Solar heater

Solar heater having a collector wherein heat transfer fluid is heated by solar radiation and a heat-dissipating conduit operatively connected to the collector so that fluid from a return line normally flows through the collector and the heat-dissipating conduit. Flow control means are operatively connected to the collector and the heat-dissipating conduit so that at times the heat transfer fluid flows through the heat-dissipating conduit, the amount of said fluid flow increasing with an increase in temperature of said fluid and decreasing with a decrease in temperature of said fluid.

BACKGROUND OF THE INVENTION 
Because of rapidly escalating energy costs, there has been a steady 
increase in the use of solar collectors for the purpose of preheating 
water for domestic and industrial purposes. Numerous preheating systems, 
which vary in the degree of complexity and practicality, have been 
proposed. In many of the systems, a heat transfer fluid is circulated 
through a series of solar collectors in which it is heated by solar 
energy. The heat transfer fluid is then circulated through a heat exchange 
system in which the energy from the heat transfer fluid is delivered to a 
load such as water. The heated water is then used directly, stored for 
later use, or heated an additional amount by auxiliary heating means. 
Most solar heating systems are designed for maximum efficiency, so that 
they will be relatively effective during most of the daylight hours in all 
seasons, even in colder climates. Most solar heating systems have 
provisions for storing the thermal energy during the peak energy gathering 
periods, so that the energy can be used during periods where little energy 
is collected. However, since solar systems are geared to function during 
non-peak periods, excessive heating of the heat transfer fluid sometimes 
occurs during the peak periods which tends to create problems in the solar 
system. Excessive heat prevents the use of some materials which might 
otherwise be used in the solar collectors, because of desirable qualities 
such as thermo-insulation, lightweight, and cost. The principal 
disadvantage of excessive heat is the effect that the heat has on the heat 
transfer fluid itself. Many materials commonly used as heat transfer 
fluids break down at high temperatures. For example, many types of 
antifreeze solutions break down at high temperatures and lose their 
chemical stability. This causes chemical corrosion of many of the 
components in the entire system. The deterioration of the components 
comprising a solar collector is also exacerbated by unnecessary exposure 
to high temperature. Also, replacement of these transfer fluids is 
expensive. These and other difficulties experienced with the prior art 
devices have been obviated in a novel manner by the present invention. 
One of the most serious problems encountered in solar heater systems is 
"stagnation". "Stagnation" is defined as a condition in which there is no 
fluid flow in the system. Some of the causes of stagnation are: 
1. a mechanical or electrical failure in the pump, 
2. accidental shutting of a valve in the system, 
3. failure of a thermo sensor in the system, 
4. failure of an automatic control element, 
5. shutdown of the solar loop because of a fully charged situation at the 
heat exchanger or load. 
Stagnation may occur for one or more of the above reasons even if the sun 
is shining. When this occurs, the heat transfer fluid heats up quickly in 
the collectors beyond the chemical stability of the fluid. The system must 
then be drained and the fluid replaced. Also, there is some corrosive 
damage in the system if the condition is not discovered quickly. 
It is, therefore, an outstanding object of the invention to provide a solar 
heater which is provided with a temperature control means for the heat 
transfer fluid which prevents overheating of the fluid. 
Another object of this invention is the provision of a solar heater in 
which the temperature of the heat transfer fluid is maintained below a 
preset value at the point where it is utilized for heat exchange with a 
liquid load. 
A further object of the present invention is the provision of a solar 
heater in which the heat transfer fluid is automatically cooled when it 
has reached a preset temperature. 
It is another object of the instant invention to provide a solar heater in 
which the flow of the heat transfer fluid through the system is precisely 
controlled. 
Another object of the present invention is to limit the temperature 
achieved in the solar collectors through the use of the heat-dissipating 
conduit in a thermosiphoning mode. 
A further object of the invention is the provision of a solar heater in 
which stagnation is prevented. 
A still further object of the invention is the provision of a solar heater 
in which the rate of cooling of the heat transfer fluid is precisely 
controlled. 
It is a further object of the invention to provide a solar heater in which 
the entire solar heating system is balanced with respect to the flow and 
temperature of the heat transfer fluid to provide a steady and predictable 
heat exchange condition at the point where heat is transferred from the 
heat transfer fluid to the liquid load. 
It is still a further object of the present invention to provide a solar 
heater which is simple in construction, and which is capable of a long 
life of useful service with a minimum of maintenance. 
