District Heating

What is District Heating?

District Heating (noun) The supply of heat or hot water from one source to a district or a group of buildings.

A district heating scheme comprises a network of insulated pipes used to deliver heat, in the form of hot water or steam, from the point of generation to an end user. District heating networks provide the means to transport heat efficiently. They can currently be built quite a distance from the generating plant room and distribution networks can be kilometres long. This is sufficient to carry heat across our cities, smaller communities and industrial areas. The distance a network can reach is also easily extended by simply adding more providers of heat, or ‘heat sources’, along the way.

A heat network enables valuable energy, which currently is all too often wasted in power generation or industrial processes, to be harnessed and delivered to a point of use. This removes the need for additional energy to be generated. It also allows for economies of scale, as the generation of heat in one.

large plant can often be more efficient than production in multiple smaller ones. Heat networks can also be supplied with heat from a diverse range of sources. These include:

  • Power stations
  • Energy from waste (EfW) facilities
  • Industrial processes
  • Biomass and biogas fuelled boilers and CHP plants
  • Gas-fired CHP units
  • Fuel cells
  • Heat pumps
  • Geothermal sources
  • Electric boilers and even solar thermal arrays

The ability to integrate diverse energy sources means customers are not dependent upon a single source of supply. This helps guarantee reliability, continuity of service and can introduce an element of competition into the supply chain.

Networks also have the ability to balance the supply and generation of heat, across location and over time. Over the course of the day, heat demand shifts between residential consumers to commercial, industrial and public buildings and back again. A heat network can match and manage these flows, whilst maximising the utilisation of the plant providing the heat. Demand can also be managed across seasons, with networks supporting the operation of distributed absorption cooling plants in the summer providing cooling on a significant scale.

Boilers to burn wood fuels such as wood chips and pellets tends to be physically larger and more expensive than equivalent gas or oil boilers. This is partly as a result of the physical requirements for a high temperature combustion environment and transporting the solid fuel. As boilers get larger however the disparity with gas and oil boilers becomes comparatively smaller, and so wood fuel becomes more economically attractive, especially for installations of the scale of a few hundred kW. District heating makes use of these cost advantages, as well as the administrative benefits of using a single boiler installation to provide heat to a number of buildings. These might be a number of individual houses, blocks of social housing, local council offices, a school, etc.

District heating is much more common in some European countries than in the UK. In Denmark for instance district heating provides around 60% of heating. However there are now a number of successful district heating schemes in the UK, both using fossil fuels and biomass.

A typical district heating installation consists of a highly insulated “heat main” of flow and return pipes distributing hot water (or steam) past all buildings which might be connected. A junction point allows easy connection to each building, from which hot water can be taken from the main to a heat exchanger (heat substation) within each building. The heating circuit within the building is thus isolated from the heat main. Temperature measurement of the flow and return lines, plus a flow meter (together forming a heat meter), allow the actual heat usage within each building, or even apartment, to be separately measured, and delivered heat billed for accordingly. Remote meter reading by modem, secure web interface or drive-by are all possible, as are remote diagnostics to ensure reliable operation.

In Austria there is an well established protocol for introducing a district heating scheme to a village or district. Farmers can form a co-operative to sell wood chips in the form of heat by installing and operating a district heating plant, operating as an Energy Services Company (ESCO).

District heating can be provided using the co-generated heat from electrical power generation in a Combined Heat and Power (CHP) installation. This can increase the overall efficiency of power generation by a factor of three or more.