Backyard Aquaponics
A place to discuss aquaponics

jimmy, i had glandular fever when they covered polynomials at school, stuffed me for the rest of the year, but yes, you are correct, i meant highest density

It has been really cold here the last few days and nights. Bit the bullet last night and put a 200 watt aquarium heater that I had lying around into the 1000 litre outdoor tank. During the day it is really having to heat 1300 litres (sump and tank) and at night just the tank. Anyway - seems to have been pretty effective because despite 5 or 6 degree nights and 14 degree days (worse when taking into account wind chill also), the tank is over 17 degrees right now. I will test again in the mornign to see what it is. I am quite sure that without the heater it would currently be 12 or 13 degrees going from history.

The GH and the buried tank seems to be helping me then vb, my water temp is 15c minimum to 17c with no heater - the air temp in GH is ~23/24c around noon each day (gets to 10c in morning tho)

Fish aren't totally comfortable but are eating

Hey WD, I heard on the aquaponics mailing list that the Israelis have bred a carp variety that is less bony, maybe look that up for yours?

Les -- how much do you think the ground is helping to keep warmth in the tank?

The submerged tanks are about 2c higher than the water in the gal tank, so I'm guessing at that amount - the gal tank has 1,700litres in it atm.

Working on a solar heating contraption (vb and I are in heated debate as to the best method to tackle this), with the water raised by about 4-5c above normal it will be better to come up with a more accurate figure as to loss/retention during the night

We were losing something around 1.5 degrees overnight for an 8 degree drop in air temp, for a 1500 litre tank, galvanised iron with no insulation or heating.

You can approximate the energy lost from the system depending on the temperature:
at 25 degrees, 4181 joules per kg per degree
(from Wikipedia, "specific heat capacity")

So we're talking about losing 4181 joules for every litre of water that drops by one degree, or in our case:
4181 x 1500litres x 1.5degrees = 9.4 megajoules

...and then you can figure out how much energy you need to input into the system to offset the loss. Remembering one Watt is one joule per second, so our 300W heater running for 12 hours overnight is contributing about 13 megajoules of energy to the system, which is enough to cope with about 2 degrees loss in temperature, meaning we come out with a slight temperature rise.

This has been reflected in the system's performance, as after the first night with the heater we kept the tank over 10.5 degrees (previously it had dropped to 9 and maybe lower), and after a few nights with heating it is now staying over 12. When the insulation is installed around the tank we should find that we can keep the water temp consistently at the maximum daily air temp (15-17 degrees at the moment) and as soon as that daily air temp goes up over 20 degrees regularly we should be able to turn the heater off to reduce energy consumption (presently 3.6kWh ~ 60 cents/day ~ $4/week, ouch!!).

It would be interesting to see a graph of the temp' loss over the colder hours of a larger mass say 3Kltrs, as to a 500 ltr tank and the input of energy required to stabilize.(wonder if they would both reach the same low during the morning with the smaller one getting there earlier and warming up quicker?)
high thermal mass = heat sink/release.
I was thinking about an instant hot water system purpose built of SS to manage temp' variations.
I am aware of the thought of solar heating but the time we need the heat is during the cold, so impractical.(boosters are not very efficent IMHO)
The thought of using a piece of equipment purpose built to heat is logical.
Gas fired being a better option. Creating a 'ring main'(?) controlled by thermastat for a few months of the year.
C1 ducks and awaits abuse for hijacking.

How many litres do the submerged tanks hold Les, and do they have pumps in them. The pumps will normally contribute a few degrees of heat to small tanks. My purging tank which is in my shed is staying at about 17 degrees with no heater. The shed does get cold at night so I am assuming it is the pump that is heating the water.

The surface area of the tank will be a big factor. I don`t think you could compare mass for mass without taking it into account.

Reason I asked is because if the tank is quite small and has a pump in it - you can guarantee that the pump will contribute in a significant way to the heat.

2 tanks holding 300l each with one pump - this will change to total water volume of 2,400l when I get the big one up and running