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SE Controls was chosenbecause of the transparency of their design and the system’sability to work andcommunicate easilywith the BMS.Guy NevillMax Fordham LLP

Name: Heelis, The National Trust Central Office

Location:Swindon

Title: Providing a highly sustainable ventilationstrategy, one that maintains a comfortableinternal temperature for the NationalTrust’s 430 staff, cuts CO2 emissions and keeps running costs to a minimum.

Challenge: To design, manufacture and commission a natural ventilation system for what isprobably the most sustainable, low energyoffice 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 toimproved internal working practices and London weighting payments.

The building itself is expected to generateonly 21kg of CO2 per square metreannually, compared to 169kg for a typicalair conditioned office. It has also won a number of industry accolades as aresult, including a prestigious RIBASustainability Award.

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The National Trust, as a charity, worksto 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, and49 industrial monuments and mills – as well as preserving a vast number of forests, woods, fens, beaches,farmland, downs, moorland, islands,

archaeological remains, castles, naturereserves and villages.

The Trust invests over £160 million ayear into the nation’s environmentalinfrastructure and works with over40,000 companies, including 2,000specialist conservation businesses.

For an organisation so dedicated to theecological challenges of our time, it wasimperative that The Trust’s new

The National Trust Central Office Case Study

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headquarters building would possess all the same sustainable and responsiblecredentials as its work ethos.

Inherent sustainabilityWith staff spread across four differentsites, some teams having three or fourlocations, The National Trust neededa new central office – one that couldhouse everyone under one roof andprovide its members with a better,more integrated service. As well asstreamlining working practices andcross-team communication, The Trust also wanted to reduce costs and pollution with a smaller carbon footprint.

Rather than choosing a typical countryhouse, The National Trust sought bettervalue for money in the former railwaytown of Swindon. It chose to occupy a large brownfield site in the Great

Western Railway Works, an area ofsignificant architectural heritageundergoing major regeneration.

Sustainability was a key issue for TheTrust and its move to Swindon. As such, the new build had to meetstringent and high quality benchmarks for sustainable design – aswell as providing an open plan space

conducive to interactive team workingbetween departments.

The benchmark of green buildingThe resulting building, headquartersnamed Heelis, was created bydevelopers 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, Heelisbeautifully complements the survivingbuildings of the Swindon RailwayWorks with their distinctive facades by Brunel and Gooch. Internally, thestriking structure has a generousfront-of-house atrium with a shopand café that is open to the public. It also comprises a two-storey deepopen 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 bothrequired vents leading into them –without which the cross ventilationstrategy would not be able to function effectively.

A number of ‘green’ products andsystems were also specified for theproject, including a bank of 1,554photovoltaic solar panels on the roof.Electricity generated from these panelsis used in the building. A lightingcontrol system adjusts the level ofartificial light in response to externalconditions and movement sensorsensure lights are turned off inunoccupied areas.

All of the timber used in constructionhas been harvested from sustainablewoodland, much of it originating fromNational Trust properties. Even thecarpet was specially developed usingwool from Herdwick sheep grazed onNational Trust farmland.

Blue Staffordshire engineering brickswere used as the principal externalmaterial, blending in as a contemporaryinterpretation of the surroundingstructures. They are laid in lime mortarto reduce cement use and facilitaterecycling. Cast aluminium cladding(visible on parts of the elevation) alsoprovides a subtle tribute to the railwayworks that once occupied the site.

The success of oursustainable initiatives is down to managingexpectations. Everymember of staff has hadtraining on the naturalventilation system.Liz AdamsNational Trust Property Manager

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Ensuring optimum internal temperaturesInternally, the building required aventilation strategy that would providefresh air and generate a healthyenvironment for its users. It also neededan alternative method of cooling otherthan air conditioning – one of thelargest producers of co2 emissions andincredibly expensive to run. In line withthe building’s myriad sustainabilitycredentials, air conditioning andmechanical ventilation methods werecompletely unacceptable.

A natural ventilation system from SE Controls / NVS provided the answer.Combined with large areas of exposedthermal mass that reduce the need forcooling during warm periods (concretepanels to the first floor and roof soffitthat give off ‘coolth’ to the office spaceduring a working day), the solutionworks by expelling stale air andintroducing fresh air through the use of climatic changes.

The natural solutionConsuming very little energy and withvery little carbon emissions, naturalventilation systems demonstrate howbuildings can be architecturally excitingwhile still being efficient, sustainableand, importantly, providing best value.

New low energy heating andmechanical ventilation systems canoffer impressive energy ratings in a

similar league as natural ventilationstrategies, but cost implicationsincluding capital equipment andmaintenance can make themsignificantly more expensive.

