Tuesday, January 31, 2012

Aquaponic grow room

I've begun to build my grow room inside my shop.
Over the years I have saved materials from various construction jobs.
So far all of the materials have been free.
As the project progresses I will add new photos.

Today I established a 30 gallon tank by using water and gavel from my existing pond.  Water is clearing slowly, but the real test will be when I check to see how well it's handling the ammonia.

Here is something interesting.  The bacteria in my pond filter failed to quickly establish a biological bacteria in my new filter.  I added (about 8 cups gravel in a 30 gallon tank) At first I thought the bacteria either went dormant or died in the winter, but when added to ammonia to the established system quickly converts to nitrate so it must be that it more inoculant  is required.

Windows are temporarily held in place.

Friday, January 20, 2012

Thermal Solar Collector

This guy probably has a better idea.  But I will leave the rest of my post in place because it might stir an idea

The Polycarbonate sheets shown here are refered to as Twin Wall and 5 Wall. They are extremely strong and UV protected, and often used for greenhouse glazing.

While I have seen polycarbonate used as a collector's glazing I have not been able to find an example of this type of material used as the conduit for a thermal solar absorber.

This light weight material would appear to be near to perfect for this application if placed in an insulated box with a black background.  An extra layer of glazing may not even be necessary.

The area would be well utilized with water passages, and at $57.00 for a 4x8 sheet the price is reasonable.

A manifold could be created by cutting back the inner walls by about 1/2 " and then sealing the end with an end cap.  A PVC quick connect could then be inserted into the side of the end cap for the plumbing.

Wood sides, rigid insulation, and twin wall polycarbonate, with a black absorber behind the polycarbonate sheet.  I've shown the end cap as translucent to provide an exposed view of  the inside channels which have been cut back  to create a manifold.  The extra strength of the end cap will make the quick connect more secure.   The end caps can either be sealed with an ultrasonic or solvent weld.

The melting temperature of extruded polystyrene is 240F well above the maximum temperature I would expect. 

2" of extruded polystyrene would offer an R-Value of about 10.

For a 4' x 8' collector the polycarbonate should weigh about 18 lbs. and 2" of  extruded polystyrene about 6 lbs.   A wood case is going to be the heaviest part of the panel.  A  4x8 sheet of 1/2" plywood weighs about 48 lbs.  and 24' of 1x4 pine weighs about 24 lbs. for a total of 18+6+48+24=96 lbs.  72 lbs coming directly from the case.

If a case were made of aluminum sheet metal,  I expect it would weigh about 25 lbs less and it would look more professional.  Since I often work alone I'm always thinking of weight.

Update 2012.01.22:

I found a some information about experiments using "Black Liquid Collectors" first built by Minardi and Chuang in 1975 which used a heat transfer liquid consisting of 3 parts Prestone II, 2 parts water and 3 grams India ink per liter.  The liquid was translucent, but it absorbed 98% of the incident solar radiation withing the first 1/4".

Minardi and Chuang performed further experimentation with tube spacing and and various additives.  Graphite was found to be the most absorbent.  It was also found that when the tubes were spaced one diameter apart the efficiency improved.  This is thought to be due to the greater angular collection area and the collectors ability to collect scattered light.  Similar results have been noted with Evacuated Heat Tubes.

Twin wall polycarbonate may not have the advantage of increased angular collection area, but the simplicity and cost of this system still makes it an attractive option which I look forward to using.

Monday, January 9, 2012

Thermodynamic Math

 I suggest using the site above.  

This page is a work in progress which I will continue to update
I'm seeking help from others for this and any other advise.
I checked my visitor stats and it appears this is a popular page.  I feel bad that I have yet verify these calculation, and want to say right up front -  These spread sheets need to be checked by someone familiar with this topic.   

I'm going to leave these two spread sheets alone for awhile, but if you would like to take a look at my progress, you may download them at these links.  
ThermDynamicDensity Spread Sheet - Formulas for Specific Density, Heat Density, Volumetric Heat Density, Conductance and conversions between the various system units.

 BTU Calculator  - Examines Costs and Design of Thermal Collection, Storage, and Heat Exchange

I'm anxious to get started, and I feel that I have learned enough to proceed with the aquaponic system before working out all the details of temperature control, and a mathematical model of the entire system. It really comes down to conservation, and in my case 80% of the loss will be through the glazing.  It seems the more economical approach will be to address this one issue.

I can't guarantee that the formulas are correct, but you may find them useful if you too are trying to work through these calculations.  My goal is to create a spread sheet that will offer a systematic approach, and all the calculations required in the design of a year round thermally balanced (72F +/- 10F) aquaponic green house system using solar to accomplish a minimal utility demand.

