Short cycling and bursting, and improving efficiency from an oversized boiler

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  #1  
Old 12-16-16, 08:12 AM
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Short cycling and bursting, and improving efficiency from an oversized boiler

Good day!

I've been reading through a number of posts on this forum, trying to figure out what the best next step is for my girlfriend's heating system.
The existing system was installed by the previous owner in a haphazard way that seemed to just involve throwing money and very little planning at the problem.

Last night we got down to about 5 degrees, pretty much our coldest / design temp. I clocked the last few cycle times of the boiler and we had 5 cycles about 3 minutes 20 seconds, 1 cycle that made it up to 4:10, and 2 times that it turned on for about 3 seconds before turning back off.

I'm not sure what was going on during the 3 second cycles, it could be that a thermostat was close to being met... half of them are old honeywell mercury thermostats that don't have a swing adjustment.

The 3 minute 20 second cycles seem consistent even when all zones on the Taco continue to call for heat.

Other issues:
- when the FHA is running, the plenum and ducts seem to leak a bit, the basement gets hot, and by the there's basically no airflow in the ducts furthest from the air handler. The plenum and ducts have lots and lots of bends and turns.
- the barometric damper is damaged and frequently gets stuck closed
- the inlaw apartment takes hours to get hot. How high can we set the temp on the radiant water?

So the question: What to do now, and what to do next year?
Budget is only about $150-$200 this winter, and a bigger spend next summer.

Options I've been considering:
- Replace the aquastat with one that has a wider differential
- Install an outdoor reset control (PC700 or tekmar) that has a configurable 20 degree differential
- Try to learn about under firing the boiler somehow
- Replace the thermostats with electronic ones to avoid what (i'm guessing) is
causing the 2 second bursts
- Replace the damper, and try to learn how to set the weights on it
- Spend a day attacking the FHA plenum and ducts with a couple of rolls of aluminized tape to try to cut down on all of the leaks

Bigger spend:
- Get an HVAC tech to come and hope they know what they're doing... to properly set the damper/draft and possibly underfire the boiler
- Replace the plenums and uninsulated ducts to improve airflow to the extremities
- Install FHW in the rest of the extremities and dedicate the FHA system to the main house where it seems to work better
- Set aside the money to plan for when the V7 finally cracks
- Add a primary circulator because that seems to be what people do for newer installs so it must be better

The background:

The house is a 3500 sq ft modern/open floorplan house with a zillion windows and not the best insulation.

Primary heat is from a Burnham V7 with an L8148A Aquastat
DHW is from an indirect with an additional solar circuit

The boiler is a PV75WC-TBWN serial number 64155910, it has an output rating of 166MBH, with a 1.65 GPH firing rate according to the sticker on the side. Burner is a Beckett AFG, and I assume that it has the correct nozzle and settings to run at 1.65 GPH

There's forced hot water heat in the bedrooms, forced air in the main house and office/bathrooms, in-slab radiant in the inlaw apartment, and a heat pump minisplit to cover a poorly heated end of the main house.

There are 4 zone pumps and there is no primary circulator:
1 - forced hot water with two zone valves to split between the bedrooms
2 - air handler for the forced hot air, with two zone baffles to split between the main house and office/bathrooms
3 - radiant
4 - dhw

I added a Taco SR504-EXP-1 to replace the various relays that were strewn about (one wasn't ever connected to the boiler to call for heat, one was completely fried...)

The circulator output from the L8148A is also dead, but there is no primary circulator (it had been hacked to control one of the zone pumps... no longer)
 
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Old 12-16-16, 09:58 AM
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Welcome to the forums.

This is just a welcome... so far.... as I'm a little lost in reading your post. You seem to have a vast array of mixed equipment. This pushes the issue slightly out of the DIY help we can provide and into a professional "on site" help area.

I'll be back and others will add their thoughts.
 
  #3  
Old 12-16-16, 11:11 AM
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I guess the short question i'm trying to get diy help with is what is the best option to fix the short cycling we're experiencing?

should I put in an outdoor reset with a 20 degree differential?
or should I replace the aquastat with one that'll do a 20 degree differential?

trying to get the simplest efficiency boost out of what's currently here before spending more on a pro next spring/summer.

If you like, feel free to delete this post and i'll write it up simpler, i can't edit the original post anymore.
 
