On air: BSkyB's naturally ventilated studios

You probably don’t think much about the carbon footprint of television programmes, but as competitors picked up their pugil sticks for the latest series of Gladiators, BSkyB claimed that the TV show used 35% less energy than its previous incarnation.

This is part of the broadcaster’s plans to go carbon neutral. So is the £233m production centre it is building at its headquarters in Osterley, west London, which it claims will be Europe’s most sustainable broadcasting facility. If all goes to plan, Harlequin 1 will consume about a third less energy than a conventional design.

Due to open in 2011, the centre will include a familiar array of low-energy technologies. There are 80m-tall wind turbines, which are yet to get full planning approval but could provide up to 90% of the office’s energy for lighting. There is a biomass-fuelled combined cooling and heating plant, which should offset 20% of the building’s carbon emissions. And there is the obligatory rainwater harvesting system.

What is more unusual is that BSkyB is planning the world’s first naturally ventilated television studios. There are good reasons why naturally ventilated television studios aren’t the norm. Top of the list is noise. Studios have strict sound criteria. The standard is a noise rating of 25, at which level you have to concentrate hard to hear any noise (a typical office has a rating of 35-40). This is tough to achieve if air from the outside is allowed in, especially in a quasi-industrial park adjacent to the A4 and under the flight path to Heathrow.

“The site is quite challenging,” says Ian Knowles, acoustic engineer on the project. “The worst types of noise are the low frequency ones from things such as lorries.” To exclude these a typical television studio uses a “box in box” construction, which means the studio is constructed as a separate concrete unit that sits on elastomeric bearings within the main structure. This isolates it from vibration and structure-borne noise.

But integrating this approach with natural ventilation is tricky. “There would be a hole in the studio to the outside, which would defeat the purpose of sound insulation,” says Knowles.

The studios

BSkyB’s headquarters will include eight television studios and two floors of data processing and editing suites, which will house 400 computer servers. Above these will sit the “transmission platform”, a densely packed area of kit where the signals are broadcast to satellites. These are critical facilities, and the number one priority is the ability to air programmes 24 hours a day, seven days a week. In addition, the people and equipment generate a lot of heat, so temperature control is crucial.

For the natural ventilation to work, there needs to be minimal resistance to the air entering the building. Only this way can fresh air in from outside be pulled into the studio by the small negative pressure created by warm air rising up and out of the building through its nine chimneys. Herein lies the problem: to stop any external noise entering the building, acoustic attenuation is required, and this resists the flow of air.

To overcome this, Arup Associates, the architect on the scheme, included extremely large air paths to allow the air to travel at a low speed. This reduces the pressure drop and ensures that enough fresh air can be delivered to carry away the heat from the studio.

From street level, air passes through a set of openings and enters a 1m-high chamber that stretches out beneath the studio’s entire footprint. The support structure in this space is clad with an acoustic lining that creates a labyrinth along which the air passes and provides the first barrier to noise. It then leaves this chamber through further attenuators fixed to the back of holes in the floor slab and is ducted up to low-level wall boxes.

As the air is warmed inside by lighting and equipment, it rises and passes into the ceiling void and out of the chimney. Each studio is more than 7m tall.

Of course, it isn’t possible to naturally ventilate the spaces all the time. When external conditions are inappropriate – if it’s too hot or humid – it switches to mechanical ventilation and cooling. At street level, a set of acoustically lined doors can be closed to seal the studios from the outside.

Naturally ventilating studios in this way isn’t cheap. Mike Beaven, who leads building services and environmental engineering at Arup Associates, says the capital cost of this pioneering approach is beyond the usual cost of mechanical ventilation and cooling. “If we had the usual constraints of a three or five-year payback, we wouldn’t have been able to do this,” he says. Luckily, BSkyB’s view was that as long as the measures cut energy use, payback could be overlooked.

The design team is hoping to gain an “excellent” BREEAM rating for the building, but Beaven says this isn’t the main goal. “We’re doing things for the right reasons,” he says. “We’re not chasing credits.”

Instead, the philosophy has been to drive down energy consumption as much as possible without losing functionality.

Paul Brislin, a director at Arup Associates and the architect for the scheme, says: “BSkyB is not after high-end corporate facilities – what it wants is to get the most out of its technology, and that really drove the design.”

Two of the nine chimneys through which warm air will be vented from the studios.

Continuing the theme

The office space for the broadcaster’s 1,400 staff also employs natural ventilation. It’s a simple set-up – staff can open aluminium sash windows in the facade, which cross-ventilate to more giant chimneys in the building’s interior. The decision to open and close these will be taken to the occupants. Brislin says if staff have control, they are more tolerant of temperatures, which means they can operate in a wider band than the normal 21-24ºC. A traffic light system on the wall and emails are used to let everyone know when weather conditions are suitable. Otherwise, the system defaults to mechanical ventilation and cooling.

Having chimneys dropping down into offices is unusual, but they break up the space and provide social hubs, says Brislin. They also deliver natural light into what is a very deep building.

And what of the energy-intensive data processing areas at the heart of the building? The density of the heat load in these spaces means it is impossible to naturally ventilate them continuously. In addition, they require fine control of conditions – the temperature needs to be about 22ºC, plus or minus a degree, and humidity should be 50%.

However, it was agreed that these tight conditions could be relaxed to allow the option for fresh air cooling when outside conditions allowed. In this event, outside air is delivered directly into the space via the air conditioning units, cutting down the cooling load.

Overall, the building’s natural ventilation strategies are predicted to reduce the energy load by 7.5%. Construction of Harlequin 1 should be completed towards the end of the year, after which the massive fit-out of the IT systems can begin. At the moment just how much energy the facility will consume will depend on whether the wind turbines and biomass plant get the go-ahead, but even without these the building will break new ground.