Abstract:
A conventional control system for an electrical heating or cooling apparatus has a thermostat 103 which controls a compressor 102 to cycle on and off. For peak load periods, a load shedding signal is sent out by the power company which controls a duty cycler 100 via a radio receiver 101. The duty cycler 100 sets reference ON and OFF times from the last thermostat cycle, and thereupon over-rides the thermostat by preventing the ON time of each cycle from exceeding, and the OFF time of each cycle from being less than, the reference ON and OFF times. To prevent tampering, the reference ON and OFF times may be restricted by preset maximum and minimum values respectively, and reset during a load shed period if the thermostat ON and OFF times fall short of or exceed the reference times respectively. Alternatively, the reference times may be taken from the last thermostat cycle whose times are within preset limits.
Abstract:
A condition control system for e. g. a boiler is responsive to a pressure (or temperature) signal PR to generate an on/off firing signal 22 and a firing rate signal 26, by a proportional control path (via 50) and an on/off path (51). The system operates in 2 modes: proportional (modulating), and cycling, determined by a limit switch signal LS. To minimize the cycling rate when cycling, the system is forced into the lowest fire rate when first fired up; the rate of change of pressure is sensed (at 86) and the signal LS changes the mode to proportional if the pressure falls (indicating that the low fire rate is inadequate). In the proportional mode, integral action (via 57) is used to adjustthe setpoint PSET (via 44) to reach a stable operating state. In the cycling mode, the setpoint PSET is adjusted in dependence on the duty ratio of the cycles.
Abstract:
A conventional control system for an electrical heating or cooling apparatus has a thermostat 103 which controls a compressor 102 to cycle on and off. For peak load periods, a load shedding signal is sent out by the power company which controls a duty cycler 100 via a radio receiver 101. The duty cycler 100 sets reference ON and OFF times from the last thermostat cycle, and thereupon over-rides the thermostat by preventing the ON time of each cycle from exceeding, and the OFF time of each cycle from being less than, the reference ON and OFF times. To prevent tampering, the reference ON and OFF times may be restricted by preset maximum and minimum values respectively, and reset during a load shed period if the thermostat ON and OFF times fall short of or exceed the reference times respectively. Alternatively, the reference times may be taken from the last thermostat cycle whose times are within preset limits.
Abstract:
A condition control system for e. g. a boiler is responsive to a pressure (or temperature) signal PR to generate an on/off firing signal 22 and a firing rate signal 26, by a proportional control path (via 50) and an on/off path (51). The system operates in 2 modes: proportional (modulating), and cycling, determined by a limit switch signal LS. To minimize the cycling rate when cycling, the system is forced into the lowest fire rate when first fired up; the rate of change of pressure is sensed (at 86) and the signal LS changes the mode to proportional if the pressure falls (indicating that the low fire rate is inadequate). In the proportional mode, integral action (via 57) is used to adjustthe setpoint PSET (via 44) to reach a stable operating state. In the cycling mode, the setpoint PSET is adjusted in dependence on the duty ratio of the cycles.