Case Study: The National Trust Central Office - RIBA Product Selector

‘
SE Controls was chosen
because of the
transparency of their
design and the system’s
ability to work and
communicate easily
with the BMS.
Guy Nevill
Max Fordham LLP
secontrols.com
Case Study
The National Trust Central Office
‘
The National Trust, as a charity, works
to preserve and protect the coastline,
countryside and buildings of England,
Wales and Northern Ireland.
It currently opens to the public over
300 historic houses and gardens, and
49 industrial monuments and mills –
as well as preserving a vast number
of forests, woods, fens, beaches,
farmland, downs, moorland, islands,
Name:
Heelis, The National Trust Central Office
Location:
Swindon
Title:
Providing a highly sustainable ventilation
strategy, one that maintains a comfortable
internal temperature for the National
Trust’s 430 staff, cuts CO 2 emissions
and keeps running costs to a minimum.
Challenge:
To design, manufacture and commission
a natural ventilation system for what is
probably the most sustainable, low energy
office development in the UK.
Products:
● OSO control system
● 307 actuators installed on 213 windows
● 156 actuators installed on 78 roof vents
Benefits:
Running costs to be reduced by
£550,000 a year, with further savings
of over £650,000 expected thanks to
improved internal working practices
and London weighting payments.
The building itself is expected to generate
only 21kg of CO 2 per square metre
annually, compared to 169kg for a typical
air conditioned office. It has also won
a number of industry accolades as a
result, including a prestigious RIBA
Sustainability Award.
archaeological remains, castles, nature
reserves and villages.
The Trust invests over £160 million a
year into the nation’s environmental
infrastructure and works with over
40,000 companies, including 2,000
specialist conservation businesses.
For an organisation so dedicated to the
ecological challenges of our time, it was
imperative that The Trust’s new

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headquarters building would possess
all the same sustainable and responsible
credentials as its work ethos.
Inherent sustainability
With staff spread across four different
sites, some teams having three or four
locations, The National Trust needed
a new central office – one that could
house everyone under one roof and
provide its members with a better,
more integrated service. As well as
streamlining working practices and
cross-team communication,
The Trust also wanted to reduce costs
and pollution with a smaller
carbon footprint.
Rather than choosing a typical country
house, The National Trust sought better
value for money in the former railway
town of Swindon. It chose to occupy
a large brownfield site in the Great
‘
The success of our
sustainable initiatives
is down to managing
expectations. Every
member of staff has had
training on the natural
ventilation system.
‘
Liz Adams
National Trust Property Manager
Western Railway Works, an area of
significant architectural heritage
undergoing major regeneration.
Sustainability was a key issue for The
Trust and its move to Swindon. As
such, the new build had to meet
stringent and high quality
benchmarks for sustainable design – as
well as providing an open plan space
conducive to interactive team working
between departments.
The benchmark of green building
The resulting building, headquarters
named Heelis, was created by
developers Kier Ventures
and architects Feilden Clegg Bradley
in collaboration with The National Trust,
natural ventilation specialists
SE Controls / NVS and
Max Fordham LLP .
Cutting edge in its design, Heelis
beautifully complements the surviving
buildings of the Swindon Railway
Works with their distinctive facades
by Brunel and Gooch. Internally, the
striking structure has a generous
front-of-house atrium with a shop
and café that is open to the public.
It also comprises a two-storey deep
open plan office.
Two courtyards were included in
the scheme, introduced by
Max Fordham LLP and the architect,
to enable cross ventilation. In such
a deep space, the courtyards both
required vents leading into them –
without which the cross ventilation
strategy would not be able to
function effectively.
A number of ‘green’ products and
systems were also specified for the
project, including a bank of 1,554
photovoltaic solar panels on the roof.
Electricity generated from these panels
is used in the building. A lighting
control system adjusts the level of
artificial light in response to external
conditions and movement sensors
ensure lights are turned off in
unoccupied areas.
