District energy (DE) technology is something different to cogeneration/CHP, but they share both the local angle and the emphasis on energy efficiency. Indeed, many DE systems incorporate cogeneration technology at their hearts. With district heating, heat is generated at a central plant and distributed as hot water or steam to local buildings; district cooling systems distribute chilled water for air conditioning; district energy systems do a bit of both and may also send electrical power to client buildings.

A major difference is that DE systems serve many host buildings, sometimes several hundred including homes, which make up a whole town or city area. Cogeneration systems tend to serve one client building or industrial facility.

And that multitude and diversity of loads is a strength for DE. For a new large-scale CHP plant to be viable, the host industrial site or commercial building must have good prospects for staying in business for quite a few years – not always the case. Conversely, a city full of buildings is (almost) permanent – some buildings may close, but public sector and commercial buildings usually look good for a few years.

At the recent International District Energy Association (IDEA) conference held in Washington DC, we learned of the enormous scale of new district cooling systems being installed in the Middle East. While around 130 US buildings were connected to DE systems in 2008, some 3000 buildings in two or three Middle East countries were connected to district cooling systems (see page 11).

In this annual review issue of the magazine, the UK CHPA’s Dominic Bowers discusses the prospects for district energy growth in the UK, while other articles describe the renaissance of district heating in Germany and the design of heat stations for towns and cities.

Review articles take a long look at the status and prospects for CHP and on-site power in both North America and Europe, while Sytze Dijkstra analyzes the worldwide picture for micro-CHP. Technology-based articles take a detailed look at the use in cogeneration plants of a particular gas turbine from Alstom and an engine generator set from Waukesha. Other features summarize the latest IEA report on policies that succeed in supporting new CHP capacity, and the use of biogases in cogeneration in Germany and bagasse in Brazil.

Steve Hodgson

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