Cyberhenge

"In a world with holes in the ozone layer and persistent poverty, our mission at the Earth centre is to promote understanding of sustainable development and to help people become involved in their own lives," he says.

Smales has taken nearly a decade to realise this temple to ecology. After nine long years of feasibility studies and fund-raising, a desolate expanse of sterile colliery spoil has been transformed into a thriving example of sustainable development, a hands-on £41.5 million visitor attraction with a serious message.

That message has been played out to the full inside the Planet Earth Galleries, the main exhibition building for the Earth Centre. Here, in a subterranean "Cyberhenge", visitors are bombarded with visions of environmental cataclysms. Cracked and glowing globes symbolise pollution and resource depletion, while lighting, audiovisual projections, and sunlight-powered prisms symbolise an alternative, more sustainable world.

Other galleries contain interactive displays and light sculptures detailing man's relationship with the Earth and the Universe. While most spaces are intentionally gloomy, the north wedge of the building houses the Exit Gallery, a mainly daylit space which symbolises mankind's wake-up call to a sustainable future.

Predictably, the client expected all buildings on the site to be ecologically sound, energy efficient and preferably autonomous in operation. Equally predictable is the list of architects and engineers Jonathan Smales appointed to turn this dream into reality.

The entire 400 acre Earth Centre site is a showcase for the likes of architects Feilden & Clegg, Alsop & Stormer and Future Systems, while m&e consultant Atelier Ten has designed some very low energy services for three of the Phase 1 buildings – the Planet Earth Galleries, restaurant and WaterWorks exhibition building. Although the buildings at Planet Earth are currently powered by fossil fuels, plans are in hand for power to be generated on-site by renewable sources – wind, solar and biomass.

The buildings

The Planet Earth Galleries and the separate restaurant building – eat.organic@earthcentre – present an understated entrance for visitors. The space between will eventually be linked by a 800 m² canopy of photovoltaics to demonstrate renewable sources of energy while providing up to 30% of the Planet Earth Galleries' total energy requirement.

The two-storey restaurant is a relatively simple building, receiving heat and power from plantrooms between the Planet Earth Galleries. Underfloor heating is used in the double-height glazed refectory and mezzanine, while sliding wall doors and motorised clerestory windows (operated by mullion-mounted switches) provide routes for natural ventilation.

Directly opposite the restaurant is Feilden Clegg's Planet Earth Galleries' building, a single-storey structure set into the steeply sloping hillside. Only a bluff south-west facing limestone retaining wall is visible, albeit relieved by large glazed doors to the exhibitions and the inevitable EarthShop where visitors can buy tee shirts, soaps, and solar powered radios.

Figure 1 shows the basic layout of the building (with a cutaway showing the basement). To the south, the building is covered by a turfed roof, penetrated by the ventilation extract and rather more visually appealing solar panels and sun-tracking devices that illuminate the galleries. To the north, the turfed roof gives way to banks of motorised solar shades arranged across the wedge-shaped, glazed roof of the Exit Gallery.

To say that the ground conditions at the former colliery site were poor would be a gross understatement. Whatever rock is below the slag and spoil is heavily faulted, necessitating a concrete raft foundation instead of piling. This raft protects the building from differential settlement and spreads the weight over the ground's poor load-bearing capacity.

However, as this would have meant a slab thickness of around 1·5 m, the design team decided on a honeycomb form of construction. This decision was a stroke of good fortune for the services consultant Atelier Ten, which was toying with the idea of using the heavyweight fabric to cool internal spaces. Voids created by the honeycomb construction provided the ideal opportunity for a thermal labyrinth – a space where incoming ventilation air can travel a serpentine route, emitting or absorbing heat according to season.

The thermo-labyrinth

What sounds simple actually required considerable design thought, and no small number of Tas computer simulations. The simulations identified the relationship between thermal loads, the surface area required for the labyrinth and the volume and velocity of the supply air. The designers even considered ways to boost the labyrinth output, such as water jackets on the walls or concrete cones to increase surface area and turbulence, and thereby heat transfer.

