Backyard Aquaponics
A place to discuss aquaponics

It has been a good discussion indeed!

I think you summed it up nicely here



Let me paraphrase that to "the ultimate efficiency is using what you have (daylength & temps) to grow what you can"

There are fish for all temps and plants for all seasons.

I said as much in a post to my system thread (or the jade fungus thread) Many of my fish problems have come about by trying to keep the jades in a location that has temperatures not ideal for them sometimes.

I've learnt my lesson of fighting nature

that is not to say that slight "outside natures specs" can not be run with radient solar heating.....................i never DID learn from my lessons LOL

look forward to seeing some great results doug

I don't recall which heating calcs these were, but from memory weren't we looking at the water-water HE in the tank rather than something in the sun?



Probably, sunlight hitting a suitable surface acts like a current source, whereas air temp is like a voltage source.



If you're talking about the pipe near the roof of your room, the surface area of that looked too small to me - assuming 500W/m^2 and 2m^2 surface area you're only collecting 2kW. I think to heat your tank you're going to need a much larger surface area, or some kind of concentrating system.

I think my concern is more about $/W than efficiency - I'd rather spend $100 on 100m^2 of 20% efficient heat collection than $100 on 2m^2 of 80% efficient heat collection.



Yes, it is the basis of progress!



Good stuff! Improved simulation always improves productivity, and it's one important reason why even if cheap energy disappears, we'll be using computers.

njh, why would you want a bulky heat exchanger? No spare room in my building, so small, hi efficient is much better than large low efficient.

Oh yah, you are in a warm place where exchangers can sit outside.

No, it's a question of monetary efficiency. No point in spending lots of money on something that produces less. Let's take 5MJ/m^2 as your winter daily average. Then my proposed design would generate 100MJ on average, your design would generate 8MJ on average. Given a choice between 100 and 8 for your dollar, which would you choose?

If money is no object, you want to ship your product or you are space constrained, then higher efficiency makes sense. That's not true of most people It is in fact quite straightforward to improve the efficiency to 50% by spending just a little more - you might like to think about how.



That's a mistaken logic. All the heat that goes into your greenhouse ends up in your greenhouse. Thus putting a heat exchanger in the greenhouse merely moves that heat around. If you are serious about solar heating you will need to put your collector outside! Once you've made that leap you realise that pumping water around in little black pipes is the wrong solution.

But if you move the heat around in your greenhouse to a place (like a large mass of water) where you can better store the heat overnight, isn't that a good thing, too?

Exactly Janet. The daytime temps do not need augmenting. But the heat stored in the day in the water is very valuable circulating thru the growbeds at night.

Another consideration is keeping the fish tank water warm enough for the fish to grow. My large concrete tank is not in the sun and will tend to average day/nite temp of room plus the effect of a large surface area below ground picking up ground temp. Temp changes in such a large heat capacitor will be very slow. Anything I can do to add heat is good (all year here - no chance of overheating I think).

njh, you mentioned your design. I do not remember seeing it. Could you help me locate it. Maybe something there to improve my heat exchanger?

Sure but I thought you lived in cold, dark places? Such places will not get enough sun during the day to store enough heat for the night. So you'll end up having to heat with other energy. As I keep saying, I'm not doubting the idea can work, I'm doubting the idea is economically a good idea. I could leave a 100m roll of black polypipe in the sun and produce water too hot to touch, but the actual amount of heat I collect will be worth less than the losses and pumping costs and certainly not enough to heat my tank to any appreciable level.

Come on Doug, you're an engineer, do the maths and show that your system can collect enough to keep itself warm. From your pictures I estimated you have about 2m^2 of collector area, which might collect 5kWh a day. Is that going to be enough? A lighted match is quite hot to touch, but it's not going to keep a GH warm overnight.

njh,

5kwh is running a 1000 watt heater for 5 hours.

I will take that heat day after day for little cost because I run my pump under computer control at a duty cycle that gathers the heat into the tank at a reasonable cost in electricity. We pay $0.10/ kwh, so it is only $0.50 per day or $15/mo or $180/yr (less with cloudy days).

I am surprised you do not think 5 kwh is worth collecting.

I do not think you will collect 5kWh (I was using 100% collector efficiency, which is very doubtful - 25% is more likely with an open air black pipe), and I don't think it will prevent you needing supplimentary heat. If you are just interested in collecting a little bit for show, then fine, but I would rather aim for getting the majority of my heating from the sun.

I could be wrong, but you haven't presented any calculations at all yet, so it's all conjecture. (Am I right about 2m^2? Am I right about 2.5kWh/m^2 day mid winter? what is your heat losses?)

If you have computer control, why aren't you measuring the actual heat output? My heating system records MJt provided by the system, MJe used, and various performance measures based on fish and plant growth rates. What you don't measure you can't improve.

I would be aiming for a few hundred kWh a day if I were in your climate.