Combustion Testing Results

Unknown

Combustion Testing???

Diciocco

Combustion Testers- Compared

I recently had the opportunity to test several different testers on one furnace to get some comparison of results.

These readings were taken after 10 to 15 minutes of running time over a period of about four hours allowing time for the furnace to cool down.

The furnace is a Bryant 80+ furnace about 5 years old. Input is 125,000 BTU's at 3.6" W.C. gas pressure

Bacharach 125

CO2 -7.8%

O2 7%

Net Stack 365 degrees

CO 32

CO air free 48

Efficiency 80.9%

Draft -.03

Excess Air 44.8

A seperate Bachrach 125 recently calibrated

CO2 7.7%

O2 7.7%

Net stack 365 degrees

CO 28

CO air free 43

Efficiency 84.6

Draft -.04

Excess Air 47.8

I will post the Testo instruments readings a little later

Timco

What is the best indicator that an analyzer should be calibrated? Is self-calibrating an option? I am confident I can follow factory instructions and I heard they sell kits. I have a Bach 125 pro.

Thanks, Tim

Brad White_185

The value in posting

what you did here and what you propose, Timmie, is invaluable. So many readings and values, not to mention deviations between competitive models of combustion testers is a real help.

Diciocco

I use charts that

show the tracking of CO2 and O2, that way if they are off I will know by the fact that the two do not follow one another. An example if you read 4.8% O2 then CO2 should be 9.5%. I also notice that when the O2 sensor starts to go I will read more than 20.9% O2. The frequency of use is also a good indicator, going back to the old days of the fluids and the limited number of tests with the CO2 fluid versus the O2 fluid I would actually keep track of how many tests I had done. I still do that with the electronic testers. The O2 sensors also go after about two years or less even with limited use as they start going the minute they are exposed to air.

I personally do not do any of my own calibration, I prefer having the factory do it for legal reasons. Some of the new testers however make it very easy to do it your self and it eliminates turn around time on your tester. That with some companies can be a problem with as much as a month to six weeks on some.

Diciocco

It is interesting to

note with the readings I am going to post on one furnace that the readings are very close to one another. The differences I find on meters is the pump speed which means you get slower results with some faster with others. The Testo units which elimiate O2, CO2 and NOX from the final air free CO reading also may give slightly different readings. Other than that it is my opinion that the only other criteria is cost of the equipment up front, factory repair speed and the ability to field repair. I also like the units that have a rechargeable battery option. Some now offer a soft ware program which allows download of data so you can develop a data base of customers and keep long term records for comparison.

Diciocco

Here are some more readings

TESTO 325

CO2 - 6.2%

O2 - 9.8%

Stack temp - 382.4 degrees

CO 18

CO air free 34

Efficiency 81%

I want you to notice the CO2 reading compared to the O2 reading they did not track on the chart, the O2 sensor failed while we where conducting the test which showed after purging the meter as we had a reading on O2 in the air of 23.4%, should only ever be 20.9 or less.

TESTO 330-1

CO2 - 7.6%

O2 - 7.3%

Stack temp 374 degrees

CO - 17 ppm

CO Air free - 26 PPm

Efficiency 82.9%

Diciocco

Finally the last two meters

Wohler

CO2 - 7.5%

O2 - 7.6%

Stack temp - 347 degrees

CO 27 ppm

CO air free 43 ppm

Efficiency 80.1 %

Excess air 57 %

UEI Eagle 125

CO2 - 7.5%

O2 - 7.6%

Stack temp 385 degrees

CO - 23 ppm

CO air free - 41 ppm

Efficiency 80.7%

Excess air 57.1 %

My thanks for the assistance of Norwich Public Utilites personnel on this test and also Propane Plus for the loan of a meter.

All these reading on the furnace was with natural gas with a BTU content of 1027 BTU's per cubic foot and specific gravity at .652 with a room air temperature between 70 to 76 degrees. Testing was done 18" away from the exhaust point of the combustion air blower. This is not a power vented unit as it is into a type "B" gas vent about 22 feet high with a 45 degree offset and a negative draft varying between -.02 to -.04. All air for combustion is taken from within the building.

All the instruments with the exception of the TESTO 325 had recently had factory calibration.

I have tuned this furnace to its maximum firing rate which when clocked is sligthly higher than rated input. The regulator on the White Rodgers gas valve is set at 3.65" W.C. A test of the heat exchanger was done about a month ago and it is tight and with a camera inspection (the Inspector camera) is in excellent shape.

