Part 9 of Decarbonising the Built Environment: a Global Overview, by Tom Ackers
Download the whole series as a PDF here
In this part, I cover the operational energy used in buildings – that is, mainly, the energy used for heat, light, cooking and electricity – and the greenhouse gas emissions from this energy use.
I will provide an overview (section 9.1), a focus on space heating and cooling, the biggest user of operational energy (section 9.2), and a note about the effect of global warming on that (section 9.3). Then I look at what determines the thermal performance of buildings, i.e. how well they keep out winter cold or summer heat (section 9.4), and end with some points about Passivhaus standards (Section 9.5), which forms a link to the tenth and final part on how operational greenhouse gas emissions can be cut.
9.1. The operational energy of buildings
The chart below shows the global built environment’s operational energy-related emissions for 2018.
This is an excerpt from the chart in part 5 that showed both operational and embodied emissions of buildings.
All three rows show different breakdowns of (i.e. different ways of looking at) the same emissions. The third row shows the direct and the indirect energy-related CO2 emissions of residential and non-residential buildings. Additionally, I have included my rough estimate for the methane emissions associated with heating buildings, worldwide; and a recent estimate for the non-renewable CO2 wood combustion emissions associated with household cooking (see Appendix 3, in the PDF version).
As I mentioned in part 5, CO2 wood combustion emissions are a component of the category “land-use, land-use change and forestry” (LULUCF). They are not included in the IEA’s “energy-related CO2 emissions” data.
The percentages here are proportions of all global sociogenic greenhouse gas emissions for 2018.
Excluding wood combustion emissions, the energy-related operational emissions of buildings worldwide were ~10 Gt CO2e, or 17.5% of all greenhouse gas emissions. That compared, for example, to energy-related CO2 emissions of global transport of 7.6 Gt CO2 (13.1% of all greenhouse gas emissions).
Buildings’ operational energy-related emissions comprise: space heating and cooling, water heating, lighting, cooking, and the use of various electrical equipment and appliances.
In part 5, I noted that globally, operational carbon from buildings comprises ~75% of the lifetime emissions associated with buildings, versus ~25% from buildings’ construction.
In the chart, residential and non-residential CO2 totals are divided into direct and indirect emissions. Direct is basically in-situ fossil fuel combustion, e.g. with a gas boiler. Indirect is mostly emissions associated with the production of electricity. (Again, direct emissions under the heading “energy-related CO2 emissions” do not include wood combustion.)
However, “direct” emissions do include the CO2 emissions upstream of in-situ combustion, in the energy supply chain.[1]
The chart shows that residential buildings are responsible for around 60% of buildings’ operational CO2 emissions worldwide, and non-residential buildings for 40%.
The level of buildings’ operational energy use is, broadly speaking, determined by the number of buildings, and the scale of energy consumption in each of them.
The graph below shows the level of operational energy use for the world’s buildings, broken down by end-use. These are quantities of energy, including all fossil-based and non-fossil-based sources.
Many low-income households across the world depend on non-fossil fuel sources of energy.
For example, in Nigeria, roughly half of final energy consumption across the economy as a whole comes from household operational energy consumption. But around 65% of that comes from biomass – wood, charcoal, animal dung – mostly used for home cooking. In Nigeria, only about 60% of the population have access to electricity.
Biomass combustion in the home is enormously damaging to public health. According to the IEA, almost 500,000 people died prematurely in sub-Saharan Africa in 2018 because of cooking with solid biofuels – “a figure that equals the combined death toll of malaria, tuberculosis and HIV/AIDS”.
Biomass combustion also produces more CO2 combustion emissions per unit of energy than coal does. The fact that that CO2 originally came from the atmosphere, and can eventually be reabsorbed by new plant growth, hardly recommends most biomass combustion as a useful “net-zero” energy source. Wood combustion in homes is a major cause of net forest loss. Moreover, most methods of biomass combustion are incredibly inefficient at transferring the chemical energy stored in biomass into a useful form.
