Idle time OWB experiment

[doctorb]

Ran a liitle observational experiment today with my 2300.  I was working on some delivered wood down near my stove this morning, and I noted the time that my OWB had just shut down into idle mode (temp. 195).  I had never really known how long it would take for the water temp. to drop to 185, starting the burn cycle again.

It was the perfect time to check this out.  Outside temp 45 degrees.  No one else home.  No laundry or showers.  Nobody going inside and out of the house.

It took 1 hour, 22 minutes for the stove to kick back on.  While that is longer than I expected, I would imagine that some of you would have significantly longer idle times than that.  Why?  I have a 300 foot run to my house, and I split my line, once it enters the house, to supply two separate basements with two separate heat exchangers and DHW exchangers.  Heat loss is occurring all the time in these systems, and mine should have more heat loss than most.

So, how long does your system stay in idle mode?  It would be interesting to see the comparisons between different units and under different conditions.

[beenthere]

I'd think temps of 45 deg would be tough to make any big decisions about what was happening. I put two pieces of ash (a split ash limb of about 6" diam and 18" long) in my wood boiler last night about 10 pm.
The water is still up to 180 deg and it is past noon and no additional wood added. The sun came out today and there is no call for heat.
Although, mine is indoor boiler and not OWB so not meant as a comparison but not surprised the OWB was not cooling down very quickly either.

[doctorb]

beenthere-

I agree that there are many, many variables which will affect the idle time.  For instance, what temp is your thermostat set to kick on?  Mine is at 65degrees during the day (we are empty nesters for the first time this year, so there's often no one home during the day).  I think that idle time is an interesting marker of the work a stove must do to keep up with demand, and could give some info on estimating fuel consumption in a given climate. 

[stratford 50]

My furnace cycles from 185 down to 180 and then starts. Idle time is all over the place with many variables to consider. Doctor B how do you get the 10 degree start up and shut down temp swing ? curious ?

[thecfarm]

That is a real good question and I have no idea either. With my system I have two lines about 50 feet,one goes into the house,2 heat exchanges,one side arm and a box for the hot tub and the other line has another heat exchanger.
beenthere circulators shut off too when there is no call for heat. Or my did in my other house with an indoor boiler.I suppose all of the OWB run all the time.

[r.man]

Not all circ pumps run all the time. I know of a boiler man whose house stat called the circ pump on and a sensor on the line called the indoor fan on when the line got hot. One big advantage of this is the fan shuts off if the line cools too much. Doctorb I would be more interested in knowing your cycle time if your indoor stuff was offline. This would eliminate the sun effect, use effect and leave you with ground and furnace heat loss. I do mean main circ pump on, hot water heaters up to temp and main air fans or secondary pumps off.

[AsaG]

E-2400 here with ~160' of underground pipe feeding three buildings, pumps running, water temperature range 175-185°F, no calls for heat, outdoor temperature at start was 35°F, outdoor temperature at conclusion of monitoring  28°F

1:40 PM  185°F - end of cycle
1:50 PM  187°F - normal over-shoot
5:05 PM  182°F - call for cycle still a long way off
5:28 PM  182°F - house starting to chill a bit, wife unhappy and test aborted.

5:30 PM the better-half drawing a bath, laundry running and heat turned back on - won't be too long before it fires up. 

[Local4Fitter]

Asa that's a long time. I also have a 2400 (first year) and love it so far. Looking at doctorb's experiment, it seems he left the heat on in his house. What are you getting for temp drop from boiler to house? I'm dropping 8 degrees over 90 ft. underground and another 40 ft.inside insulated with cheap armorflex type covering. I have a set of temp. gauges at my oil burner inside and I use the readout on the 2400. Not sure how accurate either is.

[doctorb]

I have no idea how the ten degree bracket for the burn cycle/idle cycle is programmed, but that is what the 2300 was suggested to do, and mine has done so from the beginning.  A 5 degree bracket seems kind of narrow to me.  I am sure that it can be programmed.  Other members on the FF have tinkered with it.

Yes, the heat was on in my house, and I can not tell you if there was call for heat during this observation.  It was just the most controlled conditions I have ever watched my stove under.   I could certainly turn off the furnaces and just run the stove without heat exchange and see how much longer the idle time is. 

I don't really think that any solid answers are going to come of this exercise, but I find it interesting to know how often my stove kicks in under relatively mild conditions.  Maybe, if we have a real cold Christmas, I could do it again.  That will have the thermostats turned up, the shower and laundry and dishwasher going, and people coming and going like a bee hive.

[AsaG]

Asa that's a long time. I also have a 2400 (first year) and love it so far. Looking at doctorb's experiment, it seems he left the heat on in his house. What are you getting for temp drop from boiler to house? I'm dropping 8 degrees over 90 ft. underground and another 40 ft.inside insulated with cheap armorflex type covering. I have a set of temp. gauges at my oil burner inside and I use the readout on the 2400. Not sure how accurate either is.

