Patent application title: FREE-CONVECTION, PASSIVE, SOLAR-COLLECTION, CONTROL APPARATUS AND METHOD
Ra Puriri (St. George, UT, US)
IPC8 Class: AE04D1318FI
Class name: Stoves and furnaces solar heat collector solar collector forms part of building roof
Publication date: 2011-07-14
Patent application number: 20110168165
A structure and method of solar energy collection use a building roof
acting as a heat collector, conductor, and convector passing thermal
energy to air in a volume below. The air may stratify according to
temperature, with flow controls maximizing temperatures by operating
dampers, valves, or both in the air and a liquid working fluid,
respectively. A finned heat exchanger may be a hydronic baseboard-type
heating unit operating to transfer heat in the opposite direction, into
water inside the central pipe. A thermo-mechanical actuator, such as a
wax motor may provide passive control, and heat may be collected in an
open circuit of culinary water, a closed loop, or a double loop system.
Ducting aids stratification, temperature maximization, and heat exchange
to enforce pre-selected temperatures in the air and water working fluids.
1. A method of solar energy collection comprising: providing a building
having a structure comprising a thermal conductor positioned to define a
first space and comprising a first surface exposed to solar radiation and
a second surface exposed to the first space; converting into thermal
energy, by the first surface, solar radiation incident thereon;
convecting; by the second surface thermal energy to air in a volume
defined by the conductor, and a substantially solid region conducting
heat between the first surface and the second surface; stratifying the
air within the volume in accordance with a temperature profile of the air
in the volume; controlling a maximum temperature in the air by operating
a damper controlling a rate of a flow of air in the volume; receiving the
flow through an exchanger extracting heat from the flow at substantially
the maximum temperature of the temperature profile and into a fluid
cooler than the maximum temperature; transporting the fluid to a location
outside the exchanger; and passing the heat away from the exchanger for
use outside the volume.
2. The method of claim 1, wherein the exchanger comprises fins extending into the flow.
3. The method of claim 1, wherein the exchanger is a hydronic heating element operating in reverse to heat water passing therethrough.
4. The method of claim 1, wherein the flow of air is further passing through the volume.
5. The method of claim 1, wherein the flow of air is further substantially contained and circulating within the volume.
7. The method of claim 6, further comprising operating the damper in accordance with the maximum temperature by a thermo-mechanical actuator.
8. The method of claim 7, wherein the thermo-mechanical actuator comprises a wax motor.
9. The method of claim 7, wherein: the exchanger is a hydronic heating element operating in reverse by extending fins thereof into the flow to extract heat therefrom into a stream of water contained in a conduit intimately connected to extract heat from the fins into the water.
10. The method of claim 9, further comprising evacuating condensate from the exchanger to a location outside the volume.
11. A method comprising: providing a building having a roof comprising upper and lower surfaces, the upper surface exposed to solar radiation incident thereupon; providing the building having a cavity enclosing a first volume below the lower surface and containing a quantity of air movable therewithin substantially unobstructed in at least one direction; locating a director positioned in the first volume and having upper and lower ends, separated in the at least one direction, and a channel substantially enclosed to extend between the upper and the lower end; positioning a heat exchanger in the channel exposed to the air; heating the upper surface by the solar radiation; heating the lower surface by the upper surface; heating the air by the lower surface in contact therewith; transferring heat from the air into a transfer fluid in the heat exchanger; transferring heat from the transfer fluid into a second volume to be heated.
12. A method comprising: providing a building having a roof comprising upper and lower surfaces, the upper surface exposed to solar radiation incident thereupon; providing the building having a cavity enclosing a first volume below the lower surface and containing a quantity of air movable therewithin substantially unobstructed in at least one direction; modifying the structure of the building with ducting directing a flow of air in the cavity to flow through the ducting; providing an exchanger within the ducting and receiving heat from the flow providing a damper controlling the flow of air; and providing an actuator operable to selectively open and close the damper.
13. The method of claim 12, further comprising positioning a director positioned in the first volume and having upper and lower ends, separated in the at least one direction, and a channel substantially enclosed to extend between the upper and the lower end; positioning a heat exchanger in the channel exposed to the air; heating the upper surface by the solar radiation; heating the lower surface by the upper surface; heating the air by the lower surface in contact therewith; transferring heat from the air into a transfer fluid in the heat exchanger; transferring heat from the transfer fluid into a second volume to be heated; the transferring, further comprising providing dampers controlled by temperature in the heat exchanger; the transferring, further comprising providing vents controlling the flow of air through the heat exchanger; and the transferring, further comprising providing ducting directing the air through the heat exchangers.
14. The method of claim 13, further comprising providing vents extending between rafters and extending to the ridge, and passing the air out through a vent in the ridge.
15. The method of claim 12, further comprising: providing a cooler remove the heat from the air; providing a condenser within the volume condensing water from the air upon cooling of the air; and circulating the air within the volume to remove the heat into the cooler and water to a location outside the volume.
 This application claims the benefit of co-pending U.S. Provisional Patent Application Ser. No. 61/295,062, filed on Jan. 14, 2010 for FREE-CONVECTION, PASSIVE, SOLAR-COLLECTION, CONTROL APPARATUS AND METHOD.
 1. The Field of the Invention
 This invention relates to heat exchange and, more particularly, to novel systems and methods for passive solar energy collection.
 2. The Background Art
 Attic and roof structures are struck by solar energy as radiation, largely as a nuisance, damaging roofs, overheating attics, and generally achieving little good. Solar collectors from the 1970s found support on rooftops, at some considerable capital expense, ongoing maintenance costs, reliability problems, unsightly structures, and hard-earned tax credit with a headache. Solar radiation occurs in greatest concentrations in places that need the least space heating. Mainly attic ventilation is about passing enough air through an attic to keep moisture evaporated, while encouraging ambient air to cool the attic to about ambient temperature through small openings and screens designed to keep out birds and insects.
 What is needed is an apparatus and method to modify roof structures to improve heat transfer, protect solar heat collection devices inside the roof structure instead of on top thereof, maximize the temperature of working fluids in heat transfer, and minimize costs while improving reliability with minimum maintenance. Minimizing risk by simplifying the fluid handling systems and using well adapted, readily available hardware would be a plus.
BRIEF SUMMARY OF THE INVENTION
 In view of the foregoing, in accordance with the invention as embodied and broadly described herein, a method and apparatus are disclosed in one embodiment of the present invention as including a structure and method of solar energy collection using a building. A roof acting as a heat conductor has a top surface converting solar radiation to thermal energy, which is then conducted down through to the bottom surface. The bottom surface of the roofing buildup convects thermal energy to air in a volume below.
 The air may be stratified within the volume of an attic or other space according to a temperature thereof. Controlling a maximum temperature in the air by operating a damper relies on controlling a rate of a flow of air in the volume. The air flow passes through an exchanger extracting heat from the flow at substantially the maximum temperature.
