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Hello all - I am working on a feasibility study for a small-scale aquaponics farm, and have come up with a great idea for a greenhouse plan. I have found all my ideas are great ideas until someone shoots them down with a shot of reality, but then I can either scrap the idea, or rework it into a really great idea!

 

I would greatly appreciate comments from those who have experience - especially those who have been producing commercially. Here is the design:

Design goals –

1)      Low-cost

2)      Maximum use of greenhouse space

 

The Tank is a 3-1/2 foot wide channel, 4 feet deep, in the concrete slab floor.

  • Concrete is an inexpensive material. It must, of course be coated in a waterproofing epoxy paint.
  • The temperature of the concrete will be pulled towards the temperature of the ground, which, at 4 feet deep and below, is the annual average temperature of the region. (In southern middle Tennessee, this is around 63 degrees F). This is advantageous if the optimal temperature range of the fish to be grown is at and above this temperature, otherwise insulation should be used below and around the slab.
  • Batches of fish are separated from each other with PVC and PE netting on frames.
  • Water is pumped out on one end, and filtered water introduced at the other.

 

3-1/2 feet above the tank are media grow beds (ebb and flow) on steel benches. The fish tank is accessible below the grow beds, and a space at both ends of the tank channel are left open for introducing and harvesting the fish. The media grow beds are 4 ft X 8 ft X 11-3/4 inch wooden boxes coated inside with fiberglass resin (or other suitable waterproofing coating).

There will be additional rows of grow beds to achieve a 1:1 tank volume to media volume ratio. Water is pumped continuously to each of the four banks of grow beds in sequence to keep the water level in the fish tank fairly constant. The fish tank water level would reach the top if the pumps were turned off and the grow beds drained completely, but normally will be a several inches below the top when the pumps are running. The grow beds along the outer greenhouse walls are 2 feet in width instead of 4, so that they can be tended easily.

Beneath the grow beds that are not above the fish tank, are deep water raft beds, for growing salad greens. The water from the media grow beds drains into the raft beds. The raft beds drain into the fish tank. The raft beds are built into the slab similar to the fish tank, and are 1 foot deep.

Question – Will there be sufficient light in a greenhouse beneath the grow media beds for the lettuce and salad greens to grow well?

Both the fish tank and raft beds will have a 2 inch lip on either side to keep debris from the floor next to the tanks from being swept into the tanks when the floors are cleaned.

 Lots of other details, but this is the main focus.

 

TimW

 

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Yes, this will work Tim, seems like the raft beds are usually in line before the media beds (anyone?)

Floor level grow beds will be hard to service, recommend built up beds (12-24") using the earth from the fish tank hole to back fill the stem walls before you pour the bottom of the grow bed tanks, other wise you'll have to pay to haul that earth away in time or money

Don't forget to add NFT pipes hanging from the roof, lots wasted space and sunlight up there too

Be sure to add an earth coupled heat exchanger while you have the backhoe handy, saves lots of money and works well for both heat and cooling

Where are you getting your funding?

all the best,

Jim

The general consensus is media filled grow beds before DWC rafts (to acts as a sort of solids pre-filter...speaking of pre-filtering if you do incorporate NFT pipes you want to make sure that you are sending them 'clean' filtered water...how you do this is up to you, but solids and NFT don't work well long term...heck or even mid-term). So you're all good there...

Jim makes a good point...If you are taking the time to build a greenhouse and wish to operate it long term, some of the stuff that folks are doing/have done won't really apply, since in a year or two's time, many of those folks' hobby AP systems are collecting dust in parts and pieces strewn about the garage and attic...their fleeting love affair with AP having long since ended. Whereas you will need to clean, maintain, make repairs etc...so make sure your pipes, pumps, fittings and everything else is/are accessible for long-term maintenance. Harvesting fish may be a bit more difficult, but it sounds like you're going to partition off sections into workable lengths anyways...Supporting off the ground DWC troughs filled with water is of coarse going to take some hefty solid construction (and more money than building them on the ground).

Although your fish tank is 'insulated' keep in mind that your media beds and DWC troughs aren't (unless of coarse you insulate them) and that flooding and draining a media bed during the winter will cool your water down significantly (if the surrounding air is cold). the media acts as a cold sink/heat sink, so the option of running constant flood in the winter is a good one... 

Sunlight to the bottom tier depends on your location, location of the greenhouse, and how close the vertical distance between tiers is. Folk's descriptions of something "growing well" seems utterly subjective most of the time. Particularly if they are not having to sell/earn from what they are growing.

Pick an appropriate fish for your temps/region...unless you own stock in the local power company...

Good Luck Tim!

...(the idea/research phase should probably take much longer than the building/executing phase :) so keep at it until you are satisfied (and know why you are satisfied) with what you come up with...

Thank you for your thoughts --

 

I forgot to mention there is to be a space above each end of raft bed free of media grow beds - new plants are introduced at one end, and harvested at the other, with the rafts inched along under the media grow beds. I was hoping very little tending would be needed between the two. Am I wrong?

 

I like what I see reading about the zipgrow towers. Could the zipgrow take the place of deep water rafts for salad greens? In any case, vertical grow towers above the media grow beds looks like a good idea if I can figure out a good way to access them. Maybe something like a dry-cleaners' rail system? That would be cool!

 

Funding - Any suggestions? I have been looking over the USDA FSA web sites - they may be able to help. I'm sure there will be tons of red tape, but I have a good deal of planning to work through before I am ready to approach anyone. I am an unemployed engineer (for way too long) and my credit is now trashed. I plan on working a CSA marketing program for the sale of the produce.

 

Fish - Yellow perch like it 65 degrees F and above. I plan to do more investigating of the local river fish and pick one that grows reasonably fast and is good to eat. I do not expect to make much money from the sale of fish, but I would like to be surprised.

 

Heating and cooling - I plan to use solar collectors to heat an insulated tank of anti-freeze, and use pex pipe in the fish tank to reheat water coming back into the tank. The beauty of this plan is that other sources of heat can supplement when necessary - I want to experiment with methane digesters for electricity cogeneration, and engines put off a lot of heat as well. Truck radiators can be used to transfer the heat into the air in the greenhouse, and the same radiators might be used with cool well water in the summer to provide some cooling. I plan to use shade cloth over the greenhouse in summer to reduce summer sun by 30% or more. If I paint the concrete floor in the aisles white in summer and black in winter, the slab should help me too. Since I plan to use fish acclimated to the local average temperature, I will not be insulating the underside of the slab, but will insulate the sides. I will use two layers of greenhouse film (plastic) with a blower to keep air between them.

 

The greenhouse idea above is for fish that are half-way grown and older. For the younger fish, I plan to have a nursery and elementary school building with a few small tanks, 55 gallon drums and IBC totes for the fish. The accompanying greenhouse would not have a fish tank.

 

Thanks again for the suggestions,

 

TimW

Keep you media beds above your dwc tanks at least 18 inches smaller in width (currently testing) and aprox 2 feet above ... may want to check how the sun moves in you particular area so that you can calculate shadow. Plants should have at least 4 hours direct sunlight a day (based on current research).

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