An apparatus and a method for controlling an HVAC system in a building are provided. The apparatus may include: (a) sensors provided at different locations inside and outside of the building each providing an electrical output signal representative of a measured condition, wherein the sensors sense two or more of the following conditions: temperature, carbon dioxide and volatile organic compound conditions; (b) an embedded computer receiving the electrical output signals of the sensors and based upon which provides a plurality of output control signals; and (c) HVAC actuators operating in accordance with the output control signals, wherein the HVAC actuators affect a climatic condition or an air quality condition at one or more locations where the sensors are located.