Low cost, high efficiency solar heating window insert & through-wall device
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This passive solar heating invention is designed to be a single or full window installation (for most sliding and double-hung windows) that is the simplest, lightest, and most cost effective answer to the world-wide demand for clean, cheap, renewable energy. The bias in designing this invention was to give the home resident the option of half a window for viewing. If the resident decides the view is inconsequential, then a full size installation will more than double the heat output of ‘Tersol’ or through wall installation, if feasible. Permanent installation would not increase cost, and would provide for a much larger unit with accompanying output.

Trumbull, John Manning (Shelby Twp., MI, US)
Application Number:
Publication Date:
Filing Date:
Primary Class:
Other Classes:
237/1R, 126/704
International Classes:
F24J2/00; F24J2/46
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Primary Examiner:
Attorney, Agent or Firm:
John M. Trumbull (Shelby Twp., MI, US)
What I claim as my invention is:

1. This design is meant to take advantage of its simplicity, weight and cost per unit of energy realized. a. There is nothing on the market that is close in these attributes. b. It was conceived to help lower income people and to be sponsored by utility companies, or state and federal governments. c. Most installations would be sliding window, owner installed. Much larger units could be through wall.

2. The construction and material used in this invention were carefully based on the environmental sustainability, material toxicity, and renewability. a. While many components were researched, the ones selected are the most environmentally friendly, e.g., hook and loop fasteners, Luan plywood, molded Styrofoam, precut cedar moldings, acrylic latex pain, aluminum foil, and ⅛″ standard window glass. b. My expense per unit, buying retail materials, was about $20.00. Volume manufacturing is expected to be ½ or $10.00 less than the cost of a cheap parasol. Payback time for the retail cost of ‘Tersol’ is planned to be accomplished in the first Winter installation period; about 12 weeks at a 40° latitude.

3. The efficiency of this solar energy producer is due to certain design features. a. Due to the arrangement of the angle of the collector panel to the glazing which takes into consideration the natural change in air density and also the clearance distance between collector and glazing at top and bottom of box. The collector angle and intake area speeds exhaust air. See FIG. 4a/28 of air movement up and through the box. b. Since BTU's can't be stored in this medium, a flat black collector of heavy aluminum foil as opposed to heavier aluminum sheet metal or copper is sufficient, at a great cost savings c. The insulation, arrangement and thickness is designed for maximum heat transfer d. The interior of the box has either black coating or aluminum to facilitate maximum heat transfer.



This device is similar to what is known in the field as “TAPS”: Thermo Siphoning Air Panel or window box heater, but differs primarily in cost, efficiency, weight, and complexity. The device is constructed on a stressed-skin basis, involving ⅛″ MDF or Luan plywood glued to a one-to-two inch thick extruded polystyrene foam board.

This invention was originally conceived as a simple, light weight auxiliary heater for various sizes of sliding and double hung standard windows for small homes, mobile homes, and apartments. I know of no current device that would be as measurably efficient and affordable to lower-income people that could be self-installed; it is designed for very low cost per BTU or Watt obtained. Through-wall application is also feasible, particularly new construction.


This device is a slanted box-like object about the size of a window air conditioner. It utilizes a light, yet strong frame made of cedar: ⅛″ MDF (medium density fiber-board) and foam insulation. The collector is a heavy weight aluminum foil backed by a 1″ thick foam. The foil is painted flat black and has Corinthian-like grain embossed on it. The front of the frame has one ⅛″ thick glass or acrylic glazing, single or double, and a carefully tested angle is maintained between the glass and a collector. The box contains a bottom intake vent and a top exhaust vent specifically sized in relation to the area. There are closable flaps for night time or no sun condition. There is no opening to the outside. Both intake and exhaust air come from the room, inside the mounted window and pass from bottom across the collector and exhaust out top after being heated by the sun. This box design is at least five times more efficient insulator that the window in which it is attached. Steel security pins can anchor both sides of the box to the window sill. Geographic application would be any window facing between 150° Southeast and 240° Southwest, and latitudes from the 20th parallel all the way north. World-wide suitability is expected particularly in countries with large low-income populations.