 The heat exchanger uses a fluid cooler than the maximum temperature of the air, and may use an open cycle of culinary water, a closed loop of any suitable fluid, or the like. The heat exchanger may comprise fins extending into the air flow, including a hydronic baseboard-type heating unit operating to transfer heat in the opposite direction, into water inside the central pipe.
 A damper may operate by any suitable means, such as a thermostat, and may use a wax actuator dependent on local temperature near the heat exchanger or under the roof layer to control air flow heating water in the heat exchanger. A thermo-mechanical actuator, such as a wax motor provides passive control, but may be replaced by conventional controls if desired.
 Suitable collectors may evacuate condensate from the heat exchanger as water is condensed from the humidity in the air being cooled. The condensate may be conducted in a channel, pipe, or the like to a location outside the volume used as the solar heat collection region so as to not increase humidity by re-evaporation, which could also present heat loss for the collection process otherwise.
 Air in the volume (e.g., attic, ducts, ventilation spaces, etc.) may be freely movable therewithin by free convection, and may be substantially unobstructed in at least one direction. Ducting or some other director may be positioned in the volume to conduct air through at least a portion of the lower and upper ends, directing the heated air through the exchanger or banks of exchangers in series, parallel, or both. A channel may substantially enclose a heat exchanger against substantial escape of air, except in the direction of flow. The flow may transfer heat in the air flow, collected from the roof's under surface, through the heat exchanger, which extracts the heat from the air into a transfer fluid in the heat exchanger.
 A damper controlling the flow of air, and valving controlling the flow of water may both be passive or active, or one of each. In any event, the controls may support limiting air flow to obtain maximum temperature in the air from the roof, and maximum temperature in the water from the air. Air and water flows may be restricted to maximize temperatures, and thus, the thermodynamic availability of the heat collected. Contrary to much of solar collection technology, solar radiation need not be concentrated to raise the thermodynamic availability of the fluid stream collecting the heat.
 An actuator, such as a wax actuator or wax motor may operate as a thermostat to selectively open and close the dampers, valves, and the like to enforce pre-selected temperatures in the air and water working fluids.
BRIEF DESCRIPTION OF THE DRAWINGS
 The foregoing features of the present invention will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only typical embodiments of the invention and are, therefore, not to be considered limiting of its scope, the invention will be described with additional specificity and detail through use of the accompanying drawings in which:
 FIG. 1 is a schematic block diagram of a passive solar heat exchange system in accordance with the invention, controlling temperature rise for increased thermodynamic availability by promoting stratification and restricting air flow;
 FIG. 2 is an end view of one embodiment of a dampered, stratified, solar collection system under a roof, using the roof for solar energy absorption;
 FIG. 3 is a schematic diagram of the air flows associated with stratified heating within an attic space of a building such as a house;
 FIG. 4 is an end view of a heat recovery system in accordance with the invention installed in a trussed attic space;
 FIG. 5 is an end view of a trussed attic space containing a substantially closed circulation system down drafting cooled air in accordance with the invention;
 FIG. 6 is a partial, cutaway, end view of the system of FIG. 5 showing the open air path through the soffits and lower vents, along the underside of the roofing materials, through the heat exchange elements, and ultimately through the top damper and exiting out the ducting created by a vent cap;
 FIG. 7 is a perspective view of the apparatus of FIGS. 5 and 6, illustrating alternative locations for storage tanks, one high and suitable for free convection heating, and the other set low and thus remaining cooler than the exchanger absent forced convection;
 FIG. 8 is an end view of the apparatus of FIG. 7, relying on a larger tank located principally above the heat exchangers in order to maintain maximum temperature by free convection of the liquid, heat-exchanging fluid;
 FIG. 9 is an end view of one embodiment of an alternative heating system relying on passive solar collection through windows provided with curtains as absorbent receptors of solar radiation and directors of (e.g., effectively ducting) heated air toward the heat exchange element in accordance with the invention;
 FIG. 10 is a perspective view of one embodiment of a dry, rooftop, solar collector relying on transparent, insulating cover over a duct provided with an absorbent top surface to collect heat without requiring large expanses of conventional, liquid, carrier lines;
 FIG. 11 is a side elevation view of one embodiment of a damper controlling horizontal or vertical flows, depending on orientation of the wall element, of incoming or outgoing air heated in accordance with the invention;
 FIG. 12 is a side, cutaway, elevation view of a duct, illustrating various alternative embodiments of dampers to control the flow of air through the heat exchange elements thereof;
 FIG. 13 is a partial, cutaway, end view of a heat recovery system collecting passive solar energy from a roof, where the insulation is placed between the rafters in the roof, rather then at the base of the attic; and
 FIG. 14 is a schematic end elevation view of a building containing various alternative embodiments of elements including controls, storage tanks, pre-heaters, water heaters, and connecting lines, illustrating various alternative embodiments for maintaining free and forced convection of heating fluids such as water passing through heat exchangers implemented in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 It will be readily understood that the components of the present invention, as generally described and illustrated in the drawings herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the system and method of the present invention, as represented in the drawings, is not intended to limit the scope of the invention, as claimed, but is merely representative of various embodiments of the invention. The illustrated embodiments of the invention will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.
 Referring to FIG. 1, a system 10, apparatus 10, or method 10 in accordance with the invention may include ducting forming a wall defining a channel. It may be appropriate to talk about ducts 12 or ducting 12, meaning the channel, and the walls, respectively, formed as ducts 12. In general, the ducting 12 is responsible to conduct air, and need not be closed completely imperviously. For example, conventional heating, ventilating, and air-conditioning (HVAC) technology includes plastic, metal, and sometimes wooden chambers and conduits that effectively act as ducting 12. Similarly, the entire structure of a room or attic may act as a plenum as part of a circuit (closed or open) of air flow.
 Typically, controlling the restriction on the flow of air, and thus the flow of air through ducting 12, through one or more vents 14, 16 may obstruct the flow and control temperatures. Since temperature is a direct function of mass flow rate of air, for a particular amount of heat available, temperatures may be maintained at higher values (within temperature and transfer limits of a heat source) by restricting the amount of air available to receive the heat transferred into the air. Thus, a vent 14 may be placed low in the air flow system, high (e.g., as upper vent 16) in the air flow system, or both may be employed.
 Typically, the vents 14, 16 may be completely open at all times. In other situations, the vents 14, 16 may be provided with dampers 18 to selectively open and close flows, such as by closing the vents or opening them. In yet other alternative embodiments, the vents 14, 16 may be open at any or all times, while the dampers 18 are placed elsewhere in the flow. Regardless of the location of a damper 18, so long as it is within a single path of ducting 12, it may partially or completely obstruct the flow through that ducting and thus through any vents 14, 16 in the direct path of the air flow through that ducting 12.
