Indoor air quality and energy issues of refrigerant modulating air-conditioning systems in the tropics

The concept of refrigerant modulating air-conditioning systems for medium sized office buildings is increasingly becoming popular owing to their simplicity in installation and maintenance as well as the potential to conserve energy. However, it is important to evaluate the issues of ventilation and indoor air quality (IAQ) associated with such systems. In this paper, the results of an integrated IAQ-energy audit of two buildings in Singapore, employing the refrigerant modulating air-conditioning systems are presented and compared with those from conventional central air-conditioning systems. Two different designs of providing the outside air to the occupied zones are considered and it is observed that the design involving a direct connection of the outside air duct to the fan coil units is better than the design that involves supplying the outside air directly into the occupied zones. Key performance parameters such as the ventilation index, air exchange effectiveness characteristics and the energy index of the refrigerant modulating air-conditioning system are comparable to conventional central air-conditioning systems.