FIG. 1 shows an isometric sectional view of a passive solar heater here after referred to as “Terasol”. The unit (10) fits into a sliding or double-hung window or is installed through a wall (12). The unit consists of rear panel (20) bottom floor (22) and a top (26). The side walls (24) are not visible in FIG. 1. The side walls, top and bottom have insulation adhered to them with an aluminum foil backing. Sunlight (32) passes through a single glass or acrylic glassing (30) and heats the collector (40) which consists of a flat black surface, metallic base (44), and insulation (46). The collector is fixed to the walls at a specific angel. Sunlight (32) heats the collector (40) and insulation keeps heat in the closed box

FIG. 2 shows a sectional view of Terasol unit (10). The unit fits into a window (12) and is secured by the weight of the window and/or steel security pins, not shown. (15) shows the standard 60° angel of glass and frame (30). The wall, to bottom, and back are held together by hook and loop fasteners. The unit (10) consists of (26) top, back (20), sides (52 bottom (22) ⅛″ MDF or Luan plywood. The sides (52) are fitted into a groove or dado. Detail shown in FIG. 8—no tools are required for assembly.

FIG. 3 shows a sectional view illustrating “Terasol's” operation. Sunlight passes through the glazing and heats the collector. This starts the thermo-siphoning cycle (24) that draws air from the lower vent (60) into the preheat chamber (51) and up and across the collector (40) and out the top vent (62). All air is drawn from intake vent (60) which ideally is 15″-20″ from the room floor. There are no openings to the outside; two specific features increase heat output.

    • a. The ratio of the volume of air entering intake door (60) to the volume of air exhausted at output vent (62), which is approximately 1.5:1.0
    • b. The angle of the collector to the glazing from top to bottom—(see FIG. 5) which is approximately 1.0:1.5. These ratios are chosen by design and tests to take into consideration—the density and temperature of air from entrance (60) to exit (62). The more this flow can be sped up, the more BTUs will be transferred. Since the collector is not a heat sink maximum speed, thus volume is achieved

FIG. 4 shows an alternate embodiment where the collector (40) can be rotated along axis ‘A’ to compensate for changes in extreme latitudes. A handle (74) is lifted and moved until notch (76) has engaged the slot (78).

FIG. 5 shows the change in collector angel (34) between glazing and collector (40).

FIG. 6 shows the front (outside end) of the unit (10) with angled edges (72) (gray) that represent strips of aluminum set 60° to the glass face. The height of (70) should be 1½ times the width of the base.

FIG. 7 shows the back of the unit (10) facing the room or area to be heated. Hook and loop fasteners (23) attach back (20) to sides and top. Upper (63) and lower (61) vent hinges will be reinforced and glued nylon hinges.

FIG. 8 shows a cross section at the rear of wall (20) and top wall (26). The walls are located by a nib and dado (41) that fits into groove (41). The unit can be assembled or taken down for storage. If unit is left in window, vents should be closed and/or the glassing should be covered in summer months.


This device is applicable to any area in the world that conforms to the latitude and compass requirements. Its efficiency will vary depending on compass, latitude and percent of sunny days in area. Eg. Bangor, Me. versus Northern Arizona. Obviously, it would be more efficient in California than where it was tested in Southeast Michigan.

The chart below illustrates a few of the test results I obtained in Royal Oak, Mich.:

Temperature ° F.
IntakeExhaustDifferentialRun Time
“Terasol”76°117°41°(6 Hours)
Prime: 12:00-3:00 PM
“Carrier”70°120°45°About 9 Minutes
Gas Furnaceevery 40-60 minutes
  • NOTE: Volume of air passed, not calculated, but should be equivalent for a daylight period. The amount of total BTUs created depends on the size of the collector. This example shows that this size unit, 20″×25″ is equivalent to the output of one furnace room register. Under ideal climate condition this size solar heater show in illustration should produce over 22% of heat required for the 900 sq. foot bungalow in Royal Oak, Mich. Typical published output for current commercial passive solar panels is 36 KWH per sq. foot of collector, or 30-120 K BTUs per hour.

The construction design incorporates an easy knock-down feature to facilitate flat-box shipment and quick and convenient storage for the Summer months. The “Terasol” can be kept in window if outside glazing is covered during warm weather. It is believed by the inventor that the value and uniqueness of this device lies in three areas and will be detailed in the claims section.