Kuuma Vapor Fire 100: Supply and Stack Temps vs Time over 20 hours

[JRHAWK9]

I decided to buy a -GATEWAY- for my Thermoworks Smoke which I use to monitor my supply and stack temps. This sends temps to the cloud every minute or so and allows one to export the data to a CSV file to play with in a spreadsheet. Supply temps are taken in the plenum, but the HVAC probe I have in my main duct ~12' downstream has pretty much always read the same. Stack temps are taken on the top side of the 45° angle stove pipe within 12" of the collar. The computer on the Kuuma was set to minimum burn the whole time. Draft is about -0.045".

I decided to give it a try now that we are getting some below average temps for this time of year which more resembles a normal winter than fall. It was 10° last night with a high of 23° today.

As you can see by the "Supply Temp" graph below, I loaded for the night last night at around 9pm (53.5lbs). The supply temps shoot up when I load because I manually shut off the blower and then turn it back on when I'm done loading. I loaded on about a coffee can volume of coals. Then you can see I loaded again in the morning around 7am or so (48.8lbs). I did not re-load when I got home from work at 4:45 or so because the house was 75° and wanted to give it some time to drop a couple degrees. My blower shuts off when supply temps get down to ~96°, which is based on previous graphs of when my supply temps jump up abruptly at the end.

Here are the stack temps. You can easily see the computer constantly doing it's thing throughout the night maintaining the rate of burn.

Thought some of you may find this interesting.

 

[JRHAWK9]

Here's the small 19lb load I did between the morning and night load I just loaded. House temp back up to 75°.

The dip down to 220° is from when I pulled the probe out of the pipe and wiped it clean.

 

[brenndatomu]

Thought some of you may find this interesting.

Well, I do...

 

[JRHAWK9]

I may play with different drafts to see what, if any, differences in trends I see.

 

[RockyMtnGriz]

Interesting. Looking forward to the effect of draft settings.
You're running a variable speed fan aren't you? Wouldn't that work to hold the supply temps pretty much constant?

 

[jebatty]

Good data vs anecdotal impressions is always good. My experience is with hot water gasifier boilers, not forced air furnaces. That said, the Kuuma maintaining near constant hot air supply temp at 115-120 and stack temp 275-350 shows excellent performance and efficiency. Also shows that a kick-*ss furnace, wood, NG or oil fuel, that blasts out hot air, cycling on and off, is not needed for comfortable heating and likely also is quite inefficient.

 

[JRHAWK9]

Interesting. Looking forward to the effect of draft settings.
You're running a variable speed fan aren't you? Wouldn't that work to hold the supply temps pretty much constant?

yep, I am. It does what it can do in order to do so. It's still wood burning, so it will never release a consistent level of BTU's. This data has all been while on minimum burn, so the computer is keeping the burn rate at a minimum. Once it gets about 3/4 or so through the burn, when the damper starts to remain open over longer periods of time, the supply temps start to rise. I'm guessing this is from more volume of hotter air passing through the heat exchanger, therefore it has the means to extract more heat from the flue gasses compared to when the computer spends a lot of time on pilot. Here's an example and a copy/paste from a previous PM. I suspect, remembering from past years, once I start to turn the computer up to maintain a hotter burn rate my supply temp graph will be flatter, as it will be maintaining a hotter fire during the heart of the burn and I will be loading more aggressively like I accidentally had to do the other day (see quote below).

Here's the copy/pasted example from the other day:

I kinda got off track last night/this morning with my loadings in the colder single digit weather we had the past couple nights. I loaded more than I would normally last night (58lbs) while leaving the computer on minimum seeing it's been doing a great job keeping the house 71° - 73° in single digits lows at night and mid teen highs during the day. This led to waking up 8.5 hours later to more fuel left in the firebox than I wanted and at pretty much at the max of supply temps. oops! So I ended up raking the coals forward and then turning the computer to high to burn them down faster while I got ready for work. This then just raised the supply temps a bit more. About an hour later I re-Ioaded so I could go to work and put the computer back down to low. I loaded on about twice as many coals as I would have preferred to. The supply temp curve starting last night till this morning in between loadings is the complete opposite of what you would expect. It's a bell shaped, but inverted. LOL Seeing as how I loaded at higher supply temps last night than I wanted to (for the same reason, as I loaded too much wood after work) and put the computer back on low after loading, the supply temps gradually fell back in line to what they should be with the computer on low....115-117 to only start rising towards daybreak this morning at the end of the burn as normal. After loading this morning they are now doing the same thing....falling back down to normal.

I suspect, and based upon past years, once we get colder weather and I turn the computer up I will see a more "flatter" supply temp curve, as the supply temps will be higher earlier on in the burn and stay there until later in the burn during the coaling stage until I decide to re-load.

 

[Beaster]

Very interesting information, nice job!

