Is it possible to test a boiler efficiency?

Gordy

captainco said:

That is the one product I have tested in 38 years that actually works near its rating.

What product? Mod/cons in general, or htp

Gordy

I ask because they don't work out to their rated efficiency. By either input verses doe/ibr, or input verses heating capacity as htp likes to use.

captainco

ChrisJ Have a birthday party?? Obviously with some scaling the efficiency might go down, but scaling should be minimized.

Gordy - IBR makes it look like its only 8% more efficient than a standard boiler. Not even close. That is just another reason why all these ratings are screwed up. IBR knocks off at least 10% regardless. Then they come up with a couple of other small deductions? The 10% is usually jacket losses, but I am pretty sure most of these are indoors and jacket losses heat the building.

captainco

Gordy - Most are efficient but not much more than 3-5% between any of them. Obviously the hotter the water the lower the efficiency. I forget what outlet water temperature they are tested, but then I am old!

Paul48

@captainco's point has been made, and argued here, many times. We've heard about CI boilers, that were not grossly over-sized, that were replaced with properly sized and controlled mod/cons. The claims of 30% savings have led to many arguments. Some saying that it was not possible.

HVACNUT

> @captainco said:
> Although this is not exactly 100% scientifically correct...

>>On the Main Wall, @RayWohlfarth started a discussion on the worst job sites you've ever been to.
I would say any job where there was a wacky engineer on site.

bob_46

Nobody is mentioning that the btu content of natural gas can very as much as 60 btu/ft/cu with day to day changes in barometer. How does that affect all your calculations ?

Paul48

@captainco did mention that.

D107

HO here. I think Dan H explains boiler ratings well here: https://heatinghelp.com/systems-help-center/boiler-ratings-explained/ though not in the combustion detail offered by
captainco.

So as I understand it, combustion efficiency (AFUE) is Gross Output (DOE Heating Capacity) divided by fuel input. The difference between those two is accounted for by stack and jacket losses. The net output, I think it's being called IBR here, accounts for piping heat losses, raising temp of piping to water temp, and the pickup factor--heating up all the water.

So the consensus is here that even if you're just trying to measure combustion efficiency, the IBR is the truest measure? Of course overall efficiency is even more important, but I was hoping my old boiler was operating at 77%, not 68%. I'm sure a good installer would say before I install let's try to insulate, re-design piping system, install new controls where necessary.

captainco

The output of a boiler is determined by the calculated efficiency of a combustion analyzer and no actual btu measurement. So if the analyzer shows 80% efficiency on a 100,000 but boiler the output is assumed to be 80,000 btus. Then IBR automatically knocks off another 10% to 15% for additional assumed losses. Its closer to correct because it is lower, but still misrepresents actual efficiency in many situations. Is it ever close? Only one person or Being knows for sure and that will require a really long distance call. Percentage of difference or change from one set of readings to another is somewhat determinable, but the actual efficiency is not.

Interpreting good readings from bad takes a little understanding but in the end our job is to maximize efficiency whatever it is. It just may not be what everyone has been led to believe.

ChrisJ

What about air conditioning systems and refrigeration?
How is their EER and BTU/H ratings figured?

captainco

Is that the Exaggerated Equipment Rating(EER) or the Super Exaggerated Equipment Rating(SEER)?

I, myself, plead insanity on this one. See who else wants to get in trouble:)

larryjbjr

My, seemed like such a simple question. Had no idea the can of worms I was opening.

captainco

larryjbjr said:

My, seemed like such a simple question. Had no idea the can of worms I was opening.

But look at all the fish you caught! That's a good thing!!

ChrisJ

larryjbjr said:

My, seemed like such a simple question. Had no idea the can of worms I was opening.

That wasn't a can, it was a drum of worms.

bob_46

Question for the captain , when I started in the trade almost every furnace I saw was rated for 100º rise now they are half that or less. How come?

hydro_newbie

@captainco, I also have a couple questions. I'm trying to understand the article you posted in the thread earlier. In the various examples of 82% efficient combustion readings (different O2 percentages), how do you calculate the flame temperatures?

