Froling wood boiler installation underway!!

[EricV]

You messed this thing up big time Piker!! That ain't my basement, you missed!!

Looks great. I love my Tarm but these new units that draw air rather than push look really nice.

Eric

 

[DaveBP]

Piker, could you summarize what the controls actually control? Yes, the burn obviously. But does it take input from sensors in the storage tank? From the heating loads? Are they expecting to be directly coupled to the storage tank as a hydraulic separator would be or is it expected to divide its supply water between the loads and the storage? This could be a separate 'report' thread for the idle curious if you don't like derailing your own thread. Bioheat doesn't go into much detail about this on their website.

Inquiring minds want to know.

 

[Piker]

Piker, could you summarize what the controls actually control? Yes, the burn obviously. But does it take input from sensors in the storage tank? From the heating loads? Are they expecting to be directly coupled to the storage tank as a hydraulic separator would be or is it expected to divide its supply water between the loads and the storage? This could be a separate 'report' thread for the idle curious if you don't like derailing your own thread. Bioheat doesn't go into much detail about this on their website.

Inquiring minds want to know.

That's a good idea... summarizing a typical control scenario on a burn that is. I will take some time to write this up prior to posting it to make sure I get everything correct. The control definitely has alot of capabilities.

As far as piping the boiler... it's going to pipe up like any of the other gasifiers; provide some fashion of cold water return protection and some thermal storage and you're good to go. I am a big fan of piping storage as a hydraulic seperator, (it really doesn't get any simpler) and that method works with this boiler just as the nofossil "simplest pressurized" design does. (not much difference in how those two methods actually work from a hydronics perspective) Bioheat also offers some fantastic piping schematics for the most common systems that you will come across. I guess what I am getting at, is that you don't need special piping of any sort to install and operate this boiler properly... aside from a termovar or loading unit.

That's all for now... my apologies for the length of time it's taken to get this information posted, but I've just been swamped lately. I promise to get to it all as soon as I can.

cheers

 

[Piker]

So here's a quick synopsis of how the controls on the Froling react on a typical burn.

Lets assume the boiler has finished a load of fuel the day before, and is currently cold and in the "Off" mode. Both primary and secondary air ports will be closed. First of all, the boiler needs lit. (of course) To do this you open the outer insulating door which covers the loading door, the lighting door, and the combustion chamber door. As soon as this door opens, the draft fan turns on at 100%, and the primary air shutter moves to fully open. Wood is placed in the upper chamber, and some newspaper is placed just inside the lighting door. I generally leave the lighting door cracked for just a couple of minutes (really, just a couple... 2, maybe 3) to get a good roaring fire going. Close the lighting door, and close the outer insulating door.

Once the outer door is closed, the boiler goes into the "Heating up" phase. The draft inducer goes to 85%, and the air shutters begin metering primary and secondary air individually to tune the residual O2 content in the exhaust stream. If the boiler does not reach it's minimum stack temperature within a set time frame of closing the insulating door, it assumes there is no fire present in the boiler, and goes back into "Off" mode. Once the minimum stack temperature is reached, the boiler enters the "Heating" phase.

During the initial part of the "Heating phase," the boiler does not turn on it's thermal storage circulator. Once the temperature of the boiler reaches 65° C it will then release the storage circ and begin sending heat to your tanks or your zones. After the circulator circuit has been energized, the boiler then adjusts the burn conditions to maintain the user selected "Boiler Setpoint." The default boiler setpoint setting is 85°C. As long as the boiler temperature remains under this setpoint, the draft fan will operate at 85%. Once the boiler reaches and begins to pass the "boiler setpoint," the draft fan will begin reducing speed in an attempt to match the boilers output with the load. The Froling can modulate down to 50% of it's rated output while maintaining it's efficiency. I believe the draft fan will run at around 30% or so at it's slowest speed.

