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| United States Patent | 4177795 |
| Link to this page | http://www.wikipatents.com/4177795.html |
| Inventor(s) | Schultz; Robert T. (1021 Cliff Dr., Santa Barbara, CA 93109) |
| Abstract | A device, and controlled solar heating system incorporating the device, for
providing an electrical control signal responsive to the rate of flow of
species of radiant energy through an area. The device includes means for
providing an electrical input signal responsive to the rate of flow of the
species of radiant energy, such as solar energy, and an electrical circuit
for receiving the input signal and for providing a control signal in
response to the input signal. Solar cells may provide the input signal to
a Schmidt Trigger Circuit set to provide two control signals at
predetermined rates of solar energy flow through an area. The device,
incorporated into a solar heating system, may be used to control the
circulation of fluid through solar heating panels. |
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Title Information  |
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| Publication Date |
December 11, 1979 |
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| Filing Date |
August 11, 1977 |
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Title Information |
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Description |
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BACKGROUND OF THE INVENTION
A. Field of Invention
The invention relates to solar heating systems and to devices for sensing
the availability of energy and for providing control signals in response
thereto.
B. Description of Prior Art
Solar heating systems which utilize solar heating panels for absorbing
solar energy and transferring the energy to a fluid being circulated
through the panels are common. Such systems in general require a device
for sensing whether or not sufficient energy is available to obtain a
transfer of energy in the desired direction and to justify the expenditure
of energy in the circulation of the fluid.
Indirect methods and devices employing such methods for sensing the
availability of sufficient energy and controlling circulation based on
such sensing are in common use. Typical examples are methods and devices:
(1) dependent upon the sensing of the temperature of the fluid in the
heating panels or the differential temperature between the fluid in the
panels and in a storage tank (or at a position in a storage tank) or
similar location; and (2) dependent upon the sensing of the air
temperature near a solar heating panel or the differential air temperature
between a position near the solar heating panel and a position in or near
the location where heating is desired.
Sensing and means for sensing the availability of solar energy in a solar
heating system is broadly disclosed in Wright U.S. Pat. No. 3,906,928,
along with very elementary circuitry; however, the specific embodiment for
a sensor which is disclosed apparently is a temperature sensing device--a
thermal switch. The use of photosensitive devices in units using solar
heat is disclosed in Minnick U.S. Pat. No. 3,981,295 and Harris, Jr. et al
U.S. Pat. No. 3,620,206.
Electrical circuits for providing control signals in response to
temperature are used in various applications, as shown for example in
Futaki U.S. Pat. Nos. 3,583,224, Gardner et al U.S. Pat. No. 3,413,438 and
Enders U.S. Pat. No. 3,436,564.
SUMMARY OF THE INVENTION
A triggering device for providing an electrical control signal responsive
to the rate of flow of species of radiant energy through an area. The
device includes means for providing an electrical input signal responsive
to the rate of flow of the species of radiant energy through the area and
an electrical circuit for receiving the input signal and for providing a
control signal in response to the input signal. The device may use solar
cells for sensing and providing an input and a Schmidt Trigger Circuit for
receiving the input and for providing a control signal. A solar heating
system, including solar heating panels, means for circulating the fluid
through the panels and means for switching on and off said circulation,
may incorporate the device as a control for the means for switching.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of a controlled solar heating system in
accordance with the invention.
FIG. 2 is a graph of typical current versus voltage curves for a solar cell
at various rates of flow of solar energy per unit area, and a graph of a
typical load line connected across the solar cell.
FIG. 3 is a schematic circuit diagram of a triggering device in accordance
with the invention incorporated into the system of FIG. 1.
DETAILED DESCRIPTION
Key elements of a controlled solar heating system 10 in accordance with the
invention, shown in FIG. 1, include: a number of solar heating panels 12;
a means 18 for sensing the rate of flow of solar energy through an area in
the vicinity of the panels; a storage tank 14 with, when the system is in
operation, the hottest fluid near the top; a pump 16 for pumping fluid
through the panels, storage tank and pipes 17; a triggering circuit,
represented by the blocks designated 20 and 22, responsive to the sensor
means; and a switch 24 for turning on and off the pump in response to the
control signals from the triggering circuit 20 and 22.
Apart from the operation of the sensor means 18 and triggering circuit,
represented by the blocks 20 and 22, said sensor means and triggering
circuit together comprising a triggering device, the operation of the
heating system can be readily perceived from FIG. 1. A fluid, in the form
of cold water, can be introduced into the circulation system through an
input valve 26 connecting said system to an external source, such as a
city water system. Heated water can be removed from the circulation system
for use through an output valve 28 for removing water from near the top of
the storage tank 14. When the switch 24 is closed, water circulates
through the panels 12 as well as through the remainder of the circulation
system. When the switch is open, the pump is not in operation, and the
circulation, for the purpose of transferring energy from the sun to the
water, is not operative.
