Zone valve
Encyclopedia
A zone valve is a specific type of valve
used to control the flow of water
or steam
in a hydronic
heating or cooling system.
In the interest of improving efficiency and occupant comfort, such systems are commonly divided up into multiple zones. For example, in a house, the main floor may be served by one heating zone while the upstairs bedrooms are served by another. In this way, the heat can be directed principally to the main floor during the day and principally to the bedrooms at night, allowing the unoccupied areas to cool down.
This zoning can be accomplished in one of two ways:
or compressed air
may be used instead. In either case, the motor is usually connected to the water valve via a mechanical coupling.
For electrical zone valves, the motor is often a small shaded-pole synchronous motor
combined with a rotary switch that can disconnect the motor at either of the two stopping points ("valve open" or "valve closed"). In this way, applying power to the "open valve" terminal causes the motor to run until the valve is open while applying power at the "close valve" terminal causes the motor to run until the valve is closed. The motor is commonly powered from the same 24 volt
ac
power source that is used for the rest of the control system. This allows the zone valves to be directly controlled by low-voltage thermostat
s and wired with low-voltage wiring. This style of valves requires the use of an SPDT thermostat or relay
.
Zone valves can also be constructed using wax motor
s and a spring-return mechanism. In this case, the valve is normally closed by the force of the spring but can be opened by the force of the wax motor. Removal of electrical power re-closes the valve. This style of zone valve operates with a perfectly ordinary SPST thermostat.
For vacuum- or pneumatically-operated zone valves, the thermostat usually switches the pressure or vacuum on or off, causing a spring-loaded
rubber diaphragm to move and actuate the valve. Unlike the electrical zone valves, these valves automatically return to the default position without the application of any power, and the default position is usually "open", allowing heat to flow.
Highly sophisticated systems may use some form of building automation
such as BACnet
or LonWorks
to control the zone valves.
Disadvantages:
Disadvantages:
Valve
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
used to control the flow of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
or steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
in a hydronic
Hydronics
Hydronics is the use of water as the heat-transfer medium in heating and cooling systems.Some of the oldest and most common examples are steam and hot-water radiators. Historically, in large-scale commercial buildings such as high-rise and campus facilities, a hydronic system may include both a...
heating or cooling system.
In the interest of improving efficiency and occupant comfort, such systems are commonly divided up into multiple zones. For example, in a house, the main floor may be served by one heating zone while the upstairs bedrooms are served by another. In this way, the heat can be directed principally to the main floor during the day and principally to the bedrooms at night, allowing the unoccupied areas to cool down.
This zoning can be accomplished in one of two ways:
- Multiple circulator pumpCirculator pumpA circulator pump is a specific type of pump used to circulate gases, liquids, or slurries in a closed circuit. They are commonly found circulating water in a hydronic heating or cooling system...
s, or - A single circulator pump and zone valves.
Zone valve construction and operation
Zone valves as used in home hydronic systems are usually electrically powered. In large commercial installations, vacuumVacuum
In everyday usage, vacuum is a volume of space that is essentially empty of matter, such that its gaseous pressure is much less than atmospheric pressure. The word comes from the Latin term for "empty". A perfect vacuum would be one with no particles in it at all, which is impossible to achieve in...
or compressed air
Compressed air
Compressed air is air which is kept under a certain pressure, usually greater than that of the atmosphere. In Europe, 10 percent of all electricity used by industry is used to produce compressed air, amounting to 80 terawatt hours consumption per year....
may be used instead. In either case, the motor is usually connected to the water valve via a mechanical coupling.
For electrical zone valves, the motor is often a small shaded-pole synchronous motor
Shaded-pole synchronous motor
Shaded-pole synchronous motors are a class of AC motor.Like a shaded pole induction motor, they use field coils with additional copper shading coils to produce a weakly rotating magnetic field. But unlike a shaded pole induction motor , the synchronous version of this motor uses a magnetized rotor...
combined with a rotary switch that can disconnect the motor at either of the two stopping points ("valve open" or "valve closed"). In this way, applying power to the "open valve" terminal causes the motor to run until the valve is open while applying power at the "close valve" terminal causes the motor to run until the valve is closed. The motor is commonly powered from the same 24 volt
Volt
The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the...
ac
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
power source that is used for the rest of the control system. This allows the zone valves to be directly controlled by low-voltage thermostat
Thermostat
A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...
s and wired with low-voltage wiring. This style of valves requires the use of an SPDT thermostat or relay
Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal , or where several circuits must be controlled...
.
Zone valves can also be constructed using wax motor
Wax motor
A wax motor is a linear actuator that is sometimes used to replace a magnetic solenoid in an application where a short range of linear motion is required.The wax motor has three principal components:* A block of wax* A plunger that bears on the wax...
s and a spring-return mechanism. In this case, the valve is normally closed by the force of the spring but can be opened by the force of the wax motor. Removal of electrical power re-closes the valve. This style of zone valve operates with a perfectly ordinary SPST thermostat.
For vacuum- or pneumatically-operated zone valves, the thermostat usually switches the pressure or vacuum on or off, causing a spring-loaded
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...
rubber diaphragm to move and actuate the valve. Unlike the electrical zone valves, these valves automatically return to the default position without the application of any power, and the default position is usually "open", allowing heat to flow.
Highly sophisticated systems may use some form of building automation
Building automation
Building automation describes the functionality provided by the control system of a building. A building automation system is an example of a distributed control system...
such as BACnet
BACnet
BACnet is a communications protocol for building automation and control networks. It is an ASHRAE, ANSI, and ISO standard protocol....
or LonWorks
LonWorks
LonWorks is a networking platform specifically created to address the needs of control applications. The platform is built on a protocol created by Echelon Corporation for networking devices over media such as twisted pair, powerlines, fiber optics, and RF...
to control the zone valves.
Comparison with multiple circulator pumps
Multiple zones can be implemented using either multiple, individually-controlled circulator pumps or a single pump and multiple zone valves. Each approach has advantages and disadvantages.Multiple Pump System
Advantages:- Simple mechanical and control design ("SPST thermostats")
- RedundancyRedundancy (engineering)In engineering, redundancy is the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe....
: If one zone pump fails, the others can remain working
Disadvantages:
- Higher initial installation cost. Circulator pumps cost more than zone valves
- Circulating pumps have a shorter life span than a zone valve
- Higher power consumption. Operating circulators draw substantial power any time the zone is actively heating. Zone valves, by comparison, draw little power at any time and many designs only draw power while in transition from open to close or vice-versa.
Zone Valve System
Advantages:- Lower initial installation cost.
- Lower power consumption.
- Ease of maintenance certain modals.
Disadvantages:
- Zone valves can be unreliable. Zone valves operated by electric timing motors aren't "fail safe" (failing to the "open" condition).
- No inherent redundancy for the pump. A zone-valved system is dependent upon a single circulator pump. If it fails, the system becomes completely inoperable.
- The system can be harder to design, requiring both "SPDT" thermostats or relays and the ability of the system to withstand the fault condition whereby all zone valves are closed simultaneously.
Typical manufacturers of zone valves
- Belimo
- Mut Meccanica
- Taco
- HoneywellHoneywellHoneywell International, Inc. is a major conglomerate company that produces a variety of consumer products, engineering services, and aerospace systems for a wide variety of customers, from private consumers to major corporations and governments....
- ASC
- Boss
- Orkli
See also
- Zone damper
- zone valve