Abstract: An activity zone of a house is selectively isolated with respect to a sleeping zone during nighttime intervals by selectively blocking the flow of conditioned air into the activity zone, while allowing the usual flow of conditioned air into the sleeping zone. The air flow passage in each supply duct is blocked by an inflatable air bladder disposed within the air flow passage. An air compressor is coupled to the bladder for inflating it to cause it to expand against the sidewall of the duct and seal the air flow passage during the isolation mode of operation, and for drawing air from the bladder to cause it to collapse and open the air flow passage during the conditioned air supply mode of operation.

Abstract: A system for determining the optimum stop time of an air conditioning system within a building so that energy can be conserved by shutting down the temperature control system an amount of lead time prior to end of occupancy of said building wherein said amount of lead time is arranged to confine space temperature within a comfort range as said space temperature drifts during said amount of lead time, said system including a space temperature sensor for sensing space temperature within the building, an outdoor air temperature sensor for sensing outdoor air temperature external to the building, and a controller connected to the space temperature sensor, the outdoor air temperature sensor and the temperature control system for determining temperature drift rate within the building and for turning off the temperature control system before the end of occupancy of the building by an amount of lead time dependent upon the temperature drift and the outdoor air temperature.

Abstract: An energy management controller is coupled via a clock line pair, a "data out" line pair and a "data in" line pair, to a plurality or group of stations each having energy using equipment. Each station is electrically coupled to each line pair at spaced points along the line pairs. Each station counts the number of clock bits from the controller. After each group of a predetermined number of clock bits are received, each station provides an address count that is incremented by one after each group of clock bits are received. By setting each station to a different address count and enabling each station to transmit and receive data only during its respective address count period each station can be individually accessed by the controller without specifically addressing each station. During the address count period for each station serial bits are transmitted to and received from that station by the controller for actuation and control of the energy using equipment for that station.

Abstract: A two wire rechargeable battery powered electric time controlled thermostat apparatus adapted to be connected by two wires to a source of alternating current voltage and control apparatus for controlling the supply of temperature condition medium to the space wherein the thermostat is located with a rectifying circuit means in the thermostat apparatus for recharging the battery from the source over the two wires.

Abstract: A programmable electronic thermostat for use in a building having a furnace and an air conditioning system adapted to generate energizing signals for the furnace and the air conditioner. An operator programs the thermostat with a series of desired temperatures over a repetitive heating or cooling cycle. During the winter, relatively high temperatures will typically be programmed during the period when the building is occupied and relatively low temperatures during unoccupied periods. The thermostat includes a clock that interrogates the program to generate the desired temperature for the present time which is compared to the measured temperature within the building to generate control signals for the furnace. In order to energize the air conditioning system during occasional periods of occurrence of high temperature, a control temperature is derived for the air conditioner.

Abstract: An electronic thermostat for controlling multiple temperature altering apparatus of an animal enclosure or the like employs a linear sensor comprised of an elongate black body, tubular probe containing a semiconductor active element of a current source which produces a sensor current that varies linearly with changes in temperature. A voltage divider to produce a plurality of temperature sensor signals which are used to produce primary of override actuation signals. The set temperature signal is selectable between two set point limits which are selectively variable to calibrate different scales. A plurality of detectors respectively compare the plurality of sensor signals with a common set temperature reference signal to produce a plurality of detection signals at a plurality of preselected temperatures associated therewith.

Abstract: A clock operated thermostat having both automatic heat-cool changeover and optimum start is disclosed. Programs for the optimum start and automatic changeover are incorporated in a microcomputer based clock thermostat and eliminate any possibility that a homeowner can inadvertently program a sequence that would cause a conflict between the heating and cooling equipment.

Abstract: An electronic thermostat utilizing a switched power supply which operates either from a voltage appearing across an open circuit at a heater or air conditioner activation circuit (de-energized state) or from a current flowing in the activation circuit upon short circuiting (energized state) of the activation circuit. The power supply provides an uninterrupted source of power to the electronic thermostat which controls the source of input power to the power supply in addition to the state of the activation circuit. The electronic circuit implements a piecewise linear, with hysteresis loop discontinuity, control function.

