No matter how long I study or stare at the animation, I can’t find the connection between that design and mine (if I can call it that).
See if I have this correct. The main goal with this type of heating design is to store the heat generated by the fire. A secondary function of generating instant heat can also be incorporated into the design if we so choose, but at a loss of total stored heat. An acceptable trade off in most instances, and usually preferred.
A metal 55-gallon drum is certainly the way to go if one wants to pump a lot of heat into the living space in a hurry. There’s a lot of surface area there to give off that heat. But what if it starts to get too hot in that living space but there isn’t enough heat yet stored in a mass to last throughout the day and night? (if that’s even possible. Some say it is.) I don’t have nearly enough information yet to know how often the fire needs to be lit and attended to so all I have to go on is knowing what I want to achieve and a life’s worth of common sense to try to figure it out. And what I think this system is able to achieve, if designed correctly for any given set of circumstances, is to give off a measured amount of heat immediately, just to take the chill out of the air, while at the same time store the majority of the heat produced to maintain a comfortable atmosphere throughout the day. That, at least, is the goal I have in mind. I’m thinking that the metal drum is simply going to give off too much heat. Heat that I would prefer to save for later. I don’t want to have to open a window to keep from overheating.
But from a maintenance standpoint, the drum has an advantage over a fully brick-encased heat riser. I would think it would be easier to replace the drum, or just remove it, tend to any issues inside of it, then replace it. Unless the drum were partially encased in cob. Then it would be a draw. With a brick encased heat riser the entire assembly might have to be demolished and rebuilt should any issues arise. These are things I consider as I move forward. But the brick riser has an advantage over the drum for the fact it won’t readily give of its heat but rather would transfer it to the mass for storage.
I’m not sure if a heat riser is dependent on a bell or not. That is, that the heat on the outside of the riser created by the heat inside the bell, is necessary for complete combustion of the gasses created by the wood. But I would think not. The system would burn dirty until the heat penetrated the heat riser’s insulation and firebrick. So with that train of thought, with a stand-alone heat riser, more heat is available for storage, and less heat is lost into the living space.
Then there’s the stand-alone downdraft tube. Another disadvantage if there were issues on the inside. But there’s a lot less heat involved so I think less likely to have issues. Heat related issues anyway. There’s two ways I look at this design since posting this thread and getting feedback. It can be a simple transfer tube, or be used as a heat sink. If the volume of air inside this tube were the same as the heat riser, it would be a transfer tube. If the volume of air were greater than the heat riser, it would become a heat sink. I liken it to a solid rod being pushed through a similar sized hollow tube. The rod would displace about 99.9% of the air in the tube. Make the rod diameter smaller and pass it through that same tube, the rod will displace less air, and in incrementally smaller amounts as you downsize the rod incrementally (The same being true in increasing the volume of the downdraft tube). If all of the heat in the downdraft tube is not continually and completely replaced, the tube will become hotter faster because hot gasses will linger in the tube (instead of getting displaced) heating it up, especially at the top of the tube since hot air rises. There would now be less heat available to heat up the mass in the next part of the system. I think if one does want to get some relatively instant heat from the system, I think the downdraft tube is the place to get it from. It’s inside diameter being the determining factor. Please correct me if I don’t have the science correct on this one. It’s a grey area for me. As is most of the system.