Let's assume typical 10' X 20' greenhouse for growing veggies is empty and is all exposed concrete black floor with solid black (opaque) insulated knee high walls all around. The rest of it is glass sides and roof. Also, assume reflective radiant barrier was hung on those knee walls inside covering them all and laid across covering all the flooring, too, in the early cool morning. Ground and air inside and out all the same, say 70 degrees F. Hours later the sun rose, outside air temperatures climbed to 100 degrees F, with the greenhouse fully exposed to the sun all day. No outside air exchange via doors or windows. Question is; would the temperature of the interior air likely be significantly or appreciatively lower inside, with the radiant barrier coverings, compared to if there were no radiant barrier coverings at all? I'm thinking it might, as more of the radiation penetrating is being reflected back out the glass instead of being absorbed by and warming up those black floor/walls where interior air is then in contact with them, too, being warmed up even more. Any thoughts on how significant an air temperature difference there might be? (Not inside and out, just interior air comparison with radiant barrier or without.) One other question; same scenario above with radiant barrier, but room now has a large 200 gallon tank of 70 degree F water and it's painted black on the outside. It will be absorbing some of that radiant heat that would have reflected out and also some of that radiant heat that would have otherwise heated up the radiant barrier itself a little that it did not reflect and tank will also be absorbing some of the heat in the interior air itself, too. Question is; do you think tank does much good cooling interior air that comes in contact with it when tank is also intercepting radiant heat that was otherwise destined to go back out the glass? Thanks for any thoughts.