Abstract: A conventional hot water heating system generally of the type for heating water in multiple units of hotels, motels, schools and the like and using any heating medium has a processor and control assembly which is operationally connected to at least a water temperature sensing means and a heating control means thereof. The processor and control assembly divides the time into exact time periods, say one-half hour, and the time periods are grouped into a group of consecutive time periods, say a week. Taking any individual time period, the time periods are checked around the time period which the present time period is a repeat and time periods directly preceding the present time period, and the operational water temperature for the present time period is chosen, as well as the amount of heat required to maintain the water at that temperature on a percentage basis of heating taken from one hundred percent.

Abstract: An electro-optical display in a programmable electronic thermostat includes a plurality of selectively energized display elements which cooperate with a 24-hour time indicia to provide a continuous visual display of the time periods during which a specific programmed space temperature is to be maintained.

Abstract: A sheet metal enclosure is used for spray painting automobiles and for heat curing the paint. A fan draws filtered air through the enclosure. An air supply permits spray painting. Quartz tube radiant heaters are mounted flush with the interior walls of the enclosure for heating the painted vehicle. A safety interlock prevents simultaneous enablement of the sprayer and heaters. Further, there is a first time delay before the air supply is enabled to assure that the heaters are cool before spraying paint, and a second time delay before the heaters are energized to permit the fan to exhaust paint fumes before applying heat.

Abstract: An adaptive control system uses a controller for controlling an air temperature treatment apparatus at a reduced energy consuming level during periods of non-occupancy of a building and for energizing the air treatment apparatus before occupancy so that a desired internal building temperature is reached by a time of occupancy.

Abstract: A clock operated thermostat that provides setup temperature from an energy saving temperature is disclosed. The amount of overshoot caused in the space in which the thermostat is installed is measured, and a constant in the operation of the thermostat is corrected. The correction continues to occur each time a setup occurs until the overshoot has been reduced to an acceptable level.

Abstract: A zone control apparatus for central heating and/or cooling systems having a central fluid heating and/or cooling plant and conduits for directing the heated or cooled fluid to the rooms in a house or other building being serviced by the system. The zone control apparatus comprises one or more flow control devices operatively associated with respective fluid conduits in the central heating and/or cooling system, and a cycle controller for cycling the flow control device or devices between high and low (or no) flow conditions at times strategically selected to correspond to periods of high and low use of the room or rooms with which the flow control devices are respectively associated. Accordingly, the apparatus operates automatically to eliminate unnecessary heating or cooling of individual rooms or zones during cyclical periods of low or no use whereby substantial energy savings and other benefits may be obtained with minimal compromise in comfort.

Abstract: There is disclosed a control apparatus for operating any one of a plurality of parallel connected boilers as a lead boiler, with the others operating as lag boilers. The control apparatus enables a lag boiler to assist the lead boiler during a prolonged operating period to share the burden and the therefore prolong equipment life and increase system efficiency. The control apparatus enables each boiler to serve as the lead boiler while employing full modulation, other boilers such as the lag boiler also employ full modulation. The control apparatus also causes an automatic switch over between boilers after a malfunction of one of the boilers in a rapid time.

Abstract: A sub-base for use in conjunction with thermostats for controlling air conditioned spaces includes a false heat device and a radio frequency receiver and control circuit for turning on and off the false heat device to provide temperature setback control for the thermostat. The sub-base may be mounted between the thermostat and the existing wall mounting structure and is adapted to be connected to the thermostat control conductors for a source of power for the sub-base and to receive radio frequency signals transmitted over the thermostat conductors.

Abstract: An electric device for monitoring the usage of equipment that is being shared by one or more entities or individuals during a predetermined schedule and that needs to be made available to any one of these entities or individuals outside that schedule. The device includes timing means programmable for any schedule and capable of activating complementary relays, one of them a normally open and the other one a normally closed. The contacts of one of these relays being connected to a suitable point in the equipment being shared so that its operation may be interrupted or turned on. A plurality of second relay means, one associated with each one of the entities, are also connected to that point in the equipment so that each entity may be able to connect the equipment. Also, there is an elapsed time meter associated with each one of those second relay means so that the time that the equipment is used, outside the predetermined schedule, by a particular entity may be measured.

Abstract: A multizone control system utilizes a series of timers to ensure that all of the heat supplied to the system is utilized. Timers are used to control transfer of heat from the temperature modifying plant to the zones. The timers are further arranged to bring "on" additional heat to the heat anticipator of the zone of lower demand thereby tending to synchronize the operation of zones and allow for more efficient supply of the heat exchange medium throughout the areas being controlled.