I don't have to tell you how fantastic it is to be able to match output with demand. As the storage tanks start to return warmer water to the boiler, and the delta T between the tanks and the boiler diminishes, the boiler automatically adjusts it's output to compensate. No need to increase flow rate with a dimished Delta T... just let the control on the Froling lower the output to match flow. Ingenious.

Towards the end of the burn, the residual O2 content in the exhaust stream will begin to rise regardless of air settings. Once the O2 content rises above the setpoint, the boiler shuts down the draft inducer, closes both the primary and secondary air ports, and goes back into "off" mode. At this point, the boiler still has quite a few coals inside the upper chamber and is quite certainly still warmer than the storage tanks. To deal with this, the boiler is monitoring storage tank temperatures at top and bottom, and will compare the temperature of the bottom tank sensor with the boiler temperature. Once the difference between the boiler termperature and the tank bottom temperature falls below a user defined amount, the boiler considers the tanks to be fully charged, and will turn off the circulator. This process does a couple of things... A) it ensures that the residual coal bed will have ample chance to cool once the draft fan shuts off, which will prevent the production of steam inside the vessel. B) it extracts every last btu from the boiler before shutting down. Of course, if the boiler should for some reason go over it's maximum setpoint, the circulator will come on and stay on regardless of the differential between the tank bottom and the boiler.

Overheat due to power out is obviously handled with the standard gravity loop with a normally open zone valve. Overheat with power on is simply a mechanical aquastat wired in parallel to the thermostat on your largest heating zone.

All in all, this control is pretty amazing. I'm not an engineer, so I can't speak to the requirements for developing such a unit, but the time and research invested in plotting curves for the primary and secondary air flows must have been intense of an by itself. One of the biggest benefits of this boiler is that while the controls are quite sophisticated, the actual operation of the boiler couldn't be any simpler. It's actually much simpler to operate than the typical forced draft gassers... which we all know require a little expiramentation in order to glean the best results.

I suppose that's all for now. I don't think I missed anything regarding how the controls work... if I did I'll have to catch up on it later.

cheers

 

[chuck172]

I wish there was an after-market kit which would enable some older gassifiers to modulate their output to satisfy the demand. It seems like a do-able modification.

 

[Mac-HD]

An aftermarket kit would be too costly- you would need the controller - lambda sensor, a variable speed fan that would adjust the burn- etc. And to install something that would cost $3-4000,- on an old boiler- just wouldnt make any sense. That is the point when it is more cost effective to modernize- and install a new boiler.

M.

 

[BulldogAcres]

Hi,
Love all the copper.
I have one concern about your flue. Looking at your pictures the flue looks like single wall stove pipe. When I used single wall, it had to be 30 may have been 36 inches from a combustible surface. Your flue looks very close to the ceiling and joists.

 

[Piker]

Hi,
Love all the copper.
I have one concern about your flue. Looking at your pictures the flue looks like single wall stove pipe. When I used single wall, it had to be 30 may have been 36 inches from a combustible surface. Your flue looks very close to the ceiling and joists.

Not so... the vent pipe is simpson duravent... double wall with 6" clearance to walls, 8" clearance to ceilings. We're good to go at about 12" to the joist.

cheers

 

[BulldogAcres]

Just never saw black double walled flue pipe. All we have around here is the double wall stainless steel. The black flue pipe is always single wall. Probably makes it easier for the county inspectors. Who gets to shine the copper pipe.

 

[Piker]

Just never saw black double walled flue pipe. All we have around here is the double wall stainless steel. The black flue pipe is always single wall. Probably makes it easier for the county inspectors. Who gets to shine the copper pipe.

For everyone's information on the vent pipe we used:
http://www.duravent.com/?page=6.php

It's good stuff... stainless on the inside... aluminized steel on the outside.
I've never really liked the look of the shiny stuff.



cheers

 

[webie]

I wish there was an after-market kit which would enable some older gassifiers to modulate their output to satisfy the demand. It seems like a do-able modification.

