The Aeroponic Wall System

(Updated Sunday, February 02, 2003 )

In the image above, you can see our first attempt at "Aeroponics."  This hydroponic system feeds the crop by spraying a mist of nutrient solution directly onto the roots at a preset interval.  The "Aerotubes" Darrin invented are sloped at a steep 1/2" per foot to allow the condensed nutrient to rapidly return to the supply tank, where it is reused.  

In the example above, we have three tubes in production, growing a few varieties of lettuces: Red Oak Leaf, Bronze Mignonette, and Butterking in the two upper tubes, and some varieties from a packet of "Mesclun Blend Salad Greens."  We cannot identify the large things in the center of the lowest tube, but on the left and right sides you can see Red Giant Mustard - a tasty addition to any salad.  Next to the left Mustard plant, you can just make out "Garden Cress," a piquant Mesclun green.

Here's a close-up of some Oak Leaf from the Mesclun Blend seed packet.  It germinated in a Grodan 1" rockwool cube in mid-October and was placed into a 2" net pot in the Aerotube in the last week of October.  This is three weeks from a seed, in early November... 

Withdrawing the net pot reveals the root system as it begins to develop inside the Aerotube...

After six weeks in the Aerotube aeroponic system, Bronze Mignonette looks like this when withdrawn for harvest!

If you are interested in the construction of this aeroponic system, you'll find that information below!  However, visitors to this WebPage should note the following...

 As hydroponics go, aeroponics is one of the more mechanically dependant methods.  If the pump, solenoid valve, or timer were to fail and prevent the nutrient solution from reaching the roots, they would quickly dry out and crop death would soon follow.  Also, an interruption in electrical service could wreak havoc.  We are quite fortunate to have our greenhouse connected to our home's alternative energy system.

We keep spare parts handy, but that's no guarantee for avoiding catastrophe!  There are much simpler methods of growing lettuce with hydroponics.  (Water Culture is an excellent example, and it is widely used by many commercial growers around the globe.)  Darrin chose to dabble with aeroponics as he was most intrigued by the technique.  It was that interest which led us to build our greenhouse and start producing our own food. 

To construct our system, we began by preparing the support framework and pressure system to feed the individual tubes.  The support is made from redwood 2x4s, lag-bolted to the east greenhouse wall.  We fastened the supply pump and a small captive air pressure tank to the cross brace...

In the image above, you can see the nutrient reservoir, main pump, pressure tank , solenoid valve, interval timer which controls the solenoid valve, and aquarium air pump   Here are details on the parts in the image...

  1. The main pump is a 115 VAC Surflo diaphragm pump.  (Surflo # 2088-594-144)  It is a "demand" pump and has a built-in pressure switch which turns the pump OFF at 50 PSI, and ON again at about 30 PSI.  

  2. Pressurized nutrient from the pump is stored in the two-gallon gray pressure tank (available at Lowe's under the brand name Water Ace - part # RPT-2.  Sears has them under a different name too (?)  - ask in hardware for a "two-gallon captive air tank.")

  3. The 115VAC-coil 1/4"-bodied solenoid valve opens when the interval timer energizes it.  This allows pressurized nutrient to flow into the Aerotubes and feed the crop.  (Grainger or another industrial supply house can help you with this item.)

  4. The ART2 interval timer, available online from many hydroponic suppliers, is the "brain" of the automation.  ON times can be set from 30 seconds to 20 minutes, and OFF times can range from 3 minutes to 120 minutes.  We're currently running our timer ON for one minute and OFF for five minutes.

  5. An aquarium air pump is also energized with the solenoid valve.  It aerates the nutrient and keeps it stirred up while in the reservoir.

  6. The nutrient reservoir made from a Rubbermaid storage tub.

It only takes about 20 seconds for the main pump to charge the pressure tank with nutrient.  So little nutrient is used by the misting system inside the Aerotube that the main pump only runs once every three cycles, or eighteen minutes.  

Construction of an Aerotube begins with the preparation of a piece of 6" PVC 3034 sewer pipe.  In this case, we've cut them to exactly eight feet long, and spaced our holes seven inches apart.  This spacing begins and ends at six inches in from each end.  All holes are drilled with a 1-7/8" hole saw, except for the last hole in the far end.  This is drilled with a 1-1/8 hole saw.  The 12 larger holes will receive the 2" net pots, while the one smaller hole allows the misting system to enter the Aerotube...

aerotubes-drilled.jpg (25212 bytes)  

We build our internal misting rail next.  You can see below how it lays out inside the Aerotube, once it passes through the 1-1/8" hole.  Six misting nozzles are used in each rail,  every nozzle sprays an "atomized" mist in a 105 pattern, and will pass 1.6 gallons per hour (GPH.)  They are found between every other plant location: between 1 and 2, 3 and 4, 5 and 6, 7 and 8, 9 and 10, and 11 and 12... 

misting-pipe.jpg (23583 bytes)

 For simplicity, the nozzles are screwed directly into a piece of 1/2" PVC pipe.  Correctly spaced holes are drilled out to  21/64" then carefully tapped 1/8"-27.  Here are internal and external views...

   

The "feed-point" of the misting rail utilizes a 1/4" body check valve to prevent nutrient from flowing back out of the system through the lower Aerotubes.  Each rail also employs an industrial-series quick-coupler. This allows for the removal of individual Aerotubes for service or cleaning, without interrupting nutrient delivery to any other Aerotubes in production... 

mist-tube-feed-point.jpg (10941 bytes)

Each rail's quick-coupler is connected to the output of the solenoid valve via 1/4" (OD) PE tubing.  Looking into the drain-end, you can see how it all comes together, with the net pots above, and the misting rail below...

inside-tube-from-drain-end.jpg (16810 bytes)

Both ends of each Aerotube are closed with 6" sewer caps.  These are NOT glued in place, but don't leak because of the angle of each tube.  (It's important to be able to open the Aerotubes so that they may be cleaned and serviced later.)  The drain-end cap is drilled to accept a PVC 1/2" female adapter.  Into this adapter, we have screwed a 1/2" compression fitting, so that we can use flexible PE pipe to return the nutrient solution to the reservoir...

end-cap-drain.jpg (22592 bytes)

 

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