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Aeroponics — Root Temperature Control

Time flies — fast. It’s been about six months since my first aeroponics experiment. Here are the blogs on the first build: part 1 and part 2, in case you want to read them.

I live in Florida, the sunshine state, a so-called “tropical paradise”. As the commercials imply, we have lots of sunshine, beaches, cruises, palm trees, and umbrella adorned drinks. While all this is true (and usually beneficial), it hasn’t been favorable for the temperature control of aeroponics.

The Challenges

The heat in the root area poses serious challenges to an aeroponic growing style. Unlike soil-based growing systems or deep-water hydroponics, the aeroponic method has the roots suspended in air. Without thermo-capacitors like wet soil or water, the root temperature is susceptible to a greater degree of fluctuation. This ultimately causes root stress, and opens up the possibility of bacteria-related root diseases.

Maintaining lower and stable root temperatures will help:

  1. Reduce root diseases caused by bacteria.

  2. Create a temperature difference between the root and the shoot to promote a healthier transpiration process. This results in better nutrient delivery to the plants.

Therefore, root temperature control became the main focus of my second real attempt with aeroponics.

Active Temperature Conditioning

The first step was to get an active temperature conditioning unit. After scouring the Internet, I realized that getting an affordable temperature conditioning unit that would be suitable for indoor aeroponics wasn’t quite an option yet.

So I started building my own temperature control unit.

The Requirements

Here are the main requirements of the unit:

  1. Suitable for indoor use (limited noise, small foot-print, and easy on the eyes).

  2. Able to handle a small standalone aeroponic habitat. The idea is to provide customizable temperature settings for different habitats.

  3. Safe for plants, and green for the environment.

As I started designing and building, the list grew much longer…

The Design

Based on the above requirements, I went with thermo-electric components so:

  1. The noise could be manageable without compressors.

  2. It could provide both a chill/heat mode with simple structural design.

With these in mind, I begun lots of trials and failures, new designs and more failures, until gradually I found a stable state.

The final design is a detachable, portable appliance running on 24Vdc power. It consists of 3 major parts: Liquid Thermo-exhange and Circulation, Air Dissipation, and Smart Power Supply and Control.

It also got a professional makeover — looks better, right?

Design of Root Temperature Control Unit

The characteristics that I am proud of are:

  1. The unit is driven by a controller that uses a PID automation algorithm, which automatically adjusts workload and energy usage according to the temperature differences between target and feedback.

  2. The power control on the circuit board uses induction design and stable DC driving current to maintain relatively high efficiency. A power controller like this is usually costly. (Here is more information about Peltier effect, efficiency and an example.)

  3. The unit contains an internal pump that can self-drive nutrient circulation through the chilling/heating components. This only happens after first time use though, as priming of the pump is still needed.

  4. ABS case material is fire retardant.

  5. The tube and other parts that touch and are in proximity to the nutrients are food safe.

  6. The unit is detachable from the main growing system. It can be placed in a desired area, for example, outside of a grow tent.

  7. It supports both vertical and horizontal positions.

Temperature Control Unit Internal Structure

While all this sounds good, the biggest factor that affects cooling/heating is heat dissipation. The better the air circulation, the better the result. I always make sure to get good ventilation when I use the unit.

Together, with some of my geek friends, we managed to make s0me real life and attractive prototypes. Here is one:

Prototype of Temperature Control Unit

More Heat Capacity

In the original aeroponics model designed six months ago, the nutrient reservoir was located outside of the root chamber. In the current design, the nutrient reservoir is combined with the root chamber.

The benefit of the new model with the reservoir, is that the root area temperature can be stabilized by the high heat-capacity of water, reducing temperature fluctuation in the root chamber.

The extra bonding between water molecules also gives liquid water a large specific heat capacity. This high heat capacity makes water a good heat storage medium (coolant) and heat shield. — wikipedia

While it seems too scientific, I know it to be true from first hand experience. Temperature in South Florida (with the nearby ocean) is more stable than that of Las Vegas (a city created in a near desert).

The new design uses the bottom of the root chamber as a reservoir. The nutrient pipes leading to the spray nozzles are submerged in the reservoir, so that the nutrient spray has a temperature very close to the targeted one.

The spray and the resulting airflow helps circulate the air and unify the temperature in all zones of the root chamber.

Passive Thermo-insulation

It is intuitive to just beef up the root chamber’s heat insulation. Better insulation equals less susceptibility to ambient temperature change and less energy expenditure to maintain the temperature difference between reservoir and room temperature.

It is also worth mentioning that light should be avoided in the root chamber. This prevents algae from growing and clogging the nutrient spray nozzles.

The result

After several prototype iterations, the units were put to the test. The results were good! It can go down to 5°C (41°F) when the room temperature is about 28°C (100°F).

In the real growing trials, the unit was able to keep the root chamber and nutrients at 18°C (64°F) for 2 months and onwards, while ambient room temperature fluctuated between 20–29°C (68–84°F).

If you have questions, or are interested in making one, or want my friends and I to build you one like ours, leave comments here.

Stay tuned for the next post: Aeroponics — a remote accessible aeroponics controller.


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