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!
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.