All of the timber used in construction
has been harvested from sustainable
woodland, much of it originating from
National Trust properties. Even the
carpet was specially developed using
wool from Herdwick sheep grazed on
National Trust farmland.
Blue Staffordshire engineering bricks
were used as the principal external
material, blending in as a contemporary
interpretation of the surrounding
structures. They are laid in lime mortar
to reduce cement use and facilitate
recycling. Cast aluminium cladding
(visible on parts of the elevation) also
provides a subtle tribute to the railway
works that once occupied the site.

Ensuring optimum
internal temperatures
Internally, the building required a
ventilation strategy that would provide
fresh air and generate a healthy
environment for its users. It also needed
an alternative method of cooling other
than air conditioning – one of the
largest producers of co2 emissions and
incredibly expensive to run. In line with
the building’s myriad sustainability
credentials, air conditioning and
mechanical ventilation methods were
completely unacceptable.
A natural ventilation system from
SE Controls / NVS provided the answer.
Combined with large areas of exposed
thermal mass that reduce the need for
cooling during warm periods (concrete
panels to the first floor and roof soffit
that give off ‘coolth’ to the office space
during a working day), the solution
works by expelling stale air and
introducing fresh air through the use
of climatic changes.
The natural solution
Consuming very little energy and with
very little carbon emissions, natural
ventilation systems demonstrate how
buildings can be architecturally exciting
while still being efficient, sustainable
and, importantly, providing best value.
New low energy heating and
mechanical ventilation systems can
offer impressive energy ratings in a
Image courtesy of Max Fordham LLP
similar league as natural ventilation
strategies, but cost implications
including capital equipment and
maintenance can make them
significantly more expensive.
SE Controls / NVS displayed its firstrate
partnering and project
management approach by working
with M&E engineers Max Fordham LLP,
Schüco (Glazing Systems Supplier)
and Parry Bowen (Glazing Fabricator)
to design, install and commission a
natural ventilation system that would
fit perfectly with the building’s
design principles.
Working with the building’s sense of
airiness and open plan space, the
winning strategy has enabled the
scheme to achieve an ‘excellent’ BRE
Environmental Assessment Method
rating. This is alongside providing
occupants with the flexible, open plan
and healthy working environment they
desired from the outset.
An innovative ventilation strategy
Based around the company’s OSO
controller and a series of different
actuators, the system was fitted to the
façade windows and banks of roof
vents. In total, 307 actuators were
installed on 213 windows and 156
actuators on 78 roof vents.
The innovative OSO Controller acts
as an intelligent interface between
the actuators and BMS (Building
Management System), with which it
communicates using the LonWorks
interface. As required, the BMS
communicates with the OSO Control
Systems and appropriately opens or
closes windows and rooflights around
the building, depending on the
‘
temperature signals received from the
sensors placed around the offices.
Though SE Controls / NVS were able
to offer a full stand alone battery
backed control system, there were
clear technical and financial advantages
in allowing the BMS to be in overall
control – a flexible approach
encouraged by SE Controls / NVS to
give clients a best value solution.
The fact that occupants
could control the vents
with override switches
was also a very
important element.
Guy Nevill
Max Fordham LLP
‘
As the temperature inside increases
above a set parameter, the warm stale
air rises. The rooflights are opened to
allow this warm air to escape, rather
than filling the ceiling space - and
eventually the whole room - from the
top down. The façade windows are
opened to allow cool fresh air to be
drawn in, replacing the stale air. This
is a typical application of the stack
ventilation principal, utilising the
buoyancy effect of warm air to create
low pressure areas at the bottom of the
stack. This in turn draws replacement
air from wherever possible – ideally,
in this case, an open window. As
the temperature levels return to
normal, the windows and rooflights
close incrementally.
During the summer, a night time
cooling strategy is triggered - in part
due to a comparison of internal and
external temperatures during the day.

