Abstract
Calculating thermal load of building is important to find exact A/C equipment and air handling unit, to achieve comfort operation and good air distribution in the air-conditioned zone. It should be taking into account the highest temperature in summer and lower of winters that occurs in the region. Building's location, construction's materials other interior's load must be considered for estimation of accurate thermal load. All equations needed for heat transfer through the building and for the interior's load are used to get the thermal load. Then, all equations can be inserted in a personal program like M.S. Excel, to get the results. An alternative way is to use available software, like HAP 4.2 and Elit “RHVAC”. In this paper hand calculation is used to estimate the thermal load for existing building and the results were compared by the outcomes from HAP 4.2 program. It is shown that there is little difference between the two results due to defining the thermal resistance for the used materials of the wall, roof, and windows. Also the sources of constants used for the equations are not the same.