4.11 Embodied Energy in Retrofit

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By the end of this lesson you will have learned:

more about the embodied energy associated with low energy retrofit.

  1. The “Carbon Burp”
  2. How much material is used?
  3. The “Carbon Payback”
  4. Carbon Savings in the longer term

Embodied Energy – the “Carbon Burp”

The carbon burp refers to the CO2 emissions that occur as a result of a retrofit. This can be from the material extraction, processing, manufacture, installation and related transport of materials and products used.

We then compare these to the total lifetime CO2 savings resulting from the retrofit – the assumption being that the measures are robust and deliver savings consistently, on an on-going basis over a long period.

 

Going back to the 3 CLR modelled house types introduced in Lessons 4.8 to 4.10, and the different energy efficiency retrofit scenarios assessed (e.g. IWI and EWI), the embodied energy of the main materials used has also been considered.

To keep the exercise simple and manageable, whilst retaining a good degree of realism, we have focused on the manufacture and installation of the key energy efficiency measures: insulations, windows and doors.

This is intended to represent the majority of the materials used for achieving low energy performance. The exercise doesn’t include repair, maintenance or the various items of ‘consequential’ work. We use embodied carbon data from the University of Bath ICE database (see http://www.circularecology.com/embodied-energy-and-carbon-footprint-database.html accessed 04/01/16).

The 3 CLR modelled house types use a variety of insulation types in this exercise.

For example:

  • with less vulnerable and higher thermal performance (with higher embodied energy) materials used in some situations e.g. insulations used in cavity walls and in solid floors and
  • with lower embodied energy materials such as woodfibre insulation for example used for IWI.

The choice of different materials for different applications is ultimately made by the retrofitter, and the scenarios illustrated below are simply for illustration as part of this exercise. A minimum of underlying detail used in these calculations is shown here – for example the embodied energy of different sorts of window upgrades is not detailed.

More research – and consistent, standardised accounting and reporting – is generally needed in this area.

The carbon pollution produced as a result of these measures occurs in the period leading up to and during the retrofit work and we have, perhaps inelegantly, described this as a ‘burp’ of CO2 emitted in order to achieve on-going CO2 reductions from space heating – the ‘carbon burp’.

2. How much material is used?

The graph below shows the relative amounts of each insulation material (or window/door assembly) used, expressed as the relative amount of carbon dioxide emitted by each in tonnes of CO2:

PU: polyurethane
EPS: expanded polystyrene (in this case of the ‘graphitised’ or ‘grey’ type)

Graph showing volume of insulation materials used in different types of retrofit.
Graph showing volume of insulation materials used in different types of retrofit.

Above The bungalow in this illustration uses a lot of PU for the medium and deep retrofits as the poor form factor requires a low wall U-value and the cavity is filled with PU foam as well as additional layers of insulation.

3. The “Carbon Payback”

The graphs below show the CO2 produced by each house’s space heating as dark blue bars.

  • The first column (year 1) is before/during retrofit (we assume in this exercise that around the retrofit period the house remains continuously heated during the heating season).
  • The CO2 emissions from space heating after retrofit are shown in columns 2- 5 and are assumed to represent the on-going annual post-retrofit emissions.
  • Added to year 1 is the carbon dioxide ‘burp’ related to the key retrofit materials – shown as pale blue patterns (keyed).

Remember that CLR sets different energy targets depending on whether a house is to have external wall insulation or internal wall insulation, as it is generally easier to make deeper savings when insulating externally, and as we need to maximise CO2 reductions across the UK stock, we need to maximise the opportunities.

This means that in these illustrations the externally insulated houses achieve lower emissions each year at the expense of greater emissions in year 1 (and slightly longer carbon payback periods), but deliver greater lifetime CO2 savings overall.

 

Obviously it is possible – guided by cost benefit analysis and the client’s brief – to choose ‘carbon sequestering’ EWI materials or those that have lower embodied energy. This exercise simply illustrates the principle of ‘carbon payback’ and suggests orders of magnitude when compared to lifetime CO2 pollution.

