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Post by brogers on Oct 22, 2020 20:33:56 GMT -8
I'm wondering if anyone as created a condensing chimney. Seems possible. Maybe a forced air draft, preheat incoming combustion air, drain, side wall exit?
I'm not able to install a chimney to the requisite code height so am exploring alternatives.
Not much on the internet about it.
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Post by Vortex on Oct 23, 2020 0:27:40 GMT -8
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Post by brogers on Oct 23, 2020 11:58:26 GMT -8
Thanks. Just read that.
As the challenge is draft maintenance, I'm thinking about what "power sources" are available. Off the top of my head with some WAGs thrown in:
- Riser power/heat pump (expanding gases, increasing heat)
- declining temperatures across the exhaust stack.
- reduced pressures across the exhaust opening as a result of external forces (wind)
- stack diameter (could decrease over the length)
- stack exhaust shape (perhaps a parabolic exit nozzle like shape)
- external air source to stove to reduce negative pressures and perhaps create positive pressure (varies with temperature differential).
- Fan
If all the passive options were maximized, perhaps a natural draft is possible?
Other ideas?
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Post by gadget on Oct 25, 2020 12:48:17 GMT -8
There is not allot of people on here interested in non chimney wood heaters but if your goal is just eliminate the chimney its not that difficult to do. That is unless you don't plan on using a blower or draft inducer. I've built a couple of heaters without chimneys, both had draft inducers. My last one used PVC pipe for the flue gases. Here is a video of the flue exit; www.youtube.com/watch?v=YZJLq8aDg0cI use free draft inducer fans from old furnaces and they work great and draw little power, usually under 100watts. They come in metal or plastic. If you go the plastic route, you have to extract enough heat out before it reaches the plastic fan. My last heater flue temps typically stayed around 120F at full heat. Contact a local HVAC guy and ask for some pull out scrap furnaces. I've done lots of experiments with blowers/draft inducers and the potential is near limitless compared to natural draft. I've destroyed high temp 2300F ceramic fiber blanket within a few hours of burn time. You can reach some incredibly high temperatures with forced induction. Think bright white flames. This is not the best out come though for heater life. I'm working on a completely new design if time allows this fall/winter. Here is 2 of my previous experimental builds; donkey32.proboards.com/thread/3552/el-tornado-experimental-build-threaddonkey32.proboards.com/thread/3473/mini-rocket-forced-inductionBoth heaters changed allot during the builds, I have gained allot of info on what works and what doesn't. My next build focuses on 90% of the heat going into water heating in a small package and a design safe enough to not have to be next to the heater while its running. I've been doing allot of work with direct solar heating and solar electric heat pumps so unfortunately my wood heaters are on the back burner for now.....
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Post by brogers on Oct 25, 2020 19:35:19 GMT -8
Gadget,
thanks for the links. Read many of your posts.
There doesn't seem to be much discussion the delves into the theory and maximization of what I call the "draft engine". Perhaps I don't know where to look. I'd like to get the stack temp down as much as possible without resorting to induced draft. I don't know what the limits are and how those vary across designs. I have read that folks are getting stack temps down to 250 or less. But I'm obviously thinking about lower and either no chimney or an alternative chimney. . .
100 watts seems like a lot to me for a fan. I'm angling towards a net zero house with superinsulation and a 10kw solar system. I'll need to add solar thermal and also a rocket or two for things like my sauna and heating hot water (save for another thread).
So centering on the "draft engine" for a sec: If a builder creates a functional rocket stove, then they've got the high temps/ expanding gases. Get the air from outside to avoid negative pressures. Design an exhaust path that has the least amount of friction as possible, extract as much heat out as you can (e.g. air to water heat exchanger with a pump controlled by stack temps), decrease stack diameter as temps drop, add a stack passive mechanical stack cowl, . . . then. . . how low could you go.
There must me other options or experiments possible.
As far as heating water goes, I'll look for a current, existing thread and engage that.
Ben
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Post by gadget on Oct 25, 2020 22:00:18 GMT -8
Gadget,
thanks for the links. Read many of your posts.
