Incrasing efficiency in a oil fired boiler

Tony_55

I have a peerless boiler wv3 3 section with a tankless coil and a honey well aquastat L 7224 c 1004 model. House is 2200 sq ft and has 3 zones. The tankless coil of course has a mixing valve. What can I do to increase efficiency - Can i still put a Taco 702 outdoor reset on this. Should i put a Storage type electric water aqua booster or an indirect type . Is this feasible with this set up. I know a lot of questions but all help and suggestions welcome

Robert O'Brien

Sure!

The goal is to reduce idle loss,an indirect will help in that regard as long as you don't continue to maintain temp in the boiler.An aquabooster won't in most cases,the boiler still maintains the LL at a fairly high #.The PC 700 will work fine.Good luck! Save some oil!

CMadatMe

Increasing Efficiency

Here are the steps I would take.

1. Do a heat loss of your home.

2. Measure the heat emmitters (baseboard in each room)

3. Compare the heat loss of each room to the max btu output the baseboard will give you at 180 degree water. (I'm in NY so, we design for 0 degrees outside)

4. Get rid of the coil and add an indirect.

5. Add a priority zone control to control your zones. (I use Taco). Make sure your zone control is the EXP version. The plug in outdoor reset control will plug into this.

6. Add the outdoor reset control.

7. Set a heating curve based on your heat loss and your comparision of baseboard per room max output compare to the heat loss of each room.

6. Clean and service the boiler have the boiler down fired if needed based on the heat loss. Make sure you get a combustion test done. 

7. Your on your way to save some fuel.



Best of Luck

Joe Mattiello

Taco PC700-2

The Tankless boiler needs to operate at the minimum temperature approx. 140 degrees, so when you have a DHW demand the boiler readily delivers.  This type of system is difficult to run more efficient, because of the minimum temperature requirement.  In my opinion, the best alternative to the Tankless coil is an indirect water heater.  Now you only fire the boiler when the water heater internal temperature drops below the minimum temperature set point.  The indirect DHW heaters alternative, minimizes the risk of a flooded basement, and eliminates the need to maintain 140 degrees 360 days a year. 

 

Additionally, you can use the Taco PC700-2 to operate the boiler based on outside air temperature, and operate ate the temperature required to satisfy the load, without firing to high limit.  The only time the boiler fires to high limit, is on the coldest days, and when the DHW calls for heat.  This system begs you to show it off to your Saturday night guests at the house!!    

 

For your convenience, I attached a tutorial on outdoor reset

John Ruhnke

RE:

I agree with Radiant Wizard on everything except down firing the boiler. The thought process is that if the boiler is over sized then down firing will reduce short cycling. This won't work on a chimney drafted boiler. Here is why. On a chimney drafted boiler there is only one speed and one amount of air will move through that boiler. It is control ed by the draft of the chimney. The goal for best combustion efficiency is to match that with the right amount of fuel. Down firing the boiler leaves to much excess air that is not needed for combustion.



 First the flame heats the air as it moves through the combustion chamber. The air then holds 100% of that flames energy. The air then either goes up the chimney or transfers its heat to the cast iron boilers surface. Any excess air not used in the combustion process robs the combustion air of energy and carries it up the chimney. Using a combustion analyser you can measure the excess air by measuring the oxygen content. On an underfired boiler you will never get that 02 number very low.

Robert O'Brien

John

I have to disagree,the vast majority of primary air is provided by the fan on a power burner.You're correct that EA drives up stack temps,but judicious downfiring will increase combustion eff,reduce short cycling and be a lot quieter to boot. You can't downfire every unit and sometimes you can't drop it by an awful lot,but most of the time you can.

John Ruhnke

RE:

Robert,

First off. EA lowers stack temps. It doesn't raise it. Second off, Jim Davis who teaches Combustion Efficiency has tuned more equipment for combustion efficiency then anyone I know. He is followed up by Energy Auditors who do an advanced form of HDD before and after analysis. He only gets paid on the % he saves his clients in fuel. What he found is that down firing a boiler decreases combustion effiency and increases fuel use per hdd.



Have you tested your therory of combustion? What are your results? How did the tests come out?

Steamhead

Some boiler manufacturers

such as Peerless, Smith and Slant/Fin, offer the same basic boiler block with different firing rates to cover a wider range of applications. So, in effect, at their lower rates these boilers are "downfired".



As long as the stack temp is high enough to prevent condensation, the excess air is not excessive and the CO is low, you should be OK at a slightly lower rate. Keep in mind that ANY change in combustion setup MUST be tested and verified with a digital combustion analyzer.

Tim McElwain

Excessive Excess Air will cause the flame to cool

however it increases the internal combustion package size and that means higher flue temps. There is a point with really excessive air and underfiring when stack temp will go down but it is way beyond what boiler manufacturers allow for minimum input. 

I also am not a fan of derating boilers but it gets difficult when the boiler is oversized to begin with and energy saving additions have been made to the dwelling reducing the heat loss drastically. Probably better to think new boiler at that time.