The triggering circuitry, in the blocks 20 and 22, provides a control
signal in response to the output of the means for sensing 18. In the
embodiment of FIG. 1, the sensing means 18 employs solar cells as the
sensing element.
A solar cell is essentially a photodiode with no bias voltage applied
across it. Typical voltage versus current characteristics for a solar
cell, at various rates of input of solar energy per unit area (measured at
a cell surface for receiving the energy) are shown in FIG. 2. Also shown,
is a voltage versus current characteristic for a typical resistor load
connected across the solar cell. The curves 30, 32 and 34 represent
increasing rates of flow across the receiving surface of the solar cell.
Line 36 is the load line. From the graphs, it is evident that a resistor
connected across the solar cell which will result in a load line near the
"I" axis, provides a good means for monitoring the rate of flow of solar
energy incident on the receiving surface of the solar cell. A potential of
approximately 0.5 volts is a typical open circuit voltage for a solar cell
which is fully radiated.
FIG. 3 shows three solar cells 38, employed as the sensing element in the
sensing means 18 of FIG. 1, at the input of the triggering circuit
represented as the blocks 20 and 22 in FIG. 1. The solar cells respond in
the manner indicated by the curves 30, 32 and 34 of FIG. 2 to the rate of
flow of solar energy per unit area incident at their surfaces 39, with the
voltage and current for the three cells in series approximating the
summation of the curves for each of the cells. The resistors 40, 42, 44
and 46 are chosen so that the resistance of the resistor 40 in series with
the resistor 42 approximates the input resistance seen by the solar cells.
Thus the resistance of the resistor 40 in series with the resistor 42
substantially determines the slope of the load line, such as the line 36,
for the cells. The circuit is a Schmidt Trigger Circuit having a
configuration which is well known to those skilled in the art. Its method
of operation is similarly well known.
With the input transistor 52 off and the reference transistor 54 on, a
reference voltage is established at the reference node 56. The solenoid 62
(which has a resistance), a resistor 64, and a resistor 58 in parallel
with a potentiometer 60, act as a voltage divider which establishes the
reference voltage. With the input transistor 52 off and the reference
transistor 54 on, the current through the solenoid 62 is not of sufficient
magnitude to provide a magnetic field which is strong enough to close the
switch 24. Thus, the pump 16 is not in operation.
The rate of flow of solar energy incident at the surfaces 39 of the solar
cells 40, through the electrical output of the solar cells, will determine
the voltage across the resistor 42. Still assuming the input transistor 52
is off and the reference transistor 54 is on, when the rate of flow of
solar energy rises to a level sufficient to establish a certain
predetermined voltage across said resistor, said level being in the
vicinity of the reference voltage, the input transistor 52 will turn on
and the reference transistor 54 will turn off. As a result, the current
through the solenoid 62 will reach a level sufficient to provide a
magnetic field which in turn is sufficient to close the switch 24. When
the switch 24 closes, the pump 16 will turn on and circulation through the
solar heating panels will commence.
With the input transistor 52 turned on and the reference transistor 54
turned off and with the rate of flow of solar energy falling, a second
predetermined voltage across the resistor 42, also in the vicinity of the
aforementioned reference voltage, translates to a predetermined rate of
flow of solar energy at which the transistor 52 will turn off and the
reference transistor 54 will turn on. As a result, the switch 24 will
open, the pump will be disconnected and the circulation will cease.
The difference between the voltage across the resistor 42 at which the
input transistor 52 turns on and the voltage at which it turns off is due
to the well known phenomenon of hysteresis. As indicated, this hysteresis
is used in the design of the device shown in FIG. 2 to provide for the
commencement and termination of circulation at different predetermined
rates of flow of solar energy. A design which provides for a turn on rate
of approximately 0.5 langleys per minute and a turn off rate of
approximately 0.4 langleys per minute has proved efficient in the
embodiment of a controlled solar heating system shown in FIG. 1. The
predetermined levels may, of course, be varied.
Again referring to FIG. 3, the ac to dc converter and voltage regulator
block 50, provides a bias voltage for the Schmidt Trigger Circuit. The ac
source, which is a line source, supplies power to the pump as well as to
the Schmidt Trigger Circuit. The capacitor 68 across the collectors of the
transistors 52 and 54 reduces oscillation, and the shunt diode 70 is to
protect the input transistor 52 from being burned out when there is a
large decrease in current through the solenoid 62.
Although solar cells have been shown as the element for sensing the rate of
flow of energy and for providing an input signal, and a Schmidt Trigger
Circuit has been shown as the electrical circuit for receiving the input
signal and providing a control signal, it is evident that the invention
encompasses other means for receiving species of radiant energy and
providing an input signal and other circuits for receiving said input
signal and providing a control signal.
It will also be appreciated that the description of the embodiments of the
invention that has been given is by way of illustration and modifications
in detail may be made without departing from the spirit of the invention.
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