Keeping it cool

Scientists don't know why Suwannee River sturgeon jump. Let's say hypothetically for the purposes of this post that it's too stinkin' hot in the river. No matter the reason they can mess you up if they hit you, so let's all consider boating somewhere else during sturgeon jump season.

Scientists don’t know why Suwannee River sturgeon jump. Let’s say hypothetically for the purposes of this post that it’s too stinkin’ hot in the river. No matter the reason they can mess you up if they hit you, so let’s all consider boating somewhere else during sturgeon jump season.

I mentioned here before that our main question in the pilot scale will be temperature control. Let’s talk about that a little more.

The question isn’t whether we can keep the temperature in the sturgeon comfort range. We definitely can. The question is “Can we do it with just evaporative cooling, or do we need a chiller?”

Evaporative cooling is cheap and simple, although it can use a lot of water. A chiller is basically an air conditioner for water– the little gizmo inside a water fountain that you hear kick on if you stand there drinking for a long time is a little tiny chiller. They also make very big chillers. And if evaporative cooling alone doesn’t cut it, we’ll need one of those very big chillers. We’re hoping to avoid that since chillers are expensive equipment, they use a lot of energy, and to make them efficient you need a cooling tower. That needs a lot of water just like simple evaporative cooling. So as you can imagine we’re hoping to avoid the need for a chiller.

I’m optimistic that we can make with just evaporative cooling. The ground in Florida (under the top sun-soaked 8 inches or so) stays a steady 75F or so year-round. That just happens to be the exact temperature that we want the water to be. I’ve found that even in August down here, you can find comfortably cool spots outside. It’s always a place that’s consistently shaded, there’s some water or transpiring plants, and a breeze– even just a hint of airflow will do it. Bamboo trail at Kanapaha Gardens, I’m looking at you!

Bamboo trail at Kanapahaaaaaaaahhhhhhhh......

Bamboo trail at Kanapahaaaaaaaahhhhhhhh……  (source)

Accordingly, the sturgeon farm at Mote Marine in Tampa two hours to our south manages to keep their temperature in the ideal range just with shade and natural evaporation from the tanks’ surface. In a happy coincidence, that’s exactly the environment we’ll have in our system. Shade and water.

Unlike Mote, we’re going to flow the water through a lot of shallow beds in a greenhouse. It’s possible the water could heat up in the beds since they’re in a greenhouse and will have little evaporation because of being covered by the plant rafts. On the other hand, those beds are dug into cool-ish ground surrounded by ground cloth to keep it from absorbing too much sunlight and heat, and the rafts are made of inch-thick styrofoam. The water might not heat up much at all. The only way to find out is to try it out– hence the pilot scale.

In the end the pilot will tell us whether we need to spring for electric chillers or not. This will make a big difference when we build the full-scale system– in terms of energy supply, how you situate everything on the ground, and definitely in how much the system will cost. We’re keeping our fingers crossed for good results with evaporation alone.

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2 thoughts on “Keeping it cool

  1. I am curious. Is geothermal not an option for cooling for you? In our area the ground stays 52 degrees and you can run water through buried pipes to cool it (or heat it when a heat pump is hooked to it). I imagine the cost to running water through a burred pipe would long term be less then the cost of water loss, but then again our area might be different since we have so much ground water to transfer heat out of the pipes. Also I can imagine digging all those pipes underground would be expensive too.

    • Geothermal technically can work. It’s a really good option for temperate regions. (Your URL looks like you’re in Canada?) But, an important thing to keep in mind is that groundwater’s temperature tends to be the annual average air temperature in the area. So in our area, that means the groundwater is 75F. That’s actually the perfect temperature for what we want.

      But it also means that if our water heats up while we’re using it, our groundwater can’t cool it down very much. We’d need a lot of acreage of tubing underground. That’s expensive to install as you note, and also needs a big pump to push the water through it. Big pumps use a lot of energy and also tend to heat the water as it passes through the active pump. So it can be a little counterproductive for the amount of temperature change we’d get out of the ground. Or we could install a (very expensive) heat pump to actively move heat from the fish water to the groundwater. However. If we use a heat pump, one that uses an evaporative cooling tower as its heat sink would probably be more efficient most of the time than one one that uses warm groundwater. Geothermal works really well in temperate climates– not so much in the tropics/subtropics.

      On a social-logistics note, we’re doing our first 1-2 years on rental land– so we can’t make permanent modifications to it. In an ideal world I’d love to try geothermal just to get a concrete idea of how much it can do in these parts, but that would depend on having a landlord who think it’s a good deal to tear up a lot of dirt just to stick in tubes that would only get used for a year.

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