by Jens Christoffersen and Nicolas Roy, VELUX Group | Photography by Adam Mørk
It is well acknowledged that daylight is vital for human health, but do we see the quality of our homes as an important parameter to our own health? And do we know what are the potential benefits of having good daylight conditions at home?
This article presents findings on the effects of daylight in a demonstration building project, Maison Air et Lumière, located south of Paris in France. It includes an evaluation of daylight performance against the Active House specifications and the proposed European Daylight Standard (prEN 17037), as well as key findings from a one year post-occupancy period during which a family resided in the house.
In the ‘dark’ about the importance of daylight
A recent series of survey, the Healthy Homes Barometers, reveal that 76% of Europeans report needing to turn on electrical lighting during daytime hours, while only 20% reported being too dependent on electrical lighting. This is raising the question, are we sufficiently aware of the importance of daylight in our homes?
“76% of Europeans report that they need to turn on the light during the day
The Healthy Homes Barometer 2017 presents findings from a study by Ecofys on the relation between quality of dwellings and health in Europe. It uses the Eurostat database EU-SILC 2012 (Survey on Income and Living Conditions), and shows that about 6% of all European households report living in a dark home and are 52% more likely to report poor health when compared to households not living in a dark home.
A ‘brighter’ future ahead?
Proposal for European Daylight Standard (prEN 17037)
Daylight performance in an interior space depends largely on the availability and properties of natural light at the building’s location (i.e. the prevailing climatic conditions).
“It is evident that today’s standards/guidelines for daylight in buildings need upgrading
The proposed European Daylight Standard (prEN 17037) suggest to change the basis of daylight evaluations from simple glazing ratio requirements to `daylight factor targets’ based on the occurrence of outdoor illuminance levels from recorded climatic data. The `climate connectivity’ of the proposal states that a space should achieve a target daylight factor at work plane 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 an interior illuminance higher or equal to 300 lx. In addition, a minimum target daylight factor based on the provision of an interior illuminance higher or equal to 100 lx is required over the entire work plane, see example below.
The table below presents an example of target daylight factors for different locations in Europe, it shows that higher targets are needed for countries located in Northern Europe to compensate for the decrease in daylight availability when compared to southern locations.
The method can easily be introduced since it requires only modest enhancements of existing daylight prediction tools. In addition, the proposal will provide a sound `footing’ for the eventual progress to evaluations founded on full-blown climate-based daylight modelling.
Active House Specifications
The Active House Specifications focus on three main challenges faced by residential buildings in today’s societies: comfort, energy and environment. The comfort related aspects put a strong focus on good daylight conditions, thermal comfort and fresh air from natural ventilation. The specification for daylight conditions, based on BS8206-2, use the average daylight factor (Davg) method measured at work plane height, where different performance class can be achieved, with 5% Davg or more being the highest level of performance. The table below presents the 4 performance classes and corresponding daylight factor levels.
According to BS8602-2, rooms with Davg of 2% or more can be considered daylit, but electric lighting may still be needed to perform visual tasks. A room will appear strongly daylit when the Davg is 5% or more, in which case electric lighting will most likely not be used during daytime.
Evaluation of daylight performance in Maison Air et Lumière
The architectural concept for Maison Air et Lumière is based on a compact volume with multiple roof pitches, and carefully positioned façade and roof windows to bring in daylight from all directions. The 130 m² floor area extends over one and a half storeys, and the house has a window-floor ratio around 1:3.
The daylight analysis for all main living spaces show good daylight conditions and the house perform well according to the European Standard as well as the ActiveHouse Specifications. The daylight analysis uses the VELUX Daylight Visualizer, which is a professional and validated simulation tool for the analysis of daylight conditions in buildings. The figure below shows the daylight factor simulation output on the ground floor and first floor.
The table below shows that recommendations according to the European Standard are met in all rooms of the house with levels far exceeding the target recommendations. With regards to the Active House Specifications, almost all living spaces achieve the highest class for daylight performance (i.e. higher or equal to 5% Davg), and two rooms meeting the second class (i.e. higher or equal to 3% Davg).
Post-occupancy evaluation
For a one-year period where a family of 4 lived in the house, we performed measurements of the indoor environment including lighting use, thermal conditions, indoor air quality, occupant presence and all occupant interactions with the building installations, including all operations of windows and solar shading.
Below is a temporal map showing monitored data from all electrical sockets within the living room, the X-axis shows months of the year and the y-axis shows time of day. The dark blue colour indicate instances where electric light might be switched on, otherwise its switched off. It is a complete year of measurements (September 2012-13) and equivalent to the period where a family of four lived in the house.
The map shows that electric light is rarely switched on in the morning, while the evening period shows a clear tendency for electric light being switched on after sunset, thus suggesting that daylight is used as an autonomous light source during daytime. Additional analysis showed that outside weather patterns and days of the week did not have much impact on the light switiching patters in the house.
“One of the hypothesis was that if room has an average daylight factor of 5% or more, then the electric lighting will most likely not be used during daytime.
The post occupancy evaluation (POE) showed that the residents rated the daylight levels in the demonstration house as “much higher” and state that they turn the electric lights on “less often” than in their former home. The family report high satisfaction with the daylight level and find it “appropriate” in the kitchen, the living room, and the bedrooms. Sunlight penetration is preferred all day in the kitchen and living room, while higher preference for morning sunlight in the bedrooms.
Conclusion
It is important to emphasize that national legislation that mandates minimum window size cannot be considered as adequate daylight legislation, as it does not translate the actual daylight provision inside the room or building; it is not considering outside boundary conditions, facade elements, glazing properties etc.
Maison Air et Lumière demonstrates that good daylight conditions can lead to significant savings on electricity use for lighting during daytime and provide the occupants with a high level of satisfaction.
We will be presenting a paper on this topic at the LuxEuropa 2017 conference in Ljubljana, Slovenia, on September 18-20.