With these and other objects in view, as will be apparent to those skilled 
in the art, the invention resides in the combination of parts set forth in 
the specification and covered by the claims appended hereto. 
SUMMARY OF THE INVENTION 
In general, the invention consists of a solar heater comprising a collector 
having an inlet at one end, and outlet at the other end and a passage 
extending from the inlet to the outlet. Heat transfer fluid from a return 
line flows through the passage from the inlet of the collector to the 
outlet of the collector and absorbs solar energy during the passage. A 
heat-dissipating conduit having an inlet and an outlet is operatively 
connected to the collector so that fluid from the return line normally 
flows through the collector and the heat-dissipating conduit. 
A temperature responsive valve controls the relative flow of fluid through 
the collector and the heat-dissipating conduit so that an increase in 
fluid temperature causes more fluid to flow through the heat-dissipating 
conduit and a decrease in fluid temperature causes more fluid to flow 
through the collector. 
More specifically, the heat-dissipating conduit is located above and is 
parallel with the collector, so that thermosiphoning takes place from the 
collector to the heat-dissipating conduit when stagnation occurs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, the solar heater of the present invention is generally 
indicated by the reference numeral 10 and includes a solar collector array 
generally indicated by the reference numeral 12. The collector array 12 
comprises a plurality of flat solar panels 14 arranged in series or 
parallel on a roof or other external structure 15 and facing in a 
generally southerly direction. A passage in the form of a conduit 16 
extends through the interiors of the solar panels 14 from an inlet 18 to 
an outlet 20. The inlet 18 is connected to a return line 22 and the outlet 
20 is operatively connected to a supply line 24. The return line 22 and 
the supply line 24 both lead to a heat exchanger 26. Load fluid pipes 28 
are also connected to the heat exchanger 26. However, the load fluid and 
the heat transfer fluid are in separate systems so that the load fluid and 
the heat transfer fluid do not mix. The load pipes 28 are also connected 
to elements, not shown, which comprise the load, such as a hot water 
heating tank or a thermal energy storage tank. For example, a conventional 
hot water tank could be used with the heat exchanger 26. In such a system, 
water is circulated through the heat exchanger 26, so that it flows from 
and to the pipes 28 and the hot water elements by means of a pump 30. 
The return line 22, the supply line 24, and the conduit 16 form a closed 
loop system containing a heat transfer fluid which may be of any 
conventional type but a mixture of water and antifreeze is preferred. Heat 
transfer fluid is circulated in the closed loop by means of a pump 32 in 
the supply line 24, so that the fluid flows in the direction of arrow 31. 
The pump 32 may also be located on the return line 22, if desired. The 
heat transfer fluid flows into the conduit 16 of the panels 14 from the 
inlet 18, is heated by solar radiation, and then through a junction such 
as a T fitting 33 into the supply line 24 from outlet 20. It then passes 
through the heat exchanger 26, wherein energy from the heat transfer fluid 
is transferred to the liquid load being circulated through the heat 
exchanger by the pump 30. 
The solar heater 10 also comprises a heat-dissipating conduit located above 
the panels 14. The heat-dissipating conduit is generally indicated by the 
reference numeral 34, and consists of a pipe 36 provided with 
heat-dissipating fins 38. One end of the pipe 36 is connected by a 
junction such as a T fitting 40 close to the inlet 18. The opposite end of 
the pipe 36 is connected to the thermo-actuated valve 42. The valve 42 is 
also connected to the T fitting 33. The valve 42 includes a temperature 
sensing probe 35 which extends through the T fitting 33, through the 
outlet 20 and into the last panel 14. The probe 35 responds to the 
temperature of the heat transfer fluid in the panel 14 and is effective to 
open or close the valve 42, depending on the temperature of the fluid. 
When the heat transfer fluid is cold, the valve 42 is closed by the probe 
35 and the heat transfer fluid flows only through the conduit 16 of the 
panels 14 to the supply line 24. When the heat transfer fluid is hot, the 
valve 42 is opened by the probe 35 and the heat transfer fluid flows 
through the conduit 16 and the conduit 36 to the T 33 and then into the 
supply line 24. The valve 42 is fully open at a maximum preset heat 
transfer fluid temperature and fully closed at a minimum preset heat 
transfer fluid temperature. When the valve 42 is fully open, there is a 
maximum flow through the conduit 34 and, consequently, maximum cooling of 
the fluid. When the valve 42 is fully closed there is no flow through the 
conduit 34 and, consequently, no cooling of the fluid. Fluid temperatures 
between the maximum and minimum temperatures of the heat transfer fluid 
will cause the valve 42 to be partially open, the extent of opening 
varying proportionately with the sensed temperature of the fluid. 
