saving oil--nozzle size

Peter Zelchenko_2

We do have a sooting problem. We've just trusted the oil company to do the right thing.

kevin nagle

saving oil--nozzle size

I work for a oil co installing boilers, but my question is-will I save oil using a smaller size nozzle?
I have a wgo-4 with a beckett clean cut ,it came as a package with a 1.25 80B, the techs tell me me its over fired and to use a 1.10 80B----------KN

Leo_12

Is it

Is it sized properly for the house? Boilers are designed to run best with the specified nozzle. If you go too small it will work harder to try to do it's job. If you go too big it will run bad use more oil and soot up. A drop down as suggested may work but make sure it is set up using combustion test equipment. If the boiler is sized properly it takes care of the heating load and hot water load. A GO 4 is a four section boiler, hopefully you have a large house because three section boilers heat most of the homes I service. If changing nozzle sizes track your fuel usage to prior years to see if you gain. We had a guy lower nozzle sizes just because he could, the boilers were usually dirty at tune up time. I put them back to proper specifications and now they run clean. There were no complaints from the customers. A dirty boiler acts as insulation reducing heat transfer and costs more to run.

Hope this helps,
Leo

Leo

bill_97

In a word ..... yes

My own boiler has a variable nozzle selection . From .60 to 1.10 gph . The specs say the lower the nozzle size the higher the efficiency . I verified that fact playing with different sizes in my boiler .

There is a point where the nozzle size is too small for the boiler and efficiency drops off ( as well as other bad things ) . I believe the WGO can be downfired by 10 percent but check to make sure first .

realolman

My boiler

is too big for my house.

It is my opinion that down firing saves me fuel. Back in March, I had a discussion with a member of this forum who has much more experience than I, who says it does not.

I have sensors hooked up to the boiler and my monitoring says that the stack temperature is lower and the water temperature rise in comparison to the time the burner runs favors the smaller nozzle.

I can only speak for myself, but I am satisfied that it saves me fuel.

Robert O'Brien

Why is the AFUE?

3% points higher on the WBV03 firing .60GPH than the WBV03 firing 1.10GPH.The only difference is the input

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

bill_97

It's the same

for the Burnham V8 . The higher the input the lower the AFUE .

realolman

I know this

is probably going to sound dumb, but I just want to be sure what you're saying... you are saying that it is more efficient with the smaller nozzle than the larger one, aren't you?

Peter Zelchenko_2

6.5gph versus 2.5gph

I have a Smith 19A 6-section that is rated for 6.5gph but fired at 2.5gph because the boiler is so oversized. The nozzle is sized to the steam load.

Should I be firing at a higher rate? The oil company decided what to install.

tommyoil

Be Careful

When lowering the firing rate be mindful of the manufacturers recommended specifications. You can have a high steady state reading using a smaller nozzle but if the stack temp is not where the mfr suggests, the result will be a FALSE reading. Readings outside what the mfr specs suggest, indicate that the equipment is NOT operating as it was designed to. Pay some heed to mfr parameters when setting up your equipment. Less may not be better. JMO.

Jim Davis_3

burners are sized for boilers not homes

Nozzles and burners don't heat homes they heat the heat exchanger. Heat exchangers heat homes. The hotter the heat exchanger the more heat you get. Down sizing nozzles may give higher calculated efficiencies but in most cases they give less delivered efficiency. The only time lowering the nozzle size could save is if the bigger nozzle was firing lousy or set up bad. 2.5gph instead of 6.5gph has to be costing 25% to 35% more energy.

Bruce_26

Smaller Nozzle > Higher AFUE

AFUE ratings are not the best way to judge efficiency. The reason you see a boiler with 4 different nozzle selections and 4 different ratings is that with a smaller nozzle and less oil the stack temperature is lower. I believe that the Brookhaven Lab is aware of this and may be devising a new and more accurate test of efficiency. Once this new rating system is in use I expect there will be a lot of unhappy boiler manufacturers.

bill_97

Nozzles and burners don't heat homes ?