 Dampers 18 may be placed as lower dampers 18a or upper dampers 18b in the flow. However, a damper 18 may not be placed at a high or low position, but may be placed anywhere within ducting 12 to provide the required obstruction. It is proposed in several embodiments that actuators 19a, 19b associated with dampers 18a, 18b operate based on temperature.
 For example, in one embodiment, an actuator 19 may be a wax actuator having an operating material of a blend of wax that expands with temperature. The wax operates on a piston to expand or contract the overall length of the actuator 19 by extension of a piston thereof. Thus, in one embodiment, the dampers 18 may be controlled by actuators 19, which are themselves responsive to temperature.
 For example, in one embodiment, an actuator 19 on one damper 18 may act to seal the system 10 off in cold weather. By the same token, another damper 18 may be controlled by an actuator 19 that will restrict airflow to achieve a particular temperature at a particular location in the system 10, such as near the exchanger 20 to maintain an air temperature sufficiently high to ensure a proper temperature of liquid in the heat exchanger 20.
 For example, high thermodynamic availability is a direct function of temperature differential. Accordingly, in order to provide a good supply of sufficiently hot water, from the heat exchanger 20, it may be advisable to restrict the flow of air through the heat exchanger 20, assuring a higher temperature. Thus, a particular actuator 19 operating on a corresponding damper 18, may be engineered, designed, or otherwise set to restrict the flow through a damper 18 or past a damper 18 whenever the temperature of the consequent air flow is not at a sufficiently high air temperature, such as one for which the system is designed or desired to operate.
 In general, a line 21 may pass through a heat exchanger carrying a fluid such as water. In certain embodiments, an exchanger 20 may actually be transferring heat into another heat exchange system in a "double loop" arrangement. In such circumstances, the fluid in the line 21 need not be potable water. For example, a water providing with a certain amount of alcohol, glycol, or other antifreeze agent, and may even include salt, as a mechanism to maintain the line 20 free flowing and without any freezing. In other embodiments, the line 21 may carry a once-through pass of culinary water that is simply pre-heated to whatever extent it can be before being sent off to other systems such as a water heater for final heating.
 In one embodiment of an apparatus in accordance with the invention, the line 21 carries water while an array of fins intimately bonded to the line 21 exchanges heat between the passing air and the line 21. Thus, a comparatively larger area exposed to air may accommodate the reduced heat transfer coefficient in air, while the comparatively smaller area of the line 21 corresponds to the comparatively higher heat transfer coefficient of water.
 In general, a volume 22 such as the enclosed body of an attic 22 may host the ducting 12 and the exchanger 20. In typical embodiments, a solid conductor 24 basically comprises the roofing. Typically, the conductor is a composite of various materials. For example, tiles, shingles, membranes, and other roofing materials on top of wooden substrates such as plywood, composition board, concrete, steel, or the like may form the conductor 24. The conductor 24 is typically solid, although it may contain spaces, gaps, air, or the like.
 The conductor 24 may also include insulated spaces. However, in many embodiments of an apparatus in accordance with the invention, the enclosed volume 22 is not interior to insulated spaces. For example, if rafters pitched along the angle of a roof are themselves insulated, then ventilation will typically be provided along the rafters above the insulation, and below the roofing materials that form the conductor 24.
 Meanwhile, in an uninsulated attic, the enclosed volume 22 of space or air typically sits above insulated joists or horizontal members of truss work. Here, the angled portions of a roof are called rafters. The horizontal portions of roof trusses are called joists here, although people sometimes refer to them as rafters also. Nevertheless, in certain roof structures, insulation is placed exclusively over the ceilings of lower floors, and the attic remains unused. This is typical when truss work fills the attic such that it is not habitable space not readily accessible space for living storage.
 Typically, radiation 26 from the sun 30 may strike an absorber 28. The absorber 28 is typically an upper surface of the same material that forms the conductor 24. For example, the stone surface of an asphalt shingle, the surface of a ceramic, clay, concrete, or other tile, or the like may form or define the absorber surface 28. Accordingly, radiation 26 from the sun 30 strikes the absorber 28 and is converted from its short wavelength, high frequency wave form to thermal energy that may then be transmitted by conduction through the conductor 24. Of course, a certain amount of the absorbed energy found in the absorber 28 may be convected away by ambient air.
 Opposite the absorber 28 or absorber surface 28 of the conductor 24 is the convector 32 or convector surface 32. Typically, the convector 32 engages in two types of heat transfer. That is, convection 34 involves conduction of heat from the convector 32 to adjacent air, followed by a net flow or bulk flow of the air as it moves, e.g., as it heats and rises in free convection. Thus, convection 34 is a combination of conduction and bulk air flow.
 Meanwhile, the same surface that operates as a convector 32 may also serve as a radiator 36. For example, radiator surface 36 maintains a temperature that may be substantially higher than other portions or surfaces within the space 22. Accordingly, energy may radiate from the radiator 36 as infrared radiation 38. Infrared radiation is not as effective as solar radiation. For example, typically, radiation 38 transfers between a comparatively warmer surface to a comparatively cooler surface only at about the same rate that energy convects away from a heat transfer service by convection 34.
 Heat transfer controls many aspects of a temperature within the space 22. To the extent that a heater exists completely below a particular point in a freely flowing, inviscid fluid of any state (liquid, gas, vapor) the entire process of convection 34 will usually dominate. The heated space 22 has little temperature gradient above the source of heat. Typically, where convection is unobstructed inside, and only free convection cooling is available outside, any type of a heating element in a free pool of fluid will heat all of the fluid above the heating element to some stable temperature. Only a very slight gradient, typically a few degrees will exist between the top of the pool of fluid and the top of the heating element.
 By contrast, throughout the depth of the heating element, a temperature gradient will exist. Below the heating element, the temperature will have a steep gradient or be an almost uniform temperature, depending on whether any significant heat source is below, often having only the gradient imposed by conduction downward.
 Thus, where a conductor 24 is made of the roof of a building, such as a slanted roof, heat is added all the way along the length of the roof. Thus, heat is added at the lowest levels, heat is added at the highest levels, and heat is added at intermediate levels. Accordingly, the enclosed volume 22, space 22, or attic 22 will typically stratify, providing strata 40 at different temperatures.
 The air strata 40 may have some maximum temperature stratum 40a at the top, with subsequently cooler strata 40b, 40c, etc. down to the lowest stratum 40m, and temperature may vary continuously.
 The strata 40 exist exactly because heat is added along substantially the entire height of the space 22 or the volume 22. In any system where heat is added in one location and extracted from another, a gradient will exist. Nevertheless, it has been found that wherever water or air is free to move, the entire temperature gradient between a heat source and the upper level of the tank or containment vessel holding the fluid is typically only a matter of a degree or two unless some very significant (e.g., liquid or forced convection) is occurring to take heat away from the containment region.
