VOICES | JULIE GODEFROY What does zero mean? Julie Godefroy H aving a set of commonly agreed, clear and comprehensive definitions for net zero buildings is necessary for investment, specifications, trusted and consistent reporting, certification and, ultimately, regulations. There has been great progress on this in the past few years first with the UK Green Building Council (UKGBC) framework, and then the London Energy Transformation Initiative (LETI) one-pager on operational carbon (energy use), which is supported by CIBSE. As a next step, LETI and the Whole Life Carbon Network (WLCN) recently produced a full set of definitions, including operational carbon, as well as embodied and wholelife carbon. CIBSE now has two important opportunities and decisions on which members can engage: CIBSE LETI FAQ on definitions DR JULIE GODEFROY is technical manager at CIBSE as they are required to support decarbonisation of the energy system, as highlighted by National Grid ESO. The definition implies that either the building is supplied by its own onsite renewables, or it uses a Power Purchase Agreement for renewable energy or a green tariff demonstrating additionality, with guidance on tariffs provided by the UKGBC. Once the electricity grid achieves carbon, this will include nuclear energy so, not meeting the definitions requirement for all energy to be from renewable sources. A clarification in the definition is, therefore, required to cover that point. In addition, and assuming that the end point is accepted as carbon, this triggers the question of what happens in the few preceding years: is there a point at which grid electricity is not yet carbon, but is so low carbon that additional renewable capacity is no longer considered beneficial or required by the definition and, if so, when? Under some National Grid scenarios, such near zero content could be achieved in the first half of the 2030s the not-distant future when planning a building so, again, a clarification in the definition may be useful already. Biomass is provided as an example of residual direct emissions. Residual indirect emissions intend to cover those from the transmission and distribution of electricity, and well-to-tank emissions. This needs explaining, with guidance on how to calculate them. If hydrogen did become available for use in buildings in the future, the definitions requirement that all energy should be generated by renewables implies that only green hydrogen would be allowed, and all indirect emissions associated with generation, storage and distribution would have to be offset. This needs explaining and, at a future point, guidance given on calculations. Again, this may seem a long way off, but the governments ambition is for trials at the neighbourhood and village scales in 2023 and 2025 respectively.1 How does the definition apply if a building is supplied by green gas produced on site from, say, anaerobic digestion? Should green gas tariffs be allowed as Should green gas tariffs be allowed, as they are for electricity, or would this risk encouraging continued reliance on the gas grid? The LETI-WLCN definitions provide principles, but it is difficult to cover, in a succinct and clear way, the range of situations that a building and its energy supplies may face in practice. CIBSE will now be working with LETI to produce a set of FAQs on these definitions, to support clients and project teams, and bring consistency in how definitions are applied. Clarifications will be provided, along with illustrations of a range of situations. Some examples of what the FAQs will cover are provided below. They focus on the definition for a carbon operational energy building, which currently reads one where no fossil fuels are used, all energy use (Module B6) has been minimised, meets the local energy-use target (for example, kWh.m-2 per year) and all energy use is generated on or off site using renewables that demonstrate additionality. Any residual direct or indirect emissions from energy generation and distribution are offset. The incorporation of energy-use targets in the definition may be queried by some: why is it required if energy supplies become zero carbon? Energy efficiency and demand reduction are, of course, supported by CIBSE, and it is right that they are integral to the definition, 16 October 2021 www.cibsejournal.com CIBSE Oct21 pp16-17 Julie Godefroy.indd 16 24/09/2021 17:30