Winter OWB shutdown - will she freeze?

Mopar70 · January 31, 2015, 10:42:31 PM

I stand corrected
typing out loud
" spaced the obvious underground insulation"
you called me and yourself out on that one.

doctorb · February 01, 2015, 10:45:11 AM

Temp is down to 55 degrees this AM. One part of the system is frozen....the small water level valve at the back is attached to a transparent piece of plastic tubing, where you read the water level in the stove. That is frozen. It has happened one time before, when I shut down due to my back not letting me feed the stove, but no ill effects occurred. Hadn't thought of that again until Mopar's post. Thanks.

I do not think the temps have fully bottomed out. My understanding from my reading about geothermal is that the ground temp below the freeze line is about 48-50 degrees. So I think, potentially, that's as low as the temp may go.

With regards to heat loss to, and now the concept of heat gain, from the ground, my observations tell me that there is energy exchanged from the ground to the pipe and, in this case, visa versa. When it snows, the ground above the pipe gets covered like any other part of my lawn, and it stays that way for days. During snow melt, when the snowpack gets thin, the first areas to show grass are right over the pipe. So some heat gets out. Not too much, but I do have a 6 degree difference from my stove to my basement. (This figure may also be contributed to by my differing types of thermometers at each end of the run.) That energy must be going into the ground during normal stove performance. Now, I have set up a system where the heat may be absorbed by the pipe, keeping the whole system from freezing. I'll keep monitoring.

bandmiller2 · February 02, 2015, 07:55:54 AM

Insulation doesn't prevent heat/cold transfer just slows it down, very interesting experiment. Frank C.

doctorb · February 02, 2015, 09:05:58 PM

Water temp this morning at 53 degrees. I picked up the parts from my "new" CB dealer on Friday. However, the steel at the back of the stove has bubbled a bit, so the plates they provide do not sit flush against the back wall. The experiment, however, is officially over. Had a welder out to my place today who was great. Removed what needed to go and we placed the plates onto the back wall of the firebox as directed by CB. Started burning at about 4 PM and was at 185 degrees by 7 PM.

So, what's the take home message?

My OWB was shut down for 9 straight days during a very cold stretch of weather, and the water temperature only got down to 53 degrees. Certainly, the key has to be continuing the circulation of the water. But given the maintenance of water temps in the 50-60 degree range for several days without the addition of additional heat from my basement, I think it very unlikely that this system will ever freeze, as long as the pump remains running.

I learned a lot doing this.

beenthere · February 02, 2015, 09:11:41 PM

Great to hear you are back up and running..

stratford 50 · February 03, 2015, 08:27:56 AM

If possible Dr B, a few pictures would be helpful, well done on the experiment.

doctorb · February 03, 2015, 12:55:02 PM

Here's the crack at the back of my stove. The vertical cut was an expansion joint cut in by CB. The crack runs from the middle of this now warped expansion cut to an air hole, which is now shaped like a peanut. What the pics don't show is the bubbled out nature of this steel.

Her's the cut-out to get rid of the cracked and warped steel:

And here are the new steel plates attached to the back wall of the firebox.

As a bonus, I finally took the time to learn how to post pics. Thanks, stratford 50. I needed to get over that tiny hump and you pushed me to do so. Pretty easy, I must say.

bobby s · February 03, 2015, 03:54:54 PM

I think your firebox might be a bit different than mine. Is that 2" round hole for a gas ignition or is coming from one of the solenoids out back? What exactly is are new steel pieces doing? Guess I'm missing something. Thanks for posting the pictures and keeping us updated. Glad you're back up and running.

bobby s · February 03, 2015, 07:01:24 PM

Quote from: bobby s on February 03, 2015, 03:54:54 PM
I think your firebox might be a bit different than mine. Is that 2" round hole for a gas ignition or is coming from one of the solenoids out back? What exactly is are new steel pieces doing? Guess I'm missing something. Thanks for posting the pictures and keeping us updated. Glad you're back up and running.

Ooops- just realized the steel plates are mounted flat against the back wall. I thought they were held off when I first saw the picture. I assume to force airflow out to side holes.

doctorb · February 03, 2015, 07:38:11 PM

Apparently, the area around these back holes generates significant amount of heat, and the steel in this area has been cracking and warping. CB made these plates for two reasons: 1) As a repair for problems like mine and 2) to enable removal of the plate for better clean out of the air chambers. My welder told me that they will provide some protection for the remaining steel of the back of the stove, but they themselves might get cracked and warp. Replacing them will be easy, if that eventuality cones to pass.

Yes, that large central tube is the propane ignition area, which I have never used. Wish I had not purchased a dual fuel model, though. That has been a waste of $. This unit has run well for me and does not let the fire burn out. Only times I've needed a restart is after a thorough cleaning, like yesterday, or if I was was extremely delayed in returning home. Very, very rare. I did not need the gas starter option.

