passive aeration of water from the growbeds

[Pat Chesney]

As some of you have noticed, I am designing a sustainable solar greenhouse. In my quest to limit the watt draw needed from the solar array and batteries (particularly at night) I have been searching all sorts of arcane methods for pumping water and using as little electrical devices as possible. One question I need some answers to concerns aeration. 

I have read that ebb and flow grow beds aerate the water passing through it. Does anyone know if I design a system that uses 2 grow bed sizes for 1 fish tank size how much aeration would a grow bed deliver to the fish? I am designing an Affnan bell siphon with an aerator attachment on the bottom to dump from the grow beds. I am going to build his shuttle valve design for an indexing valve.

I know that I will have to do a DO test to really see how much oxygen a grow bed delivers, but I wondered if anyone had already done anything with that.

When I get my pumping system built and documented, I will post documentation on it. I have found a method to pump large amounts of water using air alone as the force with a pump with no moving parts.

Actually, I have found and built prototypes of two different types of pumps that do this. I will be getting air from the pumping as well as the grow beds due to this. 

Thanks

[Pat Chesney]

Yes, that is definitely true. We are digging down for a sump and rising up slightly above the fish tank height. The total submergence will be 7.5-8 feet deep. This gives you an easy lift of 1.5 -2 feet.

I found a magnetic pump today that shows 37 watts. Even using an inverter from 12 volts gives me less that 45 watts to move 12 gal/min. That is hard to beat. If I can store air from the windmill, I might be doing ok with the air lift. That's a lot of water to move for 45 watts. It is a March 140-3. External magnetic pump. It is giving me pause.

What if a person stopped circulating the grow beds during darkness? Would there be harm to the system while it is dormant for 12 hours? I have plenty of power from the solar panels during the day. The batteries are the problem. I can run quite a few air bubblers during the night if I am not circulating the grow beds for less power. I can also time the pump to run part time at night to stretch the batteries.

I will try to send you the spreadsheet. I haven't tried to send anything through this forum privately.

What people don't know is a battery will self-destruct if you use over about 15% of its rated amp-hour. Using 15% will make a battery last for 20 years. Using 50% will burn it out in about 5 or less. Batteries are mucho expensive.

[RupertofOZ]

You can stop circulating to the grow beds overnight... I do so consistantly during our Australian winter... to keep tank temps as high as possible...

 

But.. and I say again...  BUT... you MUST have additional external aeration.... and you must have a battery backup system attached to it...

And IMO... the same applies.... if you rely on passive aeration from water movement...

[Carey Ma]

Wow! What a fascinating discussion this is turning out to be. I too am a big proponent of pneumatics, but never thought of using it for pumping water . How wonderful. I must know more! I have been working on a capillary action pump for years and thought I was onto something, but it does not even come close to being suffice for commercial applications.

Wow. I'm so excited, but I'll have to put this reading off until I finish my latest business plan. 

Cheers to you'all.

[RupertofOZ]

Air pumps can move considerable amounts of water.... but only at head heights of less than 500mm... which is about the limit of their effeciency in realtion to other means...

[TCLynx]

many people run timed water pumping round the clock to do the flood and drain without the siphons.

And many people shut water pumps off overnight but this only works when the fish load is low enough that ammonia levels don't start to spike before morning.  Safer to do in winter when fish will be slower/not eating as much and the water holding more dissolved oxygen anyway.

[Brian Cheatham]

Hey Pat, I am running my system off using an airlift similar to yours. My type of airlift is called a geyser pump because it pumps up water in giant air bubbles once every second or two like a geyser. I like this method because, like yours, there are no moving parts and it gives me the added benefit of aerating my tank AND lifting the water to my bed. Mine is on a small scale right now (only a 20 gallon tank and water is only lifted about 2'), but I think if sized up it would work just as well. I have a small 20 Watt air pump attached to a 6 way splitter. From this I use 2 aquarium air stones and 3 or 4 pvc fittings to lift my water up the pvc and into the above tank. Since only 2 stones are needed for my pump, the other 4 air valves I have can be used for aeration of my tank. Currently I have only one stone in the tank along with the geyser pump (which also puts off excess air into the tank) and the other 3 valves are not being used. So 1 pump and 3 air stones for entire system. I tried the same method on a larger 300 gallon tank and had it almost perfected except the air pump was barely too small to get enough flow to my beds to trip my siphons, so I switched to a water pump. But I am a believer in the airlifts and their benefits and with a little work, you can easily get an airlift or geyser pump to give you all of the water and oxygen you need. 

[Pat Chesney]

Yes, Brian.

I have built two larger geyser pumps. One if a 1" tube and the other is a 1.5". I didn't have the cfm correct during my test, so I am not sure about the output of these pumps. We considered them but found out we like the more constant flow of the air-lift pump. I have not given up on the geyser pump by any means, but the air-lift is functioning within our design constraints for the present.

