Daylight can cut electricity bills
Svein Tønseth
In eight "guinea-pig" offices in an office building in Trondheim, lights are dimmed or switched off automatically when daylight is bright enough for office work. In rooms that face south in this building, controlling lighting can save up to 30 - 40% of the energy used for lighting purposes. In north-facing rooms, savings can come to 20 - 30%.
Olve Mogstad and his scientist colleagues at EFI have measured the energy-saving potential of working by daylight in this Trondheim office building.
These are among the results of a year-long programme of measurements made by EFI (The Norwegian Electric Power Research Institute) in the building last year.
Lighting control equipment based on daylight sensors is being tested out in this 15-year-old building. The tests are the first stage of a full-scale study of the amount of energy that can be saved by utilizing daylight as working light in office buildings. In Norwegian non-domestic buildings, lighting uses between 30 and 60 percent of electricity consumption, depending on whether the building is also electrically heated.
Indirect gains too
"A number of people have claimed that the heat generated by lighting fittings is essential to keep office temperatures comfortable without other sources of heat. Our studies show that with very few exceptions, room temperatures stayed between 20 and 25 degrees during the whole of the test period. This indicates that controlling lighting can also produce indirect energy gains in the shape of reduced needs to cool rooms on hot days," says Olve Mogstad, an EFI scientist.Two systems
Two different control systems are being tested. One of them switches off the lights when the level of daylight exceeds a specific limit, and switches them on again when the lighting level becomes too low. The other is a dimmer system that adjusts the light output of the light fitting in the ceiling in step with available daylight, in order to maintain more or less constant lighting levels at desk level."The difference in potential savings is small in the south-facing rooms; 30 - 40% for the dimmer system, as against about 30% for the on/off system. In north-facing rooms in this building the dimmer system can save up to 20 - 30%. As far as the on/off system is concerned, gains are virtually zero on the northern side of the building. Bigger windows would probably have raised this figure," says Mogstad.
The full-scale tests are continuing in a new office building in Trondheim, where experiments will also be carried out on optical arrangements for directing daylight and sunlight further into the building.
Renaissance for windows?
EFI is collaborating closely on this project with SINTEF/NTH building technologists."For some time, there has been a tendency in Norway to cut down the area of windows. If daylight is used for working light, it may become more appropriate to optimize the size of windows," says Professor Øyvind Aschehoug of NTH's Faculty of Architecture.
He regards daylight research as a possibility for Norway to develop export-oriented industrial products for the window market. "There is a great deal of interest in other countries for energy savings based on utilizing daylight. In this connection new window materials are also in demand. We will find the big markets for such technologies in countries with more expensive and less environmentally friendly electricity generation systems than we have in Norway," says Aschehoug.
The research project is being financed by the Research Council of Norway, and is being carried out in collaboration with industrial companies, consultants and governmental agencies. The project is part of the EU's Joule II programme.