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Can Aeration Heat the Water?  RSS feed

 
Jason Warren
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Does anyone have an aeration system that helps heat or cool their fish water depending on where the supply air is coming from and how hot it is?

Thank you,
Jason
 
John Elliott
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I don't think you've had any responses because the answer to your question is most likely -- "not very well".

I say that because of the large difference in heat capacity between air and liquid water. Not the heat capacity per unit mass, if you had 100 grams of hot air, it would serve to heat up 100 grams of cold water. But you have to consider the volumes involved. That 100 grams of water is half a juice glass, while 100 grams of air is close to 4 cubic feet, the size of an average trash can. You'll have to be passing an enormous volume of air through the water to get any significant heat transfer. Instead of using all that energy to move air, you might as well just heat the water directly.
 
Dale Hodgins
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It gets worse. If the air is dry, it will absorb water and you will experience evaporative cooling. Only by using totally saturated air, can this be avoided. This is why the very dry air from a trompe works well as a water cooler. Wind passing over water cools it in the same way, even if that wind is a little warmer than the water.

If air were heated without any moisture being added, that air now has the capacity to evaporate more water and it would be less dense than cool air. It all adds up to a whole lot of pumping for little gain or for some loss of heat. Aerate just enough to keep oxygen levels in check.
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When the goal is cooling, air can be quite effective. Allow as much wind as possible to contact the water. Nothing cools faster than the addition of cold well water. This can be done using a heat exchanger and the energy requirement varies according to well depth. If cold well water is available near the surface, this sort of cooling can be very economical.
 
Jason Warren
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Thank you Dale and John for your insight.

I have a 1100 sq ft solar greenhouse under construction with 3 x 1000 gallon fish tanks. I'll need to aerate the fish tanks, and I'll be cycling water through my grow beds. It seems a waste to electrically heat my fish tanks and then vent hot air out of the structure. I'm brainstorming ways to transfer the daytime heat into the water.

I'm already building a sub terrain heating and cooling system where in the heat of the day I pump some of the air through one large grow bed to extract heat and humidity into the grow bed media. Since I'm already cycling water and cycling air when its hot, I'm wondering if I can reclaim a radiator, cycle the aquaponics through the radiator and place that radiator inline with the intake duct work of my sub terrain heating system. It seems the radiator would start to cool the air flowing through it and might even condense and reclaim some of the humidity. A regular radiator or air duct heat exchanger might get clogged, maybe 50' of black 3/4 line in an air pendulum would be better.

My understanding is that any method of cycling water and air and using heat exchange is more energy efficient then creating heat. Pumps and fans range between 40 and 120 watts while heaters are around 1100 watts.

Best Regards,
Jason
 
John Elliott
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I'm getting a better picture of what you have in mind, Jason.

That water is a very large thermal mass, and the amount of energy to vent some overly hot air on the warmest days of summer is small in comparison. I take it there are never days where it gets so warm that you have to cool the water, or does it?

I think the best return for your efforts will be spending the time and money to make the water heating as efficient as possible. Things like having the tanks in thermal contact with solar absorbers, using the fish tank water to cool surfaces that regularly get too hot, etc.

Do you have data on how much temperature swing you have in the air and how much the water temperature changes during those swings? You say this is under construction, so maybe not. Maybe after you get it working and have a few months of data, some possible refinements may jump out at you. No matter how much planning goes into engineering before construction, there are always ways to optimize parameters after the thing gets built.
 
Jason Warren
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John,

I don't have data yet. Just sort of pre-planning. I'm using a concrete mass for the tanks and north wall, they are in contact with each other. Plus my greenhouse is pretty well insulated. low e glass on west and east, solexx on south.

I'll have to wait and see what it does. Sort of a mess right now, but I hope to have it all painted, the windows in this next week, the grow bed filled, and the tanks start filling.

Thank you,
Jason
 
Jeremiah Robinson
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Location: Madison, WI
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Hi Jason,

I'd love to see some pictures or diagrams of how you'll be moving air through the soil and your beds. Thought I'd heard of everything - I'm intrigued.
 
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