Retrofittable tankless passive solar water heater

Abstract

A tankless solar water heater for heating domestic pressurized water having a flexible insulated heat exchanger housing that contracts to accommodate volume reduction when the solar heating fluid cools. A check valve releases gas and solar heating fluid if interior pressure exceeds ambient pressure by more than one pound per square inch, without admitting air into the container or the heat exchanger when volume of the solar heating fluid reduces due to cooling.

Description

TECHNICAL FIELD

The present invention relates to a solar water heater for heating pressurized domestic water that does not require a separate large capacity hot water storage tank that occupies valuable living space; is passive because it does not have any pumps or other moving parts in normal operation, so that service life is increased; and is retrofittable to use any smaller capacity hot water tank from an existing electrical, gas, or other non-solar domestic hot water heater.

BACKGROUND ART

In most developed countries, domestic water is required to be pressurized by a central utility so that water flows through pipes when a faucet is turned on. In conventional solar hot water systems, domestic water is heated during the day by being pumped (using a separate circulation pump) up to a solar panel on the roof of a house, where it is heated, and then the heated water returns to the house through insulated pipes, and is stored in a large capacity insulated tank for future use, usually at night. This insulated solar hot water tank must be of large capacity because the solar panel only heats water during the day, when the sun is shining, and does not heat water at night. This hot water tank typically has a capacity based on expected hot water usage of 20 gallons for the first person, and 15 gallons per each additional person in the household. Because of this size requirement, typical solar hot water tanks have a capacity of 80 gallons or higher. Solar hot water tanks eventually corrode, often in less than 10 years, and when they leak, large quantities of water are released into the house, causing damaging flooding. Further, because of the need for insulation and large capacity, conventional solar hot water tanks occupy a large amount of valuable living space.

In conventional solar hot water systems, the panels on the roof are not well insulated, so that they cool down at night. In the morning, the panels are cold, and therefore cannot heat water.

One problem with designing solar hot water systems is that water expands when heated: 5 gallons of water increases by 1 pint in volume from a 100 degree Fahrehnheit rise in temperature. The maximum temperature in a properly operating solar heating system is about 180 degrees Fahrenheit, so this increase in volume can easily occur from the coldest temperature at dawn to the highest temperature in the afternoon.

A conventional non-solar hot water system typically uses electricity or natural gas to heat up water that is then stored in a small capacity tank. For example, common sizes for the tanks of conventional electric or gas water heaters are 30, 40 or 50 gallons. Because the heater can be turned on at any time (instead of heating only during the day, as is the case with solar heating), a conventional water heater can be turned on to heat more water when the water in the tank becomes colder. Thus, when a conventional solar water heater replaces a conventional non-solar hot water system, both the non-solar heater and the existing small capacity tank must be replaced, and a large insulated solar hot water tank must be installed instead. Usually the solar hot water tank is twice or three times the capacity of the existing small capacity tank, so different or additional storage space within the house must be found. Further, the cost for replacing a solar hot water tank is usually at least twice the cost for replacing a conventional heater's tank, due to the greater size and need for specialized solar contractor to perform the replacement (normal plumbers can replace conventional hot water heater tanks).

There are also tankless electric or gas heaters that can heat sufficient water instantaneously so that no storage tank is necessary.

Some companies combined solar water heaters (using conventional solar hot water storage tanks) with gas or electric tankless water heaters. For example, Bosch sold the Aquastar 1600PS propane solar tankless water heater to receive preheated water from a conventional solar heating system having a conventional solar hot water tank.

U.S. Pat. No. 980,505 to Emmet discloses a series of tubes with vacuum chamber jackets placed side by side, connected at their open ends to a chambered header through which fluid flows into and out of the tubes, absorbing heat as it goes. Page 2, lines 77-79, state that it is difficult to make an air-tight joint or seal between a metal vessel and an outer glass envelop.

U.S. Pat. No. 4,018,215 to Pei discloses a manifold for a solar energy collector assembly in which the working media is a liquid circulated through several tubular collectors in series. Col. 1, lines 48-54, indicate thermal expansion differences cause failure in glass to metal seals. FIGS. 7 and 8 show a single-acting manifold.

