Water cooling for trout ponds in the South African summer

[Quinton Leigh]

Hi I am is desperate need of advice, I live in sunny South Africa have 10 trout dams on an estate for catch and keep purposes. Each dam is approximately 2,5 Acres and 3 metres +/- 10FT deep in certain areas. The main issue is in summer the water temperature is sitting at 28deg celsius 82 fahrenheit, This makes the fish lazy and they don't eat, therefore making the experience terrible, not only for the fish but the fisherman.

The question is how could i drop this by 5deg celsius without having to use chemicals etc. I have put in aerators to keep the oxygen levels high but this doesn't help to cool the water at all. I have looked into building fountains but i am not sure that this will have any real impact on the cooling. If anyone could assist it would be greatly appreciated.

 

[Rive]

By default, the water temperature should be around the daily average temperature of the air. This can be modified by direct sunshine (upward) and evaporation (downward).

So: plant some big trees (if there aren't any already) and/or make some wind (this one is not necessarily feasible).

 

[jrmichler]

What @Rive said. Also, you could add some pond fountains, and run them when the sun is down.

As an alternative to a pond fountain, look into spray nozzles. The goal is to make the water into small droplets that are in the air long enough to get measurable cooling. Talk to an application engineer at www.spray.com.

 

[sandy stone]

Well, maybe you could build a cooling tower. Not cheap to operate, and you would need a source of makeup water.

 

[berkeman]

Hi I am is desperate need of advice, I live in sunny South Africa have 10 trout dams on an estate for catch and keep purposes. Each dam is approximately 2,5 Acres and 3 metres +/- 10FT deep in certain areas. The main issue is in summer the water temperature is sitting at 28deg celsius 82 fahrenheit, This makes the fish lazy and they don't eat, therefore making the experience terrible, not only for the fish but the fisherman.

The question is how could i drop this by 5deg celsius without having to use chemicals etc. I have put in aerators to keep the oxygen levels high but this doesn't help to cool the water at all. I have looked into building fountains but i am not sure that this will have any real impact on the cooling. If anyone could assist it would be greatly appreciated.

Welcome to the PF.

How deep into the ground would you have to dig to get to dirt that is 5-10C cooler than the surface? If it's not too far, you might consider burying some radiator structures and pumping the pond water through them. I'm not sure of the cost and scale, but it might be worth thinking about.

Alternately, 25 Acres of white tenting material might help to drop the water temperature. Again, the cost and scale may not be practical, but it might be worth considering... Also, do you need to support fishing in all 10 ponds, or could you just support it in 1-2 ponds and move the fish from the other ponds to the fishing ponds as they get depleted?

http://www.weddingtentsale.com/wp-c...r-Shelter-aluminum-structures-for-sale-70.jpg

 

[Tom.G]

You don't say what the average daily air temperature is but it's probably close to the water temperature. As @Rive pointed out, to get below that you will need active cooling of some sort - a heat exchanger to a cooler environment, evaporative cooling (spray nozzles, cooling tower, trees), or a heat pump (water chiller, very expensive). Internally, a heat pump is just a powered and packaged evaporative cooler for concentrated cooling... with the added power used to dump the heat to a warmer environment.

@berkeman has an idea with the tenting. But I think you would need it without the walls to get enough air circulation to avoid heat build-up - essentiall a very big umbrella to block the direct Solar heating.

At 2.5 acres, large trees would only work with a long and narrow pond for shading and evaporative cooling.

Paging @Chestermiller, who may be able to supply some insight for the buried radiator approach.

Good Luck! and keep us updated on your progress.

 

[russ_watters]

You don't say what the average daily air temperature is but it's probably close to the water temperature. As @Rive pointed out, to get below that you will need active cooling of some sort - a heat exchanger to a cooler environment, evaporative cooling (spray nozzles, cooling tower, trees), or a heat pump (water chiller, very expensive). Internally, a heat pump is just a powered and packaged evaporative cooler for concentrated cooling... with the added power used to dump the heat to a warmer environment.

You seem to have some concepts jumbled around here a bit. Typically one would say "active" cooling is what you get with a vapor compression refrigeration cycle (though it is not a super common usage). An air conditioner or water chiller is "active". A heat pump is an air conditioner with the heat exchangers reversed so you provide heating. Neither are the same at all as an evaporative cooler, which doesn't use a compressor.

 

[russ_watters]

What @Rive said. Also, you could add some pond fountains, and run them when the sun is down.

As an alternative to a pond fountain, look into spray nozzles. The goal is to make the water into small droplets that are in the air long enough to get measurable cooling. Talk to an application engineer at www.spray.com.

