Aeropwnics

Lettuce aeropwn.

Here is the design of a low-pressure aeroponics system in the style of AeroFarms.

Note: I haven’t implemented this yet, so take with a grain of salt.

Table of contents

  1. Design
  2. Parts & costs
  3. Design goals
  4. Implementation

Design

Basically, the design amounts to this:

Inside each tray, the system would look like this:

I may need a plastic sheet on the bottom of the tray to direct water to the out-pipe.

Parts and Costs

Per tray ↓

Parts Cost Link Image
grow tray $35/5 X 1 bootstrap
tray lid $26/5 X 1 bootstrap
net pots $11/50 X 32 amazon
collars $24/120 X 32 amazon
grow lights $60/6 X 3 amazon
PVC pipe & joints ~$10 home depot
uniseal (1/2'') $15/10 X 2 amazon
spray fan $7/60 X 32 amazon
Total $70    

Per system ↓

Parts Cost Link Image
reservoir $20 each amazon
reservoir lid $9 each amazon
water pump $20 each amazon
light timer $12/2 X 1 amazon
shelf $40 each amazon
Total $95    

Tools ↓

Tools Cost
Drill bit (11/64'') <$1
Hole saw (2'') ~$5
PVC pipe cutter ~$15

And of course, we need nutrients and stuff.

Design Goals

To design the best hydroponics system, I want to constrain the system design across a number of goals. Ultimately, the system that best optimizes the goals is an aeroponics system in grow trays with white LED light. For a brief introduction on hydroponics, see this helpful infographic.

Reusability

Popular types of growing media include perlite, coconut coir, clay pellets, and rock wool. But the best medium is no medium. Some hydroponics systems (i.e., nutrient-film technique (NFT) and aeroponics) do not require medium; rather, the roots hang in the air. In those systems, the only required materials are collars or a cloth, both of which are reusable.

Winners: NFT, Aeroponics

Efficiency

I want to grow the most plants in the least amount of space, vertically and horizontally. The popular deep water culture (DWC) system require buckets, which require a lot of vertical and horizontal space. Grow trays are much more space-efficient. The systems that utilize trays include NFT, Ebb and Flow (E&F), and aeroponics. All commercial hydroponics farms use trays.

Winners: NFT, E&F, Aeroponics

The passive Kratky method does not use any electricity other than for lights. Other methods, such as DWC and Wicking, only use air pumps (at ~2 Watts). Aeroponics only use a water pump (at ~25 Watts), while NFT, E&F, and and Drip use both air and water pumps.

Winners (from best to worst): Kratky, DCW/Wicking, Aeroponics, NFT/E&F

Productivity

A key contributor to a high yield is aeration of the roots. See video. Even plants that are said to not require much oxygenation benefit from root aeration.

Winners (from best to worst): Aeroponics, E&F/NFT, DWC, Kratky

Another important contributor is lighting, and white light produces bigger and better tasting soybeans than do red & blue lights. See video.

Winners: White light

Another feature of lighting is the amount of usable light usable by the system. Brief terminology: photosynthetically active radiation (PAR) is the light usable by plants; photosynthetic photon flux (PPF) is the amount of PAR emitted a system, measured in μmol/s; photosynthetic photon flux density (PPFD) is PPF over a 2-dimensional space, measured in μmol/m2/s, and decreases with greater distance from the light; daily light integral (DLI) is the integral of PPFD over time, measured in moles/m2, and different plants have different requirements at different stages. With the light around 6 inches away from the plants (as in this design) and with around 14 hours of lights on, the grow lights should produce around 300 PPFD. Each LED strip in the link above can produce around 200 PPFD at 6 inches, and I think it can produce 300 PPFD when three are used side-by-side.

Key: At about 6 inches, the lights should produce around 300 moles of light.

Scalability

In NFT, E&F, and Aeroponics, growing trays make scaling easier than buckets.

Winners: NFT, E&F, and Aeroponics

Ease of use

The Kratky method is undoubtedly the easiest to install. I imagine that the others are similar in their ease of installation.

Winner: Kratky

To maintain, I imagine that the systems are similar, as long as one uses a timer.

For ease of harvesting & reusing, see Reusability. The methods NFT and Aeroponics do not require any growing media, so I only have to pull the roots out of the collars and net pots without dealing with any media.

Winner: Aeroponics

Resilience

The Kratky method is a passive method that has no risk of failures from power outages or pump failures. DWC and Wicking only use air pumps which could fail. NFT, E&F, and Drip use both air and water pumps, and both can fail. Aeroponics only use water pumps, but there is potential for failure in individual sprays.

Winners (from best to worst): Kratky, DWC/Wicking, NFT/E&F/Drip/low-pressure Aeroponics, high-pressure Aeroponics

Deep water cultures, however, risk suffering from fungal infections in the roots (see video). In NFT, the roots can get waterlogged (see wikipedia). In contrast, aeroponics do not suffer from waterlogging or root rot.

Winner: Aeroponics

Implementation

In design. Will follow video. PVC fittings guide. Maintaining nutrients guide.

Written on November 14, 2019