Will you fill the hole bucket with media or just a 6" of so net pot? with whole bucket, got EnF 15 min (or whatever it takes to flood)every 3 or 4 hours.
I grow outside, almost exclusively, in the south and usually just lay a piece of foam insulation board in front of the rez to block some of the heat. If your rez is in the 40+ Litre range, heat shouldn't be too much of a problem.

First I would like to say that is a nice looking image. Did you use Google Sketchup to create it? I grow everything outside myself. I agree with grizzman that the larger the reservoir the better. It takes a lot more energy and much longer to heat up larger volumes of water than it does to heat a small volume of water.

As for a flood and drain being less susceptible to heating up, that's really only partially true. In the reservoir down in the crawl space yes, but not up in the buckets (where the roots are). Once the system drains back down into the reservoir, the small amount of water/moisture left in the buckets will now be able to heat up much faster. As an example, take a 5 gallon bucket of water and fill it with cool water, then take a cup and fill it with the same water. Stick them both outside in the sun at the same time, and see how much longer it takes for the water in the 5 gallon bucket to heat up.

By using it as a RDWC system each bucket will have its own volume of water. For the sake of argument lets say each bucket holds 3 gallons before it overflows. Four times three is twelve. Now you have also increased the overall water volume by 12 gallons (and larger volumes of water take longer to heat up). The 3 gallons of water in each bucket will eventually get warm as is. But by running the recirculating system regularly, you replace water that's starting to warm up in the buckets, with cool water from below.

Where I live (in the desert) it gets real hot in the summers (in the 120+ range), and you may not need to do this, but it's an option. I would also insulate the buckets, tubes and feed lines. Insulate the buckets with a flexible (closed cell) foam type insulation warping. Not glued to the buckets, but warped, and strapped on very tightly (you don't want gaps). Then use pipe insulation (it runs about $1-$2 for 6 feet) on all the tubes and feed lines. The insulation will keep the cool in much longer than without it. For best efficiency on the pipe insulation, don't cut open the split down the side. Cut it to length, then slide it over the top of the tubing. Otherwise the pipe insulation eventually looses shape and comes open at the split, leaving gaps (at least in our heat).

P.S. I have always liked the idea of the recirculating water culture systems. I just haven't gotten around to building one yet.

Last summer I turned a 18gal Rubbermaid Tub into a DWC bucket. I had two sweet basil plants which pretty much covered the entire top of the tub. I had a single airpump and two 12" air stones.

Granted our summer here in Los Angeles was mild last summer, but we did get a few heat waves. The heat did not seem to bother the roots at all.

Some tips I would suggest.
1. The larger the reservoir the more stable your nutrients will be in all aspects. Temp, PH, TDS

2. Make sure you have a large enough air pump for the volume of water. Better to have too much air then too little. As the water temp increases it holds less dissolved oxygen.

3. Try to keep the system simple. I was amazed at the DWC bucket I setup. I changed the nutrient solution maybe once for the 4 months it was running. I would just simply add tap water to top it off, and after 2.5 months I stopped putting fresh nutrients in.

I make a polystyrene box for each of my square reservoirs and add a 5 litre bottle of frozen water in each one.

If the above was my system I would have a large reservoir under the deck, insulate it and add frozen bottles of water in it and pump from that one and also do what homehydro said and insulate each one.

HH wrote:
"As for a flood and drain being less susceptible to heating up, that's really only partially true. In the reservoir down in the crawl space yes, but not up in the buckets (where the roots are). Once the system drains back down into the reservoir, the small amount of water/moisture left in the buckets will now be able to heat up much faster. As an example, take a 5 gallon bucket of water and fill it with cool water, then take a cup and fill it with the same water. Stick them both outside in the sun at the same time, and see how much longer it takes for the water in the 5 gallon bucket to heat up. "
your analogy is misplaced. While a cup of water will heat quicker than a gallon, we're not talking about containers full of water. the only moisture remaining is what's attached to the medium. the heat will not migrate across the medium nearly as quickly without it being completely saturated. air is a tremendous insulator.

I'll be using 8" net pots filled with hydroton. I currently have 12 buckets wrapped with reflectix. I really haven't decided on the res size...thinking around 55 gallons.

I did use sketchup to design that, sometimes i just can't find a pen.

If you opt for a recirculating system, be sure to run as much line as possible under the deck so it'll be in the shade.

Grizz, most buckets will have a 1/2 inch or more of water even after the drain since the return isn't usually coming from the bottom of the bucket, but rather from the side near the bottom. I agree that it's not going to be the same as a cup full of water, but there will be some standing water in the bucket. Air is a great insulator, yes. But it works both ways. If the medium heats up, it won't release as much heat due to no air flow and no conduction. One way around that is to adjust the timer to flood more and for shorter periods of time during the times of day the sun hits the buckets directly, thereby cooling off the medium, roots, and the bucket surface. Of course, I agree that you should do what you mentioned and HH expanded on - put a block up to avoid the direct sunlight on the buckets and insulate the tubing - or wrap aluminum foil around the buckets. I do both on my bucket system, which is recirculating ebb and flow. It floods from above faster than the buckets can drain for 15 minutes, turns off and then drains the rest of the way. Worked great last year.

