Thermal comfort standards were based on a single man.

Every week the research group I’m part of discusses a paper from the literature. It’s a effective way of keeping up to date with new work in the field. I might get into a regular habit of writing up some thoughts from these discussions here, but whether or not this happens, I thought I would talk here about last week’s paper, “Energy consumption in buildings and female thermal demand“.

The field of building engineering spends a good deal of effort establishing standards for the effective operation of buildings. These cover a wide range of properties of a building, from comfort to sound levels. For thermal comfort, the UK follows a range of BS and EN standards – here’s a pretty comprehensive list. Thinking about these standards, and what they mean for energy demand in buildings, is an important part of the struggle to decarbonise the economy; around 30% of our energy use happens in buildings.

In the USA, ASHRAE standards do a similar job, but staggeringly the ASHRAE standard for indoor environments was determined using data from a single 70kg 40 year-old man. The paper focuses on gender differences in thermal preferences, and finds that there are differences between the sample they used and the standard which was based on one person – young adult females prefer a warmer office environment. Generally, there are a very large number of variables that are thought to determine thermal preferences.

Initially, I had assumed that if this finding was generally true that overall heat demand should be higher, if we were to satisfy everyone’s thermal comfort. But, as Clare pointed out in the discussion we had, while that might be true of cold countries like the UK, for countries where thermal energy demand relates to cooling decreasing the overall cooling energy used in office buildings might make the overall population happier. This is potentially good news for reducing climate change – the population as a whole might be happier if we used air conditioning less. Although, it probably wouldn’t be that simple.

Reading this paper was a reminder too that designing buildings that keep people happy is extremely difficult. There is a terrifying nexus of considerations that must go into this process. While a standard based on a single man is clearly deeply deficient, questions remain about the tension between general standards and the preferences of actual building users. Negotiating these tensions whilst minimising energy use is problem of a wholly greater order of complexity.

What’s a tog?

I’m a big fan of James O’Brien’s Mystery Hour. Each week, members of the public call in with questions about almost anything which are then answered, or not, by almost anyone, provided they can explain how they know what they know. A couple of weeks ago, Marcus from Dundee asked ‘What does tog mean?‘ for duvets and blankets. Melvin provided a correct answer, that ‘Essentially, it tells you how quickly heat travels across the duvet.’. But the development of a the tog has a much richer history. And so this instalment is all about the tog, a tog-blog, if you will.

The internet is surprisingly patchy when it comes to in-depth information about the tog. There are various duvet manufacturers that tell us summer duvets are up to 5 tog, and the warmest winter duvets around 15 tog. The higher the tog, the warmer you are over night.

There’s a little more detail about the technical definition of the tog, in terms of its measure of thermal resistance. In fundamental S.I. units, a tog is 0.1 K/W.  Since there’s usually a big difference between skin temperature and room temperature at night time, your body loses heat to the surroundings. You feel cold if the rate of heat loss is too great. But, as this paper found, sudden infant death syndrome can be associated with overheating, so getting togs right is important.

The methods for measuring togs is outlined in British Standard 4745:2005, using the aptly named ‘togmeter’. You can watch the dreamy process here:

What the internet is almost totaly unhelpful with is the tog’s origin. Wikipedia mentions the Shirely Institute with no reference. This is corroborated by a 2007 Spectator article, Feather your nest, which again mentions the 1940s and the Shirley Insitute’s connection to British Cotton Industry Research Association. So, feeling adventurous, I called up the Memoirs from the institute from 1942-1946 to the British Library. The year range I chose was a total punt, but I got lucky.

Here, for the first time (as far as I know) in digitised form is the spectacular genesis of the tog.

The first description of the tog. The transmission of heat through textile fabrics - part II' p.343 by F. T. Peirce and W. H. Rees Shirley Institute Memoirs, Vol XXII 1944-1945  The first description of the tog. The transmission of heat through textile fabrics – part II’ p.343 by F. T. Peirce and W. H. Rees Shirley Institute Memoirs, Vol XXII 1944-1945

The paper was written by F. T. Peirce and W. H. Rees and published in the 1944-45 edition of the Memoirs. It’s an excellent example of the cultural and historical contingency of physical units – the equivalence of a tog to a ‘light summer suit’ demonstrates who was being borne in mind, and the mention of clothing too thick to fight in a sobering reminder of the times in which the tog was developed.

