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Claims  |
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Having thus described my invention what I claim is:
1. In a heating system having a medium for storing heat, a solar heat
collector for variably heating the medium with the variable intensity of
solar energy, and a heat exchanger for withdrawing heat from the heated
medium, a method of storing heat in the medium comprising storing
different portions of the medium at different temperatures, supplying
medium from the portion of the medium stored at the lowest temperature to
the collector for heating the medium with the greatest thermal efficiency
of the collector, combining the heated medium from the collector with one
of the portions of the stored medium, and supplying medium from the
portion of the medium stored at the highest temperature to the heat
exchanger for providing the greatest thermal efficiency for the heat
exchanger.
2. A method as set forth in claim 1 which includes sensing the temperatures
of the portions of the medium and of the medium heated by the collector
and directing the heated medium to a first portion of the medium which is
at a temperature nearest below the temperature of the heated medium to
permit heating of at least certain portions of the medium during periods
of less than maximum solar energy intensity while preventing the
degradation of the temperature of at least a certain other portion of the
medium which was previously heated during a period of greater solar
intensity to a temperature higher than the temperature of the heated
medium.
3. In a heating system having a fluid medium for storing heat and a solar
heat collector for variably heating the fluid with the variable intensity
of solar energy, a method of storing heat in the fluid comprising storing
different portions of the fluid in at least first and second compartments
at different temperatures, sensing the temperatures of the portions of the
fluid stored in each compartment, supplying fluid from the compartment
which stores fluid at the lowest temperature to the collector to permit
heating of the fluid with the greatest thermal efficiency of the
collector, storing the heated fluid in the first compartment when the
fluid stored therein is at a temperature nearest below the temperature of
the heated fluid, and causing the heated fluid to be stored in the second
compartment when the fluid stored therein is at a temperature nearest
below the temperature of the heated fluid.
4. A method as claimed in claim 3 which includes inhibiting the supplying
of the fluid to the collector whenever the temperature of the heated fluid
is less than the temperature of the coolest portion of the fluid.
5. A method as claimed in claim 3 wherein the heating system additionally
has means for using heat withdrawn from the fluid, said method further
comprising withdrawing heat from a portion of the fluid stored at a
highest temperature for providing the greatest thermal efficiency for the
means using the heat.
6. In a heating system having a medium for storing heat, a solar heat
collector for variably heating the medium with the variable intensity of
solar energy, and a heat exchanger for withdrawing heat from the heated
medium, an apparatus for storing the heated medium comprising storage
means having a plurality of compartments for storing different portions of
the medium at different temperatures, means for supplying the medium to
the collector from the compartment in which the stored medium is at the
coolest temperature for heating the medium with the greatest thermal
efficiency of the collector, control means for returning the heated medium
from the collector to one of the compartments, and means for supplying
medium to the heat exchanger from the compartment in which the stored
medium is at the highest temperature to provide the greatest thermal
efficiency for the heat exchanger.
7. A system as claimed in claim 6 wherein said control means includes means
for sensing the temperatures of the portions of the medium in each
compartment and of the medium heated by the collector, and means for
directing the heated medium to the compartment in which the stored medium
is at a temperature nearest below the temperature of the heated medium.
8. In a heating system having a fluid medium for storing heat, a solar heat
collector for variably heating the fluid with the variable intensity of
solar energy, apparatus for storing the fluid comprising storage means
partially divided into a at least first and second compartments for
enabling different portions of the fluid to be stored in different
compartments at different temperatures, means for sensing the temperature
of the fluid stored in each compartment, means for supplying fluid to the
collector from the compartment in which the stored fluid is at the lowest
temperature to permit heating of the fluid by the collector, means for
sensing the temperature of the fluid heated by the collector, and means
for directing the heated fluid from the collector to the first compartment
for storage therein whenever the fluid stored in said first compartment is
at a temperature nearest below the temperature of the heated fluid, and
for directing the heated fluid from the collector to the second
compartment for storage therein whenever the fluid stored in said second
compartment is at a temperature nearest below the temperature of the
heated fluid.