  #4  
Old 12-16-16, 11:40 AM
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I didn't see that you told us the model of your existing aquastat. Many aquastats have an adjustable differential - for example, my Honeywell L4006A, which I have set at 15 deg.
 
  #5  
Old 12-16-16, 11:55 AM
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its an L8148A. I think it has a fixed 8 degree differential
 
  #6  
Old 12-16-16, 03:33 PM
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You could replace the aquastat with one that has an adjustable differential. Gives you something to play with.

Those old mercury thermostats often had a heat-anticipator setting, a sliding potentiometer. If it isn't set to the correct current draw, it will result in cycles that are too short or too long. There are usually arrows labeled "shorter" and "longer."

I don't think adding an outdoor reset is the right way to solve short-cycling.

You have several different heating sources serving a total of 3500 sq-ft? One of the first things I would do is run a heat-loss calculation - that will give you the heat loss, room by room. (There are freebie heat-loss programs listed in a "sticky" on this site.) Then, estimate the rating of the heating emitters serving that area. Those two chores may take you several days to complete.

Underfiring the boiler won't increase the heat output - it will decrease it. You asked about the highest temp you can run your boiler at. Try 180 deg.

As Pete intimated, probably best to post, attack, and solve one problem at a time - and then move on to the next.
 
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Old 12-16-16, 04:50 PM
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V,
Lets start with the zone valves. What is the brand. If they are Taco the heat anticipator on your t-stats controlling those ZV's must be set to .9 or they may run erradic. 3 sec runs). The pointer on those HW mercury stats goes from .1-1.0. Make sure you have the right setting.

Next, you have a fairly large boiler for the whole house but you must look at the size of the zones. For example the bedroom zone. How much total radiation is on that zone. That large boiler running for just that zone will take no time at all to reach limit in the boiler. Even though the stat may still be calling and the pump running the boiler is satisfied until it cools down and comes back on.

The same with the other zones. The Indirect takes little time to heat and so does the air handler. Although the boiler might have been sized for the total heat loss breaking it down to zones you can get away with much less.

I don't think I'd put money into another aquastat because it wouldn't change the time it takes the boiler to heat up, just longer between cycles and lower water temp between cycles which means less heat going out.

To centralize your problem you might try to have all stats calling for heat and see how the boiler operates. You should get longer cycles because the hot water being made in the boiler would be heating all the radiation and not just a small portion.

As far as the draft regulator goes it adjust to draft conditions and be set with a draft gauge brt it isn't part of your short cycling problem.

It would be wise to seal up the ductwork with your tape and check to see if dampers were installed in the runs to balance the system. You may be able to damper some down to redistribute the air to the ones that need it.

I realize this is a lot to digest but I hope this helps a little.
 
  #8  
Old 12-17-16, 06:57 AM
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Zone valves are Taco.
I'll check the anticipator settings, but all the stats are different, I may just swap all the stats to the same electronic type with an adjustable swing.

I think you're right, there just isn't enough total radiation in either the zones or the house as a whole, so some is hot, some is cold, and the boiler is barely trying.
I'll get an HVAC contractor to come out next spring to quote installing baseboards through more of the house.

Longer cycles with less heat going out should get me the efficiency I'm after. Under-firing probably would too.

The thoughts on getting more heat from the radiant are unrelated and i should've left them out... that system is working as expected (and the tenant should stop turning the heat down so much)
 
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Old 12-17-16, 08:56 AM
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V,
One thought on the stats. To the best of my knowledge they do not have adjustable anticipator settings any more. I mention this because there have been some problems with getting the Taco ZV's to operate properly. Honeywell makes a round stat that comes with a resister separately packaged and must be installed on terminals #1 & #2 on the ZV. If you opt for the Honeywell round don't throw the resister away, read the instructions and save yourself a headache.

Taco ZV's has the highest amp to operate properly and not all stats work with them. This is not only the new ones but this was also older models as well but was never really publicized.

I am not sure what other stats have but some come with dip switches that can be set for the different types of systems. Just something to be aware of.

Hope this helps.
 
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Old 12-17-16, 09:45 AM
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Thanks for checking in guys. Boilers are not my specialty so your help is appreciated.
 
