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A zone valve can be used to regulate the temperature in different areas of a structure that is heated primarily by a hydronic system. Hydronics involves the use of heat transfer to warm or cool a structure using water as the primary medium. Areas of the structure can be divided into artificial zones through which water flow is controlled by valves. Each zone valve typically consists of a motor unit that is mechanically connected to a valve body. Most zone valves used in homes are electronic, though commercial and industrial applications often use units that are operated by compressed air or vacuum.
Hydronic systems that make use of zone valves may include separate cold and hot water pipe loops or single integrated systems. Early hydronics typically involved a boiler for heating water and a chiller or cooling tower to cool water, each of which had its own set of pipes throughout a building. Modern systems include compact units known as chiller boiler systems which can direct hot or cold water throughout a home or other structure with the use of zone valves. Each room or other area in the building can have its own zone valve to allow hot or cold water into the associated pipes.
Most home hydronic systems use electronic zone valves composed of an electric motor and a valve body. The motor may be a simple alternating current (AC) unit that can either fully open or close the valve depending on which side is energized, or it can be a device that activates through the heating of a wax pellet. Units with wax motors are typically closed by spring action unless power is applied to the thermistor to heat the wax. Each zone valve is typically controlled from a central location, though separate thermostats may be present in each room.
If the power fails or motors malfunction, electric zone valves often have a manual bypass feature. This can be useful in maintaining a comfortable temperature in each zone even if the control system is not functioning properly. Without this feature, a zone valve with an AC motor would remain in its last position, while wax motor valves would close shut due to the spring action.
Large buildings often use zone valves that are actuated by a centralized source of compressed air or vacuum. In both of these cases the natural state of the valve is typically open, so the application of vacuum or pressure can force it shut. A variety of complex building management systems can be used with these types of zone valve, allowing the environment to be tightly controlled from a central location.