9. A system as claimed in claim 8 additionally having means for using heat
withdrawn from the fluid, said apparatus further comprising means for
withdrawing heat from a portion of the fluid stored by said storage means
which is at the highest temperature for providing the greatest thermal
efficiency of the means using the heat.
10. A system as claimed in claim 8 in which said storage means includes
overflow means interconnecting said compartments to permit the fluid
stored in one of said compartments to flow into the other one of said
compartments whenever the level of the fluid in said one compartment
reaches a predetermined value.
11. A system as claimed in claim 8 which includes heat exchanger means for
withdrawing heat from the fluid for heating a structure, said apparatus
further comprising means for supplying fluid to the heat wxchanger means
from the compartment in which the fluid is at the highest temperature.
12. A sytem as claimed in claim 1 which includes means for disabling said
means for supplying fluid to said collector whenever the temperature of
the heated fluid is less than the lowest temperature of the fluid stored
in said compartments.
13. In a heating system having a fluid medium for storing heat, a solar
collector for variably heating the fluid with the variable intensity of
solar energy, apparatus for storing the fluid comprising storage tank
means having a plurality of compartments for permitting different portions
of the fluid to be stored in different compartments at different
temperatures, temperature sensing means including an individual
temperature sensor associated with each of said compartments for sensing
the temperature of the portion of the fluid stored therein, pump means
connected to an outlet of one of said compartments for normally supplying
fluid from said one compartment to said collector for heating thereby,
said temperature sensing means including a further temperature sensor for
sensing the temperature of the fluid heated by the collector, and control
means responsive to the temperature sensing means for directing the heated
fluid to one of the compartments for storage therein when the fluid stored
in said one compartment is at a temperature that is nearest below the
temperature of the heated fluid, and for directing the heated fluid to a
further one of the compartments for storage therein when the fluid stored
in said further compartment is at a temperature that is nearest below the
temperature of the heated fluid.
14. A system as claimed in claim 13 wherein said storage tank means has
first, second and third compartments, and wherein the heated fluid is
normally directed to said first compartment, said control means including
first means for causing the heated fluid to be directed to said second
compartment for storage therein whenever the temperature of the fluid in
the first compartment exceeds the temperature of the heated fluid, and a
second means for causing the heated fluid to be directed to the third
compartment for storage therein whenever the temperature of the fluid in
the second compartment exceeds the temperature of the heated fluid.
15. A system as claimed in claim 14 wherein said control means includes
third means for disabling said pump means whenever the temperature of the
fluid in the third compartment exceeds the temperature of the heated
fluid.
16. A system as claimed in claim 14 additionally having heat exchanger
means for using heat withdrawn from the fluid, which includes further pump
means connected to an outlet of said first compartment for supplying fluid
from said first compartment to said heat exchanger means.
17. In a heating system having a medium for storing heat and heating means
for heating the medium, a method of storing heat in the medium comprising
storing portions of the medium at different temperatures to permit heating
of the portions independently of one another, supplying medium stored at
the lowest temperature to said heating means for heating the medium,
sensing the temperatures of the portions of the stored medium and the
heated medium, causing the heated medium to be stored with a first portion
of the medium which is stored at the highest temperature whenever the
temperature of the first portion of the medium is nearest below the
temperature of the heated medium, and causing the heated medium to be
stored with a second portion of the medium which is stored at a lower
temperature whenever the temperature of the second portion of the medium
is nearest below the temperature of the heated medium.
18. In a heating system having a medium for storing heat and heating means
for heating the medium, apparatus for storing the medium comprising
storage means having a plurality of compartments for permitting different
portions of the medium to be stored in different compartments at different
temperatures, temperature sensing means for sensing the temperatures of
the medium stored in each compartment and the heated medium, and control
means responsive to the temperature sensing means for directing the heated
medium from the heating means to one of the compartments for storage
therein when the medium stored in said one compartment is at a temperature
that is nearest below the temperature of the heated medium, said control
means directing the heated medium to a further one of the compartments for
storage therein when the medium stored in said further compartment is at a
temperature nearest below the temperature of the heated medium. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates to a heating system having means for storing heat.