Abstract: A domestic hot water heating system which disables the normal aquastat during set-back periods where the temperature of the water source is sensed at the output manifold and the temperature of the water also is sensed a predetermined distance along the manifold to determine a demand or lack of demand for hot water. The system will enable the aquastat during a set-back period when demand is made and disable the aquastat when there is no longer a demand.

Abstract: A temperature measuring system which includes a CR oscillator circuit and a logarithmic transformation circuit. The CR oscillator circuit employs at least a thermistor as the resistance element for forming a time constant with a capacitor which serves as the capacitance element, the oscillation frequency of the oscillator circuit varying with a change in ambient temperature. The logarithmic transformation circuit subjects the information obtained from the CR oscillator circuit to a logarithmic transformation, whereby said information is logarithmically compressed to provide numerical data approximately dependent upon ambient temperature.

Abstract: Energy saving temperature and humidity sensing and control processes, system and apparatuses operate effectively in response to signals received from occupants and to dynamic responses of building and its heating, ventilating and air conditioning system. The disclosed processes, apparatuses and system utilize thermostats equipped with a drift ramping and hold time to save energy; the thermostats only need resetting to a neutral/comfort set point which is accomplished by means of a push button or touch plate.The disclosed systems are pre-programmed and set so that occupants will be confortable although the temperature within the building drifts because the rate of drift is controlled to a gradual and normally unnoticed change.

Abstract: An analog computing circuit which controls a boiler or other heating system in a building, has a timer actuated setback which reduces the temperature of the building at night in such a way that as the ambient temperature approaches the lowest temperature in the temperature range for which the heating system is designed, the magnitude of the temperature drop in the building approaches zero. The analog computing circuit includes a timer actuated boost which is timed to start at a fixed time each morning. The boost causes the heating system to supply heat to the building, after the temperature in the building has been reduced the previous night, at a rate sufficient to raise the temperature of the building to its design level by a predetermined time in the morning.

Abstract: Apparatus for controlling a water heater thermostat for increased efficiency in fuel usage. A mounting bracket is adapted to fit on several different common types of thermostat control boxes. In one embodiment the bracket removably receives a controller housing. In another embodiment the mounting bracket and the controller housing are a unitary structure. A motor in the housing is coupled to a slip ring engaging the thermostat knob to raise and lower the thermostat temperature setting in accordance with sensor actuated circuitry responsive to incoming and outgoing water temperature. The coupling enables the apparatus to accommodate thermostats with different size knobs and rotatable in opposite directions, in addition to coupling to various size thermostat housings.

Abstract: Apparatus for controlling a water heater thermostat for increased efficiency in fuel usage. A mounting bracket is adapted to fit on several different common types of thermostat control boxes and to removably receive a controller housing. A motor in the housing is coupled to a slip ring engaging the thermostat knob to raise and lower the thermostat temperature setting in accordance with sensor actuated circuitry responsive to incoming and outgoing water temperature. The coupling enables the apparatus to accommodate thermostats with different size knobs and rotatable in opposite directions.

Abstract: A control device for controlling temperature conditioning apparatus is connected to a thermostatic switch means having a circuit requiring a small current to maintain the circuit active during the open cycle of the thermostat switch means. A positive temperature coefficient resistor is placed in parallel with the input circuit of the control device to provide a low input impedance to the control device for maintaining the small current without activating the control device. During the operation of the thermostat with the switch closed, a larger current to the positive temperature coefficient resistor causes the resistor to increase in temperature and thus its impedance so the wattage dissipated by the PTC resistor is reduced to minimize the heat dissipation and thus the temperature of the control.

Abstract: A zone control apparatus for central heating and/or cooling systems having a central fluid heating and/or cooling plant and conduits for directing the heated or cooled fluid to the rooms in a house or other building being serviced by the system. The zone control apparatus comprises one or more flow control devices operatively associated with respective fluid conduits in the central heating and/or cooling system, and a cycle controller for cycling the flow control device or devices between high and low (or no) flow conditions at times strategically selected to correspond to periods of high and low use of the room or rooms with which the flow control devices are respectively associated. Accordingly, the apparatus operates automatically to eliminate unnecessary heating or cooling of individual rooms or zones during cyclical periods of low or no use whereby substantial energy savings and other benefits may be obtained with minimal compromise in comfort.

