A holistic perspective of energy management

How can lighting designers use intelligent controls to improve building energy management? Philips Dynalite Energy Management Segment Manager, Brett Annesley, explains how an environmentally sustainable development (ESD) strategy can deliver energy efficiency outcomes, while addressing indoor environmental quality (IEQ) and changing occupancy requirements.

It is widely accepted that artificial lighting contributes approximately 30% of electricity consumption in a commercial building, and buildings collectively account for 40% of total world energy use. In view of this, energy management approaches to lighting control and design may provide the key to reducing energy consumption within the commercial sector.

However, the drive to improve energy efficiency in commercial lighting is only one part of the environmentally sustainable development (ESD) equation. Considerations of equal importance include the sustainable life cycle assessment (LCA) of material used, and ensuring that indoor environmental quality (IEQ) standards meet occupant comfort demands. Together, these can be considered the three global ‘green drivers’ within the built environment.

The aim of the first of these green drivers - LCA - is to minimise demand on resources and energy consumption over the lifetime of a building. This will necessarily impact the manufacturing, procurement and delivery processes of the various constituent components. Lighting designers can help reduce the ultimate carbon footprint of a building by taking LCA into account during specification of the system. With an LCA baseline established, the lighting design itself can then play an equally significant role in ESD over the life of a building.

A flexible future

Lighting installations can be rendered more energy efficient and a building’s lighting design made more ‘future-proof’ by the implementation of these LCA principles. Future-proofing can be enhanced by the selection of products that will give an extended service life, the adoption of modular installation practices and the use of systems providing a high-resolution of control. Such high-resolution - or ‘granular’ - lighting control systems allow the lighting to be changed as required during the evolution of a building.

Changes to a building’s fabric and occupancy are usually referred to as ‘churn’. The flexibility of a lighting system to accommodate churn can be best achieved by enabling lighting grid changes and luminaire group rezoning, without the expense and disruption associated with rewiring a facility. User-friendly configuration software is an important component of these flexible installations, but is also dependent on the control technologies in place - such as digital addressable lighting interface (DALI) and structured wiring.

DALI is a dedicated lighting control protocol, where each light unit has its own individual digital address, allowing rezoning of luminaires easily across a network using an appropriate software interface. Structured wiring, by contrast, comprises combined power and data cabling that can be quickly connected and disconnected from a lighting installation, thereby facilitating physical reconfiguration of lighting systems.

While LCA is an important consideration in environmentally sustainable lighting design, the energy consumption of a lighting installation will impact the energy efficiency on a day-to-day basis. Specific strategies to reduce energy consumption include the increased use of daylight in preference - or as a bolster - to artificial lighting, and the use of sensors to automatically adjust lighting levels in accordance with natural lighting levels and area occupancy. ‘Smart sensors’ have developed from simple on/off control, into a ‘frontline’ energy-management technology, capable of adapting dynamically to changing occupancy, environment and daylight requirements.

Energy management approaches to lighting control and design may provide the key to reducing energy consumption within the commercial sector.

Daylight and detection

The use of daylight harvesting technologies needs to address both energy management and occupant comfort issues. Daylight harvesting involves the strategic substitution of artificial fluorescent light with natural light - slowly dimming lights to balance daylight entry - and this can achieve considerable energy savings. Window treatments - such as curtains, blinds and glass-transmission factors - become an important factor, as these have a direct impact on how much natural light enters the office environment.

The correct selection of blinds and sensors becomes critical to both energy efficiency and occupant comfort. Moreover, sensor positioning can be as essential as sensor selection. Positioning a photoelectric (PE) sensor within a direct pathway of reflected light from shading louvres, for example, can lead to incorrect lux levels being applied by the PE sensor.

Such demands on sensor functionality have led to the rise of multifunction sensor devices that incorporate PE detection for changing light levels, and passive infra-red (PIR) and ultrasonic for motion detection. While these sensors are commonly used in a single mode, they can also have the intelligence to be used in ‘multi-mode’ to provide logic control. For example, if the sensor detects that lux levels have fallen below a specified value, then artificial lighting levels can be increased, but only when motion is detected. In this way, lighting levels will be maintained for occupied areas only.