  #11  
Old 12-17-16, 11:02 AM
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Modern is Better and Often Cheaper Than Old

Vilord:
Options I've been considering:
- Replace the aquastat with one that has a wider differential
- Install an outdoor reset control (PC700 or tekmar) that has a configurable 20 degree differential
Those reflect the old approach to heating issues. Micro computers are now in many things, thermostats, burner primary controls, ECM circulators pumps and ODR'S. Each of these modern items does things in a more effective way than older types from 20+ years ago. They are not longer simple on-off devices.

When my burner control locks out, rather than waking up hours later to a cold house, mine sets off an alarm and display on it says why. My favorite message is "No flame"

Pumps instead of fix speed, now have computers that adjust ECM motor to pressure and deltaT setting. Replaced a dead old B&G 100 series $300 pump with a Gurndfos Alpa for $180. It uses up to 85% less electricity and automatically adjusts to setting.

The $160 Tekmar 256 Out Door Reset is a lot more than a very accurate boiler water temperature control. DeltaT is adjustable from 1 degree to whatever. It also has setting for water minimum and max temps. Is an intelligent temperature control with many variables in setup menus to optimize operation for a given building system. Even has options for different types of radiators or convectors.

To understand the broad range of features modern ODR's have to improve heating systems I would suggest reading the installation manual for one: http://tekmarcontrols.com/images/_li...f?lbisphpreq=1
Note: The Taco PC700 is a Tekmar 256 rebranded in different color package for a lot more $$$. Comparing manuals shows that.
 

Last edited by doughess; 12-17-16 at 01:41 PM.
  #12  
Old 12-17-16, 03:14 PM
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At this point I'm looking to install a Tekmar 260. 256 wouldn't work as-built with DHW override, and I have had the worst time finding the right wiring guides to plug the 256 into the Power Control port on the Taco SR.
In my place, the boiler controls are all built in, it is a newer Buderus logamatic, the previous owner's contractor didn't install the ODR or the DHW sensor for whatever reason, and my system is running great now, I'm trying to get my girlfriend's 1990's boiler running better too.
 
  #13  
Old 12-17-16, 07:55 PM
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The Tekmar ODR has 2 wires/terminals for 24 VAC and 2 contact wires that "close" when calling for heat.

The Taco PC700 has a 4 wire plug for those connections to lock customers into paying $$$ more for their products. With Taco you spend over $400 to implement ODR versus $160 for Tekmar.

On the Taco SR use a volt meter to find the two 24 VAC leads. Find the 2 that you think are "call for heat" and verify by temporarily connecting them to see if burner starts.

Your system may also have another source for 24 VAC. Tekmar units take very little 24 AC power so if you use another source it is not likely to over load anything.

Here is wiring diagram for a Buderus-Logamatic:
https://www.manualslib.com/manual/10...page=67#manual

Most of these controls are really basic stuff. Just be careful not to mix 120 VAC and 24 VAC circuits.
 

Last edited by doughess; 12-17-16 at 08:13 PM.
  #14  
Old 12-18-16, 06:33 AM
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Longer cycles with less heat going out should get me the efficiency I'm after.
Stack temperature rises with length of cycle until a “stead state” condition. Temp does not go down with longer cycles. The higher the temp, bigger heat loss. Look at any stack temp/efficiency chart to see this. The data supports shorter cycles, not long ones.

Under-firing probably would too
Basic heat exchanger data shows lower thru put is higher efficiency. The more BTU's generated in a given boiler the lower efficiency.

Short cycling is something valid in air conditioning refrigeration systems but carried to ridiculous excess in heating. Unfortunately many “heating professionals” never learned the basic physics.

The data applies to, and supports both short cycles and lower firing. Stack temperature of a boiler at 2 minutes is lower than at 4 minutes of run time. Manufacturer's data show efficiency going down with run time.

In the old days, before retention head oil burners, high stack temps of 600F plus were used to avoid fires. Residential oil burner fires back then were a frequent occurrence, but not today.
 
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Old 12-19-16, 01:48 PM
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Hmm. Very good points.

Given that the boiler is operating for just 3:20 when all three zones are calling, and even less time when just 1 or 2 call, i might attempt to check with a couple of local "heating professionals" to see what they think about firing at 80% burn rate, and pick one who's willing to tune it to that who sounds competent. Need to get someone in for the annual tune-up anyways. We replaced the draft control but don't have a draft meter, so the draft is probably all wrong.

My guess is that Taco's 4-wire plug is either:
Common, 24V supply, 24V demand output, and 24V boil input
or
Common, 24V supply, and 'call for heat' as you suggest.

