GB2265027A

GB2265027A - Controlling operation of a gas boiler

Info

Publication number: GB2265027A
Application number: GB9205334A
Authority: GB
Inventors: David E Steade; Richard C Ironside
Original assignee: Worcester Heat Systems Ltd
Current assignee: Bosch Thermotechnology Ltd
Priority date: 1992-03-12
Filing date: 1992-03-12
Publication date: 1993-09-15
Also published as: GB9205334D0

Abstract

A gas boiler 10 supplying heated water to a central heating system 15 is controlled by a computer 21 which samples at predetermined intervals a temperature signal derived from a sensor 20 located in the flow path of the heated water fluid. The computer 21 compares the detected rate of temperature rise with a target rate predetermined and supplies a control signal 23 to a controlled gas valve 19. The valve is continuously variable and is adjusted to match the actual rate of temperature rise to the target rate. <IMAGE>

Description

"A Method for controlling operation of a Gas Boiler" The invention relates to the control of gas boilers, and particularly but not exclusively to the control of a gas boiler for the supply of heated water to a domestic central heating system.

In conventional gas central heating boilers the gas valve controlling the supply of gas to the burners in the combustion chamber is controlled by a knob on the boiler control panel which sets the maximum flow of gas to the burners. The gas valve is normally electrically operated and the control knob adjusts a potentiometer which controls this electrical operation.

The heat output of the boiler is therefore a function of the setting of the "burner pressure" potentiometer on the control board.

When the boiler is first turned on, the gas valve is opened according to the pre-setting of the potentiometer and hot water is delivered to the central heating system, or other heat output system, until a desired maximum temperature is reached, whereupon the gas valve is closed and the burners turned off. The burners are subsequently turned on again, to the pre-set maximum gas flow, at intervals to maintain the desired temperature.

It will be appreciated that the rate of rise in temperature of the system will vary according to the heat output of the system. Thus, a large central heating system providing a large heat output will be subject to a slower rise in temperature than a smaller system having a lower heat output. Also, of course, the rate of rise in temperature of a single system will vary according to how many of the radiators are turned on.

However, it is desirable that the rate of temperature rise remains substantially constant, or within a limited range, regardless of the system load, and the present invention provides a method and arrangement for achieving this.

According to the invention there is provided a method of controlling operation of a gas boiler supplying heated fluid to a heat output system, the method comprising monitoring the actual rate of rise in temperature of heated fluid delivered by the boiler, comparing that actual rate of rise in temperature with a pre-set target rate, and automatically adjusting the supply of gas to the boiler in a manner to tend to match the actual rate to the target rate.

The monitoring of the actual rate of rise in temperature is preferably effected over the whole period from initiation of the gas supply to a required maximum temperature of the heated fluid being reached.

The actual rate of rise in temperature may be monitored by sampling the temperature at pre-determined intervals of time. For example the temperature may be sampled every five seconds.

The actual temperature of the fluid may be sampled by a temperature sensor located in the flowpath of the heated fluid within the gas boiler itself.

Monitoring may be effected by a computer, or other form of signal processor, which receives a temperature signal from the sensor, processes that signal to compare the actual rate of temperature rise with a target rate preset in the signal processor, and supplies a control signal to a gas valve operating device of the boiler.

The invention includes within its scope a gas boiler incorporating means for monitoring the actual rate of rise in temperature of heated fluid delivered by the boiler, means for comparing that actual rate with a pre-set target rate, and means for automatically controlling the supply of gas to the boiler in a manner to tend to match the actual rate to the target rate.

The following is a more detailed description of an embodiment of the invention, by way of example, reference being made to the accompanying drawing which is a diagrammatic representation of a central heating gas boiler delivering hot water to a domestic central heating system.

Referring to the drawing, the boiler 10 comprises a conventional combustion chamber 11 in which gas burners heat water circulating through a heat exchanger 12. An output pipe 13 from the heat exchanger 12 delivers hot water to the flow circuit 14 of a central heating system, the heat load of the system, which will normally comprise hot water radiators, being indicated at 15. The return circuit 16 of the system leads to an input pipe 17 in the boiler 10 leading the lower temperature water back to the heat exchanger 12 for reheating.

Gas for the burners in the combustion chamber 11 is supplied through a gas supply pipe 18 which is controlled by a gas valve 19. The arrangement as described so far is conventional. As previously described, in such conventional arrangements the gas valve 19 is periodically opened and closed to heat the water circulating in the system to maintain a pre-set target temperature. The gas valve 19 is thus either fully open or fully closed, the extent of opening being determined by a pre-set control on the boiler, as described above.

According to the present invention a temperature sensor 20 which may, for example, comprise a thermistor, is connected to the output pipe 13 in the boiler and delivers to a computer control device 21 within the boiler a signal 22 indicative of the temperature of the hot water delivered by the boiler.

The computer control device 21 is preprogrammed to sample the temperature signal 22 at predetermined intervals and thereby determine the actual rate of rise in temperature of the hot water delivered by the boiler. The program then compares this actual rate with a target rate of temperature rise which is pre-set in the computer device. The computer device produces an output signal 23 indicative of the difference between the actual rate and target rate, the signal being selected to control the gas valve 19, and hence the volume of gas supplied to the burners, in a manner to reduce the difference to zero. In other words the system 20, 21, 22, 23 comprises a feedback system which controls the rate of rise in temperature and tends to maintain such rate at a constant value, irrespective of variations in the heat load 15.

Typically, the target rate of temperature rise might be 3"C per minute, based on a sub-routine of 0.25 C per five seconds.

The computer control device may be entirely pre-programmed with the target rate of temperature rise so that no physical pre-setting of the system is required either during manufacture or by an installer.

However, the invention does not exclude arrangements in which means are provided for effecting adjustment of the target rate.

The arrangement according to the invention may, of course, incorporate any of the other types of control arrangement normally provided on central heating boilers, and in particular controls for determining the maximum temperature of the boiler output.

Claims

1. A method of controlling operation of a gas boiler supplying heated fluid to a heat output system, the method comprising monitoring the actual rate of rise in temperature of heated fluid delivered by the boiler, comparing that actual rate of rise in temperature with a pre-set target rate, and automatically adjusting the supply of gas to the boiler in a manner to tend to match the actual rate to the target rate.

2. A method according to Claim 1, wherein the monitoring of the actual rate of rise in temperature is effected over the whole period from initiation of the gas supply to a required maximum temperature of the heated fluid being reached.

3. A method according to Claim 1 or Claim 2, wherein the actual rate of rise in temperature is monitored by sampling the temperature at pre-determined intervals of time.

4. A method according to Claim 3, wherein the temperature may be sampled every five seconds.

5. A method according to any of Claims 1 to 4, wherein the actual temperature of the fluid is sampled by a temperature sensor located in the flowpath of the heated fluid within the gas boiler itself.

6. A method according to Claim 5, wherein monitoring is effected by a computer, or other form of signal processor, which receives a temperature signal from the sensor, processes that signal to compare the actual rate of temperature rise with a target rate preset in the signal processor, and supplies a control signal to a gas valve operating device of the boiler.

7. A gas boiler incorporating means for monitoring the actual rate of rise in temperature of heated fluid delivered by the boiler, means for comparing that actual rate with a pre-set target rate, and means for automatically controlling the supply of gas to the boiler in a manner to tend to match the actual rate to the target rate.

8. A method of controlling operation of a gas boiler substantially as hereinbefore described with reference to the accompanying drawing.