The present environmental condition controller and method provide for controlling an environmental condition in an area of a building. For doing so, a communication interface receives an environmental condition target value (xref), and an environmental condition measured value (x). A processing unit calculates an environmental condition adjustment value (yn) with a recursive function based on the environmental condition measured value (x), the environmental condition target value (xref) and an adaptive proportionality value (k). The processing unit also generates and transmits a command based on the environmental condition adjustment value (yn). The processing unit further stores in a memory the environmental condition adjustment value (yn) as a previously calculated environmental condition adjustment value (yn−1). Specific steps of the method are executed recursively. The present method may further be performed by a computer program product.