Why does natural ventilation cool a structure better than fans and intake shutters?
Research has shown that there is ALMOST NO TIME at which a minimum 1 MPH breeze is not blowing. Usually a 2 MPH to 3 MPH breeze is occurring. If the entire side of your greenhouse is open, in 17 seconds the air will breeze across a 24 wide house; or 21 seconds for 30 wide. At 3 MPH, the air will go across that same 24 house in less than 6 seconds. It takes a lot of shutters and fans to pull air 96 down the length of the structure to achieve the same result. And, by the time the air gets to the far end, it will have considerably warmed. On many summer days, shutters and fans will run 12 hours (sometimes 24 hours) a day to TRY to continue cooling. A normal hoophouse might run 2 fans using 16 to 18 amps of power running continuously. In contrast, Roll-Up sides, 6 high, will require running 2 small motors, about 3 amps each, for only about 10 minutes throughout the entire day.