Of the total final energy consumption in buildings, 35% – ~45 EJ in 2018 – is devoted just to heating interior space. That is, more than a third of all of operational energy use in the world’s buildings is used just to keep their interiors warm enough when it is cold outside. ~7 EJ (~5% of total operational energy use) is used for space cooling.
So, taken together, space heating and space cooling comprise around 40% of buildings’ operational energy use, followed by water heating and cooking; then use of appliances; then lighting.
So long as a great deal of the world’s energy generates greenhouse gases, all of these uses of energy need to be minimised, to as near to zero as possible.
9.2. Space heating and space cooling
There are broadly two different kinds of energy efficiency connected to the heating and cooling of buildings:
a. Fabric efficiency: what the fabric of the building on its own does to mitigate operational energy use. For example, how good is a building at maintaining thermal comfort without additional energy being applied?
b. Supplemental heating efficiency: the efficiency of whatever technology provides the supplemental space conditioning that is required.
The fact that so much energy is used in heating and cooling interior space globally tells us that – whatever the technologies involved – buildings must be pretty poor at maintaining comfortable interior temperatures in the first place, without the application of energy.
In the rest of this post I will focus on those issues of thermal comfort and fabric efficiency. Then in part 10, I will turn to the topic of supplemental heating and cooling.
Thermal performance and fabric efficiency
Put simply, the thermal performance of a building is its capacity adequately to maintain steady, comfortable indoor temperatures, even as the weather and the climate vary outside, and with minimal outlay of supplemental energy.
Ideally, the building achieves this as far as possible without the use of additional energy – that is passively – through the physical properties of the building fabric itself. Such buildings have high fabric efficiency.
When poor thermal performance is combined with an energy system built on fossil fuels, the result is fossil dependency and high levels of emissions.
You might think that buildings requiring energy to heat and cool them is only natural – and it can seem so, when we are used to thinking about buildings that way.
However, from an engineering perspective, this need not be the case. Very high levels of thermal performance are, for the most part, entirely within reach, at comparatively low cost.
Some effective building strategies for mitigating heat and cold have been available for millennia. Other more recent techniques and innovations are now well-established and economically competitive, compared with the operational costs of leaving them out.
The problem is that the legacy building stock worldwide is under-performing, while new buildings are often poorly and negligently designed, and poorly constructed from a thermal perspective.
As a result, the world’s existing buildings are needlessly and profoundly inadequate to the task of delivering shelter and maintaining comfort and good health for their occupants, without the constant use of energy.
Often, thermal performance is so bad that, even with the option of constant supplemental heating or cooling, the amounts required to maintain thermal comfort are so large that thermal discomfort has been normalised. This happens in the UK, for example – a country rich in accumulated resources.
Meanwhile, the prevalence of heating and cooling systems has tended to disguise, and excuse, tremendous levels of thermal inefficiency in buildings’ physical structure. The upshot is that buildings have been specified, designed and built to a lower expectation, and a lower thermal standard. They then require the additional heating and cooling paraphernalia, and energy to power it, just to remain habitable and functional.
In parts 3 and 7, I mentioned how aesthetic considerations have helped drive the use of high-emissions steel and concrete in much modernist architecture and contemporary buildings design. The building aesthetics also depended on a degree of historical and ideological blindness to the material and environmental effects of energy use – and produced an international style of climate-insensitive and context-inappropriate design.
Unquestionably, an aspect of that concerns supplemental heating and cooling systems – an almost universal affliction. Large embodied and operational emissions have been typical throughout the post-second-world-war period of fossil capital.
The Seagram Building in New York City, mentioned in part 7, is a good example. It has enormous operational emissions.
Barnabas Calder and Florian Urban note how the building’s brass mullions and spandrels “radiate the warmth of the building out into the winter cold of New York, or collect the sun’s heat in summer, making them among the main causes of the building’s exorbitant energy consumption for heating and cooling”, that task performed by vast forced-air servicing.
That servicing, in turn had “liberated the building’s envelope from its traditional obligation to keep out the winter cold or the summer sun”. Ludwig Mies van der Rohe, a prominent architect, could instead “make his glazing an artistic meditation on transparency, clarity and elegance”.
