According to different studies and experts, around 40% of the energy consumed globally is buildings’ related. Artificial lighting consumes a significant part of all electrical energy consumed. In offices from 20 to 50 percent of total energy consumed is due to lighting. And most importantly, for some buildings over 90 percent of lighting energy consumed can be an unnecessary expense through over-illumination.

Looking at the figures above it seems clear that in today’s world there are plenty of commercial buildings (the majority of them by far) in which lighting is not automatically controlled at all, in other words, someone switches on and off lights at the start and at the end of the day. Other more sophisticated buildings (few of them) implement some sort of automatic control of lighting making this switching on and off by automatic control based on presence detection, or calendar/hourly basis. And other even more sophisticated ones (very few of them all) implement really effective lighting control providing just the appropriate light level in any part of the building at anytime, having in consideration many variables like daylight coming from outside, presence of people in each area, the required light level according to workplaces, etc.

It is obvious that the more effective control we apply to lights in a building the more comfortable we’ll make it for people who spend a good part of their lives tere, and of course the more energy efficient we’ll make the building itself, with all the benefits related to it: reduction in electricity bill, reduction of maintenance budget, reduction of carbon footprint, etc. Fortunately it seems that nowadays (and luckily for all) all related to green buildings, energy efficiency, and rational use of energy sells, and sells well. According to recently published McGraw-Hill Construction's Green Outlook 2011 : Green Trends Driving Growth report , the Green Building Market has grown 50% in the 2008-2010 period despite recession.

But how to choose the appropriate lighting control system, what basic and advanced features must it provide, which of them do we need or want for our building, based on what technology, with open communication protocol or proprietary, what’s the cost and what will be the ROI, what  level of integration do we want with the rest of the building’s installations, which are the real benefits it will give to buildings’ owner, users, installer, maintainer, system integrator, etc., … Lots of questions with difficult answers, answers that greatly depend on several different variables in each case and thus with a complicated uniform response, so I defer to the answers of expert consultants and advisors in this field.

Until here in the article it has been about the theory, now let’s get down to earth and try to explain how flexible and effective lighting control can be done with real technology used for building automation, such as BACnet-based building management systems and DALI lighting, and how both can be fully integrated in real applications in commercial buildings.

Throughout the next part of the article, while explaining features of the lighting control system proposed, I will be showing some clear benefits that both systems, DALI and BACnet, can bring together to different actors in a building (owner, installers, users, system integrators…) but for sure the reader will identify many more depending on their profile and experience. 

Why DALI

Lighting control systems existing in the market provide a set of features by themselves to do effective control of lighting (switching, dimming, grouping of luminaries, scenes, etc.). Some of them are proprietary, I mean those in which different elements of the system communicate with each other using proprietary (not open) protocol. Others are open, providing just a common hardware interface and interconnection specification, an open communication protocol (available to anybody), and a set of control features available using this protocol.  This enables manufacturers of any kind to put in the market interoperable devices with this system, such as ballasts, lighting sensors, controllers, gateways, etc., making this way a truly open lighting control system, as is the case of DALI. The advantages of adopting an open system compared to a proprietary one are numerous, to name a few: a wide variety of products and manufacturers to choose from, interoperability, reduction in costs of maintenance and upgrades, security of future availability, etc.

DALI is an acronym and stands for “Digital Addressable Lighting Interface“. It is an international standard that guarantees the exchangeability of dimmable ballasts from different manufacturers. The DALI-interface has been described in the fluorescent lamp ballast standard IEC 60929 under Annex E.

Features available when installing DALI ballasts are:

• Simple wiring of control lines (no group formation, no polarity).
• Control of individual ballasts or groups is possible.
• A simultaneous control of all ballasts is possible at any time.
• Ballasts status messages (lamp fault ....).
• Automatic search of ballasts.
• Automatic and simultaneous dimming of all ballasts when selecting a scene.
• Logarithmic dimming behavior – matching the eye’s sensitivity
• System with assigned intelligence (every unit contains amongst other things the following data: individual address, group assignment, lighting scene values, fading time ....).
• Operational tolerances of lamps can be stored as default values (for example for the purpose of energy savings maximum values can be set)
• Fading: adjustment of dimming speed
• Options for emergency lighting can be chosen (selection of specific ballasts, dimming level)
• No need to switch on/off the external relay for the mains voltage (this is done by internal electronic components)

DALI has been defined for:

• a maximum of 64 single ballasts (individual addresses)
• a maximum of 16 groups (group addresses)
• a maximum of 16 scenes (scene light values)

Each ballast stores its own set of parameters:

• Individual addresses
• Group assignments
• Light scene values
• Fading times
• Emergency lighting level (System Failure Level)
• Power On Level

Information on DALI technology and a list of existing ballast manufacturers can be found at AG DALI association’s website ( http://www.dali-ag.org ).