Are you kidding me ? Some of us do have common sense , man .

I'll have to respectfully disagree with you Jim . Within the given range of firing rates in the boilers we use , if you lower the firing rate to try and match the heatloss of a home you lower the fuel consumption . Even the smallest oil boiler will be oversized for 90 percent of the homes we work in . It's a waste and kinda senseless to burn a 1.00 gph nozzle in a boiler that only needs 50,000 btuh to heat the home .

Whether the manufacturers are measuring " calculated efficiencies " or are doing a true test is very debatable .

Dingo_3

The reason

for that is tied to the fact that there is less oil burning. AFUE is very closly tied to the NET stack temperature. So the closer the stack temp is to room temp - the higher the AFUE. A smaller nozzel leads to a lower stack temp, which raises the AFUE

Dingo_3

I'd like a clearer explanation of how downsizing the nozzel *COULD* show such an energy waste. I wouldn't be surprised to find you are technically right, but can't seem to get my mind around how that might be.

Robert O'Brien

The Peerless

#'s speak for themselves.Is AFUE the perfect way to compare boilers?Absolutely not! But all else being equal,the boiler with the higher AFUE will use less fuel.

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

realolman

I have

posted this before.

This is my boiler with the valves closed so there is no circulation of heat.

Bob Bona_4

I can see

this. Two things come to mind.

A given size hunk of metal is designed/sized to be heated fully via full firing rate matched to the surface area, or else time is wasted getting the heat to the piping.

Lesser firing rates in that same chunk of metal, inside the firebox, can result in not so complete combustion/turbulence and the firebox not being fully utilized to heat the heat exchanger.

So, I can see that, and I have known that, smaller nozzles can give higher "AFUE" on paper via lower stack temps. But is that a true number? And, are the lower stack temps from the smaller nozzles partially due to the now unproportioned HX cooling the flame somewhat?

I know that at least Buderus, with their slightly postive OF boilers want full firing rate in order for complete and full combustion resulting in the proper spectrum for the cad cell to be happy. I'm sure noise reduction is a side benefit..

bill_97

But

in modulating gas boilers , doesn't the same principle apply ? I know we're not talking true modulation with oil boilers ( changing the nozzle size to modulate isn't my idea of advanced technology ) , but are you saying modulating downward doesn't have a fuel saving benefit ?

I'm hearing of more hi-lo fire oil burners coming to the scene soon , so a few manufacturers see some benefit to semi-modulation for oil .

realolman

I'm not sure what you mean

by the unproportioned HX "cooling the flame"

Wouldn't that be extracting heat from the flame that would have gone up the stack?

Bob Bona_4

I'm

just thinking out loud

Maybe I'm thinking about a chamber with a constant area to be heated (HX), but as the flame decreases, the mass of the HX and the water behind it "overpower" smaller inputs, lowering flame temp, in turn lowering flue temp?

I dunno. Brad? Jim Davis?

realolman

That seems

to be exactly what I was looking for in my case.

Seems to me that if there were some combustion problem associated with that, the analyzer should identify it.

I posted these before. I closed the valves to the boiler so there wouldn't be any circulation, and ran the burner as long as I felt the pressure was safe.

When I did the 1.1 GPH nozzle I was still working on the program to monitor the boiler. I am not confident about the elapsed time. Also I don't know what the pump pressure was. Probably 140 psi. I know that the burner was set both times using an analyzer.

The one thing you can compare are the stack temperatures. And I have confidence in the info on the .65 chart.

Jim Davis_3

Check this out

realoman - I knew something was not right so I sat here and tried to figure it out this morning. Remember you are operating the boiler under conditions that are not exact or normal and there are some additional variables (combustion numbers for the 1.1gph nozzle)that are not listed.