Diciocco

Perhaps Jim Davis

Rudy Leatherman (Bacharach) or Jim Bergman (Testo) or Bill Spohn (Testo) can chime in here and give some good info on all these tests. They are much more knowlegeable than I am on the different meters and there charcteristics.I also would encourage folks from UEI and Wohler to offer there info. I do not have a TSI but I know Jim Davis uses that meter so I am sure he can offer some info if he is available. Thanks to all who chime in.

If you do not test you do not know. What you don't know can KILL you.

Jim Davis_3

I think it is interesting that all the meters seem to calculate efficiency differently. Even though most of these calculations are still wrong, some are more wrong than others. I always use the rule on natural gas that 1% O2 equals 1% efficiency and every 30 degrees of flue temperature equals 1% efficiency. The Testo 325 efficiency should be 3% or 4% less than the 1st Fyrite Pro 125 and yet it is higher. Again They are all wrong because none of the readings could actually allow for more than about 70% delivered efficiency.

All meters measure O2, Temperature, and CO. All other readings are straight or fixed calculations and cannot deviate unless the electronic boards go haywire.

Testo and TSI combustion analyzers are NOX compensated. NOX causes most electro-chemical CO sensors to read 10-30ppm high. Not a problem, just expains why the Testo CO readings are lower.

All O2 sensors are self calibrating each and every time the meter is turned on. Any moisture on the sensors at all can cause them to drift and give wierd readings. Once dried out many recover. Most analyzers have a special re-calibration mode for their O2 sensors if necessary. If the O2 reading drifts above 20.9% this might be necessary.

I check everyones O2 sensor with my breath. Because we exhale CO2 the sensor is easily tested. Our breath should drop the O2 reading below 17% or 16% or 15%. if we exhale into the probe slowly and as long as possible. If not the sensor is bad or our hose assembly or water trap has a leak. By exhaling directly into the meter port with a short piece of tubing we can test our hose and probe assembley. Temperature can be checked by plugging in only the T-cpl and not the hose and putting probe in boiling water. Field adjustable. CO does need actual certified CO gas for calibration but can still be checked for response by just touching the end of the probe with a match for 1-2 seconds. CO should jump over 100ppm fairly easily or something is wrong. Positioning the probe properly and interpretting the readings is more important than the actual accuracy of the CO, not that accuracy isn't important. But I have seen analyzers that were off 40% still able to diagnose every unsafe problem in the field by knowledgeable techs.

Unknown

Does anyone have Bill Spohn's

e-mail address?

Glen

so I am curious -

I predominantly work on larger commercial boilers/burners. I pack two analyzers: a Kane may and a Bacharach. Love each to death. But today, we tested a WM 1588 on both NG and oil, and added a second bacharach to the mix. The oxygen levels were all +/- .1% (on NG), but all the rest of the numbers a bit different. Now I set burners to OH2 levels - and look at eff at the very last. What gives???? Is it just intrinsic programming??? I can set the kane may to gross or net eff (based on latent heat) - should I be concerned that numbers are different??? or is it just the +/- variances of calculation/manufacturing tolerances???

Jim Davis_3

Tim, this should work: bspohn@Testo.com

Unknown

Thanks Jim,

I appreciate it.

Jim Davis_3

It is intrinsic programming based on fixed parameters that each manufacturers chooses. Each has a different selection for the ultimate CO2 content of a fuel. The one thing that analyzers assume 100% of the time is the actual btus in the fuel and our ability to convert these btus to useable energy.

When looking at non-condensing appliances 100% of latent heat is lost. On gas this is usually about 14%. By the time you deduct O2 & Net Flue temperature using most charts the maximum efficiency for most 80% equipment is around 72%, not 80% to 84%.

Jim Bergmann

Tim,

I ran all of your numbers, and the O2 and CO2 are tracking perfectly. You cannot verify calibration of a digital analyzer by watching the CO2 and O2 levels because the CO2 is calculated form the O2 reading. Most analyzers for residential and light commercial combustion testing are two or 3 gas analyzers. CO, O2 and NOx if equipped. The efficiency numbers are very close to the actual appliance efficiency using Testo analyzers until you get into the condensing range. Testo does a dry gas calculation for combustion efficiency. The analyzer can determine when the flue gasses have reached the dew point, but no analyzer can determine the latent or hidden heat extracted from the flue gasses by measuring temperature. The only way to determine the latent heat removal is by measuring weight or volume of condensate. Many of the manufacturers of combustion analyzers extrapolate or guess at efficiency's once the meter determines by stack temp and excess air that it is in the condensing range and will assume that all of the latent heat was removed from the flue gasses. This has resulted in combustion efficiency numbers that exceed 100%.