A variable resistance valve 62 is located at the end of the 
heat-dissipating conduit 34 which is adjacent the return line 22. The 
resistance of the valve 62 is adjustable so that fhe amount of fluid flow 
through the conduit 34 relative to the conduit 16 when the valve 42 is 
fully open can be set to a desired optimum value for each specific 
application of the invention. The collector array 12 has an inherent high 
flow resistance compared to the heat-dissipating conduit 34. Accordingly, 
the flow through the collector array 12 exhibits a high pressure drop 
compared to the heat-dissipating conduit 34. This difference in flow 
resistance and resulting pressure drop is compensated for by the variable 
resistance valve 62. 
The lower portion of conduit 16 is provided with a pressure-relief valve 44 
which opens when a predetermined pressure is reached within the conduit. 
Air vents 46 are located at opposite ends of the heat-dissipating conduit 
34. A balancing valve 48 is located on the supply line 24. Valve 48 is 
used to adjust the rate of flow of the heat transfer fluid through the 
system. A drain valve 50 is located on the return line 22 for draining 
fluid from the system. Shutoff valves 52 and 54 are located on lines 22 
and 24, respectively. 
The operations and advantages of the present invention will now be readily 
understood in view of the above description. At the beginning of 
operation, the valve 42 is closed and the pump 32 circulates the heat 
transfer fluid through the system in the direction of arrow 31. The 
balancing valve 48 is adjusted to provide a predetermined rate of flow of 
the fluid. The cool heat transfer fluid enters the conduit 16 of the 
collector 14 from the inlet 18. As the fluid advances through the 
collectors panels 14, it is heated by solar radiation. The heated heat 
transfer fluid exits through the collector outlet 20 into the T 33 and 
into the supply line 24. If the temperature of the heat transfer fluid 
which is sensed by the probe 35 is below a preset temperature, the valve 
42 remains closed and there is no flow through the heat-dissipating 
conduit 34. The pump 30 circulates the liquid load water through the heat 
exchanger 26 wherein thermal energy from the heat transfer fluid is 
absorbed by the liquid load. 
If the temperature of the heat transfer fluid sensed by the probe 35 is 
above a preset temperature, the valve 42 opens and some of the heat 
transfer fluid from the return line 22 is directed into the 
heat-dissipating conduit 34. As the heat transfer fluid passes along the 
length of the heat-dissipating conduit 34, it is cooled and enters the T 
fitting 33 where it mixes with fluid from the collector array 12. In the 
preferred embodiment, the valve 42 operates within a low preset 
temperature and a high preset temperature. If the temperature of the heat 
transfer fluid is below that of the low preset temperature, all of the 
heat transfer fluid flows through the conduit 16 of the collector. When 
the temperature of the heat transfer fluid is above the high preset 
temperature, some of the fluid from the return line 22 is directed through 
the conduit 36. There is a continuous throttling range between the high 
and low preset temperatures during which flow of fluid through the conduit 
36 varies proportionately with the temperature of the fluid. More fluid 
flows through conduit 36 when the temperature is close to the high preset 
temperature and less fluid flows through the conduit 34 when the 
temperature of the fluid is close to the low preset temperature. This 
ensures that the temperature of the heat transfer fluid at the heat 
exchanger 26 will be relatively constant. Since the heat transfer fluid 
flows through the heat exchanger at a constant temperature and at a 
constant rate, the system provides a uniform and predictable heat exchange 
condition within the heat exchanger. The system provides uniform, even 
transfer conditions throughout the daylight hours and for all seasons. 
Wide flunctuations in thermal energy at the transfer point are avoided, so 
that the entire heating system can operate smoothly and efficiently. 
There are times when pump 32 should be running to cool the solar collectors 
(because the sun is out) but for various reasons no flow occurs through 
the solar collectors 14. This condition is known as stagnation. The pump 
may not be running because of a high-limit cutout, a loss of power to the 
pump, a pump controller failure, a pump failure of a mechanical or 
electrical nature, or any of a number of possible failure modes. In any 
case, a collector stagnation condition is deemed to exist whenever the sun 
is out and no-flow condition exists in the solar collectors. Antifreeze 
deterioration and collector damage occur as a result of the stagnation 
condition. 
