How to reuse the CO2 from exhaust in the greenhouse?

Plants recycle CO2 as part of photosynthesis and cellular respiration. The rocket stove produces a fuller burn which byproducts are CO2 and water vapor. A CO2 rich environment is conducive to plant growth. The idea is to reintroduce the exhaust in to the greenhouse and add the CO2 to improve plant growth. Those are the broad strokes of the concept, the details sill to work out are, how much to cool the exhaust and how to prevent CO2 build up, so as to not asphyxiate any one working in the greenhouse. A possibility is to create a trough around the beds and and let the heavier gas rest inside them and some how circulate them to keep the fresh exhaust around the plants while venting the oxygen. Other concerns are the rate of exhaust production and the rate of cellular respiration would need to be close as to avoid asphyxiation.

So problems to address:
1. bringing the exhaust into the greenhouse.
2. bringing the exhaust to proper temperature.
3. taking the exhaust to the plants.
4. regulating the amount of the exhaust inside the greenhouse
5. venting the excess exhaust.

Basic parameters:
one rocket mass heater
above ground construction

Any insights and thoughts to problem solve these things is appreciated, all of this is in the planing stage of pre-construction, so anything goes.

Ethan Johnson : Welcome to Permies.com, our sister site richsoil.com, and a big Welcometo the Rocket and Wood stove Forum / Threads ! With~21,000~
fellow members world wide, you should be able to come here 24 / 7 and find someone who wants to talk to you about what you want to talk about !

A few housekeeping details, and we will jump right in to it. Look at your name space on the left of your Thread, and L@@K at mine ! At the top right of this page
is the Permies Toolbox, Select the button marked "My Profile", this will take you to a new page with areas to click on, and you will be prompted to add a general
location and your Climate zone number if you know it. This helps your fellow members give you good answers to your questions, and puts you out there to let
your Permies Near Neighbors, people with Rocket Mass Heater RMH Experience / Greenhouse / RMHs in greenhouses experience to find you !

Regional differences in seasonal humidity, and best use practices create wide differences in expectations of just how much humidity your plants can be expected
to tolerate, and Then there are to high moisture Rusts and Smuts and plant mildews,that A person several states away may have no idea of let alone how to
recognise, let alone treat !

Also from the Permies ToolBox you can clickon> 'Search' Enter a subject term like CO2 in greenhouses, and then select to do a google search within the 100s
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You are not the 1st person to wonder about using the benefits of increased CO2 from the Rocket Mass Heater RMH, while plants are producers of O2 during daylight
hours, at night they switch over to becoming O2 users at night, so your time frame is greatly limited for getting a maximum benefit, especially during the short days
of early spring, late fall. Too much CO2 would actually be harmful and your life would be dependent on a mechanical method of air exchange / CO2 scrubbing, and
what do you do for a power failure, you are certainly limiting any use of a pit greenhouse do to possible CO2 Build up, that being said, some people combine a green
house chicken coup, allowing the chickens to add several degrees of Chill protection for the Plants, and a self regulating safe increase in CO2 from the Chickens,
again, our 'pClould' will have information on that !

Beyond cooling our exhaust down to the point of condensation of Water vapor , (and recapturing the latent heat of evaporation), which will be greatly buffered by the
use of your Cob Thermal Mass bench, Exhaust temps are generally so low that this is not a problem.

Trying to start a fire now to 'charge' your Thermal mass for late evening or overnight use, can cause you to be dealing with a green house that is actually colder than
the present outside temperatures, making your RMH hard to Draft, But you will quickly teach yourself how to resolve this problem !

Our government has clearly disseminated the message that They have to be ever vigilant to protect us all from the Terrorist,boogyman,bad guy, reminding us that
they have to be right every time, and the Bad Guys only once, You only need to be wrong just one time to be Dead wrong withnCO2, most members here would not
think that that was a safe Risk ! For the good of the Craft !

Think like fire, Flow like Gas, Don't be a Marshmallow, As always, your comments and questions are solicited and are Welcome ! PYRO - Logically BIG AL !