Abstract: The present invention relates to a method and to apparatus for regulating a heating installation in a premises comprising a plurality of heating generators. The apparatus comprises temperature probes (10, 20, 140) which are sensitive to the outside temperature, to the inside temperature, and to the departure temperature of the heating fluid leaving the heating generators. The apparatus further includes means (50, 60, 70, 80 and 100) for determining a reference temperature on the basis of a set temperature (Tc) as indicated by a setting unit (30). A proportional-integral regulator (120), sensitive to the difference between the reference temperature and the departure temperature of the fluid, generates a signal which is applied to threshold detectors which detect the passage of said signal through successive predetermined thresholds, thereby generating successive signals for bringing into service the corresponding heating generator.

Abstract: An apparatus for actuating the temperature setting means of a water heater is provided with a drive motor (2) adapted to move the temperature setting means from a low to a high temperature setting and vice versa. The drive motor (2) is connected to a power supply through a switching means (14). The switching means (14) is operable by a programmable timer (15) in such a manner that the temperature setting means is set on a high temperature only during at least one desired period.

Abstract: The assembly comprises a heat emitting element located in a thermostat and an electrical circuit for selectively energizing and deenergizing said element by means of local control or remotely activated circuitry. The assembly has means for allowing varying amounts of predetermined current to be conducted through said element. This allows for an unlimited variety of control over the amount of heating or cooling provided through direct or remote operation as specifically desired by the operator of the system.

Abstract: A heating system is controlled in response to the external temperature in accordance with a heating curve in which the external temperature is related to the advance heating temperature of a fluid used in heating the space. According to the invention, the heating curve is optimized automatically by approximating it with a heating curve equation having at least one parameter which is calculated at least in part from measured instantaneous values of the advance heating temperature, the external temperature or the room temperature, or values representing temperature differential such as the difference between the external temperature and the room temperature and the difference between the room temperature and the advance heating temperature. From these values, a parameter of the heating curve equation is calculated by an estimation method, e.g.

Abstract: An activity zone of a house is selectively isolated with respect to a sleeping zone during nighttime intervals by selectively blocking the flow of conditioned air into the activity zone, while allowing the usual flow of conditioned air into the sleeping zone. The air flow passage in each supply duct is blocked by an inflatable air bladder disposed within the air flow passage. An air compressor is coupled to the bladder for inflating it to cause it to expand against the sidewall of the duct and seal the air flow passage during the isolation mode of operation, and for drawing air from the bladder to cause it to collapse and open the air flow passage during the conditioned air supply mode of operation.

Abstract: An adaptive optimum start/stop controller for controlling an air treatment apparatus at a reduced energy consuming level during periods of non-occupancy of a building and for energizing the air treatment apparatus before occupancy so that the building is comfortable by occupancy, the controller including a temperature sensor for sensing space temperature within the building, a controller responsive to the temperature sensor and to real time for determining optimum start/stop times so that the building is controlled at energy conservation levels during non-occupancy and comfortable levels during occupancy, the controller adjusting the optimum start/stop times based upon the accuracy of prior start/stop times, and a communication channel for connecting the controller to the air treatment apparatus.

Abstract: An apparatus for increasing the efficiency of a conventional central space heating system is disclosed. The temperature of a fluid heating medium is adjusted based on a measurement of the external temperature, and a system parameter. The system parameter is periodically modified based on a closed loop process that monitors the operation of the heating system. This closed loop process provides a heating medium temperature value that is very near the optimum for energy efficiency.

Abstract: The supply of energy in response to thermostat demand, to heating and cooling equipment is reduced by intermittent interruption during demand intervals and prolonged intermittently upon cessation of demand in accordance with the duration of such demand intervals pursuant to memory stored heating and cooling sequences of power interruption cycles. Sensors detect the presence and absence of energy demand to time the duration of the demand intervals and control the intermittent interruption in the supply of energy for energy saving purposes.

Abstract: A hot water control system for providing necessary hot water to a structure at optimum energy saving conditions includes a programmable control system for selectively programming preselected quantities of hot water at preselected time periods over a given interval of time and includes a mode selector for selectively overriding the control system to permit adjustment of the system to meet unscheduled changes in demand. The system includes mode selectors for selecting the programmed mode wherein predetermined supplies of hot water are available at predetermined time periods over a seven day period or the like and other modes may be selected such as pilot only operation, normal service wherein the water heater operates in its normal manner, pilot off or complete shutdown of the system for periods of time such as for vacation and the like.

