a thermodynamic cycle instead of a mass and heat balance.


Originally posted by Jim Davis


Having started out in 1978 testing only commercial and industrial appliances it was impossible to set large equipment up with gas pressure and clocking meters and expect them to run efficient. 25 million BTUs is alot more dangerous than 100,000.

Yes and big power burners you have air adjustment, this is a residential thread and not much air adjustment these days on a lot of newer furnaces.

Not arguing a manifold pressure, but I am in favour of clocking it. I would say clock it trust your analyzer, and don't screw around fine tuning something to 95%.

Jim Davis
01-15-2006, 11:56 PM
CARNAK you doing a good job in keeping me on my toes and I can see it will take a while to convince you of what testing in the field has taught me. But then I can't do that because you have to. All the formulas, all the theories and all the numbers don't mean a thing until you apply them in the field. No we never adjust equipment for the lowest CO but somewhere in a range of 11ppm to 99ppm which is 3 times less than equipment is certified to produce. The biggest descrepency in this business is that we give inanimate objects the ability to make decisions and Mother Nature to control our mechanical rooms. These are things that I recommend eliminating from the get go. No we never know the BTU value of fuel which is why setting pressure without measurement is inaccurate. Can't clock a meter on propane or oil. Don't have a clue of the BTU's of fuel at 10,000 feet above sea level or the density of air. But my analyzer has the ability to measure the reality of what is happening. Don't know if you have ever owned a combustion analyzer, how long or how many times you have used it. Your questions are good and I appreciate your challenges. To date know one in the field has found anything other than the truth in all things I teach, which were all learned in the field. What they have really found it that many of the things you have stated, which actually have come from others, to be absolutely false. You have to believe what you are told until you have the ability to prove different. That is the challenge I give everyone but only those that are qualified and have the aptitude will seek the correct answer. 100% of the time when equipment has been tuned by output versus input fuel savings were seen and the life of the equipment prolonged. Not sure if you are still in the West Indies as your profile indicates, but this would tend to make checking these things a bit difficult. Just notice that others have agreed with me that share the same knowledge and no one else has replied that has proven otherwise. Still trying to figure out a way to explain better how your calulations don't really work. Be back next Friday.

rsmith46
01-15-2006, 11:58 PM
Originally posted by Jim Davis
Feel like I am doing a whole seminar.
Last remark first. The BTU delivered to the space will be 25% greater per cubic foot of gas with the 3.8% O2 reading.

To get from 12.4% to 3.8% you increased the gas pressure and input BTU, how does that translate to 25% more efficency?


It is more dangerous to set gas pressure with just a manometer and clocking meters. You cannot tune the input of any device. You are suppose to tune the output.
Don't teach to set by O2. We set gas pressure by CO. It is a true indicate of how much fuel the appliance can burn and vent properly. Then we use Flue Temperature and Air Temperature. Oxygen is a bonus number that lets you know where you started and where you finished.


After you use your analyzer to set gas pressure to 25PPM CO you do check to make sure that haven't gone outside 3.2 - 3.8 in WC. and clock the meter to make sure your within 5% of recommended firing rate don't you? I don't see a problem with that.

I set my gas pressure, then clock the meter and check with Analyzer to make sure I'm within 5% of proper firing rate and operating properly. Same difference either way as I see it. Either way is going to change by 5% when the BTU content of the gas changes.

Jim Davis
01-16-2006, 01:21 AM
Kind of working two sites at one time. rssmith the national fuel gas code standards for CO in heating appliances is 400ppm "air free". I do not come any where close to following that standard because it is not safe. The BTU's of gas can vary 10% day to day. When we set an appliance at 4" WC we still maintain more than 10% safety for variance. You are more intelligent and more qualified to set up appliances not using the gas pressure gas meter numbers. These are not measurements of performance, just theoretical inputs. You cannot tune anything by input. You only can make it run. If you read the codes you will see they were not written by anyone who has ever been in the field(GAMA Magazine Summer/Fall 2005) AGA & NFPA state in the code that they have never been tested or verified to be functional. You are better than most by your comments because it shows you care. You just need some correct information that has been verified by someone in the field.

rsmith46
01-16-2006, 10:01 AM
Originally posted by Jim Davis
Kind of working two sites at one time. rssmith the national fuel gas code standards for CO in heating appliances is 400ppm "air free". I do not come any where close to following that standard because it is not safe. The BTU's of gas can vary 10% day to day. When we set an appliance at 4" WC we still maintain more than 10% safety for variance.


Their saying 400ppm is a max not what's recommended.
If you set up a furnace today at 4 in wc when the BTU content of the gas is at its low side of that 10% or 950,your no longer in a safety range when the gas goes to 1050.

The problem I see with the way your teaching to super tune a furnace is tech's will always have a tendency to turn that little adjustment screw a little more for good measure.

Jim Davis
01-16-2006, 10:23 AM
Originally posted by rsmith46

Originally posted by Jim Davis
Kind of working two sites at one time. rssmith the national fuel gas code standards for CO in heating appliances is 400ppm "air free". I do not come any where close to following that standard because it is not safe. The BTU's of gas can vary 10% day to day. When we set an appliance at 4" WC we still maintain more than 10% safety for variance.


