Aeroponics

In this chapter, we venture into aeroponics, a technique of growing plants without soil or an aggregate medium, invented in the 1920s and perfected by NASA in the 1990s. Inside an aeroponics tote, roots are suspended midair and frequently sprayed with atomized nutrient solution. The solution is broken up into fine droplets using high-pressure (7bar / 100psi) misting nozzles. High-Pressure Aeroponics (HPA) is a water-efficient method of growing plants. Due to the complexity of the setup, it is recommended for avid DIYers, for fresh starters, a soil-based Hempy bucket or Dutch bucket is more suitable.

Since the bottom of the aeroponics tote will also act as a nutrient reservoir this design is between aeroponics and hydroponics once the roots reach the water level.

This chapter splits into:

Tote: Large light-proof plastic container with a lid that has holes for net pots, bottom section acts as a reservoir
Aero module: Arduino monitoring and controlling the aeroponics system
Spray+Bypass: Solenoids controlling the flow of the nutrient solution
Tank: Pressure tank storing the nutrient solution
High-pressure pump: Re-charges the tank once the pressure drops below a certain point
Misting loop: Made from PE tubing, quick fittings, and brass misting heads that produce a fine mist
Car battery UPS: Ensures the misting cycles continue during a power outage

Gbox420 sketch: Aeroponics_Tank
SketchUp 3D Warehouse: Gbox420 - ShowRoom - Aero Tank tab
Or visit the Gbox420 GitHub page and download the entire project.

Requirements

When NASA optimized the HPA setup they observed the fastest root development and nutrient uptake when the nutrient solution was atomized to 30-80 micron-sized droplets. To get such small droplets the nutrient solution needs to be pressurized to 5.5 - 7 BAR / 80 - 100 PSI and forced through misting heads with an orifice size of 400 to 600 microns ( 0.4-0.6 mm / 0.016"-0.025" ). These small holes can easily become clogged, so filtering using a very fine metal mesh filter is a must. Timing the misting cycle is also a crucial point as roots cannot be allowed to dry out. The usual timer setting is spraying every 5-10 minutes for a couple of seconds only.

These metrics are from the article Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics written by Imran Ali Lakhiar, Jianmin Gao, Tabinda Naz Syed, Farman Ali Chandio & Noman Ali Buttar (2018), Journal of Plant Interactions. Based on these requirements the optimal and widely available parts can be sourced from ordinary plumbing components, especially drinking water lines, motor-home, and washing machine parts. Most waterline components are required to withstand a minimum of 10 BAR / 145 PSI pressure (Please make sure to double-check this on the manufacturer's specifications!), we will be on the safe side using a maximum of 7 BAR / 100 PSI pressure.

"The jet spray nozzles with 0.000635 m (0.025-inch) and 0.0004064 m (0.016-inch) orifice under the operating pressure pump at 551580.5832 and 689475.729 Pa (80 to 100 psi) deliver the drop size of 5–50 microns and 5–25 microns respectively. The ideal droplet size range for most of the plant species is in-between 30 and 100 microns. Within this range the smaller droplets saturate the air, maintaining humidity levels within the growth chamber. The conventional wisdom is that droplets below 30 microns tend to remain in the air like a fog and fail to achieve continuous plant growth. While droplets size more than 100 microns tend to fall out of the air before containing on the plant root, and too large droplet means less oxygen is present in the growth chamber."

Modern plant cultivation technologies in agriculture under controlled environment: a review on aeroponics

With aeroponics the following benefits can be achieved:

Re-circulating reservoir → No wastewater, smaller reservoir size
Oxygen keeps bacteria away → Healthier root system
No soil → Pests have no place to live. Lot less mess after harvest
Excellent for cloning cuttings

Drawbacks:

Component/power failure is fatal to the plants. Roots dry out within hours without frequent misting
Way too complex compared to the gains

For an overview on misting cycles check out this AeroponicsDIY's article.

Parts

Arduino Aero_Tank: Arduino sketch running on the Aero module. Controls the pump and solenoids, reads the pressure and weight sensors.
Tote: Non-transparent container with a lid that has holes for net-pots. Also serves as a reservoir.
Misting loop: Made from 1/4" PE tubing with Quick Connect fittings for brass misting nozzles. Placed inside the aeroponics tote to spray the plant roots with atomized nutrient solution.
Pressure tank: 12 liter / 3.2 gallon expansion tank for storing the pressurized nutrient solution. Re-charged every ~2 hours.
Drain tap: For manually draining the pressure tank during maintenance.
Pressure sensor: Monitors the tank pressure.
Pump: Diaphragm pump capable of creating 7 bar / 100 psi pressure to re-charge the pressure tank. Controlled based on the pressure sensor readings, turned on when the pressure drops below 5 bar/75psi and turned off at 7bar/100psi.
Spray solenoid: Controls the flow of the pressurized nutrient solution into the misting loop.
Bypass solenoid: Releases pressure from certain parts of the system. Used in multiple scenarios:
- Pump self-priming: To remove air from the tubes when the pressure pump turns on.
- Blow-off pressure pump: To release pressure from the pump's discharge side after re-filling the pressure tank.
- Blow-off misting loop: To release pressure from the misting loop when it is time to stop spraying.
Pre filter: Filters the water leaving the reservoir. Removes any plant material/debris that could damage the pressure pump.
Fine filter: Very fine metal mesh filter connected between the Pressure tank and the Misting loop. Protects the brass misting nozzles from getting clogged.
Check valves: Installed at multiple locations, only allows water to flow in one direction.
Aero table: Table with a single large weight platform to monitor the weight of the Aeroponics tote. Used to check the remaining amount of nutrient solution.