Easy enough to test both, though if I use the tekmar 260 (which I want for the better DHW controls) then the wiring is just as easy to bypass that connector entirely, so I'll probably ignore the plug.
 
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Old 12-20-16, 07:50 AM
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A boiler run time is not some magic number. It is a result of various factors and normally will vary from one time of day to another. I set mine up to run 2 to 4 minutes by adjusting the deltaT. Longer run times are just less efficient. The bottom line is my home is very comfortable and heatings/AC costs are low.

A simple way to get data on reducing nozzle size is to wire an elapsed time clock to primary burner control oil solenoid. Time it for a few days, collect degree date and oil consumption data. I have explained in detail on other DIY posts how to do this.

Unfortunately many “professionals” do not have a good understanding of these things. I found that early in my days as a home owner. My wife's relatives owned a large oil retailer that serviced our system. When issues arose they could not solve I got into it.

Have a long background in electronics, controls and experience with specialized industrial/commercial HVAC and heat exchangers. On professional HVAC forums I see a lots of crazy thinking and incorrect data.

What is the model number of your primary oil burner control? Some features of the Honeywell L8148A Aquastat might still be used as source of 24 VAC and starting/stopping the burner by the Tekmar.
 
  #17  
Old 12-20-16, 08:42 AM
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On this system, we're running an L8148A set to 196 degrees, with a Taco SR504-1-EXP zone control running the zone pumps.
Tekmar 260 has been ordered, waiting for delivery.

I'm intending to run 24V through the Taco's burner XX control as demand input to the Tekmar, and tie the burner end switch from the Tekmar to TT on the Aquastat, and leave the aquastat set to 196 as a safety shutoff. The aquastat was already partly damaged by the previous installer's poor decisions, so I'm not going to push things by pulling 24v (or anything else) from it.

We have no primary circulator, so I'll just leave that empty.

Zone valves and baffles are running from a separately wired 24V transformer.
 
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Old 12-20-16, 11:39 AM
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What is the model number of your primary burner control? There can be issues with some types using TT to control them.
 
  #19  
Old 12-20-16, 12:18 PM
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Oh, sorry I misinterpreted your question. It is a Beckett AFG burner with a Honeywell R8184 G 1286 primary control.
TT on the R8184 is jumpered, and it is controlled directly by 120V from the aquastat.

That comes off the safety shutoff in the aquastat (L8148A), which is fed by the aquastat's relay, which is powered by the aquastat's transformer and controlled by TT (from the Taco SR currently)

As an alternative to reduce the number of old parts that are likely to fail, I'm considering bypassing almost everything in the aquastat, and sending 120V directly from the Tekmar's boiler end switch to the input on the safety shutoff.
 
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Old 12-21-16, 07:05 AM
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You might want to consider replacing the old L8184 G with a modern primary controller with digital display. It is only $6 more than the a new G and shows live status and history. Also makes trouble shooting and diagnostics easier.

A universal controller with LCD display that will work on most US made burners is the Honeywell R7284U (get the U or P, not B model). For $75 is a best buy for a full featured unit. Other brand controllers charge extra for displays and various features.

https://forwardthinking.honeywell.co...u_feature.html

Tekmar 256 - Tekmar 256 Boiler Control - One Stage Boiler - Tekmar - SupplyHouse.com

To start the R7284 you need 120 VAC on the red/limit/start wire. The Tekmar can to do it directly, or activate a 24 volt relay to do it or last use the L8184A aquastat relay. To keep 120 Vac out of the Tekmar I put a small 24 vac relay in the AFG burner wiring box under the R7284.
 
  #21  
Old 12-21-16, 08:19 AM
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doug

I set mine up to run 2 to 4 minutes by adjusting the deltaT. Longer run times are just less efficient.
I know you know a lot about this stuff but can you explain why that would be OK? Im not saying it isnt, but it seems puzzling to me anyway, lol.

Below is the explanation I have seen in a multitude of places as to why short cycling is inherently inefficient. It just seems that a 2-4 minute run time would not be efficient. But I just follow the forum here so I can learn a few things.

Cycling Losses

A boiler cycle consists of a firing interval, a post-purge, an idle period, a pre-purge, and a return to firing. Boiler efficiency is the useful heat provided by the boiler divided by the energy input (useful heat plus losses) over the cycle duration. This efficiency decreases when short cycling occurs or when multiple boilers are operated at low-firing rates.

