Hello All I am new to this great forum. I would like some thoughts on my idea which is: I am designing a passive solar greenhouse for aquaponics. I am concerned about excess heat in the summer (I am in western NY Sate). A requirement is air exchange for a healthy interior environment. I am also trying to keep the greenhouse as protected from outdoor pests and airborne plant disease (closed controlled environment). Ok, that said, I have a small steam - feeder creek from hill runoff - so limited flow. I would like to create a siphon by placing a 2" pvc flexpipe upsteam then go upgrade to the greenhouse, pass through a exchange unit (possibly a truck radiator), blow air through the radiator to provide cooling from the 50-60 degree F water, continue flow back to the creek completing the siphon action and placing a turgo or pelton style micro-hydro generator at the flexpipe outlet to the creek. That is the concept. Distance from pipe inlet to radiator @800 ft Elevation lift from pipe inlet to radiator @15 ft Temp differential in greenhouse @35 degrees - hotter air temp to cooler water temp Elevation drop from radiator to pipe outlet/generator @45 ft Distance from radiator to creek @ 250 ft Pipe ID 2" full flow only using siphon action My first concern is can I maintain a siphon over that distance with a radiator interrupting the peak of the siphon. Would cavitation occur? If not, then first hurdle crossed. Second, is there enough temperature differential and is a radiator a practical inexpensive way to go for a cooling exchange unit? Third, with a siphon, I would assume the only working head that I can calculate for micro-hydro generation is the difference between the original pipe inlet and the outlet or 30 ft, not the drop from the radiator to the outlet or 45 ft? Would the first 15 ft (or more) of head be used just to maintain the siphon? Any input would be greatly appreciated.