8. In order to prevent greenhouses becoming too hot in sunny weather, an automatic window can be installed. This opens automatically if the temperature reaches a pre-determined value. The higher the temperature, the greater the opening becomes. Other than the heat produced by the sun, there is no external power source. (a) Research and describe how this mechanism works. (b) State whether this is open or closed loop control, give reasons for your answer. (c) Represent the system with a block diagram.