Motion-detection functionality can be further configured to perform different routines according to the time of day. During the standard working day, for instance, a sensor may be tasked to dim lights over a workstation by 25% when all occupants have been gone for 10 minutes. After hours, the same sensor might action a gradual fade-out before eventually switching off.

Occupant comfort

However well-intentioned or effective the energy management strategies within a building, they should not be implemented at the expense of IEQ - another important driver for ESD of commercial buildings. A lighting design can be flexible and save energy, but if occupants do not feel comfortable, the design can be considered to have failed.

The use of natural light not only saves energy, but also has an important bearing on the wellbeing of occupants. Studies have shown that people need to feel connected to the world outside, and exposure to daylight - when correctly managed - can measurably improve worker productivity. Fade time is critical to occupant comfort when using sensors to manage lighting levels. Typically, an extremely slow fade-time during the process of daylight linking will result in minimal disruption and a greater acceptance rate by occupants.

‘After hours’ worker comfort further provides a challenge in order to balance the associated increased energy demands with the ongoing target of energy savings. Instead of the traditional solution of illuminating an entire floor-plate after core working hours, the control system can be tasked to provide a worker with more specific illumination - such as their immediate surrounding areas and an egress path - using motion detection sensors. Gradual closure after all movement has ceased will ensure that energy is not wasted after the departure of the last worker.

The control system can be tasked to provide a worker with more specific ‘after hours’ illumination - such as their immediate surrounding areas and an egress path.

The implementation of control-management software further enables the individual user to control task lighting requirements from their own workstation, aiding individual worker comfort. Energy savings can also be realised by minimising lux levels for overhead lighting in preference for individual task lighting over the desk area. This solution is becoming increasingly practical with the development of LEDs, and such a strategy may well serve to avoid conflict between individual and general lighting requirements. In a similar manner, where daylight harvesting is employed, zoning blinds will enable occupants to control their specific shading requirements.

The provision of individual control of lighting and shading is endorsed by the green building rating tools for the USA (LEED), Australia (Green Star), and the UK (BREEAM). These tools award rating points for buildings where individual local control is provided.

Commissioning and building tuning

While the selection of energy-saving strategies - such as daylight harvesting and sensing technology - is important, the real skill is to bring it all together with a professional and accountable commissioning approach. Commissioning guidelines are provided by CIBSE Code L and M for the Australian Green Star and by ASHRAE under the LEED tool in the US. It is becoming an increasing requirement to implement commissioning guidelines such as CIBSE or ASHRAE as the nominated standard to safeguard against substandard installation and commissioning practices.

Poor commissioning practices have historically resulted in owner/occupiers failing to achieve their energy-efficiency targets. Project-specific applications can be audited and approved by independent commissioning authorities, however, to optimise the installed systems and ensure the design criteria are met.

Once commissioning is complete, further improvements can be realised through ‘building tuning’. This provides an ongoing performance evaluation for a new building - through quarterly assessments - for the first 12 months of occupancy. Building tuning is strongly recommended by the Green Star, LEED and BREEAM rating tools. The assessments carried out as part of this process may result in two separate energy-performance ratings - one rating applying to the building and the other for the tenancy. The effectiveness of the commissioning process may affect either rating.

Just as new buildings can fall short of their design criteria, so too do older buildings differ widely in their energy-efficiency performance. The lighting installations of existing occupied buildings can be professionally audited, however, to assess their efficiency. Comprising data logging of local distribution boards and monitoring lighting usage through lux meters, these audits will monitor when the lights are on/off and the amount of energy used during different periods. The results can prove a valuable tool in highlighting where corrective building tuning is needed - both from a facilities-management and an occupant-activity perspective.

Within the holistic approach to ESD, such building tuning will help ensure that the efforts made through the three green drivers of LCA, energy efficiency and IEQ are not wasted in the pursuit of a reduced building carbon footprint. When the right balance is achieved, the result is a building that will remain energy efficient throughout its life, and which will continue to bring good levels of comfort to its occupants long into the future.