When I am looking at efficiency or any time you look at efficiency it should be when the burner is running versus sitting idle. So lets see how many btus were tranferred while each burner was running.

.65gph @ 140# = .77gph Delta T for 4.15 minutes is 16.7 degrees. 12 X 16.7 X 8.33 = 1669 btu divided by 7635 btu equals 21% efficiency while running.

1.1gph @ 140# = 1.3gph Delta T for 5.33 minutes is 41 degrees. 12 X 41 X 8.33 = 4098 btu divided by 16833 btu equals 24% efficiency while running. That is a 14% difference in favor of 1.1gph.

It appears the only time this boiler is efficient is when the burner is off and the pump isn't running. Sorry!

Radiant heat is a major factor in heat transfer. The bigger the flame the more radiant heat. The bigger the flame the closer it is to the heat exchanger.

Convective heat is the rest of heat transfer and it is the least factor but it is accomplished by the flue gasses scrubbing the surface of the the sections. If there is not enough gasses minimal scrubbing occurs and laminar flow is created.

Way back in the late 70's I started testing and helping in-house industrial engineers tune their boilers with one of the first digital combustion analyzers on the market. Two things were discovered very early.
1. If you tune equipment correctly the calculated efficiency goes down more often than up.
2. Two stage and modulating equipment wasted energy out the gazzoo. 2-stage averaged just above 25%, while modulation averaged just above 33% assuming the combustion was close to begin with.

I did my thing now someone show me where I could be wrong. I actually taught myself something this morning and hopefully a few of you.

Bob Bona_4

I understand

what you are saying Jim, and what I was trying to articulate before..just couldn't form the thoughts into a coherent sentence

Those intangibles get me every time.

Jim Davis_3

I think you articulated just fine. But as you can see, when you crunch the numbers, one can become speechless.

realolman

But that

deleted... double post.

realolman

But that

doesn't make any sense... and here is why. The only way any heat could be transferred into the water is if it comes from the combustion while the burner is running.


The burner ran for a period of time, burned a specific amount of fuel, and any temperature rise of the water had to come completely from the combustion that occurred during that time. Jim, you agreed back in March that this was a valid test.


The delay is a factor of sensor placement and the shape, size, and water content of the boiler. If it held a thousand gallons with the sensor near the top, the delay would have been longer still. Would that have made the amount of heat transferred into the water even less?


Why doesn't the temperature rise after the burner shut down count? How could it not count? If not from the amount of time the burner ran, and burned the specific amount of fuel, Where else would the heat have come from?

Jim Davis_3

I probably agreed that it was a valid test but apparently I was wearing my stupid hat that day and misinterpreted the results.

First you say you are not sure of the run time of the 1.1gph nozzle but you operated until the pressure got to a certain point. What is additionally strange, which I didn't mention was how could it take 28% longer to build up the pressure at a higher temperature and input? Not making sense.

Remember when the burner shuts off the residual heat stops moving and stops going up the flue. Therefore there is going to be some additional recovered heat that was absorbed by the sections and left over flue gasses that is not venting as quickly and can be absorbed.

When you look at the sequence of operation, T-stat calls for heat, burner comes on and maybe the pump or their is a delay. When the T-stat is satisfied the burner shuts off and so does the pump. At that point it doesn't matter how hot the water gets because it is not needed to heat anything. I'll have to figure out another way to make this more clear tomorrow.

In a practical operating mode the pump would be running and you would probably see a similar differential(14% or more)in the temperature rise of the water @ .65gph. versus 1.1gph. I think a more fair test would be testing with the pump running continuously at the same gpm and then calculate the true difference.

bill_97

Burner shut down

There is a temperature rise on burner shutdown . I've seen a rise of 30 degrees in a new Weil Gold .

Jim , does your math take into account the higher exit flue temperature with the bigger nozzle ? And what about increased cycling ?

