Abstract: A method and system for controlling the environment of residential and commercial buildings. Movement of air within the facilities is accomplished by air handling units or fans. The speed of each air handling unit is controlled by a variable-speed drive, allowing the air handling units to run at speeds below full capacity. Environmental parameters, such as temperature or humidity, are monitored to determine the existing state of the environment, which is then compared to a desired state. The speed of the fans, or air handling units, is adjusted to alter the existing environmental state, bringing it in alignment with the desired state. The fans, or air handling units, are operated continuously, typically at reduced capacity. Other various facets are included with the system and method including the control of the mixture of air supplied to the internal environment of the building.