Last year, temperature
targets for the
building were met
which was great news.
Guy Nevill
Max Fordham LLP
‘‘
If applicable, the strategy results in
signals from the BMS to the relevant
OSO controllers to open the vents,
allowing cool night air to enter the
building and purge the interior warm air.
The thermal mass of the building
simultaneously plays its part in the
cooling strategy by cooling down over
night. As a result, in the morning there
is a degree of stored ‘coolth’ in the
exposed concrete structures.
Then during the day, warm air is cooled
by these surfaces, which in turn warm
up ready for the next night cooling
cycle. Such a cooling strategy can
typically reduce internal temperatures
by a further 1°C during the day.
During the winter, heat produced by
people and electrical equipment in the
office is retained as much as possible
by high performance building insulation
- and by minimising the opening of
windows and vents, reducing the need
for mechanical heating.
When ventilation is required, it is
important to minimise draughts and to
maximise heat retention. This ensures
that much of the heat energy carried in
the air is transferred from the escaping
warm stale air to the incoming cold
fresh air. A reduction in the chilling
effect of the incoming air is achieved
by tempering it, which in turn reduces
cold draughts. This is further
encouraged by Max Fordham’s
introduction of heat exchangers
mounted in a number of the roof
turrets (affectionately called ‘snouts’).
In the winter, the heat energy in the
escaping warm air is absorbed by the
heat exchangers and passed
via pipework to the heating trenches,
where it contributes to the active
heating of the building.
It has been shown that for occupants
of a building to truly buy into an
adaptive natural ventilation system,
people need to feel they have a degree
of personal control over it. This is no
different with The National Trust’s
employees. To provide them with such
control, each of the banks of windows
and rooflights has an override switch
connected directly to the SE Controls
OSO controllers.
This allows them to be opened or
closed as required, while relaying
information to the BMS so that it
knows the exact position of every
actuator around the building.
When a switch is pressed, the OSO
controller locks out the BMS control
signal it is receiving, ignoring it for
a preset amount of time (typically
60 minutes).
Fig.1
%
Fig. 2
400
350
300
250
200
150
100
50
0
6.0
5.0
4.0
3.0
2.0
1.0
0.0
% Working hours / Temp o C
The Last Year
Heelis performance data and graphic Courtesy of Max Fordham LLP
At the end of this manual override time
period, the OSO controller switches
back to automatic, responding directly
to signals from the BMS system again.
However, if there is an emergency
during a lockout period, the BMS
can always prematurely regain control
of the OSO by sending a separate
reset signal.
secontrols.com
Delivering tangible benefits
The innovative and integrated approach
taken in the design of the building and
its systems has resulted in the Heelis
building being one of the most energy
efficient, naturally ventilated offices in
the UK. Staff are finding that working
in an office with adaptive natural
ventilation and an intelligent
environmental system means fewer
complaints, and no reported ill
health or discomfort from air
conditioned stuffiness.
Temperature levels in the office during
the last year, including the unusually
BRE Energy Efficient Office of Future guide
DETR Best Practice Programme
ENERGY CONSUMPTION FOR TYPICAL BUILDINGS VRS HEELIS
Typical A. C.
Deg C
NOTE: ‘Other’ is the Server room power & cooling and the kitchen
GROUND FLOOR %
FIRST FLOOR %
EXTERNAL TEMPS %
24 25 26 27 28 29 30 31 32 33 34
Good A. C.
OTHER
LIGHTING
POWER
HWS
HEATING
Typical Nat Vent Good Nat Vent National Trust HQ
Building
long and hot summer, proved to be
well within recommended guidelines
set by the DETR Best Practice
Programme. This states that
temperatures should climb to 25°C or
above for no more than 5% of the
working year, and to 28°C or above for
no more than 1% of the working year.
The graph above from Max Fordham
LLP clearly shows both ground floor

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and first floor temperatures to easily
meet these criteria.
