Getting to grips with thermal comfort

John Butler reports from the latest module of the MSc Sustainability and Adaptation courses at CAT. John is a student on the MSc Sustainability and Adaptation in the Built Environment course. He normally blogs on his site and you can follow him on Twitter @the_woodlouse.

The March module of CATs Sustainability and Adaptation MSc was part B of Energy Flows in Buildings. Part A (in February) introduced us to ideas of thermal comfort and its relation to heat transfers from the human body to its surroundings. This was tied to the implications of maintaining that thermal comfort, and the impact on energy use. We learnt about calculating U-Values (used as a standard measure of the thermal efficiency of a building element), and daylighting: making best use of natural daylight in a building and calculating the resulting energy savings.

educational building
The view from a bedroom in the WISE building, home of the MSc and Part II Architecture students

Part B expanded on this getting into more detail about limiting the flows of energy through a building, whilst addressing issues around ventilation and movement of moisture. A sustainable building should maintain a comfortable environment – comfortably warm in winter, comfortably cool in summer, ideal humidity levels, good air quality – with minimal energy input, and without moisture ingress causing degradation of the building fabric. Throughout the week different elements of possible means to achieve this were discussed.

A recurring theme throughout the week was retrofit – upgrading the thermal efficiency of existing buildings to reduce their energy use and related CO2 emissions. The most commonly stated best-estimate is that around 80% of existing houses will still be in use by 2050; the potential contribution to reduced energy use and emissions from such a large number of buildings is huge, but presents a challenge. There are advantages and disadvantages to various approaches, from aesthetic considerations (eg: changing the appearance of a building when externally insulating it), to practical (eg: loss of space when internally insulating), to technical (eg: the risk of condensation forming at the meeting of new insulation and existing structure if it is not carefully considered). Planning and conservation concerns can also influence or restrict choices for retrofit.

viewing insulation retrofit
MSc students examine mockups of internal and external insulation, for solid-wall retrofit

There are also issues and trade-offs surrounding choice of insulation materials – the most highly efficient materials may have a greater overall environmental impact than some less efficient materials. Some are more breathable (open to passage of moisture vapour) than others, which can have both positive and negative implications, depending on application.

Another recurring theme was the need to account for future changes to our climate in both retrofit and new build. In particular, too much emphasis on designing to conserve heat could lead to overheating further down the line when atmospheric temperatures increase. Careful attention to placement of glazing and shading to control solar gain can help address this, allowing direct sunlight in to provide warmth in winter when the sun’s path is lower, and sheltering the building from the most intense direct sunlight in summer when the sun is higher.

The role of thermal mass in regulating internal temperatures was discussed in a number of lectures. Depending on climate and design, thermal mass may hang on to winter day-time heat, releasing it within the building through the night – or assist cooling by absorbing excess heat in summer, if combined with effective ventilation to purge that heat at night. Used inappropriately thermal mass may add to overheating, so its use must be considered carefully.

thermal image
Thermal imaging shows hot heating pipes (bright) and cold area where air is coming in around cables (dark areas)

A practical in the second half of the week provided a demonstration of heat loss through unplanned ventilation (ie: draughts). This was linked to the need to provide controlled ventilation (whether through opening windows or via mechanical ventilation), and highlighted the difficulties of achieving airtightness (eliminating draughts) in some existing buildings. The practical involved carrying out an air-pressure test to establish the air-permeability of the timber-framed selfbuild house on the CAT site (ie: how much air moved through the fabric of the building at a certain pressure). In groups we surveyed the building with thermal imaging cameras, before and during the test. The resulting images clearly showed how the cold incoming air cooled surrounding surfaces, demonstrating the impact of air infiltration on energy use. A scheme to retrofit the selfbuild house at CAT would have to include a means to reduce this.

air pressure test
The door-fan, used to de-pressurise a building to identify air-ingress

The end of the week saw us discussing Passivhaus and visiting the Hyddgen Passivhaus office/community building in Machynlleth, with the building’s designer John Williamson. Some myths about Passivhaus were busted (for instance: you can open windows), and the physics-based fabric-first approach was explained. The standard is based around high comfort levels combined with incredibly low energy input. While on site we investigated the MVHR unit (Mechanical Ventilation with Heat Recovery), which removes stale air from the building, and uses it to heat fresh incoming air. These are a common feature of passivhaus, as they allow the removal of moist air and other airborne contaminants and it’s replacement with fresh air, whilst minimising heat loss. This system has been the subject of some heated debates with fellow students at CAT, due to questions about the amount of energy needed to run the system and how user-friendly it is or isn’t. We were shown that when installed correctly, the system recovers more energy than is needed to run it.

Hyddgen Passivhaus in Machynlleth

As ever, throughout this course connections were constantly drawn between all the different areas covered (the inescapable interconnectedness of all things!). Nothing stands in isolation; each decision in one area can have repercussions in another. The different elements of building physics and materials must be balanced with each other and with the effect of any action on the wider environment.

temperature recording
Measuring the air temperature in MVHR heating ducts at Hyddgen, prior to calculating the overall efficiency and heatloss/recovery of the the system

The immersive learning environment during module weeks at CAT is highly effective, and very intense. It’s a wonderfully stimulating and supportive place to be, but at the end of the week that intensity needs a release in order for us all to return to our normal lives without winding up our friends and family when we get there. That takes the form of the vitally essential Friday night social, which this month was themed around a Cyfarfod Bach, a laid back Welsh social. We had beautiful music and singing, comedy, artwork, silliness, a rousing rendition of the Welsh National Anthem (not too shabby, considering only a handful of people were Welsh speakers or had any idea how the tune went in advance) and finally a leg-shattering amount of dancing, ensuring we could all go home in physical pain but happily and calmly buzzing.