 Otherwise, so long as free convection in air is the only mechanism for removing heat from a volume, across the wall, the temperature gradient above a heating element is comparatively insignificant. Likewise, where a heating element provides substantially constant heat at all levels over the height of a contained mass of fluid, such as water or air, it has been found that a gradient will be established at a very significant slope. The temperature typically will vary substantially linearly from top to bottom between the maximum temperature at the top and the coolest temperature in the contained reservoir or volume at the bottom.
 Typically, an input line 42 connects to or is a part of the line 21 through the exchanger 20. In certain embodiments, the ducting 12 conducts hot air, while the line 21 is fed water through the inlet line 42. Typically, the inlet line 42 is cold, comparatively speaking, while the outlet line 44 also connected to the line 21 and the exchanger 20 is comparatively hot.
 When warm air from the normal environment is cooled, its capacity to hold moisture is reduced. To the extent that humidity may be high, cooling of air in an exchanger 20 with comparatively cooler water passing through a line 21 in the exchanger 20 will result in condensate 46 exiting out a condensate line 46 from the exchanger 20. The condensate line 46 is not carrying away water from the line 21, or from the inside of the line 21. The condensate line 46 carries away humidity that has been chilled out, like the sweat on a cold drink container on a hot, humid day.
 As heat 46 is transferred from the air into the water or other fluid in the line 21 of the exchanger 20, the cooled air resulting may condense out moisture that was previously carried as vapor in the humidity of the air. Accordingly, a condensate line 46 may feed condensed moisture out of the ducting 12 or from regions thereabout for disposal elsewhere. Otherwise, the moisture may cause other problems.
 In general, a flow 50 of air passing through ducting 12 inside or connected to the volume 22 may pass through an exchanger 20, giving up heat 48 into the fueled line 21 on the exchanger 20, while condensing out any excess humidity as liquid through the condensate line 46.
 Referring to FIG. 2, while referring generally to FIGS. 1-14, a system 10 is shown in one embodiment. Rafters 56 and joists 58 (sometimes called rafters, but referred to as joists simply to distinguish horizontal members 58 from the angled rafters 56) together support a building 60 by tying together the walls 61, and supporting the roof 62.
 Typically, an attic 64 may define the contained volume 22 of air below the roof 62 and heated thereby.
 Typically, in an attic 64 as illustrated in FIGS. 2-3, the bottom 66 of the attic 64 may have insulation 68 to insulate the occupied space of the house 60 or building 60 therebelow. Meanwhile, in such a configuration, the roof 62 is typically uninsulated and vented. Therefore, the flow 50 of ambient air flows up through soffits or vents under the eaves of the roof 62, and along the undersurface 32 thereof. Typically, the space 22 is completely filled with air, and thus the flow 50, rises and stays closest to the convector 32 and radiator 36 surfaces of the roof 62. Accordingly, the absorber 28 of the roof 62 receives radiation 26 from the sun 30 which then heats the conductor 24 or roofing material 24. Thereupon, the convector 32 and radiator 36 proceed to convect heat into the flow 50, further heating it, as well as radiating, respectively, to the bottom 66 of the attic 64. Accordingly, some warming of the bottom 66 of the attic 64 may occur with consequent heating of air thereabove.
 Nevertheless, the majority of heat in the attic 64 will be received by the convector 32 convecting heat into the flow 50 rising along the underside of the roof 62. Typically, attics will have some type of a venting system. In certain embodiments of an apparatus and method in accordance with the invention, a damper 18 may limit the ability of air to vent through ducts 12, vents 16, or both.
 For example, typical construction may include placing vents 16 in roof structures. Vents may be formed as ridge vents, such as the duct 12 feeding air out of the attic 64 under a ridge cap or cap 70 that forms the upper vent 16. Meanwhile, soffits of eaves may be provided with lower vents 14. Typically, in a system in accordance with the invention, cooler air enters a lower vent 14, and is ducted out through one or more openings higher in the attic 64.
 Some attics may be vented by cross flow of breezes through vents in the gable of the attic. In other situations, a vent cap 70 or ridge cap 70 covers an opening or openings near the ridge of the roof 62 protecting against entry of weather such as rain and snow, while still providing exit of the flow 50 of air through the attic 64. Thus, the flow 50 may pick up much of the heat impinging on the roof 62 as radiation 26 absorbed therein and carry it out by convection through the upper vent 16.
 In an apparatus and method in accordance with the invention, maximum thermodynamic availability is desired for obtaining most efficient heat transfer into the exchanger 20 and maximum temperature. Higher thermodynamic availability results in and from higher temperatures at the highest points in the space 22 of the attic 64, thus providing maximum temperature in the line 21 of the exchanger 20.
 In the illustrated embodiment, one or more dampers 18 form, control, or both the ducting 12 directing air from the flow 50 through the exchanger 20. For example, the damper 18 may be placed below, above, or in both places with respect to the exchanger 20 in order to restrict the flow 50 of air. If the flow 50 is left unrestricted then the temperature in the exchanger is left largely to chance.
 In certain embodiments, the exchanger 20 may operate in the absence of a damper 18. However, in order to provide flows by free convection, substantially exclusively, it may be preferable to rely on the damper 18 to limit the free convection flows 50 of air. This helps maintain the thermodynamic availability of heat in the flow 50 by limiting the net mass flow rate thereof.
 Referring to FIG. 3, in particular, while continuing to refer generally to FIGS. 1-14, a system 10 in accordance with the invention may take advantage of the strata 40 formed by virtue of the flows 50 of air entering into and rising through the space 22 below a roof 62 of a building 60. As illustrated, each of the individuals 50a into the lower vent 14 of the attic space 22 of a building 60 may rise along the convector surface 32 and radiation surface 36 of the conductor 24. Typically, if the upper vent 16 is open, then the flows 50 will progress as directly as permitted toward the upper vent 16 to exit the space 22.
 However, to the extent that the flows 50b are heated faster by the convector 32 then they can rise above all the strata 40 then the air may stratify. For example, if a flow 50b is rising along a convector 32 and picking up heat, it may come to the point that it exceeds in temperature the surrounding strata 40a, 40b, 40c and so forth to stratum 40n. However, alternatively, if the ducting 12 is restricted, artificially, by design, or simply as a result of the built in floor resistance from either vent 14, 16 then a flow 50b may find that a particular stratum 40 is already hotter than the flow 50b. Thus, the flow 50b may spread out as a flow 50c at a particular level of a stratum.
 For example, a flow 50b may rise along a convector 32, picking up heat. However, as soon as the net temperature of the convector 32 can no longer effectively heat the flow 50b (which is cooling down by entraining fluid from the space 22) hotter then a stratum above it, say, for example, the stratum 40b, then the flow 50c must flow laterally under the stratum 40b, and become the stratum 40c.
 Each of the flows 50b will continue to draw into it from each of the strata 40 as the flow 50b passes by. For example, as the flow 50 traverses upward along the convector 32, it continues to pick up additional mass. One may think of this entrainment as the flow 50b growing larger, extending further away from the convector 32 and carrying more net mass flow with it. Thus, a certain degree of mixing occurs between the flow 50b, and the strata 40 of air in the space 22.
