Cool growing box + I will be at the HBSCE TOMORROW

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I intend to make a box for cool growing plants.

To explain my need, there are a lot of plants I grow that grow in climates where it is quite cold. Particularly at nights. In contrast, here the night temperatures drop under 20C for maybe a month or so.

While my larger plan is to acclimatize and grow these highlanders “normally” in our climate, acclimatizing for some does not happen fast enough and they die. Or they die when our summer hits.

I don’t intend to create “perfect” conditions for them (since the idea IS to acclimatize them), but I need some way to boost them through hard times.

I am thinking of several options.

Growing box

3168×1826 2.69 MB

This is a simple idea. A thermocol box with a dual peltier cooler on one side. Because the peltier tends to dry air a bit as well as cause condensation, something to collect the condensation and put it right back in the air with a fogger. Earthen pots for the plants inside, so they get cooled by evaporative cooling from the peltier breeze (and the somewhat inefficient cooling gets boosted a bit)

The top of the thermocol box, when growing large plants, will have a mosquito screen with holes for the pots/plants to come up through. The mosquito screen will be covered with live sphagnum moss (which also loves the cool and is also a fantastic evaporative cooler in its own right.

When there are small plants in the box, the top will be covered with (removable) glass. Mainly covered at night and open in day (or an unintended solar cooker…)

There is a controller I have that should switch the peltier on/off based on temperature. I want the cooling to come on if day temps cross 32 and stop after it drops under 30 and start at night if temperatures are above 25 and stop at 20.

This may not be perfect. The peltier may not be as effective as I imagine. Or it may become such a power hog that I’ll prefer dead plants anyway. lol

Hard to say, before I find out.

Option 2

I have a water cooling module to replace the fan on the cool side of the peltier. Can use it for periodic drip irrigation of plants that need cool roots. No construction involved, simpler to implement probably and may be better if the grow chamber turns out to be too much for the tech.

Also, I’m coming to the HBSCE tomorrow and bringing all this along to MAKE. Be there if you want to see/make it happen.

Yes this is short notice…

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Let’s explore and do whatever is feasible and possible.

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A question. I don’t have thermacol. Would it be easy to buy locally? Alternatively, we could make everything in a cardboard box and I can remove and fit it on thermacol when I get home…

Also, will thermacol be good for this kind of an application? (there will be water on the floor…)

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This may be useful for tomorrow

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So, we wired this up yesterday. It works. I’ll have to create a suitable thermal insulating box to mount it on. I will post a photo/video of it when done though it may take a while, as we finally got news that we will be moving into our own home in March. So now the question becomes whether to make one now (upcoming weather has cool nights for the most part anyway) or to install it in a more permanent and well designed way in new home (I didn’t pay for it, my parents did, but I CHOSE the layout we wanted for phenomenal sea breeze passing through the flat - this is going to result in a lot of evaporative cooling and power generation projects. My plan to conquer the world is to not even need a fan in peak summer :p)

But I digress. There is one unresolved question yet. What to do with the waste heat produced by the hot side of the peltier when it cools the box. Well, I could waste it, but that is… inelegant.

Options:

  • Use the waste heat to dehydrate a dessicant and dehumidify the air in the home this will make the indoor air seem cooler (even if it isn’t).
  • Use the waste heat to power a stirling engine to generate electricity or do something.

And then…

Among my reading on various cooling methods, I came across an interesting piece of information. Evaporative cooling works better with warm water/air. The compartments for ice or recommending cool water are more about the heat exchange from the ice than evaporative cooling. The low temperature actually makes evaporative cooling INefficient and essentially, the cooler becomes no different than putting ice in front of a fan.

This lit my bulb. In multiple ways. For one, it made me realize that using the cold air output from the peltier to power the air conditioner in the other thread will not work. The more voluminous hot air should be used instead.

But that is little more than an evaporative cooler. Which can be massively simplified by removing the consumption of the pump to pump water up, etc and replacing the whole thing with a simple “ultrasonic mist maker” - or the piezo element @jtd is using in his aeroponics set up.

Which brings me to a very curious and possible use case. An air conditioner that can be kept in the middle of a room with one side producing some minor cooling from the peltier and the other side producing a little more cooling from evaporative cooling. A bizarre side effect would be one side producing water and the other side consuming water, so the humidity of the room would probably remain unchanged.

As for use for cooling the plants in my balcony with the grow box? Hah. The heat output could be solved as simply as placing a zeer pot cooler for plants needing cool roots bang in front of it. Solved.

Indoor use mistmaker, plant growing use, zeer pot cooler. Same peltier set up.

Seems a bit too good to be true or people would have done it already?

What have I missed?

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