How much will my seaweed tanks heat up in the hot Indian summer?

[seaweedfarmr]

TL;DR Summary

I have 8 concrete rectangular tanks with open tops that I'm growing seaweed in. The water temp is already 30 C which is on the higher side for our seaweed. I want to know how much it will heat up in sunlight since that would determine whether or not I need to put a shade net or chiller.

I'm growing seaweed in outdoor concrete tanks and trying to figure out how much the tanks would heat up during the day. The water is already at 30 C and we don't want them to heat up much more.

Our tanks are rectangular and made of concrete, with internal dimensions of 1.8m (L) x 0.8m (W) x 0.7m (H). The volume of water present is ~1000 L, and the tank walls are ~0.15m thick. Ambient temperatures go up to 38 C in the summer, humidity ranges from 50 - 60%, and we're located at 16.37 N, giving a daily irradiance in April of ~5.5 kWh/m^2/day.

Given the above data, how much can we expect the tanks to heat up in a day without any water exchanges or shade? If it doesn't heat up too much, then we won't need to put a shade net or chiller. Thank you!

 

[jrmichler]

What is the ambient temperature at which the water temperature is 30 C? The difference between that temperature and 38 C is approximately how much warmer the water will get.

 

[Nik_2213]

Coral species have varied 'WTF' temperature thresholds, above which they expel their algae-related symbionts, but does your macro-algal sea-weed suffer thus ? Also, though photo-synthesising, are the tanks likely to go sufficiently anoxic to impact crop yield / foul the flavour ?

I have a feeling that you should consider partial shade covers, elevated and slanted to promote air-flow.
Also, as a contingency, low-powered pond-sprinklers, perhaps solar, to wet and cool these shades, their aerated drips oxygenating the tanks...

 

[Vanadium 50]

You don't need to do any calculations. You need to put up shades.

Best case, you are in the far south of India and it won't get much hotter during the year. If you are at thge upper limit now, you will be above it as soon as you have a series of above average temperature days. And if you are farther north, this is virtually guaranteed as the summer progresses.

 

[hutchphd]

If you need coolers, wouldn't you use them in conjunction with shades? So what is the qestion? Put up the shades and augment with coolers as necessary. Won't coolers be prohibitively expensive?

 

[Vanadium 50]

Won't coolers be prohibitively expensive?

It depends on how much you really, really want seaweed.

I don't think I was direct enough with my last post. If your water is at the limit now, and the outside gets hotter, your water will get hotter too - and thus too hot. No more to it than that.

 

[Nik_2213]

"Won't coolers be prohibitively expensive?"

Not necessarily: A couple of re-purposed car or truck 'radiators' configured as a thermo-syphon, positioned in breeze, with a gentle water spray for evaporative cooling.

IMHO, you'd do better spraying that water onto the shades, such that cooled drips fall into tank...

 

[hutchphd]

I suppose it depends upon the dew point temperature. You would still want these radiators in the shade. Shade first, radiators second. The tanks themselves will conductively, radiatively, and evaporatively evolve heat to the environment. The shade would best be removed at night..

 

[Baluncore]

Seaweed is different to fish, but fish being transported in tanker trucks can be overheated if sunlight enters the tank through the access hatches. Shade must be your first option, combined and followed by evaporative cooling, then chilling.

Is it the lower dissolved gas concentration in the seawater, that determines the temperature stress on your seaweed?

 

[Astronuc]

TL;DR Summary: I have 8 concrete rectangular tanks with open tops that I'm growing seaweed in. The water temp is already 30 C which is on the higher side for our seaweed. I want to know how much it will heat up in sunlight since that would determine whether or not I need to put a shade net or chiller.

Given the above data, how much can we expect the tanks to heat up in a day without any water exchanges or shade? If it doesn't heat up too much, then we won't need to put a shade net or chiller. Thank you!

Is one using ambient sea water, from surface or deeper? One mentions 0.7 m depth of the tanks, which is relatively shallow, so the heating may be considerable.

If one looks at seasonal sea surface temperatures, especially close to shore, one might get an idea of how warmer the water will become. One could measure the water temperature of tide pools.

One mentioned 38°C as ambient temperature. One might expect another 8 to 10°C increase from the sun, so perhaps up to 45-48°C unless there is shade and/or circulation.