Eventually I would like to incorporate a graph to show the rate of change as the differential temperatures of the thermal storage and the aquaponic system change.

Here are some links I found useful, and some considerations I have pondered.

This is Good Information and A Great Calculator!
Link to these Calculator

I feel that the ThermDynamicDensity Spread Sheet has been verified. it's unfortunate that thermodynamic formulas are presented in so many different units.  I have done my best to verify the formulas from several sources, but the conversions become quite complicated.

Some conversions come from

Below I have attempted to set these calculators equal to the same measurement of 1 BTU = 1F and 1 British Pound.
In the Volumetric Calculator I used 1 BTU / 10 Imperial Gallons. 
I derived that from http://en.wikipedia.org/wiki/British_thermal_unit
"It is approximately the amount of energy needed to heat 1 pound (0.454 kg) of water, which is exactly one tenth of a UK gallon"

CLICK HERE for a video about calculating the energy captured from the Sun.

Sunday, January 8, 2012

Garden in my shop

I had an epiphany today.  My 48' x 36' shop has south facing doors.  My plan is now to remove a roll up door and replace it with polycarbonate and build an 8'x10' aquaponic room within the shop.  The material costs will be much less than if I insulate my existing greenhouse and I should be able to control the environment much easier within the shop. 
I found a pretty decent article about how to calculate the requirements of a Passive Solar Thermal Mass System. But I'm still looking for the entire package.  It's unbelievable that this information is so hard to find.

In an effort to understand the process I created this spread sheet.   
This spread sheet contains the formulas and data for Specific Heat Density and Volumetric Heat Density.  It's is probably more than we need to know.

I would like to add Coefficient of Heat Transfer and then create a systematic approach to entering the required data in order to design a Solar Thermal Storage System.

Just for grins, I just did a measurement of an unheated room inside my shop.  This room has no insulation in the floor and R19 in the walls and ceiling of this room which takes up about 1/4 of my shop.  The outside temperature has ranged from 43F - 65F and inside the room has ranged from 46 to 56F.   So what I learned from this is that the thermal mass inside this room levels out  near the low end of our daily temperature swings.

Update June 15, 2012
It's now June 2012 and the temperatures are over 100F  With the ad of an evaporative cooler the garden room stays at about 82F.  In February with a little help from an electric water heater element in line with the pump the room stayed a comfortable 70F.   The power to control the environment is probably costing me about $1.50 - $2.00 a day at 33 cents per Kilowatt Hour.  
Compared to previous green house attempts this is extraordinary.   This is still my first year and I'm experimenting, but I think I used too much supplemental lighting during the winter months.  Next winter I will cut that back and only use it to extend the hours rather than add brighter light.

Friday, January 6, 2012

Wet Sand Thermal Storage

The chart above would make water the holy grail of thermal storage.  But I'm 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.  I'm guessing that water has the best characteristics of both, but it has to transition through some sort of pipe..  Maybe I'm just making this harder than it needs to be.
As an example of what I'm 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 can't transfer that energy back out.

Everything I read is so reticent about the design procedure.  Some questions I still have are:
  • What's the optimal relation between the size of the collector and the storage?  
  • What's the optimal flow rate through the system and 
  • What should the diameter and length of the pipes be?

Original Post - 2012-01-06

I'm exploring wet sand thermal storage.  This drawing shows tubes which would carry the air from a solar collector through wet sand in a 3'x3'x12' 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.

I'll 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
I've 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.  ;-)

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 don't 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.

Monday, January 2, 2012

To insultate or not

Today on the Aquaponics Community website in the Arizona Aquaponics Forum , I raised the question about the cost effectiveness of insulating the tanks and grow beds, 

My intention has been to build this system outdoors, and grow seasonally appropriate crops, and raise fish that would endure the cold of winter.  But Kellen Weissenbach  has pointed me in a whole new direction.

Basically Kellen showed me that I could do a lot to improve my green house at a minimal expense.  By building the system inside, the additional thermal mass of a 275 gallon fish tank, 150 gallon sump tank, and the additional mass of the gravel grow beds might make the indoor system a better choice.  I hope to have my calculations done soon and know which path I will follow. 

If you are interested in the entire exchange CLICK HERE.


The 4' high 10' long south facing window has proven adequate for house plants and seed starts, but barely enough light to grow lettuce. I use the room for cuttings, seed starts and over wintering sensitive plants.  I do enjoy the atmosphere with running water, fish and vegetation, but my gardening is done outside under open air structures that keep the rain out of the systems.

Artificial light helped, but it's too expensive.