This is just me thinking out loud. I may or may not use these ideas in my own cabin, but in case someone else is also looking for a place to start, they’re welcome to use them.
The space is so small, I can either easily turn it into a sauna or expend the same futile effort of a candle trying to heat a concert hall, so moderation is a big issue. Above all else, whatever method I choose has to be relatively self-governing since I don’t feel like waking up every 4 hours to replenish the heat (although I wake up every 4 hours anyway due to insomnia).
The first place I looked was, naturally, solar.
Electrical = No Dice
I quickly eliminated an electrical approach due to the excessive drain. No matter the output of any photovoltaic cell + battery combination, in-floor electrical heating or some sort of space heater would be too much of a drain on the power supply for the size of the cabin. According to my current estimate of the South facing roof, I would have approximately 120 square feet to play with and even if I covered every inch of it with PVs, I don’t think it would be enough.
Also, if there is an extended period of overcast in the Winter, I’ll be in serious trouble trying to maintain the heat while toning down the drain of any other appliances. This sort of juggling feels like too much of a hassle and the whole point of this was to get away from stress. I want to enjoy those little luxuries like bright lights, induction cooker, a microwave and maybe a toaster every once-in-a-while without having to resort to Watt-pinching.
Solar Hot Air?
If this is supplementary to another method, then it works the best. There are countless examples on the web of solar heaters for the home, all with varying efficiencies and ease of construction. What I wanted was something that I know for sure I can build, won’t cost a fortune and will be reasonably effective without having to turn one whole wall into a collector.
And above all else I don’t want to have to notice that it’s there.
I then looked at solar heaters using Aluminum downspouts as collectors and came across the best iteration of it so far. What I really like about this concept is how low-profile it is. Granted he’s trying to heat a full house, basement and all, but I think I can get away with less than half this size since the overall cabin is small. Best of all, I don’t always have to look at it.
It would be a fairly simple affair to wire up a fan or two, a thermometer inside the cabin and one in the collector to a microcontroller and power the whole ensemble with photovoltaics. Computer fans typically run on very low power, most are fairly quiet and are designed for variable speeds making them the ideal choice, I think. Also, I can easily replace these parts without too much expense when they break down.
But as I mentioned above, this will only work as a supplement to something else for days that are overcast for long periods or (heaven forbid) if the cabin got struck by lightning and my arrester and breakers failed frying all the electrical stuff.
I’m a bit ambivalent about all the DIY stove designs floating around out there. On one hand, these are improvised designs, but on the other hand, these are improvised designs. There’s a reason why commercial stoves aren’t made of used air, Freon, LPG or similar pressurized tanks.
Regardless of origin, the traditional approach to a stove is basically a container to burn the fuel, a one-way air input control, a baffle to delay the hot gases existing before heating the surrounding air and finally, a flue. I think it’s time we started moving away from the traditional arrangements for this combination.
I want my stove to not look like a stove.
Traditional stoves have a quaint appeal that works well in rustic settings, but that’s not the look I’m going for. Besides the efficiency issues, traditional stoves take up more room and are fairly dangerous (especially for a clutz like me). In this vein, I’ve looked at these allegedly hyper-efficient Rocket Stoves which are all the rage these days.
They turn an ordinary flame into a twirling vortex of hot gasses inside the burn chamber, shoot inside an outer chamber warming the ambient air, then in turn can be vented under a bench for warmth before being exhausted outside. That’s quite a long list of opportunities to use the hot gasses for actual heat as opposed to conventional stoves where most of it is lost to the outside air.
Alas, the Rocket Stove also has the same problem: It looks like a stove.
If you need a demonstration of how one would construct such a stove simply, this gentleman had done so with ordinary household items. The demo is in Japanese, but the explanation is very well done visually so it should still be understandable.
It also takes up too much space and it feels like there’s way too much effort and mess to get an efficient heating system going. Besides that, it still needs that tendering that I don’t like so much as mentioned at the beginning of this post and the style is all wrong. For some reason, every Rocket Mass Heater I see reminds me of the structures on Tatooine.
I’m also more inclined to go with a biomass option for fuel since it gives me the greatest flexibility for automation. If I want my stove to shut off or limit itself by automatically (I’m fine with having to start it), then conventional — therefore odd sized — wood and sticks ain’t gonna cut it. I need a steady stream of fuel in a predictable size range that’s easy to manage while at the same time being environmentally friendly.
Pellets it is!
Not only do they offer the most flexibility in terms of fuel (I can use everything from grass, hard or soft wood to even plant fiber derived cellulose), it gives me the ability to control the flame without too much handling. More fuel + more air = more heat. Less fuel + less air = less heat. And that’s about it.
I’ve been thinking of applying the rocket stove idea to pellet fuel, but most of the rocket stoves I’ve seen require manual feeding of some sort. Besides, there’s the mess problem as mentioned above. I thought this can all be improved with something very simple like a chimney connected to a burn chamber by a tube of some sort that will act as the horizontal leg of the rocket stove.
Lo and behold, someone already came up with the same idea ages ago!
This video is also in Japanese, but the product demo is very visual as above.
What I really like about this is how simple it is and how inoffensive it is visually. Most of the hodgepodge rocket stoves I’ve seen look like they belong on Serenity, the spaceship, and not in a good way. While this is a testament to the improvisational capabilities of the builder, I don’t feel like I should improvise on safety.
By combining the Rocket Stove idea with some of the concepts of the above product, I figured I can build myself a stove that ran on pellets, doesn’t look like a stove (or at least is easy to hide that fact) and isn’t cumbersome to operate. So I set about designing a stove that does just that.
This is a quick sketch of all my ideas for an “automatic” pellet stove
If the pellet hopper has a lid, I can hide the whole thing as a piece of cabinetry or even use the top of the hopper as a small table. The air supply can be a feed from under the cabin so I don’t have to drill holes in walls and other nonsense. Also, by putting the air supply inside the cabinet, I can reduce the cold air leakage into the cabin from there.
Now that I look at this, I think the only “control point” necessary would be on the air supply. If I turn down the Oxygen, the burn rate goes down and so does the temperature. Though I’ll still need a shutoff for the pellets to completely stop the burner in an emergency.
I think I can hide the starter burner in a cabinet as well or I may not even need it if it turns out the length of the flue is enough. And the best thing about this design is that I don’t have to touch anything inside the cabinet until it’s time to clean the ashes. I’m sure I can automate this too somehow, but for now, this gives me the least amount of “homework” while operating the stove.
Just load with pellets, light it, walk away. Of course, I say that now, but we’ll see how well this will turn out.