Heelis Facilities Management team
has taken a very proactive approach
to ensure staff understand all the
sustainable features of the building.
All existing and new staff are trained
on why and how the various
systems operate.
It is explained that, like all buildings,
there will be days when some staff
will feel the environment is either too
cold or too hot. As such they are
encouraged to fine tune their own
comfort by wearing layers. A quick look
around the office after hours proves
this, as almost every chair has a jacket
or cardigan hanging on its backrest.
Liz Adams, Property Manager for Heelis,
and her colleagues have even
nicknamed the building “a cardigan
building”. Liz is convinced that staff
education, which is ongoing and
includes weekly news update bulletins,
is key to the wholehearted acceptance
The Trust staff have given towards their
new working environment.
Along with photovoltaic solar panels
and other energy saving initiatives, the
natural ventilation strategy has meant
that Heelis is expected to have one of
the lowest carbon dioxide emissions
ratings of any building in the country.
The overall target for the building was
ambitiously set by Max Fordham LLP
at just 15kg CO2 per square metre per
year, compared with 169kg for a an
inefficient air conditioned office (with
a typically under-maintained air
conditioning system). This target is very
close to being met; Max Fordam LLP
has shown that Heelis has achieved
21Kg CO2 per m2 per year (excluding
catering and communications plant).
This equates to almost a third of that
achievable by a building equipped with
a highly efficient air conditioning
system, and only 13% of the CO2 footprint of an inefficient air
conditioned building.
The bar chart (Fig.2 previous page)
shows the energy consumption figures
for Heelis compared to other typical
buildings. If the ‘Other’ category is
ignored - with Heelis this includes the
public café with its various ovens and
refrigeration units, as well as significant
IT server loads - one can see that Heelis
performs significantly better than a
‘good’ nat vent building.
Initial calculations show that
The National Trust’s sustainable design
approach to Heelis has also generated
massive initial cost savings of £550,000
a year – thanks in part to choosing
natural ventilation over air conditioning.
The Trust also expects to save around
£400,000 annually in future London
weighting payments and more than
£250,000 in administrative costs,
thanks to the improved working
practices allowed by the new building
that pull together The Trust’s different
multi-site teams to one site at Swindon.
Award-winning praise
The multi award winning Heelis
building has been recognised by
RIBA for its eco-friendly attributes;
RIBA presented the scheme with
its prestigious Sustainability
Award. Judges described the
project as having:
“Sustainable design that is quite
simple, but well delivered.
A well handled natural ventilation
system with a degree of user
control, super insulation, PVs,
lots of daylight and sensor
controlled lighting”.
“The strategy delivers an
exceptionally pleasant working
environment. It somehow feels
healthy without being worthy.
There is something very direct
about the strategy that makes it
understandable to the occupants
and general public, which
means important lessons can
be passed on.”
Heelis has also achieved success by
scooping the British Council for
Offices Innovation Award 2006.
Judges said of the scheme:
“It is blessed with a most ingenious
and successful strategy for
naturally ventilating and cooling
the building. Visited by the
National Panel on what was one
of the hottest days of the year, it
was clear the strategy was a
proven success.”
“Along with natural ventilation,
together with the solid south slope
of the roofs covered with
photovoltaic panels, helped
achieve an excellent BREEAM
rating. The scheme shows how
older forms can be efficient and
green without sacrificing value.
Heelis was built to a tight budget,
yet has emerged as attractive
as any of the National
Trust’s charges.”
The project has also been presented
with the Brick Development
Association Awards 2005 for Best
Commercial Building and The
International FX Interior Design
Awards 2005 for Best Medium/Large
Office Building.

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VENTILATION
SOLUTIONS
‘
SE Controls was very
responsive to work with.
The natural ventilation
system works well,
as does the speed
and responsiveness of
the actuators.
‘
Liz Adams
National Trust Property Manager