Even now, the Seagram Building’s operations produce ~15,400 tonnes of CO2 annually – and that is not even including other greenhouse gases besides CO2. That is equivalent to the per-capita consumption-based emissions of about 1500 people living in the UK.[2]
The Seagram Building is a particularly egregious example, but it is just one of New York City’s most energy-hungry office buildings.
The ideological disinclination to think about energy use and its environmental consequences has been an epochal mis-step in the built environment.
This disinclination unfortunately still remains, in widely-shared expectations about what a “modern” building is like: what it looks like, how it feels inside.
Poor thermal performance is perhaps forgivable in old buildings. It might be that traditional, pre-war and even some post-war building types can be excused over poor thermal performance – depending on the historical availability of effective engineering knowledge, or the obscuring power of ideology.
However, when new buildings are built that way today, it amounts to professional malpractice – given the collective material resources and the engineering expertise at the world’s disposal, and the narrow sliver of time that remains to mitigate worldwide climate disaster.
And existing buildings can also be retrofitted to improve their thermal performance greatly, and improve their occupants’ thermal comfort.
In my view, existing buildings should be retrofitted wherever possible, (a) if it will mitigate the combined embodied and operational emissions of the building over something like a 30-year timeframe; and (b) if it will meaningfully lift the comfort, and improve the health, of occupants.
This means keeping the embodied emissions and material footprints of retrofit as low as possible, and making all retrofit decisions according to an independent assessment of the likely lifecycle emissions and material and environmental footprints, when compared to no retrofit.
More broadly, there is a case for appraising real needs, and redistributing the use-values associated with the built environment, in the context of a global need for contraction and convergence.
New buildings should be built only when strictly necessary from the point of view of needs, and when lower-emission retrofit options are unavailable.
Data from the IEA/Tsinghua University buildings model suggests that, since at least 2010, the rapid increase in constructed floor area worldwide has been the leading driver of the growth in buildings’ combined operational energy-related CO2 emissions.
Economic growth has tended to bias the construction of more and larger buildings, and – given a disinclination to specify for fabric efficiency – these expanded floor areas and enlarged volumes of internal air have all needed to be heated, cooled, and lit.
Economic demand has been the main driver of those floor area constructions, and the increases in space conditioning have likewise been based on an ability to pay.
In any case, the health effects for occupants of buildings of poor thermal performance, or an inability to pay for space conditioning – fuel poverty – should be evident. So too the climate impacts of the emissions that follow from space conditioning being powered overwhelmingly, still, by carbon-based fuels.
Thermal comfort
Thermal comfort can be difficult to define. I think we all know from experience that it can be highly subjective – ultimately it is a physiological and psychological state of being. It also varies according to things like your age, health and level of physical activity.
Thermal comfort plainly varies with ambient temperature – but it varies, too, with the level of ambient humidity and ventilation. These are physically related to ambient temperature, and are themselves important factors when it comes to securing thermal comfort and health.
Nevertheless, we are all familiar with thermal discomfort. It can seriously impact people’s quality of life, and can be deadly. People’s degree of risk from exposure to extremes of temperature also varies – for example, the elderly will tend to be more vulnerable, with less physiological capacity for dealing with heat or cold.
I mentioned in part 6 that international human rights law has codified adequate housing as an intrinsic human right, and that all states have committed themselves to this principle in one form or another. An important part of adequate housing, alongside things like security of tenure and affordability, is a habitability provision.
As well as things like sufficient living space for all, this also includes “protection against the cold, damp, heat, rain, wind, other threats to health”.
In the UK, there are no laws over temperatures in the workplace – only statutory guidance that suggests temperatures be roughly between 16°C and 30° – though 13°C is considered OK if work is physically strenuous. Of course at home people tend to be physically inactive, but thermal performance is not regulated across the housing stock.
In relation to keeping out cold, LETI say that a good metric for thermal comfort indoors is when the internal surface temperature is “greater than 17°C, when outside temperatures are at a minimum”. The Royal Institute of British Architects (RIBA) define “overheating” in the home as “25-28°C maximum for 1% of occupied hours”.