In the end it all came down to pragmatism. Out went the cones and in came 1·7 m high serpentine corridors formed by dense blockwork walls. These are constructed as a series of storage cells which divide the 3200 m² basement into zones along its length. They are aligned with displacement terminals in the exhibition rooms above.

In operation, the labyrinth runs in one of three modes. During summer, fresh air is drawn through two Fläkt air handling units and injected into the labyrinth cells. A night cooling strategy ensures that the labyrinth cells have considerable cooling capacity. If this proves insufficient for a very hot and/or busy day, the ahus possess adiabatic cooling sprays to condition the supply air indirectly.

Adiabatic cooling relies on mains water spray humidifiers to cool the extract air prior to passing through a thermal wheel, which then imparts cooling to the incoming airstream. In winter the spray humidifiers can be switched off and the wheel used to recover waste heat from the extract air to warm incoming fresh air.

This is a technique Atelier Ten has used before: at the headquarters of Charities Aid Foundation¹ and the Kimberlin Library at de Montfort University². In theory the system is simple and robust, although it must be said that in practice adiabatic cooling can require a fair amount of management and monitoring, along with good front-end controls.

Temperature control and mixing is achieved at the Earth Centre using dampers on the inlet and outlet sides of the labyrinth cells. Depending on prevailing conditions, these can modulate to either direct air down the cells or close completely, forcing the supply air down a bypass corridor that also feeds the displacement diffusers.

During summer nights, cool air is drawn through the labyrinth – taking the temperature down in preparation for cooling the following day. At 16°C, air bypasses the labyrinth and is routed through a builders-work header duct leading outside.

During the heating season, cold incoming air is tempered in the air handling units by a combination of recovered heat from the extract air and lphw heater batteries. The current default setting does not make use of the labyrinth to store heat from internal gains. This could be done, but would call for a knowledgeable, committed and controls-literate facilities manager.

The virtue of this system from Atelier Ten's viewpoint is that, while fabric temperature tends to be the limiting factor in most forms of thermal storage, here it is not. By separating the storage chamber from occupied spaces, the firm was able to adopt a more sophisticated and proactive thermal charge and discharge strategy. Further details on the design of the thermo-labyrinth are given in the technical file article 'Design issues for thermal stores'.

Air handling strategy

The ventilation system is the other key part of keeping the building at the right temperature with low energy use. Here, it is closely allied to the labyrinthine thermal store and low-energy heating or cooling from the thermal wheel.

A useful tweak at the Planet Earth Galleries is a bypass arrangement which can isolate the thermal wheel in stages. This extremely sensible arrangement adds flexibility and helps maintain an even temperature of supply air to the galleries. The bypass can be fully opened to track external ambient air temperature.

When the temperature of incoming air climbs to 17-18°C, volume control dampers on doors leading to the labyrinth cells open to allow air to run through the labyrinth. As the supply air temperature climbs, the labyrinth output increases – a very useful self-correcting property. However, when room thermostats sense that the cooling capacity of the labyrinth is being exhausted, the controls system brings on the adiabatic cooling.

Atelier Ten claims that the system pressure drop at the Earth Centre is fairly modest: the velocities are very low, at 0·2 m³/s in the labyrinth (a function of decent sized ahus and ductwork), and the 5 kW fan motors are inverter-driven. This ensures that a constant volume of air is supplied, irrespective of pressure variations which occur when the heat exchangers are bypassed. Total specific fan power is quoted at around 1·2 W/litre. Fan power is only at its greatest when the system is in adiabatic mode.

Displacement ventilation was selected as the best air distribution strategy for two reasons. First, the gallery has a 6 m high ceiling and second, because cooling needed to be achieved with fairly high supply temperatures of 18-21°C.

The system is proving to be self-balancing. Minor local balancing was done by hit and miss dampers on the 600 x 600 mm floor grilles, which incidentally were manufactured from recycled aluminium. During commissioning the volume of each diffuser was very even, this is a function of the low air velocity and the modest air change rate of around 3 ac/h.

The control strategy

The engineers have devised three levels of control: seasonal, daily and instantaneous.

The seasonal control comprises a summer mode, in which the boiler plant is switched off and a night cooling regime is imposed upon the ventilation plant. In winter mode the boilers run and no night cooling operates.

