Holistic energy management
Brett Annesley recommends an energy management approach to lighting.
It is widely accepted that artificial lighting contributes approximately 30% of electricity consumption in a commercial building, and such buildings collectively account for 40% of total world energy use. In view of this, energy management approaches to lighting control and design would help reduce energy consumption within the commercial sector.
However, the drive to improve energy efficiency in commercial lighting is only one part of the ‘sustainable development’ equation. The life cycle assessment of materials and indoor environmental quality standards are also of equal importance.
The implementation of life cycle assessment principles, which seek to minimise energy consumption over the lifetime of a building, can result in ‘future-proof’ installations.
Strategies include the selection of products that provide extended service life, the adoption of modular installation practices and the use of systems that provide a high-resolution or ‘granular’ level of control, which allows lighting to be changed during a building’s evolution.
Changes to a building’s fabric and occupancy – known as ‘churn’ – are best accommodated by enabling lighting-grid changes and luminaire-group rezoning, to avoid the necessity for rewiring a facility.
Digital addressable lighting interface (DALI), for example, which enables each light unit to have an individual digital address, will facilitate rezoning of luminaires across a network.
While life cycle assessment has long-term implications, energy efficiency itself will have a day-to-day impact.
Energy reduction strategies include the use of daylight harvesting in conjunction with sensors to automatically adjust lighting levels appropriately. Daylight harvesting involves slowly dimming artificial lights in harmony with daylight entry.
Multifunction sensor devices – incorporating photo-electric (PE) detection of lux levels, and passive infra-red (PIR) and ultrasonic for motion detection – are increasingly prevalent.
These can be used in either single-mode, or leverage in-built ‘multi-mode’ intelligence. For example, a system can be configured to increase lighting levels when the lux level falls below a set threshold, but only when motion is detected.
Energy management strategies should not be implemented at the expense of indoor environmental quality, however. A lighting design can be flexible and save energy, but if occupants do not feel comfortable, it can be considered to have failed.
Correctly managed exposure to daylight has an important bearing on the wellbeing of occupants, measurably improving worker productivity as well as saving energy.
The correct selection of curtains, blinds and glass has a direct impact on natural light levels, and is critical to both energy efficiency and occupant comfort. Maintaining a slow ‘fade time’ while using sensors to manage lighting levels will also typically result in greater acceptance by occupants.
‘After hours’ worker comfort provides further challenges in order to balance energy demands with savings. The control system can be configured to limit illumination for late workers to their immediate surroundings and an egress path, using motion detection sensors. Gradual closure after all movement has ceased will ensure that energy is not wasted.
Minimising overhead lighting in preference to task lighting over the desk area can also reduce energy usage and improve comfort. This could be enhanced by empowering individuals to control personal task lighting from their own workstation and is a development that is endorsed by green building rating tools such as the Green Building Council of Australia’s ‘Green Star’.
While strategies are important, the predominant challenge lies in consolidating them with a professional commissioning approach. Commissioning guidelines for this have been provided by CIBSE Code L/M for Green Star.
After commissioning, Green Star recommends ongoing building performance evaluations for the first 12 months of occupancy – a process known as ‘building tuning’. These assessments may result in distinct building and tenancy energy-performance ratings.
Existing buildings can similarly be audited to assess their efficiency through data-logging of local distribution boards and monitoring lighting-usage through lux meters. The results can prove invaluable in highlighting where corrective action is needed.
Such building tuning will help ensure that the efforts made in pursuit of reduced carbon footprint – through life-cycle assessment, energy efficiency and indoor environmental quality – are not wasted.
When the right balance is achieved, the result is a building that remains energy efficient throughout its life and brings comfort to its occupants long into the future.