U.S. Pat. No. 4,033,327 to Pei discloses a solar energy collector apparatus having several double-wall glass tubular elements connected on opposite sides of an elongated module. The elements are sealed in oppositely facing metal cups and inside the opposite elements is a cross supply tube. The cups are connected by conduits for flow of a liquid through the collectors.

U.S. Pat. No. 4,043,318 to Pei discloses over-sized test tubes having inner and outer walls, with the space between evacuated. A working fluid circulates and is heated. Several of these energy collectors are connected into a manifold for circulation of working fluid.

U.S. Pat. No. 4,212,293 to Nugent discloses a solar energy collector apparatus in which several double-wall glass tube collectors, each with vacuum jacket, depend from opposite sides of an elongated manifold. Several modules are inter-connectable to desired capacity for a particular solar powered heating or cooling system.

U.S. Pat. No. 4,440,156 to Takeuchi discloses a solar heat collector including inner and outer substantially straight tubes being closed at one end and open at the other end sealed at their open ends with the space therebetween being evacuated. A hairpin pipe for circulation of fluid media is disposed within the inner tube and includes two substantially straight sections wherein both or at least one is in surface contact with the inner surface of the inner tube.

U.S. Pat. No. 4,554,908 to Hanlet discloses an electromagnetic energy collector assembly in which a cylindrical glass tube I sealed under vacuum at one end to an inner cylindrical energy absorber having a plurality of grooves on the exterior surface.

U.S. Pat. No. 5,931,156 to Wang discloses a heat-pipe type solar collector that includes a heat absorber portion adapted to absorb solar energy to evaporate a working fluid in heat tube elements; and heat release portion communicating with the heat absorber portion and having a body of a semi-annular or annular cross-section. At night, the working fluid portion flows to the heat absorber portion to generate a vacuum for heat insulating purposes, thereby maintaining the temperature in the water reservoir.

Dewars type vacuum tubes are tubes that are placed one within the other, joined at the neck, with the space between the tubes being evacuated.

However, the inventor is not aware of a tankless passive solar water heater retrofittable to an existing domestic hot water system using Dewars type large diameter vacuum tubes.

Accordingly, it is an object of this invention to provide a solar water heater that avoids the need for a separate solar hot water storage tank.

It is a further object of this invention to provide a solar water heater that is passive, that is, has no moving parts during normal operation, to provide a longer service life.

It is a still further object of this invention to provide a solar water heater that is retrofittable to use a preexisting conventional non-solar water heater and its small capacity tank.

It is a still further object of this invention to avoid the difficulties with existing glass to metal vacuum tubes, specifically the problem of maintaining a vacuum between materials with different thermal expansions.

DISCLOSURE OF THE INVENTION

The above and other objects are achieved by a tankless solar water heater that includes an insulated container (open at an upper end), for solar heating and insulating a solar heating fluid; a flexible insulated heat exchanger housing sealingly attached over the upper end; a check valve (a one way valve that allows fluid or air to escape, but not to enter) sealingly mounted at an uppermost location in the heat exchanger housing; and heat exchanger tubing at least partially contained within the heat exchanger housing, sealingly extending through heat exchange ports in the heat exchanger housing to exchange heat between the solar heating fluid and domestic pressurized water circulating through the heat exchanger tubing. The check valve releases air (and the solar heating fluid and any gas therefrom) when interior pressure in the container and the heat exchanger housing is greater than approximately 1 pound per square inch above ambient pressure, without admitting air into the container or the heat exchanger when the interior pressure is less than the ambient pressure due to volume reduction of the solar heating fluid from cooling. The heat exchanger housing contracts to accommodate the volume reduction of the solar heating fluid from cooling. The container and the flexible heat exchanger are sufficiently insulated to reduce cooling of the solar heating fluid in the heat exchanger housing to 1 degree Fahrenheit per hour at 130 degrees Fahrenheit.

Preferably, the insulated container comprises an outer rigid transparent tube and an inner opaque tube, with an insulating vacuum in the space between the tubes, commonly called an all glass solar vacuum tube, or a Dewar's type vacuum tube solar collector.

Preferably, the heat exchanger tubing is entirely contained within the heat exchanger housing.