John Ruhnke

Antiquated Combustion Efficiency Calculations

Steamhead,

That is why you should not buy the low fire version of that boiler. The same goes for two stage burners. The Low fire is always going to be less efficient. The efficiency calculation that the manufacturers are using is not very accurate for a couple of reasons. According to Jim Davis, they are measuring combustion efficiency based on antiquated methods. Also according to Jim Davis Low Nox Blue Flame Burners are 10 to 25% less efficient then there yellow flame counter parts. They don't account for flame temps in the calculation. I devised a test to prove out what Jim Davis is talking about. I am going to meet tomorrow with Dr. Tom Butcher who is in charge of energy efficiency at BrookHaven Labs (A DOE Lab). Its a test comparing a blue flame burner to a yellow flame burner. Instead of measuring combustion efficiency I propose to measure Boiler Side efficiency. If Jim Davis is right this test will prove it.



 I believe Jim Davis. He used to tune boilers for a living. He was paid by how much he saved his clients in money. Energy Auditors followed him up with a before and after analysis. His information is based on actual field installation not laboratory tests. He then developed some new theories. He now teaches this and is seeing similar results from his students

John Ruhnke

RE:

When tuning a boiler you tune for the lowest 02 content in the flue gas. If you go too low then co will spike. So you try and keep co in a 30-70 ppm range. You do this by adjusting the fuel air mixture. A higher fuel and less air mixture (Rich) will have a higher stack temperature but be more efficient. A lower fuel and more air mixture (Lean) will have a lower stack temperature and be less efficient. Lowering the stack temps are important too. If you lower the stack temps without changing the fuel air mixture you increase efficiency.

What I mean by excess air is a lean fuel mixture. Downfiring the boiler often makes it harder to have a richer fuel mixture. Look at the o2 and you will see. The o2 tells you how lean or rich the mixture is. On a down fired boiler, while adjusting the air band, the co spikes before you can get the o2 low enough.

Jean-David Beyer

Effeciency may depend on burner.

It seems to me that W-M's burner in their Ultra 3 boilers runs at about the same combustion efficiency throughout their 20% to 100% firing range. Their carburetor, as I choose to call their gas valve, air supply blower, venturi, etc., seems to adjust the firing rate by controlling the blower speed and the gas valve measures the flow rate to determine the gas feed rate. Thus the mixture is the same throughout their firing range.



I do not suppose W-M is the only manufacturer of such burners, though different manufacturers may achieve similar results by different means. With such burners, lowering the firing rate need not lower the efficiency, it seems to me.

John Ruhnke

Modulating Direct Vent Burners........

JD,



You are right.



There are two different types of draft, Mechanical and Natural. In an appliance connected to a chimney the air flow through the boiler is not adjustable. The draft flows at one speed. On a direct vent boiler a fan controls the air speed and pressure and the air mixture can be regulated. Thus if you want to fire the boiler at 20% you can provide 20% of the air by slowing the fan speed to mix with 20% of the fuel. You then have the right fuel air mixture. Direct Vent Modulating burners can be dialed in for efficiency. A two stage chimney drafted boiler can't. The high stage mixed at 100% of the right amount of air with 100% of the right amount of fuel is set up right. The low stage still has 100% of the air because it is impossible to adjust it. But it has 50% of the needed fuel. The air mixture is the same for both stages. Thus the lower stage is set too lean and not efficient

Jean-David Beyer

How about a Beckett...

My old boiler was a downdraft GE boiler. A few years after I bought this house, I had to replace the burner and the contractor put in a Beckett one. This had a high pressure pump for the oil and a squirrel-cage blower for the air. Since after burning the oil in the air, the hot gasses had to go down to the bottom of the boiler to get to the vent pipe, I assumed that the draft was mainly supplied by the blower. Of course I could be wrong about this. At one time, they put a valve in the vent pipe that was meant to open when the burner stopped firing, and it may have done so for a moment. But later, they removed it, saying it did not make any difference with this type of boiler.



Now I never tried to diddle the firing rate on this thing, since it seemed to me the only way to do that was to change the diameter of the nozzle. I would not want to reduce the pressure, since it would probably spoil the atomization of the fuel. But since that burner was oversized (rapid cycling), maybe I could have put a smaller nozzle in there.



But now that is ancient history.

John Ruhnke

RE:

I never tuned a GE down draft boiler so I don't know if I could help you on that one. It is natural draft. Oil burners do have fans but they aren't very strong. The chimney and smoke pipe are still negative in pressure. The chimney sucks the flue gas out of the boiler. In a mechanical draft unit a blower builds up pressure and the exhaust pipe is pressurized. If you pressurize the flue gas in the smoke pipe exiting a boiler and going to a chimney you can create a deadly situation. (Co poisoning).

Robert O'Brien

John

with all due respect,you can't have worked on many oil boilers.Increase the air,increase the stack temp.Period. Try it,the greater volume of air forces the flue gases through the boiler faster raising the stack temp.

Steamhead

Not necessarily, John

Many oil-fired and power-gas-fired units of recent design now operate with positive pressure in the firing zone and flue passages. I understand that the reasoning for this is so the exit velocity of the flue gases will be reduced, and you'll get more heat transfer to the water in the boiler.



