Off-axis focused solar heater

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Drawing sheet — no readable text.

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United States Patent Office Patiented Apr. 20, 1965

desirable and there has been no extended success in solar 3,179,105 heated homes or other buildings utilizing on axis heating. OFF-AXES FOCUSEED SOLAR HEATER The present invention depends for its operation on a Gerald Fabel, 59 Glen Aye, Stamford, Conn. deliberate departure from the conditions which were con Filed Sept. 19, 1963, Ser. No. 310,063 sidered necessary for focused solar heating. It is based

on the use of an off axis focusing mirror which need not

This invention relates to an off axis solar heating sys be perfect in its surface contour and reflects, focusing tem and more particularly to such a system associated with a low degree of resolution, onto a fairly large surface with a house to be heated by solar energy. of the heat collector such as a tank for water or other In the past solar energy has been used extensively for heat absorbing means. It is deliberately intended to uti heating but in general this has been done in two ways. lize the resulting aberrations which destroy the resolution In the case of a solar heated house the roof or walls or at the focus because now the heat is not focused sharply both are provided with a heating medium which may be in a Small area but is distributed over a larger area be water or some other liquid. The sun's rays striking the cause of the large circles of confusion introduced by the surfaces heat up the medium which can be pumped to a 5 aberrations inherent in off axis operation. These aberra heat sink, for example a chamber with a large mass of tions and the lack of sharp imaging are deliberately used material such as rocks so that the heat can be stored. in order to produce a better system for solar heating, This is of course of importance because, except in un particularly of homes.

usual climates for example southwest United States, By means of the present invention an off axis mirror there are periods during which the sun does not shine 20 can be erected over the top of the house, for example, it for a day or two at a time and so it is necessary to accu may be a thin aluminum, or coated steel sheet supported mulate heat in a heat sink. The heat is then used when by pylons. The aluminum sheet may constitute part or needed for heating the house by pumping the same or a all of the roof which can effect building economies. The different medium in heat exchanging relation with the resulting catenary curves of the edges produce rough ap heat sink and with the interior portions of the house. 25 proximation of a paraboloid. No attempt is made for Solar heated houses, although they have been practical great precision. The reservoir of liquid medium acting in locations such as the southwest United States where as an exchanger, for example in the form of a shallow the duration of cloud cover rarely exceeds a day, have tank or flat black plate with attached pipes, is mounted not proven to be satisfactory in climates for example, the on a tower which is higher than the building and of course northeastern United States, where it is not unusual for 30 higher than the off axis mirror. This tower is located the sun to be obscured by clouds for a number of days in opposite the Sun, for example in the case of the northern succession and even occasionally for a week. It is true hemisphere to the north of the building. When the build that in such cases a relatively small auxiliary system may ing faces north, a tower structure may be utilized to form be used and the solar heating utilized for a major portion part of an entrance structure for the building. of the heat during the heating season. But there is still 35 For a period of several hours around local apparent insufficient heating area for climates that do not have noon, the Sun's radiations striking the of axis focusing many hours of intense sunshine and so solar heating of mirror are imaged, if one may call the extremely rough buildings has been seriously limited in its practical uti resolution produced an image, onto the heat absorbing lization. reservoir. If the mirror is a paraboloid there will be Other types of solar heating have been proposed and in 40 produced a comparatively large circle of very poorly smaller units have been practically used. These involve focused radiation. This circle will not produce temper focusing mirrors. When an accurate focusing mirror is atures that are too high for the transfer medium and there used and is aimed directly at the sun it is possible to fore one of the extremely serious drawbacks of on axis achieve extraordinarily high temperatures and this has Solar heaters for home heating is avoided. At the same been utilized for the melting or otherwise heat processing 45 time with a reasonable size of heat exchanger the roughly of highly refractory materials. A somewhat similar use focused radiation will remain on the heat exchanger for a has been for heating at lower temperatures by means of considerable period of time either side of local apparent cylindrical mirrors or troughs which have been employed noon. It should be remembered that accurate focusing for stream generation and similar power purposes. with low aberration produces high temperatures but adds The on axis focusing of solar heat requires some means 50 nothing to the heat because the same amount of heat from for turning the mirror so it is pointed at the sun through the Sun is distributed over the larger circle when the out the period of time when the sun is shining. In the highly aberrant off axis system of the present invention case of heating of buildings this requires quite elaborate is employed. Thus there is nothing lost in efficiency and mechanical drives which add to expense and present 55 there is achieved the great gain of completely stationary mirrors with no driving means and with no danger of ex maintenance problems. A second disadvantage of the cessive temperature on the absorbing vessel. At the same on axis or focused solar heating is the relatively, higher time the light supported mirror presents no maintenance temperatures which are reached. Even if the area of the heat absorbing surfaces are comparatively large, tempera problems which are encountered with moving drives. In tures are produced which are too hot for many media al the preferred embodiment where the mirror forms part or though they can be used for relatively high temperature 60 all of the roof structure proper there is involved but little or, in some case no additional investment.