I have done extensive testing of combustion and thermal efficiency, and have faith in the combustion efficiency calculation. The important thing to remember, is this is a COMBUSTION efficiency calculation not and AFUE calculator. An 80 and 90% can have very similar combustion efficiencies yet very different thermal efficiencies as the way the heat is used after combustion takes place determines the thermal efficiency and AFUE. It is entirely possible to have combustion efficiencies of 80% with and AFUE of 60% You must also consider standby losses like that of a pilot and or draft hood when determining ultimate efficiency.

Unknown

Thanks Jim for your

input, I really appreciate yours and Jim Davis expertise. There was a recent question up on the Wall from Gary Wilson which I think you just answered.

This is what he posted:

"When I was at a Jim Davis seminar years ago, he said the calculations in today's combustion analyzers are a joke, and that if the flue gas is cooler than the air or water which is being heated, you are going backwards, made good sense to me."

So he goes on to ask: "How is it you can extract heat from the flue gas and send it into the heated medium when the heated medium is already hotter than the diminished flue gas temp?"

Ther was some interesting discussion on this subject. I agree with your statement concerning latent heat as the answer to this question do you agree.?

I find also that many times techs when testing a condensing unit do not use a sensing probe in the intake air pipe to the unit but rely on the ambient air measurement from the room.

Jim Bergmann

Combustion

Tim,
it is not possible for the stack temperature to be lower then the return air or return water temperature in a condensing appliance. The coldest the stack temperature can get is to that of the return air or water temp, and that would be ideal. I however see flue gas temps normally about 25-50 degrees above the return air in a condensing appliance. I think someone misunderstood something that Jim said. The intake temperature probe is used to calculate an accurate net stack temp, and that will affect the combustion efficiency calculation.

Unknown

Could the flue temp

be lower than the outgoing temperature forced hot water condensing boiler I believe is the question.

don_185

Thats a good

Thats a good question Timmie.One that I would think some of the wetheads here could answer quickly.

I've not tested many condensing boiler however, I know on condensing furnaces that the stack temps are at or just alittle below the discharge airtemp.

I would think the same would be true for a condensing boiler.

Unknown

My experience has been that

flue temp is affected by the air being brought into the combustion process and its temperature on condensing equipment, in particular with boilers. It most cases it is directly from outdoors and when temps outdoors are very low 10 degrees or less the outlet flue temp is usually lower than boiler water temperature. This depends of course on whether the system is modulating and is either at low fire or high fire. In cases where the incoming air passes over the heater before being drawn into the combustion chamber this tends to equal out or in fact give flue gas temps between 110 to 125 degrees or higher depending on boiler water temperature. I believe the hidden factor (no pun intended) is the latent heat which is not measured as sensible temperature.

Glen

OK then -

on my Quintox - the efficiency "range" can be set, eg, for a CI boiler or condensing. That difference is about 11%, which in my view is a practical number (rather than theoretical) of latent heat available. I can also set parameters of calorific values of the gas tested - which in western Canada varies a bit depending on gas field the fuel is coming from; not so much as the CH4 contained but the dilutant gases present. I rarely use that function as an "average" result is fine most days. I think the only constant is really the O2 available - which is why I think O2 is the parameter we should be most interested in. CO, Nox, Eff can all be manipulated by burner setup - which in the short term look like great numbers on paper - but may not be healthy for the long term firing of the burner. As always interesting discussion - that should be prefaced by "it depends".

Jim Bergmann

Combustion

Well, It depends....
The testo 330 also can be adjusted for the heat content of the fuel. The problem is it changes all the time. I agree though, the O2 is by far the most important number you read on an analyzer. Some things to remember

On a non condensing draft induced appliance at least 50% excess air is required for safe combustion and the correct amount of dilution air to prevent condensing.

The O2 should be stable. A dropping O2 level will eventually lead to formation of CO. If the O2 is dropping during operation, the burner should be shut down until the problem is corrected.

Draft hood equipped appliances can run O2 levels that equate to as little as 20% excess air if they are operating properly.

Excess air is a necessary evil. As the carbon content of the natural gas changes, a buffer of O2 is required to assure complete and safe combustion.

When setting up a power burner with a field adjustable pressure switch, the inlet air should be blocked until the burner is producing 400ppm COAF then the pressure switch set to cut out. This assures when the burner starts to starve for air due to a dirty wheel or other reason that the burner will drop out on the switch before it makes massive amounts of CO. Riello requires this on there larger burners to assure safe operation.

If your analyzer does not have NOx filters, the CO reading can be much higher than it actually is. As much as 25 to 35 ppm higher with ease. NOx is a cross interferent with all CO chemical sensors made.