The system has particular and preferred utility in a heating system using
solar energy as a source of heat.
Several factors related to the production of heat for structural space
heating systems, hot water heatins systems and other heating systems have
recently coalesced to encourage new technologies for producing heat in
such heating systems. Specifically, the cost of heat energy has continued
to rise. In addition, the vast consumption of heating energy, particularly
in urban areas, has provided substantial problems of pollution, and, most
recently, a shortage of traditional hydrocarbon fuels has developed. Each
of these factors has contributed to recently increased interest in sources
of heat energy alternative to those traditionally employed and more
efficient utilization of heat energy produced from all sources. One such
alternative energy source is energy radiated from the sun.
Solar energy has, of course, long been known but has not been significantly
exploited for two principal reasons. The first reason is the relatively
low density of the energy per unit area of a surface collecting the
energy. The low energy density requires both substantial surface areas and
relatively long times for the collection of a required quantity of heat
energy. The second reason is the uncontrollable availability of energy
from the sun to times which may not coincide with the desired times of
energy utilization. Specifically, solar energy is only available during
daylight hours and even during daylight hours varies in available
intensity with the angle of incidence of the energy which, of course,
depends upon the time of day, and varies with the degree of cloud cover.
Both of these problems may be mitigated by means for the storage of heat
energy accumulated during times of excess availability for later
distribution. Such heat storage means may also have utility with heating
systems employing traditional energy sources by permitting consumption of
the energy during convenient times such as off-peak hours in the
availability of electric energy or hours of relatively low pollution.
One system for the storage of heat energy, particularly heat energy from a
solar collector, is disclosed in U.S. Pat. No. 3,369,541 issued Feb. 20,
1968 in the name of Thomason. This patent discloses two embodiments of a
heat storage device each having a tank containing a heat-storing, fluid
medium. A pump circulates the fluid from the tank to a solar-energy heat
collector and returns the heated fluid from the collector to the tank for
storage. Heat exchange passages adjacent the tank receive a flow of air
which is heated in the passages and discharged into a structure as space
heat. In only one embodiment a collection of stones or other heat storage
and heat exchanger material surrounds the tank in thermal communication
with the tank for the storage of heat brought to the tank by the fluid and
in heat exchanging relation with the air to be heated by pumping the air
through interstices between the stones or other material.
In both embodiments disclosed in the patent the tank for storing the heated
fluid medium is internally entirely open to permit uninhibited mixing of
portions of the fluid heated to different temperatures, for example, fluid
heated at times of different solar energy intensity. Moreover, inlet and
outlet passageways for conveying the fluid to and from the solar heat
collector are disposed in diagonally opposite corners of the tank; this
arrangement would appear to promote a generally rotary, mixing circulation
of the fluid in the tank as caused by the jet action of the fluid
withdrawn from the tank for heating in the collector and returned to the
tank for storage. Mixing differently heated portions of the fluid will
degrade the higher temperature of fluid portion heated to the temperature
toward the lower temperature of other fluid portions of the tank.
In the patent, water is suggested as the fluid. In the embodiment having
stones for the storage of heat, it is believed that the stones, although
21/2 times heavier than water, have a specific heat of only 1/4, to
provide a thermal heat storage efficiency only 60% of that of a system
utilizing only water for the storage of heat.
Systems for heating hot water with solar energy have been commercially
available for a number of years. However, it is believed that these
systems have only a heat collector and a tank for the storage of water
heated in the collector. A discharge pipe then distributes the heated
water to hot water outlets as well known in plumbing systems distributing
hot water from water heaters using more conventional energy sources. As
with conventional water heaters, it is believed that the tanks storing
solar heated water rely on convection currents of the water, with or
without an internal pipe structure for directing the convection flow of
the water, to maintain a uniform temperature of heated water in the tank.
The uniform temperature of the water in such water heaters is considered
desirable to provide the maximum quantity of water heated to a desired
temperature, usually a temperature preset with a thermostat connected to
the water heater.