So, presumably, reliable indoor ambient temperatures of ~17-23°C in the daytime could be taken as the outer range of thermal comfort in a home, wherever you are in the world – going down to 16°C at night time.
In 2021, the Welsh Government published a report, Tackling Fuel Poverty 2021 to 2035, in which they defined a “Satisfactory heating regime”. In homes without elderly or disabled people, it would be “21°C in the living room and 18°C in other rooms for nine hours in every 24 hour period on weekdays, and 16 hours in a 24 hours period on weekends”. For homes with older or disabled people, on every day of the week it would require temperatures of “23°C in the living room and 18°C in other rooms achieved for 16 hours in a 24 hour period”.
In any case, one of the main ways to secure thermal comfort, and protection from the elements – especially in the context of costly commodified energy and climate change – is by ensuring that all homes perform well thermally, and have good to excellent levels of fabric efficiency.
What that looks like will vary, depending on where a building is. When it is cold outside, you want your building to capture and retain heat effectively. But when it is hot outside, you want your building effectively to shade its interior from the sun, and efficiently dissipate the heat that does enter.
9.3. Buildings in a changing climate
Climate change is also now having accelerating effects on the habitability of buildings. 2023 is “virtually certain” to be the hottest year on record – the hottest year in “millennia” – with 2015-2022 already the eight warmest before that.[3]
However, the need for thermoregulation in buildings is becoming more acute at both ends of the temperature scale, alongside an increased need for flood and storm protections. Many existing buildings are becoming ever more inadequate to the task of providing comfort without massive, and sometimes impossible outlays of energy.[4]
Urban population growth and construction in warmer climates are compounding the effects of heat for urban dwellers via the “urban heat island” effect – the tendency for urbanised areas to be warmer due to the presence of heat-absorbing urban materials instead of vegetation, and the heat-producing effects of various domestic, retail, transport and industrial activities.
The quantity of electricity used for space cooling internationally doubled between 2000 and 2018. And heatwaves across China in 2022 drove widespread use of air conditioning, and took China’s electricity demand to an all-time high (see also part 4). With hydropower reservoirs out of action, and with as-yet inadequate renewables and power storage capacity, this was one of the factors that led to increased recourse to coal. Even retired coal-fired capacity was brought back online. These events seem also to have reinforced coal as the backstop of China’s energy transition.
A further turn of the screw is that the refrigerants used in cooling systems – the fluorinated gases or F-gas – have high global-warming potential, and a tendency to leak. So their increased use, like the Chinese coal burned to cool people down, has further added to the burden of greenhouse gases in the atmosphere.
And at the other end of the scale, we have more frequent and severe extremes of cold. Fossil-fuel dependency and price rises, combined with buildings’ poor thermal performance, are also exposing people to heightened risk from winter cold.
The technical challenges of ensuring people are warm or cool enough at home cannot be overcome without also overcoming the social causes of inadequate housing.
9.4. What determines buildings’ thermal performance?
What makes buildings perform well, or badly, thermally? The following basic principles of architectural design all play a role – but they are too often poorly implemented or left out of new buildings entirely, and absent in older buildings.[5]
Readers may know, or recall from school physics classes, the three main ways that heat transfers across a medium: by radiation, conduction, or convection.
Radiation is the transmission of energy in the form of waves or particles – and any object that is warmer than its surroundings transfers heat from itself to its surroundings by radiating heat from its surface. Conduction works instead by physical contact, with heat energy propagating from one molecule to the next through a given substance. Convection transfers heat through a fluid, like air or water, via the movement of the particles themselves.
Much about a building’s thermal performance is determined by the physical qualities of its outer walls, windows, floor, roof and outer doors. These comprise the building envelope – where the building meets its environment. In thermal terms, the envelope serves either to block, or to permit, the transfer of heat into or out of a building – by radiation, conduction or convection.
An important concept in this regard is bioclimatic design: the principle by which buildings passively work with local climatic conditions to take advantage of whatever natural daylight, heating, cooling, and ventilation effects are available. The aim is to maximise comfort and health for a building’s occupants, with minimal use of supplemental energy.
