6. Hardware  Touch screen to input required temperature  Sensor to input temperature  ADC to convert analogue data to digital  Actuator switches radiator on  LED screen to display actual temperature and required temperature

9. How Air-conditioning Works Cool low-pressure gas is compressed into hot high- pressure gas by the compressor. When the gas moves through the condenser, it cools down into a liquid. This liquid passes through an expansion valve and it evaporates into a cold low-pressure gas. When the liquid is changing, it absorbs heat from the inside of the building. A fan blows air across metal fins as a result of the heat being absorbed. This causes the room to cool down.

10. How Air-conditioning Works 1) condensing coil, 2) expansion valve, 3) evaporator coil, 4) compressor

11. Microprocessor Control  The system controls the amount of heat being let out of the system  The valve is controlled by microprocessor to reduce or increase the flow of refrigerant  Microprocessor compares the pressure of the refrigerant to the preset value  If pressure of refrigerant is above preset value microprocessor opens valve wider  If pressure of refrigerant is below preset value microprocessor makes valve opening narrower  Touch screen is used to input the required temperature  Microprocessor compares the temperature of the room to the preset value  If temperature of the room is above the pre-set value the fans remain on/are switched on by the microprocessor or microprocessor increases their speed  If temperature of the room is below the pre-set value the fans remain/switched off by the microprocessor

12. Sensors used in Air-conditioning  Two temperature sensors to control the amount of heat being let out of the system.  Pressure sensor to control the valve to reduce or increase the flow of refrigerant.  Temperature sensor in the rooms where the system operates to control the heat loss from individual rooms.

14.  Your new task is to move the heat from the inside of a refrigerator to the outside to keep your food fresh. How can you move something you can't see?  Not only that, but you can't open the door to get at the heat inside, or you'll let the heat straight back in again. Your mission is to remove the heat, continually, without opening the door even once. Tricky problem, eh? But it's not impossible—

15. Refrigeration Simplified (kind of…)  By compressing gases, we make them hotter; by letting them expand, we make them cooler. How can we use this handy bit of physics to shift heat from the inside of a refrigerator?  Suppose we made a pipe that was partly inside a refrigerator and partly outside it, and sealed so it was a continuous loop.  And suppose we filled the pipe with a gas. Inside the refrigerator, we could make the pipe gradually get wider, so the gas would expand and cool as it flowed through it. Outside the refrigerator, we could compress (squeeze) the gas and release its heat.  The compressor is attached to a grill-like device called a condenser (a kind of thin radiator behind the refrigerator) that expels the unwanted heat. Finally, the gas that circulates round the pipe is actually a specially designed chemical that alternates between being a cool liquid and a hot gas. This chemical is known as the coolant or refrigerant.  If the gas flowed round and round the loop, expanding when it was inside the refrigerator and compressing when it was outside, it would constantly pick up heat from the inside and carry it to the outside like a heat conveyor belt.

17. Recap…  Condensing unit Allows refrigerant to cool/cools gas to form liquid Is situated at rear of refrigerator  Evaporation unit Absorbs heat from surrounds thereby cooling it Is situated inside refrigerator

18. Refrigeration (Hardware)  Sensor to monitor temperature inside refrigerator  Contact switch or pressure sensor to check if the door is closed  Number pad/touch pad/touch screen to input required temperature  LED display/screen to indicate current temperature inside the refrigerator  Actuator to activate buzzer  Buzzer if door is left open  Actuator to activate compressor  Actuator to activate valve

19. Microprocessor Control  The required temperature is input/set  Then the microprocessor reads temperature from sensor  Data from the sensor is converted to digital using an ADC  The temperature of refrigerator/value read by sensor/current temperature is compared to pre-set value  if greater than preset value microprocessor activates/sends a signal to actuator  if greater than preset value microprocessor/actuator switches compressor on  if greater than preset value microprocessor/actuator opens valve  if it is below the preset value microprocessor activates/sends a signal to actuator  if below the preset value actuator/microprocessor switches compressor off  if below the preset value actuator/microprocessor switches valve off  microprocessor sends data to LEDs indicating the current refrigerator temperature  microprocessor compares data from pressure sensor with zero/checks contact switch  if it is zero/contact broken microprocessor sends a signal to the actuator  if it is zero/contact broken actuator/microprocessor switches the buzzer on