Solar heater units

A shallow tank which is inclined when the unit is in operative position and having a relatively large surface to face in the direction of the sun, and a wide tube or a plurality of tubes extending over this large surface and communicating at one end directly with the interior of the tank near the lower end thereof and communicating at an opposite end directly with the interior of the tank spaced above its lower end, thermosiphon circulation being maintained as liquid in the unit is heated by the sun when in the tube or tubes and flows therefrom into the tank, down through the tank and back into the tube or tubes. It is preferable to provide an insulation shield over the end of each tube which directs liquid into the tank.

This invention relates to solar heater units for heating liquids such as 
water. 
There are a number of solar heaters in the prior art such as, for example, 
those illustrated and described in U.S. Pat. No. 2,122,821 dated July 5, 
1938 and U.S. Pat. No. 2,705,948 dated Apr. 12, 1955. To be satisfactory, 
solar heaters must heat the water rapidly and be able constantly to 
maintain a fairly large volume of hot water for immediate use. Most of the 
heaters of the prior art are rather cumbersome and slow acting. 
The solar heater of U.S. Pat. No. 2,122,821 has a plurality of relatively 
large tubes extending between a small lower header and a large upper 
header. The lower header has upper and lower openings aligned with each 
tube, while the upper header also has upper and lower openings aligned 
with the tube. The upper surfaces of the tubes are exposed to the sun, but 
these tubes are of such large cross sectional area that only a relatively 
small quantity of the water in the tubes is near the tube surface exposed 
to the sun. The water in the upper portions of the tubes is heated by 
solar radiation and travels upwardly into the upper header, while 
comparatively cooler water travels downwardly along the lower surfaces of 
these tubes to the lower header. Thus water in each tube is moving in 
opposite directions along the upper and lower surfaces. Not only is a 
small proportion of the water exposed to the solar radiation, but the 
counterflow idea makes for relatively slow movement of the water in the 
tube. 
U.S. Pat. No. 2,705,948 discloses a solar heater having a plurality of 
spaced tubes extending substantially horizontally between two vertical 
headers, these tubes being slightly inclined upwardly. Although the tubes 
are relatively small in diameter, there is no water being heated in the 
spaces between these tubes, and all of the water heated in the tubes 
enters one of the vertical headers in order to flow upwardly into a tube 
extending into the upper end of an insulated tank which is spaced below 
and overlaps said inclined tubes. The downward flow of the water is in 
this tank, and all of the water which is to enter the tube grid has to go 
through a single pipe to the lower end of the other of the headers. 
Regardless of the size of the grid, the fluid flow is controlled by the 
single pipe directing the hot water into the top of the tank and the 
single pipe directing cooler water out of the bottom of the tank. 
The solar heater of the present invention is very neat in construction, and 
designed so that a very large percentage of the water in the heating 
section thereof, which consists of one or more tubes, is exposed to solar 
radiation. A large volume of water in comparison to the size of the total 
unit is exposed to this radiation and the water flows directly from each 
tube into a tank which is positioned beneath and in overlapping 
relationship with the heating section, and flows directly from the lower 
end of this tank into each tube. Although there may be a plurality of 
heating tubes in the heating section, there may be only one relatively 
wide tube or duct communicating at opposite ends directly with the 
interior of the tank. In addition, the tank is preferably made relatively 
high with respect to the effective height of the tube or tubes in the 
heating section. With these arrangements, there is a rapid circulation of 
the water through the unit so that as the unit is exposed to sun the water 
is heated very rapidly and maintained at its upper heated level. The rapid 
circulation is the result of a good thermosiphon system maintained by 
sufficient gravity as well as a density gradient. 
This unit is such that it can be portable so as to be moved into different 
positions to expose the tube arrangement thereof directly to the sun. The 
unit can be completely self-contained so that it can be moved from place 
to place in order to provide hot water at these places. With a completely 
self-contained unit, water can be withdrawn therefrom into containers, but 
it will be necessary manually to provide additional water to the unit from 
time to time. On the other hand, the unit can be connected into a pipe 
system so that when hot water is withdrawn therefrom, cold water 
automatically enters the unit. The unit can be connected to a reserve tank 
through a temperature control valve. 
A solar heater unit in accordance with this invention comprises a shallow 
tank having a relatively large surface to face in the direction of the sun 
when the heater unit is in operative position, said tank when in the 
operative position having a lower end positioned below the level of an 
upper end thereof, tube means extending over said large surface and 
communicating at one end directly with the interior of the tank near said 
lower end and communicating at an opposite end directly with the interior 
of the tank spaced above said lower end, whereby thermosiphon circulation 
is maintained as liquid in the unit is heated by the sun when in the tube 
means and flows from said opposite end of the tube means into the tank, 
down through said tank and through said one end back into the tube means. 
The tube means can be in the form of a relatively wide and shallow tube or 
duct, or it can be in the form of a plurality of tubes. In a preferred 
form of the invention, an insulation shield is provided over the tube 
means where the latter communicates at its upper end with the tank in 
order to shield said upper end from the sun.