I have heard of another guy using avariable speed controller on his solo to slow the combustion blower down . Not sure if this will hurt the combustion blower or not
I had another thought on this and was wondering if a guy could use a tekmar 157 control to control the combustion blower and as the delta T closes between your supply and return water temp have the tekmar slow the combustion blower down .

 

[Piker]

Just remembered something that I forgot about the control on the froling... based on storage tank temperature, it gives you a handy little graphic display on how much wood you can place in the firebox without overheating or going into slumber (idle) state.

cool.

cheers

 

[DaveBP]

Just remembered something that I forgot about the control on the froling… based on storage tank temperature, it gives you a handy little graphic display on how much wood you can place in the firebox without overheating or going into slumber (idle) state.

Just for yucks, what units does it use for wood to add? Pounds? Kilograms? Cubic meters!! Not face cords I betcha.

 

[Piker]

Just remembered something that I forgot about the control on the froling… based on storage tank temperature, it gives you a handy little graphic display on how much wood you can place in the firebox without overheating or going into slumber (idle) state.

Just for yucks, what units does it use for wood to add? Pounds? Kilograms? Cubic meters!! Not face cords I betcha.

Basically it just recommends anywhere from a partial load of wood to a full load. While this is a neat feature to have, you have to keep in mind all the variables involved... mainly moisture content and species. Obviously the boiler is not weighing the fuel load or measuring it's moisture content... although perhaps one day that will be an option.

Three days with no fire in the boiler... I'll fire it up tomorrow morning so we can keep making DHW... and perhaps take a few measurements. I suspect the tanks will be quite cool by then... probably below 100, so any data that I get as far as btu's delivered to the tanks will be slightly skewed from normal tank cycles between 120 and 190. So far, I haven't had to burn more than 1 full load to get about 70°+ temp rise in the system. This is a significant increase over what we're used to... and again, this is being done with a smaller firebox. I still have one of the other boilers here on the floor that we're warehousing for a customer... I should stuff it full of wood, and then take that same wood and put it in the Froling just to see how much difference there really is in what you can get into the respective fireboxes. The froling has a nice square box with nothing interfering with getting a full load... the other boilers have air tubes running up the side that take up some space, so the real world difference between what you can get into each firebox might not be the same as the manufacturer's specs on volume.

At any rate, so far so good with the new install. One nice feature of this boiler is the insulating door on the front that covers the 3 inner doors. We get alot less heat off of the boiler itself than we did previously... which makes warm weather firing for DHW a little more comfortable... and keeps the basement a little cooler in the winter, which should save a bit on firewood by not wasting heat where we really don't need it.

cheers

 

[TCaldwell]

Piker, Sounds like a great boiler, do you have access to a contact that would indicate what the o2 % this boiler maintains for a setpoint, based on the lambda sensor feedback. My guess is between 7/8%. This should be readily available tech data, just curious
thanks tom

 

[Piker]

Piker, Sounds like a great boiler, do you have access to a contact that would indicate what the o2 % this boiler maintains for a setpoint, based on the lambda sensor feedback. My guess is between 7/8%. This should be readily available tech data, just curious
thanks tom

I believe the residual oxygen content is maintained at 9%.

I never did get around to firing the boiler today... I've had a few days off here and the kids have been taking advantage of some daddy time. Good stuff. Maybe tomorrow. I think I will go all out on this one and weigh the wood and test for the average moisture content as well.

cheers

 

[TCaldwell]

Piker, 9% residual o2, a little higher than i would have thought, a little high on the excess air but helps on keeping the hx tubes, flue and o2 sensor clean. Was this info in a tech manual, or, i am interested in reading what else they might have to offer. thanks
tom

 

[Piker]

Piker, 9% residual o2, a little higher than i would have thought, a little high on the excess air but helps on keeping the hx tubes, flue and o2 sensor clean. Was this info in a tech manual, or, i am interested in reading what else they might have to offer. thanks
tom

