Fluidized Sand Filter using Airlift

Rob Nash asked me why I was doing this, I started to explain my reasons for looking outside of conventional aquaponic methods.  While writing I came full circle and saw that he was right.   It comes down to adding more media beds.  
Ive been saying its all about the Nitrates and began to see that as my primary goal.  I kinda got off track from the real goal which is to provide Nitrates to as much high density growing space as possible.
Ive got to quit thinking like an aquarium owner and more like a farmer.

But Ill keep this post available because the mistakes I make are something others might be able to learn from.
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Im still playing around with ideas for a fluidized sand filter.  I would really like it to run on airlift.

Heres a concept drawing.   I have done some small scale experimenting, and Im feeling like these concepts shown here may not work.  Joeys videos below demonstrate a proven system using both an air pump and a water pump.

* Further design has taken me away from Airlift Pumps and static bio filters, and into Moving Bed Filtration using an impeller pump. 

This idea may be a starting point for design, but my recent tests have shown that fluidization would be difficult to achieve as shown. 

Uaru Joey has a couple very good videos. 

Starting at 17:45 Joey talks about the amount of K-1 and other helpful specifications

Starting at 17:45 Joey talks about the amount of K-1 and other helpful specifications 

Here is a low cost filter I made as an experiment. 

Ill keep you updated.  Id like to hear suggestion.
CLICK HERE for my Moving Bed Media experiments

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Wet Sand Thermal Storage

The chart above would make water the holy grail of thermal storage.  But Im still looking for a complete equation that will show me how to build a balanced system that will take advantage of all the energy the solar collectors deliver.  I feel that it is important to consider the coefficient of transfer aka conductivity.  Im guessing that water has the best characteristics of both, but it has to transition through some sort of pipe..  Maybe Im just making this harder than it needs to be.
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As an example of what Im saying.  How effective would it be to put 100000 sq ft of solar collector on Lake Superior?  Not very...  Also the transfer rate must be considered.   A material that can hold a million BTU is not effective if it cant transfer that energy back out.

Everything I read is so reticent about the design procedure.  Some questions I still have are:

• Whats the optimal relation between the size of the collector and the storage?  
• Whats the optimal flow rate through the system and 
• What should the diameter and length of the pipes be?

Original Post - 2012-01-06

Im exploring wet sand thermal storage.  This drawing shows tubes which would carry the air from a solar collector through wet sand in a 3x3x12 box.

The ends of the pipes terminate inside of a 6" manifold on each end.
I need to do the math, but by comparing this system to others I estimate that if a 25F differential is attainable, it would store about 50,000 BTU of useable heat. 

I have calculated that the night time losses will be about 15,000 BTU/Hr if the outside temperature drops to 20F, so I may need to make the system a bit larger, but this does not account for the thermal mass of the 400 gallon aquaponic system with 3/4 yards of gravel, which I will hold at 70F with an electric tank heater.  Hopefully the solar system will significantly reduce the requirements of the electric heater. and provide a buffer in case of electric failure.

Ill add to this post as I figure out more of the design, and requirements of the entire system. But these raw numbers seem to indicate that the environment would be controlled even on the coldest nights.

Heat in the Summer is also a concern, but an evaporation cooler will be able to maintain the air at less than 90F, and the thermal storage could be cooled during the night.  A 3/4" PEX pipe could be embedded in the cool sand and used during the day too keep the tanks cool, but the nighttime Summer temperature differential is not as large and may not provide a significant advantage.   I will continue look for answers, but after reading about this simple solar stock tank, I feel quite certain this design will work.

One of the problems I see with this design is the coefficient of heat transfer through the wall of the tubes.
 In an effort to avoid this I have another design I want to run the numbers on.  The idea is to make stacking 16x16x8 Thermal Storage Blocks out of concrete. 

Click here for my SketchUp Files

Update 2012.01.08
Ive had an idea.
To increase the conductivity and coefficient of thermal transfer in the Thermal Storage Blocks; metal filings could be added to the concrete... Just spinning my brain cells.  ;-)
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To make these blocks PVC pipe could be wrapped in wax paper and placed in a form.  Concrete would then be poured into the form and later when the concrete has cured, the PVC pipes and wax paper would be removed. 

These blocks could be stacked to create the thermal mass, and the holes would provide direct contact for the air arriving from the solar collectors.  I suppose ordinary cement blocks could be used, but these blocks would be engineered with less air space, and more concrete for a greater storage capacity per cubic meter.

I dont know if there is any advantage to wet sand over dry concrete,  but one other advantage I see to the blocks is that construction would be simpler because the manifold would not have to be water tight.

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