Winter mortality figures, and why they matter

Happy new year, let’s talk about death. This instalment is about mortality and how it varies with season. The ONS reports daily mortality figures, combined here for England and Wales, between 1970 and 2014 (current population 57.8 million) are shown below.

Each one of the 25 million deaths in England and Wales between 1970 and 2014. Source: ONS Each one of the 25 million deaths in England and Wales between 1970 and 2014. Source: ONS

The first thing that’s striking about this chart is its seasonal variability. Broadly speaking the number of daily deaths oscillates between 1000 and 3000 deaths per day, peaking in the winter months. Over time there is a reduction in the average daily death rate; In 1970 the population of England and Wales was under 50 million, and yet more people died every day, which is consistent with an increase in life expectancy in recent years.

However, this doesn’t tell us much about why people die, and what the seasonal variation means. The extent to which more people die in winter than summer is encoded in the excess winter mortality (EWM) figures. These record how many more people die in winter than summer. Not all causes of death are seasonally effected, but the majority of EWM is caused by respiratory diseases (including flu), cerebrovascular disease, heart disease, and dementia. It’s rare that people die of direct exposure to cold in the UK, though it does happen. Typically, older people are at a greater risk of winter diseases, although, sometimes, certain strains of flu effect the young more than the old.

The impact of cold housing on EWM is discussed in the Marmot Review. The authors found that “in the coldest quarter of housing, [EWM] is almost three times higher as in the warmest quarter”. The UK does not compare well to Europe. Even though the winter is colder in countries such as Finland, the EWM figures are lower.

Excess winter deaths over 9 years in Europe. Source: Excess Winter Deaths in Europe: a multi-country descriptive analysis. Source Excess winter deaths over 9 years in Europe. Source: Excess Winter Deaths in Europe: a multi-country descriptive analysis. Source

Why should we care about mortality statistics? In a 1990 article “life and death”, Amartya Sen wrote of their importance as means of measuring society, as a window on inequality and a measure of wellbeing.  Sen was specifically looking at instances of famine in developing countries, as well as gender and racial inequality; a similar approach reveals that suicide is the leading cause of death among people aged 20-34 in the UK, for example. The impact of winter in the UK, and how the state of housing relates to it, is reflected in the numbers. But with all things, stats are just one side of the story, the lived experience of people enduring cold homes and poverty is also a vital part of the story.

Further reading

Interesting graphs on excess winter mortality here

An incredible database of all causes of death recorded by the WHO is here

The failure to reduce the suicide rate among young men is discussed here

Living in fuel poverty, videos are here

Finally, an amazing video of Amartya Sen speaking at a City Council meeting in Cambridge MA regarding the application for an additional curb cut near his home. Nobel prize winning economist meets local politics…

A short history of Fuel Poverty

Fuel poverty is usually defined as the inability of a household to afford sufficient warmth. The causes and consequences of fuel poverty are complex, but typically the inhabitants of a fuel poor household will suffer uncomfortably cold temperatures because their home is bad at retaining heat. Future blog posts will examine some of the negative health impacts of cold houses, but here I give a broad overview of the recent historical development of fuel poverty.

While poor housing conditions have been considered with varying focus and effectiveness by government for at least the last 150 years, fuel poverty in its present form is a more recent phenomena. Following the advent of the 1973 oil crisis, groups like the National Right to Fuel Campaign were set up in 1975 with the goal of keeping fuel poverty on the political agenda. An early publication was Paul Richardson’s ‘Fuel poverty’ in 1978 which focused on the fuel usage of low income council housing tenants. Richardson highlighted three paths available to those experiencing fuel poverty, which were “to run up arrears, potentially leading to disconnection of their fuel supply; to reduce their standards of heating to levels which may be undesirably low; or to cut back on other items of expenditure, which may be equally undesirable” (Richardson, 1978).

