Temple Bar in Dublin has two innovative examples of practical energy conservation, the "Green Building" and the district heating system in its west end. Both were ideas first proposed by the director of buildings at Trinity College Dublin.

Mr Tim Cooper is the man responsible for the fine collection of period and modern buildings that grace the Trinity campus. He also oversees a very active building conservation research programme, coming up with ways to restore and protect facades damaged by pollution.

Energy conservation is another dimension of his work, seeking to reduce the college's energy costs by improving the thermal performance of the buildings in his charge. This expertise was brought into play in Temple Bar, first with the Green Building and later with the district heating system.

"It started back in the 1970s when we had an energy crisis," Mr Cooper explains. He began studying the energy performance of the buildings, analysing why some were better than others. "I came up with the idea of developing an ideal building," one that would be warm in winter and cool in summer, without demanding too much energy.

The EU funded such research, and Mr Cooper won a £500,000 (#635,000) grant. He originally wanted to build on a site on the Grand Canal, but this was put on hold. "I was left with a £500,000 grant for an optimal building. I went to Temple Bar Properties and they were extremely positive."

The result was the Green Building, a building that meets nearly its entire energy requirement from renewable sources. It uses hot water from deep underground to support a heat pump that warms the building. It has an atrium with a roof that opens, its glass trapping solar heat during the day. If things get too warm, the roof can also be opened to cool the building during the summer.

Its solar panels produce electricity for lighting and 60 to 70 per cent of the building's entire hot water requirement without costing a penny. It even has three wind turbines for electricity generation, but these have been tethered in recent months because solar heating has been adequate. "The running costs are all free," Mr Cooper says.

"I had also been asked by the Civic Offices design team how to save energy." He recommended the same warm ground water/heat pump approach, but as there was also a great deal of building planned for Temple Bar, Mr Cooper began to consider the larger picture. "The idea staring us in the face was combined heat and power."

He founded a campus company, Conservation Engineering, which installed a CHP unit in the Civic Offices as part of a £1.2 million (#1.524m) district heating system that now provides heat for virtually all the new apartments and hotels in the west end of Temple Bar.

The 20 cylinder gas-powered reciprocating CHP engine installed in the Civic Offices provides about 90 per cent of the electricity used by the complex. Heat produced by the engine is captured as hot water, which is then pumped through underground pipes to heat the Civic Offices, four hotels, one hostel, 53 apartments and also Christ Church Cathedral.

"What we did was recover the waste heat and pipe it out to the hotels and apartments." The pipes are highly insulated, with a 200 mm outside diameter but a much narrower 90 mm internal water-carrying diameter.

"Most of the buildings have boilers in place," Mr Cooper says, but these are now used as backup. "There is great redundancy in the system. All the new buildings that belonged to Temple Bar Properties and the hotels are on the district heating system."

Buildings hooked into the system are metered so that entry and exit temperatures can be measured. A "black box" system measures the amount of heat drawn off by the building and users are billed accordingly. "We log the amount of heat delivered and this can be read monthly."

A building might also "sell" energy into the system if its own boilers are in use, and water leaving the system is warmer than when it entered. In this case the building is credited for providing rather than using energy. "It is remarkably simple," Mr Cooper contends.

"But it is expensive. The capital costs are high and it is expensive to control." There is an incentive for the participants however. Each receives a discount of between 5 and 25 per cent on their heating costs.

CHP makes "huge sense" from an environmental point of view, Mr Cooper adds. It has been calculated that a single CHP unit would reduce carbon dioxide output equivalent to the carbon locked into 900 acres of rainforest.