 Nevertheless, no particular flow 50b can rise above a stratum 40 hotter than flow 50b is itself. Thus, air in the stratum 40a has received heat from all layers below. However, air in the stratum 40n receives heat only from the lowest portion of the roof 62, because the flow 50b entrains air from the strata 40, it exchanges not only momentum but heat energy. Therefore, the net temperature or net average temperature of the flow 50b is increasing as the result of additional heat added by the convector 32, but decreasing as a result of mixing with the various strata 40 in passing. Thus, one may think of the flow 50b as being involved in a balancing act between the net temperature gained from the convector 32 balanced against the net temperature loss caused by mixing with the strata 40. Thus, one can readily see how the flow 50b may top out at a particular stratum 40 short of the top stratum 40a in the space 22.
 Ultimately, heated air in the space 22 will arise through the duct 12 and exit out the vent 16, driven by the net effective density of the air outside the building 60 compared to the net density of the air in the space 22 within. One may thus think of the flow between the vents 14, 16 as a chimney-like effect as the more dense column of air outside the building 60 displaces, through the vent 14, the lighter density air in the space 22. Accordingly, air incoming through the vent 14, may actually flow immediately into the bottom stratum 40n as hot air from the uppermost stratum 40a is rising through the duct 12 and exiting through the vent 16.
 Referring to FIGS. 4-8, specifically, while continuing to refer generally to FIGS. 1-14, a system 10 in accordance with the invention may include some type of a barrier 72 restricting air in the space 22 from rising, except through duct work 12. In the embodiment of FIG. 4, for example, flow from the vent 14 into the space 22 may fill the space surrounding the various trusses 54, including braces 55, rafters 56, and joists 58. As discussed above, the term joist 58 is used even though a roof structure 62 may not have a floor thereabove. Since typically, the horizontal and angled members of the perimeter of a truss may both be called rafters we will refer to the angled member of a truss 54 as the rafter, and the lower member, extending horizontally as the joist 58. In the illustrated embodiment, a flow 50 rising from a vent 14 may be heated by the roof 28. Meanwhile, ducting 12 provides the only escape for the flow 50.
 Accordingly, with exchangers 20 located in the duct work 12, the flow 50 must pass through one or more exchangers 20 delivering heat into the lines 20 therethrough. Thus, the incoming line 42 provides a substantially and comparatively cooler stream of liquid, such as water, into the exchangers 20. In the illustrated embodiment, the cooler water from the inlet line 42 goes first to the top exchanger 20. This is not necessary. In certain embodiments, the inlet line 42 may go first to the bottom exchanger 20, and then pass into subsequently higher exchangers 20. In fact, such an arrangement will flow much more readily and naturally without the need for a check valve 74. A check valve 74 may be placed in the line 42 in order to assure that fluid (water) is always passing only in one direction through the exchangers 20.
 Also, the water passing through the exchangers 20 may or may not be the same water as is drawn off for use by an independent draw line 76 or draw 76. For example, insulation 78 around a tank 80 may provide a reservoir of hot water received from the outlet line 44 of the exchangers 20. Thus, the maximum temperature in the tank 80 is at the top thereof where the inlet line 44 delivers hot water. Meanwhile, the coldest water in the tank 80 is at the bottom thereof and is fed into the inlet line 42 to the exchangers 20.
 In certain embodiments, the inlet line 42 may simply be connected to the building water supply. Thus, the line 42 may feed directly into the exchangers, and thus provide pressure, flow, and a water supply to be heated by the exchangers 20. In such an event, the outlet for the tank 80 may simply be in the draw 76. Alternatively, the line 42 may be thought of as two lines, one serving the building 60 out of the tank 80, and the other feeding from the building water supply into the exchangers 20, to provide the outbound outlet line 44.
 In the illustrated embodiment of FIG. 4, the duct 12 exits the roof 62 through a vent 16. The illustrated vents, sometimes called turtle vents 16, at particular locations may permit exit of the flow 50 only after that flow 50 has passed through the exchangers 20. In other embodiments, a ridge vent, or even an end vent may be ducted to dispose of or to conduct out of the space 22, the hot air being released to ambient air.
 Check valves 74 may assure that water can only flow in one direction into the exchangers 20. If the highest exchanger 20 is provided the coldest flow of incoming water from the line 42, then the density in the line 42 is higher and the water column therein is heavier than the column in the exchangers 20 themselves. With the buoyancy effect of hot water against cool water, cool water will tend to drop, thus drawing water backwards out through the line 42. To assure that this did not occur, the line 21 of the top exchanger 20 may be placed below the lowest point of the tank 40. Thus, the weight of the column of water in the exit line 44 may be lighter than the column within the tank 80 and the line 42 feeding into the exchangers 20. Any transient circumstances otherwise may be cured by the check valve 74 prohibiting flow backwards through the line 42.
 One reason for placement of the feed line 42 feeding water first into the topmost exchanger 20 is to assure that the hottest air from the space 22 strike the bottom exchanger 20 first, and that the bottom exchanger 20 be the last unit to heat the water thus heating water to its maximum possible temperature before being discharged into the tank 80.
 Alternatively, the free convection flow through the lines 42, exchangers 20, and line 44 may be best served by feeding the cool water from the line 42 into the bottom exchanger 20 first. However, this tends to reduce the driving temperature difference heating water in the upper exchangers 20, driven by the hot water below, already heated by the comparatively hottest air passing through the bottom exchanger 23.
 Referring to FIG. 5, while continuing to refer generally to FIGS. 1-14, certain embodiments in the space 22 may be comparatively closed. For example, in the illustrated embodiment, a flow 50a is rising along the convector 32 in the space 22. The flow 50a may stratify, mix, or otherwise fill the space 22. Ultimately, however, from the space 22, a flow 50b may be ducted upward through the ducting 12. The flow 50b may then turn down through the array of exchangers 20.
 Again, the chilling effect of water in the line 21 is operating to push the colder flow down through the exchangers 20. Each exchanger 20 chills the flow 50c, with the upper exchanger 20 receiving the hottest air available. As the air cools, it drops down through the ducting 12 to the next lowest exchanger 20. Ultimately, the coolest air drops down past the bottom exchanger 20 and exits as the flow 50d back into the bottom of the enclosed space 22.
 Meanwhile, the tank 80 with its insulation 78 in the illustrated embodiment may feed a flow 42 into the bottom exchanger, from whence the flow 82a feeds to the next exchanger 20, followed by the flow 82b to the next exchanger, and so forth until the flow 82c feeds the last exchanger 20 at the top of the duct 12. Finally, the last exchanger 20 provides a flow 44 into the top of the tank 80. Thus, the air flow 50c drops down through the ducting 12, while the heated water flow rises through the various exchangers 20 and ducting 12.
