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Global lighting performance

The study conducts a comparison between usage and energy savings of manual, automated and motorised external blinds in a commercial setting in Switzerland. The first part of the study consists of an observational study, followed by a simulation study which estimates the electricity consumption of lighting and highlights the potential differences in energy savings between automated and manual use.

Key Findings

  • ‘Automated blinds can reach energy savings of several kWh/m² per room per year.’
  • ‘…occupants are poor managers of their solar control systems.’
  • ‘Motorised facades encourage a better use of the natural light potential.’

Further Detail

The movements of external manual blinds on two office buildings with south and west orientations were recorded every hour over the course of one year. An east facade which had external motorised (but not automated) blinds was also recorded. A total of 125 blinds were observed.

  • On average across the three facades there was an average of 1.74 movements per week, per blind, and less than 12% of the occupants moved their blinds once per day.
  • On the south facade the number of movements were the lowest, on average 1.46 movements per week. During the summer most of the blinds were closed, blocking the sun out all day.
  • The motorised facade had substantially more ‘up’ and ‘down’ movements, potentially because the blinds are easier to use.

The automated simulation trialed two methods. Firstly, the continuous method which changed blind positions every hour based on solar radiation levels and sun position and, secondly, the reset method where blinds are raised at the start of the day and at lunch.

Blind lowering by occupants has been calculated based on the Daylight Glare Probability (DGP) within the room. Assuming blinds will be lowered when occupants are 1.15m away from the glazing experience DGP > 0.45.

The continuous method could reduce lighting consumption by 35% by utilising natural daylight. The reset method is less effective on south and east facades, reducing energy consumption by only 25% but still saving 35% on the west facade.

To read the report click here.

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