I have the relevant air sensor, it’d be really hard to blind it because it makes noise, and the behavioral effects thing is a good idea, thank you.
Just randomizing would be useful; obviously, your air sensor doesn’t care in the least if it is ‘blinded’ or not. And if it’s placed in a room you don’t go into, that may be enough. As well, maybe you can modify it to have a flap or door or obstruction which opens or closes, greatly changing the rate of CO2 absorption, and randomize that; or if you have someone willing to help, they can come in every n time units to replace the filler or not, giving you both blinded & randomized comparisons between high-CO2-removal vs low-CO2-removal conditions based on whether they pulled out the used filler or not, since the fan presumably still makes the same noise regardless of whether it has brand-new filler removing CO2 at maximum rates or expired tired filler removing only a little CO2. (Remember, experiments work fine comparing 100% removal rates to, say, 10% removal rates; it doesn’t have to be exactly ‘on’/‘off’, that’s just a bit more statistically-efficient because it has a slightly larger effect size, and you have to remember the estimate is a bit lower than the ‘true’ estimate because the ‘off’ condition has 10% of the benefits of the ‘on’.)
Just randomizing would be useful; obviously, your air sensor doesn’t care in the least if it is ‘blinded’ or not. And if it’s placed in a room you don’t go into, that may be enough. As well, maybe you can modify it to have a flap or door or obstruction which opens or closes, greatly changing the rate of CO2 absorption, and randomize that; or if you have someone willing to help, they can come in every n time units to replace the filler or not, giving you both blinded & randomized comparisons between high-CO2-removal vs low-CO2-removal conditions based on whether they pulled out the used filler or not, since the fan presumably still makes the same noise regardless of whether it has brand-new filler removing CO2 at maximum rates or expired tired filler removing only a little CO2. (Remember, experiments work fine comparing 100% removal rates to, say, 10% removal rates; it doesn’t have to be exactly ‘on’/‘off’, that’s just a bit more statistically-efficient because it has a slightly larger effect size, and you have to remember the estimate is a bit lower than the ‘true’ estimate because the ‘off’ condition has 10% of the benefits of the ‘on’.)