There doesn't seem to be much discussion the delves into the theory and maximization of what I call the "draft engine". Perhaps I don't know where to look. I'd like to get the stack temp down as much as possible without resorting to induced draft. I don't know what the limits are and how those vary across designs. I have read that folks are getting stack temps down to 250 or less. But I'm obviously thinking about lower and either no chimney or an alternative chimney. . .
100 watts seems like a lot to me for a fan. I'm angling towards a net zero house with superinsulation and a 10kw solar system. I'll need to add solar thermal and also a rocket or two for things like my sauna and heating hot water (save for another thread).
So centering on the "draft engine" for a sec: If a builder creates a functional rocket stove, then they've got the high temps/ expanding gases. Get the air from outside to avoid negative pressures. Design an exhaust path that has the least amount of friction as possible, extract as much heat out as you can (e.g. air to water heat exchanger with a pump controlled by stack temps), decrease stack diameter as temps drop, add a stack passive mechanical stack cowl, . . . then. . . how low could you go.
There must me other options or experiments possible.
As far as heating water goes, I'll look for a current, existing thread and engage that.
Ben
It seems like 250 was a number I had seen come up allot for lower but still reliable flue for most designs, its probably not a linear function of pumping loss vs temps lowering. Nature loves exponentials. The big challenge is as you add heat exchange, you also add friction and there is no way around this that I know of. I personally would go the standard chimney route without hesitation unless it is not an option. 99% on folks on here would agree. I would not worry about the extra heat going out the pipe. Your heater will burn clean and the lost heat will not be as much as a metal box stove. Your focus on insulating your house will have a much higher gains per effort then anything else you do. Just a suggestion, I am not know for doing it the easy smart way so who am I to say right? Personally, I would not try to much lower then normal without an inducer, I just don't see much wiggle room to prevent smoke backs on those windy days. I've read so many problems with staring and reliability issues mostly tied to weak draft. That chimney code height is import to keep the draft stable. If you have not bought your solar setup yet and you definitely want it, I would consider getting it sooner rather then later. I think silver is going to go up from here and next year some time, it could drive panel prices up very high. If you had that much solar grid tied you could put in a nice heat pump system. Why? because why spend all that time cutting, chopping, moving, storing , loading, etc...wood when you can have the Sun relocate the heat for you from outside your home to the inside with zero labor on your part? We are in the golden age of heat pumps. Keep wood as a backup or when you want a nice fire or your sauna. I have about 8500 watts of panels and am going the heat pump route but DIY. I do allot of refrigerant work so I know the benefits of heat pumps. Its easier to move heat then to create it. 10K solar would do very well. especially at a 4 to 1 COP. Combine that with hydronic radiant flooring...that would be nice and very efficient. You can take care of your domestic hot water with the same system. Don't bother trying to use a rocket for heating usable amounts of domestic water. Lots of issues here. From all my testing and experiments I have learned placing the wood heater inside a water tank or having fire tubes inside a water tank is the safest, most efficient way to do it. Thats basically your modern outdoor wood boilers/furnaces. best option is tied to a large reserve tank to capture hot batch firing. I'm building my next wood heater into a 55 gallon barrel that will be surround/submerged into water.
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Post by Combustron on Oct 26, 2020 4:59:41 GMT -8
Newbie here with what may or may not be a new idea... Economizer + Reheater
A flue gas condenser or "economizer" becomes more efficient as its outlet temperature decreases, but this kills your draft. A possible solution is to reheat the cooled flue gases by routing them through an additional heat exchanger or "reheater" upstream of the economizer. This way, you can still extract the latent heat from any condensate while also having a sufficiently hot chimney temperature to maintain draft.
See my crudely drawn MSPaint diagram below... By adding a bypass flue with a damper, you could effectively control the temperature of the flue gases entering the chimney by varying the portion of the gases being reheated.
