Energy availability in Egypt is one of the major problems that confront the government.Energy consumption in residential buildings is considered to be the biggest section that consumes electric energy generated by the electric power stations.The continuing increase in the number of residential buildings requires a corresponding increase in the number of power stations in order to meet the increased demand.Unfortunately such an increase will result in significant depletion of traditional energy resources.With the rising of the energy economic cost,an urgent thought started to reduce the consumption by all possible rationalization and efficient use means.The consumed energy in buildings increases year annually according to several factors,the major ones being the increase of the number of air-conditioners installed,and their operating hours.In the present investigation a residential building is considered to consist of three floors and six apartments of 100 m2floor area for each apartment; this building has been drawn by software called “Designbuilder”.The present investigation is carried out on the left apartment on the 3rd floor(typical floor)on two cases; one with thermal insulation in the walls and the roof and the other without thermal insulation.The present paper illustrated here,using “Designbuilder” software,three comparisons between the sensible cooling load,air-conditioner energy consumption rate,cost of the energy consumed and the CO2 produced by power plant,due to the energy consumed on the two cases,at three different room temperatures.The room temperature was set at; 24℃,22℃ and 20℃ respectively.