Preferably, also, the check valve vents the solar heating fluid and gas therefrom in case of boiling.

In a preferred embodiment, the invention has a plurality of insulated solar heating tubes, preferably eight, each with a flexible insulated heat exchanger housing sealingly attached over each of the upper ends, with a check valve sealingly mounted in the uppermost portions of the heat exchanger housings.

Heat exchanger tubing is mounted at least partially within each of the heat exchanger housings, with the heat exchanger tubing being connected in series between heat exchanger housings. In this manner, when solar heating fluid filling the insulated tubes and the heat exchanger housings is heated by the sun, heat is exchanged between the solar heating fluid and domestic pressurized water circulating through the heat exchanger tubing. The flexible heat exchanger housings contract to accommodate volume reduction when the solar heating fluid cools at night, and the check valves releases solar heating fluid and any gas therefrom if interior pressure in the tubes and the heat exchanger housings exceeds ambient pressure by more than one pound per square inch, without admitting air into the tubes or the heat exchangers when volume of the solar heating fluid reduces due to cooling. The tubes and heat exchangers are sufficiently insulated to reduce cooling of the solar heating fluid in the heat exchanger housing to 1 degree Fahrenheit per hour at 130 degrees Fahrenheit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective exploded view of a presently preferred embodiment of the present invention.

FIG. 2 is a side elevational view of a vacuum tube according to the presently preferred embodiment of the present invention.

FIG. 3 is cutaway view of the vacuum tube of FIG. 2 along the line A-A.

FIG. 4 is an exploded perspective view of a heat exchanger housing and heat exchanger according to the presently preferred embodiment of the present invention.

FIG. 5 is a side cutaway view of a presently preferred embodiment of the check valve of the present invention.

FIG. 6 is a side elevational view of the vacuum tube of FIG. 2, the heat exchanger housing and heat exchanger of FIG. 4, and the check valve of FIG. 5, in assembled configuration.

FIG. 7 is a top end view of the series of heat exchanger housings on the vacuum tubes depicted in FIG. 1.

FIG. 8 is a perspective assembled view of the presently preferred embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, shown is a perspective exploded view of the presently preferred embodiment of a tankless solar water heater according to the present invention 10, comprising eight cylindrical vacuum tubes 20 with flexible heat exchanger housings 30 sealingly attached to the upper ends 22 of each of the vacuum tubes 20. Preferably, the heat exchanger housings 30 are received, aligned, and retained in position in an insulated box 40 lined with polyurethane, fiberglass, or other insulating material (not shown) with an insulated lid 48. Preferably also, the lower ends 24 of the vacuum tubes 20 are received, aligned, and retained in position by a preferably aluminum bottom support holder 60 (comprising a base 62 and top 64, with split rubber hose bushings 66 and 68 to hold the vacuum tubes), and covered by a bottom cover 70. The bottom support bracket 60 and box 40 are preferably joined together by angle members 80.

Referring to FIG. 2, shown is a side elevational view of a vacuum tube 20, comprising a transparent outer tube 22 and a coaxial opaque, preferably black (with a radiant energy absorbing coating) inner tube 24. The space 26 between the outer tube 22 and inner tube 24 is evacuated, to provide thermal insulation for the inner tube 24. Preferably the inner tube 24 has a capacity of approximately 3.5 gallons.

Referring to FIG. 3, shown is an end cutaway view of the vacuum tube of FIG. 2 along the line A-A. As can be seen, the inner tube 24 is coaxial with the outer tube 22, and the space 26 between them is evacuated.

Referring to FIG. 4, shown is an exploded perspective view of a heat exchanger housing 30 and heat exchanger tubing 32 according to the presently preferred embodiment of the present invention. An adapter end plate 90, preferably of stamped brass, is preferably sealingly attached to the upper end 34 of the heat exchanger housing 30 (see FIG. 6), and has two heat exchanger ports 92, a check valve port 94, and an optional fill port 96 (which is plugged, capped or otherwise closed after the heating fluid fills the entirety of inner tube 24 and the heat exchanger housing 30, with any dissolved or entrained air later being released through the check valve as described below). The heat exchanger housing 30 must be made of a flexible material, such as silicon, to be able to expand and contract to accommodate changes in volume due to heating and cooling, as described below.

