Air Conditioning Heating Refrigeration 2.1 – Control Systems

Maintaining constant physical conditions/ Continual feedback systems Air conditioning systems Central heating systems Refrigeration Car manufacture: Industrial robots Medical applications: Intensive care Process control

Hardware requirements Robot/ output devices: fans, heaters, boilers, etc Temperature sensor Moisture sensor Pressure sensor Light sensor Actuators (pump/ motor etc) ADC DAC

Software requirements Control software

Introduction to Air Conditioning An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner.

Introduction to Central heating Central heating is used to warm the different parts of the house. They do this through the use of radiators Some central heating systems also provide hot water to different parts of the house such as the kitchen, and bathrooms Water is heated by the boiler and is then pumped through pipes to the radiators and hot water taps (when turned on)

Introduction to Refrigeration The fundamental reason for having a refrigerator is to keep food cold. Cold temperatures help food stay fresh longer. The basic idea behind refrigeration is to slow down the activity of bacteria (which all food contains) so that it takes longer for the bacteria to spoil the food

How things work Air Conditioning Refrigeration Central Heating

Air Conditioning This is how the evaporation cycle in an air conditioner works The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas (red in the diagram above). This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid. The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas (light blue in the diagram above). This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building.

Refrigeration The compressor compresses the refrigerant gas. This raises the refrigerant's pressure and temperature (orange), so the heat-exchanging coils outside the refrigerator allow the refrigerant to dissipate the heat of pressurization. As it cools, the refrigerant condenses into liquid form (purple) and flows through the expansion valve. When it flows through the expansion valve, the liquid refrigerant is allowed to move from a high-pressure zone to a low-pressure zone, so it expands and evaporates (light blue). In evaporating, it absorbs heat, making it cold. The coils inside the refrigerator allow the refrigerant to absorb heat, making the inside of the refrigerator cold. The cycle then repeats.

Central heating systems Radiant systems function by warming the walls, floors, or ceilings of rooms or, more commonly, by warming radiators in the rooms. These objects then warm the air in the room.

How they are controlled Air Conditioning Refrigeration Central Heating All of the systems above, work on the following same principles: Sensors – process of continual monitoring Preset values – set by the user/ built at time of manufacture Micro-processor – makes judgments based on the data received from the sensors and makes changes to output devices Continual feedback systems

Air conditioning unit in the classroom The air con unit is a constant feedback system When you turn it on a temperature sensor, senses the temperature of the air Set the temperature manual or automatic – pre set value The micro processor of the air-conditioning unit records the temperature set (pre – set value) If the temperature of the room gets hotter or colder the temperature sensor will send a signal to the microprocessor The micro processor will compare the reading against the pre-set value air conditioning fan motor unit will speed up or slow down to make the room hotter or colder The temperature of the room is monitored and reacted to on a continuous basis

Fridge in your house Number pad or dial to set the required temperature (pre set value) If temperature inside the fridge drops then the temperature sensor will sense this and send a single to the micro processor The actuator that controls the compressor will be turned on and more cold air will be pumped into the fridge When it has reached the pre – set value the compressor will be turned off

The fridge door On the door of a fridge is a contact switch (senses if the door is closed or open) If the door is left open a warning buzzer will sound (when closed the buzzer will not sound any more) When the door is closed the micro processor will calculate how long the fridge door has been left open in relation to the pre set temperature value The compressor is switched on and cold air is circulated until the pre-set temperature is reached

Central heating in a house The thermostat, a heat-sensitive switch, is the basic control that regulates the temperature of your home. If the temperature drops below the pre set value then the micro processor will turn on the furnace/boiler to heat the water in the radiators. This water in the system is constantly pumped around the house through pipes to the radiators. When the set air temperature is reached the furnace/boiler is turned off