1. A method of controlling an environmental maintenance system that includes a plurality of actuators and a plurality of sensors, each sensor measuring a value of a physical condition of an environment, the method comprising: receiving sensor values S corresponding to the sensors; determining a potential change dU to operation levels U of the actuators; calculating, with a computer system, a first contribution to a penalty function by: applying a transfer model to dU to determine a predicted change dS in the sensor values S, the transfer model providing a relation between changing an operation level of an actuator and resulting changes in sensor values; determining new sensor values S New from the predicted change dS; and using S New to determine the first contribution to the penalty function, the first contribution being based on a relationship of each new sensor value relative to one or more respective setpoint values; calculating, with the computer system, a second contribution to the penalty function by: determining new operation levels U new , corresponding to the potential change dU to the operation levels U; for each new operation level, determining a cost of operating the corresponding actuator with the new operation level; and aggregating the costs to obtain the second contribution; determining a first value of the penalty function based on the first and second contributions for the potential change dU; determining an optimal change to the operation levels U of the actuators based on values of the penalty functions for a plurality of potential changes to the operation levels U; and setting the operation levels of the actuators based on the optimal change.