Bump : Big AL

hum

You are thinking in the right direction, no waste, using the CO2 for the plants. Your question is the on the rate of consumption of CO2 by plants and the rate of CO2 production by RMH. Quick example:

If you burn a 10 pound branch in the rocket mass heater, lets assume that 50% is CO2 and 50% is water from the combustion, your plants need to grow 5 pounds worth of new plant material to remove all the CO2 from combustion!

Fire tends to produce CO2 at a rate 100 to 1000 times faster than plants can take it up. In chemical kinetics it is called the reaction rate, r. The reaction rate for plant growth has a value of around 1, slow. The reaction rate for combustion is 100 to 1000 depending on how fast the burn is, fast. Thus, you would need a very large amount of plant mass (100 to 1000 times) than you burn in firewood mass. From the example, a small farm will probably put on 5 pounds of new plant material in a day and remove the CO2 from a 10 pound branch burned during during the night.

(reaction rates taken from, Chemical Reaction Engineering, Scott Folger)

More info:
http://en.wikipedia.org/wiki/Reaction_rate

On a more global level this is why CO2 is building up in Earth's atmosphere, humans are able to produce CO2 faster than nature can grow with it.

[edit] added missing word.

same discussion at https://permies.com/t/15043/wood-burning-stoves/capturing-rocket-mass-heater
what about compressing it and store it for later use?

Iz

Never used rocket exhaust but I have seen many many different greenhouse heat setups. It seems like at least in my climate the Issues regaurding CO2 could be taken care of with appropriate venting. A greenhouse need not be air tight. Many have windows and roll up sleeves and the like. Around here even as little as an extra 3 or 4 degrees can mean the difference between hibernation and death and would be well worth pursuing in my views.

So I've been doing this for a few months now. My system is a 6" rocket mass heater in an aquaponics greenhouse. My heater is in the greenhouse to help keep it warm, the exhaust system is a series of brick channels under one of my raft tables so it heats the water and then my final exhaust goes into a T. One side of the T exits the greenhouse, the other points in and I have a 25' piece of 6" flexible tubing I can use to direct the CO2 where ever I need it to go.

Some thoughts. First, not sure what folks are talking about with the amount of CO2 produced. Burning 1 lb of wood produces around 1.8 lbs of CO2. I know that might seem counterintuitive, but it's because of all the oxygen brought in. 1 lb of CO2 is roughly 8.5 cf. If you want to calculate parts per million (ppm) to decide how much wood to burn to get the right CO2 ppm, you need to figure out the volume of your greenhouse. My greenhouse is 10' x 24' x 8' or 1920 cf. If normal CO2 concentration is around 400 ppm and I want 1500 ppm (a good number to boost plant growth), the way I calculate it is turn ppm into a decimal (1500/1,000,000 = .0015) then multiply that by my total volume in the greenhouse and that gives the number of cubic feet of CO2 I need. .0015 x 1920 cf (the volume of my greenhouse) comes out to just under 3 cf, which means burning a pound and a half of wood will give me enough CO2 to get over 1500 ppm (there's already CO2 in the air). Given that the plants are using some and there's always air loss, I aim for 1500-2000. Some day I'd like to buy a CO2 meter, but they're fairly expensive and it hasn't seemed worth it yet.

There are a few things to think about before you try to boost CO2 with your rmh exhaust. First, CO2 is heavier than normal air, so you need a way to get the exhaust to the right place and let it "fall down" to a degree and circulate. A second big question for your system is the temperature of your exhaust. I have about 32' of duct for a 6" system with four u-turns, so my exhaust exits the system never hotter than 80 degrees or so. But if you're air is coming out really hot, you'll need to be careful about how you pump it near your plants or you'll dry them out/burn them. Third, your burn has to be incredibly clean. Every once in a while I have some wood that was wetter than I thought or some pine that is really oily, and the burn is smoky. I never pump the exhaust into my greenhouse until I'm a good way into burning a load of wood and I've seen that the exhaust is as clear as can be. Last, for CO2 to have the most benefits for plants, the temperature, humidity and light levels all need to be within a good range, along with good air circulation. Poking around on the internet I found a really detailed guide to CO2 enrichment, if you're interested let me know. Basically, temps around 80, humidity under 40%, bright light and good circulation and then, CO2 enrichment helps a bunch.

