Hydronic heating systems are used in homes and are used in homes and apartments worldwide. In a hydronic heating system, aboiler heats hot water that is pumped through pipes to radiators throughout the dwelling. The to radiators throughout the systems in North America, the radiators may be in a zone. Depending on size and the complexity of installation, a dwelling could have one or more zones which are typically controlled with one zone valve that is either open or closed. If there is a demand for heat in a specific zone, the zone valve opens and water flow at a fixed rate through all of the radiators in that zone until the demand is satisfied.
In a typical European system .a varisble-position valve on each radiator individually controls the water flow rate (Fig.1).A typical automatic control product for a European hydronic heating system has a temperature sensor inside the product housing to sense the room temperature .A battery –operated actustor controls the valve position in response to a command from the feedback algorithm. The set point is adjusted with a knob or button. Some products have an interface and display for the user to program set points as a function of the time of day .The feedback algorithm for these products are typically proportional or proportional integral(PI),which are common in industrial process control due to their simplicity and effectiveness[1].