Preferably the heat exchanger housing 30 is approximately 20 inches long and has a capacity of approximately 1.5 gallons, so that each combination of a vacuum tube 20 and heat exchanger housing 30 has a combined capacity of approximately 5 gallons. This will provide the ability to accommodate a change in volume of approximately 1 pint for the 5 gallons. Preferably the heat exchanger housing 30 is cylindrical and made from extruded silicone, not press molded, in order to provide easier collapsing or puckering when the volume of solar heating fluid cools down and contracts. The heat exchanger tubing 32 is preferably made of copper and is bent into two or three loops, with two preferred, to reduce costs.

Preferably each heat exchanger housing 30 contains approximately 10 feet of heat exchanger tubing 32, holding about 0.1 gallon. The ends of the heat exchanger tubing 36 extend through the heat exchanger ports 92, as shown in FIG. 6.

Referring to FIG. 5, shown is a side cutaway view of a presently preferred embodiment of the check valve 100 of the present invention. As can be seen, a copper pipe nipple 104 is brazed to and extends outwardly through the check valve port 94 in the upper portion 102 of the adapter end plate 90 shown in FIG. 4. Although not shown, a similar copper pipe nipple is brazed to and extends outwardly through the fill port 96, and the ends of the heat exchanger tubing 36 are also brazed to and extend through the heat exchanger ports 92 by approximately the same distance as the pipe nipples. Preferably, a silicone insert 106 is placed inside the nipple 104 to retain a check valve 110, which has a barb end 112. As can be seen, the barb end 112 is inserted and retained in the silicone insert 106. Inside the check valve 110, a chamber 114 contains an O ring at the bottom, and contains a stainless steel spring 116 that biases a stainless steel ball 118 against the O ring 119 to seal off the check valve 110. If pressure inside the vacuum tube 20 and heat exchanger housing 30 overcomes the bias of the stainless steel spring 116, then the contents of the heat exchanger housing (air, the solar heating fluid (preferably water) and gas from the solar heating fluid (preferably water vapor)) are vented through the purge outlet 118. Preferably the stainless steel spring 116 and stainless steel ball 118 are selected so that the check valve 110 releases air, water and water vapor through the purge outlet 118 when the interior pressure in the vacuum tube 20 and the heat exchanger housing 30 is greater than approximately 1 pound per square inch above ambient pressure, without admitting air into the vacuum tube 20 or the heat exchanger housing 30 when the interior pressure is equal to or less than the ambient pressure due to volume reduction of the solar heating fluid, as described below.

Referring to FIG. 6, shown is a side elevational view of the vacuum tube 20, the heat exchanger housing 30, heat exchanger tubing 32, and check valve 100, in assembled configuration, showing the outer transparent tube 22, the inner opaque tube 24, the evacuated space 26 between those tubes to form a vacuum, the heat exchanger housing 30, the heat exchanger tubing 32 (illustrated with only two loops in this embodiment), the heat exchanger ports 36, and the adapter end cap 90, showing the heat exchanger ports 92, check valve port 94 and optional fill port 96. The adapter end cap 90 is retained inside the heat exchanger housing 30 by a stainless steel clamp 97. As can be seen, the heat exchanger housing 30 overlaps the upper portion 22 of the vacuum tube 20 and is then clamped by a stainless steel clamp 120. The inner tube 24 is joined to the outer tube 22 at a lip 28. Preferably the inner diameter of the inner opaque tube 24 is approximately 3.5 inches and the outer diameter of the outer transparent tube is approximately 4.75 inches.

Referring to FIG. 7, shown is a top end view of the heat exchanger housings 30 on the top ends of the series of vacuum tubes 20 (not shown). As can be seen, the ends 36 of the heat exchanger tubing 32 (not shown) extending from the heat exchanger ports 92 are connected in series, so that water circulates through all of the heat exchanger tubing of each heat exchanger housing 30.

Referring to FIG. 8, shown is a perspective assembled view of the presently preferred embodiment of the present invention, which shows more clearly how the heat exchange tubing 32 of each of the heat exchange housings 30 is connected in series, and how each heat exchange housing 30 is clamped onto each vacuum tube 20 with a stainless steel clamp 120, and how the adapter end plates 90 are retained inside the top end of the heat exchanger housings 30 by stainless steel clamps 97.

