Cooling plant roots when sunlight hits balcony

Cooling plant roots when sunlight hits balcony

Write about: Growing highland carnivorous plants in Mumbai’s superhot climate.

What STEM activity are you doing today? I am making a design to automatically cool pots for some plants that require cool roots (or they die) when the sun hits the balcony.

What is the STEM take-home point of today? Many ways to skin this cat. I’m hoping to make yet another one at the lab in a couple of weeks. Will share my plan. Seeking ideas to improve.

What is the STEM activity picture you want to share today?

Not sure if image shows up. If it doesn’t, let me know, I’ll post it somewhere else and try to add a link.

It is the partial plan for automatically running a fan when sunlight hits the balcony (for heat sensitive plants that want their pots always cool).The Peltier generates electricity (google Seebeck effect) if there is a strong temperature difference between two sides. One side has sponge with a constant drip of water cooling it with evaporative cooling. Other will focus sun rays to high temperatures onto the peltier.

Direct sun hits balcony, peltier generates power, runs a tiny fan onto the surface of wet clay pot.

Solved. :smiley:

But there are drawbacks to this plan. I’m concerned that the magnifying glass may make things too hot and eventually burn the gadget itself. There ware ways around this, one being to keep the distance between the Fresnel lens and the peltier less than the focal length, so that the light is concentrated imperfectly by design. Another idea was to use hotglue for the frame, so that if things heat up too much, the hotglue will melt and the gadget will fall apart, breaking the focus of the Fresnel. Sort of like a pretty destructive fuse.

Another concern is that the gadget may not create enough power to power a fan. This isn’t exactly the sort of high performance generating we expect from large solar panels, etc. The minor power however could be used to trip a switch to run a fan off the mains - this is cheating. lol

An alternative may be to focus the fresnel onto the glass tube of a small “educational toy” Stirling engine (also google it up…) and attach blades directly to the wheel it turns. This could work better and should probably be the first option.

The last, failsafe option is to use a small solar panel to run a fan. The most reliable and sadly, also the most boring option. lol.

What is your idea? How can this be improved?

What is the big STEM idea you want to share with us?

This is the idea… I’m not familiar with this format of posting.


I also have other ideas for projects I want to make. Many of them centering around cooling:

Also using a Peltier Module - cool grow "chamber"

For this, I intend to section off a small part of the balcony and cool it more dramatically using a combination of thermacol for insulation, evaporative cooling and two peltier modules (in this case given current and moving heat from one side to the other (and thus re-moving heat from the chamber). I have the equipment I need to make this. Matter of making it. I am useless at electrical wiring. If anyone can help, grateful.

Mini wind turbine from scrap bicycle wheels

Taping adjacent spokes of a bicycle wheel to create angled blades, taking out the bearings and attaching the wheel to a generator motor, which in turn attaches to a charge controller and whatever after that (did I mention I was useless with the electrical stuff?). The ball bearings part of the wheel could probably be repurposed to make a swivel mount, so that the gadget can always face the wind for maximum generation (like you see in commercial windmills) - no rocket science, just a single vertical “wing” attached to the opposite side of the turbine. Wind blows, gadget swivels to offer least resistance, making our generator face the wind head on. Done.

There are some others. Not sure if they should be mentioned here, or separate threads or if you people are interested… will see replies and decide how to proceed.

Happy to be here. :slight_smile:


Overwhelmed by the post. Suddenly the dark cloud burst open with several STEM projects. I am sure @jtd and @Ashish_Pardeshi will have something to say with your project.

Very happy that you joined us. We will discuss this project at this thread, and eventually, move this into a project for others to replicate.


Hahaha. I should have joined long ago. Like the lab, this forum is just my kind of thing and I don’t even have to figure out babysitting kid to participate. lol.

I keep doing these kind of things. Of interest to members may also be a misting system (which isn’t that big a deal, since parts were purchased and assembled and a timer added) and the result of that misting system - the ability to grow plants much better and grow several carnivorous plants from outside our climate. My current passion is to grow “ultra-highland” nepenthes species. Many of which will die if they don’t get cool night temperatures for extended periods. In the process, I am busting a lot of conventional wisdom in the growing community as well - for example the use of fertilizers. For some reason, the use of fertilizers helps the plants cope with adverse conditions better - though traditionally, carnivory is the source of energy for CPs and many have a reputation of being harmed by high TDS water.

But this is a somewhat longterm project and I don’t know how to share it short of trips - which are also inadequate to observe, manipulate and explain the acclimatization process over time. Etc.

Though I suppose if Raghu is game to babysit kid often, we could set up a parallel garden at the lab - we had discussed this, then it went nowhere…

Hi @Vidyut. Peltier devices are very poor generators / coolers. A peltier of sufficent size to drive a small fan would be too bulky.
The maximum junction temprature is 200C. At which point the device junction will melt. But I think that it will fail at a much lower temprature - 125C - failure mode being detachment of junction from ceramic base.
The device functions due to temprature differential. The cold side will have to be cooled externally, which will require more power than what the peltier will deliver, as you mention.
As a heat pump peltiers are very ineffecient. Their advantage is no moving parts, compact size and very accurate temprature control.

A Stirling engine - Direct conversion of heat energy to thermal pump - might be a much better option.
Additionally one can use it to generate electricity.
Philips Holland actually made such a device in the 60s. Kerosene fired.


I was thinking of getting one of these @jtd

And then to either use them to drive a fan (gears? rubber band?) or directly fix blades onto the wheel (may not be possible for this specific design, but there are other designs.

What kind of fabricating capabilities do we have, @Nagarjuna?