I'm still convinced using the smallest nozzle a boiler is rated for will increase efficiency .

realolman

I knew

I shouldn't have posted the 1.1 gph chart. In the post to which I attatched the two charts, I specifically said that I was in the process of writing the program and installing the hardware that monitored all this. The 1.1 gph chart was made in 2006. The only thing I had confidence in was the stack temperature, which was 100° higher with the 1.1. The stack temperature was the only thing I intended for anyone to compare in the two charts.

I am completely satisfied and confident with all the information I presented in the .65 chart. That was made in March 2008.

Now then... to address your points:

First you say you are not sure of the run time of the 1.1gph nozzle but you operated until the pressure got to a certain point. What is additionally strange, which I didn't mention was how could it take 28% longer to build up the pressure at a higher temperature and input? Not making sense.
I embarked on this because I like messing with computers and electronics, and I want to make my boiler as efficient, and heat my home as economically as I can.

I am sharing it here because I think it is useful and I am kind of proud of it. I doubt too many people have such information compiled about their house and heating system.

First I tuned the burner with the analyzer and set the pump pressure. Then, I shut off the boiler and let the water temperature drop to a point that I felt was reasonable. I closed all the valves to the boiler so there could be no circulation. Then I fired the boiler and recorded the results, while monitoring the stack temperature with the analyzer as well as the computer, and watching the gauge on the pump. I turned it off when I thought the pop off might go. On some tests, occasionally it did.


Remember when the burner shuts off the residual heat stops moving and stops going up the flue. Therefore there is going to be some additional recovered heat that was absorbed by the sections and left over flue gasses that is not venting as quickly and can be absorbed.

I agree, and I think that the reason the smaller nozzle works for me is in part because of the 100° lower stack temperature and the smaller volume of gas going up the stack. I put in a smaller static plate and low firing rate baffle when I changed nozzles.

When you look at the sequence of operation, T-stat calls for heat, burner comes on and maybe the pump or their is a delay. When the T-stat is satisfied the burner shuts off and so does the pump. At that point it doesn't matter how hot the water gets because it is not needed to heat anything. I'll have to figure out another way to make this more clear tomorrow.

Again I agree. But that was not the point of my experiment. The point of my experiment was to determine how many BTU of the 140000 or so that should be in my gallon of fuel oil are being transferred into my water. It is my opinion, based on ther results of considerable monitoring, that the smaller nozzle does a better job of that with my boiler. With less lost up the stack.

In a practical operating mode the pump would be running and you would probably see a similar differential(14% or more)in the temperature rise of the water @ .65gph. versus 1.1gph. I think a more fair test would be testing with the pump running continuously at the same gpm and then calculate the true difference.

If you can tell me how I can be sure that I am placing a consistant equal load on the boiler for both tests, I would be glad to do that. I decided that closing the valves with no loss to circulation was the best way to achieve that.

I would burn a known quantity of fuel by timing the burner run, measure the entire transfer of heat and compare the two.

I had to live in the house while I did that, and am paying for the fuel, make all this equipment, and write the program, and do these tests, and go to work and make a living.


Attached is one of the charts of the fuel I expect to use based on the dozen or so sample days indicated by the dots.

It doesn't prove anything to the point here, just to show that I am checking.
I have about two years worth of data, I did not compile two years of data with the larger nozzle to use as a control... and I am convinced that the smaller nozzle works best for me.

I'll be checking it again next winter, and you can be sure I will be here with my results... whether any of you are interested or not.

Jim Davis_3

I think one of the biggest industry fallacies or misunderstandings is that lower flue temperatures always represent higher efficiencies. I have spent 38 years showing that increasing flue temperatures can be more efficient. But it takes alot more than a simple statement to make sense. Obviously a sooted up appliance has a higher flue temperature and is less efficient. The correct statement is you need to bring the flue temperature to a proper range for the what we are trying to accomplish.

Which is more efficient: 100# gas steam boiler with a 320 degree flue temp or one with a 420 degree flue temperature.