Their saying 400ppm is a max not what's recommended.
If you set up a furnace today at 4 in wc when the BTU content of the gas is at its low side of that 10% or 950,your no longer in a safety range when the gas goes to 1050.

The problem I see with the way your teaching to super tune a furnace is tech's will always have a tendency to turn that little adjustment screw a little more for good measure.

That is all built into the numbers. But before we adjust fuel we make sure we have 100% control of combustion air and venting. The fact that that has never happened in 25 years is fact. Following minimum standards provides minimal results for consumers. By exceeding minimum and maximizing safety and efficiency we are doing the job the customer expects. Can't give you all the basics here for you to totally understand, but as long as I get you thinking and questioning the first step has been accomplished.

Jim Davis
01-16-2006, 10:25 AM
Originally posted by atphvac
To Jim Davis:

When is your next CO class in the NJ, NY, PA area? AL D. said essentially that we are all morons until we attend your CO class.

Norfolk,VA-Feb, DC - April. Promise if you come that you will report back here how crazy I am.

Carnak
01-16-2006, 10:28 AM
Some higher heating values, Btu per cubic foot dry fuel at 60F and 30 in Hg.

Carbon Monoxide 321

Hydrogen 325

Methane 1012

Ethane 1773

Propane 2524

Butane 3271

Was a note saying that if the fuels were saturated with water vapour to deduct 1.74%.

When you look at the values of Btu per pound of fuel, hydrogen blows them all away at 61,095 Btu/lb. Methane was in second at 23,875.

ACFIXR
12-12-2013, 11:25 PM
CARNAK you doing a good job in keeping me on my toes and I can see it will take a while to convince you of what testing in the field has taught me. But then I can't do that because you have to. All the formulas, all the theories and all the numbers don't mean a thing until you apply them in the field. No we never adjust equipment for the lowest CO but somewhere in a range of 11ppm to 99ppm which is 3 times less than equipment is certified to produce. The biggest descrepency in this business is that we give inanimate objects the ability to make decisions and Mother Nature to control our mechanical rooms. These are things that I recommend eliminating from the get go. No we never know the BTU value of fuel which is why setting pressure without measurement is inaccurate. Can't clock a meter on propane or oil. Don't have a clue of the BTU's of fuel at 10,000 feet above sea level or the density of air. But my analyzer has the ability to measure the reality of what is happening. Don't know if you have ever owned a combustion analyzer, how long or how many times you have used it. Your questions are good and I appreciate your challenges. To date know one in the field has found anything other than the truth in all things I teach, which were all learned in the field. What they have really found it that many of the things you have stated, which actually have come from others, to be absolutely false. You have to believe what you are told until you have the ability to prove different. That is the challenge I give everyone but only those that are qualified and have the aptitude will seek the correct answer. 100% of the time when equipment has been tuned by output versus input fuel savings were seen and the life of the equipment prolonged. Not sure if you are still in the West Indies as your profile indicates, but this would tend to make checking these things a bit difficult. Just notice that others have agreed with me that share the same knowledge and no one else has replied that has proven otherwise. Still trying to figure out a way to explain better how your calulations don't really work. Be back next Friday.

Excellent thread...........................

ACFIXR
12-27-2013, 12:20 PM
Still trying to figure out a way to explain better how your calculations don't really work. Be back next Friday.

Jim,did you ever figure out how to explain why Carnaks calculations don't work?

ch4man
12-28-2013, 11:14 AM
thanks for finding and bring back a great thread. it was threads like this that really set the wheels in motion for me to start learning again.

bookmarked!

Jim Davis
12-30-2013, 12:13 PM
Jim,did you ever figure out how to explain why Carnaks calculations don't work?

Carnak, may he rest in piece left us a few years ago. He was one smart cookie and a real challenge. I probably don't have half the IQ he had however I did have 500% more field experience.

Everything he discussed in written in book after book, engineering course after engineering course. However when looking at real field measurements and results they never matched.
One of the first things I noticed back in the late 70's and early 80's is that as I helped industrial boiler engineers adjust and tune up their large boilers was that the calculated efficiency on the analyzer went down more often than it went up. And even when it did go up it was slight however fuel usage went down substantially and everyone wanted to know why. I am talking tens of thousands of dollars and savings in the 15% to 30% range.

Rather than using all kinds of scientific mumbo jumbo I have tried to relate things to what anyone could understand, including myself. One example was holding a thimble of water 1" above a candle versus 2".

For years I have taught that combustion analyzer efficiency calculations are way of track, 90% of them not even within a safe or mechanical possibility and then the other 10% could be off 10% to 50%.

Btus are Btus and they are measureable on the outlet side of equipment. When measured correctly it is easy to see that equipment isn't operating close to its rating at factory specs.
Factory specs are written on the conservative side because most manufacturers realize how most of their equipment is going to be installed. If it runs the mechanic runs.

I have always taught my students not to believe me, but to prove I am wrong. But then it is not me, but all the data I collected from the field that would be wrong.

Carnak was great in helping everyone think a little bit harder but actual measuring in the field provides the real answers we can believe.