Emergency Air - how much?

funku

Is there a rule of thumb to determine the right amount of air when there is a power outage?

Some variables are volume, temp, fish numbers, size, type. A bit tricky, but say I have 2000L with 100 trout or barra, under 'normal conditions', how much air would be a good conservative amount for 2 hours?
For untended systems, filtering would also be needed.

Similar conditions would occur when partial pumping overnight. How much air is running in this case when there is partial filtering occurring? I found out it can be critical.
F

RupertofOZ

Franc, there is a formula that determines the minimum amount of oxygen required for any amount of fish... at xxx body weight... ie... bio-mass... and the amount of oxygen required for feed conversion...

I'll dig it up later and post it...

Allowance must also be made for the metabolic rate of the fish, which is determined by the temperature of the water... and to some extent the species of fish....

Meanwhile I have emailed you regarding a battery backup unit... and posted some pics in my thread... http://www.backyardaquaponics.com/forum ... 62#p190662

Ian

Hi all,
This is a method of calculating (as far as possible) DO requirements. It was supplied by a member of another Forum, but I'm sure he won't mind it being shared.

Quote:

Depends on what fish species, density, water temp and feed rate. Then dependencies on what type of aeration you are planing to use and how efficient it is at what depth.....

Key Points:
Diffusers may provide dissolved oxygen at 450grams/750watts/hour.
Generally active fish will consume 400-800 mg of oxygen/kg fish/hour.
Generally pond air pumps will provide 90 liters air/watt/hour

Example:
Lets assume you are stocking at 20kg per cube, 1meter deep, water temp is 25C and you are feeding 2% biomass per day. We are not including any bio filtration oxygen demands in this calculation and assumes this is an indoors recirc system. Air calculations are always rounded up!

Oxygen demand worst case:
Fish 20kg x 800mg = 16grams per hour
Feed 400grams (adds another kg) 1 x 800mg = 1gram per hour
Total 17 grams of oxygen consumed per hour.

Oxygen production:
450grams / our 17grams = 26
750watts / 26 = 30watts
30watts x 90 = 2700 liters per hour
2700/60minutes = 45 liters per minute
or 0.06 cubic meters per hour - Which would also equate to 3 cubic meters per hour per tonne. This changes with density per cube.

After all that assuming we find you may need a 45 liter per minute pond pump, however we must keep in mind we did not allow for any other bio loads on the system such as bacteria and the like, so lets throw in a 30% error margin and bump that pump up to 60 liters per minute air pump. You will need a bigger one if you also have a bio filter and other fun stuff. This is just for the fish tank.

Thanks to Crusty.

Cheers IanK. :mrgreen:

funku

IanK
That's exactly what I was looking for. Thanks to you and crusty.
My estimate has been 1/3 of what is required - a funku moment.
A more serious re-design is needed me thinks.

Rup, that is a good unit. I went the roll-my-own path and got a 300W inverter which I intend to hook up to a car battery with heavy duty charger. Having run & charge all the time to simplify power dropout circuitry. With my paultry 10-20W bubblers I thought this would be sufficient for more hours than I needed.
F

newfarmer

I have been looking into some options for higher air supply, and came across these DC air pumps that may be worth your consideration...
http://www.aquariumproducts.com.au/dc_air_pumps.php

I have just ordered the 35W one, and when it arrives plan on setting up in the way you describe above (minus the inverter).

I have found that the air supply for the battery backup pumps drops significantly when the switch over to battery supply (as compared with the 240V supply listed on their boxes), so it will interesting to see how it goes, as the output looks really great.

funku

The 60W one looks like the compressor my brother used to spray paint. He's had it for over 20 years. A beaut little device
F

newfarmer

Yeah the 60W one has been around for a while, I think the 35W is a new model.
I have been procastinating about it for a while, and once the 35W option appeared, decided to give it a go.

Originally I was looking into solar, but the pannels were out of my price range, so decided to go down this path. Once it turns up I plan to run some tests on how long it will run off the car battery. The charger I got is one of the new fandangle ones that appears to suggest it will not deterioriate the battery when constantly connected to the battery (time will tell I suppose).

When you buy your battery, I would look for the deep cycle battery, as opposed to a cranking battery, but I'm sure you already have looked into that.

Lungy

I have the 35w dc air compressor hooked up to a power fail switch and 5 x 120 amp hour deep cycle batteries which are charged by solar panels.
So far it works really well.

Lungy

Oh I have a 140 A/H deep cycle battery which I bought in jan this year and is now surplus to my requirements if someone in Perth wants to make a offer(it cost me $250)so far it hasn't been drained once and kept at float voltage.

newfarmer

Lungy wrote:

have the 35w dc air compressor hooked up to a power fail switch and 5 x 120 amp hour deep cycle batteries which are charged by solar panels.
So far it works really well.

What size solar pannels do you have connected?
Do you have a dc water pump also hooked up for circulation in the FT? If, so, what type?

Lungy

I don't have a dc water pump running and I have 2 x 64w unisolar panels

newfarmer

Awsome...

I'm not afraid to give something a dip out of my comfort zone, but this might be a bit of a stretch for me at present.

Very impressive setup Lungy.

DanDMan

The Kwik Tek Airhead 12 Volt Hi-Pressure Air Pump is a 12 volt blower. When you block the pressure relief valve (limits pressure to 1.4 psi for mattress inflation)it will push air down 6 feet in water!

They don't cost all that much either and deliver a LOT of air.

funku

DanDMan
That's some blower. Have you run this blower & Have you used it continuously?

I found some details
AIRHEADs new 12 Volt Hi Pressure Air Pump w/ Pressure Release Valve produces 3 times the pressure of other 12 volt air pumps. Adapters are provided for all popular valves including stem, Boston, Leafield, Bravo, Hulkey Roberts and more. A removable pressure release valve limits the output to 1.4 psi, the perfect inflation pressure for towables. This powerful pump draws too many amps to plug into a cigarette lighter. Hook it up to your car, truck or boat battery with the alligator clips connected to a 10 foot power cord. Volume: 410 liters/min. Draws 28 amps.

Definitely worth looking around for those not so ordinary devices.
F

TCLynx

But 28 amps is gonna drain the battery pretty quick isn't it? (Then again, I expect my backup to be able to run for close to a whole day and only drain the battery by half)

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Emergency Air - how much?

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