Steam for power generation. The temperature factor is The mirror extends normally beyond the walls of the perhaps less serious than the great complication required house and makes gutters unnecessary. It is of course in the drive for large mirrors which must be continuously necessary to provide a drain pipe in the center so that pointed at the sun. 65 Water which collects will be allowed to flow off. This The on axis focused solar heating has constantly however presents no serious construction problem and in striven for accurate focusing. This is one reason why the the mirror has to be continuously driven to point at the sun. can case of many architectural styles for modern houses be combined with a small central court.

For maximum efficiency of course accurate focusing has many advantages but the disadvantages of the cumber 70 of While the present invention is not limited to the use Some drive and high temperature at the focus have ren which can be type a particular of heat sink, two types of heat sinks directly applied will be discussed here.

dered this method of heating buildings economically un In the first of these a covered swimming pool is used with

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water as the heat storing medium. On an economical FIG. 1 is an isometric view of a house utilizing the basis, a covered swimming pool, is an ideal sink for the invention, following reasons: FiG. 2 is a simplified section through the center of the - (1) A swimming pool has a large water capacity and Same house.

can thus provide a desirable long term heat sink. The wall of the house is shown at 5 the same reference (2) Swimming pools are usually made of concrete numeral being used for the west wall of FIG. 1 and the which is a good insulator. north Wail of FiG. 2. In fact in the two figures the (3) Since the water is kept in the pool all year round, Sarine functional elements all bear the same reference the cost of emptying and refilling the pool in the spring and numerals. The house is provided with a thick concrete fall is saved. O slab heat sink 2 with embedded heating pipes 3. The (4) The use of an insulated removable cover on the concrete also contains dispersed therein a relatively large pool is highly desirable from a safety standpoint where amount of parafin which of course cannot be shown on there are small children in the household. the drawing.

(5) Since the swimming pool provides family recrea Over the ceiling of the house, and preferably spaced tion, its cost does not constitute a cost chargeable en 5 therefroin, is an aluminum mirror shown generally at 50. tirely to the present invention. This is a moderately thin sheet of aluminurn which is In addition, since the Swimming pool may be opened, Supported by four pylons ii. Each edge of the mirror which is not the case with a normally used buried water hangs as a catenary and is normally reenforced with wire tank, aluminum barrels of paraffin may be inserted into or light cable (not shown). The four catenaries cause the pool in the winter to greatly increase its heat storage 20 the mirror as a whole, to assume the approximate form capacity as a heat sink. The function of this parafiin of a paraboloid.

