‘Climate connectivity’ in the daylight factor basis of building standards

Abstract

Citation: MARDALJEVIC, J. and CHRISTOFFERSEN, J., 2017.`Climate connectivity' in the daylight factor basis of building standards. Building and Environment, 113, Additional Information:• This paper was accepted for publication in the journal Building AbstractThis paper describes a proposal for a daylight standard for CEN countries. It is now widely accepted in the research community, and increasingly so amongst practitioners, that the standards/guidelines for daylight in buildings are in need of upgrading. The essence of the proposal is that the 'target' for daylight provision should be founded on the availability of daylight as determined from climate files. The proposal is in fact a refinement of an approach originally described in a CIE document from 1970, and which appears to have been largely overlooked since then. The proposal states that a design should achieve a target daylight factor at workplane height across a specified percentage of the relevant floor area for half of the daylight hours in the year, where the target daylight factor is based on the provision of 300 lux. A key feature of the refinements are the formulation of the methodology such that the likelihood for misinterpretation and 'game-playing' is greatly reduced, if not eliminated altogether. The method, founded on cumulative diffuse illuminance curves, could be introduced relatively swiftly since it requires only modest enhancement of existing daylight prediction tools. In addition, the proposal will provide a sound 'footing' for eventual progression to evaluations founded on full-blown climate-based daylight modelling. BackgroundBy the late 1800s the pressure to accommodate an increasing number of people in the cities of the developing world led to taller and more tightly-packed building forms, thereby reducing and often eliminating entirely the direct view of sky from much of the useable, internal space. This in part led to the need for some objective measure of the daylighting performance of a space which could, if required, function as a tool to evaluate buildings at the planning stage. Daylight was at that time still the preferred source of illumination for both manual and clerical work -it was also 'free'. The work of Nordhaus has shown that the real cost of artificial light has dropped by nearly four orders of magnitude over the last two hundred years [1]. It is only over the last decade or two that we have come to appreciate once again the true importance of 'good' daylighting design for buildings. However the legacy of many years of effective downgrading of daylighting in the overall consideration of building design is still apparent today. Many standards for daylighting have hardly changed over 40 or more years, and often make no account of the actual availability of daylight. Attempts to progress matters have often resulted in less than satisfactory outcomes, e.g. vague or confusing criteria and/or methodologies. For example, the various 'clear sky options' recommended in both LEED and ASHRAE have resulted in approaches that ...

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