Method for expanding an automation facility with at least one field device, wherein the automation facility - has at least one automation device and at least one field device, which are connected to a communication link (7, 8), and - is planned into a project by an engineering method for solving an automation problem such that the at least one automation device processes a projected control program that comprises a plurality of control modules when controlling a process, characterised in that - at least one virtual field device representing a real field device and a control module for controlling the virtual field device are planned into the project, - the current communication load is determined by the communication user, which communication load comprises the load caused by the communication of the process control and the load caused by the communication between the virtual field device and an expansion module of the at least one automation device planned into the project, wherein the expansion module comprises the control module for controlling the virtual field device and has an interface for exchange of information between the expansion module and a control and monitoring device, - the current control load of the at least one automation device is detected by the expansion module, which comprises the load caused by the process control and the load caused by the processing of the control module planned into the project, and - the control module planned into the project is linked into the control program as a function of the current communication load and the current control load, if this control module is enabled by a user for connecting the real field device to the bus (7, 8) via the control and monitoring device, wherein the current communication and control load is displayed to the user on the operator control and monitoring device. - has at least one automation device and at least one field device, which are connected to a communication link (7, 8), and - is planned into a project by an engineering method for solving an automation problem such that the at least one automation device processes a projected control program that comprises a plurality of control modules when controlling a process, characterised in that - at least one virtual field device representing a real field device and a control module for controlling the virtual field device are planned into the project, - the current communication load is determined by the communication user, which communication load comprises the load caused by the communication of the process control and the load caused by the communication between the virtual field device and an expansion module of the at least one automation device planned into the project, wherein the expansion module comprises the control module for controlling the virtual field device and has an interface for exchange of information between the expansion module and a control and monitoring device, - the current control load of the at least one automation device is detected by the expansion module, which comprises the load caused by the process control and the load caused by the processing of the control module planned into the project, and - the control module planned into the project is linked into the control program as a function of the current communication load and the current control load, if this control module is enabled by a user for connecting the real field device to the bus (7, 8) via the control and monitoring device, wherein the current communication and control load is displayed to the user on the operator control and monitoring device.