as a medium to increase the sink's heat capacity is dis Cin the north side of the house is a tower formed of cussed as a part of the description of the second type four columns 2 and two pipes 5. At the top there is of heatsink which follows. Supported a blackened plate 7 of considerable area to The water is heated by circulating liquid from the heat 25 which is attached a grid of pipes 4 which connect to the exchanger through suitable pipes. pipes 5. Transparent or translucent upper and lower The second type of heat sink which can be used with Surfaces 8 and 9 respectively are situated on either side this invention, consists of a thick concrete slab below the of the plate 7. These surfaces transmit short wave radia house. This concrete slab of course contains embedded tion but do not transmit long wave infrared and produce pipes which circulate the heating medium from the heat 30 a "greenhouse' effect on the plate 7 with its pipes 4. A exchanger and it is possible to utilize a very signple change hinged double faced mirror 6 is mounted adjacent an edge of phase heat storing means which is not practical with of the plate 7. When swung down it serves to reflect some ordinary solar heating. High molecular hydrocarbons additional radiation from the mirror and when swung up such as paraffin wax melt at temperatures from 40 to 60 cuts off radiation to the plate 7. This latter function or 80 C. and have a very high latent heat of fusion, not Sometimes of importance on hot days in the late fall and too greatly less than that of water. Concrete is easily early spring.

made with incorporation of large amounts of parafiin The liquid medium which is circulated through the wax dispersed therein. The wax does not react with any pipes 4 may have any suitable composition which will constituents of the concrete or with pipes and it is stable resist freezing at the temperatures encountered. It can and does not deteriorate over many years of use. Paraffin 40 be a hydrocarbon or water with suitable antifreeze addi or similar compounds which store heat by change of phase tives. The liquid, is circulated by conventional circulat could not be used in the ordinary solar heated house be ing pumps (not shown), through pipes in heat exchanging cause the rays striking a surface frequently did not pro relation with the water in a swimming pool 13 which is duce sufficiently high temperature to melt the paraffin. shown in FIG. 1 and/or through heating pipes 3 in a con While the present invention does not produce the enor 45 Crete heat slab 2 as is shown in FIG. 2. mous temperatures of an axis focused solar heating, the The location aid height of the heat exchanger 7 is temperature is considerably higher than is produced by the chosen with respect to the curvature of the mirror () so unfocused sun's rays on an ordinary flat surface and is that during the winter months near local apparent Iloor amply high to impart to the circulating liquid absorbing the Sun's rays will be focused at points on the lower sur medium in the heat exchanger a temperature sufficient 50 face 9 of the heat exchanger. The circle moves across i to melt paraffin. The aluminum barrels full of paraffin the surface from West to east as the sun passes from the referred to above perform the same function of increas easterly meridional angle in the morning to a westernly ing the heat storage capacity of the swimming pool. meridional angle in the afternoon. As the sun's declina Solar heating is only needed in the winter. In the tion changes throughout the heating season the circle of Summer it is not only not needed but is undesirable. 5 5 the roughly focused image moves across the plate 7 from Therefore considerable problems are presented in the north to South. This is taken into consideration in con ordinary solar heated house because the relatively, large structing the mirror and the heat exchanger which should amounts of heat transfer medium are heated up by hot sun have the proper distance and the mirror the roper curva on long summer days and remain hot during the night, ture for the latitude of the building which is to be heated. thus presenting either uncomfortable temperatures or 80 The drawings do not show dimensions accurately to scale extra load on an air conditioning system if such is em but approximate the general dimensions and curvature ployed. The present invention solves this problem and useful in the latitude of northern New England. at the same time makes an improved house for summer. FiG. 2, on which it has been stated before similar ele During the summer months the sun's altitude is so ihigh ments bear the same reference numerals, is a section in near local apparent noon that the focused image misses diagrammatic form and shows rays for winter and sum the heat absorbing reservoir on the tower altogether. in mer. It also illustrates the concrete slab heat sink modifi other words, the heating is automatically shut off. At the cation. -

same time the aluminum mirror reflects the sun's rays Rain accumulating in the mirror 10 flows off at the and keeps the house much cooler than an ordinary house. Center of the building through an opening 4 above a Thus the same element performs two entirely different 70 Small courtyard. The sides of the mirror act as over functions at different times in the year which is an im hangs inaking it unnecessary to provide gutters thus per portant added advantage of the present invention when forning automatically an additional useful function. It used for the solar heating of homes. is, however, necessary to keep driven rain from Striking The invention will be described in greater detail in con the ceiling of the house. This is effected by the tilted junction with the drawings in which: 5 Sofit 15. In a fairly large house, such as shown, it is de