This decrease in efficiency occurs, in part, because fixed losses are magnified under lightly loaded conditions. For example, if the radiation loss from the boiler enclosure is 1% of the total heat input at full-load, at half-load the losses increase to 2%, while at one-quarter load the loss is 4%. In addition to radiation losses, pre- and post-purge losses occur. In the pre-purge, the fan operates to force air through the boiler to flush out any combustible gas mixture that may have accumulated. The post-purge performs a similar function. During purging, heat is removed from the boiler as the purged air is heated.
Minimize Boiler Short Cycling Losses
 
  #22  
Old 12-22-16, 03:51 PM
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Oil Burner Short Cycle Delusions

The Beckett "Guide to Oil Heat" manual for servicemen has a whole chapter on efficiencies. See page 26 Figure 39 chart of Efficiency vs Net Stack temperature. The chart is two dimensional, but a third dimension "time" is significant to understanding what is happening.

During a burner cycle efficiency changes from flame start to time when steady state is reached. That is very significant when looking at cycle time length. It declines until reaching steady state, then goes down even more. Ending a cycle before steady state is simply more efficient.

For non condensing boilers there are many places you can get stack temperature data / efficiency data. All of them show highest efficiency at lowest stack temp.

Lowest temp on hydronic boiler is at burner start, say 140F A typical profile for a boiler is after 1 minute stack is 250F/ ~87%, at 2 minutes 350F/~85%, 3 minutes 450F/~82% or before if it reaches steady state, at which point efficiency goes down slightly.

On any cycle, short or long, temp goes down from the start. That is hard data, not an opinion. Have not seen any data showing rising temps with improved efficiencies on long cycles.

Check your own system. On eBay buy a PID/digital thermometer with stainless probe for less that $25. Dual Digital F/C PID Temperature Controller Control TA4-SNR with K thermocouple | eBay

3M cable K Type Thermocouple 100MM Probe Sensor For PID Temperature Controller | eBay

The "Cycling Looses" quote is mixing up different things, including types of efficiency. Rather than tilt with wind mills I will just go with the data.
 

Last edited by doughess; 12-22-16 at 06:20 PM.
  #23  
Old 12-23-16, 06:14 AM
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I'm not convinced.
Just looking at stack temperatures, especially at the start of the burn, does not take into account the full picture.
Unless I am mistaken, I'm sure that I read that there is a higher percentage of fuel that leaves the stack unburned during the first minute of combustion as compared to the second or third.
You'll have less heat losses to the stack, but also less heat transferred in the exchanger, and a dirtier burn, meaning more soot and scale collecting on the heat exchanger, causing it to lose even more efficiency.

Beckett's Guide to Oil Heat efficiency chart numbers are based on the steady state stack temps. It doesn't have that third dimension, time, and IMO you can't just measure the stack temp over time and blindly add it that dimension. A lot more measurement and calculation needs to be done first, and I haven't seen that data.
 

Last edited by vilord; 12-23-16 at 06:34 AM.
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Old 12-23-16, 11:51 AM
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Vilord, you are correct. Until steady state combustion is achieved the stack temperature is MEANINGLESS for calculating combustion efficiency. Doug is a smart man but he is absolutely WRONG on this point.
 
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Old 12-24-16, 09:34 AM
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My whole point is that during a boiler cycle, conditions and efficiency change. Being aware of those changes helps to optimize a system.

Some people seem to have a fixation on steady state, just as others focus on the winners of a races. Yes, it is a significant point, but only one very brief point. My oil bill is based on gallons used, not how many cycles it ran successfully or how long they were.

Unfortunately for the DIY site there is no real peer review. I try to use hard data but find some members are regurgitating it. I never calculated combustion efficiency, only used data from a Beckett
chart for it.
 

Last edited by doughess; 12-24-16 at 11:31 AM.
  #26  
Old 12-25-16, 06:16 PM
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John Siegenthaler is recognized as an engineering guru of hydronic heating. His Modern Hydronic Heating explains the problems with short cycling - efficiency and otherwise.

Running a combustion analysis is very educational. Starting the test with a cold boiler, circulating water, and flue, the flue gas temperature is initially low, which indicates high boiler efficiency - but that is misleading. The reason all those temps are low is that the heat from the previous cycle was lost.