Operation of the tankless water heater of the present invention will now be explained. After assembly of all the components of the embodiment 10 shown in FIG. 1, each of the inner tubes 24 and heat exchange housings 30 is completely filled with a heating fluid, preferably water, optionally through fill ports 96. The tankless solar water heater is then placed in the sun at an appropriate orientation for maximum solar exposure, and with the check valves 100 at the highest points. The pressurized domestic water supply is then connected to the ends of the series-connected heat exchanger tubing 32, so that the domestic water circulates through the heat exchanger tubing 32 under the normal domestic pressure. Thus, no pump is necessary, so that the system is not vulnerable to shutdown because of a pump failure.

The radiant energy of the sun will heat the opaque inner tubes 24, which will heat the solar heating fluid inside, up to a maximum of approximately 180 degrees Fahrenheit. Preferably, an optional anti-scalding valve is provided to prevent water of this maximum temperature from entering the shower, bath, sink or other fixture. The transparent outer tubes 22 form a vacuum 26 around the opaque inner tubes 24, so that the solar heating fluid is insulated against heat loss, much like a Thermos bottle. Because heat rises, the heated solar heating fluid will rise to the top of the vacuum tubes 20 and into the heat exchanger housings 30. Initially, this heating will drive out air that has been entrained in the solar heating fluid, which will then create outward pressure on the check valve 100, which overcomes the urging of the stainless steel spring 116 and stainless steel ball 118 against the O ring 119. The air will then vent through the purge outlet 118. The solar heating fluid will also expand as it heats up, and may also generate gas, and this will similarly be vented through the purge outlet. After the solar heating fluid reaches its maximum temperature of about 180 degrees Fahrenheit, it will start to cool down when the sun starts to go down. This cooling will cause the solar heating fluid to contract, which will create negative pressure in the vacuum tube 20 and heat exchange housing 30. This negative pressure will urge the stainless steel ball 118 against the O ring 119 even more strongly, so that the check valve 100 will close even tighter. Because the heat exchanger housing 30 is flexible, it will contract by puckering inward to accommodate the volume reduction caused by this cooling.

After perhaps a few weeks of operation, all entrained air and excess solar heating fluid will be driven out of the vacuum tube 20 and heat exchanger housing 30 by the expansion from the maximum temperature achieved. The check valve 110 will then effectively remain shut indefinitely, and the heat exchange housing 30 should now fill to its maximum capacity only when it again achieves the highest temperature. At this point, the system is completely closed to the atmosphere, except that, in the unlikely event of boiling of the solar heating fluid, the check valve 100 will open.

The heat exchanger tubing 32 is preferably connected in series, so that domestic hot water flows through approximately 10 feet of heat exchanger tubing, therefore becoming heated almost instantaneously.

This construction allows the elimination of a solar hot water tank because the vacuum tubes 20 and heat exchanger housings 30 are insulated, so they maintain the temperature of the solar heating fluid for much longer than conventional uninsulated solar panels. Heat loss at the maximum temperature of 180 degrees Fahrenheit will occur at a rate of about 2 degrees Fahrenheit per hour. Thus, from the maximum daytime temperature of about 180 degrees Fahrenheit, usage for heating water will cause the solar heating fluid to cool to about 130 degrees Fahrenheit in the evening. This is still a very substantial temperature, because the maximum temperature desired to avoid scalding is about 120 degrees Fahrenheit.

At a temperature of about 130 degrees Fahrenheit, the solar heating fluid will cool at about 1 degree Fahrenheit per hour. Thus, even throughout the night, the solar heating fluid will maintain a satisfactory temperature. At this rate, by the time the solar heating fluid cools down below 100 to 120 degrees Fahreneheit, which is quite usable for domestic hot water purposes, the sun will rise and warm the solar heating fluid again. Indeed, the US Consumer Products Safety Commission's Document 5098 entitled “Tap Water Scalds” recommends that hot water heaters be set to a maximum temperature of 120 degrees Fahrenheit, but points out that a five minute exposure to water at this temperature could result in third degree burns.