The term fuel poverty was first used in parliament on the 28th of July 1977 by the Labour MP for Walthamstow, Eric Deakins, in a debate about heating costs. “The problem of what has been termed fuel poverty is one that has to be attacked on two fronts: first we must ensure that poorer people can pay for the fuel they require and, secondly, we must see to it that everyone—particularly those most at risk from the cold, such as the elderly and the increasing number of the elderly who are very old indeed—get enough warmth.” (HC, 1977)

A key early academic work was due to Boardman (1991). This work laid the foundations for many of the policy developments in later years, most notably the 10% definition – which says that a household is in fuel poverty if it would have to spend more than 10% of its income on fuel in order to achieve a comfortable home. The book argues that fuel poverty is a distinct form of poverty, not merely an aspect or direct consequence of general impoverishment. This is most readily observed in the distinction that Boardman draws between the purchase of fuel and warmth – the former is independent of the housing structure and heating efficiency, while the latter is fundamentally determined by the ‘technical characteristics of the heating system’ as well as the thermal characteristics of the dwelling. This distinction is not true of other commodities such as food, for which the characteristics of static capital such as cookers do not determine the calorific or the nutritional value, and thus cost, of food consumed.

Fuel poverty first received specific legislative attention in England and Wales under the Warm Homes and Energy Conservation Act 2000. Following the recommendations of the 1999 inter-ministerial group on Fuel Poverty (Gilbertson, 2006), the bill required the secretary of state to set up a programme to deal with fuel poverty, which is defined in the bill as “the inability of a household to keep warm at reasonable cost”. Around the same time, a scheme called Warm Front (WF) was implemented. Between 2000 and 2013 it improved the energy efficiency of 2.3 million English homes (Sovacol, 2015). Sovacol highlights failures of targeting in WF, citing a report which found “only 42 percent of fuel poor households received assistance under WF and that 75 percent of those participating were not, in actuality, fuel poor”, other assessments he cites found similar inaccuracies. Recently, the most significant government policy shift in the field of fuel poverty was the move away from the 10% definition towards the Low Income High Cost definition (LIHC).  Alongside this, the Energy Company Obligation (ECO) obliges the energy suppliers to provide energy efficiency measures for alleviating fuel poverty under three schemes. As of December 2016, the long future of ECO is under consultation.

Over the last 40 years, the historical development of fuel poverty has been one of multiple transformations. Initially, in the late 1970s it was the focus of non-governmental organisations and action groups. Over time central government took the issue more seriously, and fuel poverty arguably received greatest attention in the Warm Front program which ran through the first decade of the 21st century. More recently, government austerity policies have seen a reduction in expenditure on interventions, and a general shift of the focus away from direct policies to one in which non-governmental bodies are responsible for dealing with fuel poverty.


Richardson, P. (1978) Fuel Poverty. Papers in Community Studies, 20, University of York

HC (2015) Energy and Climate Change Committee – Ninth Report Smart meters: progress or delay? Link 

Boardman, B. (1991). Fuel Poverty: From Cold Homes to Affordable Warmth London: John Wiley & Sons Ltd.

Gilbertson, J. Stevens, M. Stiell, B. Thorogood, N. (2006) Home is where the hearth is: grant recipients’ views of England’s home energy efficiency scheme (Warm Front) Soc Sci Med, 63. 946–956

Sefton T (2004). Aiming high: an evaluation of the potential contribution of Warm Front towards meeting the Government’s fuel poverty target in England. CASE report 28. Centre for analysis of social exclusion. London, UK: London School of Economics and Political Science.

Sovacool, B . K. (2015) Fuel poverty, affordability, and energy justice in England: Policy insights from the Warm Front Program, Energy 93, (1) 361-371

How hot is too hot? Thermal comfort in the UK’s changing climate.

The UK climate is getting hotter. Predictions suggest that the south east might be 5°C hotter on average by the end of the century (Hulme, 2002). The government is also legally committed to reducing our CO2 emissions. These projected changes will require us to drastically rethink the way we live, and carefully design and modify our buildings with these considerations in mind.

Before we look at the risks of overheating, it’s important to remember how deadly cold winters can be to those who can’t afford to heat their homes. Last winter (2014/15), fuel poverty lead to the deaths of 15,000 people in the UK. This winter the effect is likely to be less dramatic, as temperatures have been so mild that met office records have been broken, but excess winter deaths will be with us in the UK for some years to come – unless homes fuel poverty is tackled.

UK Average Temperature Anomaly over the last 100 years. (Data source: Met Office ) UK Average Temperature Anomaly over the last 100 years. (Data source: Met Office )

The main determiner of domestic energy use (and CO2 emissions) is heating. The amount a home is heated depends on many interrelated factors such as the physical characteristics of the house, the weather outside but also on the preferences of the occupants. The occupant preferences are complicated to model but the key factor at play is people’s thermal comfortPut simply, this is whether people feel comfortable in a given set of conditions. Thermal comfort itself depends on a whole host of factors like an individual’s metabolism, how much people wear or what activities they’re up to – gyms need to be cooler than offices, for example.