In mid-season the system operates to the daily control algorithm. This runs in tandem with temperature sensors installed at strategic locations. The control algorithm adjusts the target temperature to which the labyrinth is cooled each night, based upon average external temperatures for the previous three days. The higher the external temperature, the lower the target temperature the labyrinth has to achieve to meet the following day's cooling requirement.

The instantaneous control regime monitors temperatures in the gallery and controls dampers in the labyrinth. The dampers direct air supply either straight to the supply grilles or via the labyrinth bays to maintain conditions in the gallery.

Other services

Given its passive engineering, the Planet Earth Gallery building is minimally serviced. Heat raising relies on three 120 kW gas-fired condensing boilers, which could, in the future, be modified to use biomass fuel.

The lphw circuit has lower than usual return temperatures, enabled by the large air handling units which allow larger heater batteries, to ensure that the boilers always operate in condensing mode. Two port control valves enable flow rates to be matched to demand by variable volume pumping.

Photovoltaics will be introduced across the site as funding becomes available, most notably for the 800 m² canopy that will link the restaurant building with the galleries. Already small solar panels are being used for domestic hot water, with a gas-fired water heater as standby.

The glass-roofed Exit Galleries have solar protection from external motorised louvres. These cut out around 80% of the solar gain. Motorised louvres were less costly than fixed louvres as the support mechanisms for fixed louvres would have to be more robust to withstand snow loading.

Given the nature of the site, rainwater collection would seem an obvious sustainable measure, but this was ruled out on cost grounds. In any case water use is likely to be low.

The labyrinth is equipped with a smoke detection system linked to life safety alarms. Being connected to the air handling plant therefore makes it possible for the labyrinth to act as a conduit for products of combustion. In the unlikely event of this occurring, a spring-loaded door can open at one end of the labyrinth to exhaust smoke. This door is fitted with sensors that can warn the Trend bems that it has tripped, in which case someone has to go down into the labyrinth and close the door.

Unfortunately, this door has the effect of short-circuiting ventilation air from the buffer corridor to the extract plant, so that labyrinth cells are short-changed on supply air. As always, the trick is good monitoring which, on the day of the visit, seemed rather lacking: the bems repeater terminal was hidden behind a locked door. Evidence, if it were needed, that fit and forget passive engineering always has fit and manage elements somewhere along the line.

WaterWorks and water conservation

The Planet Earth Galleries are only the start of the experience. Further into the park other buildings and features display forms of sustainable construction, technologies and techniques designed to appeal to children as well as adults.

The Water Works building has been designed more for insects than humans. Designed by Alsop & Stormer, with Atelier Ten again handling the services, the building is home to the Living Machine, a full-scale sewerage treatment system consisting of bacteria-gobbling plants.

The process starts with the toilets and waterless urinals and thence to a bio-fence and reed beds to a settling lagoon. The bio-fence uses algae to clean the water, the algae being periodically siphoned off for use as fertiliser. All treated water is used to irrigate the gardens around the site.

There are many water-saving devices throughout the site – enabling the Earth Centre to claim an 80% reduction in water use compared to a conventional visitor attraction. For example, Atelier Ten has used vacuum toilets with around a seventh of the water consumption of a low flush cistern.

The walls and roof of the WaterWorks building are largely constructed of ethylene tetrafluoroethylene (etfe) panels fixed to aluminium mullions. The panels are inflated to around 220 Pa to give the plastics foils some structural stability and to improve the material's insulation properties. The U-value is around 1·2 W/m²K.

The air pressure in each panel is maintained by a 220 W blower, switched on and off by a pressure switch connected to a reference cushion. The blower is claimed to operate for only 50% of the time, so energy use is low.

To maintain an internal temperature of 6°C in winter, Atelier Ten installed a 40 kW wall-hung condensing boiler to supply lphw to finned convectors around the building perimeter. Illumination is provided by 150 W SON lamps.

Elsewhere at the Earth Centre other wacky images of sustainable technology appear round every corner of the cycle and pedestrian trails that criss-cross the site. There is the solar piano for example... no, hang on, if you want to know how that works, I strongly suggest you go there and hear it for yourself.