This thesis is mainly discusses a control method denoted as “Distributed PID Gain Control” (D_PID) which can be applied in fan coil units of HVAC systems in MICE buildings. Regarding the high requirements of energy saving in commercial buildings HVAC systems; nowadays, fan coil unit systems, which have being applied in building’s HVAC systems, are increasing for air conditioning control. Most of the existing implementations of the fan coil unit system are PI or PID controllers, the rest are “on/off” controllers; However, the PI or PID parameters of these controllers are usually fixed by the manufacturers and are not adjustable. Due to different applications or locations of the multi-use building rooms, their thermal characteristics are different, their air conditioning requirements and the corresponding air conditioning controls are different as well. Thus, a fixed fan coil unit PID Control (F_PID) method is inadequate to fulfil the various rooms’ air conditioning requirements; the proposed D_PID method is introduced. This method is to provide individual room air conditioning control in relation to its individual thermal characteristics. In this thesis, a PID parameters adjustable DDC controller is used as a fan coil unit controller, with regard to the different room’s thermal characteristics; different PID parameters will be tuned up and employed in a DDC controller for the room’s air conditioning control. In this experiment, the results show that the performances of these experimental air ii conditioning controls using the D_PID method have been significantly improved, most of the time the room temperature can be maintained around the set-point within a range of +/- 0.5 degree Celsius.