Ans. 420 degrees, because 320 degrees can not produce 338 degree steam!

But backing up, still don't understand how the pressure at the higher firing rate rose slower.

The flue temperature is also representative of the temperature of the boiler sections. The higher the flue temperature the hotter the sections(assuming they are clean). Therefore how did the boiler firing at 1.1gph and a 600 degree flue temperature only gain 36 degrees after the burner shut off while the cooler one gained 45 degrees? Should have been the opposite.

Laws of physics = 1. the greater the temperature difference the greater the rate of tranfer
2. For every load there is one efficient force to move it.

I see a lot of high efficiency gas furnaces with plastic flues that have flue temperatures around 90 degrees. 90 degrees is the temperature of the last pass of the heat exchanger. 70 degree air passing over it isn't going to get very warm. But raise that temperature to 120-140 and now we can accomplish something.

Again the chart shows that while the burner is firing @ .65 or .77gph with the lower flue temperature the change in water temperature is much lower than 1.1 or 1.3gph in about the same amount of time.

When I first started calling on industrial accounts I constantly heard that cycling was bad and less efficient. Most of the industrial boilers I tested were controlled so they would almost never shut off. Many of them were process versus just heating. But then the next thing that I heard was complaints about how often they were rusting out and leaking and failing. Once re-controlled to cycle, as close to high-fire as possible(minimized most modulation and staging), these problems almost disappeared. To an in-house engineer, reducing failures was more important than the 25% to 40% they ended up saving on fuel. I am talking about boilers that are 10 to 50 million btus. My position for years was to solve my customers problems and complaints versus comforming to "thats the way its always been done".

Resetting boiler water temperatures is the efficient method to derate equipment and save fuel, not lowering firing rates.

This coming winter the best test will be how much oil you buy. Fire one month at the lower rate and one month at a higher rate. We can compare degree days and see how many gallons per degree day. Obviously the burner setup is critical.

Oil should run: O2 - 4-6%
Flue T - water temp + 350 to 450
CO - <100ppm
Smoke - 0 - trace(20 pumps versus 10)

Just for the record I am not saying you didn't use less fuel at the smaller firing rate, I'm just saying the reason
is not because of that.

jp_2

are you talking

about oil boilers only?

what I have seen, points to higher efficiencies from lower delta T's.

I admit I do not understand it completely, but i was told during a nuclear plant tour that close delta T's equalled higher efficiency. veissman data also points to closer delta T's and higher efficiency.

Jim Davis_3

Talking about all fuels. Lower Delta T's is less heat transfer - lower efficiencies. Unfortunately most of these types of statements are being made by persons looking at the calculated efficiency of an analyzer that are usually bogus.

Steamhead (in transit)

Someone- I forget who

told me once that modern boilers are fired much more "aggressively" than older ones. This seems to be a way to get more capacity into a smaller unit.

But with a given heat exchanger, it's also possible to fire it so aggressively that the efficiency drops. The heat exchanger simply cannot absorb that quantity of heat, so more of it goes up the chimney. Ron Jr., this may be what you're talking about when you mention how the efficiency goes up as the firing rate is dropped on those Peerless and Burnham boilers. Another factor in this is that the smaller air-intake (band and shutter) settings on a burner firing at a lower rate would tend to reduce off-cycle losses, by allowing less air to draft thru the boiler when the burner is off.

Another thing to consider is that there are a LOT of oversized boilers out there. Too many installers still use the "label" or other inaccurate methods to size boilers. I haven't seen a customer yet who would replace their relatively new boiler if it was found to be oversized, so we have to do the best we can in these cases. If a digital analyzer is used, a slight down-firing on such a boiler can be done safely, the heat exchanger will absorb a greater percentage of the heat from the burner, and short-cycling will be reduced which results in less wear on the equipment and saves some fuel in itself. Obviously, we don't want to down-fire too much, this can lead to flue gas condensation, sooting, high CO and other ills.

