Shaping light and air

Engineers and architects are working together to harness natural sources of energy.

The manipulation of light has always been fundamental to the architect. Past emphasis for the lighting engineer has been on artificial lighting, but nowadays both lighting engineers and architects are grappling with natural light as a passive solar energy saver.The challenge is to capture and use daylight, without glare and without subjecting interiors of buildings to solar overheating. The last condition does not mean that we should not also admit sunlight, especially when thermally advantageous, as a useful passive solar gain. Provided glare does not interfere with particular activities, dynamic patterns of sunlight and shade with buildings can be emotionally very satisfying - at least to the same extent as any artificially introduced lighting drama.

Roots in history

The science of air and 'air quality' in buildings also has a respectable history for both architects and engineers. Having said that, it was the medical profession that led the main advances in 19th century understanding. A Scot, Dr David Boswell Reid, acted as heating and ventilation consultant for the select committee set up to oversee the procurement of the refurbished and new parliament buildings in London after the great fire of 1834. For the remainder of the 19th century and into the early 20th century, mechanical ventilation systems made use of structural, and also aesthetically important, elements of buildings in order to temper and transport air from outside to rooms.

Such systems often relied on natural thermo-circulation for exhaust as well as sometimes working in tandem with natural ingress and egress of air via windows or grilles. This aspect of air circulation could be loosely attributed to solar influence - indirectly due to wind pressure differentials; and more directly by convection instigated by radiated solar absorption on, and re-radiation between, surfaces.

Today we may refer to such a hybrid passive-active approach as 'mixed mode', the balance between automated and manual environmental control dependant on building category. As with light, the aim is to reduce carbon emissions, while at the same time rendering the internal environment more stimulating and responsive for occupants.
Therefore, one might say that the science of shaping light and air concerns the tectonics of both reason and emotion, the latter having equal status with the former. Architects have a reputation for tugging at emotional sensibilities through illusion; while engineers tend to be associated more with numerically supportable reason. However, qualities of light are psychologically linked with perceptions of airiness; and engineers, who are engaged in teams with architects, cannot help but be drawn into this kind of design dichotomy. It may be expressed as one of passion and pragmatism, poetry and prose or the sensorially sublime and routinely rational.

The semantics do not really matter, but the line of thinking does. Therefore, a small number of built projects will serve to illustrate recent successes and dilemmas from this perspective; rather than attempting to delve into technical detail on matters such as advanced glazing or air handling systems.

Skin and substance

With its play on two clichés 'style and substance' and 'skin and bones', 'skin and substance' is intended to convey issues such as integration, materiality, enclosure, structure and form. The anthropogenic allusion reminds us that buildings are there to shelter the activities of people, not forgetting the health-giving qualities of light and air.

Architect Peter Zumthor pursues concepts from theoretical inception to constructed reality with rigour and passion. For example, he writes about 'The Hard Core of Beauty' and 'The Magic of the Real' and has expressed his approach with the word 'atmospheres': "We perceive atmosphere through our emotional sensibility - a form of perception that works incredibly quickly, and which we humans evidently need to help us survive."

Zumthor's multi-storey gallery at Bregenz on Lake Constance, Austria shows material asceticism expressed conceptually. Deep-sided concrete boxes are stacked within an ethereal container, with vertical diffusing glass 'shingles' on all four sides of a square plan directing light horizontally into generous voids above a diffusing glass ceiling. All façades receive sunlight for most of the year, respectively facing 30° off cardinal points. Daylight and a memory of sunlight, when it occurs, shimmers through this luminous lid, augmented as required by artificial lighting.

Gravity rules and three concrete spines connect the boxes. These are held back from the façade to accommodate stairs and lifts and disposed in pinwheel formation, permitting varying amounts of light to enter - least from the southerly and most from the westerly side. Such is the diffusion, it is hard to distinguish between walls that slice through the ceiling and those that stop. Atmosphere and illusion are at play.

The contrast between the only two visible materials, polished concrete and milky glass, is also palpable - white light and dark density. This aspect of heaviness in the walls and floors is reified environmentally. In the tradition of 19th century precedents, ducts for transport of fresh air are embedded within the masonry; and respective cooling and heating effects according to ambient conditions are augmented by cool or warm water, embedded in the concrete.

