Many production processes generate heat as a by-product. That heat can be used directly for heating buildings or else can be stored in the ground.
More and more server centres for data storage are needed. Those centres have significant cooling requirements and produce large amounts of heat. Microsoft and the University of Virginia are working on a way to decentralise large data centres and use the energy in residential areas. [Kijk, 2012]
For instance, residual heat from greenhouses can be used for heating homes and offices.
The above image shows the demand for residual heat as well as the heat suppliers. For example, old buildings require higher temperatures for heating and passive houses very low temperatures. On the supply side, it is the decentralised biomass plants and cogeneration plants which can supply high temperature heat while data centres can provide low temperature heat.