Also, in the examples, assumption #2 says that the ratio of nitrogen to oxygen in air is about 4:1 (79% to 21%). I think (please correct me if I'm wrong), that this is how you arrive at the various percentages of nitrogen for the various oxygen percentages (12% O2 -> 48% N2, etc). But, aren't we talking about the percentage of oxygen in the flue gas? Shouldn't we expect the ratio of oxygen to nitrogen in that gas to be different than normal air? The nitrogen isn't being consumed in the combustion process, but the O2 is (or rather, its being converted to CO2 and H2O?).

Can you help me understand this better? Apologies if I'm hijacking the thread a bit (and/or asking silly questions)...feel free to PM if it's easier!

NY_Rob

Paul48 said:

@captainco's point has been made, and argued here, many times. We've heard about CI boilers, that were not grossly over-sized, that were replaced with properly sized and controlled mod/cons. The claims of 30% savings have led to many arguments. Some saying that it was not possible.

Using my CI boiler for the 2015-2016 heating season and my new HTP UFT80 Mod-Con for the 2016-2017 heating season- with actual HDD info for my area and real gas consumption figures from my meter (not estimated bills).... I saw a 18% decrease in gas consumption with the Mod-Con, and a 22% efficiency increase when adjusted for temperature difference between the two winters.

I just finished replacing 22ft of Fine Line 30 fin-tube with high efficiency/low temp Heating Edge2 baseboard this weekend to help lower my supply temps this winter hoping raise efficiency a tad more.


I imagine it wouldn't be hard to hit a 30% savings with a mod-con if the house had all high efficiency/low temp baseboard where you could run 120F supply water all winter long vs. running a mod-con at higher temps with conventional fin-tube that was designed for 180F SWT.

ChrisJ

I don't know about your house @NY_Rob but my heatloss is far from linear because infiltration isn't linear. That being the case you can't correct for hdd differences in that manner

Gordy

@NY_Rob was the old ci boiler properly sized, and setup correctly?

@chris if you are diligent in your observation of HDD data you can track apples to apples HDD. If you do this over a period of a season, or two it's good data.

I had the leisure of a weather station in close proximity of my home. You can calculate your own HDD with a semi decent home weather station, yes HDD does not account for wind, solar influence, shade etc.

captainco

bob said:

Question for the captain , when I started in the trade almost every furnace I saw was rated for 100º rise now they are half that or less. How come?

d

If you look at the actual rating plate inside the furnace it will say maximum rise 100 degrees or maximum plenum temperature 170 degrees.
The actual rises are lower because new furnaces have heat exchangers with more surface and require 30% to 50% more airflow

The minimum temperature rise on an old furnace was 75 degrees if you wanted it to deliver its rated btus.

New furnaces the rise is 60 degrees for the same reason.

captainco

hydro-newbie - Not a hijack but a good thoughtful question and if there is anything I like to do is make people think versus being robots.

The O2 and N going in is 4 to 1 O2 combines with carbon to make CO2 and CO. It combines with Hydrogen to make H2O. Nitrogen combines with O2 and makes NO.

The same amount of molecules that enter the furnace, exit it. Some are in a different forms or combinations but still the same amount.. You could say the ratio of unused O2 versus unused N is different. Much higher percentage of N but overall the total flue gas contains the same amount that entered. Does that make sense?

I found a flame temperature chart for natural gas in an industrial burner book in the early 80's. The actual maximum temperature of natural gas is around 3570 to 3590 degrees depending on whose book you read. Keeping math simple I rounded off to 3600 degrees.
I still read tech books that say the maximum temperature of natural gas is 2500 degrees. Heck, that is how hot a candle can burn. Having worked with industrial process such as Kilns and Steel Treating, some of these operate with temperatures in excess of 3000 degrees. I used to sell 3200 degrees fire brick for lining old boilers. That is hardened in a Kiln that is hotter than 3200 degrees.

captainco

NY-Rob you are quite correct. One a properly installed and operated Mod-Con 20% saving should not be out of the question and even more.