So why is water temp important? I am addressing that due to scubastan's comment. Basil may do well in the warmer water, but tomatoes will suffer due to reduced uptake of nutrients. Nutrient uptake varies based on water/medium temps and is quite evident in tomatoes. When the temps climb, you will find some varieties suffer BER no matter what you supplement with. Keep the temps down and you won't be so likely to lose lots of tomatoes. Romas, in my experience, are particularly sensitive to this. Plus, higher temps can encourage bad microbe growth.

Something I have never tested and think I might tonight: Is the amount of heat transferred to water from an air pump significant? Those pumps can get hot and subsequently heat the air they are pumping into the water. If I get around to testing it, I'll post it. It won't be a strict test, though. I also need to get around to testing how much heat a submersible pump transfers to water. Obviously, in both instances it will depend on several variables such as manufacturer, ambient temps, air flow, condition of pump mechanics, how dirty the pump is, size of pump, size of tubing, etc.

The image doesn't show an ebb and flow return. Should it or is it under the buckets?

It's my understanding that artwk doesn't have it setup as a flood and drain system, just that he was contemplating it. My analogy may not be prefect, but I don't think it is misplaced either. As Joe pointed out no mater how you design it, there is going to be some amount of water at the bottom of the buckets. Most likely a cup or two of water will be left, and that was what I was basing it on. Also going by the image of the system design, and the holes in the bucket lids that will hold the plants, I can tell those 5 gallon buckets were not going to be completely filled with growing medium. But it could be covered to do that (not what I was thinking though).

Yes air is a great insulator, but not as an open cell material. That's why I made a point of suggesting to use "closed cell" insulation to insulate the buckets, and lines. The same principal applies to any growing medium also. When the system drains it will be sucking warm/hot air down into the growing medium (because it's open cell). That doesn't mean the going medium is automatically going to be as hot as the air as soon as it is sucked down. But it starts warming up from there, and how fast it continues to rise depends on all the other factors, like the original water temp, the actual air temp, if the containers are in direct sun, if the containers are insulated or not, how much growing medium there is, as well as what type of growing medium used. But regardless, one thing is always going the same, and that's that smaller volumes of water heat and cool faster than larger volumes do. That's what I was trying to point out.

Joe,
I have also considered the heat that's introduced by the air pump. But From my standpoint, my concerns are not from the motor heating the pump, but from the actual air temp that surrounds the pump itself. Simply because the air pump sucks in the surrounding air in order to pump it through the line, and into the air stones. Because my reservoirs, and air pumps are outside, this is a concern to me. If the air temp is 100 degrees, I wind up pumping 100 degree air directly into my reservoir.

The only way to fix this is to place the air pumps inside the house, and run the lines all the way out to the reservoir. But that would be pointless unless the lines were insulated. I'm considering running the air lines under ground (6-8 inches or so) to keep them insulated, but that makes it difficult to move things around later. Not to mention the path needed to run them, and keep them insulated the entire way. Especially the point where they need to leave the house, and before it goes under ground.

I have also considered using the air pump as a source to help cool the nutrient solution, by running the air pumps intake into the air conditioning duct. Or from inside a ice chest full of ice, and/or dry ice. The ice chest would need a place for fresh air to enter it for sure, or it wouldn't be adding any oxygenation to the nutrient solution. But the ice would cool the air down before it's sucked into the pump, and out to the air stones. This is one experiment I have been wanting to test sense last summer. Thinking about it now, I have a small air pump that isn't doing anything at the moment.

I despise air pumps, especially for larger setups. A waterfall provides more oxygen than an air pump can IMO.

So i think I have decided on RDWC. Pump size will need to change the solution >10 times an hour and with a 2ft waterfall I should have plenty of oxygen. Here's praying the res stays in the low 70s.

The inside of the buckets look like this..
{{gwi:1000760}}
I'm assuming the buckets would siphon out once the pump shuts off as the res is a few feet lower than the buckets. I'm considering a larger diameter return line to keep up with the flow rate I'm after.

I have run a system like this in the past with good results from a 1000watt hps. I'm expecting stellar results from Mr. Sunshine.

If you use 1/4 inch tubing and drain back to the pump you risk clogging the tubes.

If you use the existing drains as siphons by extending them down (similar to how bato buckets work) you can't pair them, as the first bucket to drain will break vacuum for both.

If you use individual drains, the common drain pipe needs to be below the buckets, as it, not the reservoir position, will determine your low water level, again because the drain pipe vacuum will break when the first bucket empties.

Love the idea of using frozen water bottles in the res!