Abstract: A time-controlled heat regulator has the capability of controlling a heat supply so as to lower the temperature of a heated area during nighttime and to increase the supply of heat in dependence upon outside temperature to begin raising the temperature of the heated area in advance of a point in time at which the heated area is desired to attain a specified temperature. The heat regulator has a time-controlled variable resistor interconnected in a bridge circuit, the variable resistor being cut into the circuit at the beginning of a longest chronologically possible heat-up phase dependent on the outside temperature. The resistance of the variable resistor changes over time until reaching coincidence with the resistance value of an outside temperature sensor. The length of time of the heat-up phase is thus dimensioned backwardly from the time of reaching the desired area temperature as a function of the prevailing outside temperature.

Abstract: The thermostat of the present invention includes a sensor for providing a signal representative of the actual temperature within a space. A microcomputer is coupled to the sensor and intermittently utilizes power at a first level when in an operating state for controllably generating output signals in response to the temperature signal. The microcomputer is adapted to be connected to a battery as a sole power source therefor. An isolating interface device such as an electromagnetic relay is coupled to the microcomputer and is adapted for connection to temperature-affecting equipment such as a heating or cooling system controller. The relay actuates the equipment in response to output signals from the microcomputer. A voltage detection circuit may optionally be provided for signalling a low battery voltage condition.

Abstract: A device for incorporation into the power supply circuit of an electrical apparatus comprising (a) a switch which is movable from one condition to another on application of power to the switch and which is held in the moved condition, as long as power is applied to the switch; (b) a signal emitter adapted to emit a power signal of short duration and being connected to the switch so that on emission of the power signal the switch will be moved to the other condition for the duration of the power signal; and (c) a current detector capable of detecting when a current flows in a line and being connected to the switch to supply power thereto when current flows in the line. The current detector may be a light emitting diode (L.E.D.) and a light detector arranged to transmit current to a relay switch coil which is electrically connected to the line by a current transformer.

Abstract: A heating system, such as a gas fired or oil fired furnace, is operated by a control system which includes a low voltage AC power supply, a low voltage thermostat for sensing the temperature in the space to be heated and a solenoid controlled relay or fuel supply valve. The control system also includes a low voltage pulsation device which is connected in series with the thermostat and solenoid and is effective, when the thermostat closes, to pulsate or cycle the solenoid causing the heating unit to be turned on and off for supplying heat in increments to the heat exchanger within the furnace. The pulsation device is adapted to be quickly and easily installed in the low voltage control circuit for the heating unit or for a cooling unit.

Abstract: A single evaporator refrigerator-freezer is controlled for operation in three modes, wherein cooling of the refrigerator compartment is initiated in a first mode by operating only an evaporator fan to cool the compartment. During the first mode, the rate of temperature change within the refrigerator compartment is calculated at predetermined time intervals and if the calculated rate is positive for at least a minimum number of time intervals, a second mode is initiated by operating a compressor to cool the refrigerator compartment. A third mode, wherein the compressor is operated to cool the freezer compartment, is initiated only after the refrigerator compartment has been adequately cooled. Means are further provided for modulating the flow of refrigerant to the evaporator to allow the evaporator to be operated at a higher temperature and pressure during cooling of the refrigerator than during cooling of the freezer.

Abstract: In this thermal system there is a central plant feeding a plurality of adjustable zone regulators which bring their respective zones to corresponding target temperatures. The system has a controller including a plurality of temperature sensors. The sensors are distributed one to a zone. Each of the sensors can produce a zone signal signifying zone temperature. The controller also has a plurality of zone actuators, each having a zone control terminal. Each of the actuators can, in response to a signal at its zone control terminal, adjust a corresponding one of the zone regulators. Also included is a control subsystem that is coupled to each of the temperature sensors and to the zone control terminal of each of the zone actuators. The control subsystem can start the central plant in response to a predetermined function of the zone temperature errors with respect to their respective target temperatures exceeding a given limit.

Abstract: The invention relates to a ventilating and heating apparatus for rooms of particularly high headrooms. It comprises one or more air-heating units and one or more room heating units. A feature of the apparatus is that the room is equipped with ventilating openings directed to the sojourn space of the room, injecting in summer and drawing in winter as well as with ventilating openings directed to the space under the ceiling, injecting in winter and drawing in summer.

