Backyard Aquaponics
A place to discuss aquaponics

Hi again Bazz BTW now I know you are a practising chemist rather than an (olchemist") I might just leave some of that chemistry theory stuff to you :-)

On the subject of solar swimming pool heaters I went ahead and put one in-line because my fish tank water was needing to be heated from as low as 14degC overnight in July/August last year. I was using an electric immersion heater and, boy, did that cost me money. I shall use it on off-peak as back-up only I hope from now on.

Mine is probably capable of about 8kW in full sunshine. It heats 5000 litres of water 1degC every 20 to 40 minutes at the moment during the day. I'm hoping that it will still give adequate heating in the shoulder seasons and even in winter when the solar radiation level is much lower (25% odd??).

We have had some cold nights just recently (maybe down to 12degC) and I've turned it on for a period of 1/2h to 2h to kick the water T up a couple of degC.

However, as of right now (isn't this ironic) as Rupert surmised I seem to be getting bigger T swings than I was in the past. Water was 18degC this morning down from 26degC the evening before, increased to 19degC with the solar collector on over an hour and then reached 27degC this evening. I'm waiting to see what it will be tomorrow morning.

The riser pipe to the solar collector which branches off my main pressure line at ceiling level is outside my fish shed and a chore to access. I didn't want to have to install two valves, one in the main line and one in the solar collector riser pipe so I just simply put one valve in the main line shortly after this branch. I thought that this height increase plus a couple of bends to negotiate would be enough to prevent any water going up to the roof when the valve was fully open on the main line especially since there are no further restrictions on the main line after this prior to return downwards by gravity.

But the size of temperature swings is now making me wonder. Is it big T swings through the day or some effect of a small fraction of water still running through the solar collector? I can't hear any water flow through it but I will keep watching it. Up until, now, it has been working exactly as I wanted...so I will see. I'm hoping I don't have to put a valve in the collector line because it will be a chore to access.

Incidentally, my original intention with the solar collector in the line was to heat the water as best as I could in cold months during the day and cool the water, if necessary, by night chilling in summer...but that was with the main line valve purposefully diverting the water to the solar collector not with the valve directing flow to bypass the solar collector!

I've attached a pic of the collector. I bought the manifolds and coils of tubing and assembled it myself but you are in for a few $100s if you use the same system.

Thanks Alchemist

Conductivity can be used to give Total Dissolved Solids (TDS) but only works reasonably well in high levels and that the dissolved solid is all as a salt eg KCl, NaCl, if other solids are dissolved then these can erronously be attributed to the salt in question. You can work this out by taking conductivity readings, dry a known volume of finely filtered water and reweigh the solids left behind.

this is a rough explanation hope it makes sense

i'll try to reword............. in an ap system you cant!

it is used in industry where the ONLY thing dissolved is a certain salt, for example table salt. X conductivity = X ppm

as soon as you throw other stuff in the mix then the correlation is no longer valid.

god knows how many solutes we have in an AP system.

you could probably get a rough reading though. maybe google NaCl conductivity vs concentration

The question was not for an AP system but for Saline water in a dam to get an idea of how much salt was init. I'm guessing though that the answer would be the same.

Yes Stuart, the same. Yes Steve it does give a rough correlation but can be very very rough

Well I went looking and while I didn't find what I was looking for I did get the answer to the question I was really concerned about.



I think the water I was concerned about was measuring between 7000 and 11000µS/cm. So that would pretty much rule out using it with most of the plants that people would normally grow. How would the fish cope.

Stuart

PS It certainly tasted salty

As a guide, seawater is around 30 -35,000uS/cm, so your looking at pretty salty water, I have heard of either trout or barramundi being raised in aquaculture using highly saline water. I think on the forum here somewhere it says that trout can be acclimatised to either sea water or fresh water.

As for plants unlikely.

Al - I read your post about the solar heater with interest and had yet scrolled down to see the picture. I have to admit that I envisaged the heater to be larger than it is - given the increase in temps you have been getting from it. I have some old collector that I nabbed from my mum and dad's roof (they weren't using it to heat their pool so thought I'd put it to good use). I think I have heaps more than you have up - so that is a positive for me, because mine will be way less efficient. I am not comfortable running the fish tank water through this type of piping when it is new, let alone old like the stuff I have (I am a bit anal about leaching possibilities). I therefore intend to pump water from a dedicated tank through the collector, heating the water as much as I can during the day. I will then run my fish tanks water through stainless stell piping located in the heated tank, with the view that sufficient heat will be exchanged to make it all worthwhile. Have all the gear, but may not put it together until the winter after this one. May run some tests before then though, just to see what sort of heat I can generate in the heat tank (insulated of course) and then exchange into the fish tank via the rather inefficient stainless pipes.

Hi VB,
My fish tank water had dropped to 21deg this morning at 0800h from 27degC max yesterday. Ambient this morning was around 15degC so this is a smaller swing. Disregarding any effect of night chilling through the solar (when water is supposedly not passing through it), this T decrease could be be due to heat losses from my drainage plumbing or from "unplugged" holes in the rafts....will keep monitoring.

What water T swings do other members get in regions where daytime/nightime T swing is quite large?

My solar collector set-up is 12 sq.m. roughly. If my understanding is correct, this would be exposed to 1000W/sq.m. solar radiation or about half that of heat radiation on an average day in Oz. ...hence 6kW of heat generated max maybe...a lot when you compare with a domestic hot water heater.
The suppliers say that you need about the same area of solar collector as swimming pool to heat the swimming pool water up 8degC or so in summer. eg for a small 8 x 4 above ground pool like I've got you would need 32 sq m of colector (a lot more than I've got as you say but a lot more water to heat too, viz 32000l vs 5000l on my AP set-up).

What's the potential health issue with running water to your fish tank through new polypipe?

Just not food grade Al and more likely to leach nasties at high temps. Mine actualy isn't polypipe, it is more a rubber compound. I'd be less concerned with poly (I've mellowed over time).

Regarding the temp drop - this seems a bit high to me particularly given you have the beds in a poly house. Mine dropped 2 degrees overight in barra setup. Granted only 1 bed attached, but water qunatity is much smaller as well and temps probably higher here overnight. Still - I wasn't even getting the swings you are experiencing in middle of winter with temps as low as 0 degrees outside - where my whole setup was.

Al, bit hard to compare temperature parameters perhaps because of the fundamental difference between fllod and drain and constant flow.....

I'd think that a flood and drain growbed would retain a degree of radiant heat in the growbed media.... at least for a period of time anyway...

Certainly I think this could be the case up your way VB where night time temps are perhaps a little higher and closer (relatively) to the actual water temps??

What are your continuous flow channels made out of AL ??? (too lazy to go back and check)..... maybe with the constant flow of water you're lossing heat through the channels themselves transferring heat into the cooler night air, even though you're in a poly house.

What are your night time air temps in te poly house??

I'd be more concerned with new poly rather than old. Generally speaking I'd say the same thing for all plastics based on the fact that when they are new they smell and when they are older they don't.

Anything thats was older that had that sort of oxidised outer crust that old garden chairs and such get I wouldn't touch new or old.

Thanks for the response, Rupert. My channels are polystyrene lined. I commissioned another trough in the polyhouse recently I am starting to think that the T fluctuation may be coming from the many unplugged holes (now plugged) in the rafts. Will keep monitoring it. The polyhouse doors and vents have until now also been left open over night so internal T same as external (maybe down to 12degC min at the moment).