SE Controls / NVS displayed its first-rate partnering and projectmanagement approach by workingwith 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 ofairiness and open plan space, thewinning strategy has enabled thescheme to achieve an ‘excellent’ BREEnvironmental Assessment Methodrating. This is alongside providingoccupants with the flexible, open planand healthy working environment theydesired from the outset.

An innovative ventilation strategy Based around the company’s OSOcontroller and a series of differentactuators, the system was fitted to thefaçade windows and banks of roofvents. In total, 307 actuators wereinstalled on 213 windows and 156actuators on 78 roof vents.

The innovative OSO Controller acts as an intelligent interface between the actuators and BMS (BuildingManagement System), with which itcommunicates using the LonWorksinterface. As required, the BMScommunicates with the OSO ControlSystems and appropriately opens orcloses windows and rooflights aroundthe building, depending on the

temperature signals received from thesensors placed around the offices.Though SE Controls / NVS were ableto offer a full stand alone batterybacked control system, there wereclear technical and financial advantages in allowing the BMS to be in overallcontrol – a flexible approachencouraged by SE Controls / NVS to give clients a best value solution.

As the temperature inside increasesabove a set parameter, the warm staleair rises. The rooflights are opened toallow this warm air to escape, ratherthan filling the ceiling space - andeventually the whole room - from thetop down. The façade windows areopened to allow cool fresh air to bedrawn in, replacing the stale air. This is a typical application of the stackventilation principal, utilising thebuoyancy effect of warm air to createlow pressure areas at the bottom of thestack. This in turn draws replacementair from wherever possible – ideally, in this case, an open window. As the temperature levels return to normal, the windows and rooflightsclose incrementally.

During the summer, a night timecooling strategy is triggered - in partdue to a comparison of internal andexternal temperatures during the day.

Image courtesy of Max Fordham LLP

The fact that occupantscould control the vents with override switches was also a veryimportant element.Guy NevillMax Fordham LLP

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If applicable, the strategy results insignals from the BMS to the relevantOSO controllers to open the vents,allowing cool night air to enter thebuilding and purge the interior warm air.

The thermal mass of the buildingsimultaneously plays its part in thecooling strategy by cooling down overnight. As a result, in the morning thereis a degree of stored ‘coolth’ in theexposed concrete structures.

Then during the day, warm air is cooledby these surfaces, which in turn warmup ready for the next night coolingcycle. Such a cooling strategy cantypically reduce internal temperaturesby a further 1°C during the day.

During the winter, heat produced bypeople and electrical equipment in theoffice is retained as much as possibleby high performance building insulation- and by minimising the opening ofwindows and vents, reducing the needfor mechanical heating.

When ventilation is required, it isimportant to minimise draughts and tomaximise heat retention. This ensuresthat much of the heat energy carried inthe air is transferred from the escapingwarm stale air to the incoming coldfresh air. A reduction in the chillingeffect of the incoming air is achievedby tempering it, which in turn reducescold draughts. This is furtherencouraged by Max Fordham’sintroduction of heat exchangersmounted in a number of the roofturrets (affectionately called ‘snouts’).In the winter, the heat energy in theescaping warm air is absorbed by theheat exchangers and passedvia pipework to the heating trenches,where it contributes to the activeheating of the building.

It has been shown that for occupantsof a building to truly buy into anadaptive natural ventilation system,people need to feel they have a degreeof personal control over it. This is nodifferent with The National Trust’s

employees. To provide them with suchcontrol, each of the banks of windowsand rooflights has an override switchconnected directly to the SE ControlsOSO controllers.

This allows them to be opened orclosed as required, while relayinginformation to the BMS so that itknows the exact position of everyactuator around the building.

When a switch is pressed, the OSOcontroller locks out the BMS controlsignal it is receiving, ignoring it for a preset amount of time (typically 60 minutes).

At the end of this manual override timeperiod, the OSO controller switchesback to automatic, responding directlyto signals from the BMS system again.However, if there is an emergencyduring a lockout period, the BMS can always prematurely regain controlof the OSO by sending a separate reset signal.

Heelis performance data and graphic Courtesy of Max Fordham LLP

Delivering tangible benefitsThe innovative and integrated approachtaken in the design of the building andits systems has resulted in the Heelisbuilding being one of the most energyefficient, naturally ventilated offices inthe UK. Staff are finding that workingin an office with adaptive naturalventilation and an intelligentenvironmental system means fewercomplaints, and no reported ill health or discomfort from airconditioned stuffiness.