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sirable not only to provide cables along the edges of the erture of the system, the resolution, being sufficiently mirror but to provide two transverse diagonal supports low so that unit areas of the heat exchanger do not from pylon to pylon. As the nature of these supports acquire a temperature substantially in excess of involves conventional building design and they are not a the boiling point of water, and necessary functional part of the present invention they are (c) means for circulating a liquid heat transfer medium not shown on the drawings. through the heat exchanger. The invention has been illustrated in conjunction with 2. A system according to claim 1 provided with a heat a solar heated home. This is the most important single sink incorporating dispersed high molecular hydrocarbon field of utility for the invention but it should be realized change-of-phase material and means for circulating the that the off axis solar heating can be applied quite gen O heat transfer medium through said heat sink. erally and does not need to be used for heating of a 3. A solar heated house comprising a house and a dwelling or for that matter for the heating of a building heating system therefor according to claim 2 the focusing at all. While therefore in a more specific aspect the mirror being above the house and extending beyond the present invention is directed to solar heating of homes in house walls.

a broader aspect it is not so limited and this use is merely 5 4. A solar heated house according to claim 3 in which a typical illustration. the mirror is centered over the house and is separated While the relative positions of the mirror and heat ex therefrom by an air space.

changer must be maintained for the particular latitude in 5. A solar heated house according to claim 4 in which which the invention is to be used, it is not necessary that the mirror is a suspended thin sheet of aluminum. the mirror be exactly centrically located over the roof of 20 6. A solar heated house comprising a house and a a house. Nor is it necessary that the house be approxi heating system therefor according to claim 1 the focus mately square. There is an advantage where terrain and ing mirror being above the house and extending beyond other constructional considerations permit in having the the house walls.

mirror more or less centered over the roof of the house 7. A solar heated house according to claim 6 in which because it then provides overhangs and heat insulation 25 the mirror is centered over the house, and is separated in the Summer. But of course as far as the operation of therefrom by an air space.

the present invention is concerned the location of the 8. A solar heated house according to claim 7 in which mirror with respect to the building may be varied. the mirror is a suspended thin sheet of aluminum. I claim:

1. An off axis focused solar heating system compris 30 References. Cited by the Examiner ing in combination, UNITED STATES PATENTS (a) a fixed, substantially horizontal focusing mirror 811,274 - 1/06 Carter -------------- 126-27 having a vertical axis and the mirror surface being 2,396,338 3/46 Newton ----------- 237 substantially symmetrically distributed with respect 2,584,573 2/52 Gay ----------------- 237-1

(b) a heat exchanger for heat transfer fluid having sub 2,998,006 8/61 Johnston ----------- 126-271 stantial lateral extent and located above the mirror 3,001,331. 9/61, Brunton ------- 126-270 X and displaced laterally from the axis of the mirror 3,072,920 1/63 Yellott --------- 126-271.X. in a direction opposite to the sun's azimuth at local apparent noon, the location and height of said heat 40 OTHER REFERENCES eXchanger being such that solar radiation is roughly Thomason, Harry E.: Reflector Improves Solar House focused to form an image of extremely low resolu Heating. Reprint from Sun at Work, First Quarter, 1962. tion on the lower surface of the heat exchanger in the form of an extended image of the entrance ap JAMES W. WESTHAVER, Primary Examiner.