The New Green Standard: Zero Carbon Without a Net

What should our targets be in green building design? Many like the idea of net zero energy. I have never been crazy about it, given that it doesn't really reduce demand, it just pretends to offset it. I preferred architect Elrond Burrell's concept of Radical Building Efficiency, as in Passive House, which does a fine job of dealing with operating energy, but has little to say about embodied carbon, the upfront carbon emissions released making all the materials that go into a building.

But there is perhaps a better target proposed by Emily Partridge, senior architect and "climate action leader" at Architype (designers of the Enterprise Centre shown above, which I have called the world's greenest building). It's straightforward and to the point: zero carbon.

Zero Carbon Without a Net

Partridge describes how most of the profession is still talking in terms of net carbon, even as they begin to take embodied carbon into account. She quotes the definitions from the UK Green Building Council:

• Net zero carbon – operational (in use) energy: When the amount of carbon emissions associated with the building’s operational energy on an annual basis is zero or negative. A net zero carbon building is highly energy efficient and powered from on-site and/or off-site renewable energy sources, with any remaining carbon balance offset.
• Net zero carbon– construction (embodied) energy: When the amount of carbon emissions associated with a building’s product and construction stages up to practical completion is zero or negative, through the use of offsets or the net export of on-site renewable energy.

But she then points out that these targets are often missed, and often meaningless.

Building simulation modelling generally considers renewable energy to offset energy demand on a 1:1 basis. In reality, there is a daily, and seasonal difference between most renewable generation and the energy demand of a building. In summer, energy is exported and potentially wasted. In winter, more energy is needed from the grid, which in turn requires high carbon intensity generation to make up the deficit. Seasonal storage is possible, but current technology means some energy losses and costs.

There will be many who will argue this point, as they do every time I make it, saying "What a bunch of nonsense. By definition 'net' means the positive and the negative together when added up becomes zero. This is unsubstantiated drivel." But as Partridge points out, it is not so simple. This is where "radical efficiency" comes to the rescue; by reducing demand so significantly (as you do with Passive House) that the red and blue heating and cooling bars almost disappear. Then you don't need much PV at all, the building itself helps out as a thermal battery, and you get very close to zero operating carbon emissions without a net.

Embodied Carbon Without a Net

This is even harder to do without a net. For years embodied carbon's importance was downplayed because operating emissions so dominated the picture. But as buildings get more efficient, that's not true anymore; Partridge explains:

Embodied carbon includes emissions caused by extraction, manufacture or processing, the assembly of every product and element, plus the transportation of those goods. Its relative significance is increasing as both the grid decarbonises and operational energy reduces.

But embodied carbon can be reduced significantly through the choice of materials; look at the palette for the Enterprise Centre, it is so natural and high fiber that you could almost eat it for breakfast. "The embodied energy of new buildings can be reduced by using materials which use less energy to produce and are made from natural materials, such as timber and recycled newspaper insulation, instead of steel, concrete and plastic insulation."

Getting to true zero embodied carbon without a net is going to be really hard; foundations are a particular problem, as are mechanical and electrical services. But it is a great target, a great way to think about building. It also helps when deciding whether to demolish and build new or to save and upgrade.

As Emily Partridge concludes:

The drastic impact of the current pandemic has not changed the fact that we are in a climate emergency. We need to be completely clear, honest and truthful, use the knowledge and the technology we already have, and drop the greenwash.

It's time to throw away the net, to forget about the "fuzzy math" of offsets which were never serious for flying and are not much better in building. It's time for true zero carbon as the new target. It's hard, but it can be done.