Rocket Mass Heater in a yurt

[MT Rod]

Haha, it is great to see those guys are still getting into mischief.

I worked at the corner of downtown and downtown in Missoula for 18 years. I knew Geof back then, and Paul took classes with my ex-wife at the University of Montana years ago. I knew them both from potlucks and such. I still recognize their faces, but for some reason they look older... but I have lived in China for 9 years now.

I hope to get back there this summer for a few days, I have a yurt or 2 to raise.

I know mass heaters work, I lived in an old apartment building in Germany (it had been Luftwaffe pilot's barracks in WWII) in the 1970's that would freeze your butt off if you didn't build a really hot fire about every 3 days and burn it all day.

After the walls warmed up they would stay that way for a day or so and then it started cooling off pretty quickly. There were 3 rooms and a kitchen, so you had to have a fire going hot in one of them all the time, the fire, the warm walls and the door cracked open heated the rest of the rooms in the house up to "sweater weather". Basically the whole building was a mass heater.

I would stop while riding my bike home and help myself to a bag of coal off an unused pile that was on the back of the kaserne where I worked. I picked up a paper grocery sack 3/4th full and stuck it in the rack on the back of my bike six days a week. There was a small white enamel coal/wood burner cook-stove in the kitchen. It would not keep the place warm alone, but it helped a lot.

In two rooms the heater was a big cabinet sized, vented kerosene stove. Oil was expensive then, probably still is, even though the cost has come down per barrel.

In those days I wasn't thinking about DTU's.

Rod
rodyurtlocker.com

[hierony]

Poked around some, found some numbers.

Wood: 8600 btu/lb (ideal, no

moisture

& oxygen burn/lab)
Typical 6200 btu/lb (20%

moisture

, semi-realistic)
Yak 5800- 7600 btu/lb
Goat/Sheep 5200 btu/lb
Kiang: 6900 btu/lb
Cow manure 8600 btu/lb ideal
5500 btu/lb practical (15% ash, 25% moisture)

Metric
Wood, typ 14.4 MJ/kg
Yak 13-17 MJ/kg
Goat/Sheep 12 MJ/kg
Kiang 16 MJ/kg
Cow manure 13 MJ/kg practical

Sources: yak/sheep/goat/kiang; wood; cow

Note: These are energy density numbers, expressed in energy/weight. Normally wood is sold by volume, making volume density (weight/volume) important--this avoids inconsistencies due to moisture weight but is probably just due to tradition & ease of measuring volume rather than weight of a cord.

Corn stover and wheat straw are both pretty good fuel sources, too, when dry (8200 btu/lb or so). Crappy when wet, however (4100 btu/lb). Wood chips are somewhere around the 4000 btu/lb, if I recall from an epa study pdf I lost...

Alas, I was not able to find numbers for dog manure energy density. Given that dogs are somewhat omnivorous like humans and have historically been feed with human food/scraps, a crude estimate would put the energy density of their poop as similar to humans, which is seemingly 9900 btu/lb (23 MJ/kg) completely dry (source). Normal water content is 20-70%. But finding enough dog/human excrement to burn daily might be a bit of a chore/require lots of dogs & humans. In which case, you're probably better off just using their body heat directly...

[Bob Rowlands]

That made my morning.

[MT Rod]

I am not sure what a Kiang is... but that is some noteworthy research, good shit as some would say.

I am also pondering how many cords of dog poop I would burn in a Montana winter, It might work if you had some sled dog teams too...

Luckily I don't have any dog teams, the neighbors always hate you for the noise. That and the fact that I am living approximately at the Tropic of Cancer, (no relation to the Miller book) in China for a little longer.

Next year it is yurts in Ecuador.

Rod
rodyurtlocker.com
Home Page.

[wrdanner]

Originally Posted by hierony

What are you making your platform out of? Are you building or buying your yurt? How do you plan to insulate it?

Everything is open for consideration at this point. The yurt will be on the coast of North Carolina so I'm trying to figure out how to deal with the humidity and hurricanes. I'm considering building the yurt myself. Having no air underneath the yurt would be the most sound way to approach the hurricane issue but that also makes it more difficult should we require HVAC to deal with the hot summers. There will be some shade where we're building but I just don't know how uncomfortable the yurt will get without it. There will be a garage attached to the yurt and the kitchen/bathroom are in there. The thought was to have HVAC for the kitchen/bathroom and then if we found it was necessary, run ducting under the yurt. This requires the yurt to be built off the ground though.