Sure, the best efficiency would be to heat your house at, say, 120 degree. That would require extra costs for heat emitters.
 
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Old 12-26-16, 07:27 AM
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[URL="I read that there is a higher percentage of fuel that leaves the stack unburned during the first minute of combustion as compared to the second or third."[/URL] Vilord

That was true fifty years ago before retension head burners, atomizing nozzles, solenoid valves and modern controls. Back then when power was applied to burner, ignition spark began and motor/blower/pump started turning. Oil began dribbling out of nozzle, after a brief period a sooty flame started then got better for rest of burn period. When power was removed at end of cycle,motor slowed to stop. Oil spray became a dribble, then nothing. Again a very sooty flame period.

Today's modern burners flame starts after 15 or 20 seconds with an instant fire ball, zero smoke/no soot. Shutdown is instant.

Old boilers, vent pipes and chimneys often filled with soot leading to frequent fires. Building codes required emergency off switches at basement entrances to make it easier for firemen and home owners.

Back then, to reduce the soot problem, systems were set up with less efficient, high 600F stack temps. At $0.15 a gallon oil was cheap. Some of that thinking has carried over to today. i.e. higher temps from long cycles are good, short cycles are bad.

On the issue of stack temp/efficiency chart and time. Vilord's concept is that the data is valid only at “steady state”. OK, but what is happening at other times in the cycle?? Stated or not, “time” is always there.

Steady state temp is not the holy grail of heating. Changing a boiler firing rate can move move it on any boiler. To do things intelligently it helps to understand how the whole system/process works.

Rather than just accepting what was “read” I collect the data on my system and measure the results of changes. Do not need combustion analyzer data to know that lower stack temps are better. Those driven to avoid short cycling just pay more to heat.
 

Last edited by doughess; 12-26-16 at 07:43 AM.
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Old 12-26-16, 11:03 AM
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That was true fifty years ago before retension head burners, atomizing nozzles, solenoid valves and modern controls. Back then when power was applied to burner, ignition spark began and motor/blower/pump started turning. Oil began dribbling out of nozzle, after a brief period a sooty flame started then got better for rest of burn period. When power was removed at end of cycle,motor slowed to stop. Oil spray became a dribble, then nothing. Again a very sooty flame period.
Thank you for posting that, it shows that on this point you are lacking valuable information.

Fifty years ago was 1966. Shell Oil developed the flame retention burner in the 1940s. Flame retention retrofit kits were readily available, even in the DIY market, in the late '60s and early '70s. The cost was about $20 as I recall. I don't have a date for when the last non-retention head burner was manufactured but I strongly suspect it was prior to 1960 by several years.

Even prior to the flame retention head the fuel pumps had spring-loaded pressure cut-off valves that prevented any oil spray below about 80 to 90 percent of the adjusted pressure, most often 100 psi back then. The oil did NOT "dribble" out of the nozzle at start up and shut down UNLESS the pressure cut-off valve had failed. Atomizing nozzles? You would need to go back to the '40s and the old General Electric low-pressure air/oil burners or maybe even a rotary burner to escape the pressure atomizing nozzle.

There has been little improvement in the function of the oil burner primary control since the advent of the visual flame scanner. Even with the thermal stack control the "controls" had nothing to do with combustion, being merely a safety device to stop the pump motor and thereby stop the introduction of fuel when there was a failure to ignite the fuel. Granted, the reaction time of a visual flame scanner is faster than the stack switch but (as is evident in some of the posts) there are still some stack switches in service.

Adding the time delayed oil solenoid valve HAS improved safety but the improvement in combustion is minor.

I used to buy old burners for five bucks a pop from places like St. Vinnie's and Goodwill and I NEVER had one that started off smoky and/or died off smoky UNLESS the previously mentioned pressure valve was faulty. Granted that a burner without a flame retention head will not fire all that well into open air but a flame retention head model also benefits greatly from a lightweight combustion chamber. Without the combustion chamber it WILL take significantly longer to achieve a steady state of combustion and ignoring modulating burners, steady state combustion IS the holy grail when it comes to combustion analysis.
 
  #29  
Old 12-27-16, 11:38 AM
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Dumb versus Smart Controls

Furd: Adding the time delayed oil solenoid valve HAS improved safety but the improvement in combustion is minor.