Air enters each gallery through narrow slots between walls and floor, rising gently, with occupants causing mild convective plumes; and leaves through the gaps between the ceiling tiles. Once in the void it will pick up heat from any artificial lights that are switched on, and flow into the soffit of the next floor slab. The displacement ventilation principle is the same as that adopted for the House of Commons by Dr David Boswell Reid, although his system had to cope with exhaust fumes from 19th century gas lighting.

Although the ventilation makes passive use of the thermal capacity, it is otherwise an active system, which excludes any form of environmental control and is divorced from the strategy for lighting other than picking up heat lost from light fittings. The environmental tempering is very indirectly solar-influenced in that the underground aquifers, which support it in an energy-conscious manner, are part of the biosphere. However, this is a pedantic issue since boundaries between solar design and environmental design have become increasingly blurred.

Diverse interactive and holistic means to a low-carbon end are to be welcomed. Another multi-storey gallery of 'exclusive' environmental note is that by Caruso St John Architects in Walsall. The approach taken by Zumthor at Bregenz is explicit materially, engages with lighting in a somewhat more mysterious manner and the means of ventilation is completely obscure without access to working details (about which we know Zumthor is fervent). Adam Caruso and Peter St John are also very engaged with materiality. However, their resolution at Walsall is more eclectic in this regard, while their manner of dealing with light and air bears comparison with Bregenz.

For example, in the temporary galleries on the penultimate level, the floor is power-floated concrete, and the ceiling deep concrete ribs, while the vertical surfaces are MDF, plasterboard and glass. The heavy material is texturally differentiated, while opaque, light-coloured walls are both a backdrop for artwork and a concealer of services. Solid looking spatial dividers are hollow service ducts.

Conditioned air enters through slots at the top of these walls and returns horizontally back to the main vertical ducts in an equally hidden manner. The concept is simple. As air is transparent it can discreetly travel in a transparent container, in this case the space between the inner etched glazing of a ribbon clerestory window and the double-glazed external skin. The window-duct also contains asymmetric light fittings and venetian blinds to further adjust light levels.

Thus it is a multiple service space for light and air - an understated passive-active hybrid. Perhaps ironically, it is not the window-duct that represents the highest environmental risk. If the air entering at the top of wall-ducts is not adequately chilled relative to the bulk of the air within the gallery, the potential exists for a 'short circuit' directly to the high-level windows.

The design idea relies on adequate density for the fresh air to initially descend to floor level. This risk was apparent to the author during a visit on a cool and wet day. The atmosphere in the gallery was too stuffy, indicating that the under-floor heating was functioning, but not the ventilation.By way of contrast, the 2003 extension to the modern art gallery (Kuntsbygning) in Århus by architect Mads Møller takes higher risks with ventilation, and seems to work well. This is an underground space, which is both naturally top-lit and top-ventilated. The devices for both are raised lanterns. One is linear, forming the southwest boundary to a sculpture court above; a second is shorter and allows access by stairs down the southerly side of a curved wall; and the last is an asymmetrically positioned cube.

All three have automated opening lights, but it seems remarkable that such an apparently ad hoc system can be effective. Would a hot and still day leave it wanting? Certainly the basement configuration means that there is little to thermally stress the envelope; while the stair-access lantern should act as a passive thermal accelerator promoting enhanced thermal buoyancy for extraction in the absence of wind. As for light, although the daylight requires some artificial supplement even on a bright day, the impression remains of a vibrant naturally lit space.

Møller's approach to natural ventilation bears comparison with a new arts centre and library in Glasgow by Gareth Hoskins Architects with Max Fordham as services engineer. Called 'The Bridge', it connects an existing community swimming pool and a further education college. The library comprises a series of stepped levels, which ease circulation between the new entrance foyer, two floors of the college and the lower entrance into the theatre. These 'terraces' are both side-lit from generous east-facing fenestration and top-lit by relatively small circular roof-lights dramatically located around a forest of slender columns. The roof-lights are electrically opened as required, allowing fresh air to enter and leave according to positive and negative pressure balances. A low temperature serpentine within the concrete floor provides background heat.

