The key to the latter is to have the mix of buildings on the network. A load based on 100 percent residential will create a very limited demand for heat in summer. But add industrial premises, and the demand is raised, particularly if absorption chillers are used to convert the heat into cooling.
These sorts of schemes are not just limited to big cities. The use of smaller wood-fired district heating schemes are popping up in smaller communities, especially in the more remote areas of Northern England, Wales and Scotland.
Kielder, a remote forestry village in Northumberland, has installed a 300 kW biomass boiler to provide heat through a district heating network to a range of community and residential buildings. Of course, being a forestry village surrounded by the Kielder Forest, the fuel for the biomass boiler is all around, significantly reducing the transport costs and the associated emissions.
What about other renewable technologies? Well, the Austrians are exploiting a true renewable source for district heating: solar power. The Austrian solar engineering company SOLID has designed and constructed Austria's largest solar thermal plant on the UPC Arena in Graz, commissioned in 2002. Here, 1407 m2 of solar panels capture about 540 MWh of solar energy per annum to be supplied into the district heating network. This gives a reduction of 250,000 kgCO2 per annum over oil-fired boilers.
Having the energy (hot water) feeding directly into the district heating network also removes the need for costly buffer storage vessels. Maximum benefit can be gained from the heat generated from the panels - it all goes into the network and nothing is dumped.
This is where there appears to be a split in the district heating strategy between the UK and the rest of Europe. In the UK the schemes are generally a single source of heat production, while many European schemes have multiple heat-producers supplying heat to the network. The latter can lead to much larger schemes.
Can this be done on a mass scale in the UK? Are the barriers too great? The evidence is that offsite generation for multiple buildings, particularly for heating, can yield significant carbon savings.
The International Energy Agency is pushing the use of district energy, with Pieter Boot (Director of the IEA's Long-Term Office) announcing "a new effort working with cities to capitalize on district energy and energy efficiency to make a major impact in addressing climate change."
Boot highlighted the role cities can play to increase the use of district energy: "Cities like Copenhagen, Helsinki, Seoul and Toronto have taken an important step towards achieving climate and energy-savings benefits for the past several decades through a concerted effort to advance district energy," he said. "Other cities can learn from their example."