Aquaponics 101 – Heat Exchange

How come things are never where we want them to be?  Take people as an example.  Are we ever happy where we are?  Of course not, so we buy cars, bikes, airline tickets to go somewhere else.  And what do we do when we get there?  Yep, you guessed it, we just come straight back home again.

Now where, you may ask, am I going with this line of thought, and what does it have to do with Aquaponics?  I’m not sure if you remember some of my posts from last Summer, but at that time my major headache was the heat, with temperatures in my home greenhouse hitting 40 degrees plus.  At this air temperature, the water was hitting 35 degrees !!

Now we are faced with the opposite problem.  Outside ambient temperatures are as low as 6 degrees.  Inside the greenhouses I am currently working with, the air temperature is about 12 degrees at night and the water temperature is as low as 16 degrees.  At this temperature the poor Tilapia are hardly eating and certainly not growing.  The Koi out at the commercial site seem quite happy as do the goldfish in the outside pond.

So what is the answer?

Well there are two things we can do.  Firstly, only grow Tilapia during the warmer months and during the Winter months move over to a cold water species like trout.  This is all very well in theory, but then you have only say 6 months of warm and 6 months of cold water, and 6 months is certainly not enough to grow either Tilapia or Trout to  decent size.

Secondly, we can heat the water.  Problems here are firstly the high capital cost of a heat pump and secondly the cost of electricity.

Last week we bought a 5.3KW heat pump for the commercial tunnel but so far it seems a it small and the best we can get the temperatures to is about 20 degrees.  We used this unit because I assumed that it used about 5KW of power (ie 25 amps) but somehow I hadn’t read the manual properly and it in fact only draws about 1KW (ie. 6 amps) so we could have gone a lot bigger.  I am probably going to move this unit to my small greenhouse at home and put in a bigger unit.  This is what the heat pump looks like.

As far as plant growth is concerned, everything looks good and all of the seeds that I planted have come up despite being in the middle of winter.  We planted numerous plants as well as tomato, gem squash, butternut, chilli, asparagus and cucumber seeds.

At the new Gouna site, erection of the greenhouse frame is going well, and if it hadn’t been for the rain on Friday, we would have had them both completed.  We’ve got the construction down to an art now and we can build the whole structure without even using a ladder, just one section at a time. Some images below.

Enough for now.



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