New solid state LED lighting technologies
New LED lighting technologies developed in Australia promise to slash energy consumption without harming product longevity. PROFESSOR JOHN MO and GANESH SEN report their recent research findings.
RMIT University is committed to reducing its carbon footprint and providing a safe and green university for students and staff. To achieve this goal, Building 28’s Research Lounge was nominated for a pilot research project (B28 project). The Research Lounge was developed as a pilot to investigate how new Solid State Lighting (LED) technologies could be used to provide a cost-effective sustainable solution for retrofitting buildings.
Unlike conventional light-for-light replacement, the B28 project takes an innovative approach in the design and engineering of a retrofit solution. In order to maximise energy utilisation efficiency and with virtually no rewiring, the lighting circuit in the Research Lounge has been reticulated in DC mode, the native operating environment of LED. The entire installation encompassing some 100 luminaires was installed within two days, with preassembled DC switching gear, line protection and distribution enclosure installed during the commissioning of the project.
The innovative system design provides numerous opportunities for energy savings and reduced wastage to landfill. Specifically designed DC electronics and identical LED light engines were utilised for multiple locations, providing better illumination distribution than the previous CFL (compact fluorescent lamp) and T5 luminaires. Initial concern about the effect of DC voltage drop at luminaires furthest from the power source without increasing conductor sizing proved to be unnecessary, as power electronics designed and incorporated within the LED luminaires are able to compensate for any voltage drop in the circuit. The original four lighting modes at B28 – full light mode, lecture mode, presentation mode and off mode – have been retained using the existing Dynalite lighting control bus. The LED luminaires are controlled by a new DC pulse width modulation (PWM) power circuit, which further reduces the loss of power due to resistive current control circuits.
The DC circuit unlocks the option for future direct renewable energy feeds from either solar, wind or solar sources – combinations of power sources that could be feasibly utilised to operate the DC reticulated lighting system. The lighting system has been designed as a renewable ‘energy ready’ system and can be implemented in two stages if there are financial constraints in implementing the system as a fully renewable energy-enabled system. The B28 lighting control system has been designed with smarts and a programmable inverter charge controller capable of auto-detecting power feeds either from renewable source or alternatively sourcing the power feed from the main grid if the renewable source is deemed inadequate – or, in an extreme case, if the renewable system malfunctions.
The DC lighting system design also incorporates a 48VDC platform with a four-hour battery bank storage, which, when fully charged, is capable of supporting the lighting load for up to four hours of continuous usage without power feed from the grid or renewable source. The smarts in the control system are also capable of feeding the excess renewable energy generated to the grid when the battery bank is fully charged.
The renewable power feed option is currently on hold for the project until arrangements for a solar panel feed can be finalised. The current operation of the lighting system relies on power from the main grid to charge the battery bank, which in turn feeds the lighting load via a DC to DC converter and an automatic switch over controller. A redundancy is also part of the design, which will route a direct feed from the AC grid to power the lighting circuit via AC-DC switch mode power supply if the DC power platform malfunctions, which is highly unlikely.
The complete retrofit solution for the existing lighting system, including light fixtures, switchgear and lighting circuit with dimming option, and interfacing among the components, has produced very encouraging outcomes.
Prior to the change, the research team measured the total energy usage of the lounge over a period of two weeks. The result showed a total energy consumption of 210 kilowatts per hour, in a combination of the four lighting modes. Further analysis of the utilisation model shows that only 71 kilowatts per hour is required under the new retrofitted scheme; that is, an energy usage saving of 65 percent.
This research utilises a number of mathematical and logical techniques to analyse risks of the new system. Reliability of the LED lighting system was one of the key discussion points during numerous project forums with industry partners, including Cree and the luminaire OEM (original equipment manufacturer). The findings evidently showed that an LED engine designed with appropriate thermal measure and driven within the electrical design constraints as specified by the LED semi-conductor manufacturer is less likely to fail prematurely. The main concern with most off-the-shelf LED luminaires was that the drive electronics were put together without proper design consideration for the luminaires’ operative environment (i.e. power source and ambient temperature). The LED luminaires’ AC-DC driver electronics is very susceptible to voltage surges and not being able to maintain constant current feed to the light engine. The B28 lighting model reticulated in a DC environment is less likely to be exposed to high voltage spikes as the control electronics at the DC distribution source will filter and rectify an appropriate DC feed to the load.
The longevity of a DC-reticulated LED lighting system will significantly reduce maintenance and facility management services costs, as our analysis shows a life cycle of a suitably designed system can exceed 10 years. Test data from Cree’s LM79 and LM80 laboratory findings showed no noticeable deterioration of light intensity over five years. Using a failure mode and effect analysis (FMEA) approach, the research team analysed data from laboratory tests, LED manufacturer, light designer and other sources to estimate the causes of faults and the system’s reliability. The result shows that further savings can be realised given the high utilisation rate and frequent mode changes at the Research Lounge.
The B28 project was steered with encouragement and support from the director of property services Darren McKee; Supervising Professor John Mo from the School of Aerospace, Mechanical and Manufacturing Engineering; ABB’s Low Voltage and Automation Products Division; Cree’s technical and engineering team; Reiz lighting, which provided research and development and manufacturing of the luminaires; Ganesh Sen and David Scott from Eco Hospitality Refurbishment.
Professor John Mo is discipline head, Manufacturing and Materials Engineering, School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University.
Ganesh Sen is business development director at Eco Hospitality Refurbishment.