Backyard Aquaponics
A place to discuss aquaponics

i don't think you will achieve much with such a small coil of plastic in the air.. plastic is insulating more than you think and convection is not very good at heat transfer..

maybe seal with silicon and fill with radiator coolant? (has antifreeze and anti corrosion stuff)

you will also find that the tanks in the center will probly never freeze as the heat input (water in) is inbetween the cooling coils and the tanks..

but if your pipes drain at night when the temp drops and you turn your pump off they may have a chance to freeze..

for a system like this i think an air-con would be better.. they are made to run at a higher heat transfer and a higher temp (cool a room of 50Sq metres from 40°C to 25°C lets say) not at freezing temps and in such an insulated area with an already frozen mass inside.. you must remember that a freezer is design more to MAINTAIN a sub zero temp in 1.5Sq metres then to drop 50Sq metres 15°C in half an hour
anytime you turn her on