The relatively low energy density and variable availability of solar energy
additionally present another problem. Specifically, a medium heated by a
solar heat collector is often heated to a temperature only slightly above
that at which it was introduced into the solar heat collector. It is then
quite possible that for a large part of a day the solar heat collector
could heat the medium to a temperature warmer that that at which it was
supplied to the collector but cooler than the warmest temperature to which
a portion of the medium was earlier heated. Operation of a system under
such conditions will degrade the maximum temperature of the heat storing
medium even though additional heat was supplied to the entire system
during the heat collecting operation.
This problem is not ordinarily encountered in heating systems utilizing
traditional sources of heat energy because these sources of heat energy
are selected to provide heating temperatures which are substantially in
excess of those required in the system. Moreover, the traditional sources
of heat energy usually provide substantially constant heating
temperatures. For example natural gas flames at a substantially constant
temperature of about 3800.degree. F., a constant temperature substantially
in excess of that required from systems for heating structures or hot
water.
It is also well-known that the thermal efficiency of heat exchange devices
both for the collection and utilization of heat is greatest with the
greatest disparity of temperatures between the media between which heat is
to be exchanged. It is therefore desirable in a system having means for
heating a medium to introduce the medium into the heating means at the
lowest possible temperature. Similarly, it is desirable to introduce a
medium into means for utilizing the heat of the medium at the highest
possible temperature.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a heating system
having a medium for storing heat and means for heating the medium without
degrading a higher temperature of a previously heated portion of the
medium.
It is a further object of the invention to provide a heating system having
a medium for storing heat and means for withdrawing heat from a highest
temperature portion of the medium to provide the greatest thermal
efficiency to the heat withdrawing means.
It is still a further object of the invention to provide a heating system
having means for heating a lowest temperature portion of the medium to
provide the greatest thermal efficiency to the heating means.
It is still further object of the invention to provide each of the
foregoing objects in a system using solar energy as means for heating the
medium.
To these ends the invention provides in a heating system having a medium
for storing heat, means for heating the medium and means for withdrawing
heat from the medium for use, a method and apparatus for storing heat in
the medium between a time at which the medium is heated and a time at
which the heat is withdrawn for use.
The method comprises at least partially dividing the medium for separating
portions of the medium potentially at different temperatures and directing
heat from the heating means only to a portion of the medium at a
temperature below the temperature to which the heating means then heats
the medium. By directing the heat only to a portion of the medium at a
temperature below that to which the medium is then being heated, the
method functions to store heat in the medium during periods in which the
heating means heats the medium only to a temperature below that to which
another portion of the medium was previously heated without degrading the
higher temperature of the other portion of the medium.
In a particular embodiment, the means for heating the medium is a solar
heat collector, the available heat from which varies with the variable
intensity of the solar energy. The method then functions to permit the
system to store heat in the medium during periods of marginal or
less-than-maximum solar heat energy intensity without degrading the
maximum temperature of a portion of the medium previously heated to a
higher temperature during a prior period of greater solar heat-energy
intensity.
In another embodiment the method additionally comprises withdrawing the
heat only from a highest temperature portion of the medium to permit the
greatest thermal efficiency of the means withdrawing the heat for use. In
still another embodiment, the medium is a fluid which is supplied to the
means for heating the medium. In this embodiment the method additionally
comprises supplying a lowest temperature portion of the medium to the
heating means to permit the greatest thermal efficiency of the means
heating the medium.
The apparatus comprises means at least partially dividing the medium for
providing portions of the medium at potentially different temperatures and
means directing heat from the heating means only to a portion of the
medium at a temperature below the temperature to which the heating means
then heats the medium for storing heat in the medium when the heating
means heats the medium only to a temperature below that to which another
portion of the medium was previously heated without degrading the maximum
temperature of the previously higher-temperature-heated portion of the
medium. In the particular preferred embodiment wherein the means for
heating the medium is a solar heat collector, the apparatus aso provides
means for storing heat in the medium during periods of marginal or
less-thann-maximum solar heating of the medium without degrading the
temperature of the highest temperature portion of the medium.