With that said, you still have to keep the chimney draft under control. Excessive draft on a positive-pressure unit can make it go negative over the fire. This will reduce its efficiency. Excessive draft can also pull the flame off the burner's retention head, causing bad combustion, rough starts etc. This is true of both positive- and negative-pressure units.



Stack temperature is affected by several things. Excess air is one. Draft is another. Still another is the amount of heat-transfer surface available to the flame and flue gases, and how well they contact the heat-transfer surface. This is why savvy techs used to (and still do) install baffles in coal-converted boilers- these caused turbulence in the flues which made the hot gases make better contact with the cast-iron.



Modern packaged boilers are fired rather aggressively, in order to pack as much capacity as possible in a smaller space. So, up to a point, reducing the firing rate while maintaining the same amount of heat-transfer surface will result in better efficiency and lower stack temp. A 2-stage burner can be a big help here, especially on a steam system where you don't have to turn down all that far.



But again, you don't want to go so low that the flame is cool enough to create CO, or the stack temp is low enough to create a monsoon in the chimney. That's where the knowledgeable pro with the proper digital combustion analyzer comes in.

Jean-David Beyer

Many oil-fired and power-gas-fired units of recent design

"Many oil-fired and power-gas-fired units of recent design now operate with positive pressure in the firing zone and flue passages."



But the old GE boiler that I replaced could hardly be called of recent design. It must have been designed around 1950,  since it was the original equipment in the house. It looked like this, starting on page 10:



http://www.heatinghelp.com/files/articles/1025/177.pdf



and that may have been it. The diagram on page 9, for one of their steam boilers, was a lot like it. It is essentially a tin can with a fire in it inside a larger tin can with water in it, so it had no flue passages at all, at least as what I think currently used terminology refers to.

John Ruhnke

RE:

Steamhead,



Yes the chamber and boiler passage ways are sometimes under pressure. Never the chimney or smoke pipe leading to the chimney though. They are always negative. Otherwise co would spill through the vent damper or barometric. That's deadly. Baffles or turbulators work great in a boiler with over sized flue passages. It captures some of that heat in the exhaust gas. The more surface contact the better. That lowers the stack temp without changing the 02. You said "So, up to a point, reducing the firing rate while maintaining the same amount of heat-transfer surface will result in better efficiency and lower stack temp." This is where Jim Davis disagrees with the combustion efficiency calculation found on your Combustion Analyser and used by the manufacturers. That lower stack temp is the direct result of the extra air diluting the combustion air. Jim has field tested this and backed up by Energy Auditors. You can't always believe your analyser.



Robert,



I have had my Fyrite Pro Analyser for more then ten years now. I have tuned countless amounts of equipment with it, both oil and gas. Lets say you try and tune a boiler and the best you can get is 12% 02. If you adjust the air band and set it at 11% the co spikes high so you have to tune it back to 12%. The stack temp might be 400. Then you increase the fuel pressure. Now you can adjust the 02 lower to lets say 8%. then the stack temp would be higher like 450. Now you raise the fuel pressure some more. o2 hits 6% and again the stack is higher lets say 475. You just saved a lot of money for your client. This only works if the equipment is under-fired to begin with. If you have the right fuel pressure or nozzle size for the boiler to begin with then raising fuel won't help efficiency cuz you can then go to rich. Once you have that sweet spot. (Lowest possible 02) Always back off a little. Add some air for safety. If the sweet spot is 4% o2 then back off to 5% or so. The draft in that chimney will change with the seasons. If the mixture goes to rich the co spikes. You don't want that happening after you leave. Then you work on lowering stack temps. Brushing the boiler passage ways increases air contact with the cast iron. This increase in heat transfer lowers the stack temps and saves your client money. Adding bricks or baffles on those old coal fired boilers lowers stack temps too.

Robert O'Brien

John

You're missing the point.You stated excess air lowers stack temp and that is incorrrect.It lowers flame temp and INCREASES stack temp due to the higher volume or air through the HX. Referring to anecdotal evidence from a supposed NCI guru does nothing to strengthen your credibility.I've asked Jim Davis in the past to provide some corroboration to his anecdotes and he has not,if you can,I'm all ears and would be very happy to apologize and reconsider my position.

John Ruhnke

Different Definition?

Robert,



Maybe we have different definitions of extra air? I am now calling it extra air rather then excess air. There is air needed for combustion and yes that lowers flame temperature when added. Then in situations the stack temperature can rise. I am talking about atmospheric equipment here. If the amount of fuel is smaller then needed for that boiler (underfired, lean, down fired), Then a situation exists. In that situation you will have more air moving through the boiler then is needed for the combustion process. This extra air dilutes with the combustion air. It drops the stack temps. I have tuned boilers and watched it happen. I have raised the fuel level, dropped the o2 and watched the stack temp rise. According to Jim Davis this drop in stack temp that happens is less efficient. That is in contradiction to the efficiency formula used by scientists. It is my goal to relay this to Dr. Tom Butcher today. I will see him today. I am going to propose doing some experiments which will prove or disprove Jim Davis's Theories.

Robert O'Brien

John

The title of the post is "Increasing efficiency in an oil boiler"  Isn't that what we're discussing?