Question: What is the normal approved venting material for Mod-Cons in the US not Canada.

captainco

HDD from one year to another can be misleading. Over a long period they will average out. I worked with some energy auditors in the 80's that factored in percent of sunshine, wind and rain. Agreed daylight hours in the winter are short, but 6 hours of sunshine versus six hours of wind and rain changes makes a difference. I used to subscribe to the NOAA monthly weather data charts. Amazing how much information and measurements they contained

NY_Rob

@Gordy
The CI boiler was 100K BTU in with 80K BTU out, it was installed when the house was built in 1964. The house is about 1,800sq/ft with a quarter basement, the rest on slab, four upstairs bedrooms. Our area was a "development" where there were only two basic styles of homes available.. a high-ranch and a "splanch" like ours that actually has three living levels plus the quarter basement. AFAIK all the homes (probably 100+) in our area got the same capacity boiler if they opted for gas vs. oil. I never see any oil trucks in our development, so I believe all the homes are gas.
I have calculated my DD heatloss at a tad under 30K BTU's, so the original boiler was somewhat oversized... but I understand that was SOP back then. I have to assume it was setup correctly (according to early 1960's standards and practices) as it lasted 52 yrs with no major issues, a comfortable home and reasonable energy usage.

In reality, even the new 80K mod-con with it's 10:1 turndown is oversized for my house, but I can limit it's max output by as much as 50% if desired and other "tricks" i.e. step modulation and CH Anti-Cycling delay make it "fit".

Regarding the specific numbers... it was easy to compare actual gas usage between the two winters because I knew I was going to replace the CI boiler eventually and I had been tracking it's usage closely via my gas meter for the previous two winters.

For the HDD data I have a online weather station on my roof... it's part of the Weather Underground Network:
https://www.wunderground.com/personal-weather-station/dashboard?ID=KNYSELDE7
You can go back as far as Feb of 2015 to see hourly weather data for my property. Whenever I've compared it to the commercial station at our local regional airport (Long Island MacArthur Airport) the two stations have been very close. I used the airport wx data for both winters to be consistent.

I had the gas consumption data and the HDD data, I did the easy math on the consumption delta (18%) between the two systems/winters... another member here calculated the 22% efficiency gain for me using my HDD data.

ChrisJ

NY_Rob said:

@Gordy
The CI boiler was 100K BTU in with 80K BTU out, it was installed when the house was built in 1964. The house is about 1,800sq/ft with a quarter basement, the rest on slab, four upstairs bedrooms. Our area was a "development" where there were only two basic styles of homes available.. a high-ranch and a "splanch" like ours that actually has three living levels plus the quarter basement. AFAIK all the homes (probably 100+) in our area got the same capacity boiler if they opted for gas vs. oil. I never see any oil trucks in our development, so I believe all the homes are gas.
I have calculated my DD heatloss at a tad under 30K BTU's, so the original boiler was somewhat oversized... but I understand that was SOP back then. I have to assume it was setup correctly (according to early 1960's standards and practices) as it lasted 52 yrs with no major issues, a comfortable home and reasonable energy usage.

In reality, even the new 80K mod-con with it's 10:1 turndown is oversized for my house, but I can limit it's max output by as much as 50% if desired and other "tricks" i.e. step modulation and CH Anti-Cycling delay make it "fit".

Regarding the specific numbers... it was easy to compare actual gas usage between the two winters because I knew I was going to replace the CI boiler eventually and I had been tracking it's usage closely via my gas meter for the previous two winters.

For the HDD data I have a online weather station on my roof... it's part of the Weather Underground Network:
https://www.wunderground.com/personal-weather-station/dashboard?ID=KNYSELDE7
You can go back as far as Feb of 2015 to see hourly weather data for my property. Whenever I've compared it to the commercial station at our local regional airport (Long Island MacArthur Airport) the two stations have been very close. I used the airport wx data for both winters to be consistent.

I had the gas consumption data and the HDD data, I did the easy math on the consumption delta (18%) between the two systems/winters... another member here calculated the 22% efficiency gain for me using my HDD data.

On your roof?!

Temperature sensors are to be mounted 4 to 6 feet off of the ground, and twice as far from a structure as the structure is high or more. I.E. if a house is 20 feet high you need to be 40 feet or more from it. They are also to be 100 feet or more from any black top.

They also need to be installed in a Stevenson screen.

ChrisJ

@captainco So I'm confused...

I have a gas grill rated 35,000 btu/h. Does this grill actually produce that in heat or is that a lie?

hydro_newbie

captainco said:

I found a flame temperature chart for natural gas in an industrial burner book in the early 80's. The actual maximum temperature of natural gas is around 3570 to 3590 degrees depending on whose book you read. Keeping math simple I rounded off to 3600 degrees.
I still read tech books that say the maximum temperature of natural gas is 2500 degrees. Heck, that is how hot a candle can burn. Having worked with industrial process such as Kilns and Steel Treating, some of these operate with temperatures in excess of 3000 degrees. I used to sell 3200 degrees fire brick for lining old boilers. That is hardened in a Kiln that is hotter than 3200 degrees.

