Two important energy savings initiatives based on research undertaken at City University have been put into commercial use over the past 12 months.

Energy saving light dimming technology emerged from a challenge made to Professor Henry Chung Shu-hung, from the University's Department of Electronic Engineering, by the Mayor of Heshan, China. He wanted dimming technology that could be applied to large scale public lighting.

"I had already undertaken work on energy saving lamps. But in Heshan, the Mayor asked me about developing a system for large networks of public lighting, enabling his city to reduce power consumption by 20 per cent across the network," Professor Chung recalls.

He assembled a team that included colleagues and students at CityU. Their goal: to research efficient dimming technology for a range of high intensity discharge (HID) lamps with magnetic ballasts. HID lamps are used in public lighting systems. Although electronic ballasts had been developed for individual lamps, magnetic ballasts were regarded as more reliable, robust and cost effective for street lighting

Twelve months later the group produced the preliminary technology outline. A grant from the RGC resulted in the development of a prototype that produced energy savings of 20 per cent. Further developments led to a system that provided 40 per cent energy savings.

The technology has been transferred to e.Energy Technology Limited, an associated company of CityU Enterprises Limited, and has won product awards in Hong Kong and Australia. It is operating in Hong Kong and China with potential sales this year to Singapore and Australia.

In a separate development, Professor Chung and two students designed an energy efficient burn-in system for switching mode power supplies. This system is based on an energy recovery concept that uses a highly efficient DC/DC converter and grid connected inverter to feed power output

from supplies back into an AC grid. As a result, the energy drawn from a grid in the burn-in process is reduced and the power feeding back into the grid is high quality with low harmonic distortion.

Professor Chung says this is a win-win development with significant environmental benefits.

Burn-in is the process by which components of a system are exercised prior to being placed in service, and often prior to a system being completely assembled from those components.

A conventional burn-in method causes significant heat dissipation with additional cost and energy required for factory ventilation. It also indirectly generates huge amounts of greenhouse gasses.

Professor Chung's concept produces significant savings in electricity. High-quality power is fed directly back into the grid and, by integrating modern power electronics and computer technologies, various testing profiles can be programmed into this 'green' burn-in system. Efficiency has reached between 75 and 80 per cent and the cost of ventilation systems is reduced.


The project has been developed with the support of Hong Kong's Innovation and Technology Fund and Astec International Limited, a division of Emerson Network Power, and is being applied commercially to a system that tests power supplies in China with a projected annual cost saving of HK$5 million.

Andrew Leung and River Li, CityU students who conducted the project, won the Gold Award for best innovation research at the Hong Kong Information and Communication Technology (HKICT) Awards 2007.

Professor Henry Chung Shu-hung
Department of Electronic Engineering
City University of Hong Kong
eeshc@cityu.edu.hk