When stagnation occurs, the fluid in the panels 14 is heated to the high 
preset temperature. This temperature is sensed by the probe 35 which 
causes the valve 42 to open, thereby establishing a flow path between the 
solar collectors 14 and the heat-dissipating conduit 34. Since the 
heat-dissipating conduit 34 is physically above the solar collectors, a 
thermal driving head is established to induce thermosiphoning. 
Thermosiphoning is defined as a flow of fluid resulting strictly from a 
density difference caused by a temperature difference in the two vertical 
legs of a closed loop flow path. For purposes of this invention, the cold 
leg with the denser fluid exists in the vertical (or inclined) pipe in 
which valve 62 is located. The hot leg, so called, comprises all of the 
vertical or inclined passageways within the solar collector panel 14. 
The denser fluid in the cold leg falls relative to the lighter fluid in the 
solar collector panels, thereby creating a flow through the 
heat-dissipating conduit 34. As fluid flows through the heat-dissipating 
conduit 34, the fluid cools and becomes more dense. As the fluid flows 
through the collector panels 14, the fluid heats up and becomes less 
dense. As a result, the thermosiphoning process continues until either the 
sun sets or power is restored. One of the major advantages of the system 
is that thermosiphoning occurs automatically and requires no electrical 
power to either initiate or effect the thermosiphoning. 
If power is restored during an on-going thermosiphoning condition, flow 
through the heat-dissipating conduit 34 will be instantly reversed by the 
pumping action. The thermally activated element in valve 42 will shut very 
shortly, assuming there is sufficient load on the system. If the 
overtemperature condition persists such that the preset temperature 
continues to be exceeded, a parallel flow condition will be established 
whereby heat transfer fluid from return pipe 22 will split at fitting 40, 
a portion of which will flow through pipe 18 and into the solar collector 
inlet, and the balance will flow through variable resistance valve 62 and 
through the heat-dissipating conduit 34. 
Referring to FIG. 2, there is shown a modified solar heater, generally 
indicated by the reference numeral 60 and all comparable portions are 
identified with the same reference numerals, except that the numerals in 
FIG. 2 are differentiated by the use of a prime. The main difference 
between the systems shown in FIG. 1 and FIG. 2 is the manner in which the 
heat-dissipating conduit is connected to the supply and return lines. 
Further, the heat-dissipating conduit does not have to be physically 
mounted above the collector array 12'. 
Referring to FIG. 2, the outlet end of the heat-dissipating conduit 34' is 
connected to a first junction such as a T fitting 64. The T fitting 64 is 
also connected to the return line 24'. Thermo activated valve 42' is 
connected to the inlet end of the conduit 34' and to T fitting 33' which 
constitutes a second junction. The T fitting 33' is connected to the 
outlet 20' of the collector conduit 16' and to the T fitting 64 by a 
connecting line 66. A balancing valve 63 is located in the connecting line 
66. 
The valve 42' includes a probe 35' which extends through the fitting 33' 
and the outlet 20' into the last collector panel 14' for sensing the 
temperature of the heat transfer fluid within the panel. 
When the probe 35' senses a fluid temperature which is at or below a low 
preset temperature, the valve 42' is closed and all of the heat transfer 
fluid from the outlet 20' flows through the connecting line 66 to the T 
fitting 64 and to the supply 24'. When the temperature of the heat 
transfer fluid which is sensed by the probe 35' is at or above a high 
preset temperature, the valve 42' is opened and the fluid from outlet 20' 
flows through the conduit 34' and the connecting line 66 to the T fitting 
64. The relatively hot fluid from line 66 and the relatively cool fluid 
from conduit 34' combine in the fitting 64. The combined fluid flow then 
continues to the supply line 24'. As in the preferred embodiment, there is 
a throttling range of the valve 42' between the low preset temperature and 
the high preset temperature. The balancing valve 63 is adjusted to provide 
a desired optmum relative flow ratio between the line 66 and the conduit 
34' for the open position of the valve 42'. 
The embodiment shown in FIG. 2 will not provide thermosiphoning for a 
stagnation condition. 
The embodiment in FIG. 2 does not necessarily require the use of a 
temperature-responsive valve with a probe that extends into the collector 
outlet 20'. The thermo activated valve 42' may be one utilizing an 
internal or an external sensing element. 
It is obvious that minor changes may be made in the form and construction 
of the invention without departing from the material spirit thereof. It is 
not, however, desired to confine the invention to the exact form herein 
shown and described, but it is desired to include all such as properly 
come within the scope claimed.