Zero tolerance

It’s an ambitious target. In the next decade the government is proposing that all new houses should be ‘carbon neutral’ in their energy use in a bid to tackle climate change and slash carbon emissions by at least 60% by 2050. In the midst of the UK’s warmest winter on record, the news will be welcome to many. But for the developers and designers who must put the aspirations into practice, much of the detail about how it would work remains unclear – particularly given the government’s commitment to building more affordable homes.

The plans were announced by Communities secretary, Ruth Kelly, at the end of last year as part of the consultation document ‘Building a greener future: towards zero carbon developments’. Among other ideas, the report suggests all new homes receive a star rating to reflect their energy efficiency for potential buyers. A stringent tightening of Building Regulations and planning rules to reduce carbon emissions is also on the table.

At first sight, new homes might seem an ineffective target for cutting CO2 emissions because they account for a relatively small percentage of the total building stock. However, Kelly believes the case for targeting new builds is strong. In 2004, according to government figures, the domestic sector accounted for around 27% of total UK carbon emissions (almost 40 MtC), coming largely from energy for heating, hot water, lighting and appliances. The government says measures to improve existing stock could save 7 MtC a year. Yet a further 30 MtC saving must be found by 2050 to counter emissions from the new homes needed to accommodate predicted population growth.

With this in mind the government wants to introduce a 25% reduction on 2006 Part L requirements by 2010, increasing to 44% by 2013 and culminating in ‘zero carbon’ homes by 2016. Crucially, the definition of zero carbon refers to total energy use and is described in the consultation document as encompassing all the energy used in the home.

Brian Moffat, technical director for Miller Homes, Yorkshire, suggests the government isn’t fully cognizant of the implications of the changes it wants to make. “One of the biggest issues at the moment is getting everyone to understand what the challenges of building zero-carbon homes are for the industry,” he says. “The government needs to make sure that everyone, including organisations like the National House Building Council, insurers, planners and building control, are aware of the issues, and not just impose the new regs on the industry. If we’re to see an increase in micro wind turbines, solar panels and green roofs on buildings, planners have to be receptive to it.”

Brian Mark, founding partner of sustainability consultants Fulcrum Consulting, has doubts about whether reaching zero carbon is feasible at all. “At present on a normal site we are struggling to provide a 20% reduction on CO2 through the use of renewables.” Part of the problem is not all sites are suited to renewable technologies. “Micro wind turbines fail to deliver because of the poor wind profiles on inner city sites, while high-rise accommodation can’t provide enough roof area to install solar hot water heating or PVs to satisfy every apartment,” says Mark. Combine this with the increase in use of electrical appliances and the reduction in the size of apartments – Fulcrum is designing units as small as 25 m2 which contain almost the same appliances as a 60 m2 house – and the possibility of zero carbon seems ever more elusive.

At David Wilson Homes, technical director Paul Slater points out that very few zero-carbon developments currently exist. “The only guidance we have to go on is the Code for Sustainable Homes. In this, the five- and six-star ratings are aimed at achieving zero carbon but we’re a long way off those levels.”

According to Mark, to get to a 40% reduction in carbon emissions via renewables you have to go for large-scale, off-site generation. This outlook is shared by Sue Riddlestone, director of BioRegional Development Group, one of the partners behind the BedZED eco-village. “The government definition of zero carbon seems to suggest that all energy should be generated on site,” she says. “However, generating all the energy on site from renewable sources, while it is the ideal and attractive option, is not always possible or the best thing to do. It might be better to generate some of the energy off site, or from larger renewable energy plants supplying the wider community.”

Getting utility providers and ESCOs involved, specifically by bringing them into the consultation, could be the way forward, Riddlestone says. “In all cases it is necessary to establish an energy service supplier as developers themselves are really in a different business.”

Among the handful of zero-carbon developments in the UK, BedZED in Sutton, Surrey, is probably the best known. For periods between 2002 and 2005 it managed a zero-carbon output, but currently the scheme is importing electricity from the grid following ongoing problems with the CHP plant (see box story, below).

Learning from the lessons of BedZED, BioRegional is still making zero carbon the key aim of its Z-squared scheme – a 2000-home, mixed-use development intended for a site on the Thames Gateway. The design aims to use a supply-mix that minimises carbon emissions. This includes natural gas- and biogas-fired CHP, as well as a number of 1 MW wind turbines to meet energy demands. In addition there is an electrical connection to the national grid to meet peak demands and allow export of wind-derived electricity. It is claimed this could result in a 70% saving in CO2 emissions compared with a conventional design.

Finding the remaining 30% is trickier. Biomass CHP is one solution. However, to run a biomass plant of a suitable size for Z-squared would require a substantial amount of fuel to be imported to the site. A limited supply could be provided by the 10-20 hectares of land set aside for flood prevention but this would only enable a small-scale biomass CHP, which is not yet proven technology. BioRegional has undertaken a separate study to look at the possibility of using pallet waste and other urban biomass sources to run zero-carbon CHP. The study suggests there is sufficient waste wood in the Thames Gateway and plant growth commercially available for biomass to substitute gas-fired CHP. However, Mark says that, “it would not overcome wider future demand and sustainability issues”.

Tackling individual dwellings

Community-scale CHP makes the most sense when it comes to reducing carbon emissions says Richard Quincey, technical director of consulting engineer Gifford. “Mixed-use developments linked to centralised systems are the key”. But what about detached dwellings? Quincey built a low-energy house in Devon (BSj 09/05) for himself two years ago. He claims that the energy consumption is 75-80% of a typical house. Despite this, it still has annual CO2 emissions of 1.5 tonnes. The reality of getting it to zero is remote. The first 50% is relatively straightforward to achieve, he says. The following 25% is tougher and the final 25% is very difficult indeed. “On a local, individual scale you can do things such as increased insulation, mechanical ventilation with heat recovery, low energy LED lighting and solar hot water heating but despite this you are still left with a residual electrical load that needs to be met.”

Technology is undoubtedly part of the answer. “Manufacturers are developing products such as boilers linked to solar thermal panels; we need more technologies like this coming through,” believes Slater, of David Wilson. “We are looking at technologies such as micro-CHP, but the biggest drawback at the moment is the low frequency noise issue.”

The other issue is cost. Quincey is looking at retrofitting PVs to his house but the payback period, even with a grant, is about 40 years. “Cost is always a significant factor,” he says.

Miller Homes, which has developed sites with Eco Homes Excellent ratings, has carried out studies into whether customers would be prepared to pay more for a home that incorporated renewables. Moffat says: “What we found was that most expected it at no extra cost. The problem is the payback might be in the region of 10 years and a lot of people’s horizons don’t stretch that far. They might see themselves being in a property for just five years.”

To make its proposals more achievable, Riddlestone believes the government needs to look into fairer pricing for energy produced by small-scale, renewable energy generators that is exported back to the grid. “The renewable energy produced at BedZED is purchased for a substantially lower price than the energy pulled off the grid. In Germany the price paid is the same, whether you are buying or generating, and in California a premium is paid.”

The proposed changes to Building Regs certainly pose a challenge. But it’s clear the government isn’t clued up about the kind of preparations needed to give the proposals a sporting chance. What matters is that the industry makes its views known about the changes – and it only has until 8 March to submit comments as part of the consultation. Once the problems are aired, solutions can be sought. And Riddlestone for one is adamant that zero-carbon housing development is achievable. “It needs the right leadership and support from government and is very site specific,” she concedes, “but it is possible.”