Without a flexible, high temperature housing and check valve, it would be necessary to incorporate external expansion tanks, float valves and pressure relief valves for operation. In areas where the temperature can fall below freezing, these exterior components could freeze or suffer freeze damage.

Although a single set of 8 vacuum tubes can be used, it is preferred that 2 or 3 sets of 8 tubes each be used in households with 2 or more people.

This construction is advantageous for servicing, because the components are all individually replaceable. For example, if a vacuum tube 20 breaks, if a heat exchanger housing 30 fails, or if heat exchanger tubing 32 leaks, each can be quickly removed and replaced. The adapter end cap 90 and check valve 100 are removable as well.

The construction is low profile and provides very good weight distribution for support on roof structures.

This invention is preferably retrofittable to existing conventional non-solar hot water heaters, using their existing smaller capacity tanks for additional solar hot water storage, and their electrical or gas heaters as backup heaters for prolonged cloudy periods. In this arrangement, solar heated water from the invention would flow into the existing tank and would be usable directly. Because the water heats almost instantaneously in the series-connected heat exchanger tubing 32, as described above, the invention can continue to heat water as long as the working fluid (preferably water) in the vacuum tubes 20 and heat exchanger housings 30 remains hot enough. As explained above, the fluid in the vacuum tubes 20 and heat exchanger housings 30 remains hot enough overnight, until the sun heats them again. If, however, there is a prolonged period of cloudy weather, then the existing heater can warm the water in the tank.

Further, this invention can supply solar preheated water into the tank of an existing conventional non-solar hot water heater, which can dilute the preheated water's temperature to reduce the chance of scalding, and also act as a backup in case there are prolonged cloudy periods that prevent adequate solar heating. It is preferred that the aggregate capacity of all the vacuum tubes 20 and heat exchanger housings 30 be approximately twice as much as the capacity of the conventional heater's tank.

While the present invention has been disclosed in connection with the presently preferred best mode described herein, it should be understood that the best mode includes words of description and illustration, rather than words of limitation. There may be other embodiments which fall within this spirit and scope of the invention as defined by the claims. Accordingly, no limitations are to be implied or inferred in this invention except as specifically and as explicitly set forth in the claims.

INDUSTRIAL APPLICABILITY

This invention is applicable whenever it is desired to provide solar heating of water without using a solar hot water tank.

Claims

1. A tankless solar water heater for heating domestic pressurized water, comprising:

an insulated container, open at an upper end, for solar heating and insulating a solar heating fluid;

a flexible insulated heat exchanger housing having heat exchange ports and a check valve port, sealingly attached over said upper end, wherein said check valve port is located at an uppermost location of said heat exchanger housing;

a check valve sealingly mounted in said check valve port;

heat exchanger tubing at least partially contained within said heat exchanger housing, sealingly extending through said heat exchange ports to exchange heat between said solar heating fluid and said domestic pressurized water circulating through said heat exchanger tubing when said solar heating fluid fills said insulated container and said heat exchanger housing;

wherein said check valve releases air, and said solar heating fluid and any gas therefrom, in said container and said heat exchanger housing, when interior pressure in said container and said heat exchanger housing is greater than approximately 1 pound per square inch above ambient pressure, without admitting air into said container or said heat exchanger housing when said interior pressure is less than said ambient pressure due to volume reduction of said solar heating fluid from cooling;

wherein said heat exchanger housing contracts to accommodate said volume reduction of said solar heating fluid from cooling; and

wherein said container and said flexible heat exchanger are sufficiently insulated to reduce cooling of said solar heating fluid in said heat exchanger housing to 1 degree Fahrenheit per hour at 130 degrees Fahrenheit.

2. A tankless solar water heater according to claim 1, wherein said insulated container comprises an outer rigid transparent tube and an inner opaque tube, with an insulating vacuum in the space between said tubes.

3. A tankless solar water heater according to claim 1, wherein said solar heating fluid comprises water.

4. A tankless solar water heater according to claim 1, wherein said heat exchanger tubing is entirely contained within said heat exchanger housing.

