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Epiphytic Utricularia Grow Chamber

collin

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Joined
Apr 13, 2015
Messages
135
Location
Los Angeles, CA
Hello! I built a grow chamber. My goal was to create a small slice of Venezuela in my care. So, that means warm, dry-ish days and cool, humid nights. Given that I live in a small apartment (cold basement? I wish) in southern California (humidity? what is that?), a small grow chamber in my living room is my best option. There were a couple additional constraints - this grow chamber cannot be too loud (as it is often only a few feet away from myself and my fiance) and it "cannot look like a science experiment" (in the words of my fiance). Eh, probably for the best that there aren't tubes and wires everywhere.

But before I get in to the build, I want to say that this setup is absolutely overkill for several species in the section. Many people grow alpina and humboldtii on sunny windowsills and the plants are perfectly happy. That being said, other species are a bit more demanding to grow. So, if you're interested in growing plants from this section (and I really encourage you to do so as they are wonderful plants) please don't think you need a fancy grow chamber. You don't. Anyway, here's what I ended up building.


After a bit of research, I decided to use water to regulate the temperature of the tank. Heating is easy, a small aquarium heater should be fine. Cooling is a bit trickier, but I had seen some water-cooling setups for terrariums before. The ones I had seen seem capable but they also appear to have some room for improvement. Most of the setups use an aquarium chiller and a pc water cooling fan/pump; this seemed to work just fine when the fans are turned up relatively high. But, I didn't want to rely on high wind speeds to transfer heat as that would increase transpiration, causing stress for these plants.

So, I found a peltier aquarium chiller; I figured that it should have plenty of capacity to cool a 20 gallon high aquarium. They are also pretty quiet (there's no compressor like in an air conditioner, just a fan). Most importantly, it wasn't going to look like a bomb (as it undoubtably would had I tried to make one). In order to transfer heat from the water to the air and plants, I decided to make the water reservoir out of aluminuim and put it inside of the tank. I also put an 1/8" aluminum plate on the bottom of the tank to further help with heat transfer, but I'm not sure how relevant this bit is to the efficacy.

You can purchase aluminum plate cut to size from a commercial metal distributor (or online). After buying the aluminum, I filed down the corners/edges, sanded the corners/edges, scuffed it up with scotch brite, and washed it. I taped it together with painters tape and used silicon sealant to seal up the box (I ended up using loctite silicone waterproof sealant, but GE 1 probably would have worked as well). After letting it cure for 24 hours I leak tested for another 24 hours. Once I verified it was watertight, I removed any excess silicone and spray painted it (it would have been better for lighting if I left it reflective - but I chose form over function here). I did not spray paint the place where the bottom plate meets the reservoir; a square on the bottom plate and the bottom of the reservoir remain unpainted to facilitate heat transfer. After the paint dried I added small hot glue "feet" to the bottom of the aluminum plate (so that it wouldn't scratch up the bottom piece of glass). I then put everything in the tank and tested it out.

https://flic.kr/p/2kTz9G6
It's not entirely done - there are a couple of things that need to be finished. I need to cut out the top out of acrylic and finalize the control electronics (which are responsible for the mess of wires in the back). For the control electronics, a raspberry pi regulates the lighting, humidification, temperature, and fans of the tank. The lights go on/off at sunrise/sunset in Venezuela (adjusted to my timezone, if the sun sets at 630 in Venezuela the lights turn off at 630 my time). In the morning, an aquarium heater kicks on to heat the water. At night, an ultrasonic humidifier turns on to increase the humidity and the aquarium chiller switches on to cool the water. In order to save energy, the setup will read the current humidity/temperature from a few sensors and will automatically turn on/off the appropriate devices in order to match the target humidity/temperature. The target is calculated based on historic weather data from Arabopo, Venezuela (1500m). For example, at 7PM on April 15th it will try to match the humidity/temperature from the average 7PM in April. Yes, it's a bit extra. This is all a bit extra. There are three fans in the setup; they are all waterproof 12V computer fans running at 3.3V - they're running a lot more slowly and quietly than normal. They just slowly move the air - they don't blow the plants around.

And at this point, I'm sure you're thinking, "Cool, but how effective is the system? A fancy control system doesn't mean much if the components don't do their job." But yes! Both the aquarium chiller and heater do an excellent job with this set up. It is able to increase/decrease the temperature by 5-6C (9-11F) from ambient - although it takes a few hours to do so. This means that it has no problem reaching 15C (59F) on the average night or 30C (86F) on the average day (in my home, at least). The only difficulty is that the system does put out a fair amount of heat - especially during the day. It would require less human intervention if I had AC - but I'm more than happy to open up the sliding door in the afternoon to help cool my living room down a bit. I normally do so when it's warm, anyway.

At the end of the day, I'm really happy with the setup. Integrating these plants into my living space means that I'm able to appreciate them every time I walk by, while sitting on the couch, from across the room while eating dinner. It means that I get to share them with friends and family (who are now vaccinated and starting to visit), with my fiance (who now takes a moment to check out their progress every morning [she is away for the weekend and mandateted that I need to send her a picture if any flowers open while she is away {they won't, maybe in another week or two}]). But yes, this is absolutely 100% overkill for growing most of these plants. The process of building it was half of the reason why I built it. It isn't perfect, though. The biggest difficulties that I have are related to humidity regulation. I don't have a good solution to decrease the humidity during the day that doesn't involve venting the aquarium (and thus decreasing the temperature). And, the humidity naturally condenses on the cold aluminum at night, decreasing the humidity when it needs to be high. I'm happy to hear any suggestions for these problems!
 
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Gadzooks

Supporter
Joined
Jan 28, 2021
Messages
153
Location
Connecticut
I love what you have done here! This shows such a commitment to meeting the needs of the plants in your collection. How did you compile the historical climate data and map that to the controller?
 

collin

Supporter
Joined
Apr 13, 2015
Messages
135
Location
Los Angeles, CA
Thanks @Gadzooks. There are several places that have freely available climate data. The NOAA has a bunch of free data available. World Weather Online also has a lot of data, you can either purchase a CSV from them or scrape it from their website. You can find real time data from Open Weather Map, if you'd prefer to take that route as well. I also used Falling Rain to help me correlate weather stations with elevation data.

Here's the climate data for the location that I chose, and you can copy it over to your own google sheet with this link.

Once I had the hourly climate data, I calculated the average temperature for each hour and month combination (ie midnight in January, 1 AM in January, etc).
In order to figure out which devices need to be turned on to match the target temperature/humidity, I needed to read the temperature/humidity in the grow chamber. There are plenty of sensors which do this. You can buy sensors which have already been wired and assembled in a waterproof case here and here. Alternatively, you can assemble the sensor (found on mouser or digikey) in a waterproof casing yourself to save a few bucks. Most sensors have a python package already written for them so reading is as easy as writing "sensor.read_temp()".
From there, it's just a matter of turning on and off various devices in order to heat/cool/vent/humidify the grow chamber. There are two ways to do this, with varying degrees of fire risk. If you aren't an electrician and aren't comfortable messing with the 120V power, you can buy an enclosed power relay. If you are an electrician or don't mind messing with high voltage power, you can build one yourself for much cheaper. Either of these works the same way, by raising the voltage of one of the inputs the device is switched on. When lowing the voltage, the device is switched off. A raspberry pi (and an arduino) both have general purpose input/output pins which can you programmatically set low/high, depending on your needs.

But yeah, that's pretty much it. Calculate the average, read the temperature/humidity, set the appropriate pins to low/high. Happy to share the python script if you're interested (although it is still a work in progress).
 
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