If you took a 2 liter bottle of soda, set it straight up, then took the cap off, it would be full of liquid. Then poke a hole in the bottom of it. As the liquid drains out the bottom, air would be sucked in through the top. Once all the liquid drained out of the bottle, it would then be filled with air. This is a fundamental law of physics, and no mater how much one might try, they cant change the laws of physics. I know of no place on earth that is immune to the laws of physics. Perhaps in the Bermuda triangle, I here strange things happen there. But where I live nobody or thing is immune to the laws of physics.
When the flood and drain system floods, the water pushes air out of the system and root zone as it floods. When it drains the water drops and the water is replaced by air. Unless your system and root zone is vacuum sealed, air will replace the water as it drops. Of coarse the
growing medium and roots themselves will take up some of this volume, but not 100% of it. There is a simple way to tell how much. Just fill your growing chamber (where the root zone will be) with the growing medium of choice, then fill it with water to the desired level. Then let the water drain out of the bottom into a measuring cup (or container). The amount of water that drains out will be the volume of air that is sucked down into the root zone when the system is drained.
Also, I am aware that the air being sucked down into the root zone is cool down by the wet growing media. This is also another fundamental law of physics. But the fact is there is also another fundamental law of physics going on, the heat in the air doesn't just disappear like it was never there. It does go somewhere. The heat is exchanged with the water, and the growing medium itself. This fundamentally alters the temp in the root zone. If introducing a warm liquid to a cold liquid, the laws of physics state the cold liquid would get warmer. It would simply be imposable for a cold liquid to get colder by adding a hot liquid to it.
I gave an example earlier that the root zone temp would rise if hot air was introduced into it, I did not say how much. This is because I simply don't know, I have never done any testing to find out. I do know it will rise however, that's a fact. I don't know how much, it may not be much of a problem at all, there are many variables that will affect the heat exchange. If I wanted to know how much it's affected, I would get a digital thermometer with a probe (with proper temp range of coarse). Insert the probe into the growing medium between the middle and the outside edge of the container. Then simply watch the changes in temperature thought the cycle at the hottest parts of the day.
P.S. If I had a problem, I would try two things (after insulating the root zone, pips, tubing etc.). The first is to increase the frequency of the waterings (shortening the length of time not to water log the roots). The other is to try to cool the
nutrient solution down below 68 degrees.