Applying a novel extra-low temperature dedicated outdoor air system in office buildings for energy efficiency and thermal comfort

• A novel dedicated outdoor air system was proposed and investigated.
• The proposed system adopts extra-low temperature outdoor air for space cooling.
• The extra-low temperature air was generated by a multi-stage direct expansion coil.
• Heat pipe was added to the proposed system to recover the waste cooling energy.
• Energy and exergy analysis as well as thermal comfort analysis were conducted.

A novel dedicated outdoor air system consisting of a multi-stage direct expansion coil and a zero-energy heat pipe to generate extra-low temperature outdoor air to avoid moisture-related problems was proposed in this study. The proposed system’s performance in achieving the desirable air conditions and better energy efficiency objectives is compared with a conventional direct expansion system for air-conditioning of a typical office building in Hong Kong based on simulation investigations. The simulations were carried out using equipment performance data of a pilot study, and realistic building and system characteristics. It was found that the proposed system, as compared to the conventional system, could reduce the annual indoor discomfort hours by 69.4%. An energy and exergy analysis was also conducted. It was revealed that the proposed system could reduce the annual air-conditioning energy use by 15.6% and the system exergy loss rate by 13.6%. The associated overall exergy efficiency was also found 18.6% higher. The findings of this study confirm that the proposed system is better than the conventional system in terms of both energy and exergy efficiency and the desirable air conditions.