Domestic Water Heater
Domestic water heaters supply hot water to small residential and commercial buildings. Cold water is fed to the heater, then heated by resistor elements before being fed to a pump and the point of use. This type of heater is called an electrical resistance heater due to the electrical resistors it uses to heat the water.
Water enters the heater tank through this connection.
After the water is heated, it exits the water heater through this connection. A pump provides the necessary pressure difference to obtain flow from the heater to the point of use.
Air Purge Valve
It is necessary to ‘bleed’ air from the heater tank when the tank is initially filled. A small valve is opened as the tank is filled so that air can escape the system as the incoming water fills the tank; the valve is then closed when water begins to flow out of the valve. Ball valves are often used as air bleed valves because they are cheap and can be opened and closed quickly (1/4 turn valve design).
Sacrificial Anode Rod
An anode is a sacrificial element within the water heater. The purpose of an anode is to protect other metal components of the system from corrosion (the anode corrodes instead of the other metal components within the system). In this 3D model, an anode rod is installed in the middle of the water heater. An anode rod is usually manufactured from zinc, magnesium, or aluminium, with a steel centre piece connecting it to the anode plug; the plug screws into the heater tank.
Pressure Relief Valve (PRV)
A spring-loaded pressure relief valve (PRV) prevents over-pressurising of the heater tank. If the tank should become over pressurized, the tank may rupture and fail, which is not desired. A PRV has a spring that keeps the valve closed during normal operation, but if the pressure increases above a given setpoint, the spring will become compressed and the valve will open. Once the valve is open, water drains from the tank thus relieving the system pressure. A drain pipe ensures the water is fed directly to a drain, which increases safety for personnel (the water may be quite hot). After the system pressure has been relieved, the spring returns the valve to the closed position.
An electrical resistor element is housed within this tube. A resistor element becomes hot when current flows through it. Heat energy generated by the resistor is transferred to the surrounding tube and then the surrounding water. In this manner, the water is heated.
A drain valve is used to drain water from the heater tank. The drain valve is typically only used shortly before maintenance of the water heater occurs. In larger water boilers, the drain valve controls the properties of the boiler water (conductivity etc.) and is a far more important component. A water heater of this size will usually use a ball valve design.