5. A tankless solar water heater according to claim 1, wherein said check valve releases said solar heating fluid and any gas therefrom if interior pressure in said container and said heat exchanger housing exceed ambient pressure by more than one pound per square inch, to minimize air and gas from said solar heating fluid in said container and said heat exchanger housing, and to maintain said interior pressure of said solar heating fluid in said container and said heat exchanger housing at a maximum pressure of one pound per square inch above ambient pressure.

6. A tankless solar water heater according to claim 1, wherein said check valve vents said solar heating fluid and gas therefrom in case of boiling.

7. A tankless solar water heater for heating domestic pressurized water, comprising:

a plurality of insulated solar heating tubes, each having an upper end, for solar heating and insulating a solar heating fluid contained therein;

a flexible insulated heat exchanger housing having heat exchange ports and a check valve port, sealingly attached over each of said upper ends, wherein said check valve port is located at an uppermost portion of each of said heat exchanger housings;

a check valve sealingly mounted in each of said check valve ports; and

heat exchanger tubing mounted at least partially within each of said heat exchanger housings, each sealingly extending through said heat exchanger ports;

said heat exchanger tubing in each of said heat exchanger housings being connected in series with heat exchanger tubing in another of said heat exchanger housings;

whereby when solar heating fluid fills said insulated tubes and said heat exchanger housings, heat is exchanged between said solar heating fluid and said domestic pressurized water circulating through said heat exchanger tubing;

whereby said flexible heat exchanger housings contract to accommodate volume reduction when said solar heating fluid cools;

whereby said check valves release said solar heating fluid and any gas therefrom if interior pressure in said tubes and said heat exchanger housing exceed ambient pressure by more than one pound per square inch, without admitting air into said tubes or said heat exchanger when volume of said solar heating fluid reduces due to cooling, to minimize air and gas from said solar heating fluid in said tubes and said heat exchanger housings, to maintain said interior pressure of said solar heating fluid in said tubes and said heat exchanger housings at a maximum pressure of one pound per square inch above ambient pressure, and to vent said solar heating fluid and gas therefrom in case of boiling; and

wherein said tubes and said flexible heat exchangers are sufficiently insulated to reduce cooling of said solar heating fluid in said heat exchanger housing to 1 degree Fahrenheit per hour at 130 degrees Fahrenheit.

8. A tankless solar hot water heater according to claim 3, wherein said heat exchanger tubing comprises approximately 10 feet of ½ inch copper tubing in at least two loops, each approximately 20 inches long and approximately 3 inches wide.

9. A tankless solar water heater according to claim 3, wherein each of said solar heating tubes comprises a transparent outer tube and an opaque inner tube, with a vacuum between said inner tube and said outer tube.

10. A tankless solar water heater for heating domestic pressurized water, comprising:

an insulated solar heating means, having an upper end, for solar heating and insulating a solar heating fluid contained therein;

a flexible insulated heat exchanger housing means having heat exchange ports and a check valve port sealingly attached said upper end, wherein said check valve port is located at an uppermost location of said heat exchanger housing, for insulating said solar heating fluid contained therein and for contracting to accommodate volume reduction when said solar heating fluid cools;

heat exchanger means mounted within said heat exchanger housing means, sealingly extending through said heat exchanger ports, for exchanging heat between solar heating fluid in said heat exchanger means and domestic pressurized water circulating through said heat exchanger means when said solar heating fluid fills said insulated tubes and said heat exchanger means;

a check valve means sealingly mounted in said check valve port for releasing air and said solar heating fluid and any gas therefrom if interior pressure in said solar heating means and said heat exchanger housing means exceeds ambient pressure by more than one pound per square inch, without admitting air into said solar heating means or said heat exchanger means when volume of said solar heating fluid reduces due to cooling, whereby air and gas from said solar heating fluid in said solar heating means and said heat exchanger housing means is minimized, whereby said interior pressure of said solar heating fluid in said solar heating means and said heat exchanger housing means is maintained at a maximum pressure of one pound per square inch above ambient pressure, and whereby any gas from boiling of said solar heating fluid is vented in case of boiling; and

wherein said solar heating means and said heat exchanger housing means are sufficiently insulated to reduce cooling of said solar heating fluid in said heat exchanger housing means to 1 degree Fahrenheit per hour at 130 degrees Fahrenheit.