WS 8 Automated solar shading - an efficient and profitable ... - ES-SO

Sustainable Energy Use in Buildings − Summaries of Selected REHVA Workshops of Clima 2010
WS 8 Automated solar shading - an efficient and
profitable instrument for optimizing HVAC
design and control in a holistic approach
Chair: Dick de Leeuw, De Leeuw Ltd, dick@deleeuw-ltd.co.uk
Co-sponsor: ES-SO European Solar Shading Organization
Organiser: Emeric Motte, Somfy, emeric.motte@somfy.com
Presentations:
• Energy transfer through windows: Emeric Motte, Somfy, emeric.motte@somfy.com;
• How innovative fabrics regulate the energy transfer: Peter Winters, Dickson, pwinters@dicksonconstant.com
• The influence of solar shading on HVAC design: Marc Altazin, CIAT, m.altazin@ciat.fr
Introduction
Brief summary of the workshop
The instant power (in W) entering a building
through a window is
B = A*
[ I * g −U
* ( θ i −θ
e )]
where
A
I
g
U
θθ
i
θθ
window surface (m²)
irradiation (W/m²)
solar factor
heat transfer coefficient (W/m².K)
indoor temperature (°)
e outdoor temperature (°)
To minimise energy demand, B should be
as great as possible during heating periods,
and as small as possible during cooling
periods.
When I and θe are highly variable and not
manageable, g can be dynamically managed
thanks to automated solar shadings,
to control the heat gains according to the
energy needs of the building and the
weather conditions.
Among all solar shading types, roller
blinds with technical fabrics, whether interior
or exterior, have interesting features
for managing daylight and heat gains to
provide comfortable and healthy working
and living conditions.
Great care is required to select the most
appropriate fabric (colour, solar energy
transmittance, reflectance, openness factor,
…), as many parameters have to be
taken into account: position (exterior, interior),
climate, façade orientation, task performed
inside …
On a building currently in a refurbishment
phase, the use of automated solar shadings
lowering the total solar energy transmittance
of the windows from 0.5 to 0.05
lowers the HVAC energy need by 34%.
Taking this into account in sizing the
HVAC system, the total energy savings
reaches 43%.
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Sustainable Energy Use in Buildings − Summaries of Selected REHVA Workshops of Clima 2010
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kWH / Yr
Light transmission coefficient of a window without/ with exterior/with interior roller blind:
no impact of the position of the blind vs. the glass panes.
Total solar energy transmission coefficient without / with exterior/with interior roller blind:
high importance of the position of the blind (fabric type has to be selected according to position).
Energy need of a building in
3 different configurations:
- windows with a total solar energy
transmission coefficient of 0.50 +
CIAT system ILD150
- windows with a total solar energy
transmission coefficient of 0.05 (with
roller blinds) + CIAT syst. ILD150
- windows with a total solar energy
transmission coefficient of 0.05 (with
roller blinds) + HVAC optimization

