Cooling system for trout / heating for perch

[craigb]

I was thinking that it would be easy to keep the water cool for growing trout.

The idea is to get a chest freezer and run some pipes through it. Say 2 * 90mm or 4 or more 25mm pipes running through the centre of the freezer. You would have to drill some holes and seal the gaps.

Fill the freezer with water and allow it to freeze. Perhaps it might be better to do it in stages, and allowing a small amount to freeze before adding more to it.

Because of the large amount of ice in the freezer, once frozen the freezer wouldn't have to work so hard to keep it frozen. Any water that passed through the pipes would get cold and trout love and thrive in cold water.

You could use it a number of ways, reticulate the water from the grow beds through the freezer back into the pond. Or have a separate system that continually pumped the water through.

On the reverse side you could run some pipes past the freezer motor which would be running hot to warm water that ran into the perch tank. I don't think the heat exchange would work as well as the cooling would though.

I need to look into it more, a mate of mine used a fridge motor to heat up a old church in Bowral NSW. Somehow they reversed the system and ran copper pipes under the flooring filled with water that the fridge motor heated up - very efficiently. Fridges are not that expensive to run and it would make a great cheap system to keep the perch warm during winter.

[echidna]

Problem is the contact of the water with the copper. While a water-cooled condensor might have a steel outer casing the refrigerent inside is still usually running in copper piping. If you can source a stainless steel milk chiller or want to play with an ammonia system then no problems, but most small compression/expansion systems use copper piping. (Does change once you get into bigger tonnage units, but for non-commercial systems...)

[Murray]

That's not a bad idea Craig. Just run the pipes through another tub if water and have some stainless steel or similar piped heat exchanger.
I threw out an old freezer just a few months ago. It was working really well except it had become really daggy.

[craigb]

Hi Echidna, I'm not sure what the problem with water contacting the copper pipe is? Could you expand a bit. From memory and the sketchy details I was given it seemed a sort of heat exchange was taking place.

Murray, I had another thought that a freezer could be a great place to run trout fingerling's in summer (If you can get them)growing them to a stage where you can fatten them in a bigger pond over winter.

Another issue I think that could be explored more is producing bio gas with vegetable waste. It could be used to power a gas water heater, gas generator, gas lighting which would create warmth in a hot house.
http://www.arti-india.org/content/view/45/40/

[echidna]

The heat exchanger is usually a tube in shell condensor. The refrigerant flows inside the copper piping and the transfer fluid (water) flows around the outside of the copper pipes.

As to the idea of freezing a large volume of water in a freezer, you may not like the resulting power bill. There's the power to required to reduce the water's temperature to zero degrees. X. Then there's the power to force the phase change to ice. Y. Then there's the power to cool the ice further. Z. X+Y+Z = $$$$$$. Add to that, water expands when frozen, so you'll likely crush the capillaries inside the evaporator (the inner skin of the freezer) and render it useless. Serious ice-making is almost always done with ammonia plants because of the huge costs in forcing the phase change.

[craigb]

G'day Echidna,

As to the idea of freezing a large volume of water in a freezer, you may not like the resulting power bill. There's the power to required to reduce the water's temperature to zero degrees. X. Then there's the power to force the phase change to ice. Y. Then there's the power to cool the ice further. Z. X+Y+Z = $$$$$$. Add to that, water expands when frozen, so you'll likely crush the capillaries inside the evaporator (the inner skin of the freezer) and render it useless. Serious ice-making is almost always done with ammonia plants because of the huge costs in forcing the phase change.

One way you could get around it is to buy bags of ice and fill the freezer with the bagged ice. This way not only will you have the ice, you will also have cold air circulating around the bags and the pipes. I doubt if it then would cost much more to continue running the freezer as there would be no need to open the lid of the freezer to take stuff out all the time.

Yes the freezer will need to work a bit harder with the warmer water running through it, though the idea is not to freeze the water in the pipes - rather to cool it down enough to lower the water temp in the fish tank which then could cause the trout to thrive during the warmer weather. And because the lid is not opened allowing much cold air to escape I think the extra running costs would be only marginally more.

[Murray]

FF uses bags/blocks of ice to keep his trout cool.... I am sure he has said that in a post somewhere.
Next season I am dead keen to get some trout, and whatever it takes to keep them at the ideal temp.
I know we all like to keep our costs down, and that we should, but personally I don't mind paying a bit extra to be able to eat my own home grown fish.
I think that any new project takes a little while to work out the best way to do things for your own particular situation.
Anyway, the price of fresh fish these days, I think you would have to work at it to get the costs of home grown up to anywhere near bought fish prices.

[fishfood]

Thats right murray i froze tupperware containers of water in an old deep freeze one or two a day gave me an extra month

[craigb]

Thanks Murray and Fishfood.

One of the difficulties I see with my idea is that if the water was too cold the conversion of the bacteria in the grow beds would be hampered. I think it needs between 18 - 30 degrees for it to work properly.
Perhaps the problem could be rectified by cutting back on the number of fish in the system to allow the system to work a little slower?

[echidna]

G'day Echidna,



One way you could get around it is to buy bags of ice and fill the freezer with the bagged ice. This way not only will you have the ice, you will also have cold air circulating around the bags and the pipes. I doubt if it then would cost much more to continue running the freezer as there would be no need to open the lid of the freezer to take stuff out all the time.

Yes the freezer will need to work a bit harder with the warmer water running through it, though the idea is not to freeze the water in the pipes - rather to cool it down enough to lower the water temp in the fish tank which then could cause the trout to thrive during the warmer weather. And because the lid is not opened allowing much cold air to escape I think the extra running costs would be only marginally more.

A slightly better method is to use the ice with water to bring the water temperature down to +0.0 degrees ie slightly above freezing. The freezer thermostat will be useless to keep the temperature there, but this idea http://mtbest.net/chest_fridge.html will work very well. You'll still have a very good T Delta to cool the incoming water, but in a cheaper way. Depending on the total volume in the system you may have to throttle flows to avoid too great a temperature range. Also consider the effects of "cold feet" on the plants. There is some evidence tp://www.aloha.com/~craven/coldute.html that this can be beneficial with some crops.