Central Heating Control

This circuit is used for optimum regulation of the flow of hot water in a central heating system. It measures the water temperature, and arranges for a particular valve or pump in the system to be switched on to achieve a user-defined tem- perature distribution in the home. Residual heat in the cen- tral heating system can thus be used to lower the cost of fuel. Fig. 1 shows that water in tem- perature range I can be used for the central heating and the storage vessel, while that in range II is also suitable for directing to the boiler. In most cases, it is not recommended to re-use water with a temperature below 30 °C. The circuit ar- ranges for an alarm to be activated when the water tem- perature falls below 5 °C, or exceeds 95 °C. The circuit diagram of the cen- tral heating control appears in Fig. 2. Relays Re, and Re5 are activated upon measuring the maximum and minimum per- missible temperature, respect- ively. The temperature sensor is a Type LM35, which has a scale fac...