A low-energy building policy starts with clear definitions

Is it a zero energy, net zero energy, low carbon, or renewable energy building?

During the past decade and particularly over the past five years, we have seen a growing number of ambitious policies in the EU and the US that aim to drastically improve the energy performance of new and retrofitted buildings. This is a potentially successful strategy to reduce carbon emissions. In the UK, the built environment is responsible for 53% of the carbon emissions. Other OECD countries show similar figures, so there is indeed plenty of room for improvement.

However, when surveying all of the different policies, the lack of clear and consistent definitions becomes obvious. What is the precise definition of low energy, very low energy, net zero energy, low carbon, net zero carbon, and renewable energy buildings? Are these terms used in a consistent way? And how are they interrelated with each other?

This is the subject of the excellent paper ‘Differentiating among low-energy, low-carbon, and net-zero-energy building strategies for policy formulation’ by Charles J. Kibbert and Maryam Mirhadi Fard. This paper surveys the various terminologies, investigates the differences in use, and provides a series of recommendations.

The following conclusions and recommendations stand out:

1. Definitions of net-zero energy, low energy, and renewable energy buildings should be standardized to ease communications, avoid misunderstanding, and support international collaboration in this field.
2. The focus should be on reducing carbon emissions, because global warming is currently the greatest threat to the global environment. In the medium term, carbon neutral buildings should be the aim.
3. The more that energy requirements are met by renewable energy, the more the need to account for primary energy becomes questionable. Moreover, the accounting system for primary energy is inordinately complex. Reducing carbon emissions should be the final goal, not reducing the primary energy consumption.
4. In parallel with a strategy for implementing low energy buildings, the base-load component of the public electricity grid should be shifted towards low-carbon energy sources. This would indirectly lead to an enormous reduction in the carbon footprint of the built environment.
5. Distinguishing between on-site and off-site renewables is problematic, as it is difficult to draw a clear border. But such a distinction it is also unnecessary. Where the renewable energy systems are precisely located should be a question of economics; let investors go for the lowest Total Cost of Ownership.

Finally, the paper states that the success of improving the energy performance of buildings will ultimately depend on two crucial factors: the price of electricity and building standards and legislation.

Whether the carbon emission reduction will be achieved by energy efficiency investments or by renewable energy investments will depend upon the incremental difference in cost per kWh of avoided grid electricity.