I would like to talk to you about the air pump model you used. My constraints with a small solar system are limiting me since I do not want to drain my batteries down below a 15% discharge. I have already seen that I need to add two more batteries to the two I already have in the system. I have the solar panel wattage to add those batteries.

I am not finding the breakthrough in air pumps that I need. I did find a magnetic water pump that draws 37 watts and delivers 13 gal/min. That is astounding from a low power consumption angle. I have not found an air pump that will give me the 2.21 cfm at 3.25 PSI to match that flow rate with that level of consumption. If I can find a reliable air pump that is durable and can match the 37 watts, I would go there in a heart beat. I like the pump adding air to the water. That seems like a big positive to me.

[Pat Chesney]

Thanks to Rupert and TC for your responses. Every little tidbit is adding together to weave a tapestry of knowledge. I do appreciate it very much.

As I mentioned to some of you, I found a March Pump 140-3 that is rated at 37 watts and delivers 13 gal/min. That is huge. It is hard to beat. I am aiming for 1000 gal/hour, but that is getting up there at 780 gal/hr for 37 watts. I can drop down to one pump at night and stay pretty high on my flow. In the daylight, I would have all the power I need to run two pumps. Does anyone know anything about this pump?

If I could find an air pump that would deliver the numbers mentioned above in the post to Brian, I would prefer to follow this design out to its conclusion. But 37 watts is a hard number to reach anything that low.

Rupert, I was designing air bubblers to run at night at a much reduced wattage. Thanks for the warning.

It seems that the fish species has a lot to do with the DO level necessary. For instance, carp might do ok with reduced DO while some other species might not.

[Pat Chesney]

Carey, I will be glad to share anything I learn and the spreadsheet too, if you are interested. Just let me know when you are ready to look into it.

Carey Ma said:

Wow! What a fascinating discussion this is turning out to be. I too am a big proponent of pneumatics, but never thought of using it for pumping water . How wonderful. I must know more! I have been working on a capillary action pump for years and thought I was onto something, but it does not even come close to being suffice for commercial applications.

Wow. I'm so excited, but I'll have to put this reading off until I finish my latest business plan. 

Cheers to you'all.

[Jon Parr]

Pat, you should probably switch to deep cycle batteries. I found this article helpful:
Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates. The major difference between a true deep cycle battery and others is that the plates are SOLID Lead plates - not sponge. This gives less surface area, thus less "instant" power like starting batteries need. Although these an be cycled down to 20% charge, the best lifespan vs cost method is to keep the average cycle at about 50% discharge.
Read more here: http://www.windsun.com/Batteries/Battery_FAQ.htm
Even if you could find one air pump to suit your needs, I would recommend using the two smaller ones, because if one fails you will still have a backup. In fact, I would use the two on different battery circuits too if possible, for the same reason.

[Pat Chesney]

Thanks Jon,

I do have deep cycle batteries. I did a lot of research on these 2 or 3  years ago and set up a system with a MPPT charge controller and the whole works. My research at the time revealed that deep discharging would hurt the batteries much more than is normally expected. I have been on this page you sent me several times in the past. My batteries are 100 amp/hr AGM batteries made in Germany. I will look over the charge/discharge life cycle again in case there is new information. I appreciate your comments. It is possible that I made an error in my calculations or I am remembering the harmful discharge level incorrectly. Like I said, I did this 2 or 3 years ago. I am not as young as I used to be and I may have forgotten. (I'm 59 and the synapses don't seem to fire as good as they used to.) That is why I have notes and spreadsheets on it.   At any rate, my controller was set back when I was fresh from the research and it will not allow my batteries to use more than the optimum amount of power. I will look on it and see what the discharge limit is. It may be set for 50% rather than 15%.

I even have a book on how to build and repair lead/acid batteries. We have a supply of lead and acid on hand for future needs. I have soldered a lot of lead in a "prior life" (master plumber since 1975. Started on the truck with my dad at age 13) So, I know what is involved with working lead more directly than most would.

I like what you are saying about redundancy. I will take that into account with whatever I design.

 

[TCLynx]

In general the less deeply you discharge the batteries the longer their life will be but if you don't get to use the batteries then what is the point, kinda like maybe if you only discharge 15% you might get an extra few years off the batteries but if you need twice as many batteries in order to get 8 years out of them instead of 5 years, well is it really worth the extra cost to replace say 4 batteries every 5 years or 8 batteries every 8 years?    (I'm just tossing up numbers here as examples, they have no bearing on any research or reality, I'm only recommending looking carefully to avoid false economy.)

I sized my battery backup to hopefully never need to go deeper than a 50% discharge on my deep cycle battery.