Beckett literature describes improvements from solenoids in combustion as follows:

Beckett CleanCut pump - BENEFITS OF A SOLENOID VALVE: The quick acting solenoid virtually eliminates smoke at shutdown by allowing the burner air flow to complete combustion of any residual oil vapors in the combustion area before the motor coasts to a stop. ... tests performed at Beckett show that this rapid shutoff contributes to less smoke at shutdown and reduced coil soot ups.
The rapid cutoff is especially helpful if there are rumbles or pulsations at shutdown with certain applications. This is superior to the slower hydraulic pump cutoff, which is dependent upon the motor coast-down speed. Reduces wear and tear on switches, relays and the motor. (End of quote)

Frud: "There has been little improvement in the function of the oil burner primary control since the advent of the visual flame scanner"

Both Beckett and Honeywell descriptions list improvements in modern primary controls:

Beckett -The Development Of Modern Primary Controls: Advances in electronics technology are making an exciting impact in our oil heat industry. These developments have enabled control manufacturers to put high performance features into residential primary controls. Residential controls are now being made available to you that have features that were previously found only with the expensive primary control units for commercial or industrial applications. Features like valve-on delay (pre-purge), burner motor-off delay (post-purge), and interrupted duty ignition are becoming universal. Preignition, limited reset and recycle, and alarms contacts are also helping to make today’s controls advanced and powerful tools.

Honeywell: The R7284 Primary Control Helps you keep track of system quality by accessing memory data that gives a clear picture of day-to-day performance. The error history capability defines when and how the controller encountered problems, and helps maintain knowledge when there is more than one technician involved in servicing the unit. There is also a baseline feature that uses a cycle-trend reading to determine if something is out of the norm, allowing troubleshooting during service check-ups before a no heat call occurs. (end of quote) (It also displays live status and CAD cell resistance, lockouts and faults.)

Old generation dumb primary controls (with CAD cell) i.e. Honeywell R8184G (frequently seen in pictures on this site) lack many of the newer smart control features and often cost the same.

Some may want to stick with old dumb controls. Others may not be aware of the advantages and lower costs of improved products when replacing a failed part and miss the opportunity to improve their system.
 

Last edited by doughess; 12-27-16 at 12:16 PM.
  #30  
Old 12-27-16, 06:59 PM
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More from Beckett on modern primary controls

The Development Of Modern Primary Controls - IMPORTANT TECHNICAL ADVANCES

As the electronics industry constantly develops, many of its products and techniques have been applied to burner controls. Some of the developments that are key to us are the following:

Relays have become smaller and more reliable. It is now common to see several relays inside each control, so that the motor, ignitor, and valve may all be controlled by separate relays. Solid state relays are increasingly being used instead of the traditional electromechanical relays.

Microcontrollers (small computer chips designed specifically to control other electronics) have increased the ability to control the burner’s components separately and with more intelligence. A microcontroller’s software code can easily add control functions and make complex decisions, eliminating the need for large decision-making circuits. Circuits are now needed mostly to provide processor and 24 Volt power, convert sensor signals, and drive relays.

Timers have developed from being controlled by bimetal switches to being controlled by semiconductors. Now, many different timers can all be running at the same time. Timings are less affected by temperature, vibration, light, line voltage, etc. They can be accurate to within fractions of a second, instead of varying by 10% to over 50% for some traditional controls.

Flame sensing has progressed from stack mounted bimetal switches to cadmium sulfide sensors (cad cells) and ultraviolet sensors. These sensors can more quickly and accurately sense the flame, and they also have the ability to sense the varying brightness of a flame. Software programming can monitor the rise and fall of a cad cell resistance to better interpret its signal. For instance, the cad cell signal can be smoothed out to help prevent nuisance lockouts. The Honeywell R7184 can display the cad cell resistance (see the Quick Reference Guide on page 4), so you do not need to use an Ohmmeter.
NOTE: For proper operation, it is important that the cad cell resistance is below 1600 Ohms.

LED & LCD displays offer you an increasing amount of diagnostic information such as recycling, flame status, or different lockout modes. Indicators like these are making it easier than ever to know what was happening before you arrived at the installation.

Self checking and system checking to ensure a safe, proper starting and operation of the burner are now standard procedures in microcontroller-based controls.