Abstract: A system of determining optimum start/stop times for HVAC equipment in a building utilizes quantized inside and outside air temperature values as the controlling data input. Lead-times necessary to achieve the desired control temperatures, given input and output temperature levels are stored in a matrix in a central processor storage. System performance is monitored and results are used to modify the lead-times so that the operating system can more closely achieve the desired results.

Abstract: The invention disclosed herein is a temperature dependent duty cycler control system which provides a duty cycle off time locus responsive to a sensed temperature and is characterized by two selectable off time periods which are connected by slope controllable ramping functions. The system also includes means for coordinating operation of several heating and/or cooling units by making real time determinations of the most efficient average number of units which should be running at a given time and by maintaining a priority order of rotation of the units available to be shed.

Abstract: A control system for a low mass hydronic boiler is disclosed which includes a sensor for measuring the temperature of the fluid exiting the boiler. The level of fuel flow provided to the boiler is reduced when the water temperature exceeds a predetermined high temperature limit. The level of fuel flow provided to the boiler is increased only after the water temperature has decreased below a predetermined reset temperature limit and a predetermined interval of time has elapsed.

Abstract: A duty cycling switch for use with a furnace which mounts onto the exterior wall of the furnace plenum and opens and closes in response to the temperature of the plenum wall. The switch is adjusted to deactivate the burner when the plenum wall heats up to a temperature caused by the continuous operation of the burner for a predetermined period of time. The duty cycling switch acts to reactivate the burner when the plenum cools down below this temperature. A duty cycling switch for use with an air conditioner is also disclosed which mounts onto the plenum wall and opens and closes in response to the temperature of the plenum wall. It is adjusted to deactivate the compressor of an air conditioner unit when the plenum wall cools down to a temperature caused by continuous operation of the compressor for a first predetermined period of time and reactivates the compressor after the plenum wall exceeds this temperature. The furnace duty cycling switch is preferably an adjustable bimetal switch which opens on rise.

Abstract: An electronic multiple-setback thermostat for residential and commercial use includes an internal clock having a week-long cycle. The thermostat is programmed by the operator, usually manually actuable input devices, to control the furnace/air conditioning system to achieve a schedule of temperatures over the weekly period by simply inputting the temperature desired to be attained at the time of entry. Each temperature entry may be programmed to reoccur on a daily basis or to modify the program on a once-a-week basis. The thermostat employs an internal clock which controls memory addresses so that each memory location is representative of a short time period during the weekly cycle. A desired temperature signal is entered in a memory location determined by the clock state at the time of entry and is read out to the control system each time that time state reoccurs.

Abstract: A liquid temperature control apparatus controllably heats a liquid from a temperature before a control to a desired reference temperature by varying the magnitude and/or application time period of a power for energizing a heater on the basis of a difference between a voltage corresponding to the actual temperature before a control and a reference voltage corresponding to the reference temperature. The parameter on which the magnitude and/or application time period of the heater power is to be based may be the sum of a first voltage differential between a voltage corresponding to the actual temperature before a control and the reference voltage and a second voltage differential between a voltage corresponding to an actual temperature after the start of a control and the reference voltage.

Abstract: A method and apparatus for controlling the temperature of a space. The actual heat load for a space under the conditions prevailing at a time is determined based upon information available to a temperature sensor. The average heating/cooling percentage rate for relatively short duty cycles is adjusted based on this information whereby the actual heating/cooling load during this duty cycle interval may be approximately matched. The percentage rate may be overridden in the event an abnormal temperature situation exists. The method and apparatus of this invention has particular application when utilized with radiant heaters.

Abstract: A duty cycle controller for an air conditioning system. Solid state switches are connected in series with the heating and cooling switches of a thermostat in circuits for energizing the cooling and heating subsystems, respectively, of an air conditioner. A switch control circuit, when enabled, causes the solid state switches to be conductive when set and nonconductive when reset. Timing signals from a counter applied to the switch control circuit determine the state of the switch control circuit and thus the duty cycles for the heating and cooling subsystem. The controller is provided with a safety circuit which disables the switch control circuit to render the solid state switches nonconductive for a predetermined period of time after a power interruption or after a cooling or heating switch of the thermostat opens. The controller assures that each heating and cooling duty cycle begins with a full energization period. The length of the heating and cooling duty cycles can be readily varied.