Meeting the need for daylight without excessive solar gain

In areas of deep-plan offices that receive little, if any, daylight, lighting should be provided by suspended direct/indirect luminaires.
Focusing too much on reducing solar gain into office buildings will lead to buildings that are unpleasant to work in. People benefit from daylight. HARRY BARNITT discusses how to balance the requirements of Part L and people’s need for good lighting.Zumtobel Lighting has long championed the view that lighting is crucial to the success of the workplace environment, where wellbeing, motivation and efficiency are all influenced by it. Lighting to engage the most important asset of a business, its people, should be designed by lighting professionals — not based on outdated codes and recommendations, but founded on the latest findings of lighting science. Ideal environment Research into the effects of lighting on motivation and stimulation in both Europe and the USA has proved that an ideal working environment includes a mixture of daylight and direct and indirect artificial light, with an element of control given to the user. The oxymoron that is glass façades combined with the requirements of Part L requires a different approach. The requirements of Part L demand greater energy efficiency, but this issue cannot be taken in isolation. Logic might say that removing windows from the equation eliminates solar gain and therefore reduces the energy required to cool the space. However, lighting quality needs to be balanced with energy efficiency for a healthy and productive workplace. Good lighting is part of the mix that attracts and retains better people. It is not just motivation and productivity that is affected by these issues; a poorly planned or implemented office lighting scheme does not allow for our proven need for daylight, a preference for a ‘view out’ and the desire in the human brain for changing, dynamic light. Few workplaces are without any daylight whatsoever, yet the effects of daylight on the artificial lighting and the atmosphere of the space is rarely taken into account at the design and planning stage. Psychological need Research indicates that there is a psychological need for a view out. People consider a satisfactory view to incorporate a horizon and sky. While the ideal for all people is a view out, the reality is that only a few get that privilege. In a large office space with perimeter, intermediate and deep plan zones, it is only the first and second who may benefit. It is important for designers of office space to address these issues for all staff and not just the few. In these situations, the challenge is to balance the control of view, glare and solar gain. Solar gain and glare are both factors which point to the days of the fully glazed façade being numbered. Incorporating daylight into the building-services mix offers both opportunity and risk. Daylight can provide anything from 0 to more than 25 000 lx. The question is how to harness these variances to benefit of the workplace environment. Daylight offers a dynamic, changing pattern to stimulate the eye; sunlight presents glare and an uncomfortably bright working environment. Blinds Fixed shading, or brise-soleil, has only limited use in the UK due to the low trajectory of the Sun in winter. Unless a great deal of money is invested in a clever façade, such as one incorporating glass that filters heat, a reasonable option would be to use adjustable blinds as part of the daylight control strategy. Indeed, Zumtobel Lighting advocates that daylight-attenuation blinds should be part of a general Cat A fit out. Blinds are currently not included, but left up to the tenant. Decorative, manually operated blinds are often installed, which do not fulfil the needs of the occupants and often give the building a untidy appearance which was not part of the architect’s original plan. Solar gain Part L puts a limit on solar gain. Efficiencies that could be gained by using automated blinds would make the initial specification and installation cost effective and help a building achieve its building emissions rate. ‘Daylight-harvesting blinds’ provide the solution to view out, glare and solar gain. There is an additional benefit of redirecting daylight deeper into the space to benefit more occupants. Daylight harvesting blinds will filter glare, reflect sunlight back outwards and can also redirect the daylight inwards. Slats can be tilted at different angles to minimise solar gain while maximising daylight in the space. Daylight harvesting Zumtobel advocates that daylight-harvesting blinds are part of the ideal office specification and should be used with automated controls driven by the readings of a sky scanner on the roof of the building and linked to the artificial lighting. For maximum effect, daylight-harvesting blinds must be fully automated. While this is a direct contradiction of the philosophy that people should have control over elements of lighting in the work environment, Zumtobel believes this is the only way that technical blinds, daylight and artificial light can be fully integrated. In many buildings where manual blinds are installed, they are rarely adjusted. Where technical blinds have been installed, empirical evidence shows that if people are given control of the blinds, they soon allow the blinds to work automatically — typically within only a week or two.
— In perimeter areas of offices where plenty of daylight is available, artificial lighting can be provided by recessed luminaires.
By linking a lighting-control system (such as Luxmate) to a sky scanner on the roof of the building, the amount, direction, and quality of the light is continuously measured and the blinds and artificial lighting are linked to react on an adjustable time-lag to variations. Artificial lighting can be zoned with a mix of luminaires to allow for the effective use of daylight. In the perimeter zones, recessed luminaires should be used. In transition zones, semi-recessed luminaires should be installed. In deep-plan areas, suspended direct/indirect luminaires provide the solution. As a manufacturer Zumtobel could be expected to push for less glazing and, therefore, more artificial lighting; the opposite is the case. The controlled interface between daylight and artificial light is the key. Harry Barnitt is marketing director with Zumtobel Lighting.
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