Abstract:
A power demand limiting system is disclosed for limiting peak power demand of space conditioning loads adapted to be coupled with an electric utility power supply by space temperature responsive switching means. The system includes timer means for cyclically coupling and uncoupling the space conditioning load with the electric utility power supply through the space temperature responsive switching means, and timer control means for selectively energizing and deenergizing the timer means.

Description:
BACKGROUND OF THE INVENTION 
     Electrical utilities today must have far more capacity for supplying communities and municipalities with power than that normally required. This costly, excessive capacity is needed in order to handle intermittent peak power demands created largely today by space conditioning loads such as air conditioners and electric heaters. Heretofore, electric utilities have only been able to shave these demand peaks by denying service to selected groups of customers for extended periods of time ranging from several hours to several days. To deny any customer electrical power for such periods is, of course, to provide quite a disservice. 
     Accordingly, it is a general object of the present invention to provide improved means for limiting peak power demands of consumers upon electrical utilities. 
     More specifically, it is an object of the present invention to provide power demand limiting systems for limiting peak power demand of space conditioning loads such as air conditioning and electrical heating systems. 
     Another object of the invention is to provide power demand limiting systems of the type described which may be automatically energized and deenergized as conditions effecting demand dictate. 
     Another object of the invention is to provide power demand limiting systems for limiting peak power demand of space conditioning loads of power consumers that may be energized and deenergized by electrical utilities from locations remote from the space conditioning loads. 
     Yet another object of the invention is to provide power demand limiting systems of the type described which may be easily incorporated into preconstructed space conditioning load control circuits. 
     SUMMARY OF THE INVENTION 
     In one form of the invention, a power demand limiting system is provided for limiting peak power demand of a space conditioning load adapted to be coupled with an electric utility power supply through space temperature responsive switching means. The system includes timer means for cyclically coupling and uncoupling the space conditioning load with the electric utility power supply through the space temperature responsive switching means, and timer control means for selectively energizing and deenergizing the timer means. 
     In another form of the invention, a power demand limiting system is provided for limiting peak power demand of a space conditioning load adapted to control the temperature of a designated space. Here, the system comprises a first thermostatic switch operatively responsive to the temperature of air within the designated space in series circuit with a second thermostatic switch operatively responsive to the temperature of ambient air outside the designated space. 
     In yet another form of the invention, a power demand limiting system is provided for limiting peak power demand of a space conditioning load. The system includes circuit means for alternatively coupling the space conditioning load with an electric utility power supply through a thermostatic switch operatively responsive to the temperature of air within the conditioned space, and through both the thermostatic switch and a time cycling switch that includes an actuator driven by a motor coupled with the electric utility power supply through the thermostatic switch. 
     In still another form of the invention, a power demand limiting system is provided for limiting peak power demand of a space conditioning load energizing means coupled with a source of electric power serially through a thermostatic switch operatively responsive to the temperature of the conditioned space, a double throw switch controlled by switch activating means, and a time cycling switch. The switch activating means may include an ambient temperature sensing device or a device that receives signals generated by the utility through conventional radiowave, microwave or transmission line ripple sensing means. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING 
     FIG. 1 is a block diagram of a power demand limiting system embodying general principles of the present invention. 
     FIG. 2 is a block diagram in more detail of a power demand limiting system embodying principles of the invention. 
     FIG. 3 is a circuit diagram illustrating other principles of the invention in a preferred form. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 a space conditioning load is seen to be coupled with an electric utility power supply through a conventional space thermostat and also through a time cycling switch. In this manner, activation of the thermostat serves to energize the space conditioning load only periodically in view of the presence of the time cycling switch. This system therefore serves to prevent the space conditioning load from continuously demanding power from the electric utility power supply. With such limiting systems incorporated into hundreds or thousands of consumers&#39; space conditioning load control circuits, their aggregate peak demand on the utility power supply is substantially reduced so long, of course, as the multitude of time cycling switches are not synchronized. 
     In FIG. 2, a power demand limiting system embodying principles of the invention is shown for limiting peak power demand of an air conditioner adapted to cool air within a selected space generally insulated from ambient air. The air conditioner is seen to be conventionally coupled with an electric utility power supply through a thermostatic switch Sn controlled by a space temperature responsive actuator sensitive to the temperature of air within the conditioned space. However, here it will again be seen that the air conditioner is also controlled by a time cycling switch Sx which is periodically placed operatively into the air conditioner control circuit by an ambient temperature responsive actuator. 
     The ambient temperature responsive actuator may take the form of a conventional thermostat mounted outside the house as in a meter box or on a utility pole. In this manner, once ambient temperature becomes quite elevated, as on a hot summer afternoon, the exterior thermostat places the time cycling switch Sx on line, limiting the duty cycle of the air conditioner. Since the precise time at which the exterior thermostat actuates the timer will vary from one customer, or group of customers proximate one another to another, the time cycling switches of all customers of the electric utility will not be synchronized. Thus, at any one time, some of the customers&#39; switches Sx will be closed, thereby energizing their air conditioners, while others will be opened deenergizing their units. This causes the aggregate demand placed upon the utility to be vastly diminished. With relatively short switch cycle times, such as 15 to 30 minutes, the discomfort occasioned by periodic, short-term loss of air conditioning or heating can be rendered quite tolerable for most customers. 
     In FIGS. 1 and 2 the system is shown in highly schematic form for clarity. Thus, no distinction is here made between the load control and load power supply circuits. In FIG. 3, however, an actual control circuit is diagrammed in detail which may be used in practicing the invention. Here, an air conditioner energizing coil Rc is seen to be connected across the secondary coil of a step down transformer T having its primary winding coupled with line voltage serially through a conventional thermostatic switch Sn controlled by the temperature of air within the conditioned space and a double throw switch Sy. With switch Sy in the position illustrated by the solid line, power to the load energizing coil Rc is controlled solely by the conventional indoor thermostatic switch Sn. With switch Sy thrown to the other position here illustrated in broken lines, motor M is energized to drive a cam RC which cyclically operates a microswitch Sx whereby energy to coil Rc is supplied serailly through switches Sn, Sy and Sx. For relay Rc to be then energized, not only must the conventional or &#34;indoor&#34; thermostat be positioned on, but the time cycling switch Sy must also be momentarilly in an &#34;on&#34; position. The double throw switch Sy may be controlled by an exterior thermostat as shown in FIG. 2, or it may be alternatively operated directly by the utility through conventional radiowave, microwave or transmission line ripple signals. For these alternatives, switch Sy is, of course, directly controlled by an appropriate radio received or ripple sensor. 
     An example of such radio controlled device is the &#34;Peak Load Deferral System&#34; , Model 800W, manufactured by Motorola, Inc. The ripple sensor equipment can be obtained from Landis and Gyr of New York and Zellweger-Uster Ltd. of Charlotte, N.C.; both companies call their equipment the &#34;Load Management System&#34;. 
     If an ambient temperature response actuator is utilized in the present invention, the actuator should be located remote from any temperature generator, such as the heat generated by homes with poor attic ventilation and poor wall construction. That additional heat, plus the heat from motor M, can give the actuator a false temperature reading. 
     It should be understood that the above described embodiments merely illustrate principles of the invention in preferred forms. Many modifications, additions or deletions may, of course, be made thereto without departure from the spirit and scope of the invention as set forth in the concluding claims. It should also be understood that space conditioning loads and their energizing devices, such as coil Rc, for example, are herein used interchangeably since any decision as to utilization of the load control circuitry and its associated voltage level itself or undependent power and control circuits is merely a matter of design choice predicated essentially on load power requirements.