 To ensure that maximum temperatures are reached, a thermally activated damper 18 may restrict the ducting 12 at any appropriate location. The damper 18 may be located within the ducting 12 near the exchangers 20, at the bottom thereof, at the entrance of the air flow 50b into the ducting 12, or the like.
 As a result of the extensive cooling that a flow of cool liquid such as water may cause in the flow 50c, in humid environments, a tray 84 may collect water or condensate from the airflow 50c for disposal. In certain embodiments, a condensate line 46 imbedded in the tray structure 84 may even be insulated 86 to limit re-evaporation thereof. Thus, the insulation 86 may keep the tray 84, condensate line 46, and the condensed water therein somewhat isolated from the heat of the attic space 22. The condensate line 46 may drain into an appropriate location, such as a household drain, outdoor drain, or the like, limiting humidification of the space 22 that might tend to inhibit operation of the system 10 or damage the structure of the building 60.
 In addition to the system 10 of FIG. 5, additional roof vents may be provided as free vents. For example, certain small vents 16 may be provided that will provide only minimal venting of the space 22. Thus, the system 10 operates primarily as a ducted system, as far as the air is concerned. However, in order to flush or bleed off moisture in the air and provide a small amount of makeup air, a lower vent 14 and upper vent 16 of comparatively restrictive smaller size may be provided. For clarity, the illustration of FIG. 5 does not include vents, but the system may be comprised of vents such as those shown in the other FIGS. 1-14.
 Referring to FIGS. 6-8 some attic space 22 may be living space. Even when the attic 64 is constructed in a way to provide only storage or vacant space, the attic 64 may be cooled. For example, in the illustrated embodiment, the vent 14a may feed the flow 50a into a vent 14b extending up between the rafters 56 of a roof 62. In the illustrated embodiment, a closure 88, such as sheet rock or other finished material may enclose a living space 22. The living space 22 may actually be separated completely from the ducting 12. Instead, the embodiment of FIG. 6, air through the vents 14a, 14b may pass into ducting 12 lying above the insulation 90. The insulation 90 may be separated by a vapor barrier and other material as part of the closure 88. In typical construction, sheet rock backed by a vapor-liquid-impervious layer may form the closure 88 sealing the heated space 22 away from the exterior space. The ducting 12 above the insulation 90 may conduct the flow 50 upward toward an exchanger 20.
 Passing through the exchanger 20, the flow 50 gives up heat into the line 21 for exiting out through the upper vents 16. A tank 80 (all parts and systems may be plural) may be fixed high among the rafters 56. In one presently contemplated embodiment, the exchangers 50 may be at or below the lowest point in the tank 80. Meanwhile, the tank 80 may be insulated 78 by or between the structures holding it. The tank 80 may be accessed by a simple plumbing system as discussed hereinabove, or as described in other art, such as U.S. Pat. No. 5,014,770 to Palmer, incorporated herein by reference.
 In the embodiment of FIG. 6, dampers 18 may be placed over the vents 14a, 14b, or ducts 12, as illustrated. Likewise, the damper 18 may be fixed across or within a vent 16. In certain embodiments, dampers may be placed in more than one location. For example, in one embodiment, the damper 18 may be placed to trigger on cold weather, thus shutting off the system when temperatures are so low outside that the system 10 will not operate properly. Meanwhile, those or other dampers 18, such as dampers high in the system 10 may be configured to operate only when temperatures are sufficiently high to provide suitably high water temperatures. In certain embodiments, a damper 18 such as the damper 18 of FIG. 6 may be positioned high in the system 10, such that only the existence of suitable temperatures to provide pre-determined water temperatures within the lines 21 of the exchangers 20 will open the damper 18 to allow the flow 50 to exit the vent 16. At all temperatures lower, the vent 16 may have substantially zero flow.
 In certain situations, such as systems 10 that receive culinary water destined for use from a water heater, in the "off season" of winter conditions, one may take the exchangers 20 out of service valves by passing them with the culinary water and draining them. Thus, ventilation may continue past them in winter time without fear of freezing pipes or condensation within the ducting 12. In substantially all embodiments, condensation should be considered, inasmuch as humidity is increased whenever a flow 50 of air is cooled, reducing its capacity to hold moisture.
 Referring to FIG. 7, alternative locations for the tank 80 may be not only above the exchangers 20, but sometimes below, elsewhere in the attic 64, or even on floors below the attic 64 or in a cellar or basement. However, to the extent that the tank 80 is positioned below the exchangers 20, flow will not be naturally (freely) convected from the lines 21 into the tank 80. Water will have to be pumped against the density gradient.
 Palmer, incorporated hereinabove by reference, discusses many systems for manipulating the flow of water by forced convection. Such may be incorporated into an apparatus 10 in accordance with the invention. Nevertheless, such systems are not the principal point of an apparatus and method in accordance with the invention. In contrast to Palmer, an apparatus and method in accordance with the instant invention may rely primarily or completely on passive, convective flows of both air and water. To the extent that a water line from a building may be connected through the tank 80 in a secondary heat exchange loop or path, or directly as a primary fluid in the line 21 of the exchanger 20, water flow may occur by forced convection.
 Referring to FIG. 8, the tank 80 may be formed to be of any arbitrary shape for which space exists. For some roofs, the pitch angle is sufficiently large with respect to horizontal that a large (e.g., narrow triangular or otherwise) space is available, and substantially unusable for living space. Thus, a rectangular or circular tank 80 may be suspended, supported by braces, or otherwise fixed within the structure of the rafters 56.
 Accordingly, it is contemplated that structural changes to the internal structure of an attic 64, including selecting, moving, designing, attaching to, or passing around braces 55, rafters 56, joists 58, and other truss members 54 may be done in order to install initially during construction, or as an after-construction modification to a building 60, such a system 10.
 Referring to FIG. 9, an apparatus and method 10 in accordance with the invention may also be implemented in spaces other than an attic 64. For example, in the embodiment of FIG. 9 a wall 61 may support a window 94 having one or more panes through which solar radiation 26 may pass. Glass, for example, provides a window 94 that will pass solar radiation, but will not effectively transmit infrared radiation back from a heated object inside the building 60 of the window 94.
 In the illustrated embodiment, an exchanger 20 may be located above, behind, or near a driver 96 and may be hidden by a valance 98 in front of a curtain 100, or by the curtain 100 alone. The curtain 100 may be of any suitable type. When solar radiation 26 is available, and particularly when undesirable to allow it into the space 22, due to excessive lighting or heating effects, the curtain 100 may itself become the convector 32 and radiator 36. The radiator 36 may radiate heat back to the window 94, which heat cannot readily escape.
 Thus, the flow 50 may be heated by the window 94 and convector 32 (outer surface of the curtain 100) as the flow 50 rises. The curtain 100 and window 94 form ducting 12 or a duct 12 through which the flow 50 may rise. The curtain 100 may be of any suitable material and may be colored or treated to readily absorb solar radiation.
