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1947-48 Theatre Catalog, 6th Edition, Page 426 (412)

1947-48 Theatre Catalog, 6th Edition
1947-48 Theatre Catalog
1947-48 Theatre Catalog, 6th Edition, Page 426
Page 426

1947-48 Theatre Catalog, 6th Edition, Page 426

in the same Windstorm. As a result, the type of construction originally used in the laboratory unit has been abandoned. Snow removal constituted no problem, for the smoothness of the glass caused the snow to slide off the roof as soon as a thin layer next to the glass had melted. The 1A-inch-mesh screen (hardware cloth) was considered adequate protection against hail damage in the summer and was used only in that season. Ideally, a very thorough study of nus merous fundamental problems should have proceeded, or, at least, accompanied, the designing and testing of the whole solar collector. The limits of time, personnel, and funds prevented this. However, E. R. lrigh has recently directed studies toward learning the true character of the air fiow between the heated plate, whether streamline, turbu lent, or eddying, because of thermal gra- '

dients, would be extremely valuable in establishing an optimum design. Measurements of air How and temperature should be made by careful explcrations across the cross section-of the space between the plates. Further theoretical development of the heat transfer relations should also be made and correlated with the experimental results.

It is hoped that some of these fundamental characteristics of the solar unit can be investigated in a new project, along with the over all factors previously mentioned. With this more complete knowledge, it is felt that the most practical design can be developed and

the optimum operating conditions established.



(1) The principle of solar heat collection which has been theoretically devised by K. W. Miller is workable on a practical scale.

(2) Although performance of the fullscale collector is not as good as theoretically predicted, solar heat can be recovered in the form of hot air, with an over-all efficiency of 35 to 40 percent and an average daily exit air temperature of approximately 110 degrees Fahrenheit.

(3) During periods of high heat input, as in the middle of the day, exit air temperatures of 175 degrees can be see cured with an over-all efhciency of 35 to 40 percent.

(4) By reducing the air rate to a comparatively low value, air temperatures of at least 225 degrees can be secured, but at an efficiency reduced below 10 percent.

(5) Heat recovery efficiencies which have been secured are comparable with or greater than those previously obtained by the use of other methods.

(6) The optimum plate arrangement is 2/3 overlap, 1/3 of the top surface coated black, 1A -inch spacing between plates, and cover plates forming a complete enclosure.

(7) The optimum tilt for solar heat collection at 40 degrees latitude, from October through May, is 43 degrees; optimum tilt in other localities is approximately numerically ecual to the particular latitude.

(8) Only a small reduction in radiation collected is observed when the tilt is greatly reduced; a tilt of 27 degrees at 40 degrees latitude permits the col

lection of nearly 92 percent as much heat as a unit of the same size would collect at a 43-degree tilt.

(9) A collector tilt of 47 degrees is the optimum at 40 degrees latitude for winter heating of a house having a collector area and heating requirements similar to the experimental house and having a unit storing heat for one day; optimum tilt in other latitudes would be

'be the latitude plus approximately 7


(10) As long as the problem of plate breakage remains unsolved, practical application of the equipment cannot be made.

(11) The immediate cause of plate breaking is thermal stress resulting from unequal heating of the plates; the manner in which thermal stress initiates breakage is unknown.


(1) Air flow through the unit is not streamline as predicted by Miller, but eddying because of the high temperature difference between the plates.

(2) The time lag in the outdoor units, because of heat storage in the unit itself. is between 1 hour and 1%) hours.

(3) In the collector tested, 1 cubic foot of air supplied a minute for each square foot of collector results in a heat collecting efliciency of about 35 percent, if the atmosphere is reasonably clear.

(4) Any decrease in solar input-such as that caused by clouds-causes no change in efiiciency if the air rate is not altered, but results in a lowered exit air temperature,

(5) Heat recovery efficiency is only slightly affected by changes in entrance air temperatures.

(6) On a clear day, in the test location, solar reflection and heat convection from the cover each constitute about one-third of the losses; radiation from the cover plate and conduction through the sides and bottom of the unit make up the balance of the losses.

House Unit

(1) A solar heat collector of the type herein described can be installed on the roof of a suitable house and employed in conjunction with the standard hot-air heating system to supply a portion of the heat required by the house.

(2) The household solar heating unit can be regulated entirely automatically so that, when heat is required in the house, fuel will be used in the furnace if insufiicient solar heat is available.

(3) Although the operating variables have not yet been fully regulated to secure the optimum performance, approximately 20 percent fuel saVing has resulted during one winter from the use of a solar heat collector, covering about one-third of the roof, in the one dwelling installation.

(4) Results of the operation of a water heater, utilizing the solar heated air, although based on limited data secured over a short period during which heat insulation was not in use, indicate that the domestic hot water needed during the summer can be supplied from the solar unit.

(5) The construction employed in the house unit is the most practical yet devised and is superior to the construction of the laboratory unit.

(6) The weather resistance of the collector employed in the house installation was good; snow slid from the roof, a screen gave protection from hail in the summer, and high wind caused little damage.

General lndicu'l-ions

(1) Cheap heat storage, although not studied experimentally, can be provided in order to store excess heat collected during the day for use at night.

(2) Use of the solar heat collector without the auxiliary heat storage unit is is probably impractical in most locations.

(3) With proper adjustment and insulation of the experimental house unit, approximately 34 percent of the annual heating load should be carryable by the solar unit alone; with the installation of a heat storage unit of a size adequate for overnight storage of nearly all of the heat collected which is required by the house, the combined collector and storage unit should be able to carry approximately 55 percent of the annual heating load.

(4) A well insulated chamber, containing approximately 6 tons of crushed rock, coke, staggered cinder block, hollow tile, or similar material, would provide heat storage capacity adequate for the requirement set forth above; the dimensions of such a chamber could be roughly 3x3x15 feet.

(5) As an alternative, heat storage in the form of heated water could be provided.

(6) The advantage in providing sufficient storage material to store heat for two or three days is slight and is probably more than offset by the increased cost of the larger storage unit.

(7) When heat is not being supplied to the house, the recirculation of air from solar heat collector to the storage unit and back to the collector would be advisable, because this procedure would permit higher storage temperatures and greater heat storage to the unit weight of storage material.

(8) Heat recovery efficiency should no. to appreciably different in widely separated localities, provided that the same air rates are employed and the same area of collector is presented normal to the surfs mean position at the particular latitude.

(9) in general, locations in which greater winter sunshine or lower heating loads prevail (as in most sections further south than -}oulder), greater fuel savings will result if collector and storage sizes are made the same as herein described; for the same savings the units can be smaller.

(10) Economic advantages of installations north of the fortieth parallel of latitude are doubtful, unless in regions of unusually favorable weather condiv tions or high fuel costs.

(11) The applicability of the solar heated air as the energy source in the operation of an absorption refrigerator type of air conditioner is possible; air cooling should thus be cheaply obtained in the regions where most needed.

(12) The cost of a complete solar heating installation under the conditions encountered in the experimental units should, on a large production basis, be within the economic feasibility of a small home owner,

1947-48 Theatre Catalog, 6th Edition, Page 426