In our model the carbon pollution emitted in year 1 is ‘paid back’ in around 4-5 years for EWI deep retrofits and 1-2 years for IWI retrofits – as described in the following set of graphs, for each house type with each type subdivided into EWI and IWI retrofits:

Graph of carbon dioxide payback time for a bungalow with deep EWI retrofit
Graph of carbon dioxide payback time for a bungalow with deep EWI retrofit
Graph of carbon dioxide payback time for a bungalow with deep IWI retrofit
Graph of carbon dioxide payback time for a bungalow with deep IWI retrofit

Above In year 2 (the first year after retrofit) the house starts to deliver CO2 savings from reduced space heating fuel consumption (with the 3°C comfort take). In the example above, it takes 3.4 years for the CO2 saved by the retrofit to equal the CO2 emissions related to the materials and products used to achieve the retrofit. Only after this period does the atmosphere ‘see’ on-going reduced CO2 pollution from the home.

Graph of carbon dioxide payback time for a town house with deep EWI retrofit
Graph of carbon dioxide payback time for a town house with deep EWI retrofit

 

Graph of carbon dioxide payback time for a town house with deep IWI retrofit
Graph of carbon dioxide payback time for a town house with deep IWI retrofit

 

Graph of carbon dioxide payback time for a semi with deep EWI retrofit
Graph of carbon dioxide payback time for a semi with deep EWI retrofit

 

Graph of carbon dioxide payback time for a semi with deep IWI retrofit
Graph of carbon dioxide payback time for a semi with deep IWI retrofit

4. Carbon Savings in the longer term

Although reduced, these residual emissions of course accumulate over time in the atmosphere as indicated in the graphs below.

Starting from the initial carbon burp and year 1 heating emissions, the graphs below show cumulative CO2 emissions over 60 years following each retrofit compared to emissions from the unimproved ‘basecase’ houses.

While the deepest retrofits have the highest embodied carbon in these modelled scenarios, they also save more carbon with each decade (to the end of the life span of the retrofit).

Obviously all emissions would fall if – hopefully when – the UK heat supply becomes progressively decarbonised.

Graph of total carbon dioxide production over 60 years - retrofitted bungalow
Graph of total carbon dioxide production over 60 years – retrofitted bungalow

 

Graph of total carbon dioxide production over 60 years - retrofitted town house
Graph of total carbon dioxide production over 60 years – retrofitted town house

 

Graph of total carbon dioxide production over 60 years - retrofitted semi
Graph of total carbon dioxide production over 60 years – retrofitted semi

As well as considering greenhouse gas pollution resulting from the products and materials used to achieve low energy performance, it is also important to also think about carbon sequestration related to our gardens, streetscapes and public or private greenspaces around buildings (see further reading below).

Summary:

This lesson has considered the possible embodied energy associated with low energy retrofit, including the following:

  1. The “Carbon Burp”
  2. How much material is used?
  3. The “Carbon Payback”
  4. Carbon Savings in the longer term

Suggested reading

  1. ‘Your garden eats carbon (so please feed it well!)’
    From: http://www.treehugger.com/lawn-garden/your-garden-eats-carbon-so-please-feed-it-well.html accessed 04/01/16
  2. ‘Urban plants’ role as carbon sinks ‘underestimated’
    From: http://www.bbc.co.uk/news/science-environment-14121360 accessed 04/01/16
  3. ‘Mapping an urban ecosystem service: quantifying above-ground carbon storage at a city-wide scale’
    From: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2011.02021.x/abstract accessed 04/01/16
  4. Also to start to understand more about the broader context in which energy and resources are used to produce materials and products this article on plastics is comprehensive and holistic: http://circulatenews.org/2016/01/plastics-breaking-the-mould/

 

 

 

Lesson tags: carbon burp, carbon payback, carbon sequestration, CarbonLite Retrofit, cumulative carbon emissions, embodied energy
Back to: CarbonLite Retrofit Course (C3) > 4 Energy in Buildings