Upon further inspection of the documentation I received during training... the residual O2 content setpoint is to be 8%. Sorry for the error... that's what I get for posting before verifying my thoughts. I don't think the oxygen content setpoint is by any means proprietary information, nor any of the other setpoint parameters under the service menu's of the control... but I am certain there is engineering information regarding the control and it's internal functions that customers and dealers will not be made privy to. As dealers, our training spoke to the setup, operation, and service of the controls and boiler... not so much the engineering side of things... though I find that sort of thing incredibly fascinating.

cheers

 

[Piker]

So last night I fired the boiler expecting to take measurements of boiler temp, stack temp, tank temp, o2 content, etc at hourly intervals... but guess who fell asleep at about 11:30 and failed to wake up to the hourly alarm? I did get some very impressive numbers on delivered btu's to the tanks however.

Notes on this run:
1) I did not clean the heat exchanger prior to the test, though the tubes appeared to be quite clean except for a very thin coating of fly ash.
2) I did clean all of the ash out of the upper and lower chambers, but left a couple handfuls of dead coals in the upper chamber for easy lighting.
3) The wood load in the 7.4 cu-ft firebox weighed 173 lbs... mostly oak, hickory, and beech at around 16%-20% moisture content.
4) All of the heating zones were switched off, including dhw, for the entire burn.
5) Total system volume is around 1070 gallons... if you take into consderation the thermal mass of the steel in the tanks you can add a few more gallons... perhaps 35 gallons from the tanks... another 15 or so from the boiler... (converting lbs of steel into gallons of water with respect to specific heat)


At the beginning of the burn, the tanks were reading (top to bottom) 91/91/91/90, and the boiler was reading 73°. 40 minutes after lighting, the boiler reached 149°, at which point it energized the loading unit circuit and began to charge the tanks. By the time I drug my tired bones out of bed this morning, the fire was gone, and the tanks were reading 187/187/186/184!! That's between 95° and 96° temperature rise. I was expecting about 80°, so you can imagine my suprise. This was the first time I had ever run the system with absolutely no load whatsoever.

Now I realize that we're not really measuring boiler efficiency here... but rather the overall efficiency of my system to transfer Btu's from the firewood into the storage tanks. Remember that we have "loss" from the hundred and some feet of 1.5" copper that connects the boiler to the tanks, and also some minimal "loss" through the insulation on the tanks. "Loss" is in quotations since during the heating season, nothing is really lost as the entire system is indoors.

Now depending on what you're take is on how many btu's there are in lb of wood, the overall efficiency numbers will vary quite a bit.
at 7000 btu's/lb system efficiency = 72%
at 7500 btu's/lb system efficiency = 67.5%
at 8000 btu's/lb system efficiency = 63%

I have seen ratings for wood as low as 6400 btu's/lb at 20% moisture content. see here: http://bioenergy.ornl.gov/papers/misc/energy_conv.html In which case system efficiency would be around 79%.

My gut tells me we are somewhere around 70%... which is very good. Very very good. This is an increase of 20% in system efficiency over the previous gasser we were using. Remarkable.

That's all for today. Happy Easter.

Cheers

 

[TCaldwell]

Very impressive results, i was not aware the firebox could hold that much wood, maybe next time you burn with a full firebox i would be curious what the 02% is say 15 minutes into burn, 1 hr into burn and at 2 hr. This would cover the most volitale period and represent how well the boiler can control the burn to the 8% setpoint. Also another test would be to check the 02 before you open the door at a reload, load, close door and observe the 02% , if there are oscillations and for how long before it maintains setpoint. These results would give some insight as to how well their control system algorithim is dialed in, appreciate all the postings of the install
thanks tom

 

[Piker]

Very impressive results, i was not aware the firebox could hold that much wood, maybe next time you burn with a full firebox i would be curious what the 02% is say 15 minutes into burn, 1 hr into burn and at 2 hr. This would cover the most volitale period and represent how well the boiler can control the burn to the 8% setpoint. Also another test would be to check the 02 before you open the door at a reload, load, close door and observe the 02% , if there are oscillations and for how long before it maintains setpoint. These results would give some insight as to how well their control system algorithim is dialed in, appreciate all the postings of the install
thanks tom

You are very welcome for the posts, etc. Indeed, I've never experienced results like this before. If I hadn't had two seasons of experience and data from the other unit, and had I not taken the measurements myself on this last run, I would have been hard pressed to imagine that such results were practical to achieve with a wood boiler.

