The present study attempts to reduce the supply of outdoor air in conditioning building spaces for energy saving while improving the indoor air quality. A hybrid air treatment system incorporating a cooling system is introduced for tropical climates. The air treatment system (ATS) comprises an ozone-based oxidation process and an air scrubbing device. The air purification process has been experimentally investigated. Experimental results demonstrated the feasibility of the proposed ATS to provide improved indoor air quality. A validated mathematical model has been employed to study the air cooling and dehumidification process through the cooling coil. The reduced outdoor air intake facilitates a higher chilled water supply temperature resulting in an improved chiller performance and reduction of cooling load. The energy consumption performance of the proposed hybrid ATS air-conditioning system has been evaluated for an office building experiencing tropical climatic conditions. The cooling load on a design day has demonstrated that the reduction of outdoor air intake enabled marked energy savings potential in terms of the cooling demand. By analysing the building performance based on tropical climatic data, an annual energy consumption saving of up to 64.6 kW h/m(2) can be achieved via the hybrid ATS air-conditioning system. (C) 2017 Elsevier Ltd. All rights reserved.