Backyard Aquaponics
A place to discuss aquaponics

The following is my interpretation of the effects of ground temperature, based on my limited physics knowledge.
(If someone has knowledge which shows this to be wrong, please let me know so that I can learn from that knowledge.)

Earth below a few meters deep has an almost constant year round temperature.
Burying things at this depth provides a stable median temperature (Coober Pedy suffers freezing nights in winter and extreme daytime temperatures in Summer, yet underground homes there have a stable temperature between these extremes).
Lesser depths have greater temperature swings around this median temperature.
Surface temperatures can be above air temperatures in the sunshine, but follow the air temperature rapidly when shaded.


If you have a pond which is buried ~1 metre deep and not insulated from the ground, it will follow within a few degrees of the ground temperatures at the depth of the tank.

In summer, the ground will provide a cooling effect, in winter it will provide a heating effect.


Pumping the FT water through grow-beds will alter the temperature of the FT, and in this case the ground temperature will be forced to follow the air temperature with some delay due to the thermal mass of the whole system.

I hope this assists the discussion.
Tony

Tony great post , absolutely 100 % correct. No I'm not after a date:)

By the way ,, sorry if I'm "thread hi-jacking".

I am aiming for a temperature range of 23-28 Celsius ( Ideal for Jades). Let's say a constant 25 C is the tareget.
I live in Sydney , very close to the ocean , therefore, soil temperature would be exactly same plus minus a miniscule.

Ocean temperature vary between 18 -23 C.

If I bury the tank , I need to add heat 24 hours per day 7 days a week ,,etc etc.
The heat loses into earth would be great , need to build a small nuclear reator:)

Air temps are far more easily insulated against and air has far less mass , therefore far less effect.. Earth is a massive heat sink , great if you want to keep things at a stable temperature but a massive negative if that stable temperature is below or above , what you require.
Example ,, if i was living near the Ocean in Cairns , ocean temps ideal , therefore soil temps ideal and i'd DEFINATELY be digging holes for my tanks.

I know this is taking things to extreme ,, but have you ever seen an under-ground Igloo?

for those who are interested BOM posts soil temps at different stations
http://www.bom.gov.au/catalogue/observations/about-agricultural.shtml
http://www.bom.gov.au/watl/ down the bottom right is the selection area for each state's ag observations

http://www.bom.gov.au/products/IDQ60604.shtml Queensland
http://www.bom.gov.au/products/IDN65176.shtml New South Wales
http://www.bom.gov.au/products/IDV65176.shtml Victoria
http://www.bom.gov.au/products/IDW65176.shtml Western Australia
http://www.bom.gov.au/products/IDS65176.shtml South Australia

You have all the good stuff down there, we have to resort to sinking copper tubing with water pressure from a hosepipe and a long lead temperature probe to measure soil temps

Tony is right on the money as the tank will only be as warm as the coldest part of the system which is likely to be the growbeds due to low air temps and evaporative cooling effects.

Jim is in a great position to monitor his tank temps as its already been running for 7 months. It might be interesting to see how his temp swing averages out after a year or two.

Pumps should probably be turned off ,or an alternate pump drain system from a none fish source,at night to prevent beds adding to the heat load.

I hope that the effort I put into burying my fish tank was not wasted- I only partially agree with Hex and Chappo re the effect the earth will have on the water temperatures. My fishtank is insulated with expanded polystyrene sheeting- 25mm on the base and 30mm on the sides. And I am clearly seeing a benefit as far as temperature stability is concerned.
However I have today also insulated the growbeds with 75mm fibreglass batts bonded to a reflective layer and then a layer of Sisalation.
The layer of Sisalation was really to protect the somewhat fragile reflective layer on the batts.

Kewl Jim...... F1 tyre covers for AP

P.S.... what are your temps down your way lately Jim.... (air and water)?.... and how are your fish going?

Rupe, outside day temps vary from highs of low 20's and lows of freezing- light frost so far down to about -1.
In my shed the lowest air temperatures so far has been about 6 degrees. The lowest water temps so far has been 13 degrees.
The fish are doing well but are eating a lot less as expected with these temperatures.