Temperature control is a process in which change of temperature of a space (and objects collectively there within) is measured or otherwise detected, and the passage of heat energy into or out of the space is adjusted to achieve a desired average temperature.
A home thermostat is an example of a closed control loop: It constantly assesses the current room temperature and controls a heater and/or air conditioner to increase or decrease the temperature according to user-defined setting(s). A simple (low-cost, cheap) thermostat merely switches the heater or air conditioner either on or off, and temporary overshoot and undershoot of the desired average temperature must be expected. A more expensive thermostat varies the amount of heat or cooling provided by the heater or cooler, depending on the difference between the required temperature (the "setpoint") and the actual temperature. This minimizes over/undershoot. This method is called Proportional control. Further enhancements using the accumulated error signal (Intergral) and the rate at which the error is changing (Derivative) are used to form more complex PID Controllers which is the form usually seen in industry.
A thermostat is a component of a control system which senses the temperature of a system so that the system's temperature is maintained near a desired setpoint. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature. The name is derived from the Greek words thermos "hot" and statos "a standing".
A thermostat may be a control unit for a heating or cooling system or a component part of a heater or air conditioner. Thermostats can be constructed in many ways and may use a variety of sensors to measure the temperature. The output of the sensor then controls the heating or cooling apparatus. A Thermostat may switch on and off at temperatures either side of the setpoint the extent of the difference is known as hysteresis and prevents too frequent switching of the controlled equipment.