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Lee Woo Sing College at The Chinese University of Hong Kong (CUHK) recently achieved a significant reduction of up to 67%* in air-conditioning electricity consumption in its Dining Hall by introducing a mixed air-conditioning mode that combines traditional variable refrigerant volume (VRV) air conditioning with a new-type fresh air unit (FAU). The low-humidity air treated by the FAU provides a comfortable experience comparable to traditional air-conditioned environments, even at an ambient temperature of approximately 27^oC.

Traditional air-conditioning systems consume additional energy during the cooling process by heating the air, evaporating moisture and then cooling it down again to control indoor humidity. For larger spaces with high ceilings such as assembly halls, the air conditioning often needs to be set to a lower temperature to compensate for energy loss during air circulation, further exacerbating energy wastage.

In response, Lee Woo Sing College implemented the Mixed Fresh Air Ventilation Mode, adding an FAU at ground level in the Dining Hall to complement the existing traditional air-conditioning system. The FAU effectively treats the fresh air entering the hall, lowering the overall temperature by 2^oC and reducing humidity to approximately 70%. As comfortable fresh air is directly circulated at ground level, the existing air-conditioning system can be adjusted to a higher temperature, or even partially or completely switched off during off-peak hours with fewer people in the area. This has resulted in an average annual saving of 30% in air-conditioning electricity consumption for the Dining Hall, with a maximum saving of 67%*.

Professor Yam Yeung, Master of Lee Woo Sing College, expressed his delight at witnessing the significant energy-saving benefits of the mixed mode. He said: “During the trial period, we found that even when the air conditioning was set to a relatively energy-efficient 24^oC or turned off during off-peak hours with the ambient temperature at about 27^oC, our students generally reported feeling comfortable or even found it more pleasant than the traditional air-conditioned environment set at lower temperatures.

“This successful experience provides a viable solution for building energy management at CUHK and in other academic environments. CUHK and Lee Woo Sing College have always been committed to promoting sustainable development. This achievement further demonstrates the University’s leading position in carbon reduction, environmental conservation and energy saving.”

The mixed mode has also been introduced to other areas in the College, including the lobby, central kitchen, fitness room and 11 pantries in its hostel. The College will continue exploring ways to extend the mixed mode to more campus locations, working towards carbon neutrality. 

About Lee Woo Sing College at The Chinese University of Hong Kong

Lee Woo Sing College at The Chinese University of Hong Kong adheres to the motto “Wisdom, Humanity, Integrity, Harmony” and is dedicated to providing students with a diverse learning environment and a rich campus life. Lee Woo Sing College has consistently been at the forefront of green education. In 2012, it introduced Hong Kong’s first Smart Meter system in its hostel. Subsequently, it installed Hong Kong’s first CIGS solar system on the campus rooftop, as well as other energy-saving measures. A team of Green Life Ambassadors formed by students also assists the College in promoting green education.

* Comparison between April 2025 and April 2019 (full operation of catering centre in the Hall before pandemic): Electricity consumption for air conditioning in April 2025 was 7,100 kWh, while electricity consumption for air conditioning in April 2019 was 21,420 kWh.