Abstract: A controller having two cascaded PID control loops in the control of unit ventilators of the type which have a heating coil, a fan, and a damper for admitting outside air into a room in which the unit ventilator is located. The controller utilizes the sensed room temperature and a room temperature set point to generate a set point for the temperature of the air being discharged from the unit ventilator, and utilizes the discharge temperature set point and the sensed discharge temperature to control the damper position and the operation of the heating coils of the unit ventilator.

Abstract: A two-stage gas furnace control system automatically shifts into a high fire only mode if, in two consecutive low fire heating cycles a limit switch is tripped to indicate that a gas valve is stuck in a high fire condition. In this way, continued operation is allowed to proceed in a safe manner. Provision is also made to lock out the system from further operation if, while in the high fire only mode, the limit switch is tripped in a predetermined consecutive number of cycles or if, while in a preemptive low fire only mode, the limit switch is tripped.

Abstract: The control system of an induced draft furnace includes a provision for turning on the inducer motor when a flame is sensed outside of the normal sequence of a heating operation. In particular, if the thermostat is in the off position when a flame is sensed, the inducer motor is turned on to ensure that sufficient combustion air is provided to the burner so as to forestall the occurrence of flame roll outs in the event that the gas valve is stuck in a closed position.

Abstract: In a process in which a heating fluid supplied from a furnace is utilized to supply heat to a plurality of processes, method and apparatus is provided for substantially optimizing the operation of the heater by minimizing the amount of the heating fluid which is bypassed around the processes to which the heating fluid is supplied.

Abstract: A dual probe interactive, control system for accurately controlling the temperature within a specified area has a controlling temperature probe located for fast response times and used in association with a controllable setpoint for modulating a heating/cooling source. An indicating/reference temperature probe is also placed in the same enclosure at an optimum location for indicating actual temperature. The actual temperature is compared to the desired temperature to detect any droop or offset and the controllable setpoint is then adjusted accordingly.

Abstract: An integrated, microprocessor-based primary control system for a building heating system. The control system includes in one unit a microprocessor and associated circuitry for (1) establishing the high limit of heat exchanger operation, (2) establishing the low-limit of heat exchanger operation for systems having a summer/winter coil, (3) modulating heat exchanger temperature as a function of outdoor temperature, (4) detecting alarm conditions, providing audio-visual signals while locking out heat exchanger operation in response thereto, and (5) providing an override time period for domestic hot water production in systems having a summer/winter coil.

Abstract: A control apparatus for a fuel fired central heating boiler has a first temperature control circuit including a first thermistor for sensing external ambient temperature and a second thermistor for sensing the temperature of the circulating water produced by the boiler. A second temperature control circuit has a thermistor for sensing the temperature in the space to be heated. A relay is operated by the outputs of the first and second control circuits and itself controls the boiler. The first and second thermistors are connected in series and have different resistance/temperature characteristics so that a given change in the external ambient temperature corresponds to a greater change in the temperature of the circulating water.

Abstract: A method is disclosed for uniformly regulating and controlling the temperature in a multi-level building utilizing a common heat source. Only a single thermostat is required. The thermostat is placed in the room as near the end of the longest conduit and is set at the desired temperature. At least one and possibly a plurality of heating units such as radiators, each having its own output control valve, is placed on each level of the building. After the thermostat has been set at the desired temperature, each valve that controls the various heating unit is individually set. The radiator valve in the room in which the thermostat is located is opened all the way. The remaining valves are opened by a progressively smaller amount in those rooms further away from the thermostat. Once all of the rooms reach the desired temperature the valves are permanently set in order to prevent their unauthorized adjustment.

Abstract: A heating system for a motor vehicle has temperature sensors for gauging the compartment temperature as well as for gauging the temperature of the effluent hot air. These sensors are connected in series, with the compartment sensor generating the more significant control signal. The flow of heating medium, for example engine water, is regulated by a valve under the control of a regulator which compares the sensors signals with a set-point value. The valve may be cyclically actuated by pulses of fixed frequency but having a width which depends on the results of the signal comparison.