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The new SAP (Standard Assessment Procedure) consultation is out now. I am very excited because it should begin to change how we design our buildings from an energy perspective. The SAP methodology sets out how we calculate the projected energy demand and carbon emissions from homes. However, it is also the source of the carbon emission factors we use for all building energy calculations related to 好色先生TV Regulations (Part L / Section 6).

There are about 15 questions in the consultation and most of them illustrate what makes me proud of Britain and the engineering sector; lots of intelligent, technical people working hard to improve the way we do things. For instance there are tweaks proposed in the assumed U-values for old solid walls, the way we estimate space heating, heat network losses, account for electric showers, and so on.

The big thing, however, is the proposed changes to the carbon emission factors we use for gas and electricity. Under the current methodology, electricity has a factor of 0.519kg.CO₂.kWh and mains gas 0.216 (updated in 2012). It is these values, along with all the building data in our models that determines whether a building complies with the 鈥渢arget emission rate鈥�, i.e. the limit of CO₂ emissions for the building. These values are important because they determine what heating / cooling technologies are low carbon and what aren鈥檛, or even those that can鈥檛 comply. It makes it crucial that the factors used are as up to date as possible.

Up to now the values have meant that combined heat and power systems and gas boilers have appeared low carbon and electrical systems less so. The new value for electricity is 0.399 and that will have the interesting impact of getting us almost to the point that I have said before: This is the end game in terms of carbon emissions from heating/cooling, now:

• Lowest 鈥� (electric) heat Pumps
• In the middle 鈥� gas fired boilers
• Highest 鈥� combined heat and power

Indeed, it is only a few years until an electric fan heater will be the second-lowest carbon option. For those worried about where we get all the electricity from I think our industry can respond easily, particularly considering it isn鈥檛 a problem for new builds as they have such low demand for heat anyway.

Developers, portfolio owners and managers take note: although this is relevant for new builds it will also affect your energy performance certificate in the future for existing buildings. Your electric heating systems will show a reduction in CO₂ emissions whilst CHP systems will increase. You will get the same issue with using solar power to deliver zero carbon homes, where over time the benefit of the solar power will reduce as the electricity it is offsetting is lower carbon and the overall emissions of the home will increase.

 The same will also happen for those reporting greenhouse gas emissions under the GHG protocol or sectors like higher education where there are specific reduction targets.

As it is effectively mandated in some areas to use CHP for new builds, technical advisors are finding themselves in the strange situation of advising clients with buildings or asset managers with their 鈥渓ow carbon鈥� CHP systems that their CO₂ emissions will actually rise, at least relatively, as the grid continues to decarbonise compared to other buildings /companies that are going all-electric or just using gas boilers.

Barny Evans is environmental associate director for WSP | Parsons Brinckerhoff