Sent from my SM-A705W using Tapatalk

 

[RockyMtnGriz]

I've been scrutinizing the data looking for a signal that I could use to create the feature that the Kuuma lacks, and so far, I most would want - the "extended burn" feature. I haven't asked (yet), and there's probably a good reason, BUT, so far I haven't figured out why they didn't put a switch on the computer that would close the draft when the computer comes up with a "3" signal after say, two hours have elapsed from setting the switch.
They suggest to do it - manually, but it would be so nice to just load the amount of wood needed, and set the switch to maximize the hang time of the coals - automatically. It would be particularly good for those of us who only have soft wood to burn that doesn't coal so much.
I'm still looking and pondering... if I could use something to cut power to the computer or draft on that signal, I'd have something.
The other thing that would be good, would be computer that can adjust the btu output based on the signal (cross counts, perhaps - like an engine O2 sensor??) from the room thermostat. So far, I don't see what use the room thermostat is. But I think that's going to be more complicated - requiring either an aftermarket computer, or a next gen Kuuma computer - and I doubt either will happen anytime soon.

 

[JRHAWK9]

I have played around with shutting the computer off.

I shut the computer off about 8 hours and 10 minutes into a 42.5lb load from last night. I could have done it earlier, but I did it shortly after I got up. I also increased my draft a couple days ago to the -0.05"/ -0.06" area. Seem to get higher plenum temps. Anyway, here's the result of shutting the computer off. The stack temps drop immediately, which is to be expected. However, the supply temps also seem to dip ever so slightly. If this is the case, the end result is the blower will not run any longer. It can be argued, by comparing the two different degradation of temps over time, the blower may actually shut off earlier when the computer is turned off. At least in this instance, shutting the computer off did not do much of anything in terms of extending the blower run time or turning the BTU's saved from going up the chimney into usable/measurable BTU's.

Just to clarify, the spike in supply/stack temp at around 11:45pm is from when I had the blower off and the door open while loading. The blower shut off at around the 96° mark.

I've been looking at a handful of these charts leaving the fire die out with the computer on and the supply temp is always pretty much a linear line until the blower shuts off, like this partial one showing the fire dying out with the computer left on.

 

[brenndatomu]

I've been scrutinizing the data looking for a signal that I could use to create the feature that the Kuuma lacks, and so far, I most would want - the "extended burn" feature. I haven't asked (yet), and there's probably a good reason, BUT, so far I haven't figured out why they didn't put a switch on the computer that would close the draft when the computer comes up with a "3" signal after say, two hours have elapsed from setting the switch.
They suggest to do it - manually, but it would be so nice to just load the amount of wood needed, and set the switch to maximize the hang time of the coals - automatically. It would be particularly good for those of us who only have soft wood to burn that doesn't coal so much.
I'm still looking and pondering... if I could use something to cut power to the computer or draft on that signal, I'd have something.
The other thing that would be good, would be computer that can adjust the btu output based on the signal (cross counts, perhaps - like an engine O2 sensor??) from the room thermostat. So far, I don't see what use the room thermostat is. But I think that's going to be more complicated - requiring either an aftermarket computer, or a next gen Kuuma computer - and I doubt either will happen anytime soon.

It can (and has) been done with a timer to cut power...also could easily be done with a PID programmable controller like the ones that have been (are) being used on the Tundra furnaces for "temp control"

 

[JRHAWK9]

Here's the results of the long burn I did when we were going out of town. We left Sat around 5pm and right before we left I started a fire in a warm firebox (paper, kindling) and loaded the Kuuma full with 84lbs. Closed 'er up and walked out the door. Computer set on minimum burn. Sole purpose of this was to keep the LP furnace from running, as we would be returning Sunday night.

Interpreting the graphs below, I can conclude the following.
- Total blower runtime of ~19 hours (5pm on Sat till about noon on Sunday).
- It was doing the c-1-c thing soon after loading at around 5:45pm till about 7:45pm or so
- It was on pilot continuously from about 7:45pm to 11:30pm.
- It was doing the c-1-c thing again from around 11:30pm till about 12:45am Sunday or so
- It stayed on '1' from 12:45am till about 2:30am
- It was doing the 1-2-1 thing from about 2:30am through 4:30am.
- Stayed on '2' from about 4:30am till about 7am
- Went to '3' at around 7am
- Blower turned off at about 12pm Sunday.
- It went to 'C' (cold) around 3pm.

I moved my flue temp probe to a position where I found it to read the highest, right off the collar, on top with probe extending about halfway into the pipe.

We returned home about 27 hours after we left and the house was 71°. It reached a max temp of 79° around 7am Sunday morning. Outside temps were low to mid 30's overnight Saturday and a high of 45° Sunday afternoon.

Mission accomplished.

 

[JRHAWK9]

Left town again this weekend and loaded 99.4lbs of black locust on some coals before we left at around 6:10pm on Saturday. Returned Monday around 1:30pm. We were gone for almost 44 hours in total.