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Post by gadget on Oct 27, 2020 8:35:48 GMT -8
Newbie here with what may or may not be a new idea... Economizer + Reheater
A flue gas condenser or "economizer" becomes more efficient as its outlet temperature decreases, but this kills your draft. A possible solution is to reheat the cooled flue gases by routing them through an additional heat exchanger or "reheater" upstream of the economizer. This way, you can still extract the latent heat from any condensate while also having a sufficiently hot chimney temperature to maintain draft.
See my crudely drawn MSPaint diagram below... By adding a bypass flue with a damper, you could effectively control the temperature of the flue gases entering the chimney by varying the portion of the gases being reheated.
Economizers can be very handy for efficiency gains in some systems but if you think about it, reheating the flue gases after they have cooled could make for problems. Reheated exhaust should create a back push to the area of the colder exhaust thats in front of it. It would add more restriction from the gases back pushing. That doesn't even include the restriction losses from the heat exchanger. Gases are fascinating to work with. They are like bumper cars moving at very high speed wanting to go in every direction. Hotter gases are hitting harder then colder gases and transfer there energy to the colder gases and everything else that is colder. They seek out low pressure(colder) areas till balance is reached. Cooling gases calm down more and settle closer together. Chimneys work because of buoyancy. Gravity forces the heavier colder denser gases down which lifts the lighter hotter gases up. Chimenys basically work by floating gases out of the heater using gravity. Your rocket mass heater would not work in zero gravity. Also, the burn and flue path is like a freeway. To much restriction and you have traffic congestion. You want to avoid going from a 4 lane road to a 2 lane road as much as possible. There is the kinetic energy of the mass of the gases moving together you want to preserve as much as possible. Every change of direction of flow has large effects of loss of momentum. Heat exchangers are a mess for good flow. More laminar flow preserve momentum. Bends and heat exchangers kills flow quicker then anything. Thats why freeways try to avoid turns as much as possible. Imagine if your on a free way with a 90 degree turn. Major slow down for traffic. Always use the largest radius bends you can find/fit. The winds at the exit of the chimney can have lots of affect to the exiting gases, think cross traffic on a road. Thats why they want the chimney high above and turbulent winds coming of your roof. I use to live on a property with a long drive that gradually slopped down. On windless nights you could walk down and feel the colder air that had settle down towards the bottom. I keep the door to my stairwell closed at the bottom. The air down there is always the coldest in the house. I've seen many great ideas for trying to extracting the extra heat from flue gases over the years but nature always wins in the end. You can get that last 10-15% but you will need to cheat = add a fan. Sorry, no way around it folks. Everything in natures's workings has losses on its path to balancing out. There is no free lunch I am afraid, but that is fine. Sometimes its best to leave the last 10% for the birds, its just not worth doubling your effort for the last 10%.
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Post by Combustron on Oct 27, 2020 17:32:20 GMT -8
I've been browsing this forum for quite some time to study the "state of the art" in rocket heater/stove design and I believe there is still much room for improvements, notwithstanding any design/engineering hurdles required to make said improvements practicable. Condensing water vapor out of the flue gases represents a single large low-hanging fruit in terms of efficiency gains. Even a lowly 10% gain in relative efficiency means a substantial 9% savings in fuel required for the same heat output.
Since we are typically heating a living space to between 20-25°C, it should be possible to achieve flue gas temperatures not far above this range with the copious use of counter-flow heat exchange surfaces. This, of course, necessitates some means of enhancing the draft in order to maintain the gas velocities required for efficient combustion.
Using mechanical means to induce draft adds not only an external energy cost to heating with wood fuel, it also introduces failure modes that aren't present in a more "solid-state" design. I believe that reheating the flue gases with an additional heat exchanger presents a simple, low-maintenance means of enhancing draft in a condensing system. Ease of fire lighting and draft control can be achieved by adding bypass flues with dampers in the appropriate locations.
For my purposes, I'm interested in developing wood burning appliances with a very specific combination of characteristics that will likely be of interest to others: small size suitable for 100-1000 sq.ft. applications, 16-inch long cord wood for fuel, very high fuel efficiency, variable heat output and continuous 24/7 operation with refueling only once or twice per day. With these criteria in mind, I've been iterating a condensing rocket stove design for quite some time and I'd like to post a 3D mock-up of it someday.
