Single Coil Twin Fan (SCTF) Air-conditioning and Air Distribution System
SCTF, an efficient air-conditioning system with zonal ventilation control for improved indoor air quality, led to a NUS spin-off company, Enhanced Air Quality Pte. Ltd. founded by Assoc. Prof
Chandra Sekhar, Assoc. Prof Tham Kwok Wai and Assoc. Prof David Cheong from the School of Design and Building.
In this new millenium, more than 80% of our time are spent in air-conditioned buildings for work and leisure. Increasingly, this has led to high expectations of the Indoor Air Quality (IAQ) of our environment as it has an impact on our health and productivity. However, escalating energy costs related to air-conditioning, especially the outdoor air that is necessary for ventilation purposes, could lead to inappropriate energy conservation strategies that may result in deterioration of the quality of the built environemnt – a phenomenon commonly known as the Sick Building Syndrome. In the tropics, the high temperature and high humidity of the outdoor air tends to aggravate the problem.
The 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. The SCTF system involves a new method of conditioning and distributing air through the multiple zones of an air-conditioned building such that adequate ventilation, and consequently, acceptable IAQ is ensured throughout the operating range of a Variable Air Volume (VAV) air-conditioning system. It is also aimed at providing the necessary ventilation while optimising energy consumption level of the VAV system. It involves the cooling and dehumidification of the outdoor and the recirculated air streams separately through separate compartments of a single cooling coil without mixing them during their flow through the coil and the new method of distribution involves transmitting the two air streams separately until they reach a modified VAV box in the occupied zone. The SCTF system provides “demand ventilation” and “demand cooling” by dynamically responding to the varying needs in the 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 (eg laboratories, air-conditioned workshops etc). It is also ideally suited for retrofit applications.
The SCTF system was installed in an office with floor area of about 2500 m2 in the a new NUS building in early 2005 and it has been in operation since June 2005. The SCTF system is able to provide adequate ventilation in a typical large office premises, based on “demand ventilation” and “demand cooling” in the individual occupied zones and has good dynamic performance. The thermal comfort parameters also indicate superior performance of the SCTF system, particularly in terms of the indoor RH levels, which is attributable to the enhanced dehumidifying performance of the compartmented cooling coil.
The SCTF system has been chosen as the base air-conditioning system for a net Zero Energy Building to be built in Singapore. This is a retrofit project of an existing building of the BCA Academy and is expected to be commissioned towards the end of 2009. A combination of SCTF Air Handling Units and SCTF Fan Coil Units has been designed for this project and the primary focus has been the desired outcome of “superior” indoor environmental conditions and “energy efficiency”.