Oct 23, 2019 Last Updated 10:52 AM, Aug 14, 2019

Daylight modelling: Managing natural light in leisure buildings

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Architectural Journalist Gideon Sykes looks at the latest advances in daylight modelling and how it can help architects and specifiers determine the correct lux levels for their leisure projects.


Daylighting is the art and science of managing natural light to minimise the use of artificial lighting, reduce energy consumption, reduce carbon emissions and positively affect the performance, mood, enjoyment and well-being of people occupying a particular space.

Designing, predicting and planning for the impact of daylighting in a leisure space is often misunderstood. Daylight modelling removes the design mystery and determines the daylight requirements for any building be it a sports hall, swimming pool or other leisure facility.

It is not a new science but one which is increasingly important as reduced energy consumption is a continuing major consideration – as well as statutory requirements (such as European workplace directives) and personal well-being.

Many companies offer daylight modelling services and a few, such as Kawall, offer them free of charge when being considered for projects.

Daylight modelling as part of the design

It’s often a mistake not to use daylight modelling as part of the original concept or design. Consequently, it is beneficial that this service is used early to help achieve the best possible results for the client and to form part of the overall building strategy and goals.

For example, the service can help with the documentation required to achieve BREEAM’s health and well-being credit for visual comfort (HEA01) which requires that 80% of the occupied space meets a minimum daylight factor of 2% (3% for exemplary level).

It can help architects and specifiers with the following calculations:

1. The quantity of light transmitting materials
2. The location of light transmitting materials
3. The required transmission level of the light transmitting materials
4. Glare analysis purposes

Daylight modelling can help achieve an exact brief from the client – for example the lux level requirement or to address concerns about solar heat gain. It can help quantify daylight transmitting products, determine optimal light transmission and help with positioning on a building to prevent glare issues and provide interior lux levels.

The reports can be looked at from a cost point of view and recommendations made depending on the results. A good example of this is for Value Engineering (VE) where daylight modelling may show that windows can be reduced in size to save money yet still achieve the desired lux levels.

The report can include any or all of the following calculations:

Lux Level:
Lux is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface. For example, sports halls and classrooms would be expected to have lux levels of between 300-400.

Radiance Illuminance:
Radiance Illuminance (measurement of light level) is a snapshot of the ambient lux level (light) at any given time. This tool calculates how effective is daylight penetration at any time of the day or on any day in the year.

Daylight autonomy:
Daylight autonomy (DA) is the percentage of the time-in-use that a certain user-defined lux threshold is reached only through the use of daylight. DA is usually given as an annual value but seasonal, monthly and daily calculations can be made. It is the ideal way to achieve optimum natural daylighting conditions for the occupants, predicting when electric lighting may be required and thereby helping to reduce the cost of energy.

Glare Pattern analysis: This tool calculates luminance (measurement of glare) within a space. It is used to analyse direct glare or reflected light, such as in sports halls and swimming pools, where it is important to keep balanced light within a space to protect athletes from high contrast light ratios.

The graphic below shows direct glare coming through the windows into a swimming pool – excessive lux levels from unfiltered daylight.

The Process:
Daylight modelling is the way to calculate the most effective daylighting for any type of building. It is calculated using five years’ worth of real world weather files at the exact location of the building as well as information on day, time, position and weather patterns.

In addition, a daylight modelling team will undertake this service using data provided by the architect or client. This comprises an indication of light levels required together with building elevations, floor plans and sections.

It also takes into account proposed internal finishes, which could influence reflectance, the positions of other windows and any external influences, such as tall adjacent buildings or trees.

With this information, the team can look at an individual room or at the overall situation and design the most favourable daylighting solutions.

Daylight modelling in practice
The Redgrave Sports Centre in Great Marlow is a new sports complex comprising multi-use hall, fitness suite and dance studio and a perfect example of the use of daylight modelling.

Due to its location, designers PTAL Architects were concerned about the potential issues with lux levels so they commissioned a free daylight modelling report. The daylight modelling team ran the tests and observed issues with the 20% light transmission specified – especially around the autumn equinox with the low sun position on the South East corner. Normally the canopy roof would reduce the direct sunlight but throughout the autumn months the sun would be lower thereby causing undesirable lux levels.

The daylight modelling report further directed the design team to towards a lower light transmission at 9%. As a result, it was decided to install Kalwall clerestory daylighting around the three sides of the hall as recommended by the study.

An added advantage is that the Kalwall system bathes the interior with natural diffused daylight to create an attractive ambience without shadows or glare.

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