CPD Programme
to make employees feel more comfortable and to produce an energising work environment.’ State-of-the-art lighting control options
Figure 3: A lighting controller taking inputs from a wide range of sensors to drive DALI outputs. The system is linked with the building management system (and other controllers) through standard computer networks
be seen as either too expensive or simply impractical. One of the leading contenders for the wireless protocol is the ZigBee; unlike other wireless types, this was developed specifically for remote monitoring and control with very low power requirements. Due to its ‘mesh’ method of transmission it has, potentially, almost unlimited range within a building. Mesh networks enable individual nodes (such as sensors) to communicate with and pass data directly to other nodes, so the data travel in short hops (just a few metres) but ‘meshed’ together, linked by short-range wireless, so the information may pass over long distances. ZigBee’s fast response times are particularly relevant for lighting control: users expect an ‘instantaneous’ response when a light switch is pressed. But, as would be expected in such a fast-moving marketplace, there are other low- power wireless systems vying for position. Integrated building management and
control is increasingly being undertaken by systems that use BACNET – ASHRAE’s Data Communication Protocol for Building Automation and Control Networks; or Echelon’s LONworks. These are needed to communicate with manufacturers’ proprietary systems via ‘intelligent’ gateways and provide a framework to control and monitor subsystems (such as DALI) as well as link in the various wired and wireless networks.
Case study: New York Times HQ The New York Times Company, a global media enterprise, decided to build a new headquarters in Manhattan, New York and, as a client, wanted to take an active role in the project. The company resolved to exercise control at every stage of the project’s design and construction processes, ensuring that the new building accurately represented its corporate culture and values, and reaped real business benefits for the company, which owns 28 floors or about 62,500 sq m. The interior designer Gensler confirmed that: ‘The number one priority was to allow natural light
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were implemented to satisfy the requirement for integrated daylight with appropriately dimming electric lights, as well as to provide the flexibility to readily reconfigure spaces for alternative uses. The building design was based around a lighting power density of 13.5 W/sq m usable floor area. Using the DALI- based lighting management system, The New York Times Company’s recorded annual average light power is just under 4W/sq m – a reduction in operating power use over design of about 70%. The annual data for 2008 is shown in Figure 4. The design goal of 13.5 W/sq m was set to
meet the local building code that was in effect when the building was constructed; these regulations have since tightened to 11.6 W/sq m, and the operational lighting power use is still less than 35% of this figure. This disparity between installed capacity and the actual power consumption shows that there is a real challenge in modelling and predicting lighting energy use to provide evidence for code compliance when planning an installation. It needs to take account of operational factors such as the integration of daylight and variable occupancy. Four main strategies were employed:
• Light level tuning – ensuring that the illumination levels suited the task; • Occupancy sensing – using occupancy sensors to ensure lighting is only used (at appropriate levels) when needed; • Daylight harvesting – managing and linking solar control with active lighting systems; • Scheduling – Using easily programmable timed schedules to operate lighting zones. The relative benefit of each strategy is shown
in Figure 5. Glenn Hughes, former director of construction for the project, believes that the lighting control system has established an excellent baseline for the building, but that even greater energy savings can be achieved as the system parameters are adjusted and developed by carefully monitoring the building performance. ‘The key is having smart systems, where
all your components work in unison to give you the optimal level of light,’ says Spira the inventor of solid-state light dimming. ‘The technology is getting better and faster, which means the savings are getting better and coming faster.’ © Tim Dwyer With thanks to Richard Whitbread of Lutron for contributions to this article
4 3 2 1
4.0 3.5
3.9
3.9
Spring 2008
Summer 2008
Autumn 2008
Winter 2008
Figure 4: Quarterly averaged lighting power consumption for New York Times building
10%
30% 58% 2%
Daylight harvesting: dimming electric lights when daylight is available Occupancy sensing: turning off lights when spaces are vacant Scheduling: turning lights off during certain times of the day Light level tuning: setting the appropriate light level for each space
Figure 5: Lighting energy savings achieved through strategies employed in New York Times building
References Energy Efficiency in Buildings –
1.
Transforming the Market – June 2009, World Business Council for Sustainable Development 2. Energy consumption in the United Kingdom, 2008 Update Pub URN 08/456 – Department for Business Enterprise & Regulatory Reform Improving Productivity with Light
3.
Controls – technical white paper, Ian Rowbottom, Lutron 2009 4. Windows and Offices: a study of Office Worker Performance and the Indoor Environment – Heschong Mohone Group for the California Energy Commission, October 2003 5. Lutron Electronics Co, Inc 6. DALI manual
www.dali-ag.org/c/ manual_gb.pdf 7. After DALI: A Look at What’s Next – Francis Rubinstein, Lawrence Berkeley National Laboratory, Architectural Lighting, January/February 2005
November 2010 CIBSE Journal 65
Power consumption W/sq m
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