Another embodiment has means withdrawing heat from a highest temperature
portion of the medium for permitting the greatest thermal efficiency of
the means withdrawing the heat. In still another embodiment, the medium is
a fluid supplied to the heating means and the embodiment additionally
comprises means supplying the medium to the heating means from a lowest
temperature portion of the medium for permitting the greatest thermal
efficiency of the heating means.
In this description of the invention the term "heat" is used in the sense
of adding energy such as to tend to increase the temperature of the medium
to which the heat is supplied. However, it is specifically intended that
the invention shall also include within its scope heating in the sense
that energy is withdrawn so as to tend to reduce the temperature of a
medium, that is, to cool the medium. When the system of the invention is
so used as a cooling system, it will be additionally understood that the
terms above and below the temperature of another portion of the medium are
reversed from their ordinary meaning to indicate temperatures below and
above, respectively, the temperatures of the other portions of the medium.
DESCRIPTION OF THE DRAWINGS
A preferred embodiment which is intended to illustrate and not limit the
invention will now be described with reference to drawings, in which:
FIG. 1 is a schematic illustration of one preferred embodiment;
FIG. 2 is a schematic illustration of another but also preferred
embodiment;
FIG. 3 is a more detailed illustration of a portion of the embodiments
shown in FIGS. 1 and 2;
FIG. 4 is a more detailed sectional illustration of another portion of the
embodiments shown in FIGS. 1 and 2; and
FIG. 5 is a view of a portion of that portion of the embodiments shown in
FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows as a preferred embodiment a system for space heating a
structure with heat from solar energy. The system has a solar heat
collector 10 for heating a fluid medium supplied to the collector through
a pipe 12 from a fluid storage means at 14. The solar heat collector 10
may, for example, be of the type disclosed in U.S. Pat. No. 3,387,602
issued June 11, 1968, in the name of Thomason. A pipe 16 carries heated
fluid from the heat collector 10 to means 17 directing the heated fluid to
the storage means 14. The fluid storage means 14 then stores the heated
fluid for later use.
To use the heat stored in the fluid, a pump 18 withdraws heated fluid from
the storage means and supplies the heated fluid to a heat exchanger 20 for
heating air passed through the heat exchanger by a blower 22. Air heated
in the exchanger is then advanced into a structure, house 24, for space
heating the house. Fluid from the heat exchanger is mixed with that
returned to the fluid storage means from the solar heat collector by the
pipe 16.
The fluid storage means 14 is a tank partially divided into three
compartments or separate tanks 26, 28 and 30. In the embodiment shown in
FIG. 1 the pump 11 withdraws fluid for heating in the collector 10 from
the compartment 30 while the pump 18 withdraws fluid for heating the house
24 from the compartment 26.
The means directing the fluid from the pipe 16 to the storage compartments
26, 28 and 30 comprises pipes 32, 34 and 36, each positioned to carry the
fluid to the respective compartments as controlled by a distribution valve
38 selectively connecting each pipe 32, 34, 36 to the fluid return pipe
16. An actuator 40 moves the valve 38 to direct fluid to one of the pipes
32, 34, 36 as directed by a decision device 42.
The decision device is connected to sensors 44, 46, 48 for sensing the
temperature of the fluid in each of the compartments 26, 28 and 30,
respectively, and to sensor 50 for sensing the temperature of the fluid in
the pipe 16 and other, later described functions. The decision device 42
compares the sensed temperature of the fluid in each compartment with the
temperature of the heated fluid being returned from the heat collector 10
in the pipe 16 to signal the actuator to move the valve to direct the
fluid through one of the pipes 32, 34, 36 to a compartment holding fluid
at a temperature lower than that of the fluid then passing through pipe 16
from the heat collector 10.
