Case Studies

What’s the difference between; Carbon Neutral, Net Zero, Zero Carbon, Carbon Emissions, Carbon Offset, Decarbonisation, Greenhouse Gases, Green Energy, Operational Energy, Embodied Energy, and no doubt others?

For most of us, these terms just roll into a single basket as a piece of information to buy better, turn the lights off, turn the heating down or consider an electric car if affordable.  Of course, that’s a great start if we are all making these changes.  

However, for those of us in construction or housing it is important to understand the differences between the energies, emissions, and other numerous terms.  Even though I have researched these topics over the years I often wonder in meetings if I am understanding the objective of the discussions about carbon and the various ways in which different groups apply the terms that they use. As the meetings are often multi-professional, I suspect there are many that also feel the same.

For many an SME the often interchangeable terminology can be a minefield. This is therefore a simplified version and a personal interpretation, to support our understanding for the construction workers and professionals that are not expert in the field but want to learn more. I will start with greenhouse gases, that are a combination of natural gases, with human or animal created gases. We will not go into any detail here; as there are a number of different gases that contribute to the many different greenhouse gases that are increasing our global temperature, not just carbon. In the context of housing and construction, the main focus of this article is carbon which contributes to around 75% of the overall greenhouse gases.

Carbon Neutral/Carbon Zero

Let’s look at carbon neutral, net zero, zero carbon, carbon emissions, carbon offset and decarbonisation…Carbon is produced and can be absorbed, so what we want to do is absorb as much carbon as we produce, then we will have achieved a carbon neutral or a net zero position.  To give a rough example, let’s say I grow a tree and it absorbs 25 kilograms of carbon, then we set light to it and the fire creates 25 kilograms of carbon. This scenario will be carbon neutral or net zero, as the carbon absorbed matches the carbon created.

Carbon Emissions

When the tree is absorbing carbon dioxide from the atmosphere it is often described as carbon capture, but when the tree is burning the carbon dioxide that emanates from the fire is normally described as a carbon emission, or in the old days, smoke.

Carbon Offset

Sticking with the tree analogy, let’s say that I want to go on a foreign holiday but also want to remain carbon neutral for my travel arrangements.  My choices are planting around six or more trees to drive to Europe or hundreds of trees to go to Asia, and this process of paying for carbon to be absorbed to cover what we create is known as carbon offset.

Decarbonisation

Decarbonisation is the reduction of carbon without carbon offsetting, so that we have less carbon to absorb because we have produced less carbon emissions.

Looking at construction, before we can reduce carbon emissions, we need to know how to measure the carbon created. In basic terms we have two measurements, one for the materials and labour that are involved in building the house which we call “embodied energy” and the other for the gas and electric used in the house for future decades, which we call “operational energy”.

Embodied Energy / Operational Energy

Embodied energy is the energy required for the labour and materials used to build homes, so there are important choices to be made, such as natural slate from China that requires mining which creates emissions and the fuel to transport the slate eight thousand miles. Alternatively, there are concrete roof tiles manufactured using cement in the UK, with high levels of carbon and the distance travelled using fuel by the people building the house and delivering the materials. This seems quite simple but beware things are not always what they seem, as man-made insulations are often targeted as bad whilst sheep’s wool is easy to be seen as green, this is not always the case.  A well-insulated house with manufactured insulations that eliminate the need for a boiler can far outweigh many natural alternatives.

This means that material choices in buildings have a very significant effect on total greenhouse gas emissions. Reducing concrete and steel used in buildings (unless necessary) and designing buildings in more detail before construction to limit waste, has a big impact. We should make extensive use of sustainable materials particularly timber, which will further promote the growth of carbon capturing materials to offset overall emissions, with intelligent designs to avoid overheating or the need for heat.

This brings me nicely on to Operational Energy, which is the gas and/or electric required to run our devices, keep a house warm and heat the water for bathing or showers. To achieve carbon neutral for our operational energy we can again plant trees to carbon offset the energy we use for heating, cooking and hot water. Alternatively, we can reduce our need for energy by building all floors, walls and rooves below an average Uvalue of 0.14, meet an airtightness of below 2 airchanges per hour, add MVHR (mechanical ventilation with heat recovery) to minimise heat loss, and create enough energy with renewables to run the house, using less electric from the grid than you create. This will be a house that is carbon neutral and net zero, using green energy and not contributing to greenhouse gases in terms of operational energy. All very simple really.

My question to you is what products with high levels of embodied energy are worth the cost for low operational energy requirements?