Constructing a HEPA humidifier
Kyle et al. just wondering what the parts diagram would be for constructing the HEPA humidifier discussed in the Mycodo V2.0 build https://kylegabriel.com/projects/2015/02/automated-mushroom-cultivation.html ? Seems like a computer fan+filter+smallish humidifier controlled via a relay?
What is the size of the airspace you'll be humidifying? This will be the biggest factor for choosing the filter, fan, and humidification unit/technology. Also, what is an acceptable rate of humidification? If it's a small airspace, this should be negligible, but if it's large, you will need a sufficiently-sized humidifier to raise the humidity in a reasonable time. Will the airspace that needs to be humidified be sealed/contained or will you require fresh air exchange, and if it requires air exchange, does the air need to be exchanged continuously or periodically?
I think the container will be 6-10 liters. So I think the rate of humidification should be negligible. I plan to put the temp/humidity sensor on the bottom/center of the container inside a vented petri dish, since each petri dish will have some sample in it, to get a better reading of the micro environment inside each petri dish.
Would it make sense to have some sort of ultrasonic fogger+fan to add humidity to the cultivation chamber?
Since the airspace is so small, I would recommend using a small fan and ultrasonic fogger. You can use DI/purified water for sterility and ethanol/bleach the fogger before submersion. I'd recommend the fan to homogenize the airspace. If you don't need to refresh the air (introduce new air), then you can do without the HEPA filter and make the build much simpler (and less likely to introduce contaminants). Keeping the sensor inside a Petri dish is a good idea, however the humidity within a plate with agar will probably be significantly higher humidity than an empty plate. If you want the most accurate airapace humidity coming into contact with the culture, you might want to experiment with having the lid off, however this may be difficult to keep sterile, as the circulatory fan will potentially bring any contaminants into contact with the agar.
There won't be any agar in the petri dishes, just nitrocellulose filters so I think the RH and temp would be reflective of what the filters are seeing. I believe we are also going to line the bottom of the chamber with desiccant for dehydration.
We decided on this fogger ( https://www.petco.com/shop/en/petcostore/product/zoo-med-repti-fogger-1261126?cm_mmc=PLA-GG-_-PTC_P_SUP_PLA-GG_FY17_SCShopping-Branded-_-52383123058-_-A&kpid=go_1032659747_52383123058_244459568299_aud-474167082703:pla-554103881650_c&scid=scplp1261126&sc_intid=1261126&utm_config=tad0iunwp&utm_campaign=PTC_P_SUP_PLA-GG_FY17_SCShopping-Branded&utm_source=google&gclid=Cj0KCQiAzKnjBRDPARIsAKxfTRBW8PFR2lgp8wNWaedEdYDVQUNbRc6Dls092CqPyBVm-o1jWZ6XqEYaArKkEALw_wcB), set to the max humidity, controlled by the power outlet relay ( https://www.adafruit.com/product/2935?gclid=Cj0KCQiA-onjBRDSARIsAEZXcKbNX_IXiPLHXyq-5PEgNU_-nQPO1AhbJEm2AQSmLyfIpBZ47oWXeUUaAnydEALw_wcB). I think we could probably get a cone to fit a fan inside so this remains sealed? Do you have any recommendations on a waterproof fan for this application? I would assume we could plug both the fogger and the fan into the "normally off" spots on the relay power strip.
If there's no agar, then inside the plate should be the same as outside, as long as the air is homogeneous, which is why I would recommend a small fan within the chamber.
That fogger looks appropriate, and it makes keeping the water at the right level easy by providing the vessel and mechanism for auto-filling the vessel from the bottle when the water level drops. If you can fit the entire humidifier in your chamber, this would be the easiest for keeping the air sterile (so long as every piece of the humidifier is cleaned with bleach/ethanol prior to going in). If you do keep it outside of the chamber, you may have to consider the air introduced is going to need to push air out unless you have a duct going back to the humidifier. Some humidifiers have a dedicated intake area (sometimes with a coarse mesh filter) so ducting might be easy, but others just pull intake air from multiple locations around the humidier body, which could pose a problem if you choose to keep the humidifier out of the chamber.
For that switchable outlet, I would put a small circulatory fan plugged into the always on outlet and the humidifier plugged into the normally open (NO) outlet. The humidifier should have its own internal fan that turns on with the humidifier. This internal fan may pose and issue if it only turns on with the humidifier, as the humidifier may only turn on for a fraction of a second to regulate the humidity, which may not be enough time for the fan to move the humid air from the humidifier to the chamber. You may want to consider rewiring the humidifier fan to be always on. If this is done, it can act as the chamber circulatory fan (and an additional circulatory fan won't be needed).
How many CFM do you think the fan should be that's homogenizing the air within the chamber? I saw one at 51 CFM, probably too fast?
That seems a bit too fast to me. I'd recommend a small computer fan no larger than 70 mm. ~10 CFM should be enough.