I haven't done anything like clear experimentation to test the effects yet, but I have been playing with blowing in CO2 during the day (doing it at night doesn't help because CO2 is all about boosting photosynthesis and plants don't photosynthesize at night and it's seeming like the results are positive compared to my estimations of earlier growth. One last bummer about this system for generating CO2, you end up heating your greenhouse during the day. Out here in Northern California, it's already 75 degrees, so I'm working hard to get rid of heat. Burning my heater in the middle of the summer to get CO2 doesn't sound fun, but I can burn 1-2 lbs of wood in 20 minutes or so, so it doesn't take long to generate the CO2 you'll need.

One other huge reason to think about CO2 in a greenhouse, pest control. There's not a lot of research or guidance on this, but if you get CO2 up to 10,000 ppm, a level way past deadly for humans, leave it there for somewhere between 10-50 minutes, it also kills insects. It will kill any beneficial insects you have in the greenhouse, but it kills aphids, mites, anything. I've only done some limited testing with this and so far the results have been less than amazing. I did a few tests of burning 3-4 lbs of wood (to make sure I had enough CO2) in my greenhouse with it all sealed, left it for a few hours and came back later to check and it had almost no effect. I tried again with my flex tubing, blowing the CO2 almost directly onto the plants, again, almost no effect.

I did an experiment of taking a plant that was covered with aphids, putting it in an empty garbage bag, then filling the garbage bag with exhaust from my system - pretty much pure CO2. I checked 30 minutes later and 90% of the aphids were dead, but a bunch were just sleepy/groggy and started moving around after a few minutes.

I've seen this documented quite a few times (gotta love those pot growers trying out everything to boost production and I've got an aquaponics guru friend who swears by it, so I'm going to keep playing with it. I'm gonna try a few more test runs with infested plants in a garbage bag, see if I can figure out the time frame that does the trick. Then, my next idea is to put a small "tent" over one of my aquaponics rafts and fill that with CO2 and try that out. Aphids are a major problem for all the leafy greens I produce, so figuring this out is a significant priority.

I'm always curious to hear tricks folks use in their greenhouses and how rmh's fit into that. Let us know what you're thinking and trying - Rick


The box in the picture is at the end of my table where the exhaust exits. There's a fan in the bottom of the box that sucks the air through the table and provides draft for the rmh (blasphemy, I know, but it works great so far) and lets me direct the air where I want it to go. I have a cap for the T and I just cover whichever side I want blocked and let the air flow out the other.

Indoor composting or a very small charcoal burner would seem a safer and simpler way to add some co2.

Ernie, Erica and I go into extreme detail on why it is a terrible idea to harvest CO2 from a rocket mass heater for a greenhouse in this podcast: https://permies.com/t/18871

Currently have had greenhouses for nurseries or private hobby running on 26 years and working as a provider in neurology I am not afforded the time I use to have to have the spring nursery but I do 100% believe that with a stove such as this (much easier to maintenance than my miniature stove set up) the plants get the right amount of co2. I see sites advertise that you need “pure forms of co2 only” and I would like to see studies showing plants do any different or better by creating a carbon footprint to produce carbon. I make wine and my husband makes beer so we understand those manufactured systems. Try watching one explode due to neem oil getting in the wrong o-ring. The wood stove, or in this case your system is what I have seen plants respond to more often when stressed. I have brought back citrus trees and grown avocados in 10’ weather due to these systems so I would love to know more and help promote this. My system is simple but has heat activated fans with heat exchanges and my c02 monitor runs an average of 600-700 still in the green but without the stove it runs 200 and that means my 02 is far to high for my plants. Great for me but not my plants. C02 is needed and it has to be usable. Theresawaack@yahoo.com or I am on Gab gardening sites for profile purposes and being able to share this.
https://gab.com/TheAGressor

Would pumping CO2 from an exhaust of a stove create an oxygen free atmosphere that may kill you?