 For example, the insets show various embodiments including a series of tubes such as reeds, bamboo, plastic, or the like forming a substantially continuous curtain 100. Likewise, certain expandable (e.g., folded) panels made of paper, polymer fabric, or the like may be extended or drawn up.
 Likewise, Venetian-type curtains 100 having a series of louvers may also operate successfully whether in a substantially open or closed visual configuration. For example, even if the louvers are not in their most nearly vertical orientation, then they still tend to absorb heat, and convect heat back into the flow 50.
 An exchanger 20 located in the duct 12 formed by the curtain 100, window 94, and valance 98 may receive the flow 50 and extract heat therefrom into the contained fluid (e.g., water, etc.) heated and delivered into the tank 80. In the illustrated embodiment, the line 42 may be the water inlet line to the exchanger 20.
 In an alternative embodiment, the inlet line 42 may be provided directly to the exchanger 20 from the household water supply. In such an event, the line 99 may actually feed out to some other appliance, such as a water heater, space heater, other energy storage or manipulation system, or the like. For example, in some embodiments, the heat in the water of the tank 80 may actually be used to run a refrigeration cycle. In one embodiment, the energy provided by the heat in the tank 80 may be run through a cycle, such as, for example, the Servel cycle used in natural gas or propane refrigerators.
 Thus, homes 60 in hotter climates where solar energy 26 or solar radiation 26 is most abundant may benefit by a source of energy for driving refrigeration systems. In the Servel cycle, for example heat from the tank 80 may heat a boiler boiling a vapor out of a solution (an absorbed or condensed gas out of the solution). The gas or vapor and liquid may then be cooled at a location cooler than the tank 80, such as the outdoor ambient. Though the outdoor ambient itself may be uncomfortably warm it is still cooler than the tank 80. Subsequently, the chemical reaction of absorption of the vapor back into the solution is a net endothermic reaction, cooling the fluids now a solution. The combined, cooled solution may pass through a heat exchanger to cool an enclosed space such as a room or refrigerated space to be cooled. The fluid, now warmed by the exchanged heat, may be run through the entire cycle again.
 In alternative embodiments, the tank 80 may be filled at some location other than its highest point, operating as a pre-heater. As a pre-heater, the tank 80 may provide an initial quantity of energy to a flow, which flow will then be heated further by another auxiliary or principal means. By any of these methods, the net energy gained from the tank 80 resulting in the solar radiation 26 may be used to provide useful work or heating energy.
 Referring to FIG. 10, various solar collectors 102 or solar units 102 may also benefit from an apparatus and method 10 in accordance with the invention. For example, a solar unit 102 may have a cover 104 such as a flat plate, various tubes, or the like forming a convective barrier resisting loss of collected heat while providing transmission of light therethrough. Thus, the cover 104 may transmit light to a layer or surface 32 below, acting as a convector 32. The convector layer 32 may heat up as a result of absorbing solar radiation, thus acting as both a surface absorber 28 and a convector 32.
 A damper 18 may operate anywhere in a duct 12 to limit the flow of air through the apparatus 102. Accordingly, the damper 18 controls flow through the duct 12 between the convector 32 and the cover 104. As air enters the lower vent 14, a flow 50 passes along between the convector 32 (e.g., absorber 28 acting also as a convector 32) and the cover 104.
 The damper 18 controls the flow to assure that the temperature of the air flow 50 at the exchanger 20 is suitably hot to provide the desired thermodynamic availability of energy. For this reason, one of the simplest configurations may involve placing the damper 14 above or below the exchanger 20 and very close thereto. In this way, when the temperature at the exchanger 20 is at the proper temperature, then a simple wax actuator, for example, may operate to open and close the damper 18 exactly at the temperature required by the design.
 The upper vent 16 may be covered by a shield 106 or flashing 106. The flashing 106 may assure a suitable degree of weather protection to prevent damage or cooling by precipitation such as rain, snow, ice, or the like.
 As the convector 32 heats air in the duct system 12, below the cover layer 104 and above the convector surface 32, the heated air rises along the angle of the roof toward the exchanger 20. Notwithstanding the flow 50 will be cooled substantially by one or more exchangers 20 in the path of the flow 50, the long column of hot air in the duct 12 provides sufficient buoyancy to drive the flow 50 out of the upper vent 16.
 Referring to FIG. 11, while continuing to refer generally to FIGS. 1-14, a damper system 18 may include more than simply the necessary means to substantially close or obstruct a passage in a duct 12. For example, in certain ventilation systems, a cover 108, often having louvered slats therein, and therefore often referred to as a louver 108, may be secured by fasteners 109 to a wall 61 or other portion of a building 60.
 The cover 108 may be replaced in the illustrated embodiment by any suitable ventilation port or vent 14, 16. For example, in certain embodiments, the wall 61 illustrated may actually be a soffit under the eave of a house. In other embodiments, the walls 61 may be at the end wall of a gable. In still other embodiments, the wall 61 may actually be a rafter 56 and the cover 108 may be replaced by any suitable type of cover such as a wind turbine, a turtle vent, a ridge vent, or the like.
 In general, a damper system 18 may operate to selectively open and close any a particular vent 14, 16 desired. In many embodiments, a damper system 18 may include a closure 110, such as a vane 110 or panel 110 effectively closing a duct 12 or an opening of a vent 14, 16.
 In one embodiment, a panel 110 or closure 110 may pivot on a hinge 111 or other pivot mechanism 111 between an open and closed position. An actuator 112 may be of any suitable type, including electrical, hydraulic, thermal, or any other type. In response to temperature, the actuator 12 may provide an infinitely variable, continuous range of positions for the panel 110 between fully open and fully closed.
 In one presently contemplated embodiment, the actuator 112 may be a wax actuator (e.g., wax motor), relying on the volumetric change in the wax with temperature. Contained within the apparatus 112, expansion and contraction of the wax drive a piston 113. Upon heating, the wax expands pushing the piston 113 in one direction. Upon cooling, the wax drives the piston in the other.
 The actuator 112 may be designed so the piston 113 retracts into the housing upon a rise in temperature or extends out of the housing upon a rise in temperature. This may be done by placing the thermally expanding material either in front of the piston face or behind it with respect to the direction of motion. In the illustrated embodiment, the piston 113 draws into the actuator assembly 112 as temperature increases, thus drawing the piston 113 to reduce in length, drawing the bracket 114 toward the actuator 112, and opening the panel 110 or closure 110 of the damper system 18. As the damper system 18 is opened, the flow 50 may enter into the enclosed space 22. As temperature changes the volume of the wax adjusts to a new equilibrium value, acting as a thermostat.