Temperature levels in the office duringthe last year, including the unusually

long and hot summer, proved to bewell within recommended guidelinesset by the DETR Best PracticeProgramme. This states thattemperatures should climb to 25°C orabove for no more than 5% of theworking year, and to 28°C or above forno more than 1% of the working year.The graph above from Max FordhamLLP clearly shows both ground floor

Last year, temperaturetargets for the building were met which was great news.Guy NevillMax Fordham LLP

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% Working hours / Temp oCThe Last Year

BRE Energy Efficient Office of Future guideDETR Best Practice Programme

OTHER

LIGHTING

POWER

HWS

HEATING

GROUND FLOOR %

FIRST FLOOR %

EXTERNAL TEMPS %

Fig.1

ENERGY CONSUMPTION FOR TYPICAL BUILDINGS VRS HEELISFig.2

NOTE: ‘Other’ is the Server room power & cooling and the kitchen

Typical A.C.

400

6.0

5.0

4.0

3.0%

Deg C

2.0

1.0

0.024 25 26 27 28 29 30 31 32 33 34

350

300

250

200

150

100

50

0

Good A.C.

Building

Typical Nat Vent Good Nat Vent National Trust HQ

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and first floor temperatures to easilymeet these criteria.

Heelis Facilities Management team has taken a very proactive approach to ensure staff understand all thesustainable 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 areencouraged to fine tune their owncomfort by wearing layers. A quick lookaround the office after hours provesthis, as almost every chair has a jacketor cardigan hanging on its backrest.

Liz Adams, Property Manager for Heelis,and her colleagues have evennicknamed the building “a cardiganbuilding”. Liz is convinced that staffeducation, which is ongoing andincludes weekly news update bulletins,is key to the wholehearted acceptanceThe Trust staff have given towards theirnew working environment.

Along with photovoltaic solar panelsand other energy saving initiatives, thenatural ventilation strategy has meantthat Heelis is expected to have one ofthe lowest carbon dioxide emissionsratings of any building in the country.The overall target for the building wasambitiously set by Max Fordham LLP at just 15kg CO2 per square metre peryear, compared with 169kg for a aninefficient air conditioned office (with a typically under-maintained airconditioning system). This target is veryclose to being met; Max Fordam LLPhas shown that Heelis has achieved21Kg CO2 per m2 per year (excludingcatering and communications plant).This equates to almost a third of thatachievable by a building equipped witha highly efficient air conditioningsystem, and only 13% of the CO2

footprint of an inefficient airconditioned building.

The bar chart (Fig.2 previous page)shows the energy consumption figures

for Heelis compared to other typicalbuildings. If the ‘Other’ category isignored - with Heelis this includes thepublic café with its various ovens andrefrigeration units, as well as significantIT server loads - one can see that Heelisperforms significantly better than a‘good’ nat vent building.

Initial calculations show that The National Trust’s sustainable designapproach to Heelis has also generatedmassive initial cost savings of £550,000a year – thanks in part to choosingnatural ventilation over air conditioning.The Trust also expects to save around£400,000 annually in future Londonweighting payments and more than£250,000 in administrative costs,thanks to the improved workingpractices allowed by the new buildingthat pull together The Trust’s differentmulti-site teams to one site at Swindon.

Award-winning praiseThe multi award winning Heelisbuilding has been recognised byRIBA for its eco-friendly attributes;RIBA presented the scheme with its prestigious Sustainability Award. Judges described the project as having:

“Sustainable design that is quitesimple, but well delivered. A well handled natural ventilationsystem with a degree of usercontrol, super insulation, PVs,lots of daylight and sensorcontrolled lighting”.

“The strategy delivers anexceptionally pleasant workingenvironment. It somehow feelshealthy without being worthy.There is something very directabout the strategy that makes itunderstandable to the occupantsand general public, which means important lessons can be passed on.”

Heelis has also achieved success byscooping the British Council forOffices Innovation Award 2006.Judges said of the scheme:

“It is blessed with a most ingeniousand successful strategy fornaturally ventilating and coolingthe building. Visited by theNational Panel on what was one of the hottest days of the year, itwas clear the strategy was aproven success.”

“Along with natural ventilation,together with the solid south slopeof the roofs covered withphotovoltaic panels, helpedachieve an excellent BREEAMrating. The scheme shows howolder forms can be efficient andgreen 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 presentedwith the Brick DevelopmentAssociation Awards 2005 for BestCommercial Building and TheInternational FX Interior DesignAwards 2005 for Best Medium/LargeOffice Building.

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VENTILATION S O L U T I O N S

SE Controls was veryresponsive to work with.The natural ventilationsystem works well, as does the speedand responsiveness of the actuators.Liz AdamsNational Trust Property Manager

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