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Zero Carbon Houses

The Zero Carbon Hub (ZCH) was set up in 2008 to support the delivery of ‘zero carbon’ new build homes from 2016, as a public/private partnership drawing support from both Government and the industry.

Following pressure from the construction industry, an earlier ruling had redefined ‘zero carbon’ as a 70% cut- to provide some flexibility and avoid what was seen as potentially excessive costs. However, that’s now been reduced further, with new lower ZCH recommendations emerging. That led to a jibe from Friends of the Earth, who said ‘Let’s stop calling these houses zero carbon.’

The Zero Carbon Hub reports’ basic approach is a combination of:

• Ensuring an energy efficient approach to building design

• Reducing CO2 emissions on-site through low and zero carbon technologies and connected heat networks.

These first two steps are together referred to as Carbon Compliance (CC).

In addition, there is a third step:

• Mitigating the remaining CO2 emissions through Allowable Solutions (AS), which secure carbon savings away from the site. That in effect means importing green power via the grid e.g. from (remote) wind farms, but there imports, and any other imports (e.g. during winter) are meant to be balanced, over the year, with power exported when there is excess.

However, houses can still have net emissions: the ZCH report outlines recommendations for the actual ‘built’ performance of the houses, within 2016 Building Regs, as follows :

10 kg CO2(eq)/m2/year for detached houses 11 kg CO2(eq) /m2/year for attached houses 14 kg CO2(eq)/m2/yr for low rise apartment blocks (up to 4 storeys)

These recommendations apply to the actual built performance, and so cannot be directly compared with current design standards. However, on top of any potential carbon savings from moving from designed to built performance, the improvements on the 2006 standard would they say be:

• 60% for detached houses • 56% for attached houses • 44% for low rise apartment blocks

In terms of low carbon supply options, the report says ‘Various technologies are available to provide low and zero carbon (LZC) heat. However, as the Carbon Compliance limit is tightened it becomes increasingly difficult to achieve simply through LZC heat generation. LZC electricity generation may also be needed, for which there is a smaller range of options. In practice, the mainstream technology currently usable for a wide variety of individual dwelling types and locations is photovoltaic (PV) panels, which are usually installed on the roof and convert light to electricity. Other options, such as wind turbines and CHP, are only appropriate in some situations and their use should not therefore be the basis for setting a national regulatory limit’.

It was therefore agreed that feasibility should be assessed by reference to the amount of PV required, taking this as a proxy for all LZC electricity generation technologies and assumed that an area equivalent to 40% of ground floor area was the appropriate reference point for feasibility. For heating, the electric option used is the air source heat pump as ‘it is a more efficient use of electricity than instantaneous electric and more widely deployable than ground source heat pump’, and gas options used are gas condensing boiler for houses and gas condensing combi boiler for apartments. Biomass options might be taken up later. Solar water heating in included in all cases.

On this basis it was concluded that the earlier proposed 70% improvement in Carbon Compliance from 2016, over 2006 levels, was ‘not deliverable as a national minimum standard for all dwellings’. Which means that more ‘allowable solutions’ will have to be used. The study tries to assess the cost of both carbon compliance and allowable solutions, and suggests that that, for a typical detached house, they might be £5,400 (CC) and £6,900 (AS) above the cost of meeting the 2010 regulations, in 2016 prices. It also suggests that these cost are comparable, at around £250k per acre in total, with the cost of meeting the other existing regulatory requirements (~ £400k per acre), although this depends on location, and, crucially, it says, on the price of AS. It chose £75 per tonne CO2 as a reasonable figure . But it says ‘There is a risk that it is hard to be sure that off-site measures are truly additional to what would have occurred anyway. Addressing this risk should be an important feature of how Allowable Solutions are defined’.

That sounds a little odd. Why do Allowable Solution sources have to be additional? What are commercial wind farms etc for if not to supply demands like this (and of course others) - and, one would think, at lower cost than PV? But the idea seems to be that, to avoid developers ducking out and simply buying in green power, the remote power has to be dedicated to and created by the house demand. Clearly, as ZCH say, we need more guidance on allowable solutions!

We await the governments response.
http://www.zerocarbonhub.org

Posted by Dave Elliott on March 5, 2011 5:25 PM | Permalink