As a rough rule of thumb, offices should at least 20°C, but what about an upper limit? How hot is too hot? The answer, as with many things in building science, isn’t simple. Zero Carbon Hub have published a review that looks into the various measures of overheating. The industry is split as how exactly to define overheating – some say there should be maximum acceptable temperature for buildings (around 28°) others say it depends on the outside temperature because people adapt and are more accepting of warmer temperatures in the summer. So where does this leave us?

The most recent example of the deadly impact of high temperatures comes from 2003. Across Europe, the extreme temperatures claimed the lives of over 70,000 people. In the England the toll was lower, at around 2000 excess deaths. This demonstrates that the heatwave was not felt equally everywhere – France suffered particularly badly where the high temperatures killed around 15,000 people.

Average temperature anomaly July 20 – August 20 2003 (source: Reto Stockli and Robert Simmon, based upon data provided by the MODIS Land Science Team) Average temperature anomaly July 20 – August 20 2003 (source: Reto Stockli and Robert Simmon, based upon data provided by the MODIS Land Science Team)

Of course, like excess winter deaths, the deadly effects of high temperatures are not evenly distributed through society – the worst effected are usually older, sick or less well off. The UK government has responded, based on the projection that the 2003 extreme temperatures will be ‘normal’ by 2040. The NHS has published a Heatwave Plan for England which outlines what needs to be done in the event of a heatwave.

Responsibility also falls on landlords, local authorities and building owners to ensure that buildings are fit for habitation and work. The UK building stock is diverse and measures that work for one situation might not be effective in another. Careful attention is required to ensure any retrofit an owner installs, whether they be the installation of solar shading or improved ventilation, do not increase the energy consumption of the building. Air conditioning systems are often less efficient than natural ventilation.

The house I grew up in was a poorly insulated 17th century Welsh farmhouse, so the risk associated with overheating there are far less than those of being too cold in winter. But in general the UK housing stock is not currently equipped to deal with temperatures that are projected to occur in the decades to come. As ever, it tends to be that those in society least able to make changes to their living conditions are those at greatest risk of harm.

A balance needs to be struck by policy makers to ensure the overheating risks are addressed without compromising the essential work in improving housing efficiency and reducing our CO2 emissions. Given the lessons of 2003, this problem is far greater than issues of comfort, but potentially one of life and death.


M Hulme, Tyndall Centre for Climate Change Research, & UK Climate Impacts Programme. (2002). Climate change scenarios for the United Kingdom :  UKCIP02 Norwich: Tyndall Centre.

Academic references I have collected are available here

“…at the scale observable by our unaided senses”

One of the reasons Physics is seen as difficult to understand is because it tends to consider, in the popular imagination at least, very strange and far away things. The early universe, for example, was very much unlike anything that happens near us now in almost every respect. It was hot and dense and full of particles and not-really-particles interacting in ways they don’t often interact anymore – more about all this can be found here – understanding this requires understanding difficult maths and complicated observational techniques, and that makes Physics seem tricky.

The primary information that comes from experiments about very small things and very big things is almost totally inaccessible to anyone who doesn’t have very expensive equipment. You can’t see the glow left after the big bang with the naked eye, it’s so faint that it has no direct effect on our daily lives.  The curiosities of quantum mechanics are totally shielded from our direct perception, and there’s no way anyone is going to get anywhere near a black hole, probably ever.

But, as I discovered while auditing the a class of L Mahadevan in fall 2010, there are far stranger things than electrons that we know much less about which are present in our everyday lives. The work that Professor Mahadevan and his group does is eloquently characterised as considering phenomena ‘at the scale observable by our unaided senses’, and shows that the mathematics which describes the curvature of a lily petal is arguably more subtle than that which describes the electron, or even the precession of planets around the Sun. Mahadevan’s group considers the physical and mathematical origins of the diverse structures observed in biology, so called soft-matter, from the folds of the human brain to the self organising thermo-regulation of bee swarms.

from Liang and Mahadevan (2011)  from Liang and Mahadevan (2011)

At the early stages of my Physics training I was driven by the strange attraction of fundamental physics. While there’s definitely value in considering very small and far away things, it took a long time to appreciate that there is a great deal of fascinating work to done at the length scale of the everyday.