My boiler is right at 80' from where the lines enter the basement.  In full bypass, I drop <2°F round trip.  I took my measurements, at the OWB, where the supply exits the pump and the return enters the boiler using a temperature probe connected to a Fluke meter.  I used CB's ThermoPex buried 6' deep.  In the bottom of the trench, I sprayed 8" of 2# closed-cell urethane, placed the ThermoPex and then sprayed another 12" of 2# closed-cell urethane.  Needless to say I'm a little OCD about heat loss.  :D 

As an aside, on my 2400, the measured supply temperature runs 5-7° cooler than what is displayed on the control.  I hope to get the FireStar II w/XP controller sometime this week.  Then I can really let my OCD rip.  8)

[stumper]

I have no idea what my idle time would be.  I know it was long enough to allow the fire to go out in the shoulder heating times (I suspect 4 to 6 hours with light demand).  That was the reason that I had to buy and install a pulse timer.  I understand that this engineering error was addressed in later models.  I have two old style tube themometers in back of my boiler so the readings are not exact, but during lower heat demand I see no line loss.  However, I do not have a typical line installation either.  My line is buried 4.5 feet plus (below the normal frost line of 4 feet), and encased in 3/4 stone with about 3 inches of rigid insulation then more stone, all underlain with a 4 inch under drain, to keep any water away.  Additionally, my run is just shy of 75 feet. 

Based on snow melt patterns and other clues, I think most of my lose is at both of my boilers.  My indoor boiler is always warm to the touch and my outside boiler always melts the snow and ice around it through the winter (way more the the melting proximate to the septice tanks).

[Local4Fitter]

My lines start at 4' deep coming out of the house and drop to 7' deep where the future garage/shop will go. I went deep so I wouldnt interfere with the footings. I could have gone around the area but at $13 dollars per foot I'll dig deeper. I buried my thermopex in sand so stones wouldn't cut through the outer covering. It sat for a couple days before I had a chance to back fill and ground water rose up and covered the sand. 7' deep in cold water or 2' deep in frost, which is the lesser of two evils?  I will have take some temp readings at the back of the boiler and verify whether the controller is accurate.

[martyinmi]

Last winter I had a few days off(recoup from kidney stone lithotripsy)and I did similar testing. I can't remember the btu loss numbers off the top of my head for sure, but I did my tests with both the pump off and the pump on.
I believe that with the pump off my boiler would lose close to 1000 btu's/hour.
With the pump on and the house and sidearm not calling for heat I would lose a bit over 5000 btu's/hour between the boiler and the buried line. I have a little more than a 2* round trip temperature loss in my line with no heat load. That jumps up to 27-30 degrees when both appliances are calling for heat.
I buried ThermoPex 18" deep through my yard and 24" deep across my driveway as per CB's recommendations at the time. My underground run is about 90'.
I was a little disappointed with  the boiler heat loss, and a lotta disappointed with the line loss.
I can't find my notes on the computer, so I'll see if my friend at work saved them on his computer last year when I sent them to him while he had the internet.
I based my calculations largely on the study that Dean186 had outlined shortly after he put his boiler on line.
I believe that my heat loss calculations amounted over a full cord of Red Oak heat loss per average year based on 80% efficiency.
A full cord of Red Oak in this area sells for $120 - $150.

I was a bit discouraged at first, but then I tried to put a value on the benefits on not having bugs, smoke, and the wood mess in the house.

That extra $150 in wood usage is insignificant compared to the peace of mind of having everything outside.

[doctorb]

With my inefficient set-up, I am sure I am losing the heat from over 1 cord of wood per winter  (Agree, see Dean186 post).  It's not the cost, because wood is cheap heat.  It's the work.  To stay ahead for the upcoming winter and the winter after that, I would love to have the time and effort to put up one cord less per winter.

[r.man]

I have heated with an owb for about 15 yrs and will continue to do so but I try not to think about the local fellow who heated for a decade with an indoor furnace and then switched to an outdoor without adding anything or making any changes to his house. He uses twice as much wood with the owb as he did in the previous decade without any major difference in his house temp.

[beenthere]

I'd make a wild guess and figure when he switched to the OWB he also started sawing longer length firewood, splitting less, and shortened up the drying time. So he's burning higher moisture wood and using more.

I enjoy not having to go outside to tend my wood boiler.  8)

[thecfarm]

Say what you want about not having to go ouside to tend it.  ;D  I use mine to burn all my dead wood, and unwanted pine,softwood.Going to try another season doing it. I had one inside when I was young and now I have one outside when I am older and I like it. I would not want to go back to burning wood inside the house.

[stumper]

To answer the question of frost verses water, my answer would be that neither is acceptable. 

As you can tell I spent extra to drain the water away from my pipe.  Sure it cost me extra for the added trenching, the pipe and the stone but it was well worth it.

I wish I could address the poor insulation on the outdoor boiler, but other then insulating the pipes and pump in the back I do not know what I can do to improve things.  They need to be improved at construction not after.

I do not worry terribly about the heat loss in the indoor piping and boiler because my work shop is in the basement and the temp stays comfortable.  I did place 2 inches of rigid insulation around the foundation so it is kinda insulated.

Even with the ineffecencies I would rather pay for wood (either $ or sweat) then pay for oil from another country.

[Logging logginglogging]

Too Many variables for this to be of use. I bet if you conducted this same experiment with what you think are the same variables you would get a difrent result.

[sam-tip]

I just checked my firestar xp log and it took 2.5 hours to drop 10 degrees.  I run my E3200 with 25 degree diff.  Set point of 190 degrees.  In 40 to 50 degree days it only runs 4 times per day.  I also have 125 gallons of water storage outside the boiler in the garage plus the 410 gallons in the boiler.  Using blank water heater for extra storage.   When running great it will raise the water temp 1 degree per minute without heat load.  With line water extra storage and boiler storage I have about total of 560 gallons of water.  I figure it will heat at a rate of about 200,000 btu / hr. That is using a btu is equal to raising the temp 1 degree of one pound of water.

Air pulse is every 15 minutes for 60 seconds.

Doug