Sustainable Energy Use in Buildings − Summaries of Selected REHVA Workshops of Clima 2010
Discussions
1. Although attendees acknowledge the
impact of automated solar shading on the
energy performance of buildings, they
plead for more information on:
• Available types of solar shadings
Solar shading manufacturers market a wide
range of products, with lifting or lifting- and
tilting capacity, which cope with architectural,
aesthetical, climatic and lifestyle conditions.
These products have different thermal
and visual performances which need to
be differentiated to decision makers.
• integration of solar shadings info façades
Specially for double skin facades and
closed cavity facades, information should
be given by manufacturers on space requirements
(for the headrail / box of the
shading device), temperature limitations.
• solar shadings control strategies
What are the most standard control strategies,
what types of sensors are required.
These data may be specific to manufacturers,
who may not be the solar shading
manufacturers.
• integration of solar shading controls
into Building Management Systems
Due to different biding processes, controls
may sometimes be integrated into the façade
lot; in that case the HVAC/BMS lot
may not get enough information on the
controls systems which have been required,
or the HVAC/BMS companies
may not be able to specify the technology
of the shades controls.
2. Automated solar shadings are seldom
taken into account in energy performance
calculations due to:
• input values for calculation, as described
in point 1, are not always available.
• most available energy calculation
software do not take into account
dynamic solar shadings
The position of the shading device has an
impact on the g-tot (total solar energy
transmittance) and the U-value (heat transfer
coefficient) of the window. g-tot may
vary in a 10:1 ratio, U-value may vary by
0.2 between the up (open) and down
(close) positions.
Reasons not to take dynamic solar shading
into account can be:
• many software simulate on a monthstep
basis which makes it difficult to
take solar gains into consideration, this
is more relevant when simulations are
made on an hour-step basis (like in
French RT2005 and RT2012)
• the way to calculate g-tot is detailed in
EN 13363-1 and EN 13363-2 and
might be complex, specially with Venetian
blinds.
• wind dependency of performance of
exterior solar shadings
The use of exterior shading devices is limited
by weather conditions, such as wind, rain,
icing etc. In those situations the shading devices
are blocked in their upper position and
can't contribute to the energy performance.
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Sustainable Energy Use in Buildings − Summaries of Selected REHVA Workshops of Clima 2010
The shade industry has already developed
wind-resistant shading devices, and has to
carry on its efforts in that direction.
• although some components have a 5year
warrantee, most of the complete
solar shading products are sold with a 2year
warrantee
Most of the technical equipments of buildings
have a 5-year warrantee, whereas
most of the shading devices are delivered
with a 2-year warrantee, they can't therefore
be considered as building equipments.
• no maintenance budget to guarantee the
performance over time
Not being considered as technical equipments,
there is no maintenance budget to
maintain their good functioning, thus their
contribution to the energy performance
cannot be guaranteed.
• due to items d and e, the selection of
solar shading devices is too often left to
the interior architect/designer
3. Although there is a benefit in right sizing
the HVAC system, HVAC engineers are
reluctant to do so
• they have to guarantee good
working/living conditions for the
occupants all year round
Whatever the real time weather, which is
different (and may be very different) from
the meteorological weather database.
Actual occupancy, thus internal heat gains,
may also be different from what has been
originally defined.
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• thus they have to take into account
potential defaults of the building
envelope linked to improper installation
of façade components
Air-tightness and U-value of the envelope
may be affected by construction defaults,
thus actual energy needs may differ from
what is calculated.
4. Impact of solar shading on lighting
energy consumption is not well known
and valued
Daylighting autonomy, i.e. amount of daylight
over time, is a major concern for
building designers as a source of potential
huge energy savings. The highest it is, the
less artificial lighting is necessary.
It depends on many factors, such as window
size, place of the window in the façade, room
dimensions, reflection factor of the walls and
the light transmission factor of the window.
When there is a dynamic solar shading device,
this one modifies the light transmission
of the glass, thus the daylighting autonomy,
thus the complementary lighting necessary to
provide sufficient illuminance in the room.
The Daylight Factor DF is
a percentage ratio of the instantaneous
illumination level at a reference point
inside a room to that occurring simultaneously
outside in an unobstructed position.

Sustainable Energy Use in Buildings − Summaries of Selected REHVA Workshops of Clima 2010
Conclusions and future
work directions in the field
1. At Clima 2010, REHVA and
ES-SO (European Solar Shading
Organization) introduced a new
REHVA GUIDEBOOK No 12:
“Solar Shading
– How to integrate solar shading in
sustainable buildings”
REHVA GUIDEBOOK No 12
“Solar Shading” provides
extensive information on
• effect of windows on the indoor environment
• window systems
• energy effects of solar shading
• how to choose a solar shading solution
• automating and integrating solar shading
• retroffiting windows and solar shadings
• double-skin façades
• maintenance of solar shading systems.
2. In addition, ES-SO has to work on
case studies and communicate on best
practice to comfort the HVAC
industry of the benefits of automated
solar shadings.
3. ES-SO and their members have to
intensify their work to improve their
knowledge on the impact on lighting
and communicate the results to the
HVAC industry.
REHVA and ES-SO have to join efforts to spread this document as widely as possible.
ES-SO is also involved in research programs, like Keep Cool (www.keep-cool.eu) and
ASIEPI (www.asiepi.eu) in which additional relevant information is available.
Ordering information:
Contact REHVA office in Brussels:
Tel: +32-2-5141171 or send an email to: sales@rehva.eu
or order the Guidebook online at REHVA bookstore at www.rehva.eu
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