The operating scheme for the system is to direct heated fluid to a
comparment containing fluid at a nearest temperature lower than the
collector 10 heated fluid, to supply the heat collector 10 with fluid from
a compartment containing the lowest temperature fluid and to supply the
heat exchanger 20 with fluid from a compartment containing the highest
temperature fluid. Therefore, the decision device 42 is designed to cause
the actuator to direct the fluid through the pipe 32 supplying the
compartment 26 if the temperature of the fluid in the pipe 16 exceeds the
temperature of the fluid in each of the compartments, to direct the fluid
through pipe 34 to compartment 28 if the temperature of the fluid in the
pipe 16 exceeds that of the fluid in only compartments 28 and 30 and to
direct the fluid through pipe 36 to compartment 30 if the temperature of
the fluid in pipe 16 exceeds that of the fluid in only compartment 30. The
compartments thus order the fluid into strata of different fluid
temperatures with the compartment 26 at a higher or equal temperature to
the temperature of the fluid in each of the other compartments and the
temperature of the fluid in the compartment 30 at a lower or equal
temperature to the fluid in each of the other compartments. The decision
device 42 additionally has means connected to the pump 11 for cutting off
the flow of fluid to the heat collector if the temperature of the fluid
from the heat collector in the pipe 16 is lower than that of the
temperature in the lowest temperature fluid compartment 30.
The tanks are additionally interconnected by overflow devices 52 and 54.
When fluid is supplied to one of the compartments 26 or 28 other than the
lowest temperature compartment 30 from which the pump 11 always withdraws
the fluid, excess fluid supplied to the compartments 26 or 28 will
overflow toward the compartment 30. On the other hand, when fluid is
supplied to one of the compartments 28, 30 other than the highest
temperature compartment 26 from which the pump 18 withdraws fluid, excess
fluid supplied to the compartments 28 or 30 will overflow toward the
compartment 26. The overflow device 52 comprises a pipe extending from an
upper portion of the tank 28 to a lower portion of the tank 26, all of the
tanks accomodating fluid to a like level. Overflow device 54 comprises a
pipe similarly extending between compartments 28 and 30.
FIG. 2 shows another preferred embodiment similar to that shown in FIG. 1
except in the fluid storage means 14'. As illustrated in FIG. 2, the fluid
storage means 14' comprise a single tank substantially divided into
compartments 26', 28' and 30' by separators 60 forming vertically disposed
strata or portions of the fluid in the tanks. The strata separators 60
each have openings 62 interconnecting strata of the tank to form overflow
passages from one stratum to the next. The openings 60 thus function
similarly to the overflow devices 52 and 54 shown in FIG. 1. Each strata
of the tank receives fluid from a pipe 32', 34' and 36' as directed by a
switching valve 38 moved by an actuator 40 under the direction of a
decision element 42 which is responsive to temperature sensors 44- 50 in
similar arrangement with that described with reference to FIG. 1.
The decision element 42 is again biased to cause the valve 38 to direct
fluid hotter than that in any strata to the stratum or compartment 26', to
direct fluid hotter than that in only strata 28' or 30' to stratum 28',
and fluid hotter than only that in stratum 30' to stratum 30'. The stratum
26' will thus be at a temperature equal to or higher than that of any of
the other strata while the strata 30' will be at a temperature equal to or
lower than that of the temperature of the fluid in any of the other
strata. As before, the pump 18 withdraws heated fluid from stratum 26' to
a heat exchanger 20 for heating the house 24 while the pump 11 withdrawn
fluid from stratum 30' for heating in the heat collector 10.
FIG. 3 is a schematic of the decision device 42 and temperature sensors
44-50. Each of the temperature sensors 44-50 is a thermistor connected
across DC power supply busses 70 and in potential-dividing series
connection with a resistor.
The thermistor temperature sensor 44 in fluid compartment 26 (FIG. 1) is
connected at one end to one DC power supply bus 70 and at the other to
potential dividing resistor 72 and to an input lead 74 to an operational
amplifier 76. Another input lead to the operational amplifier 76 is
similarly connected between an NTC thermistor forming the temperature
sensor 50 and a potential dividing resistor 80, the thermistor-resistor
also being connected across the DC power supply. The operational amplifier
76 is connected as a potential comparitor for comparing the potentials on
the leads 74 and 78 connected to the operational amplifier. In such
well-known connections of operational amplifiers, the amplifier provides
an output potential saturated to a positive or negative value depending
upon the relative polarity of the potentials applied to the input leads 74
and 78 to the operational amplifier.
