Note: Descriptions are shown in the official language in which they were submitted.
POWER DEMAND LIMITING SYSTEM
BACKGROUND OF THE INVENTION
Electrical utilities today must have far more capacity
for supplying communities and municipalities with power than
that normally required. This cos-tly, 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 specifieally, it is an objeet 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 automatieally energized and deenergized as conditions
effecting demand dietate.
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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 ~he 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
The invention contemplates a method of limiting power
demand of a plurality of space conditioning loads adapted to
be coupled with an electric utility power supply and the
method comprises the step of interposing a space temperature
responsive switching means including a timer means, and a
timer control means for selectively energizing and deenergizing
the timer means between each of the loads and the power supply
during periods of relatively high power demand to provide the
unsynchronous, cyclical coupling and uncoupling of the loads
with the supply.
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 swltching 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 deenergi~ing the timer
means.
In another form of the invention, a power clemand
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 svstem is provided for limiting peak power
demand of a space conditioning load. The system inc].udes
circuit means for alternatively coupling the space conditioning
load wi.th an el.ectric utility power supply through a the.rmostatic
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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 limi-ting 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.
BRI_ DESCRIPTIOrJ OF THE FIGURES OF THE DRAWING
Figure 1 is a block diagram of a power demand
limiting system embodying general principles of the present
invention.
Figure 2 is a block diagram in more detail of
a power demand limiting system embodying principles of
the invention.
Figure 3 is a circuit diagram illus-trating other
principles of the invention in a preferred form.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In Figure 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. ~ith such limiting systems incorporated
into hundreds or thousands of consumers' 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 Figure 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
temeprature responsive actuator~
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The ambient tempexature 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, llmiting the
duty cycle of -the air conditioner. Since the precise time
a-t 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' switches
Sx will be closed, thereby energizing their air conclitioners,
while others will be opened deenergizing their uni-ts.
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 Figures 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 Figure 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 VL
serially through a conventional thermos-tatic switch Sn
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controlled by the tem~,erature 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
ener~ized to drive a cam RC which cyclical].y operates a micro-
switch Sx whereby eneray to coil Rc is supplied serially
through switches Sn, Sy and Sx. For relay coil R to be then
energized, not only must the conventional or "indoor" thermostat
be positioned on, but the time cycling switch Sy must also be ~ ;
momentarily in an "on" position. The double throw switch Sy
may be controlled by an exterior thermostat as shown in Figure
2, or it may be alternatively operated directly by the
utility through conventional radiowave, microwave or trans-
mission 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 a radio controlled device is the
"Peak Load Deferral System", 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,
North Carolina; both companies call their equipment the
"Load Management System".
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If an ambient temperature response actuator is
utilized in the present inven-tion, 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 addit.ional heat, plus the heat
from motor M, can give the actuator a false temPeratUre
reading.
It ihould 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 anv decision as to
utilization of the load control circuitry and its associated
voltage level itself or independent power and control circuits
is merely a matter of design choice predicated essentially
on load power requirements.