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Post by gadget on Oct 27, 2020 20:28:16 GMT -8
I've been browsing this forum for quite some time to study the "state of the art" in rocket heater/stove design and I believe there is still much room for improvements, notwithstanding any design/engineering hurdles required to make said improvements practicable. Condensing water vapor out of the flue gases represents a single large low-hanging fruit in terms of efficiency gains. Even a lowly 10% gain in relative efficiency means a substantial 9% savings in fuel required for the same heat output.
Since we are typically heating a living space to between 20-25°C, it should be possible to achieve flue gas temperatures not far above this range with the copious use of counter-flow heat exchange surfaces. This, of course, necessitates some means of enhancing the draft in order to maintain the gas velocities required for efficient combustion.
Using mechanical means to induce draft adds not only an external energy cost to heating with wood fuel, it also introduces failure modes that aren't present in a more "solid-state" design. I believe that reheating the flue gases with an additional heat exchanger presents a simple, low-maintenance means of enhancing draft in a condensing system. Ease of fire lighting and draft control can be achieved by adding bypass flues with dampers in the appropriate locations.
For my purposes, I'm interested in developing wood burning appliances with a very specific combination of characteristics that will likely be of interest to others: small size suitable for 100-1000 sq.ft. applications, 16-inch long cord wood for fuel, very high fuel efficiency, variable heat output and continuous 24/7 operation with refueling only once or twice per day. With these criteria in mind, I've been iterating a condensing rocket stove design for quite some time and I'd like to post a 3D mock-up of it someday.
As far as percentage of heat recovery, I was just throwing that number 10% around. I think a fully condense (dry exit) exhaust may be closer to 20% but there is conflicting number and so many variables. I wouldn't call it low hanging fruit, more like fruit of temptation. Where would the heat to reheat the exhaust come from? You have me curious about this. Did you see what I wrote about having a cold spot of flue gases causing flow loss in front of the reheated flue gases? You would have a low pressure area in the middle of your stove. High pressure seeks low pressure. It would partially run backwards or maybe vibrate or start to pulse. I think it is not something worth messing with, but I will just leave that as my opinion. Why not just put that heat your adding to the exhaust directly into the room? You would prevent very restrictive heat exchanger issues. My main reason I went with an induction blower route was to hide the exhaust so the guys in black suits don't come and shut me down. What I got was a giant plume of water vapor coming out the side of my greenhouse. Not exactly "Hidden" or low key. I could add 2 blowers with valves if I wanted a backup for added easy reliability but these blowers are designed to run for years and years and last a long time. As far as energy cost its very small, the money you save on not installing a chimney should be considered. I have a really nice blower that uses 60 watts. It cost me .006 dollars and hour to run or .6 pennies. It bolts directly to 2" PVC. Very cheap and easy to setup. $.10 per KWH x .060 kilawatts = $.006 per hour. 24 hours a day = $.144 per day If I ran it for a year (365 days) = $52 For a $3,000 chimney install I could run the blower for 57 years (24 hours a day 365 days a year) before I hit that cost. For just winter and partial day your talking over a hundred years. Power cost in negligible. One challenge with running a long burn batch load is keeping the wood from advancing the pyrolysis rate on its own. This happens mostly because of the insulated burn chamber. You figure that one out I would love to hear. Its a tricky problem but I think there is potential here. Blocking of air flow trying to slow it is recipe for black smoke. This is why I like the idea of a batch burn of lots of heat dumped into a buffer water tank for continues use. I'm not trying to discourage, just stating known challenges. Believe me, your goals have been worked on for decades by many other people like you. Don't let that stop you, just apply the real world physics while you design. And by all means, build a test heater this winter. Read lots of white papers. I recommend researching "condensing acetic acid from wood distillates" and "thermo oxidizer designs". Then come back and share for others your build!
