There are two approaches to consider in reducing the impact of a home’s energy use. That may be either reducing the energy consumption to a lower level, or by ensuring that the energy used in the home is from low-carbon sources, in this article we will look at the tensions between those approaches.
But before taking a dive into that, it’s good to lay out some context around domestic energy use.
Domestic energy – defined as that which is used directly to run the home – is mostly used for heating, around 61% of the total is used that way, with lighting and appliances accounting for 18% water heating 16% and cooking just 6%. So, it is immediately apparent where the significant saving can be made, or to think another way, it is clear where the costly loses are.
Carbon intensity - A modern A-rated gas boiler will emit 215 grams of CO2per kWh of heat delivered.
At the time of writing the national grid has a carbon intensity of 123g per kWh (unit) of electricity generated, this intensity is decreasing year on year as the grid decarbonises, it is hoped that by 2023 the grid will largely (over 95%) be powered from renewable sources, those sources(wind, solar and storage) still have a carbon footprint which is related to the manufacture and operation. There are many articles that can be read on that topic by searching ‘lifecycle carbon renewables’, the conclusion of most studies is that 20g of CO2 per unit needs to be attributed to electricity generated by renewables, a full ten times reduction in comparison to gas if used for heating.
And then, on top of the inherent carbon benefits of using electricity we need to consider the
When comparing low carbon and low energy homes, it’s important to understand that both aim to reduce environmental impact but with different approaches. Here’s a breakdown of the two concepts:
Low carbon homes are designed to minimize the amount of carbon dioxide (CO2) emissions associated with their construction, operation, and energy use.
Goal
- Achieve a significant reduction in CO2 emissions.
Method: a low carbon home will aim to minimise the amount of embodied carbon in any upgrades that are made to the fabric of the home, and then it will seek to heat the home (by far the largest use of energy) using low-carbon sources.
In practice this will mean:
· Performing the ‘low hanging fruit’ of fabric upgrades. Meaning ensuring that loft-insulation is to standard, draught proofing is completed – including a check of the floor in case of uncovered suspended floors and cavity wall insulation is installed.
· Avoiding complex insulation schemes with a high material footprint such as external wall insulation using petrochemical derived materials such as EPS and PIR boards and cladding.
· Electrifying the heating system with a heat pump to take advantage of the significantly lower carbon footprint of that source.
· Performing careful cost/benefit calculations before replacing windows.
Low Energy Homes
Goal - Low energy homes focus primarily on minimizing energy consumption.
Method: this will entail reducing as far as possible the amount of energy that is inputted into a home, with a particular focus on retaining heat through the winter months.
In practice this will mean:
· Performing the ‘low hanging fruit’ of fabric upgrades. Meaning ensuring that loft-insulation is to standard, draught proofing is completed – including a check of the floor and possible insulation thereof and ensuring that cavity wall insulation is installed.
· Engaging a contractor to install insulation to external walls, either externally (preferred) or internally as the circumstances permit.
· Upgrading windows to best standards, with possible changes to size and location of windows to make use of solar gain.
· Installing solar PV and associated equipment –battery and solar diverter to heat domestic water.
Which approach to take?
Traditionally the thinking has been that we should reduce energy use as much as possible by carrying out a high level of measures on homes, known as deep-retrofit. However, in recent years that thinking has started to change for several reasons including.
· Complexity of installation, meaning that projects need a variety of hard-to-find skilled and costly manpower including architects.
· Supply chain issues meaning that the best and most suitable materials are not always available for projects.
· Embodied carbon, high levels of carbon embedded in the manufacture of required materials.
· Decreasing carbon-intensity of grid electricity.
· Increasing prevalence of heat-pumps
Every home is different.
Despite the increasingly strong steer towards a low-carbon approach it should be noted that every home is different, and for some the more complex measures such as triple glazing, wall and floor insulation may be appropriate.
Want to learn more? For a data-driven deep dive into the tension between low-energy fabric-first and a low-carbon approach this video is well worth watching.
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