@captainco. Thanks for the additional info. Can you explain how you calculated the flame temperature based on the oxygen/nitrogen percentages? I don't follow that step. Does it just come from the chart you mention, is there one online you could point me to?

captainco

That is the amount of fuel it can use in an hour on high fire. Now if gas can burn at over 3000 degrees why doesn't your grill get that hot? I don't believe hotdogs and hamburgers are that good of a heat exchangers and could get really crispy at 3000 degrees.

A gas oven can use 40,000 to 50,000 btus. Gas, again can burn at over 3000 degrees. It is using the fuel and making 99.99% of its maximum btus. Where is all the heat going? Gas ovens operate with 14% to 15% O2 which means the flame is cooled with nitrogen.

During self-cleaning the oven does get over 900 degrees and vaporizes the food into CO.

captainco

hydro_newbie said:

captainco said:

I found a flame temperature chart for natural gas in an industrial burner book in the early 80's. The actual maximum temperature of natural gas is around 3570 to 3590 degrees depending on whose book you read. Keeping math simple I rounded off to 3600 degrees.
I still read tech books that say the maximum temperature of natural gas is 2500 degrees. Heck, that is how hot a candle can burn. Having worked with industrial process such as Kilns and Steel Treating, some of these operate with temperatures in excess of 3000 degrees. I used to sell 3200 degrees fire brick for lining old boilers. That is hardened in a Kiln that is hotter than 3200 degrees.

@captainco. Thanks for the additional info. Can you explain how you calculated the flame temperature based on the oxygen/nitrogen percentages? I don't follow that step. Does it just come from the chart you mention, is there one online you could point me to?

Not sure if you can find that chart on Engineering Toolbox or not. Bacharach had a different type chart but they took everything off their website. Let me see if I can attach mine.

NY_Rob

@Chris... as I mentioned in my post, I ended up using the wx data from our local regional airport which is about 10mi line of sight from us, (which serves about two million commercial passengers a year) not my rooftop unit.
It was the same consistent source for both winter's data... so even though it may or may not be in a "Stevenson screen" it's $$$ aviation grade, professionally maintained meteorological observation equipment from an official FAA Flight Service Station.
I'm going to assume that the equipment at the airport is adequate for my simple HDD calculations

Paul48

@NY_Rob
YES.........But do you have your pilots license?

ChrisJ

captainco said:

That is the amount of fuel it can use in an hour on high fire. Now if gas can burn at over 3000 degrees why doesn't your grill get that hot? I don't believe hotdogs and hamburgers are that good of a heat exchangers and could get really crispy at 3000 degrees.

A gas oven can use 40,000 to 50,000 btus. Gas, again can burn at over 3000 degrees. It is using the fuel and making 99.99% of its maximum btus. Where is all the heat going? Gas ovens operate with 14% to 15% O2 which means the flame is cooled with nitrogen.

During self-cleaning the oven does get over 900 degrees and vaporizes the food into CO.

Well I mean,
That and the food isn't in the flame, the flames are tiny compared to the heat spreaders and the space around them.

ChrisJ

NY_Rob said:

@Chris... as I mentioned in my post, I ended up using the wx data from our local regional airport which is about 10mi line of sight from us, (which serves about two million commercial passengers a year) not my rooftop unit.
It was the same consistent source for both winter's data... so even though it may or may not be in a "Stevenson screen" it's $$$ aviation grade, professionally maintained meteorological observation equipment from an official FAA Flight Service Station.
I'm going to assume that the equipment at the airport is adequate for my simple HDD calculations

I've wanted an online station for years now, but never have the time or money to do it.

NY_Rob

Paul48 said:

@NY_Rob
YES.........But do you have your pilots license?

Well, Actually.......
CFI (Certified Flight Instructor) Rotorcraft/Helicopter since 1986.
Commercial Pilot Rotorcraft/Helicopter since 1987.

