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.

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[–] 65 points 11 months ago (8 children)

I guess same as you get enough oxygen at home even if you don't open the doors and windows at all.

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  • [–] 34 points 11 months ago (3 children)

    It's called diffusion. Unless the greenhouse is hermetically sealed, and the rate of consumption does not exceed the rate of diffusion, the ratio of CO2 will be similar to that outside.

    A simple vent will be enough if not just small gaps in the structure.

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  • [–] 9 points 11 months ago (2 children)

    Also, most green houses have fans that can help circulate air in from the exterior.

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  • [–] 2 points 11 months ago (1 child)

    I'm inclined to think the fans are more for fanning the plants so they can perspire and breathe more readily. Many plants need a breeze to grow well.

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  • [–] 3 points 11 months ago

    Usually both, in my experience.

    You’ll have fans for plants that firm up stems and stuff, in addition to helping with transpiration.

    Then you’ll have fans or passive vents near the highest point that move air outside, usually for the sake of venting excess heat and humidity. If you live somewhere cold, these probably stay closed through colder times and are active/open only during the height of summer (these are often the passive vents). If you live somewhere warm, it’ll probably always be active fan-driven, and usually running.

    A lot of people have their ventilation system hooked to climate control sensors, so it only engages when it crosses a certain threshold.

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  • [–] 2 points 11 months ago (3 children)

    The oxygen level inside is lower than outside. It might affect your health.

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  • [–] 2 points 11 months ago (2 children)

    I can't tell if you're joking or not. Unless a home is small, effectively airtight, filled with people, and the doors and windows are never opened, oxygen concentrations aren't going to fall enough to be impactful.

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  • [–] 4 points 11 months ago

    CO2 levels can get too high on new construction, but that's a 600-1000 ppm increase.

    Elevation will have a much larger effect on your body's O2 availability compared to what humans can deplete.

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