As in Århus, a straightforward means of natural ventilation appears to be perfectly adequate for the modest number of occupants relative to volume. The adjacent 'black-box' theatre, is also bounded by accommodation on its other sides. Six large (circa 2 x 1.5m) low-level inlet grilles are dispersed on walls, including behind bleacher seating. Fresh air is led to them on a temperature-stabilising journey from the east side of the complex; past a primary heating coil at the entry point, with trimmer coils behind each inlet for finely adjusting to the desired temperature. Vitiated air then leaves via six 'chimneys', approximately 6m high and fitted with acoustic attenuation. In buoyancy-busting calm conditions with a poor inlet-outlet temperature difference, auxiliary extract fans are switched on automatically by BMS (building management system), their use monitored by Glasgow City Council.

Although the 'design' inlet temperature was 16°C, complaints of cool draughts when the space was lightly used led to this being permanently adjusted upwards. Such issues challenge BMS 'smartness', which should be able to cope with empty, full or partly full occupancy. That issue aside, the theatre is among an environmental design elite.
Max Fordham was also the services consultant, with architects Short Ford Associates, for De Montfort University's Queens Building in Leicester, the first modern higher education campus to naturally ventilate all main spaces, including lecture theatres. Critics of such projects suggest that very little energy is used for fans to ventilate mechanically to the same standard, with the advantage of greater control.

Certainly, projects such as the Jubilee Campus in Nottingham, by architects Michael Hopkins and Partners and services engineer Ove Arup and Partners, have adopted a relatively low-energy mechanical approach. This was claimed to be 'super efficient', based on moving large quantities of air at low velocity in order to minimise pressure drop. However, more energy was consumed than expected, with open service doors cooling air recovered by the thermal wheel offered as at least part of the explanation.

It is also possible that opening windows between rooms and atria contributed to the design intentions not being met in terms of thermal efficiency, although this facility is generally regarded as an asset in terms of ownership and adaptive opportunity for long-term users. Another risk with glazed buffer spaces of all types is that they are so attractive that managers wish to fully heat them. This happened with a significant energy penalty in the Norwegian Institute of Technology, Trondheim.

However, there are cases of atria, which form part of a heated volume, and yet perform a useful thermal function. The glazed skin of one at the Deutsches Post Museum, Frankfurt, by Gunter Behnisch and Partner is a semi-circular slice of a cone. Although considered environmentally problematic at completion, with blinds mooted, the atrium faces 30° north of east and is well shaded in summer by a large tree.

Thus significant solar transmission can only occur at the coolest point of the day. Moreover, the atrium provides a generously day-lit threshold to the basement exhibition area; acts as an efficient exhaust route for air supplied mechanically to this level; while in winter published sections (rather than text) indicate the use of heat recovery or recirculation.

A geometrically simpler wedge-shaped, south-facing atrium at Glasgow Caledonian University by Building Design Partnership has a similar rationale. Again a pivotal multi-level circulation hub, it acts as a solar preheating source in winter and assists natural ventilation in summer. Embedded shading in the form of fritting has been included in this case. Translucent photovoltaic cells were proposed for this, but discarded owing to the unwieldy process of applying for a grant. In both the last two examples, it is the atrium that is the tectonic 'light and air' triumph, imbuing the right balance of logic and sublimity into a dynamic crescendo of internal interconnection, as well as contact with the external environment.

Architectural dialogue

It appears that symbiosis between buildings (form and construction) and their 'light-air' environmental attributes sometimes entails risk. The non-domestic types chosen are all active-passive hybrids, with mainly automated control. That does not preclude limited personal adaptive opportunity. Nor does it inhibit enjoyment of the buildings, suggesting that environmental user-control is not necessarily an issue.

The examples also support the case for dialogue between disciplined rationalism and sensory empiricism. Harold Pinter's2005 Nobel Prize acceptance speech suggests similar juxtapositions. He quoted himself in 1958, justifying artistic simultaneity for truth and falsehood. A final provocative translation to such polemical thinking is by Leonardo da Vinci: "Art lives from constraint and dies from freedom." Such sentiments support 'engineering solar architecture' and 'shaping light and air' - reason inspiring emotion. 

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