The world we live in
Whether aviation likes it or not the requirements of the industry and its infrastructure are increasingly being set within the context of dealing with the effects of global warming. Although many in the industry argue aviation has little impact, it is aviation's predicted growth that is increasingly becoming the issue1, with a 25 percent growth in passenger kilometres travelled predicted by the International Air Transport Association before 20102. While architects can not influence fuel or engine technology we can contribute by significantly reducing or eliminating carbon emissions associated with designing and adapting airport infrastructure. This will help to future proof airports' building stock as governments look for substantial reductions in carbon emissions from new commercial buildings over the next 10 to 15 years3.
The current situation
This might sound a tall order for airports but by taking a systematic, if somewhat broad brush, approach to this question we can consider small elements, which will mount up over time. If we take a typical regional UK airport terminal dealing with 5 milliion passengers a year, around 20 percent of its energy demand is required for heating, 21 percent for cooling, 23 percent for lighting and only two percent for providing hot water. The equipment used for checking in, handling baggage etc. accounts for a further 19 percent of the energy, catering 10 percent, while computers and other uses accounts for the final five percent.
Energy Efficient Airport Terminal Design
More energy efficient airport terminals could be achieved through designing better building forms along with improved specification of building elements and construction details.
Using 'energy analysis' techniques it is possible to calculate that improving the thermal resistance of the windows, wall and roof fabric (by specifying, for instance, improved insulation levels in the order of 30-35% above UK statutory requirements) and reducing uncontrolled ventilation losses (by improving the air tightness of the building envelope) a 40% reduction in heating energy is possible: achieved through more energy efficient airport terminal design.
Although the energy required for cooling a terminal is one of its largest demands, external gains will be kept relatively small as long as the balance between providing sufficient glazing for passengers to look out and limiting solar gains is maintained. The provision of extensive overhang roofs is able to provide adequate shading while still allowing views out from the terminal. This leaves the internal heat gains from people, lighting and equipment to be dealt with.
Low energy cooling solutions for large open spaces can be observed in other building types, such as designed by the UK based consultant Atelier Ten at Federation Square in Melbourne Australia (home to the Museum of Australian and Aboriginal Art, National Film Archive and Cinemedia Centre)4. The energy required to cool its large open glazed atrium was reduced by around 75 percent by using a displacement ventilation system linked with an underground thermal labyrinth, using the same principles adopted by termites to cool their tower nets in hot climates. There is potential for this to be applied to terminals too.
The energy required for lighting relates to its installed capacity (based on required illumination), operating hours and its utilization. Providing additional daylighting into terminals by introducing more rooflights and daylight sensor controls to reduce use of lighting (if sufficient daylight is available) along with substituting more task lighting for higher general lighting levels may reduce lighting loads by around 25%.
Terminals are assumed to operate 24 hours a day, seven days a week and 52 weeks a year when estimating energy loads. In reality flights rarely operate through-out a full 24 hour day due to noise restrictions. A more realistic assumption might be 18 or 20 hours a day. This would bring about a 15 percent reduction in operating hours and might provide a further 10 percent reduction in energy demand as lights and equipment can be turned off etc.
Low Carbon Energy Generation
Low and zero carbon energy generation
Having reduced the energy loads for the terminal, low carbon and zero carbon energy generation supply solutions can be considered.
Although wind energy is a mature renewable energy technology the use of wind turbines has not been considered due to their conflict with airport radar systems. However, a study by the British Wind Energy Association concluded that radar systems could be modified to maintain air safety in the presence of wind farms
Solar energy could be used both for providing hot water and electricity. Even in the UK the level of solar irradiation is sufficient to provide up to 60 percent of a terminal's hot water. The use of photovoltaic panels within the UK is still problematic due to current extended pay-back periods and even a photovoltaic array covering ten percent of the terminal's roof would only generate enough electricity to provide around eight percent of the electrical demand. However, they are more cost-effective in Europe and would also generate more like 13 percent in locations with higher levels of solar radiation, like Spain.
Biomass boilers could provide all the heating and hot water loads using a carbon neutral fuel such as wood pellets. Using wood chip would require four times as much fuel, in volume terms, due to lower energy densities. Just over 150 hectares of sustainably managed short rotation coppice wood could provide this fuel.
Providing heating, hot water and electricity from an on site combined heat and power (CHP) plant might offer a low carbon option; using gas as a fuel results in reduced carbon emissions. But an alternative zero carbon CHP fuel source is available from the waste generated in operating a terminal, which could be turned into a bio-gas, through processes like anaerobic digestion and pyrolysis. A recent UK study indicated food waste might generate 90-140kWh of electricity per tonne. An airport terminal might be expected to generate around 1300tonnes of waste/ year (assuming 0.26kg of waste per passenger) with a food waste content of 50-60 percent. It could provide fuel for a CHP generating both electricity and heat, providing around 12 percent of the energy load.
Low Carbon Airport Design
If all of the energy efficient design measures were taken on board they could be expected to reduce the energy demand for a regional airport terminal in the order of 35 percent. This is in line with many studies which have investigated the potential for saving energy through efficient design. More should be achievable if operating efficiencies of the equipment could be improved significantly.
It is unlikely that any one single source of low and zero carbon energy generation will provide sufficient energy to take a terminal to its zero carbon goal. Zero carbon heating and hot water could be provided through a combination of solar hot water panels and biomass boilers. In fact a 300m wide ring of fields around a regional airport, growing short rotation coppice wood fuel, might be sufficient to meet the demand on site. This would reduce demand a further 13 percent.
Assuming that by 2020 twenty-percent of centralized grid supplied electricity will be provided from zero carbon generation sources, in line with the European Union's commitments, we have now reduced carbon sourced energy by nearly 60 percent.
Converting on site waste, into a bio-gas fuel, to provide some of the outstanding electrical demand, through a CHP, would reduce the original energy demand by 62 percent. In some parts of Europe, where sufficient solar radiation is available this could be increased to 70 pecent.
This still leaves 30 percent of our original energy demand still being provided from carbon based generation sources. This outstanding demand could be tackled in a number ways. Firstly airports could generate greater quantities of bio-gas fuel from the waste of their surrounding neighborhoods which might provide sufficient quantities to generate the outstanding electricity. Alternatively nearly 50 percent of the original energy demand could be produced through a merchant agreement with a remote, dedicated wind farm comprising just five 50m turbines in moderate wind conditions.
It is true that there will be costs associated with many of the above ideas, but surely they are worth considering, certainly in the medium term. Designers should certainly ensure that their new airport infrastructure designs should not preclude their incorporation at some time in the future.
1: Tyndall Centre for Climate Change Research (2005) Decarbonising the UK Energy for a Climate Conscious Future.
2: Paul Marlkillie (2007), Fear of Flying, The Economist, 16 June 2007.
3: Department for Communities & local Government (2007), Building a Greener Future: Policy Statement.
4: Atelier Ten, Federation Square, Melbourne, Australia [WWW], accessed August 2007