See more blogs about the MSc Sustainability and Adaptation course. 

Four reasons why it is great to be a student at CAT

CAT is a truly inspiring place to do a postgraduate course in Renewable Energy or Sustainable Architecture. Here are four things that make the postgraduate degree courses at CAT unique:


1. The structure of the degree courses

Students don’t come to CAT to study full time. They come here for a week at the start of each module for an intense period seminars, lectures and practicals – they then go home to work on their essays and reports. This means that a lot of our students are working full time alongside their degrees. I think this kind of solution will become increasingly popular as degrees become increasingly expensive and living costs fall relative to wages. We also have distance learning options.

2. The network students establish

In part because the degrees here are so immersive (when students are here they are literally living in the university building) students build up a very close network with each other very quickly. The fact that so many of our students are also working (and many of them are mature students) means that between them they have a wealth of experience which we and they really value. This is great for their careers and it also means we have developed quite a radical pedagogy where students are encouraged to share their expertise as well as lecturers.

3. Practical approach rooted in the industry

Unlike a traditional university where most of the lecturers are full time academics, at CAT virtually all the lecturers have other jobs and projects in the renewable energy and sustainable architecture industries. They can bring this experience into their lectures and it is clear that students really value this.

4. An inspiring environment

Situated in a disused slate quarry on the edge of the Snowdonia National Park, with a 7 acre visitors centre demonstrating a wide array of renewable technologies and sustainable building techniques, CAT is a pretty utopian place to study. The WISE building (Wales Institute for Sustainability Education – our graduate school building) itself is an impressive example of what can be achieved integrating stunning architecture with environmental principles. It has won prestigious awards (including RIBA) and students often comment on what a great place to study it is.


You can hear directly from our students on this blog. So far Colin, Becca and Richard have spoken about their motivation. More blogs on this subject from CAT students are coming up.



Raw experience: Richard West

I’ve never had a job that is any way worthwhile until now. I never had a job that I felt made the world any better – this gives me the potential to do that.”

Richard has been a Student on the Renewable Energy and the Built Environment course at CAT since September last year. He is doing the course part time over two years. Here he reflects on what he has got out of the course, and his motivation for taking it.

Richard West: "I've always been interested in it, probably since before it was called renewable energy"


I work in the construction industry on the technical side although most of my career was in IT. I never really aimed for IT, but I always just sort of gravitated towards it. I’ve always drifted in my career up until this point and then I made a conscious decision that this is what I wanted to do, that I wanted to be involved in renewable energy.


CAT seemed like the obvious route to do that. For me at least it has always held a sort of mystique as a world leading place where they push the boundaries. I’m not quite sure they do push the boundaries any more because most of the boundaries have been broken. But they certainly practice what they preach and they certainly have a long history of understanding the way these sorts of thing work because they use them and have been using them for a long time. All the people here who are involved in the course have practical experience of actually working with the technologies that they are teaching us about. They are not geeks from universities who have learned about these things and are teaching us from text books. The are actually engineers who live in the real world, who consult on commercial situations and who understand how things change because they work in this world. They also understand all the regulatory changes because they are affected by them every day and they pass it onto us.


The diversity of students is incredible. They are different ages – everything from recent graduates to retires. We’ve got people with an enormously broad spectrum of world experience and work experience and they all bring something to the table and you can learn something from all of them so just sitting round chatting to them is absolutely fascinating.

"We've got people with an enormously broad spectrum of world experience and work experience and they all bring something to the table"


I always look forward to it actually. Everybody is friendly, everybody is quite good fun. I can’t think of anybody here who I don’t like and the social aspect of it is good fun. It’s interesting. A lot of the time I have quite a lot of work to do so I can’t necessarily drink in the bar until midnight each night, which otherwise I would love to do. Yeah, it’s good, it’s very good.


I’ve always been interested in it, probably since before it was called renewable energy. As a child I was fascinated by the idea of generating electricity from water or from steam. I’ve always been interested in wood fired heating. Just from the very idea that I could plant a tree and it would grow and years later I could chop it down and derive heat for it – for about ten years my parents house was heated exclusively heated by wood and I was involved in that process. And I think I’ve grown up to value resources in a way that people don’t tend to these days. And so I naturally want to conserve them – it’s in my nature, that’s who I am, that’s what I like to do. I find it very unfulfilling to work in areas where there is a high degree of waste – and there is almost everywhere. I live in London so there’s waste all around me and I just don’t like it – though I contribute to it and I freely admit to that.


I see this as a way of doing something that is a bit more more worthwhile and putting something back. I’ve never had a job that is any way worthwhile until now. I never had a job that I felt made the world any better. And this gives me the potential to do that. So it’s I suppose it is my need to feel that I am doing something that’s valuable and worthwhile. And I’m hoping this will help me to indulge that need.


WISE (Wales Institut is absolutely excellent, It’s absolutely excellent. I can’t believe that somewhere like CAT has a building like this I mean it’s just absolutely fantastic. I mean just look at it. It’s there’s plenty of space, there’s plenty of light, it’s well ventilated, it’s full of natural materials and it’s just a very calm and pleasing place to be. I wish I lived in a house that was built like this.


Raw Experience is a series or articles on the CAT blog where Students on the Renewable Energy and the Built Environment masters programme describe in their own terms what it is like to study at CAT. This is their raw testament: unedited, unbiased, real.