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Post by Combustron on Oct 28, 2020 11:34:28 GMT -8
Where would the heat to reheat the exhaust come from? You have me curious about this. Did you see what I wrote about having a cold spot of flue gases causing flow loss in front of the reheated flue gases? You would have a low pressure area in the middle of your stove. High pressure seeks low pressure. It would partially run backwards or maybe vibrate or start to pulse. I think it is not something worth messing with, but I will just leave that as my opinion. Why not just put that heat your adding to the exhaust directly into the room? You would prevent very restrictive heat exchanger issues. Although it's not perfectly clear in the diagram I posted earlier, "the heat to reheat the exhaust" is coming from the exhaust itself as the same stream passes itself inside the reheater. This is what I'd call a "thermodynamic hack" that allows heat to escape directly into the chimney, where it will create useful draft in the system, while also allowing the entire exhaust flow to pass through the economizer for maximum heat extraction. The idea is to maintain the same elevated stack temperature to get the level of draft you need, while also reducing the stack losses by condensing as much of the exhaust as possible. Without a condensing economizer in the exhaust system, the reheater would be completely pointless.
This does create a zone of slightly higher pressure as the exhaust is cooled to its minimum temperature, but this cooled exhaust is then "sucked" into the chimney by the heating action of the reheater. The key to getting such a system started and running properly is adding a bypass conduit that allows the exhaust to escape directly into the chimney. Once the chimney is up to temperature and a strong draft has been established, the bypass can be gradually closed off with a damper to bring the reheater + economizer path up to temperature and maintain exhaust flow in the right direction.
Also, I don't see why heat exchangers are necessarily "very" restrictive, especially for low-heat flux and low-velocity applications like wood heating. I understand that, in a completely passive draft system, we're dealing with very small pressure differentials and Every Pascal Counts, but a few Pascals is a small price to pay for a double-digit efficiency gain. The "bell" incorporated into many rocket heater designs is essentially a large, low-resistance counterflow heat exchanger where the ambient air is the fluid being heated.
One challenge with running a long burn batch load is keeping the wood from advancing the pyrolysis rate on its own. This happens mostly because of the insulated burn chamber. You figure that one out I would love to hear. Its a tricky problem but I think there is potential here. Blocking of air flow trying to slow it is recipe for black smoke. This is why I like the idea of a batch burn of lots of heat dumped into a buffer water tank for continues use.
I believe that Peter's work on batch rocket design and experimentation is a priceless source of knowledge for anyone looking to "roll their own" rocket-style wood burner. The humble batch box heater core is essentially the progenitor design that I'm merely attempting to improve upon. In order to achieve continuous 24/7 operation with refueling only once or twice per day, it's necessary to have both a sufficiently large wood loading capacity and a sufficiently low burn rate to achieve the desired burn time between refueling.
What I'd like to have is a stove where the wood is loaded as a narrow (8-12 inch wide) but tall (3 feet!) stack of split cord wood that's gravity-fed into a small combustion chamber, much like what you'd find on a J-tube rocket but scaled up. I have seen successful J-tube designs that incorporate a fairly tall vertical feed chute that holds long pieces of wood. Scaling up this type of vertical feed chute to accommodate a stack of cord wood will require some creative design of the combustion chamber, which I'm still iterating on the drawing board. The idea is to confine the combustion to as thin a layer at the bottom of the stack as possible without it extinguishing, much like how a cigarette burns. If it can be made to work, the design should be very scalable. The heat output would scale proportionally to the base area of the wood stack, while the burn time would be proportional to the height of the stack.
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Post by gadget on Oct 28, 2020 21:16:10 GMT -8
Your biggest challenge with your latent heat recovery of that water vapor will be your heat exchanger design. It will have to be really good. There are allot of issues to over come and its hard to get that water vapor out completely especially at these gas velocities. I've failed at it. I've done heat exchanger math a few times. Take your delta t, materials, surface area, face velocity, etc.....it paints a better picture of the challenge.