Solar gain means that a building’s interior is heated by radiation in the form of light from the sun – the original “greenhouse effect”. As we all know, when it is sunny outside you will often want to shade buildings’ interiors from the sun, to prevent overheating and maintain comfort; when it is cold outside you will often want to capture that heat instead, to passively heat a building’s insides.
Optimal thermal performance, with respect to solar gain, therefore means tailoring the building to strike the best balance between these two requirements, depending on the variations in incident sun at a particular site, both over the course of a day, and over the course of the year.
Two of the most important ingredients in this respect are the orientation of a building in its surroundings, and the arrangement of the windows. In the UK, for example, according to LETI, the optimum glazing ratio for a building, on the average, is a maximum of 25% glazed surface on its south-facing side, up to 20% glazing on its east- and west-facing sides, and as little glazing as possible on the north-facing side. Getting these things wrong can have enormous costs in terms of thermal performance, and the resulting operational efficiency of a building overall.
Long eaves and brise soleil are also very simple, effective ways to manage solar gain. They allow low-level sunlight to enter and warm a building during winter months and in the mornings and evenings, while shading windows and exterior walls from high-level midday and summertime sun. Similarly, deciduous trees adjacent to a building can screen the sun in the summer, while allowing sunlight to warm a building in the winter.
One fairly high-tech way to manage solar gain through windows is with high-performance glass that has coatings to reflect away certain wavelengths of light, selectively. The G-value of glass (in Europe), or its solar heat gain coefficient (in the USA), quantify (in different ways) the solar heat gain through that glass, per unit of incident solar radiation.
Low-e coatings on glass reflect a larger proportion of long-wavelength infra-red light. When used on the outside of a window, this minimises the greenhouse effect indoors. External shutters are a lower-tech alternative, that does something similar by entirely blocking the light.
In terms of overall heat gain and heat loss, the form factor of a building – the ratio between external surface area and internal floor area –is important. It can also be measured for any individual part of a building, such as an apartment. (See the illustration below.)
The key mechanisms here are radiative heat loss/gain and conduction. Heat can be lost to the surrounding environment, or gained most readily from it, if there is a larger external area of the building exposed to outdoor conditions.
All other things being equal, this means that a detached bungalow will typically gain or lose heat easiest (it has a high form factor ratio); whereas a mid-floor apartment will typically gain or lose heat more gradually (it has a low form factor ratio). In overall thermal performance terms, that makes a mid-floor apartment more thermally efficient, as it is sheltered like a penguin between its neighbours.
For those areas of a building’s envelope that are exposed to the outside, the most effective way to prevent heat loss is thermal insulation. This also works to insulate buildings from gaining heat from outside, and can double as sound insulation on exterior or interior walls. Thermal insulation minimises conduction, convection and radiation across a building’s envelope.
One way to quantify the thermal insulation qualities of a material is with an R-value. This measures its thermal resistance, and is the product of its conductivity and its thickness. High resistance means a substance very effectively frustrates the transfer of heat energy, and therefore is a good insulator.
However, the insulating qualities of building materials are more usually given by looking at things the other way round – with a measure of the rate at which heat energy flows across a given material. U-values (heat transfer coefficients) are the reciprocal of R-values, and they quantify the thermal conductivity of materials. A good conductor is a poor insulator, and a good insulator is a poor conductor – so a low U-value means a low rate of thermal conductivity, and a high level of thermal insulation – generally a good thing.[6]
Wall insulation can be provided by many materials. They are usually classified as open cell or closed cell, depending on their physical structure.
Open cell insulation typically consists of strands of fibrous material, such as sheep’s wool, hemp, or mineral wools like glass fibre or rock fibre. As such, the material is breathable – air can migrate through it, but only very slowly – so heat loss by convection is minimal, provided the material remains dry and not contaminated with water vapour. Meanwhile, the fibres themselves are poor conductors of heat, and therefore also ineffective at absorbing and radiating heat energy outwards from the structure.