Referring to FIGS. 1 to 3 of the drawings, 10 is a solar heater unit in 
accordance with this invention made up of a base 12 having legs 13 
connected thereto at its upper end 14 so that when the lower end 15 of 
this base rests on a suitable support, legs 13 retain the base in an 
inclined position. When in use, unit 10 is preferably inclined as shown, 
although it may be positioned anywhere from the vertical to near the 
horizontal. 
Unit 10 also includes a shallow tank 20 having a surface 22 which faces in 
the direction of the sun when the heater unit is in operation. Tank 20 is 
preferably rectangular in shape, and it may be of any desired size, 
provided it is shallow relative to its length and width. For example, a 
tank about 125cms long, 60cms wide and 4cms deep has been found to be a 
practical and useful size. 
A heating section 25 in unit 10 is made up of a plurality of tubes 27 
overlying the surface 22 of tank 20 and extending longitudinally thereof. 
These tubes may be of circular cross section, but it is preferable that 
they have a rectangular cross section as shown in FIG. 3. Although the 
illustrated tubes are placed side by side, they can be spaced laterally a 
little as illustrated in FIGS. 7, 8, 9 and 10. Each tube 27 has a lower 
end 30 which communicates directly with tank 20 near its lower end 31, and 
an upper end 34 which communicates directly with the interior of the tank 
spaced upwardly from its lower end 31. In this example, the ends 34 of the 
tubes are spaced downwardly from the upper end 36 of the tank to leave the 
upper portion 37 of tank surface 22 exposed. 
If desired, all or the main portion of tank 20 may be encased in an 
insulation jacket 40, as clearly shown in FIG. 2. In this example, jacket 
40 is provided with a relatively large opening 42 in its upper surface so 
that the portion 37 of the tank surface 22 is exposed to the sun just as 
said tubes are. 
Although not absolutely necessary, it is preferable to provide an 
insulation shield 45 over the upper portions of tubes 27 where they 
communicate with the interior of the tank so as to shield these upper 
portions or ends from the sun. 
If unit 10 is to be a portable unit, it is provided with a spigot 48 
extending from the lower end of tank 20 and a filler tube 49 communicating 
with the upper end of the tank, this spigot and the filler tube being 
shown in broken lines in FIG. 2. When the unit is to be connected into a 
water system, an inlet tube 52 communicates with the lower end and an 
outlet tube 53 communicates with the upper end of the tank. Tube 52 is to 
be connected to a cold water pipe of the system, while tube 53 is to be 
connected to a hot water pipe thereof. In some cases it is desirable to 
provide a pressure relief valve 54 communicating with the upper end of 
tank 20. 
When solar heater unit 10 is in operation, it is mounted in an inclined 
position where it faces the sun. If desired, mirrors or reflectors may be 
provided for directing sun rays onto the unit. In any case, the tubes 27 
of heating section 25 are exposed to the sun, excepting the portions 
thereof beneath shield 45 when the latter is used. In this example, the 
upper portion 37 of tank 20 also is exposed to the sun. The insulation 
shield 45 protects the upper ends of the tubes from the sun so that the 
temperature of the water in these upper ends starts to drop relative to 
that of the water in the portions of the tubes exposed to the sun. The 
temperature difference between the water in said tube upper ends and in 
tank 20 and the water in the exposed tube portion is the temperature 
differential that causes the thermosiphon circulation of the water in the 
unit. As tubes 27 are relatively small in cross section, a very large 
percentage of the water flowing therethrough is close to the surfaces of 
the tubes directly exposed to the solar radiation. In effect, the sun 
heats the upper surfaces of the tubes, which act as a flat plate 
collector, while the water flowing through the tubes continuously absorbs 
and removes this heat. As the water enters directly into tank 20 from the 
upper ends of the tubes, and flows directly from the lower end of the tank 
into the lower ends of these tubes, there are no restrictions in the 
liquid flow so that a good circulation is maintained at all times when the 
unit is in operation. The use of tubes of rectangular cross section 
enables the tubes to be placed close together so as to provide the largest 
possible tube surface or flat plate collector for exposure to the rays of 
the sun. The tubes 27 preferably cover the tank substantially throughout 
the entire width thereof so that the space occupied by the heater unit is 
utilized to the fullest extent to absorb heat from the sun. As explained 
above, the insulation shield 45 assists the thermosiphon circulation, 
while the upper portion 37 of the tank represents an extension of the tank 
above the upper ends of the tubes in order to increase the head in the 
tank which, in turn, increases the rate of flow of the water in the unit 
as a result of the action of gravity. This upper portion 37 is preferably 
exposed to the sun as described in order to act as an additional heat 
absorber. The upper surface of portion 37 acts as another flat plate 
collector. 