Note, it is almost certain that you could operate the system during the day as well. The heat rejection is mostly evaporative and dependent on the wet bulb temperature, not the dry bulb temperature.

 

[russ_watters]

Alternately, 25 Acres of white tenting material might help to drop the water temperature.

This would need to be combined with a huge amount of ventilation, otherwise you are just trapping humid air and preventing evaporative cooling.

 

[Tom.G]

You seem to have some concepts jumbled around here a bit. Typically one would say "active" cooling is what you get with a vapor compression refrigeration cycle (though it is not a super common usage). An air conditioner or water chiller is "active". A heat pump is an air conditioner with the heat exchangers reversed so you provide heating. Neither are the same at all as an evaporative cooler, which doesn't use a compressor.

Well, fair enough. I used "active' trying to indicate the need for external energy input. Here in Southern California, a Heat Pump is the label attached to a vapor compression refrigeration device that can be used for both heating and cooling an environment, depending on which valves are open or closed.

Perhaps I was too general in the first instance and too specific in the second. Sorry for any confusion.

 

[russ_watters]

Here in Southern California, a Heat Pump is the label attached to a vapor compression refrigeration device that can be used for both heating and cooling an environment, depending on which valves are open or closed.

Yes; while it is of course possible to make a heat pump without an air conditioning mode, it is almost never done.

Well, fair enough. I used "active' trying to indicate the need for external energy input.

That would be confusing. In the HVAC industry a system that does cooling without a compressor (evaporative only) is often called "free cooling".
https://en.wikipedia.org/wiki/Free_cooling

They still require fans and/or pumps.

 

[berkeman]

@berkeman has an idea with the tenting. But I think you would need it without the walls to get enough air circulation to avoid heat build-up - essentiall a very big umbrella to block the direct Solar heating.

This would need to be combined with a huge amount of ventilation, otherwise you are just trapping humid air and preventing evaporative cooling.

Agreed, that was an oversight in my post. Thanks guys!

 

[zbikraw]

Usually temperature difference between day and night is in order of 10 deg C or more (when clouds are absent). You can exploit this phenomena by building second set of water containers, isolated from sunlight and fresh air, optimally underground. By pumping water between both sets during day you can obtain trout temperature between day and night ones. The exact value of temperature drop depends mainly on day/night difference and volume ratio of your present ponds and those isolated from sunlight. You can regulate it by pumping less than full volume of pounds. Adoption ancient design of pumps (for example Archimedes one) and wind energy can minimize exploitation costs and make possible pumping fishes without killing them (this requires aeration of water in second set of ponds).

 

[256bits]

the buried radiator approach.

Assuming of course that the ground, if cooler at a depth, is an infinite cold sink.
Otherwise after time the performance deteriorates as the ground temperature increases.

 

[Baluncore]

I would make a cover from 50% black shade cloth. That would intercept half the solar energy before it entered the water.
It would also reduce the cooling on clear nights, since the shade cloth will be warmer than the clear sky above.
Slide the shade cloth along overhead fence wires to expose part of the pond for fishing.

A deeper pond may thermally stratify better and so have cool water 500 mm below the surface. You might deepen the pond near the places used for fishing which would attract fish to the cool deep water.
Put air bubblers in the deep cool water to get high dissolved O₂, but avoid breaking the stratification and mixing of the different temperatures. To avoid mixing consider a coaxial tube with the outer reaching above the surface, inject bubbles at the bottom of the inner tube.

Avoid spray or fountains which increase evaporation if it will concentrate salt in the fish pond.

 

[johnbbahm]

I would start with looking at what the dew point is in your area.
If the dew point (wet bulb) temperature is 3 or more degrees C colder than the daytime highs,
then some solar power fountains could help a lot with evaporation cooling.

 

[Quinton Leigh]

Thanks Gents really appreciate the assistance, i think we are going to run the aerators at night, deepen the ponds to 6m and try putting tanks underground and pumping the water. We unfortunately don't have much resources.. even things like 3 phase power is impossible, unfortunately we are in the wild bush. Even an internet connection is a luxury.

Will post some pics of the work and let you know the result. Once again thanks for the input its greatly appreciated.

 

[johnbbahm]

Depending on what the dew point is, and if water is cheap and easy, there may be more benefit to running the aerators
during the daytime. The greatest difference between the dew point and the air temperature is usually mid afternoon.
You would loose more water, but also do a lot more cooling.
When you spray water in the air, the excited(Hot) molecules are the first to transition from liquid to vapor.