A zone valve operates the flow of hot water to specific zones of a heating system. Creating multiple zones in a building reduces energy consumption and increases the comfort. For example, a house with the ground floor as one heating zone, and the bedrooms upstairs as another heating zone. The ground floor can be heated during the day, while the bedrooms are heated during the night. In this way, the unused areas don't need to be heated. A zone valve automatically closes or opens a zone. For example, zone valves can be operated by an electrical signal from an external thermostat or timer.
In most houses the temperature is measured and controlled by a single thermostat in the living room. If this area has reached the right temperature, heating is stopped and is not available to other areas such as the upper floor. By using multiple thermostats, that control the central heating and installed zone valves, it is possible to control the temperature in different areas independently of each other. This improves efficiency and can be interesting in many situations. Some examples are:
Electric ball valves are often used as a zone valve. Ball valves control the flow by means of a rotating ball having a bore. By rotating the ball a quarter around its axis, the valve will open or close. Electric ball valves are controlled with the aid of an electric motor. They are also called actuated ball valves. Electric ball valves distinguish themselves by a large orifice, so there is a low resistance to the flowing water. The actuator includes an energy efficient electric motor and gear for rotating the ball gradually, so no water hammer occurs. The actuator has two limit switches to stop the motor automatically when the valve is fully opened or closed. The power consumption of electric ball valves is very low, as power is only consumed during opening or closing.
The valve can have two or three connection ports (2-way or 3-way). A 2-way valve can be used to (partially) close or open a pipe. Valves with internal relay can be completely open or closed (one control wire), actuators with 3-point control (2 control wires) can also be partially opened. A 3-way valve has three connection ports. This allows to switch between different circuits. Think of (solar) boilers or heat exchangers. The three-way balls have a T-shaped bore. This makes different applications possible (2 or 3 opened ports).
Aside from electric ball valves, solenoid valves can also be used as a zone valve and open/close faster than a ball valve. Solenoid valves open and close with the aid of a solenoid, an electrical coil which pulls up a ferromagnetic plunger. Solenoid valves are usually two-way (2 ports) and normally closed (opens when the valve is powered). Suitable solenoid valves are direct or semi-direct operated. Indirect operated valves are usually unsuitable, because a pressure differential of at least 0.5 bar must be present to operate properly. A heating system is generally a closed circuit, in which the pressure differential over the zone valve might be lower. A good choice for the seal is EPDM, because it is suitable for hot water. Solenoid valves open and close quickly, this may result in water hammer in fast flowing pipes. It is important to connect solenoid valves in the right flow direction, this is indicated by an arrow or text (in/out) on the housing.