Advanced features, both new and borrowed from more expensive controls, are being added to residential controls. In the near future, look for increased use of the reset button, special pump priming procedures, redundant safety features, brownout protection, advanced recycle methods, and other features that will make controls better and your job easier.

https://www.beckettcorp.com/support/...mary-controls/

doughess footnote: while this is from Beckett it also applies to other brands. The key point is all of the various technical improvements buried in these units. The Honeywell R7284U (a best buy) even has different setup options for boiler, water heater and furnace service.
 
  #31  
Old 01-03-17, 07:26 PM
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Almost done with the upgrades

The old:
4 separate Honeywell 845 relays feeding the L8148A Aquastat
(Aquastat's internal relay shot, one 845 shot, one 845 not connected to boiler)
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The new:
Taco SR504 (ebay $100) -> Tekmar 260 (ebay $85 shipped w/o sensors + supplyhouse.com $65 shipped for sensors) -> Aquastat's safety shutoff (rest of aquastat bypassed)
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Boiler is now running 145-175 or so with the tekmar's ODR controlled differential, and 175-185 for DHW, instead of 180-195 for everything.

The Tekmar sensor is mounted just after the first bend of the 2" pipe that comes off the boiler... its pretty slow to respond, though, so I might investigate using the boiler's second sensor well for the tekmar instead of having an analog temp/pressure sensor in it, and then put the analog sensor somewhere else.

Hopefully we'll do a bit better on oil consumption... dropped all thermostats down to 64 or so, as the oil tank is almost drained. Will schedule a delivery for tomorrow.

Burner service tech coming out Thursday for annual service and to hopefully put in a smaller nozzle.

Will hopefully have time before the tech arrives to mount the tekmar on the wall and add strain reliefs to the wiring.
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-Jesse
 

Last edited by vilord; 01-03-17 at 09:22 PM.
  #32  
Old 01-04-17, 08:22 AM
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There should be some well on the boiler where the original sensor was. If not peel up a small section of the sheet metal top and put the Tekmar senor between the top of boiler casting and under insulation.

Another place for sensors is where pipe exits boiler covered with insulation.

These sensors are very sensitive and when clamped to pipes reading can be offset by room air. Insulating them reduces that issue.

Boiler temp should be 180F to avoid scaling. Because of temp overshoot, when set at 180F, it can go to +190F. I set mine at 170F and with overshoot it almost gets to 180F.

Do not use the Tekmar setting for “AD” Automatic Differential. It is designed to create longer cycles and can cause dangerous over temperatures. Use a fixed deltaT, typically less than 5F.
 
  #33  
Old 01-04-17, 07:13 PM
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This boiler is severely oversized, as you may remember from the title. a 5 degree differential would mean a cycle time of about 30 seconds, which would cause the boiler to soot up and clog in about two weeks, and would not be long enough to get the stack hot enough to avoid condensation. My goal is a smaller nozzle and a burn time of about 5 mins which should be enough to let me run at 150 degrees in the spring and fall without rusting out the heat exchanger and stack.
 
  #34  
Old 01-04-17, 07:18 PM
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As for the sensor, there are two sensor well locations on the boiler. One has the old aquastat/safety shutoff (now set at 195 instead of the original 188), and the other has an analog pressure/temperature sensor.
I would have attached the new sensor right next to the output from the boiler, but the tekmar manual said that was a bad place to put it because the water won't actually be mixed, especially in the large 2" black iron pipe. It should be after the first elbow, they say.
Overshooting isn't something i'm that worried about, i'll watch a few cycles and turn down the high temp until it overshoots to what i actually want as a target
 
  #35  
Old 01-04-17, 07:44 PM
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Technology is not always what it's hyped to be.
There is a big advantage to multiple 845 relays vs the SR in that if the transformer in the SR craps out, your whole system is dead. Kind of like putting all of your eggs in one basket.
 
  #36  
Old 01-05-17, 08:46 AM
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That's true, however two of the 845's weren't working properly... I probably could have pieced together one functional from those two, and bought another 845, but how long until another one crapped out?

The whole system is 20 years old...

I decided to buy the SR and tekmar instead of one or two 845's and a new L8148A.

In other news, the oil tech was out today. We downfired from a 1.3 nozzle to a 1.2, and he said the heat exchanger is already leaking, so f' it, we need a new boiler anyways.

I guess this time we get a chance to put in the right size... sigh...
 
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