Then, if the fluid in the return pipe 16 is warmer than the fluid in the
compartment 26, the thermistor temperature sensor 50 sensing the
temperature of the fluid in the return pipe will have a lower resistance
than the thermistor temperature sensor 44 sensing the temperature of the
fluid in the compartment 26. This condition applies a higher potential to
the lead 74 than to the lead 78. The lead 74 is a non-inverting input to
the potential comparitor operational amplifier 76 to trigger a
non-inverted saturated positive potential from the operational amplifier
76. This positive potential is applied to the base of a transistor 82 to
trigger conduction of the transistor 82. The potential from conducting
transistor 82 is applied to the gate of an SCR 84 to then trigger
conduction of the SCR 84. The SCR 84 is connected in series with a coil of
a solenoid 86 forming part of the actuator 40 (FIG. 1) and across a power
supply transformer 89. Conduction through SCR 84 then energizes the
solenoid 86 to move the valve 38 to direct fluid from the pipe 16 to the
compartment 26.
If the temperature of the return fluid as sensed by the thermistor sensor
50 is cooler than the temperature of the fluid in the compartment 28 (FIG.
1) as sensed by the thermistor sensor 46, the thermistor sensor 46 will be
of lower resistance than the thermistor sensor 50. A non-output-inverting
input lead 88 of an operational amplifier 90, connected as a potential
comparitor in similarity with the operational amplifier 76, is connected
to the thermistor 50 while an output-inverting lead 92 is connected to the
thermistor 46. Under the conditions in which the returning fluid in the
pipe 16 (FIG. 1) is cooler than the fluid in the compartment 28, the lead
88 will be positive with respect to the lead 92 and the operational
amplifier 90 will provide a positive output to the base of a transistor 94
to trigger conduction of the transistor. Conduction of transistor 94
triggers conduction of an SCR 96 which, like SCR 84, is connected in
series with an actuating coil of a solenoid 98. The solenoid 98 then
controls the valve 38 to direct the returning fluid to the compartment 30.
If the returning fluid in pipe 16 (FIG. 1) is warmer than that in
compartments 28 and 30 but cooler than that in the compartment 26 the
relative resistances of thermistor-sensors 44 and 50 and sensors 46 and 50
is reversed from that just described to reverse the relative polarity of
the potentials on input lead pairs 74 and 78 and 88 and 92 connected to
the thermistor-sensors. Both operational amplifiers 76 and 90 then provide
an output potential saturated to a negative potential value. This low
potential will not trigger conduction of the transistors 82 or 94
connected to the operational amplifiers. Neither SCR 84 or 96 then
conducts and neither solenoid 86 or 98 is then energized. The switching
valve 38 (FIG. 1) then moves to a stable condition supplying fluid to the
compartment 28.
Although the system as so far described is operative, it is desirable to
additionally provide the thermistor 48 for sensing the temperature of the
fluid portion in compartment 30. The thermistor-sensor 48 in compartment
30 (FIG. 1) is also connected across the power supply busses 70 with
series resistor 100. The thermistor-sensor 48 has a higher resistance than
the thermistor-sensor 50 if the temperature of the fluid in the
compartment 30 is lower than that of the heated fluid returning from the
collector through the pipe 16 compartment 30. The potential from the
thermistor 48 is supplied to an operational amplifier 102 on a lead 104
while the potential from the thermistor 50 is applied to the operational
amplifier 102 over a lead 106. The operational amplifier 102 is again
connected as a potential comparitor for comparing the potentials on the
leads 104, 106. The lower potential on the lead 104 compared to that on
the lead 106 then triggers a positive output of the operational amplifier
102. As with the output from the other operational amplifiers, the
positive potential triggers conduction of a connected transistor 110 to
trigger conduction of an SCR 112 which is connected in series with an
actuating coil of a solenoid 114. The solenoid 114 then actuates a switch
(not shown) to turn on the pump 11 to circulate fluid through the solar
heat collector 10.