Not every situation is the same. Commercial process boilers often need to be fired to a certain level regardless of the actual load, as Jim describes with his 100# commercial steamer. But Realolman's data shows that his system is running more efficiently when down-fired. Maybe look at a smaller boiler next time, ROM?

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

Jim Davis_3

I am not sure if they even make them anymore but there used to be a boiler called an "Ohio Special". These were intentionally overfired boilers with smaller heating surfaces so that commercial and industrial plants did not require a full time Stationary Engineer. Downfiring these would save energy but might not keep up with the load.

Equipment ideally should be fired for its maximum mechanical ability. Controls should be used to address loads.

For 30 years I have studied fuel usage not calculated or fabricated efficiencies.

realolman

After I posted yesterday

and stated my reasons for sharing my results here, I realized I had forgotten probably the most important one... that I am continuing to learn by coming here. Thank you.



I agree that lower stack temperatures do not automatically equate to higher efficiency.... But I think this statement is absolutely true:

There is more heat being lost up the stack when the stack temperature is higher, and at the same time, the nozzle firing rate requires more air.


The heating load is going to require the same amount of BTU no matter what size nozzle is in the burner. My goal is to transfer the heat released from burning each gallon of oil to the house, through the water in the boiler, while losing the least amount possible through the stack.

I expect that when I lower the nozzle size the burner is going to run longer, but I know that the amount of heat up the stack every second the burner runs with the smaller nozzle is less. Using the analyzer to set each nozzle, the only question remainig is: How long does each setup run? That's what I'm trying to track.


The major difference between my house and an industrial process, is that you would vary the rate of the process to require all the heat that the heat exchanger has available to give. In other words, you increase the process throughput to just barely below the point that the heat exchanger is incapable of providing enough heat. Until the heat exchanger maximum output and the process demand is equal.

You can't do that with your house... I suppose I could open windows in order to load the boiler down to it's maximum output with the 1.1 gph nozzle, but I don't want to. This is a little different animal than an industrial process.

I think Steamhead makes some excellent, very well articulated points. Much better than I could've done.

Oh yeah... I'll be sizing my boiler a lot more closely next time, you can be sure.

jp_2

how do YOU figure efficiency

if you use no calculations and no measuring devices?

I can use a cutting torch to heat a pot of water, very high delta T's, doesn't mean thats efficient.

so you are saying that high stack temperatures mean high efficiency?

jp_2

high stack temp

one reason you have high stack temps, the rate of heat transfer to the HX is lower/slower than the burn taking place, so you are not putting heat into the HX but out the vent.

100% heat transfer would mean air intake temp = vent(stack) temp. take it from there down to zero.

realolman

i would think

that is probably exactly correct.... So what action should one take to lower those stack temps, and transfer more of the heat to the water?

Peter Zelchenko_2

I find it fascinating that through this whole interesting thread, there does not seem to be any empirical facts. You would think that there might be a design engineer for one of the boiler companies that might view this site.

I for one, am completely puzzled as to whether my boiler is inefficient due to underfiring (2.5 gpm) versus the recommended 6.5 gpm for this Smith Model 19 6-section. When I called their tech support, they said that it is more efficient underfired, but I question whether the person I spoke with really knew what he was talking about. With 5500 gallons used in a season, I want to make sure we are firing at the optimal rate.

Keith_8

Steve

What is the stack temperature?

That would be my major concern. Is your 5500 gallon fuel consumption lower this year than last? Obviously you heated the building or the tenants would have let you know about it.

If your stack temp is around 350 degrees and your able to create steam than the lower firing rate is not a problem.

My gut tells me that the firing rate is too low. At less than 40% of the recommended firing rate I have a hard time believing the inside of that boiler isn't sooting up. The heat exchanger can't possibly be clean. Your stack temp is creating condensation in the boiler and possibly ruining the chimney. Have you opened up the clean outs and looked inside?

Keith