I built a heat exchanger for a 2 stage swamp cooler out of soda cans, it ended up needing 3200 cans to meet surface area requirements. Its 8' x 8' x 18"s. Have you done the math on the heat exchanger yet to see how big it will be? Size can be a good allie in design to offset other issues like delta t. I had a very large truck radiator with 60-100F water circulating in it and the flue gases passing through the radiator fins. It was very wide and had a fairly reasonable face velocity. I was expecting tons of water vapor to collect. I got near zero. I was shocked since it was a fairly large heat exchanger. Have you seen my copper tube condenser design? You will want to avoid tiny passages due to clogging. Trust me on this, its a pain to clean. You want clean out to be easy.
I still think cooling the gases in the middle and reheating is a bad design, and will bet you a nickel it won't flow without a blower but hey I could be completely wrong. I would rather encourage you to go forward because I know even if it doesn't work, much can be learned from testing it. Knowledge you won't get from a forum. Its a fascinating idea for sure!
There is the issues of materials for a flue gas condenser. Luckily, due to the higher combustion temps in these masonry based heaters, acetic acid is more easily pyrolised in RMH's and the likes. About 1400F for 2 seconds with give you a 90% acetic acid destruction to smaller and less harmless HC's but still probably a little acidic since they will be open ended hydrocarbons (cracked but not hydrolyzed). I read once that copper was used for wood flue gas stills in a white paper but I have yet to test it myself. Aluminum is a no go, it will corrode in one season, ask me how I know... Stainless should work for a few years. If you source old furnaces, sometimes you can get really nice stainless steal heat exchangers for free. They use them in the second stage. I got one but it was fairly small from a 90% furnace, I have no idea how those gas furnaces condense water in such a small package. Im guess the volumes are much less then a wood heater which would explain the tiny chimneys they have.
Condensing regular metal box wood stove flue gases would be a sticky mess, there burn temps are to low and not enough residence time at temp. Way to much acetic acid and other tars, VOCs, etc..in the flue gases that will be condensed with the water vapor. Good news is, you should only have mostly carbon black to deal with.
If I ever tried to do a condensing flue again(with blower of course) I would try using a heat pump to recover the latent heat. It would have a higher delta t so a small exchanger could be used and the efficiency (COP) would be really good. It would suck that heat out of there faster then you can say "perpetual motion". Heat pumps open up lots of options for obeying the laws of thermal dynamics. With the blower you can keep the sensible heat too! 1
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Post by brogers on Oct 28, 2020 21:58:17 GMT -8
If you have not bought your solar setup yet and you definitely want it, I would consider getting it sooner rather then later. I think silver is going to go up from here and next year some time, it could drive panel prices up very high. If you had that much solar grid tied you could put in a nice heat pump system. Why? because why spend all that time cutting, chopping, moving, storing , loading, etc...wood when you can have the Sun relocate the heat for you from outside your home to the inside with zero labor on your part? We are in the golden age of heat pumps. Keep wood as a backup or when you want a nice fire or your sauna. I have about 8500 watts of panels and am going the heat pump route but DIY. I do allot of refrigerant work so I know the benefits of heat pumps. Its easier to move heat then to create it. 10K solar would do very well. especially at a 4 to 1 COP. Combine that with hydronic radiant flooring...that would be nice and very efficient. You can take care of your domestic hot water with the same system. Don't bother trying to use a rocket for heating usable amounts of domestic water. Lots of issues here. From all my testing and experiments I have learned placing the wood heater inside a water tank or having fire tubes inside a water tank is the safest, most efficient way to do it. Thats basically your modern outdoor wood boilers/furnaces. best option is tied to a large reserve tank to capture hot batch firing. I'm building my next wood heater into a 55 gallon barrel that will be surround/submerged into water. Gadget,
Already have 10kw solar and a heat pump water heater (I'm into air to water and no geo). Solar thermal next year and hoping to store 250k BTUs min. However, gotta get the sauna hot so heating water it is. That's a diff thread.
Chimney-wise, I do understand I'm headed into the underworld here. Been a contractor for decades and earned my ICBO inspection cert in 1989. Codes usually have a logical rationale, but in this case not an option for me. So I'm looking for ways to stay safe while not code compliant. I'll report back my results.