However, should the temperature of the fluid in the compartment 30 be above
that of the fluid supplied from the heat collector 10, the relative
resistances of the thermistor-sensors 48 and 50 will be reversed to
reverse the relative potentials on the leads 104 and 106. The output from
the operational amplifier 102 will then be a low potential which will not
trigger conduction of transistor 110 or SCR 112 to energize the solenoid
114. The pump 11 will then be shut off.
As shown in FIGS. 1 and 2, the sensor 50 is positioned in the heat
collector 10 at the junction of the heat collector with the fluid return
pipe 16. Specifically, the sensor is shown in the Figures as mounted in a
trough 51 which funnels heated fluid from a heat collecting surface 53 of
heat collector 10 to the fluid return pipe 16. The sensor 50 is mounted
for good thermal contact with the heat collecting surface 53 and, when
fluid flows through the collector, for good thermal contact with the
fluid. For example, the sensor 50 may be secured to the heat collecting
surface 53 for good thermal contact the surface in a position, such as
trough 51, which is in or near the flow of fluid heating in the collector
10 for good thermal contact with the fluid. The sensor 50 then senses the
temperature of the heat collecting surface 53 when no fluid flows over the
surface and the temperature of the fluid when it does flow over the
surface.
This mounting arrangement of sensor 50 permits the sensor to perform two
functions. When the temperature of the fluid heated in the collector falls
below that of the fluid in the coolest compartment 30, the sensor 30
senses this temperature of the fluid entering pipe 16 while the sensor 48
senses the temperature of the fluid in compartment 30 to provide relative
potentials to leads 104, 106 (FIG. 3) such that current to solenoid 114
(FIG. 3) is cut-off to stop the fluid pump 11 (FIGS. 1,2), as before
described. The temperature of the fluid in compartment 30 is then not
degraded during periods of such low solar heat energy intensity as do not
heat the fluid in the collector 10 to a temperature above that of the
fluid in compartment 30. The sensor 50 then functions to sense the
temperature of the heat collecting surface 53. When the solar energy
intensity increases to a level at which the temperature of the surface 53
rises above that of the fluid in compartment 30, sensors 48, 50 then
provide relative potentials to leads 104, 106 (FIG. 3) such that solenoid
114 turns on pump 11 (FIGS. 1,2) to again supply fluid to the collector 10
for heating. When the temperature of the fluid then sensed by sensor 50
again falls below that of the fluid in compartment 30 as from a subsequent
reduction of the solar heat intensity, sensors 48, 50 again cut off pump
11. Sensor 50 thus serves both to regulate the heating of fluid, including
the earlier described regulation of the compartment to which the heated
fluid is directed, and to regulate pump 11 to provide fluid to the heat
collector 10 only during times when the fluid can be heated to a
temperature above that of the coolest compartment.
An alternative embodiment is shown in FIG. 3 to include a device 116 which
is connected by the load 104 to the operational amplifier 102 to apply a
lower potential to the lead 104 than the potential on the lead 106 to
restart the pump 11. For this purpose the device 116 may be a solar energy
sensor such as a photo-electric device reponsive only to solar energy of
an intensity predetermined to provide a known minimum temperature to fluid
circulated through the heat collector 10. The device 116 will then restart
the pump 11 to provide the minimum heat level to fluid circulated through
the collector 10. A timer in the device 116 additionally applies the low
potential to the lead 104 periodically and for a time duration
predetermined to circulate fluid from the compartment 30 to the sensor 50
in the pipe 16. The device 116 is then cut off. Once fluid newly passed
through the collector 10 has arrived at the sensor 50, the temperature
comparison function of the thermistor-sensors 48 and 50 determines if the
solar heat collector 10 is supplying heat to the fluid. If the fluid the | | |
