OK, glad to give feedback, but have some questions first. How are you planning to maintain temperature? Is there an air conditioner working on the intake area or are you planning to load it up with ice? If you have an air conditioner, there is no need for any of the fans or separate chamber, so I’m guessing you are using ice. In that case, do you have a temperature controller hooked up to the fan power? If not, you will quickly melt the ice and it is likely that the temperature in the chamber will be too cold until the ice is gone. Assuming that is taken care of, then I see two potential issues with your design:
- You are putting heavy buckets or carboys on top of the shelf you build, and you need to make sure it is structurally sound. Styrofoam isn’t enough for that.
- There is too much airflow and you are likely to waste a lot of your cooling potential (melt ice too quickly). You really only need one fan to pull the air through to drop the temperature to what you want, and perhaps one more fan to run in the chamber all the time (except when the temperature changing fan is running) to make sure the air in the chamber is a reasonably uniform temperature.
If I was to make a recommendation, I would place the air intake on one of the side chamber on the bottom with no intake fan. There would be vents going from the intake chamber to the middle bottom chamber, then to the last bottom chamber and then finally a single vent from the third chamber to the big chamber where your beer is. A temperature sensor would be hooked to a controller which actuates a single fan to pull air out of the top chamber. When the exhaust fan is not on, you can have a very small fan to circulate air in the main area if you want, but that isn’t really critical, and I’m not sure it would really make any real difference. To minimize losses, you should also hang a flap on the first intake vent to prevent cold air from escaping into the outside, but will freely allow air to flow in when the exhaust fan creates a small pressure difference. If your insulation is decent, you don’t need very big fans for any of this, so 80 or 120mm box fans are plenty big.
If you have the intake air flow through the three chambers in series as I’ve recommended, you can load up ice into each chamber and you’ll get the ice preferentially melting closer to the intake, which could make figuring out a schedule for replacement of ice easier to anticipate.