Probably all the things I mentioned to power the "draft engine" will be in play--plus I suspect a primer fan. I don't care what the exit stack temps are that much. . . If down low, have to keep folks from getting burned or poisoned. Other than that, no biggie!
Thanks for the discussion Gagdet/Combustron. Now to figure out how to get emails when someone responds here. . .
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Post by gadget on Nov 1, 2020 21:58:45 GMT -8
If you have not bought your solar setup yet and you definitely want it, I would consider getting it sooner rather then later. I think silver is going to go up from here and next year some time, it could drive panel prices up very high. If you had that much solar grid tied you could put in a nice heat pump system. Why? because why spend all that time cutting, chopping, moving, storing , loading, etc...wood when you can have the Sun relocate the heat for you from outside your home to the inside with zero labor on your part? We are in the golden age of heat pumps. Keep wood as a backup or when you want a nice fire or your sauna. I have about 8500 watts of panels and am going the heat pump route but DIY. I do allot of refrigerant work so I know the benefits of heat pumps. Its easier to move heat then to create it. 10K solar would do very well. especially at a 4 to 1 COP. Combine that with hydronic radiant flooring...that would be nice and very efficient. You can take care of your domestic hot water with the same system. Don't bother trying to use a rocket for heating usable amounts of domestic water. Lots of issues here. From all my testing and experiments I have learned placing the wood heater inside a water tank or having fire tubes inside a water tank is the safest, most efficient way to do it. Thats basically your modern outdoor wood boilers/furnaces. best option is tied to a large reserve tank to capture hot batch firing. I'm building my next wood heater into a 55 gallon barrel that will be surround/submerged into water. Gadget,
Already have 10kw solar and a heat pump water heater (I'm into air to water and no geo). Solar thermal next year and hoping to store 250k BTUs min. However, gotta get the sauna hot so heating water it is. That's a diff thread.
Chimney-wise, I do understand I'm headed into the underworld here. Been a contractor for decades and earned my ICBO inspection cert in 1989. Codes usually have a logical rationale, but in this case not an option for me. So I'm looking for ways to stay safe while not code compliant. I'll report back my results.
Probably all the things I mentioned to power the "draft engine" will be in play--plus I suspect a primer fan. I don't care what the exit stack temps are that much. . . If down low, have to keep folks from getting burned or poisoned. Other than that, no biggie!
Thanks for the discussion Gagdet/Combustron. Now to figure out how to get emails when someone responds here. . .
Its a bit to cold where I am for air source. I do have shallow ground water at 52F thats available, no space for laying horizontal pipe unless I went with a bore field which is a possibility. I have been focusing on water to water heat pump testing since I'm putting in radiant but i do have a water coil installed in my central air. I cooled my home with 52F ground water this summer. I'm seeing some direct to panel DC heat pumps starting to be made. I would like a 48v unit that is water to water. I found a mini split 48v inverter unit in the US, but not a water to water unit yet. 1ton or smaller so I can run a couple of them in parallel. With a water output unit, it could be used with a large storage / buffer tank so you can heat the water up direct form panels while the sun is shinning and pull heat 24/7 with your radiant. That would be the perfect heat source. With 10K solar, you have some good options.
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Post by brogers on Nov 3, 2020 20:09:41 GMT -8
There are a number of cold climate air to water heat pumps. Check out Sanden and Arctic Heat Pumps.
Anyway to revisit this thread:
1: I wish I had titled this thread "strategies for exhaust stack challenges" or something more generic. I probably don't need to care about condensing . . . I do need to care about adequate draft and safety. Multiple options for me and I'm learning by the second.
2: Your idea above about an electric draft inducer (fan) is a good one. My knee jerk reaction was "no electric", but there are hundreds of options for low watt fans, and a little math showed me the cost is minimal if not zero considering the length of time a fire burns in a RMH as well as the extra BTUs one might squeeze from the stack. Anyway, I'll likely adopt the tried and true method of just doing it and then figuring out how to make it actually work later. Thanks for the ideas.
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