GB2520064A

GB2520064A - Heating control systems

Info

Publication number: GB2520064A
Application number: GB1319760.3A
Authority: GB
Inventors: Darryl Schofield
Original assignee: ADVANCED ELECTRONIC SOLUTIONS Ltd
Current assignee: ADVANCED ELECTRONIC SOLUTIONS Ltd
Priority date: 2013-11-08
Filing date: 2013-11-08
Publication date: 2015-05-13
Anticipated expiration: 2033-11-08
Also published as: GB201319760D0; GB2520064B

Abstract

The controller 20 regulates a boiler 2 having a thermostat 6, fuel burner 4, flow pipe 30 and return pipe 32. The flow and return pipes are preferably associated with a central heating system. The controller is connected to flow 34 and return 38 temperature sensors by respective inputs 36 and 40 and has an input associated with the thermostat and an output for activating the burner, preferably via a control relay 50. The controller also has a memory 44 that stores the sensed temperatures when the thermostat opens, i.e. deactivates the burner. When the thermostat closes, so as to activate the burner again, the controller delays firing of the burner, preferably by keeping the control relay open. The length of the delay is dependent on the ratio of the current flow and return temperatures to their previous, stored values. Ideally, a maximum delay is imposed when there is no change in these temperatures. The controller ideally includes a microcontroller 22, with the relay regulating opening of a fuel valve 12 to control firing of the burner.

Description

Heating Control Systems

Technical Field

[0001] The present invention relates to heating control systems that are used to control the initiation of a burner in a boiler in response to signals received from a thermostat.

Background Art

[0002] The technical problem of "dry-cycling" occurs when a control system repeatedly initiates short burn cycles of a boiler. It has been proposed in EP 1607820 A (SABIEN TECHNOLOGY IP LTD) 21/12/2005 to use a processor to regulate the initiation of a burn cycle by using temperature sensors on the flow and return paths to the boiler and use this data to control the boiler. Sabien specifically claimed the rate of change of either of these sensed temperatures as the predetermining factor in the control process.

[0003] However, seasonal changes in temperature, variation in heating demand and site-differences make the switch timings a difficult compromise, and such controllers often require on-site adjustments.

Summary of invention

[0004] Although this invention uses electronic hardware similar to that of the prior art, this invention overcomes the problems of seasonal changes and varying installation parameters, by the use of a microcontroller whose intelligent program learns and adapts to the changes in the boiler demand.

[0005] In this way, optimum efficiency settings may be achieved without need of a qualified engineer on-site. Also, the automatic controller is naturally simpler and less expensive to install, with less room for human error.

Brief description of drawings

[0006] The present invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which: [0007] Figure 1 represents a boiler with a microcontroller control system in accordance with the present invention.

Description of embodiments

[0008] As illustrated in Figure 1, a boiler 2 has a burner 4. A conventional thermostat 6 is provided and is set to close in order to generate a control signal on control line 8 when the burner operating temperature drops to a pre-set level. The system is suitable for a boiler designed to heat water in a tank or to circulate heated liquid through heating equipment such as a system of radiators in premises to be heated.

[0009] The boiler has a fuel supply pipe 10 which supplies fuel to the burner 4 via an electrically controllable fuel valve 12. The control line 8 is connected to the controller 20 of the present invention and is connected as an input to a microcontroller 22.

[0010] The boiler has a FLOW output heating pipe 30 for the heating medium, usually a liquid (typically water) and a RETURN pipe 32 for the heating medium which has been circulated through the system operated by the boiler. A temperature sensor 34 in the FLOW pipe close to the output from the boiler has an output line 36 which provides a temperature signal to the microcontroller 22. The RETURN pipe 32 also has a temperature sensor 38 close to the boiler which provides a signal on line 40 to the microcontroller 22 representing the temperature of water returning from the radiators. The microcontroller 22 also includes a memory 44 for storing historic values of the sensed flow and return temperatures.

[0011] The microcontroller 22 controls an electronic circuit including a control relay 50 which is connected to the fuel valve in order to ignite the burner 4 and initiate a burn.

[0012] The heating medium is forced to circulate from The FLOW pipe 30, around the radiators or other heating equipment and back to the boiler RETURN pipe, by means of a circulating pump (not shown). The sensors 34 and 38 therefore represent the temperature of the heated and cooled water in an indirect heating system.

[0013] When the boiler's burner operating temperature falls, the thermostat 6 closes, supplying power to the fuel valve, typically at 77C to 79C. When the burner temperature reaches maximum operating temperature, the thermostat opens, typically at 80C to 82C.

[0014] The microcontroller 22 is programmed to impose a calculated delay before allowing the fuel valve 12 to open. The delay is a function of both the ratio of current FLOW temperature to maximum FLOW temperature and a ratio of the current RETURN water and the maximum RETURN temperature.

By calculation of these ratios, for each switching event, the system naturally compensates for seasonal changes or configuration changes in the system, allowing optimum economy and maximum heating when demanded.

[0015] The delay before initiating the burn is dependent on the ratio of the flow and return temperatures to their previous values. The maximum delay is imposed when there is no change in these temperatures. The values are stored in the memory 44 when the thermostat 6 opens indicating that the burner has reached its maximum operating temperature.

[0016] Given: * OPENTIME is the time when the thermostat contact recently opened * FLOW is the current flow temperature, in Celcius * RETURN is the current return temperature, in Celcius * MAXFLOW is the FLOW temperature, recorded at OPENTIME * MAXRETURN is the RETURN temperature, recorded at OPENTIME * CYCLETIME is the recorded time between successive thermostat open operations * HOLDOFF is the calculated delay, in seconds, during which the microcontroller prevents the fuel valve 12 valve from operating.

[0017] HOLDOFF = J -N(1-MAXFLOW/FLOW) -M*(1MAXRETURN/RETURN) [0018] Where J, N and M are integer calibration values: [0019] J is the maximum number of seconds of HOLDOFF in the event that the both FLOW and RETURN temperatures are unchanged from their previous values indicating a dry-cycling risk.

[0020] N is the "gain" or multiplication factor for the flow water temperature sensitivity.

[0021] M is the "gain" or multiplication factor for the return water temperature sensitivity.

[0022] For J of 1200 seconds, typical values of N and M would be in the range 500 to 1000.