Closed cell insulation consists of a denser structure of small, self-enclosed cells – usually containing a gas with lower thermal conductivity than air. Convection cannot occur from one cell to another, and the cell walls are sufficiently thin that conduction is also minimal. The closed structure means such materials are more impervious to the passage of water vapour.
Typically these are solid foam-board products, sold as sheets. Their insulating qualities are very good within the confines of a single board, but can be compromised quite easily at cut-points and at the joins if poorly installed.
Hemp (see also part 8) is an open call fibre, and performs averagely compared to mineral wools, but not as well as synthetic products like aerogel board and evacuated panels.
Cavity walls, where a cavity is created between two layers of brick or masonry, became common in the UK in the 1920s, as a way to prevent the transmission of moisture across the building envelope. But cavities also give a space for thermal insulation. According to the Designing Buildings Construction Wiki, some typical U-values for walls are:
Then there is window insulation. As we are all aware, windows can be insulated by the use of two or more panes of glass, often separated by an air-tight gap filled with a gas such as argon. This minimises heat loss by conduction, while allowing visible light to radiate through the window. Three panes of glass instead of two is better operationally, but three versus two panes also increases the embodied carbon of a window. Yet the embodied carbon is also affected by what the frames are made of – wood, PVC, or aluminium.
A triple-glazed window unit with wooden frames will likely have lower embodied emissions than a double-glazed aluminium-framed window. In any case, the wisdom of double- or triple-glazing largely depends on climate. When low-e coatings are used on the inside of a window, this also serves to decrease the amount of infrared light re-radiated back outside from a building’s interior, therefore preserving heat on the inside. Curtains and shutters perform a similar function.
Like all building specifications, the choice of glazing warrants a whole-lifecycle approach to emissions, to balance the trade-offs in embodied versus operational emissions, and money cost.
In all kinds of insulation, one important aim is to avoid weak links in the insulating barrier, where there is either direct exposure from the inside to the outside, or a more thermally conductive passage through which heat can pass.
Weaknesses like these form thermal bridges, which tend disproportionately to shuttle heat energy, as well as damp, across the building envelope. They are very common in older buildings, but are also found in poorly designed or poorly constructed modern buildings.
Heat loss by convection is also a problem. The best way to prevent it is to make the building airtight. But this needs to be balanced with ventilation, which is needed to maintain comfort and thermal integrity. Ventilation removes stale air and introduces fresh air into the interior, thereby moderating the temperature and humidity, replenishing oxygen, venting CO2, and preventing the build-up of damp or various air-borne contaminants.
Airtightness, though, is about controlling the inflow and outflow of air. It is the opposite of air leakage, such as uncontrolled draughts, which can introduce all of those things that good ventilation is meant to control: the passage of damp air, and loss of regulated interior temperature, and so on. The motto is: “build tight, ventilate right”.
Ventilation, in turn, can be natural – that is, passively achieved through wind, cross-ventilation, or the stack effect, where cool air enters at the base of the building, is heated by the interior, and is vented out the top. Or ventilation can be achieved mechanically, or with a combination of passive and mechanical means.
Ventilation can also include a heat recovery mechanism, to transfer up to 98% of the heat from vented stale air, to warm the incoming fresh air – in which case, the net operational energy savings over even just a few years will likely outweigh the upfront cost and the embodied carbon of a device’s manufacture.
Similarly, you can have a water-based heat recovery mechanism for outgoing waste water. With those, hot water from a kitchen sink, washing machine, shower or bath, helps to heat hot water ready to use.
Looking beyond the envelope, to a building’s inner fabric, thermal mass describes the ability of a given material to absorb, store, and later release heat energy – and it is therefore an important way to transfer, and to moderate, variations in external temperature.
For example, masonry or concrete have high specific heat capacity, which means that they very effectively absorb and store heat. A trombe wall made of one of these materials can be used to collect solar radiation from a sun-facing window during the day, which it then slowly radiates back into the building over subsequent hours.
