Dissipative system

A dissipative system (or dissipative structure) is a kind of highly ordered, stable, open system which is operating far from thermodynamic equilibrium within an environment that exchanges energy, matter and entropy. Often the system is under the control of a thermostat. A dissipative system is characterized by the appearance of stability, but is continually changing. A simple example is a whirlpool: a similar shape is maintained, while water is continually moving through it. More complex examples include lasers, Bénard cells, and even life itself. The term dissipative structures was coined by Ilya Prigogine.

In cold climates houses with their heating systems form dissipative systems. In spite of efforts to insulate such houses, to reduce heat losses to their exteriors, considerable heat is lost, or dissipated, from them which would makes their interiors uncomfortably cool or cold. The house is an open system inasmuch as it is incapable of preventing heat from escaping. Furthermore, the interior of the house must be maintained out of thermal equilibrium with its exterior for the sake of its inhabitants.

In such a house, a thermostat is a device capable of starting the heating system when the house's interior falls to a set temperature, and of stopping that same system when another set temperature has been achieved. Thus the thermostat controls the flow of energy into the house, that energy eventually being dissipated to the exterior.