Abstarct: Statistics indicate residential and commercial buildings and departments have the biggest contribution of using energy whether in developed countries, almost 50 percent of whole produced energy is used in buildings meanwhile Air conditioning systems are the most important energy consumers in buildings. Due to high energy consumption in buildings, it needs to analysis of building’s operation and designing and implementation of control algorithm on Air conditioning systems, in the way of decreasing energy consumption. Modification and developing of these systems, except to decreasing the energy consumption, causes the economic efficiency and providing a comfort level for building’s resident. In this thesis, a controlling algorithm of a gas engine heat pump to achieve the comfort level and decreasing fuel costs. For this reason, a building with foundation of 64 square meters in Tehran has been simulated by using of thermal equilibrium and solving the state space of system in MATLAB. Two algorithm of On-Off and proportional implemented on model. Algorithm of On-Off, which is in fact a thermostat control algorithm, switches off the air conditioner as soon as it reaches the setpoint, and switches on the air conditioner with maximum power when it deviates from the setpoint. The results show that the current cost of using the On-Off control algorithm is 16494 Rls per 24 hours (16 hours on and 8 hours off). The proportional control algorithm, due to the difference between the user's temperature and measured temperature, the command changes the engine speed and fan speed, and by setting these two parameters, it tries to close the building's temperature to the user's adjustable temperature. The results show that the current cost of using the proportional control algorithm is 12374 Rls per 24 hours. Ultimately, the use of the control algorithm provides 44.43% savings in gas consumption and 25% savings in current costs.