LOW CARBON ENERGY DISTRICT HEATING SYSTEMS
waste recycling will mean less combustible waste being available over time. Heat pumps: These beg the question, why not just install local heat pumps and avoid the pumping and heat losses associated with the DH system (see Figure 3). It is possible that there may be some benefi ts in a DH system in areas of very high urban density, where buildings can pump heat into a network that can pump heat out. However, this model has very different operating characteristics to the current or proposed DH systems.
Conclusion It can be seen that, in all DH/CHP systems – whether centralised or distributed – the load characteristics need to be analysed and recorded in comparative studies. DH system designers need to predict and meter the actual heat and energy losses in their system to enable correct choices over the operational criteria and extent of DH area coverage to ensure maximum energy savings. It is essential that CHP and DH
Local district heating systems are increasing around the UK. Here, at the Binton Farm project, at Seale, near Farnham, Surrey, pipes are laid for a new network heating scheme fed by a biomass energy centre
impracticable on small-scale plant, it should be assumed that the small-scale fossil fuel-powered CHP systems will need to be decommissioned in the near future. DH systems will need to be fed by zero carbon fuels such as biomass, refuse combustion or even heat pumps fed from a zero carbon electricity grid. Let us consider these three sources. Biomass: Sources are not plentiful in the UK, and it is becoming increasingly clear that the transportation of large quantities of biomass from across the world, to burn in an urban area, is unlikely to be a practical solution for zero carbon heating when considered on a worldwide basis. Besides which, concerns over air quality in urban areas are likely to rise in the future. Refuse combustion: This is clearly a desirable process if the refuse is being diverted from landfi ll. However, the combustion of refuse in urban areas has very signifi cant planning considerations, not least the transportation issues related to refuse collection. In general the siting of refuse incinerators should be considered the starting point of the possible DH system, not a feature that can be added at a later date. In addition, increasing levels of
58 CIBSE Journal March 2012
systems correctly account for the energy consumption against agreed reference standards as defi ned by the EU Directive on Co-Generation. In this way the carbon savings can be assured since they will directly link to the energy savings. Moreover, all DH systems need to certify
and publish their delivered heat energy carbon dioxide content (as kgCO2/
kW.hr), both now and into the future, to allow building users and legislators to make informed choices over whether to accept the heat or opt for lower-carbon forms of heating. The delivered heat carbon content needs to account for all of the energy losses in the system on an annual basis. Only in this way can the DH systems demonstrate that they offer true low carbon heating. Finally, all DH and CHP systems need to
consider how their installation is to become virtually zero carbon by 2050, since it is clear that this will not be achieved by the current practice of arithmetic effi ciency manipulations. It is time for the building services engineering profession to regulate itself to ensure that the UK is developing its infrastructure to achieve the real carbon emissions reductions demanded in the UK Carbon Plan. Failure to do so will mean that we will continue to mislead ourselves and those that rely on our advice. CJ
● JAMES THONGER is an associate director with Arup.
www.arup.com
www.cibsejournal.com
Courtesy of CPV Ltd
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