CO2 and relative humidity.

Is anybody aware of some sort of effect that CO2 may have on humidity? I just noticed something from my sensor plots today... my CO2 solenoid got disconnected for a second and CO2 injection wasnt happening... and I saw my RH rise 10%. Anybody know what's that about?

Does CO2 increase temperature? So if you cease CO2, the temperature will drop? I know for a fact that if you drop temperature, RH increases.

Good call, i noticed my temp sensor froze during that period rebooted and the temp did drop.

LegalizeNature420 said:

Does CO2 increase temperature? So if you cease CO2, the temperature will drop? I know for a fact that if you drop temperature, RH increases.

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I dont believe that statement.whats the average rh in winter temps, 20% at most. Cold winter air is dry as fuck. Same as ac air is dry. Hotter air can hold more moisture than colder air, unless you live in the freaking desert or Africa. I grew up in Florida on the west coast, hot and humid as hell. Now I live in michigan, cold as hell.in the winter and no rh.

DemonTrich said:

Hotter air can hold more moisture than colder air

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Exactly.

Imagine a cubic meter of air at 70F can hold 12 grams of water, but in actuality (absolute humidity) has 6 grams = RH 50%

Now the temperature suddenly drops to 60F and so a cubic meter can only hold 10 grams, that 6 grams in the air = RH 60%

LegalizeNature420 said:

Does CO2 increase temperature? So if you cease CO2, the temperature will drop? I know for a fact that if you drop temperature, RH increases.

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Yeah no its totally the opposite

ruwtz said:

Yeah no its totally the opposite

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Well, there goes that theory.

LegalizeNature420 said:

Well, there goes that theory.

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Wait, RH does does drop with heat...

If hotter air holds more moisture than colder air, then if I go from hot to cold with the same water content in the air.... the RH should rise.

Totally the opposite as far as how CO2 works, or how RH/heat works?

Yesdog said:

Totally the opposite as far as how CO2 works, or how RH/heat works?

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I thought he was referring to CO2. What I stated about RH is true.

Think amazon, high temps high humidity

Think antarctic, low temps low humidity.

DemonTrich said:

Think amazon, high temps high humidity

Think antarctic, low temps low humidity.

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I think though he's talking about relative humidity, not absolute humidity, and he's actually right to say there is an opposite difference for RH - the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.

High temps does indeed hold more total water vapor, and this is absolute humidity. An 80°F room can have twice the moisture in it as the same room at 60°F.

And re CO2, I would say the method of saturation determines temperature more than the gas in isolation: using a burner, for instance, will contribute to higher temps.

When it's lights out and no ac going, my room rh spikes from 55% to 80%. Lights on, with ac it's 55%.

DemonTrich said:

When it's lights out and no ac going, my room rh spikes from 55% to 80%. Lights on, with ac it's 55%.

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yeah, night time transpiration plus no AC to dehumidify some. Add a dehumidifier.

Adding a small heater to raise the temperature by several degrees in an otherwise cool wet growroom is a simple way to reduce the percentage of relative humidity when the lights are off and can be a useful stopgap measure while working on a longer term solution.