A compact modular air-conditioning (A/C) system which improves sustainability in the construction and operation of A/C plant in three main areas: 1. using box culvert stormwater as the condensing media to increase energy efficiency; 2. adopting Design for Manufacture and Assembly where all E&M equipment are prefabricated off-site ready for connection on site; and 3. using light-weighted reinforced concrete to manufacture the module to lower embodied carbon.