The bedroom will be in the yurt so it needs to be fairly comfortable in a region where the overnight lows can stay in the low 70's with high humidity. It's possible we could go with a window unit in a glass window in the bedroom but it's all speculation at the moment. I've been trying to learn as much as I can to figure out what's the best way to approach it.

If the yurt was built on the ground, a rocket mass heater would give the yurt thermal mass. We would actually consider putting two of them in, on each side. I've looked at them on permies.com and the idea seems really cool, plus you get a seat or something else out of the surface if you do it right. This would alleviate my concern of constantly having to keep a fire running full tilt, unless we chose to add traditional

insulation

to the walls and then cover the studding to help with heat loss. The added mass will also help with hurricanes. In a hurricane, I'm less concerned with the yurt coming apart than the whole structure trying to blow away. I have no experience with this other than people's reports of them holding up well because the shape of the yurt causes the wind to push it down into the ground. I think the biggest issue here would be a lateral, sheering movement. Obviously the yurt would have to be well anchored no matter what we do but adding mass would help. Of course all that mass radiating heat in the winter also means mass that has to be cooled in the summer, unless the rocket mass heater was portable. I've seen some cool designs for portable ones as well.

[Marshall Eppley]

Dig your duct in before you build the yurt.nothing like natural

insulation

. They bury duct work in slabs all the time.

[wrdanner]

Originally Posted by Marshall Eppley

Dig your duct in before you build the yurt.nothing like natural insulation. They bury duct work in slabs all the time.

If we buried the duct work in the ground (sand) would we still want insulated duct work or would PVC do the trick with the ground insulating it? We'd transition to some type of insulated pipe if it needed to run above ground for any length.

[Bob Rowlands]

I hate to say it but a yurt is very unlikely to survive a full on hurricane regardless of what foundation it is anchored to. This is jmo. I have been in mine -very solidly anchored- in 60 mph+ wind, and was edgy. I seriously doubt it could withstand continuous 100 mph wind and driving rain. FWIW my first yurt was destroyed in a blizzard, however it wasn't anchored to the ground.

I don't mean to deter you from building one, but I'd seek heavier shelter in full on hurricane. A yurt is still a tent regardless. Good luck.

[wrdanner]

Originally Posted by Bob Rowlands

I hate to say it but a yurt is very unlikely to survive a full on hurricane regardless of what foundation it is anchored to. This is jmo. I have been in mine -very solidly anchored- in 60 mph+ wind, and was edgy. I seriously doubt it could withstand continuous 100 mph wind and driving rain. FWIW my first yurt was destroyed in a blizzard, however it wasn't anchored to the ground.

I don't understand how yurt companies can claim to sell yurts that withstand 100 mph winds then when buying all the snow and wind options. We would be doing the whole nine. 2x6 roof joists, wall supports for every roof joist, every joint connect via metal brackets, block spacers between all roof joists, etc. With all that reinforcement I personally think the skeleton of a yurt is stronger than a house provided the yurt is well anchored to the ground, and the fact that it's leaky means it's unlikely it will explode or implode due to pressure differences.

It would take a direct hit from a cat 2 hurricane to see 100 mph winds. It's unlikely the yurt will house anything more than the bedroom and dining/living area. The kitchen and bathroom will be in the adjoining garage. I'm sure well vacate the area the first go 'round and see how the yurt does.

I suppose we could move the furniture into the adjoining shed (which will be constructed to residential standards) and uncover the yurt. I know that would survive.

[kcoad]

Just came upon this post and figured I should post our experience with building a Thermal Mass Heater in a 30' yurt purchased from

Pacific Yurts

in Oregon. We built our TMH just about 2 months ago. The area we live in, Southern BC, Canada, gets fairly cold in the winter… potentially -18 degrees C. We love our TMH, as we love the look and that you can cuddle up to it… our cats love it too.

…. however…. the hottest it seems we are able to get it is 19 degrees C. The heat is nice and stable once it does heat up, but it takes a looong time to get there, and the mornings are not so comfortable. We are a little concerned, at this point, that it may not be a terribly comfortable winter. At present the outside temps are around -1 degree C, and already we walk around w/ toques and housecoats on for 2 or three hours. Lets just say it doesn't inspire one to get cracking with their day.

Eventually we plan to wall our yurt in, and I'm sure the TMH will be wonderful once we do that. Meanwhile, we may have to get some supplemental heat source. Perhaps a diesel heater? (we are on limited solar).

Re the foundation, we are on a raised platform and we did beef up the foundation under the area the TMH was to go.