The new building in Bahir-Dar Institute of Technology Bahir-Dar University found an altitude of 1800m latitude of 11.4° and longitude of 37.1°. This building has 8 laboratory rooms in the ground floor,24 staff office,9 lecture halls and 13 class rooms which requires cooling inorder to meet the required temprature and humudity. The cooling load calculation for this new building mostly depends on the window radiation load because of its maximum number of windos and its orientation is east and west direction. The cooling load is very high and the recommended type of air conditioning is the central type of HVAC system. The function of an air system is to condition, to transport, to distribute the conditioned, recirculating, outdoor, and exhaust air, and to control the indoor environment according to requirements. These design and simulation of duct air condition system involves the selection site and after selecting the site collect the building data information in order to calculate heating and cooling load to select air condition equipment and finally determine the energy performance of building. Duct design is to select suitable dimensions of duct for each run and then to select a fan, which can provide the required supply airflow rate to each conditioned zone. There are different duct design methods like velocity method, equal friction method and static regain method but equal friction method is the most common method by specifying a constant pressure drop per unit length.