District heating or community heating is the use of a centralised heat source, often housed in an ‘energy centre’, to provide heating to a number of buildings. Heat sources may include boilers, combined heat and power (CHP), heat pumps and solar thermal systems.
The types of development that are suitable for district heating systems include apartment blocks, housing estates, retail parks and office complexes. Mixed use developments (combining offices or shops that require hot water during the day with dwellings that require heating and hot water at other times) provide a more consistent heat load and can thus help to secure high efficiencies from the heating plant.
A typical district heating installation consists of a highly insulated ‘heat main’ of flow and return pipes, which circulates hot water (or steam) past all the buildings or apartment blocks which might be connected. Junction points on the mains at each building allow easy connection at any time, by which the heating medium reaches a heat exchanger (or heat substation) within each user centre. In this way, heating circuits within each building are kept hydraulically separate from the heat main. The principal uses for such heating within buildings are for space heating and domestic hot water.
Energy meters can be installed to measure the actual heat usage within each building and apartment, with the output used to bill the occupant accordingly. Energy meters (or heat meters) are based on the measurement of temperature difference between flow and return, taken together with flow measurement.
Energy meters can be read via a web interface, for ease of monitoring and administration.
Hot water in heat mains is typically supplied at around the same temperature as would be expected from a domestic boiler. This should allow existing buildings to be connected up to heat mains without the need to replace user heat emitters.
Centralised boiler plant can be expected to achieve higher efficiencies than is possible from dispersed smaller units. District heating makes it possible to use technology which is only applicable on a large scale, such as biomass and co-generation.