Research Highlights

Development of an Energy Efficient Air-conditioning System with Zonal Ventilation Control for Improved Indoor Air Quality

Principal Investigator : A/P Sekhar, Chandra
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The NUS-patented Single Coil Twin Fan (SCTF) system is an innovative air-conditioning and air distribution system that improves occupants' thermal comfort and indoor air quality in tropical buildings whilst significantly saving energy (US patent no 6,698,219 B2 and other patents pending). It provides "demand ventilation" and "demand cooling" by dynamically responding to the varying requirements in the individual occupied zones of a building. Potential applications of the SCTF technology include buildings with considerable load diversities, such as commercial and office buildings as well as those with simultaneous and distinct "process" and "human" needs (e.g. laboratories, air-conditioned workshops etc). It is also ideally suited for retrofit applications. Occupants of all these buildings will enjoy a better indoor environment which recent research and field studies have indicated increased occupant satisfaction and productivity, and significantly, this is achieved whilst saving energy.

Major findings

The newly developed SCTF system with the compartmented coil conditions distributes air through the multiple zones of an air-conditioned building such that adequate ventilation, and consequently, acceptable Indoor Air Quality (IAQ) is ensured throughout the operating range of the air-conditioning system.

The compartmented coil of the SCTF system has shown an energy saving potential of 12%.

A basis is provided for an integrated design of the cooling and dehumidifying coil that derives the optimal energy efficiency of the coil while achieving the desired cooling and dehumidifying performance and is envisaged to be of immense benefit in maintaining good indoor air quality in tropical buildings.

Findings from this research project have been presented in major international conferences (Healthy Buildings 2003, Singapore ; CIB World Building Congress 2004, Toronto ). A paper presented at the ASHRAE Annual meeting in Nashville , TN , will also be published in ASHRAE Transactions, Part I, 2004.

New Initiatives / Impact

The successful outcome of this project has led to the following new initiatives :

  • Optimisation of the compartmented coil performance of a newly developed air-conditioning system", which is an ongoing research project.
  • An energy efficient air-conditioning system with zonal ventilation control for improved indoor air quality" – This is a recently approved TEC1 project that involves the field trial of the SCTF system in half of the 3rd floor of the new University Hall and Administration building at NUS.
  • The recent incorporation (21 June 2004) of a new NUS spin-off company – Enhanced Air Quality Private Limited that deals with engineering, research and development, consultancy, manufacturing and training in the field of indoor air quality control. Assoc Profs Chandra Sekhar, Tham Kwok Wai and David Cheong are the founding directors of Enhanced Air Quality Pte Ltd.
  • 1TEC – The Enterprise Challenge project, administered by the PSD, Prime Minister's Office (
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