FIG. 4 illustrates an alternative solar heater unit 10a. This unit is quite 
similar to unit 10, excepting that the tubes 27a extend from the lower end 
31 of tank 20 right up to the upper end 36 thereof. In this example, the 
insulation shield 45a covers the upper portions of these tubes and the 
upper portion of the tank. The portion of tubes 27a between the lower end 
of shield 45a and the lower end 31 of the tank constitute the heating 
section 25a of this unit. 
Unit 10a functions in the same way as unit 10, but the former has less 
surface area exposed to solar radiation because the upper portion of the 
tank is covered by shield 45a. 
FIGS. 5 and 6 illustrate still another alternative solar heater unit 10b. 
This unit is similar to unit 10a, but it can also be made similar to unit 
10. The only difference between the other units and unit 10b is that the 
latter has a single relatively wide and shallow tube or duct 55 in place 
of tubes 27 or 27a. Tube or duct 55 overlies the surface 22 of tank 20 and 
extends from the lower end 31 thereof to its upper end 36. Tube 55 is 
about the same width as tank 20 and is very shallow, the depth of this 
tube being substantially the same as the depth of tubes 27 and 27a. Shield 
45a covers the upper end of tube 55. 
Tube 55 communicates directly at its lower end with the lower end of tank 
20 through one or more openings 58, while the upper end of tube 55 
communicates with the tank through one or more openings 59. If there is 
only one opening 58 or 59, it is preferably in the form of a slot 
extending transversely of tube or duct 55. 
Solar unit 10b functions in the same manner as the units described above. 
The upper surface of tube 55 acts as a flat plate collector, heat from 
which is absorbed by the water in said tube. 
FIG. 7 illustrates yet another alternative solar heater unit 10c. In this 
unit tubes 27 are laterally spaced apart and the layer of insulation 
between tank 20 and the tubes has been omitted. A sheet 65 having curved 
corrugations or valleys 66 is interposed between the tubes and the tank, 
said sheet being formed of aluminum or other suitable material and 
preferably having a reflective surface facing the tubes. This sheet is 
preferably formed of good heat-absorbing material. The tubes 27 are 
preferably mounted at the focal points of the corrugations 66 of sheet 65. 
The sun rays fall directly on tubes 27 and on corrugated sheet 65. The rays 
reaching the corrugated sheet are reflected back to said tubes. This sheet 
absorbs heat from the rays and radiates heat to tank 20. 
FIGS. 8, 9 and 10 diagrammatically illustrate a tube arrangement that can 
be used in either unit 10 or 10a. Tubes 27d can be of circular cross 
section, as shown, or they can be square or any other shape in section. 
In FIG. 8, a flat heat-absorbing sheet 70 formed of copper or other 
suitable material is placed over spaced tubes 27d and secured thereto in 
any desired manner, such as by soldering or welding. This sheet preferably 
covers the heating section 25 of the unit and acts as a flat plate 
collector and transmits heat to the tubes. 
In FIG. 9, a flat sheet 72, similar to sheet 70, is placed under spaced 
tubes 27d and secured thereto by soldering, welding or the like. This 
sheet also acts as a flat plate collector and transmits heat to the tubes. 
In FIG. 10, a narrow flat heat-absorbing sheet 74 is located between each 
tube 27d and each adjacent tube and is connected thereto substantially 
midway between their outer and inner surfaces by welding, soldering or the 
like. These sheets transmit heat to the tubes. The sheets 74 constitute an 
interrupted flat plate collector. 
FIG. 11 diagrammatically illustrates one of the above-described solar 
heater units, for example, unit 10, connected to a water system. A cold 
water pipe 80 is connected to inlet tube 52 while a hot water pipe 82 is 
connected to the outlet 53. Pipe 80 extends from a cold water source, 
while pipe 82 extends to the system requiring hot water. 
Another pipe 85 extends from hot water pipe 82 to an insulatd reserve tank 
86 having an air outlet 87. A hot water pipe 88 extends from tank 86 to 
the system requiring hot water. A temperature controlled valve 90 is 
connected in pipe 85. This valve 90 may be a self-acting temperature 
control valve which is now on the market and which does not require 
external power, such as air or electricity. On the other hand, the valve 
may be a standard electrically controlled valve, in which case a 
heat-sensitive control unit 92 is located within the top area of tank 20 
of unit 10 and is electrically connected to the valve, as indicated at 93. 
The pressure release valve 54 is not required with this arrangement. 
In the system of FIG. 11, solar heater unit 10 operates in the manner 
described above. When the temperature of the water in tank 20 reaches a 
predetermined level, valve 90 is operated to permit hot water to be 
directed through pipe 85 into reserve tank 86, from which it may be drawn 
off through pipe 88. When the temperature of the water in tank 20 drops to 
a predetermined level, valve 90 closes line 85, the heater unit continuing 
to function to heat the new water which has been directed therein through 
pipe 80. Thus, this control arrangement protects unit 10 from excessive 
pressures, and hot water is stored in tank 86 for use.