This post was written for the Centre of Alternative Technology's student blog, reporting on the latest module of the MSc Sustainability and Adaptation courses at CAT (I'm studying on the MSc Sustainability and Adaptation in the Built Environment course). The original blog can be found here: http://blog.cat.org.uk/2015/03/26/getting-to-grips-with-thermal-comfort/ along with some great blogs by other students on the MSc and Architecture Part II (Professional Diploma) courses, and CAT's own excellent blog covering a wide range of sustainability issues.
The view from a bedroom in the WISE building, home of the MSc and Part II Architecture students
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.
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 CO
2 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.
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 imaging shows hot heating pipes (bright) and cold area where air is coming in around cables (dark areas). There was much geeking-out while playing with the thermal imaging cameras.
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.
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.
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.
