Common Hydronic Heating System Components and the Reason for Their Use In The system
·Thermal Expansion Tank
When water or boiler fluid mixtures are heated they expand due to thermal expansion. The expansion tank has an air chamber separated by a bladder to absorb this expansion (air can be compressed water or boiler fluid mixtures cannot). Without a properly sized and pressurized expansion tank the pressure in the system would increase to the point that the relief valve would open to relieve the pressure during each heating cycle and refill each time it cooled. This constant filling of large quantities of water would cause premature failure of the boiler and boiler components and dilute fluid mixtures. The relief valve is designed as a protection of overpressure in the event of a system malfunction and not for constant cycles of water release.
·Backflow Prevention Device
The water in the boiler system is not potable water after the system is filled due to contact with boiler materials, addition of other fluid mixtures and loss of water treatment disinfection chemicals. Therefore the water from the boiler must not enter the drinking water system. This valve prevents any backflow from the boiler to the water supply.
·Automatic Fill Valve
As gases are vented from the boiler system and fluid pressure is reduced this valve automatically keeps the boiler fluid filled to the proper pressure. Normal boiler operating pressure is between 12PSI cold and up to 26PSI hot. Whenever pressure drops below 12PSI this valve will let water in to the system to keep pressure at a minimum of 12PSI.
·Air Elimination Device (Power Vent)
As water heats and gases are released these gases must be eliminated from the system. If gasses build up in the system the pump can air lock stopping water circulation (heat distribution) and the system will be noisy and inefficient. The power vent will eliminate all gases emitted from the water and some gases in solution and is the most efficient method available for this purpose.
Zone valves are the electrically operated valves that open and close as the thermostats on each zone call for heat allowing the boiler to circulate the heat to each zone independently.
The circulation pump or pumps depending on system design are used to efficiently deliver the heated water or boiler fluid to the point of use and return it to the boiler for reheating.
The aquastat relay is a thermostat that senses the water temperature in the boiler and cycles the burner on and off during the heating cycle to prevent the boiler from overheating. It also turns the circulation pump on and off when the boiler reaches set temperatures designed for the heating system.
This is the thermostat on the wall of the home for each different zone of the system. It senses the room temperature and activates the system when the room temperature set by the homeowner drops below the set point.
·Pressure Relief Valve
This is a safety device that opens to relive the pressure in the system in case of a malfunction such as a stuck gas valve or defective aquastat that could cause a system to overheat, When the pressure reaches the setting of this device it will open letting the excessive pressure out of the system and preventing dangerous pressure in the heating system. These valves must be sized to the BTU loads of the boiler systems and operating pressures.
If the heating system has more than one zone, balancing valves will be required.If more than one zone is calling for heat the water would flow through the path of least resistance (the shortest loop) therefore resistance must be added to the shorter loops so water will flow through the longer loops. This is accomplished by installing a valve in the loops with the valves on the shorter loops partially closed to add resistance to the shorter lines. The valves would be set for even flow through all the loops in the system when all zones are calling for heat.