To achieve a true net zero building, therefore, it’s necessary to consider the emissions while the building is in use, as well as considering where its construction materials came from and what will happen to them at the end of the building’s life.
In this blog post we’ll look at operational carbon as part of net zero buildings. A separate post covers embodied carbon.
What is operational carbon?
A building requires energy to operate it. Operational carbon refers to the emissions associated with providing this energy, and falls into two categories.
- Regulated emissions.
- Unregulated emissions.
Regulated emissions are addressed by compliance calculations in national building regulations. SAP (domestic) or SBEM calculations (for non-domestic buildings, respectively) require input for space heating and cooling, hot water, ventilation systems and fixed lighting. The energy required for all of these is part of the building’s regulated emissions.
Unregulated emissions result from the activities of the building user and are not accounted for in compliance calculations. Cooking, appliances and plug socket loads are all part of unregulated emissions.
Two identical houses on the same development would have identical estimated regulated emissions, because the model estimates emissions due to building fabric specification, heating installation and hot water system based on floor area.
(Of course, product installation, construction quality and services commissioning would have to be identical on both properties too).
If one house has a sole occupant, however, and the other has a family living in it, the in-use regulated emissions and the unregulated emissions are likely to be very different.
Achieving net zero operational carbon
Reducing operational emissions as part of a net zero strategy requires efficient building fabric, or a ‘fabric first approach’, as it is often termed.
In new-build construction, space heating alone typically accounts for about half of domestic carbon emissions. Drastic reductions in space heating demand can be achieved through low U-values, good thermal bridging detailing, and airtight building fabric (with controlled ventilation to ensure sufficient fresh air).
Implementing these measures means less renewable technology is then needed to reduce the rest of the regulated emissions. But what about unregulated emissions?
Over time, decarbonisation of the national grid will mean unregulated emissions become increasingly ‘unimportant’. With gas boilers being phased out and cooking becoming fully electric, all unregulated energy needs will be met by the zero-carbon grid, meaning there will be no ‘carbon cost’ to them.
Designing and specifying a building’s fabric and services to address unregulated emissions is an imprecise science. At the very least, it risks over specification through trying to compensate for excessive usage.
To a greater degree, therefore, unregulated emissions can be left to be dealt with by the decarbonisation of the grid. It is more important to address regulated emissions, incorporate solar photovoltaics (PV), and consider the potential for future battery storage technology.
What role will battery storage play in net zero buildings?
Battery storage will gradually play a significant role in our homes. Developing the technology to achieve seamless communication between the PV on a home and the batteries in an electric vehicle (EV) is seen as crucial. Many of us are likely to retain private vehicles, and the raw materials are not available to fit batteries in all homes as well as transitioning to EVs.
Because the carbon cost of electricity supply will be removed, PVs and battery storage become more about cost. Battery storage will make it possible to purchase electricity from the grid at cheaper times and store it for periods in the day when the PV cannot meet the demand.
At the time of writing, the cost of providing battery storage is generally seen as being still too high to make it attractive. There are competing standards for how PV and batteries will communicate and regulate the flow of electricity for optimum efficiency. Once one standard becomes widely adopted, however (like VHS or Blu-Ray in the home entertainment world), it will become more feasible.
Operational carbon in net zero buildings
To summarise, a building with net zero operational carbon is highly energy efficient and fully powered by renewable energy sources. The annual carbon emissions from operating it are zero, or even negative.
At present, this may only be in the form of regulated emissions, until such a time as decarbonisation of the grid means unregulated emissions are reduced to zero. Operational net zero can be achieved using only PV, but there should also be provision for the adoption of battery storage which could help to ‘future proof’ a building and lead to lower running costs for future residents.
About the author
Darren Evans - Business leader connecting with people to treat people and planet as the precious resources they are so that we can build a better future together https://darren-evans.co.uk/