 Referring to FIG. 12, the actuators 112 are not shown, in some instances for purposes of clarity. However, a panel 110a may cover a duct 12 by pivoting about a pivot 111a in response to operation of an actuator 112 against a bracket 114. Likewise, as an alternative, or in addition, panels 110b may operate between open and closed positions by direct operation of actuators 112. Whenever the duct 12 is closed off by any amount by any panel 110 of a damper system 18, the flow of air is restricted. From the contained space 22 or volume 22 of an attic 64 or other heated space, the flow 50 is continuously regulated between maximum flow and substantially stopped. All heat is concentrated into the amount of the airflow 50 permitted to pass, heated from the sun and cooled by the exchangers 20. Likewise, the comparatively cooler liquid (e.g., water) passing through the lines 21 may be restricted to obtain the maximum temperature rise available in it.
 Referring to FIG. 13, in certain embodiments of an apparatus and method in accordance with the invention, a damper system 18 may be positioned within a soffit, or over some upper vent 16. For example, in the illustrated embodiment, a panel 110 of a damper system 18 may pivot about a hinge 111 or other pivot 111 between an open and closed position ventilating a rafter duct 12 above the insulation 90 thereof.
 In the illustrated embodiment, the exchanger 20 may be idled until such time as the panel 110 is opened. Meanwhile, by a proportional actuator 112, the panel 110 may be positioned to limit flow through the duct 12 and out the vent 16, maintaining a proper temperature in the air flow in the duct 12. Maximum temperature differences provide maximum thermodynamic availability of heat to the air flow 50, the exchanger 20, and ultimately to the liquid flowing in the line 21 therein. The damper system 18 may be installed near the upper vent 16, lower vent 14, or elsewhere in a duct 12.
 Referring to FIG. 14, various arrangements of storage and use of liquid, such as water, from the exchangers 20 and tank 80 may be implemented. In certain embodiments, a tank 80 may be located high in the attic space 24 of a building 60. In the schematic diagram of FIG. 14, the tank 80 may be disposed in any suitable manner. Typically, the tank 80 will be configured to be above the exchangers 20. Absent some forced convection imposed on the input line 42, the exchanger 20 is best located below the top of the tank 80. To heat the entire tank to the maximum uniform temperature the exchanger 20 is best located entirely below the bottom of the tank 80.
 Meanwhile, the exchanger 20 may feed the heat transfer fluid flow 82 from the exchanger 20 through the outlet line 44 into the tank 80, and out the exit line 45 of the tank. As illustrated, various configurations of tanks 80 may be implemented in accordance with the invention. If the tank 80 is in the direct flow of incoming water for the building 60 such as a house 60, the flow 82 may actually be driven from the city water supply. Accordingly, such an exchanger 20 and tank 80 must accommodate the line pressure of the building 60.
 In other embodiments, the line 44 incoming into the tank 80 may simply pass heat on to another heat exchanger 118 in the tank 80, thus heating the water in the tank 80, before exiting out a line 45. In such a configuration the flow 119 into and out of the tank 80 is effectively operating in a secondary loop. Thus, the flow 119 may come from the building water supply, while the flow 82 in such a configuration may actually operate in a closed loop with the exchanger 20. In such a configuration, the flow 82 may be treated with antifreeze, of any chemical variety from salt to glycol to alcohol, and need not even include water. For example, oil, alcohol, and the like may serve well year round. The exchanger 118 provides heat exchange between the heated flow 82 from the exchanger 20 and another fluid such as culinary water or other energy destination.
 In certain embodiments, an auxiliary container such as an extra tank 120 may be used to accumulate heated or preheated water. The tank 120 may be a water heater 122 or may be a reservoir 120 located upstream of the water heater 122 itself. Thus, any amount of heat already captured in the tank 120 may be passed to the water heater 122, thus reducing the amount of heat the water heater 122 must add.
 In one embodiment, a unit 124 may control the flow 132. Typically, a unit 124 may include a valve 126 if the flow 132 is coming from the water supply for the house 60 or building 60. Accordingly, the unit 124 may simply be a valve providing access to water flow 132.
 In other embodiments, the exchanger 20 may be located other than above the tank 80. For example, where the exchanger 20 may be high in the space 22, while the tank 80 is simply replaced by the tank 120 therebelow, forced convection would require a pump 128 in a closed system, or a valve 126 in a system open to regularly receive water from the water supply of the building 60.
 In the illustrated embodiment, the flow 132 flows up through the input line 42 to the exchanger 20 to be heated. The exchanger 20 then provides the flow 132 out through the exit line 44 into the tank 80, if present, or directly to a tank 120. With or without a secondary heat exchanger 118 in the tank 80, flow through the exit line 45 from the tank 80 may provide a source of hot water, or water as a preheated liquid into a storage tank 120. Thereafter, the flow 132 may transfer directly to the water heater 122 as the flow 134 therethrough. The flow 134 may be the regular supply of water for the use of the building 60 such as a house 60.
 In one simple embodiment, the household of water supply may pass through an inlet line 42 to an exchanger 20. The exchanger may be located in ducting 12 receiving heat collected through and from the conductor 24. Heat may be passed therethrough by the convector 32 into the air flow 50.
 In one of the simplest systems to maintain, the exchanger 20 may operate in a closed loop through the tank 80, and thus rely on a closed loop flow protected against freezing, and therefore never needing to be emptied. In such an embodiment, the flow 82 through an exchanger 118 may exchange water with the tank 80. The tank 80 may be the tank 120 or feed it. So long as all the lines are properly insulated, the flows 119 from the water supply of the house may run year round. The flow 82 from the closed loop heat exchange cycle need not operate except when effective to augment or supply the heat needed by the tank 80.
 It may be seen that an apparatus 10 in accordance with the invention and a method 10 in accordance with the invention may operate to constrict flows operating by free convection involving air in a volume 22 receiving heat through a roof 62 of a building 60. Accordingly, the roof 62 itself may become a passive solar collector and heat exchanger transferring heat from an absorber surface 28 through a conductor 24 constituted by the roofing materials. The convector 32 surface of the roof eventually convects heat out therebelow.
 A flow 50 of air may be substantially enclosed, or may be open to the outdoor environment. By proper use of a damper system 18, the flow 50 may be constricted to optimize the thermodynamic availability of heat, increasing the temperature in the highest strata of the stratified air in the space 22.
 By recognizing the appropriate heat transfer mechanisms within the space 22 heated by the conductor 24 and convector 32 (and to a lesser extent by the radiator 36), provides substantially improved heat transfer, higher temperatures, and higher thermodynamic availability.
 In certain embodiments, the flows through the system 10 may actually operate in parallel to feed hot water when available and to cease operation when neither sufficient nor economical. Nevertheless, in most embodiments, an apparatus 10 and method 10 in accordance with the invention may typically provide substantial additional energy even if only preheating domestic hot water prior to entry into a water heater 122. So long as the energy input from the convector 32 into the flow 50 is sufficient to heat a water flow 132 coming into a building 60, economical preheat may be received into the flow 132.
 The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative, and not restrictive. The scope of the invention is, therefore, indicated by the appended claims, rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.
Patent applications in class Solar collector forms part of building roof
Patent applications in all subclasses Solar collector forms part of building roof