I don't have the exact numbers that you are looking for, but I do have have the first 3 hours of the burn catalogued.

At 7:52 the boiler was lit.
Boiler temp: 23 C (73 F)

At 8:32pm, (40 minutes after initially lighting the boiler, when storage circ was energized):
Boiler temp: 65 c (149 F)
Flu gas temp: 147 C (296 F)
O2: 7.8%
Primary air: 97%
Secondary air: 27%
Draft fan: 85%
tanks: 91/91/91/90


At 9:30pm
Boiler temp: 77 C (171 F)
Flu gas temp: 179 C (354 F)
O2: 9.2%
Primary air: 99%
Secondary air: 53%
Draft fan: 85%
tanks: 155/92/92/90

At 10:30pm
Boiler temp: 78 C (172 F)
Flu gas temp: 173 C (343 F)
O2: 8.1%
Primary air: 99%
Secondary air: 46%
Draft fan: 85%
tanks: 162/136/91/90

At 11:30pm
Boiler temp: 78c (172 F)
Flu gas temp: 152 C (305 F)
O2: 8.2%
Primary air: 99%
Secondary air: 18%
Draft fan: 85%
tanks: 163/161/137/95

That's all for today...

cheers

 

[Piker]

I just wanted to go back to something I said in an earlier post about skewing the results of the test with the relatively cool storage tank water. Since this last run basically fully charged the tanks, I don't think there is any skewing going on at all. The loading unit ensures that a minimum of 160° water is being returned to the boiler, so it's not like we're running 90° water past the heat exchanger, dropping stack temps and increasing thermal efficiency because of it. The only skewing of the results would have been if the tanks had never gone above 160° during the firing, as they do normally on a typical run in order to get them fully charged. The fact that the tanks went almost all the way to 190, which is where we peak the tanks at with this boiler, puts that last 30° in play as far as the drop in thermal transfer that occurs as boiler temperature increases along with the diminishing differential between the exhaust gasses before they enter the heat exchanger and the boiler water.

You have to keep in mind as well that this boiler matches the load down to 50% of it's rated output... so as the return on the boiler starts heating up, output is diminished, which keeps the stack temps low. Again, I don't have to tell you all how nice a feature this is.

I just hope I explained in a way that makes sense.

cheers

 

[Piker]

OH by the way... the Froling 40/50 can be set to run at the 40kw or 50kw setting... (136k and 170K btu). This test was run on the 50 setting.

cheers

 

[TCaldwell]

Piker, thankyou for the results, it seems under full load the inducer runs at 85% with primary air pretty much wide open, notice as the secondary damper opens to maintain setpoint the flue temp is the highest [ highest secondary burn temp] and the last reading the secondary damper is starting to close, less wood gas to burn off to maintain setpiont , and flue temp is starting to drop. I would guess the inducer % would decrease and dampers to trim for reduced output. What pleasantly suprises me is the relatively low flue temp at high output, even with a 8% 02 setpoint , [ a little excess air up the flue as stiochemeteric is 7.5% o2] . It seems as the design is to run the o2 a little lean to keep the hx tubes clean, but have added more transfer ability with the turbulators to recoup some of the heat from the excess air up the flue to maintain a high effiency %. Also there is position feedback from the dampers that is interpreted in % open for a reference. Seems very well thought out.
thanks tom

 

[jebatty]

The most reliable number I've seen on wood btu's is 6000/lb at 20% MC and 400F stack temperature. Your MC is 20% or a little below, and your stack is little lower, so I think btu's/lb would be somewhat more than 6000.