And finally COAF should be monitored for burner operation and CO for the protection of your analyzer. COAF takes the effect of the O2 into account so it can not be manipulated, The COAF should ideally be under 100ppm and always under 400ppm. The CO level should monitored to protect the analyzer from over ranging the cell. CO is a measurement and COAF a calculation.

Unknown

Thanks Jim for your

input.

Unknown

Bump

!

Jim Bergmann

Combustion Manual

Tim,
Here is a current link to the Testo Combusiton Guide.
www.testo.us/AppGuide

Unknown

Thanks Jim, I had the rough draft

you sent me a while back. I ordered the finished product and encourage everyone to get hold of it some excellent information contained in the guide.

Unknown

I ordered the guide

but it never came?

The Boiler Dr.

Interesting Comparisons

I have been following this thread with great interest. There is some excellent information being provided by very knowlegable participants. Of specific interest to to is the subtle differences between brands of analyzers. I was recently in a discussion with a manufacturer questioning my results obtained with a Testo 330-1 as compared to a Bacharach 125. I was advised my readings were consistently "substantially lower" than their instrument. Therefore my efficiency readings were "always" on the low end of published information for their equipment. Interestingly enough we had the opportunity to compare head to head/side by side. The results were very enlightening. The efficiencies were only 2% apart 92.4 vs 94.1 but the other readings were quite different:
O2 - T 4.8 B 5.6 CO - T 11 B 5 COAF - T 33 B 19 CO2 - T 11.65 B 9.8 EA - T 34.2 B 48.7 Stack Temp - T 114.7 B 99.8
I recently purchased a remote temperature probe for my Testo and compared the results using 100% outside air vs a 60/40 blend vs ambient air for combustion directly connected to the burner. I was very surprised to observe there were only small differences in the results even though the outside combustion air was recorded @ -19F @ 30 inches from the burner connection. The Bacharach unit was using only ambient air during all testing.
THe equipment tested was an ADAMS condensing oil furnace equipped with a Beckett NX burner rated @ 100,00 BTU.

I have had the opportunity to use my equipment on numerous condensing boilers prior to obtaining the remote probe. Based on the discussion in this thread I am very interested in seeing what differences there may be in equipment set up and analysis using the actual combustion air temperature.

Jim Davis_3

Kind of strange but the COAF on both meters is way off!! Usually the "Air Free" would only be 3X higher when O2 was over 14%. O2 can fluctuate because of leakage in the water traps and hose assemblies. I recommend exhaling into the probe assembly with your breath and check the O2 reading. Then use a short piece of plastic tubing and attach it to the meter and see if the readings vary. This can pick up probe assembly leakage. There is a O2 calibration span on both meters that could bring them closer in line, but that I have found fairly rare to be necessary. Because the CO2 is only a calculated value, it is never correct on any meter and can easily vary by 2% based on the manufacturers own programming. The temperatures also aren't close. Put the probes in boiler water without the hoses attached to the meters and these can be re-calibrated in the field also.
Would be interesting to know your supply and return air temperatures and the cfm to calculate actual btus delivered versus the calculation.

The Boiler Dr.

Calibration

Thank You for your response. I will do the tests you suggest on my Testo and let you know my findings.
BTW are you at all familiar with the ADAMS oil unit mentioned?

Jim Davis_3

Only got to see it and test it at Adams plant here in Cleveland. Very impressed with its simplicity. Don't agree with all the factory specs but I figure that is our job in the field. I only use 80 degree solid nozzles. Tested running at 3% O2 and 0 smoke. If people have oil it is the only way to go and at todays oil prices it has affordablility. CO(carbon monoxide) readings are critical to keep it clean. When testing unit at Adams it had rising CO which meant small amount of oil impingement. Wasn't there to service just observe so I never got to make any corrections. I do believe to get the most out of this furnace or any furnace it is better to operate as close to its maximum rating. Lower inputs calculate into higher efficiencies but don't actually deliver. Post-purge should be set at maximum to protect the burner and heat exchanger.

Jim Bergmann

Combustion

All I can figure is something was changing while you were testing. After entering your O2, CO and Stack temp, I had to use 70 degree air to get your efficiency numbers. Were you using and auxiliary temperature probe? If not, the analyzer uses the ambient temp as the combustion air temp for the calculation. Mathematically, the excess air numbers you are reporting are impossible via the equation in the analyzer. That is why I am thinking something was affecting the combustion process. My results are based from our combustion equation.

Light Oil #2

FT 114.7

O2 4.8

EFF 92.4

CO 11

CO2 12.1

Ex/A 27.4

DRFT

Coaf 14

AT 70