In this write up, an energy-saving device is introduced into the air-handling unit (AHU). Due to increases in energy costs, energy saving devices or systems have become the new preferred trend in tropical countries. A primary cooling coil system is incorporated into the AHU to recycle the condensate water in order to achieve energy savings. The warm outside fresh air is drawn through the primary cooling coil to recover the latent heat of condensate water. The large temperature gradient between the warm fresh air and condensate water enlarges the amount of energy recovered. This system is well applicable to primary AHU which serves primary air to the air-conditioning system. The cost of installing the device is negligible but in returning long term saving. Furthermore, the de-cooled condensate water can be drained off through non-insulated drain pipe. The idea generation is discussed in the introduction. Chapt