Heating, ventilation and/or air conditioning (HVAC) systems are often used to control the comfort level within a building or other structure. Such HVAC systems typically include an HVAC controller that controls various HVAC components of the HVAC system in order to affect and/or control one or more environmental conditions within the building. The HVAC components may include, for example, a furnace, an air conditioner, and associated ductwork, such as in a forced air system, and/or a boiler, radiators, and associated plumbing, such as in a hydronic heating system, as well as many other possible components and configurations.
In forced air systems, the conditioned air is typically provided by a furnace and/or air conditioner through a plenum to a network of supply air ducts that distribute the conditioned air throughout the building. A network of return air ducts is often used to return air from the building back to the furnace and/or air conditioner. A blower is used to draw the return air through the return air ducts, and drive the return air through the furnace and/or air conditioner and into the supply air ducts via the plenum. In some cases, some of the air is replaced over time with fresh outside air, often through an energy recovery ventilator or the like. Airflow in a force air system may be controlled in part through the use of one or more dampers.
In a zoned system, conditioned air is delivered to each zone based on the heat load in that zone. Dampers are typically placed in the supply air ducts that feed each zone. By activating damper actuators, the conditioned air may be delivered to only those zones that are calling for conditioned air. In some cases, a bypass damper may be placed in a bypass duct that extends between the supply duct (or the plenum) and the return air duct. This may allow some of the supply air to pass directly to the return air duct when the pressure in the plenum rises above a threshold value, such as when only a small number of zones are calling for conditioned air. A ventilator may also be controlled by one or more dampers. In each of these cases (zoning, bypass, ventilation) and others, a damper actuator may be used to provide automatic control of a damper. HVAC actuators are also employed in other contexts as well. For example, a hydronic heating or cooling system may employ HVAC actuators to control valves that govern the flow of fluids in the system.