I don’t need a powerful fan, as long as it keeps air moving. Most of the work will be done by evaporative cooling, and since the goal isn’t to cool the outer air, but the contents of the pot, as long as the air is replaced, that’s a good enough fan.


Oh wait. It appears that this gadget on Amazon already has a motor attached. I was looking at that rather poor quality photo to see how I could modify it to do the fan and realized the thing “in the way” is a generator motor. lol. This should simplify things. It could be used to generate power and attach a fan or removed and a fan directly be powered mechanically.


3d printer
Big drilling machine
Grinding machine
Dremel with drill stand for tiny holes

Coming soon Self built
Laser cutter
Delta printer


lol. I don’t even know how to use half the stuff. I’m a simple gal (so far), though me getting my hands on new tools usually results in … ideas. The drilling machine should do the trick I think for most of my needs for now. How complicated can adding a few blades be?

Oh wait. We’ll also have to mount the fresnels :woman_facepalming:

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In which case a piezo mister should be capable of delivering a fine spray of 10um droplets.

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There are TONS of these. And here I was thinking it was my bright idea. lol.

My night’s video watching is set. May get even more practical ideas…


There is already a misting system installed that covers the whole balcony. 5 seconds per 15 minutes for low humidity, 5 seconds per 5 minutes in summer. More like flash cooling the air than wetting the plants, which get watered separately as per their needs.

That is better for cooling - high pressure water through small nozzle = flash evaporation = instant cooling. Can achieve a 5C drop easy in dry weather. Maybe more.

This is for cooling the pots specifically. The breeze is less between the pots and the mist doesn’t reach well to cool either. I’ll plant the species needing cool ROOTS into the modified zeer pot planters. The planters work on evaporation. Moving the air around the planters causes more evaporation. Though now that I think this through, the difference caused by the fan may be minimal - won’t know till I find out.

Edit: If the difference isn’t much, I won’t use it, and will use the power generated to run a tiny pump for drip irrigation :slight_smile:


What is the rating of the pump?

Piezo elements do not require high pressure. Consequently only a small pump to add a few mililiters of water. The mister is placed in the root zone and consumes 5W when operated. Pump depends on height to which water is to be lifted. I use a 20 w pump to lift upto 180 cm (6ft) for a few secs every hour. In the case of a small pot 30-40cm height a 5v 100ma pump operating once every 5 minutes is good enough. Pump operation depends on surface area of water storage. Piezo element has small 10um holes, hence cannot have water more than 15mm above the piezo as the water pressure overcomes surface tensioan and leaks through the 10um hole. Power effeciency as well as peak power is important for off grid application / power failure fallback.

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Sadly, the misting system is on mains. With current capabilities, I don’t see that going off-grid unless I install solar power - not a huge fan, but off-grid still rocks.

Will check out the Piezo element in more detail and get back ASAP.

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Ah. This is the “ultrasonic mist maker”. I have these. They are great for adding humidity to the air (and I do use them for that), but for cooling, did not seem as efficient as the high pressure misting. The goal isn’t only to create vapour, it is to consume lots of ambient heat while doing so. Of course, carnivorous plants LOVING high humidity is a bonus.

The high pressure misting, forces small droplets of water into the air (or even our bottle misters). The droplets are small enough to evaporate even with available ambient heat. THAT is what produces the cooling.

Also for cooling the matka, it won’t work, because there is nothing that moves the humid air away to increase evaporation. The matka has water. What it needs is warm dry(er) air.

But this gives me an idea. If I install the fogger high enough, the fog drifting down could create a similar effect for the ambient cooling.


Two types. One with holes running at 100-200Khz and produces mist downwards. Droplet size depnds on hole size, usually 10 -15 um. Diffusion is easy as it shoots a downwards jet. No splash on top.

The second type runs at 1-2MHz and produces mist upwards. Droplet size much smaller. This one also shoots a jet of water upwards which then creates a splash. The built in electronics makes mounting, water height control and splash quite hard. Mist diffusion is a problem too unless one uses forced air. To prevent splash caused spillage the container sides need to be 2-3cm higher than water level. Most of the mist produced then settles in the container and condenses into thw conatiner water. Only a small quantity flows out into the root chamber.

Hmm. Air draughts will disrupt downwards drift. HP mister also provides directivity.

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Also, automating the fogger is a bit tricky, as I found out to my peril when it ran out of water and fried a few of my Tissue Culture explants (they need 95% + humidity when just out.

Had been toying with the idea of creating a “system” for it with an upturned bottle mounted at an acceptable height. When water level drops, some water will flow out. When it rises, the mouth of the bottle going underwater will stop the flow (like the RO water dispensers where you upturn the 20 liter bottle on top of the dispenser.

Not fully automated, but better breathing time between refills than using from only a bowl. I tend toward low tech solutions. I suppose a higher tech solution with a water level sensor could even fit it permanently to the plumbing. Fill and forget…

And yes, this is quite high on my to-do list. Something like a hydroponics pipe fitted with foggers instead of plants to be installed across the top of the balcony. And um… an inverted container fitting to serve as a water tank.

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I have the electronics working well for several months.

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So my posting had been blocked for a while (new account throttling - it is actually a good idea)

@jtd and I took the idea ahead in a private conversation, which resulted in two ideas - a fogger based cooling + misting system and an aeroponics growing tower/pot.

Will make separate threads for both and add links here.

The original script seems to have lost the plot… or evolved into better ideas.


This is a great promise. We will find out a babysitter, and soon we will have a garden of insectivorous plants at our lab.

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