Control of fluid temperature in a wet central heating system and components suitable for a central heating system.

摘要

Apparatus is provided to control the temperature of the circulating water in a wet central heating system during a heating cycle. The apparatus comprises a first temperature sensor 15 (Figure 3) for providing a voltage output related to the prevailing flow water temperature in the manner shown in Figure 4 and a second temperature sensor 16 for providing a voltage output related to the prevailing outdoor air temperature in the manner shown in Figure 5. These signals are applied to a differential amplifier 34 and the composite signal VIN is manipulated by the drive voltage controller 36 to produce a signal VOUT. The signal VOA from the sensor 15 is switched out whenever there is a demand for domestic hot water. In this case VIN may be equal to VW, the signal from the sensor 15. The signal VOUT is amplified by a buffer amplifier 37 and is regulated in a regulator 38 to provide a control voltage for a bimetallic heater element 39 in an air flow modulating valve 17 (Figure 11). VOUT is related to the air flow rate A through the valve 17 in the manner shown in Figure 8. The air flow rate A controls the rate of flow of gas from a valve (Figure 12) to a fully premixed burner 21 also supplied with air from the valve 17. Therefore VOUT controls the heat output PB of the burner 21 and in this way it is possible to control the temperature of the flow water leaving the boiler and thus the return water temperature in response to changes in the outdoor air temperature. This is of advantage where the boiler is of the condensing type since the return water temperature can be reduced to a targeted minimum value which is sufficient to satisfy space heating demands yet enables the period during which the boiler is operating in the condensing mode to be extended.