Why  BACnet

These features related to lighting control provided by the lighting systems can be fully optimized when integrated with the building management system who is in charge of controlling the rest of the building’s installations. Some examples of this: use the information of presence detectors of the security system to switch on the light in each zone only when needed, and at the same time actuate on HVAC setting the heating/aircon in stand-by mode when there is no one and back to comfort mode when there is someone; Dimming appropriately the luminaries and actuate on window blinds to reach the optimum light level in each zone at any time according to information provided by light level sensors; Control of lighting from the BMS’ scada; Logging of data for energy consumption calculations; Automated notifications to maintenance workforce when lights are failing or are about to reach end-of-life. The advantages of this integration seem to be endless.

There are plenty of different building management systems, intended for different types and sizes of buildings, with more or less capabilities, using proprietary or open protocols… I will not explain here building management systems and their goods and bads, probably the reader knows all this very well. BACnet-based building management systems are probably the most popular ones nowadays, and probably the ones with more future ahead, but I am aware that this could lead to exciting discussions depending on who you talk to. Anyway, BACnet has been chosen as the BMS for this integration of DALI lighting, but it could have been any BMS. 

A huge amount of information on BACnet can be found at BACnet website ( http://www.bacnet.org ).

Integration of DALI and BACnet. Key points to have in mind.

Integration of DALI and BACnet is made by means of gateways, one example is the IntesisBox BACnet - DALI gateway from Intesis Software, more technical details can be found at http://www.intesis.com/eng/intesisbox_bacnet_ip_server_dali_frame_eng.htm

These kind of devices should not only serve as purely gateways allowing bidirectional communication between BACnet and DALI but also providing as many configuration, commissioning, maintenance and troubleshooting tools as possible. The more useful tools they provide the more we can reduce engineering time needed for configuration and commissioning,  and later for maintenance work. It is very important to have in mind when choosing a gateway that the price of the device itself is just a small part of the whole integration cost.

Roughly, an integration process of DALI ballasts with a BACnet BMS would follow these steps:

In design phase (in the office), according to drawings of the building and desired functionality:

• Planned functionality to achieve and extent of the integration with the BMS.
• Planned assignment of desired DALI addresses for ballasts, and of grouping of ballasts.
• Planned integration of the gateways into the BACnet network (definition of number of gateways, device instance numbers for them, BACnet objects for each ballast / group / bus point to integrate.
• Construction of the configuration tables of the gateways, with mappings between BACnet objects and DALI points. At this stage, having the possibility to set groups and default levels for scenes and for security situations in this same table (all at sight in one single table) is really good, otherwise these sets will have to be done later on site for each ballast one by one. Another important point to have in mind is the easiness to make the configuration table, i.e. having the option of editing the tables using Excel can be great.

In commissioning phase (on site):
It is very important at this stage that the gateways allow Ethernet connection, this gives you non-priced flexibility to walk along the building with your laptop using for example a wifi connection to the building’s LAN.

• Scanning of DALI buses and physical identification of DALI ballasts. At this point is very important that the tools provided with the gateway allow it in a comfortable way, i.e. by winking the luminaries even before the address has been set in the ballast.
• Assignment of addresses to DALI ballasts. Here is also important that the tools provided with the gateway allow doing it in a flexible and quick way.
• Download the configuration of mappings and BACnet settings to the gateways.
• Download the settings for groups, scenes, security levels, etc. to the ballasts.
• Integration of the BACnet devices (gateways) and BACnet objects with the rest of the BMS. Here is crucial that the gateway gives access to all the DALI parameters using standard BACnet objects and properties (i.e. present_value), to make the integration simple and widely compatible with any BACnet BMS.

In general, a good integration solution for DALI and BACnet should provide the following key points:

• Robust and reliable piece of hardware serving as bidirectional gateway between both.
• Complete and flexible configuration possibilities for all gateway and BACnet parameters and for ballasts’ sets while in off-line (not connected physically to the gateway).
• Flexible scanning and physical identification of DALI ballasts.
• Maintenance and troubleshooting tools allowing connecting remotely to the installation.
• Full access to DALI parameters by means of standard BACnet objects and properties.

Application example. A simple and cost-effective automatic regulation of light level in individual spaces

Let’s propose an easy, cost-effective, yet good enough continuous regulation of light level, individually per workplace, using the integration described above and without going to closed regulation loops needing complicated engineering and control resources. Let’s explain it with a room but it can be extrapolated to any building’s space.

DALI allows grouping ballasts. DALI allows scenes (up to 16), a scene is a given light level that can be applied to individual ballasts, and to groups. Then using a light sensor in the room to give you a reference of the light level, you can group the ballasts appropriately an set levels for scenes, individually per ballast or per group, to obtain the desired light level in each workplace of the room according to the light level measured by the sensor. Having 16 available scenes in the ballasts means you can apply 16 different regulation steps, good enough for many applications.

Bibliography

Wikipedia
McGraw-Hill Construction's Green Outlook 2011: Green Trends Driving Growth report
www.bacnet.org
www.dali-ag.org

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