My Triple-Zero dream

Hardly a day passes without headlines concerning climate change – and in particular various versions of the debate about how much is man-made and how much through natural changes. To some extent this is a distraction. The ‘Inconvenient Truth’ is that we are irreversibly consuming natural resources and polluting our planet – not just the atmosphere, but also the water resources and the land. In the developed world, the energy consumed by buildings represents around half of that generated. Water consumed by building occupants represents the majority of that drawn from the mains, while building occupants generate massive amounts of waste – a typical household generates more than one tonne per year, much of which is currently going to landfill.

As a strategy for tackling these issues, URS has come up with the concept of ‘Triple Zero' which consists of::

• Zero Carbon’ development has been defined by DCLG in their publication from December 2006, Building a Greener Future: Towards Zero Carbon Development, as development that delivers “…zero carbon (net over the year) for all energy uses in the home – cooking, washing and electronic entertainment as well as heating, cooling, ventilation, lighting and hot water supply.”
• ‘Zero Water’ can be defined for the entire development as a zero demand on the municipal mains supply for all domestic uses, irrigation and other external uses such as car washing, window washing and construction activities.
• ‘Zero Waste’ means no waste going to landfill or incineration (without heat recovery), but allows for waste to be transported off site for recycling and composting.

Theory in practice

We are currently involved in the masterplanning stage of a number of large-scale developments that have adopted this concept. The strategy adapts the London Mayor’s energy hierarchy of ‘Lean, Green and Clean’ to cover carbon, water and waste through adopting passive means and best practice to minimising demand, generating renewable energy through various technologies, whilst minimising pollution to air, land and water.

With enhanced insulation, minimal air leakage and whole house ventilation with heat recovery, the Passivhaus model from Germany has already gone a long way to achieving carbon neutrality. We will be applying these principles across all uses, resulting in virtually no heating requirement. Water demand will be minimised through water efficient appliances, whilst rainwater and wastewater will be treated and used to meet most of the demand. Waste will be collected – most likely through an evacuated tube network - and recyclable material separated for collection. Material that is not easily recycled will be passed through a pyrolysis process which manufactures gas as a waste product but without atmospheric emissions.

Large mixed-use developments spread over perhaps 10 years or more will have to recognise Government objectives for new homes to achieve the zero carbon performance defined in the box above. This will be difficult to achieve with individual houses – although an honourable attempt has been made with the Kingspan Lighthouse at BRE’s Watford campus.

Benefits of pyrolysis

However, there is little doubt that local generation of energy serving potentially both new and existing buildings will be required to achieve the Government’s long term aims. Pyrolysis, often combined with gasification, has the significant advantage over incineration and biomass boilers or CHP of having no emissions to atmosphere from the process itself. The manufactured gas (syngas) of course emits pollutants when burnt, but these need be no worse than from natural gas. The toxins in the waste are to be found in an oily discharge and char waste, both of which require careful disposal.

Despite being a mature technology, pyrolysis has not taken off as a major method for processing waste. This may be in part due to the high cost of plant, but also the challenge of dealing with waste products. However, it is anticipated that the increase in demand for a ‘magic bullet’ to achieve zero carbon development induced by Government energy policy, along with recent developments in the technology, will drive costs down and make pyrolysis/gasification a viable option for gas/power production from waste and biomass for large scale development.

The bottom line is that new development has to have a smaller carbon footprint, or else carbon emissions from buildings in the UK will steadily increase and meeting the Government’s long term aims for carbon reduction will be even more difficult to achieve.