Backyard Aquaponics
A place to discuss aquaponics

Just tossing around a few ideas...

Designing a system for heating AP tanks for Barra and Tilapia over winter as cheaply as possible.

Idea is to base any designs on Fayes system.

Many tropicals, such as Tilapia and Barra like temperatures around the 25 deg C mark but tilapia for example will just about tolerate 17 deg - 35 deg C.

Here in Perth we get a nice mediteranean climate and therefore have a window for unheated tank culture of warm water fish such as tilapia, Barra, various tropicals in the baackyard in the summer months.

In winter we need to heat.

I am thinking that insulated solar, coupled with electric heaters in the very cold times may be worth a shot.

Imagine developing Fayes system to keep Barra or other warm water fish though the winter using as much sun as possible and only resorting to electricity when in dire straits. Therefore limiting cost.

For the heating option there could be some type of electronic sensor system connected to a separate tank that is heated via solar with an electric heater backup. I would imagine that the electric heater and pump kicks in to deliver heated water to the fish pond if the pond temperature drops below say 18 degrees.... (Emergency situation).

Solar pump and pond delivery pump kicks in if pond temperature drops to say 20 degrees. Water is sent back to the solar tank in a circuit.

Does anyone have any idea how this could be cheaply plumbed and cabled and what sort of simple control system might worth considering.

I think this is a good engineering design problem that can be overcome with a little thought and flair, and we have plenty of people here with the brains and the skills! Regards figures, we need to think about insulating tanks and growbeds, but despite accurate figures, I think that a basic concept could be worked out.

Imediately the use of a secondhand solar hotwater system such as an Edwards or Solarhart springs to mind. But is there a way of making a reliable system out of junk?

I doubt that I could afford such a system. but adding some sort of solar and emergency electrical heating option to the pond in a system such as Fayes would be a good excercise.

Regards sizing, lets base any rough calcs on Fayes configuration.

Worth a try?

Drawings and discussion would be great!

I guess going for a worst case scenario is the best bet
what`s the lowest expected outside temp likely to be?

Well

In Perth

Only one or two days a year I have to scrape ice off the windscreen.

Not like in ol bighty where it used to be scaping the ice of the windscreen most mornings in the winter!

I hated that job!

It seems that as far as a cheap solar heating goes, a batch heater is the best for the average do it yourselfer. Doing a two tank system as shown at http://www.epsea.org/wtr.html#plum seems like it would be cheapest if you can re-habilitate old thrown out water heaters. Many old tanks can be referbished by flushing out hard water scale with vinegar water and putting in a new heating element. The inside water heater can be your back up heat so that you always have water at the correct temperature to heat your tanks with.

If you live in a cloudy environment with many days of just partial sun, a batch heater may not be appropriate. Hooking up flat panel collectors to an inside water heater might be better because the flat panels heat water much quicker than a batch heater.

As far as how to get the heat to the tank, i think a hydronics system might make the most sense. If possible, setting tanks insulated on the sides onto a thin cement slab that is insulated from the ground with the pex tubing in the cement would be a slick set up. It would mean another pump though to circulate the water.

Well, thats some general ideas.

It`s not an easy one, there`s a million variables.
It could be useful to get an idea of what the system might be losing so the solar or whatever can be sized for the job.

Assume an average low of 10c (50F).. kinda tropical for winter i know, but if it`s lower then it`s going be even tougher

Disregarding the bottom area of fishtank and the top surface area of all the growbeds the approx area exposed to 50F air will be about 241 sqft.

Assuming these surfaces are at 68F (water temp) you`ll lose about 4,338 btu an hour to the cold air.
which equates to about 0.66 deg F per hr drop in terms of the 3k tank water.

It`ll likely be a lot more as windchill, evaporate cooling effects and radiant heatloss are too variable to factor in.

In a nutshell, a very rough approximation to keep pace with the basic losses the solar or electric heater may need to add about 1.3kw per hour to maintain 20C.

Plan A :
If you don`t lose heat you won`t need to figure a way to replace it

Insulate the 241 sqft of exposed surfaces with 2" rigid polystyrene which cuts the heating requirement to about 250w/hr, everything else being equal.

It so happens I just returned from a 45 mile trip to check out a solar hot water heating system that was offered on a local freecycle network.
It is now mine to play with. Talked my brother into going down next weekend to remove this massive system. Hey it is Labor Day weekend gotta have some labor to do right? There are 5 - 50 gallon collection tanks that are heavily insulated, electronics of some sort probably a pump as well. The solar heating units are made with a curved reflective surface and the collector pipe with fins runs in the center of the curve.
Not to sure of the btu output on a sunny day during winter on this system nor how many leaks I might encounter as it has been unused for a few years. But it will all come in handy somewhere in my AP scheme.

No. 1 issue, contain the whole system inside a greenhouse, one that is as thermally efficient as possible. if it's outside you just can't keep it warm enough...

I agree - the practice that many of us are following of turning pumps off at night is not a good one. At a minimum it means you have to run a seperate biofilter, and even then is likely to adversely affect the amount of feed you can give your fish (because of reduced biofiltration). There are many other disadvantages also. In my big system I will be attempting to avoid this practice and if it is necessary - hopefully it will be a for a very short period only.

No. 2 issue, copper tubing is normally used in solar heaters......possibly a heat exchanger is required.

I have been taking water temps of my main tank, it went to 14c during our coldest period here (air temps fell to record lows), being in Brisbane helps

Another option if it`s possible is to bury everything and use the ground to regulate temps.
I have some copper tubing as rf grounds down to about 6ft, i checked the temp at the bottom in december and it`s a good 15F warmer than the air temp outside and a lot cooler in summer.

A chart of our ground temperatures in Alaska would have the middle line at about 35F