Mopar70 · February 03, 2015, 08:01:54 PM

ive enjoyed the topic Doc, glad to see your up and running again.
I noticed you did some research on geothermal laws.
Another topic you may find worth researching "the laws of thermodynamics"
I cant help but think and type out loud again...
Snow has an Insulation value.
frost is much more apt to be present in the ground above your piping when there is no snow.
after snowfall, that same frost is insulated from outdoor ambient and is more common to your underground heat source.
depending on the amount of snow, outdoor ambient.. other factors... any existing frost could melt all together.
I never thought about the grass concept but it makes sense to me, warmer ground makes it easyer for grass to germinate.
Think of the possibilities!
you could have all your nieghbors in awe over the size of your tomato plants!!

doctorb · February 22, 2015, 08:40:23 PM

Just to let you know that I practice what I've learned through this test, I went away from last Wednesday through today. During that time, we had no days with high temps >32 degrees and had the coldest temps ever seen by me in all my years in Maryland. I had never seen a minus temp here before. We had two days of minus temps for am lows while we were away.

I shut the stove down Tuesday, and just left the pump circulating the water to my basement and back. No connection to the heat exchanger, so no heat was added from my oil furnace, which kept the house warm while we were gone. So, this evening, I went to the stove. Water temperature 62 degrees. Restarted tonight.

So, even under the coldest conditions, this stove got no where near freezing. Remarkable.

Logging logginglogging · February 23, 2015, 08:03:41 AM

Wow, great pictures, I can easily make some plates like that. my back wall is nice and flat still but I would like to put in a cleanout. I have never seen the dual fuel model of my stove before, where does that large tube go? doesn't in get junk and gunk in it?

I think I will make a cutout clean out for my stove this year, though Mine has never plugged up before.

doctorb · February 23, 2015, 10:22:07 PM

I think that large tube you see in the center is the ignition tube for the duel fuel models. I have never hooked up gas to my 2300 and wish I had not spent the extra$. Yes, it get filled with ash and doesn't seem to affect anything.

JJ · February 25, 2015, 02:47:10 PM

Hi doctorb,

Thanks for the posting. I have just returned from 3 week trip where my stove (e-2300 like yours) was shut down.
I have been letting the inside oil boiler keep heat in OWB by heat exchanger and water temp in wood boiler stays about 150F.

It was a lot colder here than where you are (3 weeks 0-10F), but I may try shutting off the inside pump to heat exchanger, leaving only the outside running next time; saving on oil by not heating the stove.

I will like to see if oil use is significantly less by not keeping the stove warm. I don't think there is too much heat lost by keeping it warm, kinda like outdoor a hot tub.

I see you still have the fire bricks in the side walls, which I had removed years ago.
Oddly my stove (wood only) has not cooked the back plate like yours, but has cracked the left channel air, where I think all my air now gets into the stove. I tend to pile the wood on the left side (being right handed I guess), as I find out early on, not to pile wood all way across, so it can fall down without bridging as it burns; so maybe I have caused it to crack from hitting it with logs while loading hot. My logs are too long (20") to load cross-wise.

Reading about your air flow problem puzzles me, as I think with door closed, wood chamber pressurizes, and the combustion happens at the bottom, there the air exits into the reaction chamber. At least is what I observe with my stove. I am under the impression, that the cracks do not matter, as long as the door seal is tight.

JJ

doctorb · February 25, 2015, 03:34:25 PM

My unscientific impression, from "protecting" my OWB in past winters through the same method you did, is that the oil consumption is significant. The water returning to your indoor oil burner has been cooled down close to the temperature of the OWB water. Do you recall when you returned what the water temp in the OWB was? Mine, from memory of last winter, was around 100-110 degrees. Don't hold me to that!

So the water in the OWB acts like a heat sink, pulling energy away from your oil burner. In three weeks I would bet that you used significantly more oil than you would have thought. Give us a follow up when you can estimate how much oil you used. Thanks.

JJ · February 25, 2015, 07:57:12 PM

Hi doctorb,
I agree there must be some loss keeping the OWB warm with oil boiler, but how much.
The way I think of it is instead of heat sink, it is heat store. Instead of oil boiler starting with room temp water (~65-68F), it has 150F pre-heated water from heat exchange.
What I find is boiler fires in short bursts with pre-heated water, instead of long burn.
Anyway, I like the idea of not heating the idle OWB. In fact the thermostat valve CB sent to me few years ago (haven't installed), seems to imply that CB is fine with unheated OWB in winter, as long as outside circulation pump is running.

JJ

beenthere · February 25, 2015, 08:43:48 PM

If I was going to use the oil boiler to heat water in the OWB, I'd only try to maintain the temp just above the freezing point. Keep the pump running, but kick warm water out to the OWB only if there was a chance of it freezing. Minimum oil burned to ward off a busted pipe, IMO. Anything above that min. temp is just heating the outdoors.

gspren · February 28, 2015, 09:26:44 AM

When I shut mine down I really need to keep it hot due to an out building with toilet and sink getting heat directly from the OWB. This winter I shut down several times for 6-7 days each and while I'm sure I used more oil it didn't seem excessive.