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It only takes three shoulder height plants (of a couple widely-available species) to recycle the CO2 produced by an adult human. Relevant talk: https://www.ted

It only takes three shoulder height plants (of a couple widely-available species) to recycle the CO2 produced by an adult human. Relevant talk: https://www.ted.com/talks/kamal_meattle_how_to_grow_fresh_air?language=en https://www.ted.com/talks/kamal_meattle_how_to_grow_fresh_ai...

googlryas 4y ago
Sure but this is about VOCs, not CO2, though lowering CO2 levels indoors certainly isn't a bad thing, especially if you're in a small room without ventilation.
gus_massa 4y ago
The numbers don't check out. It looks like he is using a weird definition of recycle the CO2 produced by an adult human. A normal person need about 2000 kcalories per day. That's approximately 500g (1/2 kg) (1 pound) of sugar. Eating only sugar is bad, but most carbohydrates and proteins have a similar kcalories to weight ratio. If the plant absorbs all the CO2 produced by the person, it must rebuild all that sugar back (and store it as cellulose, or starch or even proteins, but again all have a very similar similar kcalories to weight ratio.) So the plant must grow approximately 500g (1/2 kg) (1 pound) per day. That is like 15kg (30 pounds) per month, that is a weigh of a small child. Or like 150kg (300 pounds) per year that is the weight of one or two adults. Plant's don't grow so much. (Note that you can reduce the weight to one half is the plant only makes oil instead of as cellulose, or starch or even proteins, but it still too high.) Edit: Self nitpicking: About the reduction of weigh using oil, I used calories per gram instead of carbon per gram. Oversimplifiying: In sugar the simplified unit is COH2, that has one carbon per 12+16+2=30 atomic units. In oil, the simplified unit is CH2 that has one carbon every 12+2=14 atomic units. So the ratio is aproximately 30/14=2.14 instead of the calories ratio that is 9/4=2.5. Both are very similar, so the end remark is still correct. I'm not sure if it's a coincidence or if I think hard enough about energy per atomic bound it get obvious. Proteins are harder, because amino acids are more diverse. I left the exact calculation for someone else, but as a rough simplification let's use achain of valine. The building block is C5ONH9 that is a carbon for every (12*5+16+14+9)/5=19.8 atomic units, so it's something in between. Anyway, don't expect your plant to make too much proteins. Even soy overdosed with fertilizer has only like a 15% of proteins.
- lazide 4y ago
  Don’t forget that the plant would also need to receive enough insolation to do this AFTER inefficiencies in photosynthesis. As photosynthesis is only 11% efficient, and conversion to sugars is going to be only a partial fraction of that due to needs of the plants to support their own health and growth, we’re talking a VERY large amount of insolation. A completely impractical amount to have indoors, frankly. 2000 kcal == 2.3kwh. If we assume the plant manages to put half of it’s total photosynthesis output into sugar (very generous), and hits maximum theoretical photosynthetic rates, 5.5% of sunlight would be converted. A peak sun hour is 1kw per square meter. 5.5% of that is 50 watts. You’d need 46 square meters of peak sun for an hour to produce 2.3kwh worth of output, even assuming a lot of ideal output efficiencies. So yeah, total bullshit.
colechristensen 4y ago
This is not even remotely true. Carbon in, carbon out. In order for plants to balance that equation they have to grow about a pound of dry mass per day. There’s a reason the space station doesn’t just have a few plants up there instead of an advanced system to scrub and recycle air.
alar44 4y ago
Not even close. A human produces 2.5 lbs of CO2 per day. A full grown tree absorbs 50 lbs per year.

googlryas 4y ago

Sure but this is about VOCs, not CO2, though lowering CO2 levels indoors certainly isn't a bad thing, especially if you're in a small room without ventilation.

gus_massa 4y ago

The numbers don't check out. It looks like he is using a weird definition of recycle the CO2 produced by an adult human. A normal person need about 2000 kcalories per day. That's approximately 500g (1/2 kg) (1 pound) of sugar. Eating only sugar is bad, but most carbohydrates and proteins have a similar kcalories to weight ratio. If the plant absorbs all the CO2 produced by the person, it must rebuild all that sugar back (and store it as cellulose, or starch or even proteins, but again all have a very similar similar kcalories to weight ratio.) So the plant must grow approximately 500g (1/2 kg) (1 pound) per day. That is like 15kg (30 pounds) per month, that is a weigh of a small child. Or like 150kg (300 pounds) per year that is the weight of one or two adults. Plant's don't grow so much. (Note that you can reduce the weight to one half is the plant only makes oil instead of as cellulose, or starch or even proteins, but it still too high.) Edit: Self nitpicking: About the reduction of weigh using oil, I used calories per gram instead of carbon per gram. Oversimplifiying: In sugar the simplified unit is COH2, that has one carbon per 12+16+2=30 atomic units. In oil, the simplified unit is CH2 that has one carbon every 12+2=14 atomic units. So the ratio is aproximately 30/14=2.14 instead of the calories ratio that is 9/4=2.5. Both are very similar, so the end remark is still correct. I'm not sure if it's a coincidence or if I think hard enough about energy per atomic bound it get obvious. Proteins are harder, because amino acids are more diverse. I left the exact calculation for someone else, but as a rough simplification let's use achain of valine. The building block is C5ONH9 that is a carbon for every (12*5+16+14+9)/5=19.8 atomic units, so it's something in between. Anyway, don't expect your plant to make too much proteins. Even soy overdosed with fertilizer has only like a 15% of proteins.

lazide 4y ago
Don’t forget that the plant would also need to receive enough insolation to do this AFTER inefficiencies in photosynthesis. As photosynthesis is only 11% efficient, and conversion to sugars is going to be only a partial fraction of that due to needs of the plants to support their own health and growth, we’re talking a VERY large amount of insolation. A completely impractical amount to have indoors, frankly. 2000 kcal == 2.3kwh. If we assume the plant manages to put half of it’s total photosynthesis output into sugar (very generous), and hits maximum theoretical photosynthetic rates, 5.5% of sunlight would be converted. A peak sun hour is 1kw per square meter. 5.5% of that is 50 watts. You’d need 46 square meters of peak sun for an hour to produce 2.3kwh worth of output, even assuming a lot of ideal output efficiencies. So yeah, total bullshit.

colechristensen 4y ago

This is not even remotely true. Carbon in, carbon out. In order for plants to balance that equation they have to grow about a pound of dry mass per day. There’s a reason the space station doesn’t just have a few plants up there instead of an advanced system to scrub and recycle air.

alar44 4y ago

Not even close. A human produces 2.5 lbs of CO2 per day. A full grown tree absorbs 50 lbs per year.