Is there a specific reason you want to use aeroponics as opposed to some form of media based hydroponics? The only major crop commonly grown in aeroponics on a commercial scale is lettuce. The reason for this is that the lettuce can be pulled from the system and packaged without having to cut off the roots or even wash the growing media from them. This maintains freshness and looks good to custmers. Peppers on the other hand are harvested as fruits not whole plants. Some downfalls of peppers in aero include, the need for some form of support for the plants, and the spacing required would be very inefficient. Growing peppers in areoponics is like buying an airplane to get free peanuts; it will work, but there are better ways to get the same end result. Based on the questions you asked I will assume you do not have much background in hydroponics or horticulture. If you do decide to try peppers in aero I sugest you spend at least one season growing peppers in a more traditional hydro setup to get a feel for what is involved before you spend all the money and effort building an elaborate aero setup.

You mention using sprinklers as part of your design. True aeroponics uses a fine mist of nutrient solution not a "spray" as from a sprinkler system. I suppose it is all just words but technically running "sprinklers" in the root zone would be a modified top drip system (modified because the "drip" is coming from below rather than above). I built a system similar to this that I used to grow some basil but it was prone to leaks, clogged sprayers, and I saw no benefit over my previous ebb&flow and top drip systems.

My aero/topdrip hybrid:

The overall design

Micro-sprayers. This system was expensive to build becasue I broke 3 'taps' while threading the holes for the sprayers.

Basil needs more light than it was getting from my fluro setup. It turned a pretty lime green color. :)

I'll put my soap box away and answer the questions that you asked:

1) Whole root zone. The advantage of aeroponics is that the roots have constant access to oxygen as well as the water and nutrients they need, all at the same time. To only spray part of the roots would reduce this advantage.

2) Unless you are running an air pump and you want to get some DWC action going I'd sugest keeping the roots out of the resivior. Broken root pieces can clog the sprayers so having roots dangle near the pump's impeller (root chopper) is a bad idea.

3) You need to keep the roots from drying out. There are so many variables (water droplet size, ambient temperature, ambient humidity) I can't offer one specific answer but generally speaking, no, there is no reason you have to run the pump 24/7.

I wish you the best of luck if you do decide to build the system. If you have anymore questions feel free to ask.

I grow in an aero hybrid system and spray the entire root. I grow plants in media and a basket.

You can allow the roots to stay in the nutrient if you drain the nutrient continuously. If nutrient stagnates (pump turned off) root problems will ensue

I leave the pump on when the lights are on, 16 hr/day.

Also if you use a air stone and air pump it's ok to let your roots be in the bottom with the nuits.

mudcat65