Daylighting. 35% savings from daylighting controls in daylit spaces is typical of documented energy savings from available, monitored case studies. For example, the testing at the San Francisco Federal Building indicates that the savings potential from daylighting is between 16-41% (estimated annual savings). Since only a fraction of building space is daylit (estimate 35%), the 35% savings is diluted by 35% to obtain average energy savings of 12% across all floor space.
Tuning. Measurements at the National Center for Atmospheric Research [Mannicia 2000] suggest that the energy potential of light level tuning is about 15%. Measurements of the effectiveness of energy of bi-level switching [Rubinstein 1998] indicate that the savings from tuning could be as high as 25% if the switches are well utilized by the occupants. Studies on the energy saving impact on tuning light levels according to spectral content [scotopic work] suggest a 25% savings from that technique alone. We have used 25% savings for the energy saving potential for tuning.
Scheduling. Although occupancy sensors will capture much of the savings in occupancy-based lighting controls, the use of intelligent dimming strategies will further increase the energy savings in many applications. We assume that integrated lighting controls would result in an additional 10% energy savings compared to that from occupant sensors alone.
Energy efficiency gains:
All strategies above combined. Based on studies, it is estimated that an automatic lighting control system that combines the above strategies in a typical building environment has the potential to reduce lighting energy consumption by about 40% on average over the year compared to a lighting system of equivalent efficacy that is not controlled.
Costs (investment, operation, maintenance):
Costs for equipment and installation of sensors and control boxes including settings. 40% reduced energy operational costs compared to a baseline with no or little measures taken. In many railways some of the potential has already been exploited meaning a realistic potential is 20-30%.
Maintenance costs after implementation: As part of facility management no extra effort.
Return on investment (ROI): 1-3 years payback time depending on starting point and ambition level.
LED ligthing systems, optimising equipment, sensor equipped lighting systems