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The CST Laboratory building with photovoltaic façade |
Energy in Buildings
University of Ulster
In the developed world, buildings are responsible for between 40 and 50% of
the total energy used with a concomitant production of CO2. By improving the
thermal performance of a building and the use of photovoltaics, a significant
reduction in energy for heating, cooling and lighting can be realised.
Integrating renewable energy technologies into the façade of a building can
generate heat or electricity that can be used directly or stored for later use. Only a
small addition to the stock is made each year, so developed technologies must be
suitable for retrofit applications in existing buildings.
The Centre for Sustainable Technologies (CST) at the University of Ulster
undertakes basic and applied research into new and renewable energy systems
and technologies that enable the more efficient use of conventional energy
sources. Recent developments of advanced building façade components include
very low heat loss vacuum glazing and a low-concentration, non-tracking, building
integrated photovoltaic system.
Vacuum Glazing
In vacuum double glazing, two glass panes, typically 0.15 to 0.2 mm apart, are
contiguously sealed around their periphery. The space formed is then evacuated
to a pressure of less than 0.1Pa. Tiny support pillars 0.15mm high, 0.3mm in
diameter, 25mm apart, in a regular square grid pattern, prevent the two glass
sheets being forced together by atmospheric pressure. At a pressure of 0.1Pa
gaseous conduction and convection essentially fall to zero. This leads to radiation
being the dominant form of heat transfer between the two glass sheets.
A surface coating on the glass with a low emittance reduces the long wave
radiation. The patented technology, developed at CST, allows vacuum glazing to
be successfully fabricated at temperatures below 200°C. Consequently very high
performance low-emittance coatings can be used and, unlike higher temperature
manufacture methods, they do not preclude the use of tempered glass.
To date the U-value (total heat transfer coefficient) of the best vacuum glazing
produced in the CST laboratories is 0.86Wm-2K-1 based on a 0.5m2 glazing in
a solid wooden frame. The performance of the glazing is comparable to a good
triple glazing, while the width of the glazing system is only 8.2mm. This thin width
combined with lower weight makes vacuum glazing ideal for retrofit in existing
framing systems if required.
Ongoing work in this area is investigating the manufacturing process and
requirements to enable translation of this technology from the laboratory to
commercial manufacture. Theoretical predictions indicate that a U-value of
0.5Wm-2K-1 is possible when using tempered glass and high performance silver
based low emittance coatings.
Building Integrated Photovoltaics
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A large scale calorimeter at CST for the experimental characterisation of glazing thermal performance |
A significant component in the costs of photovoltaic installations is the
photovoltaic cell material. A potential route to reducing the cost of electricity
generation using photovoltaic solar cells is to increase the electricity produced
from each cell by increasing the solar flux on the cell surface with a low cost
concentrating system. CST is currently involved in three projects with different
partner organisations looking at concentrating technologies for concentration
of solar radiation in the range between 2 and 300 times. The partners include
Imperial College, UPM, Inspiria, ZSW, University of Ferrera, BP Solar, Whitfield
Solar and NAREC.
A design, developed at CST and taken from initial design concept, through
laboratory prototype, to the production of three systems, each of 1kW for
stationary façade mounting, uses a dielectric asymmetric compound parabolic
concentrator to achieve a concentration ratio of 2.45. This non-imaging optical
design is such that, in the United Kingdom, all direct, and a significant fraction of
the diffuse, solar radiation incident on the concentrator reaches the PV cell.
The design utilises total internal reflection allowing excellent optical efficiency to
be achieved. The dimensions of the PV cells, 6mm wide by 115mm long, allow the
concentrator system to be very compact and easily accommodated in a framing
system similar to that used for a standard double glazing.
Renewable Energy and Energy Management Courses
The centre runs a PgD/MSc by distance learning for graduates of physical sciences,
engineering, building, and environmental science, in addition to academics,
government employees and postgraduate students from developing countries
who wish to develop and enhance their understanding and knowledge of
renewable energy technologies and energy management strategies.
The Modules include
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Current Energy systems; |
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Energy Management; |
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Energy Processes in Buildings and Industry; |
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Green Building, passive /low energy design and energy efficiency; |
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Wind energy conversion technologies; |
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Solar thermal and photovoltaic processes and technologies; |
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Biomass processes and technologies; |
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Tidal and Wave conversion technologies; and, |
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MSc Research Dissertation. |
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