1,200+ hrs Twin Turbine time in Sikorsky S58.
100+ hrs Bell 206 (Longranger and Jetranger).
xx hrs Agusta A109
xx hrs Aerospatiale Astar and TwinStar
1000+ hrs Robinson R-22 as CFI

35 hrs Fixed wing (Cessna 172/182RG) time.

That's probably why I became a weather geek... as a helicopter pilot you had to constantly be aware of your area's meteorological conditions or bad things could happen

NY_Rob

ChrisJ said:

I've wanted an online station for years now, but never have the time or money to do it.

They're very reasonably priced now ($300) are connected via wi-fi and are solar powered. Once you're setup and join the network you have access to your data going back for years!

I love having my own weather station at my house....

http://www.ambientweather.com/amws1000wifi.html

captainco

Well I mean,
That and the food isn't in the flame, the flames are tiny compared to the heat spreaders and the space around them.

Easy for you to say, you haven't seen me grill out. When I grill there is two choices: crispy or extra crispy!

ChrisJ

captainco said:

Well I mean,
That and the food isn't in the flame, the flames are tiny compared to the heat spreaders and the space around them.

Easy for you to say, you haven't seen me grill out. When I grill there is two choices: crispy or extra crispy!

So one part I can't wrap my head around Jim.

So, the gas grill is rated 35,000 btu/h, and produces that, +-.
My boiler's burner is rated 125,000 btu/h input.
But you say the boiler cannot possibly be more than 70% efficient, because it doesn't condense. Why is that?

If 125,000 btu/h is there in pure heat, wouldn't condensing be a benefit above and beyond that rating? I.E. if you could some how, absorb all of the energy content AND condense, actually result in above 100% efficiency? I realize that's not possible, I'm just using it as an example.

HVACNUT

> @NY_Rob said:
> @NY_Rob
> YES.........But do you have your pilots license?
>
> Well, Actually.......
> CFI (Certified Flight Instructor) Rotorcraft/Helicopter since 1986.
> Commercial Pilot Rotorcraft/Helicopter since 1987.
>
> 1,200+ hrs Twin Turbine time in Sikorsky S58.
> 100+ hrs Bell 206 (Longranger and Jetranger).
> xx hrs Agusta A109
> xx hrs Aerospatiale Astar and TwinStar
> 1000+ hrs Robinson R-22 as CFI
>
> 35 hrs Fixed wing (Cessna 172/182RG) time.
>
> That's probably why I became a weather geek... as a helicopter pilot you had to constantly be aware of your area's meteorological conditions or bad things could happen


>>Hey, can you fly me out to East Hampton this weekend? The Citiots and the Trade Parade really cut into free time.

captainco

@ChrisJ
Let's try this. When you burn gas, your combustion efficiency is 99.99% if the CO is less than 100 ppm. 90% of that is sensible heat and 10% is latent heat. In the real combustion equation latent heat at 0% O2 is 18% of the total btus. At 6% O2 latent heat is about 14%. I had an engineer from Bacharach show me and walk me through the formula. I might as well tried readings hieroglyphics inside a pyramid??? Anyway, that would mean the maximum amount of available sensible heat of a non-condensing appliance is 86%. Every percent of O2 in the flue gas lowers that 1% more. Every 30 degrees the gross flue temperature is above ambient or combustion air temperature is another percent. These numbers are programmed in to every combustion analyzer chart there is.

It is not the O2 that steals the heat, it is the Nitrogen.

86% - 6% = 80% available heat
450 degree Flue T - 70 degrees Room T = 380 degrees

380 degrees divided by 30 = 12.67% loss
80% minus 12.67% = 67.33% efficiency.or heat transferred.
Therefore a 100,000 btu input boiler has an actual output of 67,333btus.

That 80,000 btus output rating has never been measured by any manufacturer. It is all assumed based on combustion analysis calculations that have proven to me and most of my students to be inaccurate.

I watched two one hour videos from a major industrial boiler company a few months ago (still learning after 39 years), by an engineer that has been with them for 40 years. I think both were from 2012. One was on combustion efficiency and heat transfer and the other was on NOX and re-circulatiing flue gases to lower it.
The efficiency one started out on the mark for 30 minutes and then it went to pot. The second one was one of the most evasive videos I have ever seen. I know why people are still confused.

There is a reason it takes me 3 days to teach this stuff in class.