Interpreting the graphs below.
- Total continuous blower runtime of almost 21.5 hours (6:10pm on Sat till about 3:30pm on Sunday).
- It was doing the c-1-c thing soon after loading till about 7:45pm or so
- It was on pilot continuously from about 7:45pm to 11:00pm.
- It was doing the c-1-c thing again from around 11:00pm till about 3:00am Sunday or so
- It stayed on '1' from 3am till about 8:15am
- It was doing the 1-2-1 thing from about 8:15am through 10:30am.
- Stayed on '2' from about 10:30am to 11:30am
- Went to '3' for good at around 11:30am
- Blower turned off at about 3:30pm Sunday.
- It went to 'C' (cold) around 6:15pm.

Outside temps were hovering around 15° throughout the burn at night. LP furnace stayed off until sometime Sunday night. LP thermostat was set to 62°.

Some pics of why we were away:

 

[trx250r87]

GO PACK!

 

[sloeffle]

Left town again this weekend and loaded 99.4lbs of black locust on some coals before we left at around 6:10pm on Saturday. Returned Monday around 1:30pm. We were gone for almost 44 hours in total.

Interpreting the graphs below.
- Total continuous blower runtime of almost 21.5 hours (6:10pm on Sat till about 3:30pm on Sunday).
- It was doing the c-1-c thing soon after loading till about 7:45pm or so
- It was on pilot continuously from about 7:45pm to 11:00pm.
- It was doing the c-1-c thing again from around 11:00pm till about 3:00am Sunday or so
- It stayed on '1' from 3am till about 8:15am
- It was doing the 1-2-1 thing from about 8:15am through 10:30am.
- Stayed on '2' from about 10:30am to 11:30am
- Went to '3' for good at around 11:30am
- Blower turned off at about 3:30pm Sunday.
- It went to 'C' (cold) around 6:15pm.

Can you explain what pilot, c, 1, 2, 3, and C mean on the Kuuma ? Us common folk don't have a computer controlling our wood furnace.

 

[JRHAWK9]

Can you explain what pilot, c, 1, 2, 3, and C mean on the Kuuma ? Us common folk don't have a computer controlling our wood furnace.

It's just the position of the primary air intake damper, which is based on internal firebox temps.

c: damper is fully closed and solely running on pilot air (when computer is set on minimum burn, it happens when internal firebox temps reach around 1,090°)
1: damper is slightly open
2: damper is open a bit more
3: damper is fully open
C: damper is fully closed due to a "cool" firebox. It's more like a warm to the touch firebox.

 

[woodey]

Can you explain what pilot, c, 1, 2, 3, and C mean on the Kuuma ? Us common folk don't have a computer controlling our wood furnace.

When internal firebox temps are reached and the computer shuts the primary air damper to C, then as JR said it is on pilot mode. While in pilot mode the only primary air going to the firebox is thru two 9/16" holes, this allows in the minimum amount of air needed to keep the gasification process going and to keep the fire from smothering and creating creosote.

 

[JRHAWK9]

When internal firebox temps are reached and the computer shuts the primary air damper to C, then as JR said it is on pilot mode. While in pilot mode the only primary air going to the firebox is thru two 9/16" holes, this allows in the minimum amount of air needed to keep the gasification process going and to keep the fire from smothering and creating creosote.

c is pilot, C is cold....just wanted to clarify there is a difference in case here.

There are actually 3 pilot holes on the front....there is one in the middle of the loading door as well. There are also two smaller holes on the primary air box which allows for a small amount of primary air at all times.

 

[JRHAWK9]

Circled in red.......

 

[brenndatomu]

There are actually 3 pilot holes on the front....there is one in the middle of the loading door as well. There are also two smaller holes on the primary air box which allows for a small amount of primary air at all times.

I would argue that there is only one pilot air hole on the front...in the door. The other two are secondary air. If we are splitting hairs...
(then the other 2 pilot air holes in the damper control box also...)

 

[woodey]

No doubt splitting hairs here , 2 primary on the damper and 2 for secondary on the front so what feeds the air to the intermediate inlets between the door and primary inlets

 

[brenndatomu]

so what feeds the air to the intermediate inlets between the door and primary inlets

Sorry, no quite following which ones you are talking about?

 

[brenndatomu]

so what feeds the air to the intermediate inlets between the door and primary inlets

All of the air holes inside the firebox, below the door, are primary air and fed from the damper control box on the back on the left side...if that's what you mean...

 

[woodey]

Yeah- the 2 larger inlets in front of the grate and 4-5 narrow ones above them.

 

[JRHAWK9]

I would argue that there is only one pilot air hole on the front...in the door. The other two are secondary air. If we are splitting hairs...
(then the other 2 pilot air holes in the damper control box also...)

I guess I see at it as when the computer is on pilot, all 5 holes are supplying air to the fire. The two small holes in the damper box are supplying pre-heated air to the two larger primary air inlets on the vertical front face in front of the grate, as well as the rest of the air holes on the front face. These same air inlets are used for primary air when the damper is open. The larger ones on front are supplying pre-heated air to the secondary burn tubes and the single hole in the door is also supplying secondary air.