I know that a greenhouse is not air tight so I imagine it breathes somewhat and exchanges gas with the outside. However, I also assume that it’s going to use up the co2 in it for plant growth. How does it not run out? I think you could vent it, but then wouldn’t that cool it off and thus defeat the purpose of a greenhouse? All my web searches either give climate change facts or co2 supplementation by farmers.
To put some math around CO2 usage:
The entire structure of plants is built primarily from CO2. A tomato plant and fruit grows from seeding to maturity in about 60 days, and will yield about a kilogram of dry plant mass.
That mass will be about 20% carbon, meaning each plant would need to uptake a net 3.3 grams of carbon - 12.3 grams of CO2 per day. A person exhales around 1Kg of CO2 per day, or about as much as would be needed to supply 81 tomato plants.