9.5. Passivhaus standards
The Passivhaus certification standard combines all of the above design principles and more, to achieve maximum operational efficiency for buildings passively – with the minimal use of additional energy. The standard includes benchmarks for aspects of a building’s structure and services. Good thermal performance is crucial to it.
Passivhaus certification is not just a matter of design, though.
All of these building methods depend too on high standards of fabrication and construction. What is good in theory may not work as it is meant to, if it is poorly implemented, or if the materials themselves underperform, giving rise to a performance gap.
Only in-situ testing can tell you what is really going on, once a building is made. There are diagnostic tools for testing thermal performance. For example, you can test the air tightness of a building using a blower door, and detect paths of thermal leakage using infrared thermography (IRT).
Building techniques also vary technologically, from low-tech to high-tech and industrial; the above is not a prescriptive list. Different human needs, environments, economies and traditions all suggest different paths to thermal efficiency.
Yet such is the scale of thermal wastage and the poverty of effective buildings construction worldwide, that anything and everything should be done – as with infrastructures of renewable energy – to prioritise the improvement of buildings’ thermal performance, in the context of a diminishing global carbon budget but a ballooning demand for energy. This is certainly the case wherever new construction is needed to ensure people’s wellbeing.
The political aim should be to improve the use-value of buildings for the bulk of humanity, while minimising the impact on the environment, through operational emissions, embodied emissions, material footprints and other impacts.
And wherever existing homes lack decent thermal performance – as in the UK – we need to retrofit and update them urgently, to the highest standards possible within a limited budget for embodied carbon.
□ Go to Contents and Introduction
Download the whole series as a PDF here
[1] This is my understanding of information on the IEA website here: “Indirect CO2 emissions result [only] from upstream generation of electricity and heat used in buildings.” Indirect emissions also include the emissions associated with district heating and cooling (see Part 10)
[2] Author’s estimate. That is consumption-based UK emissions including all greenhouse gas emissions, not just CO2 (CCC, 2018 data)
[3] There have been severe heatwaves in both 2022 and 2023 on several continents. In 2022, South Asia experienced an unusually early and long heat wave; Pakistan suffered deadly heat and deadly floods from rapid glacial melt. In 2023, Phoenix in Arizona, USA, had a record 19 days in a row with temperatures above 110°F (43°C). Rome in Italy had its hottest ever day in 2022, at 41°C – but that was exceeded in 2023, with temperatures reaching 43°C.
[4] A note about methodology. In relation to buildings’ operational emissions in a changing climate, metrics of “temperature adjusted” emissions are often used. These “adjust” the historical record for analytic purposes, “correcting” for temperatures deemed to be anomalous to the historical norm. This is useful for tracking, say, year-on-year progress in reducing home heating emissions through measures such as insulation. The UK’s Climate Change Committee, for example, refers to UK temperatures in 1981-2020 as a baseline. The “adjustments” to emissions can go up or down; in the UK they have tended to be on the order of 2-7% of buildings’ operational emissions.
But outside of that specific analytic use, we of course want to see “unadjusted” data. We want to see how living in a changing climate, and outside the historical norm, might increase or decrease fossil combustion.
Note that, in the UK, winters are set to become moderately warmer and wetter, due to global warming. However, that hardly helps the millions of people suffering now from fuel poverty in winter.
[5] This is a brief outline; the Designing Buildings Construction Wiki is a great resource if you want to learn more
[6] Technical note. R-values quantify thermal resistance in m2K/W (metre-square kelvin per watt). U-values quantify the thermal conductivity of materials, and are more widely used in materials specifications, and building design and construction. They are measured in W/m²K (watts per metre-square per kelvin).
One watt means that one joule of energy passes per second (1 J/s). One kelvin here is functionally the same as 1°C, and refers to the difference in temperature on either side of the material. So, for example, if a material has a U-value of 1 W/m²K, it means that, when there’s a temperature difference of 1°C across the material (say, inside and outside of a building), 1 J of heat energy flows across each 1m² of the material every second.
The U-value of an insulating material generally decreases in proportion to its thickness. From the perspective of providing insulation, a low U-value is best.
People and Nature 